Drugs 33 (Suppl. 4): 69-79 (1987)

()() 12-6667/87/0400-0069/$5 .50/0© ADIS Press LimitedAll rights reserved.

The Haemodynamic and Anti-Ischaemic Effects ofa Single Tablet of 80mg Isosorbide Dinitrate inSlow-Release Formulation and a Review of NitrateTolerance

S. Silber, A.C. Vogler, K-H. Krause and K. TheisenDepartment of Medicine, University of Munich, Munich

Summary There is increasing evidence that relatively constant plasma nitrate concentrationsinduced by 3-times-daily administration of isosorbide dinitrate can lead to an attenuationor even complete loss of the drug's anti-ischaemic effects (nitrate tolerance). We thereforeassessed the dependence ofnitrate tolerance development from the haemodynamic andanti-ischaemic effects ofa slow-release tablet formulation ofisosorbide dinitrate 80mg,administered according to different daily dosage regimens in patients with angina. Itwasfound that a once-daily regimen, with its consequent peak and trough plasma nitrateconcentrations, is capable ofprotecting against exercise-induced myocardial ischaemiafor about 12 hours with the circum vention of nitrate tolerance.

Nitrates have been used sublingually for morethan 100 years to curtail anginal attacks and orallyfor more than 25 years to prevent symptomaticepisodes (Brunton 1857; Carr 1985). Nitrates arehighly effective in all the various forms of angina;they act , in contrast to J3-blockers and calciumantagonists, by reducing preload via venodilation(Fuchs et al. 1983; Ganz & Marcus 1972). Nitratesmay improve haemodynamics independently ofmyocardial contractility and thus, in contrast to 13­blockers and calcium antagonists, are relativelysimple to administer (Cohn 1985; Frishman 1985).The adverse effects of nitrates (headache, nauseaand hypotension) are usually restricted to the initialphase of therapy. Thus, nitrates seem to be an anti­ischaemic medication of first choice. However,towards the end of the last decade, there wasincreasing evidence of a significant attenuation oreven loss of the anti-ischaemic effects during long

term oral treatment (nitrate tolerance) [Abrams1980; Aronow & Chesluk 1970; Blasini et al. 1980;Flaherty 1985; Goldbarg et al. 1969; Jansen et al.1982; Leier 1985; Livesley et al. 1973; Parker et al.1983]. In all these studies, nitrates were administer­ed at least 3 times daily, which suggested theremight be a relationship between constant plasmanitrate concentrations and the development oftolerance.

Until 1982 there had been no studies assessingthe possible development of tolerance with once­or twice-daily nitrate regimens. We thereforeinvestigated the haemodynamic and anti-ischaemiceffects of isosorbide dinitrate administered atdifferent dosage intervals (Silber et al. 1983).Relatively high single doses of isosorbide dinitrate80mg as a slow-release tablet were administered toachieve the longest possible duration of action witha single dose. These tablets were administered once

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 70

daily at 8.00 am (24-hour dose interval) or twicedaily at 8.00 am and 8.00 pm (l2-hour doseinterval). The possible development of tolerancewas evaluated from the result s of exercise testingat identical work loads on the first and fifteenthday of treatment. As dosage intervals of 12 hourslead to constant plasma concentrations, the initiallybeneficial effects of isosorbide dinitrate on exercise­induced ST segment depression and on leftventricular ejection fraction were considerablyattenuated after 2 weeks of treatment. In contrast,the once-daily regimen , with its intermittent peaksof plasma nitrate concentration, showed identicalresults on the fifteenth day compared with the firstday. The concept of preventing tolerancedevelopment by the ingestion of a relatively highsingle dose of slow-release nitrate once daily wassubsequently confirmed by other authors (Blasiniet al. 1985; Ohlmeier et al. 1986).

The purpose of this paper is to summarise thehaemodynamic and anti-ischaemic effects of aslow-release formulation of isosorbide dinitrate andto discuss the problem of nitrate tolerance from aclinical point of view.

1. Patients and Methods1.1 Inclusion Criteria and Patients

The criteria for enrolment were based onangiographically proven coronary artery disease(~ 750/0 stenosis of at least 1 of the 3 majorcoronary arteries), stable exercise-induced anginapectoris, and a reproducible exercise-induced STsegment depression of ~ 0.I5mV (~ 1.5mm)responding to isosorbide dinitrate. A'good nitrateresponse was defined as a reduction of exercise­induced ST segment depression of> 1mm 2 hoursafter the ingestion of .a sustained-release tabletformulation of isosorbide dinitrate 80mg (Isoket"retard 80, Pharma Schwarz, West Germany).Patients with inconclusive exercise ECGs (e.g .resting ST abnormalities, bundle-branch block,pacemaker, digitalis, pre-excitation syndromes) andthose with atrial fibrillation, with complex and /orfrequent arrhythmias, were excluded as well aspatients with a documented myocardial infarction

within 3 months before enrolment. Informedconsent was obtained from all patients. Furtherprerequisites were a history of no or minimal nitrateheadache and a high likelihood of goodcooperation. Patients with hypertension controlledby (3-blockers were not entered.

According to these criteria, 22 patients aged 32to 67 years (mean 52 ± 9 years) were included. Ninepatients suffered from I-vessel disease, 7 from2-vessel and 6 from 3-vessel disease. The maximalcomparable work load during control conditionswas 50 to 140W (mean 94 ± 30W).

1.2 Study Protocol

During a single-blind washout period of 4 days,placebo tablets that were visually identical with theactive drug were ingested and all anti-ischaemicmedication was discontinued with only sublingualglyceryl trinitrate (nitroglycerin) allowed . Patientscomplaining of resting angina during this periodwere excluded from further investigation. On thefifth day , isosorbide dinitrate 80mg as a slow­release tablet formulation was administeredimmediately after the acquisition of the rest andexercise data during control conditions in the earlymorning. Simultaneous recordings of exercise-ECGand exercise-radionuclide ventriculography wereobtained according to identical protocols 2, 6 and12 hours after the ingestion.

Exercise tests were performed on anelectronically braked bicycle ergometer , which isself adjusting and provides constant work loads ,in semi-supine position (300 inclination) with thelegs below heart level. The attending staff andenvironment were kept as constant as possible.Depending on the individual exercise capacity (asderived from previous stress tests) , exercise wasstarted with 50 or 80W and, if possible, increasedautomatically by a programmable computer (ELP500, Bosch) by 30W every 3 minutes. The end-pointof the control exercise test, i.e. after the washoutperiod, was defined as angina pectoris associatedwith ST segment depression of ~ I.5mm. Thesubsequent exercise tests were then performed untilthis individual work load had been reached. The

Haemod ynamic and Anti-Ischaemic Effects of Slow-Release Formulation 71

12-lead ECG (Schiller) was documented with achart speed of 50 mm /sec at 1.5 and 2.5 minutesof each work load stage. ST segment depressionwas measured 80 msec after the J -point in theprecordial lead that showed maximal ST depressionduring the control exercise test. RR intervals weredetermined from the strips recorded with 50mm / sec. Blood pressures were measured bystandard cuff sphygmomanometry, always on theright arm and by the same person.

Radionuclide ventriculography was performedat rest and simultaneously with the ECG duringexercise. The attenuation of radiation was negligiblewhen silver electrodes were used (Red dot, 3M).After standard stannous in vivo labelling of redblood cells with approximately 25 mCi (925 MBq)technetium 99m, the data were acquired with a lowenergy, all-purpose collimator and a IO-inch mobileAnger gamma camera (Dyna Camera 4, Picker) ,automatically setting an asymmetric energy windowof 15% at 140 keY and using a microprocessor forthe control of homogeneity. The data were storedon 80 Mbyte disks of the dedicated on-linecomputer (MDS/A2). By use of the equilibriummultiple-gated acquisition technique (MUGA), 21frames per cardiac cycle were generated; eachpremature beat and the 2 postextrasystoliccontractions were rejected. Ventriculograms wereacquired for 6 minutes at rest and for the last 2minutes of each exercise step in a modified LAO­position that best isolated the left ventricle. Aftertemporal and spatial smoothing of the images,digitised in a 64 x 64 matrix, the left ventricularejection fraction was calculated by a count-ratemethod applying a semi-automatic, clinicallyvalidated algorithm. Briefly, the left ventricularborder was automatically determined by thecomputer within a rectangle placed by the operatorarbitrarily around the left ventricule. The algorithmused identifies the left ventricular border on aframe-by-frame base, by use of constant thresholdsand second deri vat ive criteria. Each frame wasreviewed by the operator. For backgroundcorrection the region of interest was automaticallyset 5 pixels inferolateral to the left ventricular freewall of the end-s ystolic frame. Care was taken to

avoid surr ounding structures unrelated tobackground activit y. Ejection fractions calculatedwith this computer program correlate well withthose determined from biplane co ntras tventriculography and are highly reproducible.

1.3 Plasma Nitrate Concentrations

Blood samples were withdrawn, according tostandard requirements, into precooled, heparinisedglass tubes (-20°C).After immediate centrifugation(4000 rev/min for 10 minutes at -4°C) they werekept frozen (-40°C) until assay. Plasma wasanalysed for isosorbide dinitrate and its metabolites(isosorbide 5-mononitrate and isosorbide2-mononitrate) by a gas chromatographic electroncapture method (ECD, Hewlett Packard 5880 A)[Lut z et al. 1984]. Plasma samples were collected6 and 12 hours after tablet ingestion.

1.4 Statistical Analysis

All exercise parameters were compared atmaximal intraindividual identical work loads andevaluated blind with respect to the time of dataacquisition. Statistical analysis was performed bythe 2-tailed Wilcoxon's test for matched pairs.Probabilities (p) were considered significant at thep < 0.05 level. The p values were corrected by useof Bonferroni's adjustment (Cupples et al. 1984).All data are expressed as the mean ± I standarddeviation .

2. Results2.1 Heart Rate

The changes in heart rate after administrationof isosorbide dinitrate are shown in figure I . Heartrate at rest increased from 70 ± 12 to 86 ± 15 (240/0),84 ± 14 (21%) and 77 ± 16 (II %) beats/min at 2,6 and 12 hours , respectively. During exercise, therewas also a significant increase in heart rate from126 ± 22 to 135 ± 20 (7%),136 ± 17 (8%) and 130± 17 (3%) beats/min at 2, 6 and 12 hours ,respectively .

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 72

Fig. 3. Left ventricular ejection fraction at rest and during exercise

(at maximal comparable work load) before and after the ingestion

of a slow-release formulation of isosorbide dinitrate 80mg;

significance levels ••• = p < 0.001.

80mg

JkJ ¥... J111 :;:------ ::;~---------- .::'

2.2 Blood Pressure

Blood pressure changes after administration areshown in figure 2. Systolic blood pressure at restdecreased significantly from 134 ± 19to 126 ± 17(~6%), 120 ± 15(-10%) and 127 ± 14 (-5%) mmHg at 2,6 and 12 hours, respectively. The corres­ponding values during exercise, however, did notreach statistical significance: from 126 ± 22 to 135± 20, 136 ± 17and 130 ± 17mm Hg, respectively.Diastolic blood pressure at rest did not decreasesignificantly: 92 ± 10, 90 ± 10, 87 ± 10 and 90± 9mm Hg at 0, 2, 6 and 12 hours, respectively.

B

40

I IC 2h

I6h

a 'est.. exe,cise

I

12 h

80mg

t 0::-·__l .Jn.,.um;,.

Diastolic pressure during exercise decreasedsignificantly from 108 ± II to 102 ± 12 (-6%), 97± 12 (-11%) and 100 ± 13 (-8%)mmHgat2,6and 12 hours , respectively.

Fig. 1. Heart rate at rest and during exercise (at maximal

comparable work load) before and after the ingestion of a slow­

release formulation of isosorbide dinitrate 8Omg; significance levels•• = p < 0.D1 , ••• = p < 0.001.

Fig. 2. SySlolic and diastolic blood pressure at rest and during

exercise (at maximal comparable work load) before and after the

ingestion of a slow-release formulation of isosorbide dinitrate 80mg;

significance levels' = p <0.05, •• = p <0.01 , • • • = p <0.001.

4.. ~ j. ,y".1.. r, s l

L_-t· j 1r d,.".1n~~------ •.:.----------- .s . "xetctse&--- ------. O'·L__________ dlQstol .

fest

2.4 Left Ventricular Ejection Fraction

Left ventricular ejection fract ion at rest showeda non-significant tendency to increase from 60 ±8% to 63 ± 9%,63 ± 8% and 64 ± 7% at 2, 6 and12hours, respectively. During exercise, the ejectionfraction increased significantly from 52 ± 13% to64 ± 12%, 65 ± 12% and 64 ± 10% at 2, 6 and12 hours, respectively (fig. 3)

2.3 Double-Product

The rate-pressure product during resting controlconditions was 9407 ± 2489mm Hg . beats/min andbecame sign ificantly elevated to 10,892 ±2463mm Hg . beats/min (16010) at 2 hours . At 6hours (10,141 ± 2233mm Hg· beats/min, 8%) andat 12 hours (9867 ± 2615mm Hg· beats/min, 5%) ,the increase was no longer significantly elevatedcompared with baseline. Also, during exercise,statistical significance could be demonstrated only2 hours after drug administration (23,157 ± 5559vs25,900 ± 4757mm Hg . beats/min, 12%). Valuesat 6 and 12 hours were 25,212 ± 4861 (9%)and 24,333 ± 4658 (5%) mm Hg • beats/min,respectively.

12h

1

12h

I··

6h

I

6h

J~n.,~. Ins systolI ll,rCIS.

C 2h

I I

C 2h

200 ~80mgJ n,,-~

Ii!! 150

l~ 100a:l

8

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 73

3.1 Nitrate Tolerance

2.6 Plasma Nitrate Concentrations

3. Discussion

during long term therapy. Reports on thedevelopment of tolerance to the hypotensive effectsof nitrates are almost as old as the use of nitratesthemselves : in 1888 Stewart criticised glyceryltrinitrate as being a 'drug which is often of littleservice, because tolerance is too readily established'(Stewart 1905). The possibility of the developmentof tolerance to the reduction in blood pressure andincrease in heart rate, at least at rest, is generallyaccepted during long term oral nitrate therapy,especially when the drug is administered 3 or moretimes daily (Bogaert & De Schaepdryver 1968;Brunner et al. 1974; Schneider et al. 1984).However, there is still substantial controversyconcerning the development of tolerance to the anti­ischaemic (antianginal) effects of nitrates .

Many studies have failed to show any evidenceof weakening or loss of antianginal efficacy duringlong term oral nitrate therapy using at least 3-times­daily administration. Three open studies found nochange in increased exercise capacity duringtreatment with conventional isosorbide dinitrate 20to 50mg 4 times daily for 12 to 40 weeks (Danahy& Aronow 1977) and sustained-release glyceryltrinitrate 2.6mg 3 times daily for 24 weeks (Winsor& Berger 1975) and 6.5mg 3 to 6 times daily for12 weeks (Davidov & Mroczek 1977). In a double­blind study, Lee et al. (1978) found an unchangedpositive effect on exercise capacity in 28 patientsafter 4 weeks of treatment with conventionalisosorbide dini trate 40mg 3 times daily .Unattenuated anti-ischaemic efficacy has also beendescribed in a randomised double-blind crossoverstudy in which 11 patients were given conventionalisosorbide dinitrate 80mg 6 times daily for 4 weeks(Schneider et al. 1984).

In contrast, 7 clinical studies of 9 to 21 patientsconsidered there was tolerance development ifnitrates were ingested at least 3 times daily.Goldbarg et al. (1969) reported no difference withrespect to anginal frequency and exercise capacitywhen comparing isosorbide dinitrate lOmg 4 timesdaily and placebo for 4 weeks. Similar findings werealso obtained by Aronow and Chesluk (1970) andLivesley et al. (1973) when administeringconventional isosorbide dinitrate 4 and 3 times

I12h

I6h

o I IC 2h

Six hours after drug ingestion, concentrationsof isosorbide dinitrate, isosorbide 2-mononitrateand isosorbide 5-mononitrate were 24 ± 25, 76 ±41 and 380 ± 183 I-lg/L, respectively. Thecorresponding values at 12 hours were 5 ± 5, 37± 23 and 292 ± 8.0 I-lg/L.

Fig. 4. Exercise-induced ST segment depression (at maximal

comparable work load) before and after the ingestion of a slow­

release formulation of isosorbide dinitrate 80mg; significance levels

••• = p < 0.001 .

2.5 ST Segment Depression

The exercise-induced ST sgement depression wassignificantly reduced from 2.2 ± 0.6mm to 0.5 ±0.7mm (-77%) 2 hours after drug administrationand was similar (0.6 ± 0.6mm, -73%) at 6 hours.At 12 hours, the ST segment depression (1.7 ±0.8mm, -26%) still differed significantly frombaseline (fig. 4).

Any discussion of nitrate tolerance must makea clear distinction between the different drugeffects. There is unanimous agreement on thedevelopment of tolerance with reference to nitrate­induced headache (Crandall et al. 1931). The lesscommonly encountered nitrate-induced side effects,such as vertigo and nausea, also usually vanish

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 74

daily, respectively. Even if the coincidence ofhaving included only non-responders is very remotein the total of 59 patients studied, it must beemphasised that there were no data about the initialresponse in these studies. Blasini et aJ. (1980)founda total disappearance of anti-ischaemic effects(anginal frequency and exercise-induced STdepression) after 8 weeks' oral administration ofsustained-release isosorbide dinitrate 20 to 40mg 3times daily in 9 patients and 60mg 3 times daily in10 patients. A subsequent study by the sameauthors showed the same result when conventionalisosorbide dinitrate 40mg 4 times daily wasadministered to 11 patients for 2 weeks (Rudolphet aJ. 1983). Thadani et aJ. (1982) found that therewas a complete loss of effect 4 hours after drugadministration in 12 patients who receivedconventional isosorbide dinitrate 15 to 120mg 4times daily. However , 2 hours after drugadministration there was still a small effect on timeto onset of exercise-induced angina.

3.2 Possible Explanations for theControversy about Nitrate Tolerance

The use of different nitrate compounds cannotexplain the controversial results published, since thedevelopment of tolerance has been observed notonly for glyceryl trinitrate and isosorbide dinitratebut also for isosorbide 5-mononitrate, the principalactive metabolite of isosorbide dinitrate (Jansen etaJ. 1982). There is also no obvious relationshipbetween the total daily dosage and the developmentof tolerance. On one hand , a relatively low dosageof isosorbide dinitrate 60 mg/day may lead to amarked reduction in the anti-ischaemic effects(Blasini et aJ. 1980; Thadani et aJ. 1982); on theother hand , a dosage of 480 mg/day showedpersistent anti-ischaemic potency (Schneider et aJ.1984). The different times chosen for the firstexercise test after nitrate administration, rangingfrom 30 minutes to 4 hours after drugadministration, do not offer any explanation forthe different findings (Blasini et aJ. 1980; Jansenet aJ. 1982; Lee et aJ. 1978; Rudolph et aJ. 1983;Schneider et aJ. 1984; Winsor & Berger 1975).

Neither can the question be answered by the kindof exercise test performed: treadmill (Lee et aJ.1978; Thadani et aI. 1982; Winsor et aJ. 1975), arm­assisted step test (Schneider et aJ. 1984),and bicycleergometry when sitting (Danahy & Aronow 1977)or semi-supine with the legs above heart level(Blasiniet aJ. 1980). The duration of therapy cannotaccount for the controversial results, since, afteronly 1 week, a weakening of antianginal effect hasbeen noted (Thad ani et aJ. 1982)and , on the otherhand, no attenuation has been seen after 40 weeks(Danahy & Aronow 1977). A strict placebo­controlled randomised double-blind crossover studyprotocol is not the key answer for the interpretationof the conflicting findings because no tolerancedevelopment has been seen in such a study(Schneider et aJ. 1984),whereas an attenuation hasbeen seen in an open study (Jansen et aJ. 1982).

Since the development of tolerance to thehaemodynamic effects of nitrates is rapid, i.e.within 1 to 2 days (Blasini et aJ. 1982; Crandall etaJ. 1931; Dalal et aJ. 1983; Parker et aJ. 1983)andis reversed rapidly within hours (Blasini et aJ. 1982;Parker et aJ. 1985), patient compliance with doseingestion is pivotal in the development of tolerance.The unreliable or irregular ingestion of doses canblur the problem of nitrate tolerance in everydaypractice. Unfortunately, most studies have omitteddocumentation of patient compliance (Aronow &Chesluk 1970; Danahy & Aronow 1977; Davidov& Mroczek 1977; Goldbarg et aJ. 1969; Livesley etaJ. 1973; Thadani et aJ. 1982).

Counting the returned tablets or thedocumentation of tablet intake on the basis ofpatients' diaries is not reliable. Any evaluation ofcompliance such as this lies purely in the hands ofthe patient. A daily assessment of plasmaconcentrations is not feasible in long term studies.A practicable method for a daily compliance testis to determine the fluorescence in the patients'urine attributable to the riboflavin added to thetablets. In our studies the compliance assessed bythis method was 95070, undoubtedly higher than theaverage compliance expected for routineadministration. In addition, one should keep inmind that compliance refers not only to the fact

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 75

of ingestion itself but also to the exact time ofingesting the prescribed dose. Obviously it is noteasy to ingest the tablets regularly every 8 hours forseveral weeks. Thus, it is conceivable that patientsmay have introduced their own nitrate-poor intervalby modifying the stud y protocol. In fact, it wasshown that a 3-times-daily regimen with the lastingestion at 5.00 pm did not lead to thedevelopment of tolerance (Parker et aJ. 1985).Nitrate tolerance frequently develops with the useof transdermal glyceryl trinitrate patches (Abrams1984; Parker & Fung 1984; Parker et aJ. 1984;Reichek et aJ. 1983), since it is unlikely that patientsare non-compliant , and constant plasma nitrateconcentrations are maintained.

3.3 Causes of Tolerance Development

Animal (Sponer et aJ. 1981) and human(Thadani et aJ. 1982) studies have shown that thedevelopment of tolerance during long term nitratetherapy cannot be compensated for by increasingthe dosage (even up to a level of 8 times the initialdose). To explain the phenomenon of nitratetolerance one can also exclude reduced absorptionas well as a more rapid metabolism or fasterelimination of the administered nitrate or its activemetabolites on the simple evidence of raised plasmaconcentrations during long term treatment (Funget aJ. 1980; Parker et aJ. 1983; Thadani et aJ.1980b). Counter-regulatory mechanisms duringlong term therapy (pseudo-tolerance) [Colucci et aJ.1981; Packer et al. 1981), which occur as a reactionto nitrate-induced venous pooling with its relativevolume deficiency and decrease in the intracardialand systemic arterial pressures (baroreceptorreflex), may lead both to stimulation of the renin­angiotensin-aldosterone system with itsconcomitant fluid retention and vasoconstriction,and to a compensatory raised vasoconstrictor tone(Lange et aJ. 1972;Olivari et aJ. 1983).The essentialdifference between 'true' and pseudo-tolerancebecomes clear once the medication is abruptlywithdrawn. In the case of a true loss of effect onthe vascular smooth muscle , there are no changesin the symptoms or haemodynamics, while an

interruption of medication in cases of pseudo­tolerance may lead to undesirable withdrawalphenomena. In fact , evidence for relevant counter­regulatory mechanisms has been found in workersin the dynamite and pharmaceutical industries,who, in former days, were exposed to high dosesof transcutaneous nitrate. During the weekendbreak , typical anginal symptoms, even myocardialinfarctions and sudden death , were found after thetermination of the exposure to nitrates (Klock 1975;Lange et aJ. 1972; Lund et aJ. 1968). However, suchextreme withdrawal phenomena can occur onlyunder these extraordinary non-clinical conditions.Although it is true that patients without heartdisease were found to have an increase in theplasma noradrenaline level despite unchangedplasma renin levels, relevant withdrawalphenomena were not found (Olivari et aJ. 1983).The problem in assessing the clinical importanceof counter-regulatory mechanisms arises from thedifferent circumstances of patients with andwithout heart disease . In the case of patients withcongestive heart failure , there was no incidence ofa further increase in plasma noradrenaline withunchanged plasma renin, either during or afterwithdrawal of continual glyceryl trinitrateadministration (Olivari et aJ. 1983). These low-levelwithdrawal phenomena were interpreted as beingcaused by an 'endogenous vasoconstrictor tone',independent of the renin-angiotensin-aldosteronesystem and the plasma noradrenaline levels. On thebasis of these findings, taken together with thefailure of animal experiments to demonstrate afurther rise in plasma renin levels during long termtherapy (Kraupp et aJ. 1980), the renin-angiotensin­aldosterone system can hardly be consideredresponsible for nitrate tolerance, particularly sinceits development occurs without an increase inbodyweight (Packer et aJ. 1981). Nitrate-inducedincrease in the plasma noradrenaline level must bedifferentiated from that which is dependent uponcardiac disease itself. However, the former appearsto be slight (Francis et aJ. 1983). Withdrawalphenomena must be allocated a minor role in termsof clinical relevance. After induction of nitratetolerance with isosorbide dinitrate in pat ients with

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 76

congestive heart failure, the stopping of medicationfailed to reveal any withdrawal phenomena (Blasiniet aJ. 1982).

The anti-ischaemic effect of nitrates in stable,exercise-induced angina is caused by a reduction inmyocardial oxygen demand. It is reduced as a resultof the reduction in afterload, but, above all,because of the reduction in ventricular preload,which is due to a drop in the left ventricular end­diastolic pressure and volume. Since the possibilityof tolerance development with regard to a reductionin the ventricular afterload has been generallyaccepted and, furthermore, no importance can beattributed to the direct coronary dilation in patientswith reproducible, exercise-induced ischaemia, theloss of anti-ischaemic effects must be seen as adecrease in its venous dilation properties (reduced'venous pooling' capability). Therefore, venousplethysmography has been used by Zelis et aJ.(1975) to demonstrate a loss of efficacy during longterm nitrate therapy. The development of toleranceto long term nitrate therapy as seen in the reductionin preload has been objectively proven at rest(Blasini et aJ. 1982) as well as under ergometricexercise measuring of pulmonary arterial pressure(Jansen et aJ. 1982).

The fundamental mechanism of tolerancedevelopment after long term therapy with nitratesmust be regarded as a loss of its effect on thevessel's smooth muscle . This was seen in isolatedvessel specimens (Herman & Bogaert 1971;Needleman & Johnson 1973). The vasodilatorproperties of nitrates appear to be mediated bycyclic guanosine monophosphate (cOMP) via theactivation of guanylate cyclase (Bohme et aJ. 1978;Keith et aJ. 1982; Kukovetz & Holzmann 1983).Since in vitro, despite the induction of nitratetolerance, the vessels remain responsive to cOMP,the loss of the effects during long term nitrateapplication can be traced back to the reducedactivation of guanylate cyclase (Keith et aJ. 1982).Nitrates require sulfhydryl groups for thestimulation of guanylate cyclase (Needleman et aJ.1973). The sulfhydryl groups, referred to in earlierwork as 'nitrate receptors' whose destruction (e.g.by alkylation or treatment with oxidation

substances or 'auto-oxidation' by high-dose nitrates)led to a reduction in the efficacy of glyceryltrinitrate (Herman et aJ. 1971), are, according tomore recent research, components of thiols, whichact in their capacity as 'substrate' within theframework of nitrate metabolism for the synthesisof S-nitrosothiols in the smooth muscle cells. Ascysteine represents the principal sulfhydryl donor(lgnarro & Gruetter 1980; Winniford et aJ. 1986),the development of nitrate tolerance may possiblybe caused by a rapidly occurring exhaustion of the'cysteine pool' with a subsequently reducedproduction of S-nitrosothiols (Kukovetz &Holzmann 1983; Torresi et aJ. 1985). In a clinicalstudy, there was evidence for the enhanced efficacyof intravenously administered glyceryl trinitrate onthe systemic and pulmonary capillary pressure whenused in conjunction with N-acetylcysteine inpatients with coronary artery disease (Horowitz etaJ. 1983). Recently Packer et aJ. (1986) proved thereversibility of induced nitrate tolerance by addingN-acetylcysteine to the glyceryl trinitrate infusionin patients with congestive heart failure. These are,however, preliminary results and should beconfirmed by other investigators.

3.4 Duration of Action of a Single Dose

The measurements of haemodynamic changesafter a single dose are important to characterise theduration of drug action (Udhoji & Heng 1984; Wittet aJ. 1983; Wolf et aJ. 1981). These data, however,may not be extrapolated to the situation of exercise­induced myocardial ischaemia . Many authors haveassessed the duration of action of a single dose ofisosorbide dinitrate as conventional and slow­release formulations . When considering theduration of action of a single dose, it is not onlyimportant to describe the time during which theinduced changes were statistically significant , butmuch more to look at the duration of the maximaleffects obtained. Thus, single doses of conventionalisosorbide dinitrate 15 to 30mg showed significantanti-ischaemic effects for 8 hours, and the maximaleffects were observed after 2 to 3 hours (Danahyet aJ. 1977; Markis et aJ. 1979; Parker et aJ. 1985;

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 77

Thadani et aJ. 1980a). Single doses of conventionalisosorbide dinitrate 40mg demonstrated a markedlyless pronounced anti-ischaemic effect at 6 hourscompared with I hour after drug ingestion (Reinigeret aJ. 1984). There is unanimous agreement thatsustained-release formulations remarkably prolongthe duration of action of a single dose. Slow-releaseisosorbide dinitrate 20 and 40mg show theirmaximal anti-ischaemic effects for 5 to 6 hours(Blasini et aJ. 1980; Brunner et al. 1974; Kenedi &Giebler 1983; Lee et aJ. 1978). A significant anti ­ischaemic duration of action of 12 hours, however,has been reported with high doses of slow-releaseisosorbide dinitrate (see figs. 3 and 4) [Blasini etaJ. 1985; Ohlmeier et aJ. 1986; Silber et aJ. 1983].

3.5 Practical Implications

Since a daily nitrate-poor interval is necessaryto circumvent the attenuation of the anti-ischaemiceffects, we recommend the once-dailyadministration of a high single dose of nitrate asa sustained-release formulation (beginning withincreasing doses starting with 20mg twice daily inthe morning and early afternoon). The applicationof a once-daily high single dose as a slow-releaseformulation leads to maximal possible anti­ischaemic effects for about 6 hours with significantprotection for about 12 hours. Thus, it representsthe ideal compromise between the circumventionof tolerance development and optimal nitratetherapy.

According to this regimen, the maximum nitrateplasma concentration is achieved during the day.The problem of silent myocardial ischaemia duringthe night should not be exaggerated, since silentepisodes seem to be much more frequent during theday (Dean field et aJ. 1985). Whether the relativelylow plasma concentrations during the night aresufficient to prevent silent ischaemic episodes is stillunknown. In patients predominantly complainingof nocturnal angina, the therapeutic maximum canbe shifted to the night, the dose being ingested onlyin the evening.

Since it is obviously not possible to obtainmaximal anti-ischaemic protection for 24 hours

with nitrates alone , a combination therapy with a(J-blocker and /or calcium antagonist should berecommended in certain patients if nocontraindications exist (Silber et aJ. 1986). In orderto optimise anti-ischaemic therapy, a combinationtherapy should be preferred even when patients onmonotherapy with nitrates are free of angina andstill demonstrate signs of myocardial ischaemia(Geft et aJ. 1982; Gottlieb et aJ. 1986).

Acknowledgement

Wegratefully acknowledge the technical assistance ofMargot Vogel.

References

Abrams J. Nitrate tolerance and dependence. Amer ican HeartJournal 99: 113-123, 1980

Abrams J . The brief saga of transdermal nitroglycerin discs:Parad ise Lost? American Journal of Cardiology 54: 220-224,1984

Aronow WS, Chesluk HM. Sublingual isosorbide dinitrat etherapy versus sublingual placebo in angina pectori s.Circulation 41: 869-874, 1970

Blasini R, Briigmann U, Manne s A, Froer K-L, Hall D, et al.Wirksamk eit von Isosorb iddinitrat in retardierter Form beiLangzeitbeh andlung. Herz 5: 298-305, 1980

Blasini R, Froer K-L, Bliimel G, Rudolph W. Wirkungsverlustvon Isosorbiddinitrat bei Langzeitbehandlung der chronischenHerzinsuffizienz. Herz 7: 250-258, 1982

Blasin i R, Briigmann U, Reiniger C, Rudolph W.Langzeittherapie der Belastungs-Angina-pectoris durch einmaltagliche Verabr eichung von 120 mg 1sosorb iddinitrat inretard ierter Form . Herz 10: 163-171, 1985

Bohme E, Gra f H, Schultz G. Ef fects of sodium nitroprussideand other smooth muscle relaxants on cyclic GMP format ionin smooth muscle and platelets. Advances in Cyclic NucleotideProtein Phosphorylation Research 9: 131-143, 1978

Bogaert MG, De Schaepdryver AF . Tolerance towards glyceryltrinitrat e (trinitrin) in dogs. Archives Internationales dePharmacodynam ie et de Therapie 171: 221, 1968

Brunner D, Meshulam N, Zerieker F. Effectiveness of sustained­action isosorbide din itrate on exercise-induced myocard ialischemia . Chest 66: 282-287, 1974

Brunton TL. Use of nitrate of amyl in angina pectoris. Lancet2: 97-98, 1857

Carr CJ. History of the synthesis and pharmacology of isosorbidedinitrate. American Heart Journal 110: 197-201, 1985

Cohn IN . Nitrates for congestive heart failure. American Journalof Cardiology 56: 19A-23A, 1985

Colucci WS, Williams GH , Alexander RW, Braunwald E.Mechan isms and implication s of vasodilator tolerance in thetreatment of congestive heart-fa ilure. Ameri can Journal ofMedicine 71: 89-99, 1981

Crandall LA, Leake CD, Loevenhart AS, Muehlberg er CW oAcquired tolerance and cross tolerance between the nitrou sand nitric acid esters and sodium nitr ite in man . Journal ofPharmacol ogy and Exper imental Therapeutics 41: 103, 1931

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 78

Cupples LA, Heeren T , Schatzkin A. Multiple testing ofhypotheses in comparing two groups. Annals of InternalMedicine 100: 122-129, 1984

Dalal 11, Yao L, Parker JO. Nitrate tolerance: influence ofisosorbide dinitrate on the hemodynamic and ant ianginaleffects of nitrogl ycerin . Journal of the American College ofCardiology 2: 115-120, 1983

Danahy DT, Aronow WS. Hemodynamics and antianginal effectsof high dose oral isosorbide dinitrate after chronic use.Circulation 56: 205-212, 1977

Danahy DT, Burwell DT, Aronow WS, Prakash R. Sustainedhemodynamics and antianginal effect of high dose oralisosorbide dinitrate. Circulation 55: 381-387, 1977

Davidov ME, Mroczek WJ . Effect of sustained releasenitroglycerin capsules on anginal frequency and exercisecapacity: a double-blind evaluation . Angiology 28: 181-1891977

Deanfield JE, Shea MJ , Selwyn AP. Clinical evaluation oftransient myocardial ischemia during daily life. AmericanJournal of Medicine 79 (Suppl, 3A): 18-24, 1985

Flaherty JT. Hemodynamic attenuation and the nitrate-freeinterval: alternative dosing strategies for transdermalnitroglycerin . American Journal of Cardiology 56: 321-371,1985

Francis GS, Olivari MT, Goldsmith SR, Levine TB, PierpontG, et al. The acute response of plasma norepinephrine, reninactivity, and arginine vasopressin to short-term nitroprussideand nitroprusside withdrawal in patients with congestiveheartfailure. American Heart Journal 106: 1315-1320, 1983

Frishman WH oPharmacology of the nitrates in angina pectoris.American Journal of Cardiology 56: 81-131, 1985

Fuchs RM, Brinker JA , Guzman PA, Kross DE, Yin FCP .Regional coronar y blood flow during relief of pacing-inducedangina by nitroglycerin . Implications for mechanism ofaction . American Journal of Card iology 51: 19-23, 1983

Fung HL, McNiff EF, Riggirello D, Darke A, Parker JO , et al.Pharmacokinetics and pharmacologic effects after single andchronic doses of isosorbide dinitrate. American Journal ofCardiology 45: 438, 1980

Ganz W, Marcus HS . Failure of intracoronary nitroglycerin toalleviate pacing-induced angina. Circulation 46: 880-889, 1972

Geft IL, Fishbein MC, Ninomiyal K, Hashida J, Chaux E, etal. Intermittent brief periods of ischemia have a cumulativeeffect and may cause myocardial necrosis. Circulation 66:1150-1153, 1982

Goldbarg AN, Moran JF, Butterfield TK, Nemickas R, BermudezG. Therapy of angina pectoris with propranolol and long­acting nitrates . Circulation 40: 847-853, 1969

Gottlieb SO, Weisfeldt ML, Ouyang P , Achuff SC, BaughmanKL, et al. Effect of the addition of propranolol to therapywith nifedipine for unstable angina pectoris : a randomized,double-blind placebo-controlled trial. Circulation 73: 331-337,1986

Herman AG, Bogaert MG. Organic nitrates: tolerance at the levelof the vascular smooth muscle. Archives Internationales dePharmacodynamie et de Therapie 192: 200-202, 1971

Horowitz JD, Antmann EM, Lorell BH, Barry WH, Smith TW.Potentiation of the cardiovascular effects of nitroglycerin byN-acetylcysteine. Circulation 68: 1247-1253, 1983

Ignarro LJ , Gruetter CA . Requirement of thiols for activationof coronary arterial guanylate cyclase by glyceryltrinitrateand sodium nitrate: possible involvement of S-nitrosothiols.Biochimica et Biophysica Acta 631: 221, 1980

Jansen W, Osterspey A, Tauchert M, Schmid G, Schell U, etal. 5-l sosorbidmononitrat unter Ruhe- undBelastungsbedingungen bei koronarer Herzkrankheit.Deutsche Medizinische Wochenschrift 107: 1499-1605, 1982

Keith RA, Burkman AM, Sokoloski TD, Fertel RH . Vascular

tolerance to nitroglycerin and cyclic GMP generation in rataortic smooth muscle. Journal of Pharmacology andExperimental Therapeutics 221: 525-531, 1982

Kenedi P, Geibler B. Antianginal efficacy of long-term nitratetherapy. Zeitschrift fUr Kardiologie 72 (Suppl, 3): 233-238,1983

Klock JC. Nonocclusive coronary disease after chronic exposureto nitrates: evidence for physiologic nitrate dependence .American Heart Journal 89: 510-513, 1975

Kraupp 0, Benke Th, Placheta P, Stanek B, Raberger G. DieWirkung einer einmaligen sowie chronischen Verabreichungvon Isoket auf die Plasma-Renin-Aktivitat von Hunden. InRudolph , Schrey (Eds) Nitrate II, Wirkung auf Herz undKreislauf, pp. 17-20, Urban und Schwarzenberg, Munich,1980

Kukovetz WR, Holzmann S. Mechanism of nitrate-inducedvasodilatation and tolerance . Zeitschrift fur Kardiologie 72(Suppl, 3): 14-19, 1983

Lange RL, Reid MS, Tresch DD, Keelan MH, Bernhard VM,et al. Nonatheromatous ischemic heart disease followingwithdrawal from chronic industrial nitroglycerin exposure.Circulation 46: 666-678, 1972

Lee G, Mason DT, Amsterdam EA, Miller RR, De-Maria AN.Antianginal efficacy of oral therapy with isosorbide dinitratecapsules . Chest 73: 327-332, 1978

Leier CV. Nitrate tolerance. American Heart Journal 110:224-232, 1985

Livesley B, Carley PF, Campbell RC, Oram S. Double-blindevaluation of verapamil, propranolol and isosorbide dinitrateagainst a placebo in the treatment of angina pectoris. BritishMedical Journal: 375-378, 1973

Lund RP, Hoggendal J, Johnsson G. Withdrawal symptom s inworkers exposed to nitroglycerin. British Journal of IndustrialMedicine 25: 136-138, 1968

Lutz D, Rasper J , GielsdorfW, Settlage JA, Jaeger H.lmprovedautomated simultaneous determination of isosorbide dinitrateand its metabolites in plasma by capillary column gaschromatography . Journal of High Resolut ionChromatography & Chromatography Communications 7:58-65, 1984

Mark is JE , Godin R, Millis RM, Williams RA, Schweitzer P ,et al. Sustained effect of orally administered isosorbidedinitrate on exercise performance of patients with anginapectoris . American Journal of Cardiology 43: 265-271, 1979

Needleman P, Johnson EM . Mechanism of tolerancedevelopment to organic nitrates . Journal of Pharmacologyand Experimental Therapeutics 184: 709-715, 1973

Needleman P, Jakschik B, Johnson Jr EM. Sulfhydrylrequirement for relaxation of vascular smooth muscle.Journal of Pharmacology and Experimental Therapeutics187: 324-331, 1973

Ohlmeier H, Mertens HM, Moller M, Mannebach H, GleichmannU. Vereinfachte Langzeittherapie der koronarenHerzkrankheit mit 120mg retardiertem Isosorbiddinitrateinmal taglich. Untersuchung zur Wirkdauer undToleranzentwicklung. Zeitschrift fur Kard iologie 75 (Suppl .3): 50-56, 1986

Olivari M, Carlyle P, Levine BS, Cohn 1. Hemodynamic andhormonal response to transdermal nitrogl ycerin in normalsubjects and in patients with congestive heart failure. Journalof the American College of Cardiology 2: 872-888, 1983

Packer M, Meller J, Medina N, Yushak M, Gorl in R.Determinants of drug response in severe chronic heart failure.Activation of vasoconstrictor forces during vasodilatorytherapy. Circulation 64: 506-514, 1981

Packer M, Lee WH, Kessler P, Medina N, Yushak M. Inductionof nitrate tolerance in human heart failure by continuousintravenous infusion of nitroglycerin and reversal of tolerance

Haemodynamic and Anti-Ischaemic Effects of Slow-Release Formulation 79

by N-acetylcysteine , a sulfhyd ryl donor. Journal of theAm erican College of Cardiology 7: 27A , 1986

Parker JO , Fung HL. Tran sdermal nitroglycerin in anginapectori s. Amer ican Journal of Cardiolog y 54: 471-476, 1984

Parker JO , Fung HL , Ruggirello D, Stone JA . Tolerance toisosorbide dinitrate: rate of development and reversal.Circu lation 68: 1074-1080, 1983

Parker JO, Van Koug hnett KA, Fung HL. Transdermalisosorbide dinitr a te in angina pectoris : effect of acute andsustained therapy. American Journal of Cardiology 54: 8-13,1984

Parker JO , Van Koughne tt KA, Farrell B. Comparison of buccalnitroglycerin and oral isosorbide dinitrate for nitrate tolerancein stable ang ina pectoris. American Journal of Cardiology56: 724-728, 1985

Reichek N, Prie st Ch, Zimrin D, Chandler Th, Raichlen JS, etal. Antianginal effects of nitroglycerin patches do not last24 hours. Circulation 68 (Suppl. III): 407, 1983

Rei n ige r G, Bla s in i R , Br iigma nn U, Rudolph W .Toleranzentwicklung hinsichtlich der antiischiimischenWirkung von 1sosorbiddinitrat bei regelmassiger, mehrfachtaglicher Verabreichung. Herz 9: 146-152, 1984

Rudolph W, Blasini R, Reiniger G, Briigmann U. Tole ran cedevelopment during isosorb ide dinitrate treatment : can it becircumvented? Zeitschr ift fiir Kardiologie 72 (Supp l. III ):195-198, 1983

Schneider WU , Bussmann WD , Stahl B, Kaltenbach M. Dose­response relation of antianginal act ivity of isosorbidedinitrate. American Journal of Cardiology 53: 700-705, 1984

Silber S, Krause KH , Garner C, Theisen K, Jah rmarker H . Anti ­ischem ic effects of an 80mg tablet of isosorbide-dinitrate insustained- release form before and after 2 weeks treatmentwith 80mg once or twice da ily. Zeitschrift fiir Kard iologie72 (Suppl 3): 211-217 ,1983

Silber S, Vogler A, Theisen K. Equal anti-ischemic propertiesof isosorb ide dinitrate plus verapamil and isosorbide dinitrateplus propranolol. A randomized, double-blind and crossoverstudy . Zeitschrift fiir Kardio logie 75 (Suppl . 3): 100-105, 1986

Spo ner G, Dietmann K, Strein K, Bartsch W. Significance ofdosage interval for the development of tolerance toisosorbide-5-mononit rate in con scious dogs. IRCS Med icalScience 9: 619, 1981

Stewart DD . Remarkable tolerance to nitro glycerin, Philadelphia

Polyclinic , p. 172 (1888), from Stewart DD, Tolerance tonitroglycerin . Journal of the American Medical Associat ion44: 1678-1679, 1905

Thadani U, Fung HL, Darke AC, Parker JO . Oral isosorbidedinitrate in the treatment of angina pectoris . Dose-responserelationship and duration of action during acute the rap y.Circulation 62: 491-502 , 1980a

Thadani U, Manyari D, Parker JO, Fung HL. Tolerance to thecirculatory effects of ora l isoso rbide dinitrate . Circulation61: 526-535, 1980b

Thadani U, Fung HL , Darke AC, Parker JO . Oral isosorb idedinit rate in angina pectoris : comparison of duration of actionand do se-response relation during acute and sustainedtherapy. American Journal o f Cardiology 49: 411-419, 1982

Torresi J , Horowitz JD , Dusting GJ . Prevention and reversalof tolerance to nit roglycerine with N-acet ylcysteine . Journalof Cardiovascular Pharmacology 7: 777-783, 1985

Udhoji VN, Heng MK. Hemodynamic effects of high-dosesustai ned-actio n oral isoso rbide dini t rate in stable angi na .American Journal of Cardiology 78: 234-240, 1984

Winnifo rd MD, Kenned y PL, Wells PJ, Hillis LD. Potentiationof nitroglycerin-induced co ronary dilatat ion by N­acetylcysteine . Circu lation 73: 138-142, 1986

Winsor T , Berger HJ. Oral nitroglycer in as a prophylacticant ianginal dru g: clinical, physiologic and statistical evidenceof efficacy based on a three-pha se exper imental design .Ameri can Heart Journal 90: 611-626, 1975

Witt E, Lehmann HU, Tra ue P, Hochrein H . Langzeitwi rkungeines neu en Depo t-Nitroglycerins im Verg leich mitlsosor biddinitrat . Harnodynarnische Doppelblindstudie.Deut sche Medizinische Wochenschrift 108: 216-220, 1983

Wolf R, Sinn R, Guillen R, Koerner H . Hiimodynami scheLangzeitwirkung von hochdo siertem lsosorb iddinitra t (80 mg)in Slow-Release-Form bei koronarer Herzerkrankung.Deutsche Med izinisch e Wochenschrift 106: 1130-1134, 1981

Zelis R, Mason DT. lsosorbide dinitrate. Effect on the vasodilatorrespo nse to nitroglycerin . Journal of the Amer ican Medica lAssociation 234: 166-170, 1975

Author's address: Dr Sigmund Silber, Medizinische Kliniklnn enstadt der Un iversitat Miinchen , Ziemssenstrasse I , 8000Miinchen 2 (West Germany).