Acute Withdrawal Reactions
The continued use of benzodiazepines, including clobazam, may lead to clinically significant physical dependence. Abrupt discontinuation or rapid dosage reduction of clobazam after continued use, or administration of flumazenil (a benzodiazepine antagonist) may precipitate acute withdrawal reactions, which can be life-threatening (e.g., seizures) [se
e
Drug Abuse and Dependence (9.3)].
Protracted Withdrawal Syndrome
In some cases, benzodiazepine users have developed a protracted withdrawal syndrome with withdrawal symptoms lasting weeks to more than 12 months [see
Drug Abuse and Dependence (9.3)]
.
Adverse Reactions Leading to Discontinuation in an LGS Placebo Controlled Clinical Trial (Study 1)
The adverse reactions associated with clobazam treatment discontinuation in ≥1% of patients in decreasing order of frequency included lethargy, somnolence, ataxia, aggression, fatigue, and insomnia.
Most Common Adverse Reactions in an LGS Placebo Controlled Clinical Trial (Study 1)
Table 3 lists the adverse reactions that occurred in ≥5% of clobazam-treated patients (at any dose), and at a rate greater than placebo-treated patients, in the randomized, double-blind, placebo-controlled, parallel group clinical study of adjunctive AED therapy for 15 weeks (Study 1).
Table 3. Adverse Reactions Reported for ≥5% of Patients and More Frequently than Placebo in Any Treatment Group | | Clobazam Dose Level | |
|---|
| Placebo
N=59
%
| Low
Maximum daily dose of 5 mg for ≤30 kg body weight; 10 mg for >30 kg body weight N=58
%
| Medium
Maximum daily dose of 10 mg for ≤30 kg body weight; 20 mg for >30 kg body weight N=62
%
| High
Maximum daily dose of 20 mg for ≤30 kg body weight; 40 mg for >30 kg body weight N=59
%
| All Clobazam
N=179
%
|
|---|
| Gastrointestinal Disorders |
| Vomiting | 5 | 9 | 5 | 7 | 7 |
| Constipation | 0 | 2 | 2 | 10 | 5 |
| Dysphagia | 0 | 0 | 0 | 5 | 2 |
| General Disorders and Administration Site Conditions |
| Pyrexia | 3 | 17 | 10 | 12 | 13 |
| Irritability | 5 | 3 | 11 | 5 | 7 |
| Fatigue | 2 | 5 | 5 | 3 | 5 |
| Infections and Infestations |
| Upper respiratory tract infection | 10 | 10 | 13 | 14 | 12 |
| Pneumonia | 2 | 3 | 3 | 7 | 4 |
| Urinary tract infection | 0 | 2 | 5 | 5 | 4 |
| Bronchitis | 0 | 2 | 0 | 5 | 2 |
| Metabolism and Nutrition Disorders |
| Decreased appetite | 3 | 3 | 0 | 7 | 3 |
| Increased appetite | 0 | 2 | 3 | 5 | 3 |
| Nervous System Disorders |
| Somnolence or Sedation | 15 | 17 | 27 | 32 | 26 |
| Somnolence | 12 | 16 | 24 | 25 | 22 |
| Sedation | 3 | 2 | 3 | 9 | 5 |
| Lethargy | 5 | 10 | 5 | 15 | 10 |
| Drooling | 3 | 0 | 13 | 14 | 9 |
| Ataxia | 3 | 3 | 2 | 10 | 5 |
| Psychomotor hyperactivity | 3 | 3 | 3 | 5 | 4 |
| Dysarthria | 0 | 2 | 2 | 5 | 3 |
| Psychiatric Disorders |
| Aggression | 5 | 3 | 8 | 14 | 8 |
| Insomnia | 2 | 2 | 5 | 7 | 5 |
| Respiratory Disorders |
| Cough | 0 | 3 | 5 | 7 | 5 |
Hormonal Contraceptives
Clobazam is a weak CYP3A4 inducer. As some hormonal contraceptives are metabolized by CYP3A4, their effectiveness may be diminished when given with clobazam. Additional non-hormonal forms of contraception are recommended when using clobazam [see
Clinical Pharmacology (12.3),
Patient Counseling Information (17)].
Drugs Metabolized by CYP2D6
Clobazam inhibits CYP2D6. Dose adjustment of drugs metabolized by CYP2D6 may be necessary [see
Clinical Pharmacology (12.3)].
Strong and moderate inhibitors of CYP2C19
Strong and moderate inhibitors of CYP2C19 may result in increased exposure to N-desmethylclobazam, the active metabolite of clobazam. This may increase the risk of dose-related adverse reactions. Dosage adjustment of clobazam may be necessary when co-administered with strong CYP2C19 inhibitors (e.g., fluconazole, fluvoxamine, ticlopidine) or moderate CYP2C19 inhibitors (e.g., omeprazole) [see
Clinical Pharmacology (12.3)].
Pregnancy Registry
There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to AEDs, such as clobazam, during pregnancy. Healthcare providers are encouraged to recommend that pregnant women taking clobazam enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry by calling 1-888-233-2334 or online at http://www.aedpregnancyregistry.org/.
Risk Summary
Neonates born to mothers using benzodiazepines late in pregnancy have been reported to experience symptoms of sedation and/or neonatal withdrawal [
see
Warnings and Precautions (5.9)and
Clinical Considerations]. Available data from published observational studies of pregnant women exposed to benzodiazepines do not report a clear association with benzodiazepines and major birth defects (see
Data).
Administration of clobazam to pregnant rats and rabbits during the period of organogenesis or to rats throughout pregnancy and lactation resulted in developmental toxicity, including increased incidences of fetal malformations and mortality, at plasma exposures for clobazam and its major active metabolite, N-desmethylclobazam, below those expected at therapeutic doses in patients [see
Animal Data]. Data for other benzodiazepines suggest the possibility of long-term effects on neurobehavioral and immunological function in animals following prenatal exposure to benzodiazepines at clinically relevant doses. Clobazam should be used during pregnancy only if the potential benefit to the mother justifies the potential risk to the fetus. Advise a pregnant woman and women of childbearing age of the potential risk to a fetus.
The background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and of miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.
Clinical Considerations
Fetal/Neonatal Adverse Reactions
Benzodiazepines cross the placenta and may produce respiratory depression, hypotonia, and sedation in neonates. Monitor neonates exposed to clobazam during pregnancy or labor for signs of sedation, respiratory depression, hypotonia, and feeding problems. Monitor neonates exposed to clobazam during pregnancy for signs of withdrawal. Manage these neonates accordingly [see
Warnings and Precautions (5.9)].
Data
Human Data
Published data from observational studies on the use of benzodiazepines during pregnancy do not report a clear association with benzodiazepines and major birth defects. Although early studies reported an increased risk of congenital malformations with diazepam and chlordiazepoxide, there was no consistent pattern noted. In addition, the majority of more recent case-control and cohort studies of benzodiazepine use during pregnancy, which were adjusted for confounding exposures to alcohol, tobacco and other medications, have not confirmed these findings.
Animal Data
In a study in which clobazam (0, 150, 450, or 750 mg/kg/day) was orally administered to pregnant rats throughout the period of organogenesis, embryofetal mortality and incidences of fetal skeletal variations were increased at all doses. The low-effect dose for embryofetal developmental toxicity in rats (150 mg/kg/day) was associated with plasma exposures (AUC) for clobazam and its major active metabolite, N-desmethylclobazam, lower than those in humans at the maximum recommended human dose (MRHD) of 40 mg/day.
Oral administration of clobazam (0, 10, 30, or 75 mg/kg/day) to pregnant rabbits throughout the period of organogenesis resulted in decreased fetal body weights, and increased incidences of fetal malformations (visceral and skeletal) at the mid and high doses, and an increase in embryofetal mortality at the high dose. Incidences of fetal variations were increased at all doses. The highest dose tested was associated with maternal toxicity (ataxia and decreased activity). The low-effect dose for embryofetal developmental toxicity in rabbits (10 mg/kg/day) was associated with plasma exposures for clobazam and N-desmethylclobazam lower than those in humans at the MRHD.
Oral administration of clobazam (0, 50, 350, or 750 mg/kg/day) to rats throughout pregnancy and lactation resulted in increased embryofetal mortality at the high dose, decreased pup survival at the mid and high doses and alterations in offspring behavior (locomotor activity) at all doses. The low-effect dose for adverse effects on pre- and postnatal development in rats (50 mg/kg/day) was associated with plasma exposures for clobazam and N-desmethylclobazam lower than those in humans at the MRHD.
Risk Summary
Clobazam is excreted in human milk (
see
Data). There are reports of sedation, poor feeding and poor weight gain in infants exposed to benzodiazepines through breast milk. There are no data on the effects of clobazam on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for clobazam and any potential adverse effects on the breastfed infant from clobazam or from the underlying maternal condition.
Clinical Considerations
Adverse reactions such as somnolence and difficulty feeding have been reported in infants during breastfeeding in postmarketing experience with clobazam. Infants exposed to clobazam through breast milk should be monitored for sedation, poor feeding and poor weight gain.
Data
Scientific literature on clobazam use during lactation is limited. After short-term administration, clobazam and N-desmethylclobazam are transferred into breast milk.
Physical Dependence
Clobazam may produce physical dependence from continued therapy. Physical dependence is a state that develops as a result of physiological adaptation in response to repeated drug use, manifested by withdrawal signs and symptoms after abrupt discontinuation or a significant dose reduction of a drug. Abrupt discontinuation or rapid dosage reduction of benzodiazepines or administration of flumazenil, a benzodiazepine antagonist, may precipitate acute withdrawal reactions, including seizures, which can be life-threatening. Patients at an increased risk of withdrawal adverse reactions after benzodiazepine discontinuation or rapid dosage reduction include those who take higher dosages (i.e., higher and/or more frequent doses) and those who have had longer durations of use [see
Warnings and Precautions (5.3)]. In clinical trials, cases of dependency were reported following abrupt discontinuation of clobazam.
To reduce the risk of withdrawal reactions, use a gradual taper to discontinue clobazam or reduce the dosage [see
Dosage and Administration (2.2)and
Warnings and Precautions (5.3)].
Acute Withdrawal Signs and Symptoms
Acute withdrawal signs and symptoms associated with benzodiazepines have included abnormal involuntary movements, anxiety, blurred vision, depersonalization, depression, derealization, dizziness, fatigue, gastrointestinal adverse reactions (e.g., nausea, vomiting, diarrhea, weight loss, decreased appetite), headache, hyperacusis, hypertension, irritability, insomnia, memory impairment, muscle pain and stiffness, panic attacks, photophobia, restlessness, tachycardia, and tremor. More severe acute withdrawal signs and symptoms, including life-threatening reactions, have included catatonia, convulsions, delirium tremens, depression, hallucinations, mania, psychosis, seizures, and suicidality.
Protracted Withdrawal Syndrome
Protracted withdrawal syndrome associated with benzodiazepines is characterized by anxiety, cognitive impairment, depression, insomnia, formication, motor symptoms (e.g., weakness, tremor, muscle twitches), paresthesia, and tinnitus that persists beyond 4 to 6 weeks after initial benzodiazepine withdrawal. Protracted withdrawal symptoms may last weeks to more than 12 months. As a result, there may be difficulty in differentiating withdrawal symptoms from potential re-emergence or continuation of symptoms for which the benzodiazepine was being used.
Tolerance
Tolerance to clobazam may develop from continued therapy. Tolerance is a physiological state characterized by a reduced response to a drug after repeated administration (i.e., a higher dose of a drug is required to produce the same effect that was once obtained at a lower dose). Tolerance to the therapeutic effect of clobazam may develop; however, little tolerance develops to the amnestic reactions and other cognitive impairments caused by benzodiazepines.
Effects on Electrocardiogram
The effect of clobazam 20 mg and 80 mg administered twice daily on QTc interval was evaluated in a randomized, evaluator-blinded, placebo-, and active-controlled (moxifloxacin 400 mg) parallel thorough QT study in 280 healthy subjects. In a study with demonstrated ability to detect small effects, the upper bound of the one-sided 95% confidence interval for the largest placebo-adjusted, baseline-corrected QTc based on the Fridericia correction method was below 10 ms, the threshold for regulatory concern. Thus, at a dose two times the maximum recommended dose, clobazam did not prolong the QTc interval to any clinically relevant extent.
Absorption
Clobazam is rapidly and extensively absorbed following oral administration. The time to peak concentrations (T
max) of clobazam tablets under fasted conditions ranged from 0.5 to 4 hours after single- or multiple-dose administrations. The relative bioavailability of clobazam tablets compared to an oral solution is approximately 100%. After single dose administration of the oral suspension under fasted conditions, the T
maxranged from 0.5 to 2 hours. Based on exposure (C
maxand AUC) of clobazam, clobazam tablets and suspension were shown to have similar bioavailability under fasted conditions. The administration of clobazam tablets with food or when crushed in applesauce does not affect absorption. Although not studied, the oral bioavailability of the oral suspension is unlikely to be affected under fed conditions.
Distribution
Clobazam is lipophilic and distributes rapidly throughout the body. The apparent volume of distribution at steady state was approximately 100 L. The
in vitroplasma protein binding of clobazam and N-desmethylclobazam is approximately 80% to 90% and 70%, respectively.
Metabolism and Excretion
Clobazam is extensively metabolized in the liver, with approximately 2% of the dose recovered in urine and 1% in feces as unchanged drug. The major metabolic pathway of clobazam involves N-demethylation, primarily by CYP3A4 and to a lesser extent by CYP2C19 and CYP2B6. N-desmethylclobazam, an active metabolite, is the major circulating metabolite in humans, and at therapeutic doses, plasma concentrations are 3 to 5 times higher than those of the parent compound. Based on animal and
in vitroreceptor binding data, estimates of the relative potency of N-desmethylclobazam compared to parent compound range from
1/
5to equal potency. N-desmethylclobazam is extensively metabolized, mainly by CYP2C19. N-desmethylclobazam and its metabolites comprise ~94% of the total drug-related components in urine. Following a single oral dose of radiolabeled drug, approximately 11% of the dose was excreted in the feces and approximately 82% was excreted in the urine.
The polymorphic CYP2C19 is the major contributor to the metabolism of the pharmacologically active N-desmethylclobazam [see
Clinical Pharmacology (12.5)]. In CYP2C19 poor metabolizers, levels of N-desmethylclobazam were 5-fold higher in plasma and 2- to 3-fold higher in the urine than in CYP2C19 extensive metabolizers.
Pharmacokinetics in Specific Populations
Age
Population pharmacokinetic analyses showed that the clearance of clobazam is lower in elderly subjects compared to other age groups (ages 2 to 64). Dosing should be adjusted in the elderly [see
Dosage and Administration (2.4)].
Sex
Population pharmacokinetic analyses showed no difference in the clearance of clobazam between women and men.
Race
Population pharmacokinetic analyses including Caucasian (75%), African American (15%), and Asian (9%) subjects showed that there is no evidence of clinically significant effect of race on the clearance of clobazam.
Renal Impairment
The effect of renal impairment on the pharmacokinetics of clobazam was evaluated in patients with mild (creatinine clearance [CL
CR] >50 to 80 mL/min; N=6) and moderate (CL
CR=30 to 50 mL/min; N=6) renal dysfunction, with matching healthy controls (N=6), following administration of multiple doses of clobazam 20 mg/day. There were insignificant changes in C
max(3% to 24%) and AUC (≤13%) for clobazam or N-desmethylclobazam in patients with mild or moderate renal impairment compared to patients with normal renal function. Patients with severe renal impairment or ESRD were not included in this study.
Hepatic Impairment
There are limited data to characterize the effect of hepatic impairment on the pharmacokinetics of clobazam. In a small study, the pharmacokinetics of a 20 mg single oral dose of clobazam in 9 patients with liver impairment were compared to healthy controls (N=6). The C
maxand the mean plasma clearance of clobazam, as well as the C
maxof N-desmethylclobazam, showed no significant change compared to the healthy controls. The AUC values of N-desmethylclobazam in these patients were not available. Adjust dosage in patients with hepatic impairment [see
Dosage and Administration (2.7)].
Drug Interaction Studies
In vitro studies:
Clobazam did not inhibit CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, UGT1A1, UGT1A4, UGT1A6, or UGT2B4
in vitro. N-desmethylclobazam showed weak inhibition of CYP2C9, UGT1A4, UGT1A6 and UGT2B4.
Clobazam and N-desmethylclobazam did not significantly increase CYP1A2 or CYP2C19 activities, but did induce CYP3A4 activity in a concentration-dependent manner. Clobazam and N-desmethylclobazam also increased UGT1A1 mRNA but at concentrations much higher than therapeutic levels. The potential for clobazam or N-desmethylclobazam to induce CYP2B6 and CYP2C8 has not been evaluated.
Clobazam and N-desmethylclobazam do not inhibit P-glycoprotein (P-gp), but are P-gp substrates.
In vivo studies:
Potential for Clobazam to Affect Other Drugs
The effect of repeated 40 mg once-daily doses of clobazam on the pharmacokinetic profiles of single-dose dextromethorphan (CYP2D6 substrate), midazolam (CYP3A4 substrate), caffeine (CYP1A2 substrate), and tolbutamide (CYP2C9 substrate), was studied when these probe substrates were given as a drug cocktail (N=18).
Clobazam increased AUC and C
maxof dextromethorphan by 90% and 59%, respectively, reflecting its inhibition of CYP2D6
in vivo. Drugs metabolized by CYP2D6 may require dose adjustment when used with clobazam.
Clobazam decreased the AUC and C
maxof midazolam by 27% and 24%, respectively, and increased the AUC and C
maxof the metabolite 1-hydroxymidazolam by 4-fold and 2-fold, respectively. This level of induction does not call for dosage adjustment of drugs that are primarily metabolized by CYP3A4 when used concomitantly with clobazam. Some hormonal contraceptives are metabolized by CYP3A4 and their effectiveness may be diminished when given with clobazam [see
Drug Interactions (7.3)]. Repeated clobazam doses had no effect on caffeine and tolbutamide.
A population pharmacokinetic analysis indicated clobazam did not affect the exposure of valproic acid (a CYP2C9/2C19 substrate) or lamotrigine (a UGT substrate).
Potential for Other Drugs to Affect Clobazam
Co-administration of ketoconazole (a strong CYP3A4 inhibitor) 400 mg once-daily for 5 days increased clobazam AUC by 54%, with an insignificant effect on clobazam C
max. There was no significant change in AUC and C
maxof N-desmethylclobazam (N=18).
Strong (e.g., fluconazole, fluvoxamine, ticlopidine) and moderate (e.g., omeprazole) inhibitors of CYP2C19 may result in up to a 5-fold increase in exposure to N-desmethylclobazam, the active metabolite of clobazam, based on extrapolation from pharmacogenomic data [see
Clinical Pharmacology (12.5)]. Dosage adjustment of clobazam may be necessary when co-administered with strong or moderate CYP2C19 inhibitors [see
Drug Interactions (7.4)].
The effects of concomitant antiepileptic drugs that are CYP3A4 inducers (phenobarbital, phenytoin, and carbamazepine), CYP2C19 inducers (valproic acid, phenobarbital, phenytoin, and carbamazepine), and CYP2C19 inhibitors (felbamate and oxcarbazepine) were evaluated using data from clinical trials. Results of population pharmacokinetic analysis show that these concomitant antiepileptic drugs did not significantly alter the pharmacokinetics of clobazam or N-desmethylclobazam at steady-state.
Alcohol has been reported to increase the maximum plasma exposure of clobazam by approximately 50%. Alcohol may have additive CNS depressant effects when taken with clobazam tablets [see
Warnings and Precautions (5.4),
Drug Interactions (7.2)].
Carcinogenesis
In mice, oral administration of clobazam (0, 6, 12, or 24 mg/kg/day) for 2 years did not result in an increase in tumors. The highest dose tested was approximately 3 times the maximum recommended human dose (MRHD) of 40 mg/day, based on body surface area (mg/m
2).
In rats, oral administration of clobazam for 2 years resulted in increases in tumors of the thyroid gland (follicular cell adenoma and carcinoma) and liver (hepatocellular adenoma) at the mid and high doses. The low dose, not associated with an increase in tumors, was associated with plasma exposures (AUC) for clobazam and its major active metabolite, N-desmethylclobazam, less than that in humans at the MRHD.
Mutagenesis
Clobazam and the major active metabolite, N-desmethylclobazam, were negative for genotoxicity, based on data from a battery of
in vitro(bacteria reverse mutation, mammalian clastogenicity) and
in vivo(mouse micronucleus) assays.
Impairment of Fertility
In a fertility study in which clobazam (50, 350, or 750 mg/kg/day, corresponding to 12, 84 and 181 times the oral Maximum Recommended Human Dose, MRHD, of 40 mg/day based on mg/m
2body surface) was orally administered to male and female rats prior to and during mating and continuing in females to gestation day 6, increases in abnormal sperm and pre-implantation loss were observed at the highest dose tested. The no-effect level for fertility and early embryonic development in rats was associated with plasma exposures (AUC) for clobazam and its major active metabolite, N-desmethylclobazam, less than those in humans at the maximum recommended human dose of 40 mg/day.
Study 1
Study 1 (N=238) was a randomized, double-blind, placebo-controlled study consisting of a 4-week baseline period followed by a 3-week titration period and 12-week maintenance period. Patients age 2 to 54 years with a current or prior diagnosis of LGS were stratified into 2 weight groups (12.5 kg to ≤30 kg or >30 kg) and then randomized to placebo or one of three target maintenance doses of clobazam according to Table 5.
Table 5. Study 1 Total Daily Dose | ≤30 kg Body Weight | >30 kg Body Weight |
|---|
| Low Dose | 5 mg daily | 10 mg daily |
| Medium Dose | 10 mg daily | 20 mg daily |
| High Dose | 20 mg daily | 40 mg daily |
Doses above 5 mg/day were administered in two divided doses.
The primary efficacy measure was the percent reduction in the weekly frequency of drop seizures (atonic, tonic, or myoclonic), also known as drop attacks, from the 4-week baseline period to 12-week maintenance period.
The pre-dosing baseline mean weekly drop seizure frequency was 98, 100, 61, and 105 for the placebo, low-, medium-, and high-dose groups, respectively. Figure 1 presents the mean percent reduction in weekly drop seizures from this baseline. All dose groups of clobazam were statistically superior (p≤0.05) to the placebo group. This effect appeared to be dose dependent.
| Figure 1. Mean Percent Reduction from Baseline in Weekly Drop Seizure Frequency (Study 1) |
|
Figure 2 shows changes from baseline in weekly drop seizure frequency by category for patients treated with clobazam and placebo in Study 1. Patients in whom the seizure frequency increased are shown at left as "worse." Patients in whom the seizure frequency decreased are shown in five categories.
| Figure 2. Drop Seizure Response by Category for Clobazam and Placebo (Study 1) |
|
There was no evidence that tolerance to the therapeutic effect of clobazam developed during the 3-month maintenance period.
Study 2
Study 2 (N=68) was a randomized, double-blind comparison study of high- and low-dose clobazam, consisting of a 4-week baseline period followed by a 3-week titration period and 4-week maintenance period. Patients age 2 to 25 years with a current or prior diagnosis of LGS were stratified by weight, then randomized to either a low or high dose of clobazam, and then entered a 3-week titration period.
The primary efficacy measure was the percent reduction in the weekly frequency of drop seizures (atonic, tonic, or myoclonic), also known as drop attacks, from the 4-week baseline period to the 4-week maintenance period.
A statistically significantly greater reduction in seizure frequency was observed in the high-dose group compared to the low-dose group (median percent reduction of 93% vs 29%; p<0.05).
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