Pharmacokinetics of Levetiracetam in Neonates with Seizures

A thesis submitted to the

Graduate School

of the University of Cincinnati

in partial fulfillment of the

requirements for the degree of

Master of Science in Clinical and Translational Research

in the Department of Environmental Health

of the College of Medicine

by

Stephanie Merhar

BA, University of Virginia

MD, University of Pennsylvania

June 2011

Committee Chair: Paul Succop, PhD

ii

ABSTRACT

Objective:

To evaluate the pharmacokinetics and adverse events of intravenous levetiracetam in treating

newborns with seizures.

Study design:

This was a prospective, open-label observational pharmacokinetic study in neonates ≥ 32 weeks

gestational age and ≤ 30 days of age with seizures persisting despite treatment with

phenobarbital. A loading dose of intravenous levetiracetam was given as per the prescribing

physician, followed by additional doses based on clinical response. Blood samples were

prospectively collected and analyzed for levetiracetam concentrations. Vital signs were

monitored during levetiracetam treatment, and safety and efficacy data were collected.

Results:

Eighteen patients (median 39 weeks gestation and 2 postnatal days) were included. Initial

loading doses ranged from 14.3-39.9 mg/kg. Median (range) clearance, volume of distribution,

and elimination half-life were 1.2 ml/min/kg (0.5-2.9), 0.89 L/kg (0.4-1.3), and 8.9 hours (3.2-

13.3), respectively. No adverse events related to levetiracetam were observed. Nine out of 18

patients required additional loading doses of levetiracetam to control their seizures.

Conclusions:

LEV clearance was lower, volume of distribution larger, and half life longer in neonates as

compared to older children. Given the increased volume of distribution and lower clearance in

neonates, we recommend a loading dose of at least 30 mg/kg, followed by maintenance dosing

every 8-12 hours.

iii

iv

ACKNOWLEDGMENTS

I would like to thank my mentors for this project, Kurt Schibler and Sander Vinks. I would also

like to thank all those who helped with planning and implementation, Paul Succop for his role as

my advisor, and most of all of the patients and families who took part in the study.

v

TABLE OF CONTENTS

Introduction……………………………………………………………………………………………1

Methods………………………………………………………………………………………………..2

Results……………………………………………………………………………………………….....4

Discussion……………………………………………………………………………………………..6

Bibliography…………………………………………………………………………………………..15

LIST OF TABLES/FIGURES

Table 1…………………………………………………………………………………………………11

Table 2…………………………………………………………………………………………………12

Figure 1………………………………………………………………………………………………...13

Figure 2………………………………………………………………………………………………...14

1

INTRODUCTION

Neonatal seizures are a common problem, affecting two to five per thousand infants in

the first month of life (1-3). Recent animal and human studies have shown that seizures can

harm the developing brain (4-6), reinforcing the current practice of treating electrographic

seizures in newborns. Phenobarbital, introduced in 1914, is still the most common medication

used to treat neonatal seizures (7). However, in the one randomized controlled trial on its use in

neonates, phenobarbital was effective in eliminating neonatal seizures only 43% of the time (8).

In addition, phenobarbital has been shown to cause neuronal apoptosis in rat pups (9,10), and

children receiving phenobarbital for febrile seizure prophylaxis were found to have decreased

cognitive ability and school achievement compared with those receiving placebo (11-13). For

these reasons, there has been considerable interest in recent years in developing new antiepileptic

medications for use in neonates.

Levetiracetam (Keppra®), introduced in 2000, is an anticonvulsant with a novel

mechanism of action that has been studied extensively in adults and older children (14-18).

Although its precise mechanism of action has not been fully established, levetiracetam is known

to bind to synaptic vesicle protein 2A in the central nervous system and does not appear to

directly affect the traditional excitatory and inhibitory neurotransmitter systems (18,19). Studies

in adults have shown that levetiracetam has linear pharmacokinetics (18), which means that

changes in dose result in proportional changes in drug concentration and exposure as measured

by the area under the concentration-time curve (AUC). Levetiracetam is mainly excreted by the

kidneys, and elimination correlates with creatinine clearance (18). The major metabolic pathway

is enzymatic hydrolysis by a plasma esterase (18). The volume of distribution of levetiracetam is

similar to total body water, and it has no documented clinically significant drug-drug interactions

2

(18).

Pharmacokinetic, safety, and efficacy trials have been performed in children down to 1

month of age (14-16,20,21). Case series have suggested that levetiracetam may be safe and

effective in the treatment of neonatal seizures (22-24), and a recent prospective study in 38 term

and preterm infants showed no adverse effects of a slow titration of levetiracetam (25). The aim

of our study was to determine the pharmacokinetics of levetiracetam and to gather preliminary

safety and efficacy in neonates with seizures.

METHODS

This study was conducted at Cincinnati Children's Hospital Medical Center and Good

Samaritan Hospital between October 2008 and June 2010. The institutional review board at each

hospital approved the protocol and written informed consent was obtained from the legal

guardian of all subjects. An investigational new drug application (IND) was obtained from the

FDA to perform this study.

Eligible neonates were ≤ 30 days old and ≥ 32 weeks gestational age, with seizures

requiring treatment with levetiracetam. Levetiracetam is often used as a second line medication

for the treatment of neonatal seizures in our institution. All subjects received at least 20 mg/kg

of phenobarbital before receiving levetiracetam. Exclusion criteria included birth weight < 2000

g and known creatinine ≥ 2.0 mg/dl.

Levetiracetam injection (100 mg/ml, UCB Pharma) was used for the initial loading dose

in all patients. Dosing was not specified in the protocol and was determined by the clinician

prescribing the drug. Levetiracetam was infused over 15 minutes as per package insert. Blood

sampling was conducted using a D-optimal sparse sampling design with three samples collected

in each patient (26). Patients were divided into three groups to obtain informative time points

3

over the entire dosing interval. Group 1 had samples drawn at 2-15 minutes, 1-2 hours, and 12

hours post infusion; Group 2 had samples drawn at 2-15 minutes, 2-4 hours, and 18 hours post

infusion, and Group 3 had samples drawn at 5-15 minutes, 4-8 hours, and 20-24 hours post

infusion.

In order to prevent metabolism by esterases in the test tube, the plasma was separated by

centrifugation directly after collection (27) and stored at -700 C until analysis. Levetiracetam

concentrations were determined by the Bioanalytical Core Laboratory at Georgetown University

using a validated liquid chromatography-electrospray tandem mass spectrometry assay (28). The

lower limit of detection of the assay was 0.1 µg/mL for plasma. Within-run and between-run

imprecision (n=10) for LEV controls ranged from 2.3%-4.7% and 3.4%-8.9%, respectively (29).

Non-linear mixed effects modeling (NONMEM, version 7.1, ICON Dev. Soln., Ellicott

City, MD) with PDx-Pop® (version 4.10, 2007 ICON Dev. Soln., Ellicott City, MD) interfaced

with Xpose® (version 4.0, release 6, update 1) was used to perform the pharmacokinetic

analyses. Individual Bayesian pharmacokinetic parameter estimates were calculated using

MW/PHARM (Version 3.60; MediWare, Groningen, The Netherlands) (30). The parameters of

interest were clearance, elimination half life, volume of distribution, and area under the curve at

2, 4, 6, 12, and 24 hours. SAS (Version 9.2, SAS Institute Inc, Cary, NC) was used to analyze

associations between demographic and pharmacokinetic parameters.

Safety assessments included a physical examination before and 24 hours after the loading

dose of levetiracetam and monitoring of vital signs (heart rate, respiratory rate, oxygen

saturation, and blood pressure) every 15 minutes for one hour after the loading dose and hourly

for 24 hours. All infants in the study had a renal panel, glucose, and electrolytes drawn before

receiving the initial dose of levetiracetam. Further labs were drawn for clinical reasons and were

4

recorded in the research record. Adverse events were reported by bedside nurse in response to

an open question about whether any problems were seen after the loading dose. Study subjects'

charts were reviewed at hospital discharge to identify any adverse events occurring during the 24

hours after the loading dose and during the remainder of the hospital stay.

Seizure frequency before and after the loading dose of levetiracetam was monitored

clinically or documented using full channel EEG at the discretion of the clinicians caring for the

patient. Further loading doses of levetiracetam were administered for the continuation of clinical

and/or electrographic seizures as per the discretion of the clinical team. Efficacy was coded as a

dichotomous variable: whether or not the infant required further loading doses of levetiracetam

after the initial loading dose. Statistical analysis for efficacy data was performed using SAS

(Version 9.2, SAS Institute Inc, Cary, NC).

RESULTS

A total of 21 infants who received levetiracetam for clinical and/or electrographic seizure

control were screened for the study from October 2008 to May 2010, and 19 of these infants

were enrolled in the study. The 2 patients who were not enrolled received levetiracetam before

consent could be obtained from the parents. One of the 19 subjects was excluded due to a lab

error resulting in only 2 usable samples. The resulting pharmacokinetic data consisted of 54

levetiracetam concentrations from 18 subjects. One patient was enrolled in the study at day of

life 30 but did not receive levetiracetam until day of life 32. This was not discovered until all

samples had been drawn, and the decision was made to include this patient in the final analysis.

The patient characteristics are summarized in table 1.

A loading dose of IV levetiracetam was administered at the discretion of the prescribing

physician. Loading doses ranged from 14.4-39.9 mg/kg. Further loading doses were

5

administered for the continuation of clinical and/or electrographic seizures as directed by the

clinical team caring for the patient. A maintenance dosing regimen of levetiracetam was

initiated in most cases, and was given IV during the study period in 17/18 patients. The first

maintenance dose was given 8-12 hours after the loading dose(s).

Pharmacokinetic modeling:

A two compartment model with first order elimination provided the best fit to the data.

The most significant covariates determined in the univariate analysis were weight, postmenstrual

age, serum creatinine, and creatinine clearance. After multivariate analysis, only weight and

creatinine clearance remained in the final model. Some unexplained variability remained in the

model (32-43%), which may be due to the small number of subjects with only 3 levetiracetam

concentrations per subject.

The parameter estimates from the base model were entered into MWPHARM to

determine the pharmacokinetic parameters for each individual subject, shown in table 2. The

median (range) Cmax as predicted by the model was 39.8 (14.8-91.9) mg/L. The highest

measured concentration measured in the study patients was 87.6 mg/L, 1 hour after a 30 mg/kg

dose. There was a significant linear relationship between serum creatinine and half life (Figure

1, Pearson correlation r = 0.67, p = 0.0002). Linear relationships were also found between serum

creatinine and levetiracetam clearance (r = -0.53, p = 0.02), and creatinine clearance and

levetiracetam clearance (r = 0.66, p = 0.003).

Safety and tolerability:

Levetiracetam was well tolerated in this population. No changes in vital signs or

laboratory parameters were observed. Several infants were noted to be somnolent in the 24

hours after levetiracetam administration. However, the majority of these infants were critically

6

ill and had received both phenobarbital and levetiracetam. The somnolence was recorded as

possibly related to levetiracetam administration.

One patient with overwhelming HSV infection died after withdrawal of support 24 hours

after receiving levetiracetam. One patient with severe HIE died after withdrawal of support 10

hours after receiving levetiracetam. These deaths were deemed not related to levetiracetam

administration.

Efficacy:

This was designed as a pharmacokinetic study and was not sufficiently powered to

determine efficacy. Seizure frequency before and after the loading dose of levetiracetam was

monitored at the discretion of the clinicians caring for the patient. Nine of the 18 patients were

monitored by continuous full channel EEG during the initial loading dose of levetiracetam and

for at least 6 hours afterwards. Seven out of the 10 patients who received a 20 mg/kg loading

dose received a second loading dose of IV levetiracetam within 12 hours of the first due to

continued electrographic and/or clinical seizures. During the study period, clinical practice in

our institution changed to using a higher loading dose of levetiracetam (30 mg/kg instead of 20

mg/kg). This higher loading dose seemed to be more effective in stopping initial seizures (figure

2). A simple logistic regression model was constructed modeling the initial dose in mg/kg on

efficacy (whether the patient required a second dose of levetiracetam acutely to control

continued seizures) and the area under the ROC curve was reported. This simple model had an

area under the ROC curve of 0.77 (p = 0.10). Overall, after receiving levetiracetam, 15 out of

the 18 infants in the study (83%) did not require a third-line medication for seizure control.

DISCUSSION

7

The main objective of this study was to determine the pharmacokinetics of IV

levetiracetam in neonates with seizures. We found that levetiracetam pharmacokinetics were

different in this population than in adults and older children. The safety profile appeared to be

favorable with no serious adverse effects noted. Two deaths occurring in this critically ill study

population were deemed to be unrelated to levetiracetam treatment. We also found that

levetiracetam was effective for acute seizure control, with only 3 of the 18 infants requiring a

third line drug beyond phenobarbital and levetiracetam.

The pharmacokinetics of levetiracetam in adults and older children have been well

characterized. The half-life is 6-8 hours in adults (18) and 5-7 hours in older children (17,20).

In the only study that evaluated the pharmacokinetics of levetiracetam in neonates, the half life

was found to be 16-18 hours in newborn twins whose mother had received an oral dose of

levetiracetam 45 minutes prior to delivery (31). We found the median half-life of levetiracetam

to be 8.9 hours, which might be expected based on the lower clearance of levetiracetam in

neonates. The volume of distribution, the hypothetical volume in which an amount of drug

would need to be uniformly distributed to produce the observed blood concentration, is 0.5-0.7

L/kg in adults (32) and 0.6-0.7 L/kg in older children (17,20). The median volume of

distribution in our study was 0.89 L/kg. Because neonates have higher body water content than

adults and older children (as much as 85% total body water in preterm infants and 78% in full

term infants as compared to 60% in adults) (33) and levetiracetam distributes in parallel with

total body water, we would expect the volume of distribution to be higher in neonates than in

older children and adults.

Total body clearance of levetiracetam in adults is 0.96 ml/min/kg (18) and in children is

1.43-1.46 ml/min/kg (17,20). We found the clearance in neonates to be 1.21 ml/min/kg,

8

intermediate between adults and older children. Weight-adjusted clearance is often higher in

children than in adults, but models which allometrically scale clearance based on surface area or

the 3/4 power model often predict no difference in the size scaled clearance between these two

populations (34). Using the 3/4 power model, the standard clearance is 67.2 ml/min and the

clearance of neonates (with a mean weight of 3.3 kg, as in this study) is predicted to be 6.8

ml/min. The clearance of the neonates in this study was found to be 3 ml/min in the NONMEM

two compartment model and 4.2 ml/min in the MWPharm two compartment model, lower than

would be predicted using the 3/4 power model. Allometric scaling is able to correct for growth,

but does not correct for maturational differences in the population (34). Since clearance was

found to be lower in neonates than would be predicted using allometric scaling, we conclude that

the lower clearance of levetiracetam in this population is due to the lower GFR and possibly to

lower plasma esterase activity. In support of this conclusion, a significant linear relationship was

found between serum creatinine and levetiracetam clearance.

Based on the higher volume of distribution in neonates, the loading dose on a mg/kg basis

should be higher than in older children and adults. We found that a loading dose of 30 mg/kg

was more effective in controlling seizures than a loading dose of 20 mg/kg in our study

population. Due to the reduced clearance in neonates, the dosing interval may need to be

extended, at least until the GFR matures. Therefore, a twice daily dosing schedule may be more

appropriate than a three times daily schedule in neonates over the first several weeks of life. In

infants with reduced creatinine clearance, the dosing interval may need to be extended even

further.

Routine therapeutic drug monitoring has not been recommended for levetiracetam in the

past, as drug levels have not been found to correlate well with therapeutic efficacy (35,36). A

9

reference range of 12-46 mg/L has been proposed for adults with epilepsy (37), and most clinical

labs suggest similar reference ranges. Toxic levels have not been well established. The highest

concentration measured in our study was 87.6 mg/L and the highest Cmax predicted by the

model was 91.9 mg/L. No adverse effects were seen beyond mild somnolence even at these high

levels. Therapeutic drug monitoring may be useful in infants with impaired renal function, but

our study does not provide the data to support routine monitoring.

Infants in this study were closely monitored for 24 hours after the loading dose of

levetiracetam to assess for adverse events. Two subjects died after withdrawal of support due to

their severe underlying medical conditions during the 24 hours following levetiracetam

administration, but these deaths were not considered related to levetiracetam. Somnolence was

the only other adverse event recorded in subjects 24 hours after the dose that could possibly be

related to levetiracetam. The somnolence did not interfere with feeding or cause subjects to

require increased respiratory support. In older children, the main adverse events seen with

levetiracetam administration are somnolence, nervousness, dizziness, and irritability. In adults

and older children, small but statistically significant changes in hematologic parameters (RBC

count, mean hemoglobin, and WBC count) have been seen. These hematologic changes have not

been considered clinically significant by other investigators; therefore, we did not monitor

complete blood counts as part of the study. However, many of the infants in the study had

complete blood counts before and after receiving levetiracetam, and no changes were seen.

Although this study was not powered to determine efficacy, levetiracetam was considered

to be effective for acute seizure control in this population. In addition, as shown in figure 2, a

higher initial loading dose of 30 mg/kg appeared to be more effective than a loading dose of 20

mg/kg. When this relationship was examined with a simple logistic regression model, a trend

10

was found, but the study did not have sufficient power to detect statistical significance. Two

recent papers (24,25) have also suggested that levetiracetam is safe and effective in neonates.

These studies used lower doses (10 mg/kg BID), did not use continuous monitoring, and did not

include a control group.

This is the first pharmacokinetic study of levetiracetam in the neonatal population. We

were able to use a minimal sampling strategy to obtain pharmacokinetic parameters among

infants with variable seizure etiologies. The limitations of our study include the small sample

size with high interindividual variability. Although we intended to study preterm infants and

infants later in the first month of life, most of the patients in the study were full term and treated

with levetiracetam in the first two days of life. The pharmacokinetics of levetiracetam were

different in the neonatal population as compared to older children and adults, and in this small

study, levetiracetam was found to be safe and effective in the neonatal population. Future

investigations are needed to evaluate higher loading doses of levetiracetam in neonates, such as

the 50 mg/kg loading dose currently being used in older children with status epilepticus (38,39),

and to obtain more data on the steady state pharmacokinetics of levetiracetam in neonates.

Although levetiracetam appears to be effective in infants who have failed phenobarbital, more

information needs to be gathered on the efficacy of levetiracetam as a first line drug.

11

Table 1

Parameter n=18 % of total

Sex: Male

Female

10

8

56

44

Race: African-American

Caucasian

7

11

39

61

Cause of seizures: HIE1

Other2

6

12

33

67

Median Range

GA at birth (weeks) 38+6 35+2 - 41

Postnatal age (days) 2 0-32

Weight at time of dosing (kg) 3.5 2 – 4.4

Creatinine at time of dosing 0.7 0.2-1.6

1 HIE = hypoxic-ischemic encephalopathy

2 Other causes of seizures included ornithine transcarbamylase deficiency, hemimegalencephaly, cortical dysplasia,

perinatal stroke, herpes simplex virus, meningitis, birth trauma, kernicterus, and unknown (4 patients)

12

Table 2

Variable Median Range

Clearance (ml/min/kg) 1.21 0.47-2.89

Volume of distribution (L/kg) 0.89 0.37-1.26

Half-life (hours) 8.9 3.2-13.3

13

Figure 1

Creatinine (mg/dL)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Half

-Lif

e (

h)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

r=0.67, p=0.002

14

Figure 2

15

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