Protein SynthesisInhibitors

Claro M. Isidro M.D.

Protein Synthesis

Stages of Protein Synthesis1. Initiation - involves formation of an initiation

complex that contains mRNA, both subunits of ribosomes and the first aminoacyl-tRNA (formyl-methionyl tRNA)

2. Elongation - includes synthesis of the first peptide bond to addition of the last amino acid. Also involved Peptide bond formation - polypeptide is transferred from

peptidyl-tRNA in the P site to aminoacyl-tRNA in the A site

Translocation - moves ribosome one codon; places peptidyl-tRNA in the P site; deacylated tRNA leaves via the E site; A site is empty for next aa-tRNA

Summary

3. Termination – encompasses the release of the completed polypeptide chain and dissociation of the ribosome from the mRNA.

Protein Synthesis Inhibitors

30 S INHIBITORS• Aminoglycoside• Tetracyclines

Buy AT 30, CELLS at 50

50 S INHIBITORS Chloramphenico

l Macrolides

(Erythromycin) Clindamycin Oxazoladinones

(linozelid) Streptogramins

I. AMINOGLYCOSIDES

Older Aminoglycosides:• Streptomycin• KanamycinNewer Aminoglycosides: Gentamicin Netilmicin Tobramycin

Sisomicin Neomycin Paromomyci

n Amikacin

I. AMINOGLYCOSIDES

Antimicrobial Spectrum:• Gram (-) Aerobic Bacilli• Beta-lactamase producers: Staph. aureus N. gonorrhea• Mycobacteria

I. AMINOGLYCOSIDES

Mechanism of Action:interferes with initiation complex of

peptide formationinduces misreading of mRNA causing

incorporation of incorrect AAcauses breakup of polysomes into

nonfunctional monosomesRequire oxygen uptake, therefore

ineffective against anaerobes.Bactericidal

I. AMINOGLYCOSIDES

Microbial Resistance:•enzyme inactivation•Cell surface alteration•receptor protein alteration•oxygen requirement related

I. AMINOGLYCOSIDES

Kinetics:• Very poorly absorbed from intact GIT,

well absorbed thru IM, IV• They are highly polar compounds that

do not enter the cells readilly, poorly penetrate the BBB

• not significantly metabolized• primarily excreted unchanged through

GF

I. AMINOGLYCOSIDESClinical Uses:• severe gram (-) enteric bacteria

especially when there is suspicion of sepsis

• always used in combination with a beta-lactam antibiotic to extend coverage to include potential gram (+) pathogens

• Penicillin aminoglycoside combinations also are used to achieve bactericidal activity in treatment of enterococcal endocarditis and to shorten duration of therapy for viridans streptococcal and staphylococcal endocarditis

• Mycobacterial infections

I. AMINOGLYCOSIDES

Toxicity:• Ototoxicity (esp. with loop diuretics)

– Auditory damage – Neomycin, Kanamycin and Amikacin

– Vestibular damage- Streptomycin, Gentamicin

• Nephrotoxicity (esp. with vancomycin & amphotericin)

• Neomycin, Tobramycin, Gentamicin - most nephrotoxic

STREPTOMYCIN• ribosomal resistance to this agent develops readily,

limiting its role as a single agent• Mainly used as 2nd line agent for the treatment of

tuberculosis given at 0.5-1 g/d , IM or IV.• usually given in drug combination to prevent emergence

of resistance.• In plague, tularemia and sometimes brucellosis, 1 g/d (15

mg/kg/d for children) IM or IV + oral tetracycline is used• + Penicillin; effective for enterococcal endocarditis and 2

week therapy of viridans streptococcal endocarditis.• can cause pain at the injection site, fever, skin rashes and

other allergic reactions • most serious toxic effect is vestibular dysfunction• if given during pregnancy, can cause deafness in the

newborn

GENTAMICIN

• in severe infections (sepsis and pneumonia) caused by gram (-) bacteria that are likely resistant to other drug, used in combination with a cephalosporin or a penicillin

• given at 5-6 mg/kg/d IV in three equal doses

• + Penicillin G for bactericidal activity in endocarditis due to viridans streptococci or enterococci and in combination with Nafcillin in selected cases of staphylococcal endocarditis

Gentamicin• Neither gentamicin nor any other

aminoglycosides should be used for single agent therapy of pneumonia because penetration of infected lung tissue is poor and local condition of low pH and low oxygen contribute to poor activity

• Serum concentrations and renal function should be monitored if administration for more than a few days or if renal function is changing

GENTAMICIN• Gentamicin sulfate 0.1% - 0.3% cream,

ointment – for the treatment of infected burns, wounds, or skin lesions and the prevention of intravenous catheter infections.

• Topical gentamicin is partly inactivated by purulent exudates

• Ten milligrams can be injected subconjunctivally for treatment of ocular infections

• Nephrotoxicity is reversible and usually mild• Ototoxicity is Irreversible manifested as

vestibular dysfunction• hypersensitivity reactions are uncommon

TOBRAMYCIN

• Antimicrobrial spectrum and pharmacokinetic properties is identical to gentamicin

• Given at 5-6 mg/kg IM or IV into three equal amounts q 8 hours.

• Blood levels should be monitored in renal insufficiency

• Slightly more active against pseudomonas but not to E. faecium

• Ototoxic and nephrotoxic

AMIKACIN

• semisynthetic derivative of kanamycin• resistant to many inactivating enzymes• Strains of multiple drug resistant

tuberculosis, including Streptomycin resistant are usually susceptible

• given at 7.5 -15mg/kg/d as a once-daily or 2-3x weekly

• Serum concentrations should be monitored

• Nephrotoxic and ototoxic (auditory portion of CN VIII)

NETILMICIN

• shares many characteristics with gentamicin and tobramycin

• dosage and the routes of administration are the same

• completely therapeutically interchangeable with gentamicin or tobramycin and has similar toxicities

KANAMYCIN & NEOMYCIN• Paromomycin• Used for bowel preparation for elective surgery• Complete cross-resistance between kanamycin and

neomycin• Not significantly absorbed from the GIT; excretion of

any absorbed drug is mainly through GF into the urine• Too toxic for parenteral use, now limited to topical and

oral use• Solutions 1-5 mg/ml- used applied on infected surfaces

or injected into joints, pleural cavity, tissue spaces or abscess cavities where infection is present. ( 15 mg/kg/d)

• Ointments (Neomycin-Polymyxin-Bacitracin combination); applied to infected skin lesions or in the nares for suppression of staphylococci

KANAMYCIN & NEOMYCIN• In preparation for elective bowel surgery, 1 g of

Neomycin given orally q 6-8 hours + 1 g of erythromycin base

• Paromomycin, 1 g q 6 hours orally for 2 weeks is effective in intestinal amebiasis

• Nephrotoxic and ototoxic ( Auditory dysfunction)• Sudden absorption of postoperatively instilled

kanamycin from the peritoneal cavity (3-5 g) has resulted in curare-like neuromuscular blockade and respiratory arrest (Calcium gluconate and neostigmine can act as antidotes)

• Prolonged application to skin and eyes-severe allergic reactions

SPECTINOMYCIN• chemically related to the aminoglycosides• binds at the 30 S subunit (bacteriostatic)• dispensed as the dihydrochloride

pentahydrate for IM injection• used solely as an alternative treatment for

gonorrhea in patients who are allergic to penicillin or whose gonococci are resistant to other drugs

• single dose of 2 g (40 mg/kg)• Can cause pain at the injection site ,

occasionally fever and nausea• Nephrotoxicity and anemia – rare

II.TETRACYCLINES:

• Short Acting:Tetracyline, Oxytetracycline, Chlortetracycline

• Intermediate Acting:Demeclocycline, Methacycline

• Long Acting:Doxycycline, Minocycline

II. TETRACYCLINES

Antimicrobial Spectrum:• Rickettsia, V. cholera, M.

pneumonia, Chlamydia, Shigella, H. pylori, P.tularensis, P.pseudomallei, Brucella, Psittacosis, Borrelia

• Minocycline – carrier state of Meningococcal infections, N. asteroides, N. gonnorhea

II. TETRACYCLINES

Mechanism of Action:• enter microorganisms in part by passive

diffusion and in part by an energy-dependent process of active transport

• binds to 30S subunit, blocking the binding of amino-acyl t-rna to the acceptor site and prevents the addition of amino acids to the growing peptide

• Bacteriostatic

II. TETRACYCLINES

Resistance:• decreased intracellular accumulation

due to impaired influx or increased efflux by an active transport protein pump

• ribosome protection due to production of proteins that interfere with tetracycline binding to the ribosome

• enzymatic inactivation

II. TETRACYCLINES

Kinetics• Distributed widely to tissue and body fluids except for

CSF• Absorption occurs mainly in the upper small intestine

and is impaired by food (except Doxycyline and Minocycline)

• Must not be taken with dairy products or antacids• Cross placenta, excreted in milk• As result of chelation with Ca, they are bound to and

damage growing bones and teeth • Carbamazepine, phenytoin, barbiturates, and chronic

alcohol ingestion may shorten the half-life of doxycycline

• Excreted mainly in bile and urine (Doxycycline fecally eliminated; can be used in renal failure)

II. TETRACYCLINES

Clinical Uses:• DOC in infection with M. pneumoniae,

chlamidiae,ricketsiae,and spirochetes. • No longer recommended for gonococcal

disease due to resistance. Usually use in combination aminoglycosides

• Borrelia burgdorfi (Lyme disease), Chlamydia, Ureaplasma, Acne, Tularemia, Cholera, Leptospirosis, Protozoal infections

• Minocycline, 200 mg orally daily for 5 days – can eradicate the meningococcal carrier state

• Demeclocycline – inhibits the action of ADH in the renal tubule and has been used in the treatment of inappropriate secretion of ADH or similar peptides by certain tumors

II. TETRACYCLINES

Clinical Uses:• Tetracyclines – 250-500 mg 4x/day adults;

20-40 mg/kg/d-children above 8 y/o• Demeclocycline and Methacycline → 600

mg daily • Doxycyline and Minocycline → 100 mg 1-

2x/d

Toxicity: • Renal toxicity, local tissue toxicity,

photosensitization, GI distress, discolors teeth, inhibits bone growth in children, potentially teratogenic, hepatotoxicity, vestibular toxicity

THE 50 S INHIBITORS:

• CHLORAMPHENICOL• MACROLIDES• CLINDAMYCIN/LINCOMYCIN• STREPTOGRAMINS• OXAZOLADINONES

I. CHLORAMPHENICOL

• Bactericidal – H. influenzae, N. meningitides, B. fragilis

• Bacteriostatic – S. epidermidis, S. aureus, , M. pneumonia, L. monocytogenes, C.diphtheria, L. multocida, Salmonella sp., Shigella sp., E. coli, Rickettsia, Anaerobes

I. CHLORAMPHENICOL

MECHANISM OF ACTION:• Bind to the 50 S subunit of

microbial ribosomes and blocks the functional attachment of amino-acyl-tRNA to the acceptor site

• inhibits peptidyl transferase step

I. CHLORAMPHENICOL

SPECTRUM:• broad spectrum antibiotic• more effective than Tetracyclines

against Typhoid Fever and other Salmonella infections

I. CHLORAMPHENICOL

KINETICS:• well absorbed after oral administration; usual

dosage is 50-100 mg/kg/d• Chloramphenicol succinate used for parenteral

administration is highly water soluble• Well distributed to all tissues & body fluids, including

the CSF, ocular and joint fluids• rapidly excreted in urine, 10% as chloramphenicol;

90% as glucuronide conjugate; small amount of active drug is excreted into bile or feces

• systemic dosage need not be altered in renal insufficiency but must be reduced markedly in hepatic failure

• Newborns less than a week old and premature infants also clear Chloramphenicol less well, dosage should be reduced at 25 mg/kg/d.

I. CHLORAMPHENICOL

CLINICAL USES: • Meningitis, Rickettsia, Salmonella and

anaerobic infections; • ineffective against chlamydial infections• occasionally used topically in the treatment

of eye infections for its well penetration to ocular tissues and the aqueous humor

ADVERSE EFFECTS: • GIT, oral or vaginal candidiasis, irreversible

aplastic anemia, reversible bone marrow depression, Gray Baby Syndrome

II. MACROLIDES:

• Old Generation: Erythromycin, Oleandomycin, Troleandomycin, Spiramycin, Josamycin

• New Generation: Rosaramycin, Roxithromycin, Clarithromycin, Azithromycin, Dirithromycin

II. MACROLIDES

MECHANISM OF ACTION:• binds to the P site of the 50 S

bacterial ribosomal subunit.• Aminoacyl translocation and

formation of initiation complex are blocked

• Inhibitory or bactericidal

II. MACROLIDES

RESISTANCE:• reduced permeability of the cell

membrane or active efflux• production (by

Enterobacteriaceae) of esterases that hydrolyze macrolides

• modification of the ribosomal binding site by chromosomal mutation

II. MACROLIDES

SPECTRUM: • Erythromycin has a narrow Gram

(+) spectrum similar to Pen. G.• DOC in corynebacterial infection

(diptheria and corynebacterial sepsis)

• Also active against Chlamydia and Legionella organisms

Erythromycin• prototype• distributed widely to the body fluids except CSF• Base form easily destroyed by stomach acid & must

be administered with enteric coating• food interferes with absorption• serum half life is app. 1.5 h normally and 5 hours in

patients with anuria• is not removed by dialysis• metabolized in the liver excreted in the bile & feces• traverses the placenta and reaches the fetusCOMMERCIAL PREPARATIONS:• Oral-stearate, ethyl succinate, estolate salts: 250-

500 mg q 6 h • Parenteral- lactobionate, gluceptate : 0.5-0.1. g q 6

hours

Erythromycin

ADVERSE EFFECTS: • GIT dysfunction, intrahepatic

cholestatic jaundice (particularly with estolate prep)

• erythromycin metabolites can inhibit cytochrome p450 enzymes & thus increase the serum concentrations of theophylline, oral anticoagulants, cyclosporine, methylprednisolone and digoxin by increasing its bioavailability

Clarithromycin

• Derive from erythromycin by addition of methyl group

• more active against Gram (+) pathogens, Legionella and Chlamydia than Erythromycin

• lower frequency of GIT effects, less frequent dosing

• half life of 6 hours • given at 250-500 mg twice daily

Azithromycin

• Active against M. avium and T.gondii• Less active than erythromycin and chlarithromycin

against staph. and strep. • More active against H. influenzae and chlamydia• Penetrates into most tissues (except CSF) and

phagocytic cells extremely well• maintains high concentrations for prolonged periods

into a number of tissues (lungs, tonsils, cervix)• tissue half life – 2-4 days• long half-life allows once daily oral administration

and shortening of treatment in many cases ( a single 1 g dose of azithromycin is as effective as a 7 day course of doxycycline for chlamydial cervicitis and urethritis)

Azithromycin

• Community acquired pneumonia – 500 mg loading dose, followed by a 250 mg single daily dose for the next 4 days

• should be administered 1 hour before or 2 hours after meals; aluminum and magnesium delay absorption and reduce peak serum concentrations

• does not inactivate cytochrome p450 enzymes and free of the drug interactions that occur with erythromycin and clarithromycin

III. CLINDAMYCIN / LINCOMYCIN

MECHANISM OF ACTION: • attach to 50 S ribosomal subunit,

inhibits protein synthesis by interfering with the formation of initiation complexes and translocation reaction

SPECTRUM: • Narrow Gram (+) spectrum, excellent

activity against anaerobic bacteria; strep, pneumococci, staphylococci

III. CLINDAMYCIN / LINCOMYCIN

RESISTANCE: • mutation of the ribosomal

receptor site• modification of the receptor by a

constitutively expressed methylase

• enzymatic inactivation

III. CLINDAMYCIN / LINCOMYCIN

• Clindamycin is more clinically used than Lincomycin

• Penetrates well into most tissue except brain and CSF

• given at 150-300 mg q 6 hrs adults ;10-20 mg/kg/d for children

• well bone penetration• Metabolized in the liver, excreted in the bile

and urine• half life is 2.5 hours normally and 6 hours in

patients with anuria• more toxic than erythromycin

CLINDAMYCIN

Clinical uses:• prophylaxis of endocarditis in patients with

valvular heart disease for dental procedures• most important indication is the treatment

of severe anaerobic infection caused by bacteroides and other anaerobes that often participate in mixed infections

• + aminoglycoside or cephalosporin- used to treat penetrating wounds of the abdomen & gut, septic abortion, pelvic abscesses, aspiration pneumonia

CLINDAMYCIN• + primaquine – effective alternative to

trimethoprim sulfamethoxazole for moderate to moderately severe Pneumocystis carinii pneumonia in AIDS patients

• + pyrimethamine – in AIDS related toxoplasmosis of the brain.

ADVERSE EFFECTS: • Diarrhea, nausea , skin rashes, impaired

liver function and neutropenia• Antibiotic associated colitis caused by

toxigenic C. difficile.

STREPTOGRAMINSQuinupristin-Dalfopristin (Synercid)• action is similar to macrolides • bactericidal for staph and most organisms

except Enterococcus faecium• prolonged postantibiotic effect up to 10 h for

Staph. aureus• administered IV at 7.5 mg/kg q 8 -12 h• eliminated through fecal route, < 20% urine• Patients with hepatic insufficiency may not

tolerate the drug at usual doses• inhibits CYP 3A4 P450, which metabolizes

warfarin, diazepam, astemizole, terfenadine, cisapride, nonnucleoside reverse transcriptase inhibitors and cyclosporine.

STREPTOGRAMINS

Clinical Uses: • infections caused by Vancomycin

resistant strains of E faecium but not E. faecalis,

• bacteremia or respiratory tract infections caused by methicillin-resistant staphylococci and penicillin susceptible and resistant strains of S. pneumonia

Toxicities: • infusion related events like pain at the

injection site, arthralgia, myalgia

OXAZOLADINONES: Linezolid (Zyvox)

• inhibits protein synthesis by preventing formation of the ribosome complex that initiated protein synthesis.

• Its unique binding site located on the 23 S ribosomal RNA of the 50 S subunit, results in no cross resistance with other drug classes

• Has high oral bioavailability, half life of 4-6 h• Uses : staph, strep, enterococci, G(+)

anaerobic cocci, G (+) rods, Corynebacterium, and L. monocytogenes

• treatment of infections caused by vancomycin resistant E. faecium and other infections caused by multiple drug resistant organisms.

METABOLIC INHIBITORS

Claro M. Isidro M.D.

SULFONAMIDES

METABOLIC INHIBITORS Sulfonamides• structural analogs of PABA• competitively inhibit dihydropteroate

synthase (catalyzed the synthesis dihydropteroic acid)

• inhibits growth by reversibly blocking folic acid synthesis

• bacteriostatic

SULFONAMIDES

Spectrum of activity:• Inhibit the growth both Gm (+) and

Gm (-) bacteria, Nocardia, Chlamydia trachomatis & some protozoa

• Enteric bacteria such as E.coli,klebsiella, salmonella,shigella, and enterobacter are also inhibited

• Rickettsia – not inhibited but growth stimulated by sulfas

SULFONAMIDES

RESISTANCEoccur as a result of mutations

that:• cause overproduction of PABA• cause production of a folic acid

synthesizing enzyme that has a low affinity for sulfonamides• cause a loss of permeability to

sulfonamides

SULFONAMINDES

Pharmacokinetics: three major groups• oral, absorbable

a. short-acting: sulfacytine, sulfisoxazole, sulfamethizole b. medium- acting: sulfadiazine, sulfamethoxazole, sulfapyridine c. long- acting: sulfadoxine

• oral, nonabsorbablea. Sulfasalazineb. Olsalazine

SULFONAMIDES• topical

a.Sodium sulfacetamide ophthalmic sol’n or ointment – for bacterial conjunctivitis

b. Mafenide acetate- prevent bacterial colonization and infection of burn wounds

c. Silver sulfadiazine –prevent of infection in burn wounds

SULFONAMIDES

Pharmacokinetics• Well absorbed from the GIT• Widely distributed in the body

including the CNS, placenta & fetus• Highly bound to albumin• Acetylated or glucorinated in the liver • Excreted into the urine – mainly by

glomerular filtration

SULFONAMIDE

• SPECTRUM: gram (+) & gram (-)• Simple urinary tract infection• Ocular infection • Burn infections• Ulcerative colitis• With pyrimethamine: Toxoplasmosis Malaria

SULFONAMIDES Adverse Reaction• Hypersensitivity Reaction• Photosensitivity• Nausea & vomiting• Hemolytic anemia• Crystalluria & nephrotoxicity ( tx alkalinize

the urine by NaHCO3

• Kernicterus in the newborn• CI: Pregnancy & newborn• DI: Compete with wafarin, tolbutamide,

methotrexate for PPB

TRIMETOPRIM SULFAMETHOXAZOLE (CO-TRIMOXAZOLE)

COMBINATION CAUSES:1. INCREASE POTENCY2. INCREASE SPECTRUM3. DECREASE INCIDENCE OF RESISTANCE

MOA: blocks the sequential steps in the obligate enzymatic reaction in bacteria preventing formation of nucleotide

CO-TRIMOXAZOLE

Pharmacokinetcs• Trimetoprim: more lipid soluble,

greater Vd• Given in 1: 5 ratioCLINICAL USES• SPECTRUM: broad gm + & gm –• UTI, pneumonia, gonorrhea &

prostatitis, Acute chronic bronchitis, acute otitis media, chancroid, shigellosis, typhoid fever, nocardiosis

CO-TRIMOXAZOLE

• HYPERSENSITIVITY REACTIONS• PHOTOSENSITIVITY• NAUSEA & VOMITING• HEMOLYTIC ANEMIA• CRYSTALLURIA & NEPHROTOXCITY• KERNICTERUS• CI: PREGNANCY & NEWBORN• DI: COMPETE WITH WARFARIN,

METHOTREXATE FOR PPB

Other drug combinations1.Sulfadiazine + pyrimethamine for leishmaniasis &

toxoplasmosis2. Sulfadoxime + pyrimethamine for Falciparum malaria

NUCLEIC ACID SYNTHESIS INHIBITORS

• First Generation: Nalidixic acid• Second Generation: Ofloxacin,

Ciprofloxacin, Norfloxacin, Levofloxacin

• Third Generation: Gatifloxin, Sparfloxacin Clinafloxacin,

• Fourth Generation: Trovafloxacin, Moxifloxacin

Fluoroquinolones

• Bactericidal• Inhibits DNA Gyrase or

Topoisomerase II - Block the relaxation of supercoiled DNA that is catalyzed by DNA gyrase

• Inhibits Topoisomerase IV – interferes with the separation of replicated chromosomal DNA during cell division

Fluoroquinolones

ResistanceA. Modification of DNA GyraseB. Decreased accumulation in the

bacterial cell due to : 1. reduction of the porin proteins in the

outer membrane2. energy dependent efflux system of the

inner membrane

Fluoroquinolones

Clinical Uses• SPECTRUM: broad ; aerobic gm (+) & gm (-) but not

anaerobes• UTI• Sexually transmitted diseases : Gonorrhea,

Chlamydia, chacroid, Prostatitis• Respiratory infection due to H. influenza, M.

catarrhalis, Strep pneumoniae, M. pneumoniae• Nosocomial infection (P. aeroginosa)• GIT infections due to : E.coli, Shigella, & Salmonella • Chronic bone infection due to Pseudomonas &

Staph. aereus • Diabetic foot infections

CIPROFLOXACIN• Most widely used• DOC for anthrax• Most potent for P. aeroginosa• Synergistic with beta lactams• M. tuberculosis

NORfLOXACIN• Not effective in systemic infection

LEVOFLOXACIN

• Prostatitis ,E. coli• Sexually transmitted diseases,

gonorrhea• Skin infections• S. pneumoniae

TROVA & MOXIFLOXACINAnaerobes, P. AEROGINOSA

GATIFLOXACIN Resp infection , S. pneuomoniae

Fluoroquinolones

Side Effects•Nausea & diarrhea•Headache, dizziness, light

headedness•Arthralgia & joint swelling•Rashes & photophobia

Fluoroquinolones

• CI: PREGNANT WOMEN, NEONATES• ARRYTHMIAS: SPARFLOXACIN &• MOXIFLOXACIN: prolong QT

intervals• DI: ↓ ABSORPTION WITH ANTACID ,

FeSo4• Cimetidine interferes elimination• Ciprofloxacin & ofloxacin: ↑

theophylline levels

1-3. Three stages of protein synthesis

4. Drugs that inhibit 30S subunit5. DOC for anthrax6 & 7. Drugs that inhibit 50S

subunit8. Enzyme inhibited by sulfonamide9. Enzyme inhibited by

flouroquinolone10. DOC for anaerobic infection