There are no studies of riluzole in pregnant women, and case reports have been inadequate to inform the drug-associated risk. The background risk for major birth defects and miscarriage in patients with amyotrophic lateral sclerosis is unknown. In the U.S. general population, the background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively.
In studies in which riluzole was administered orally to pregnant animals, developmental toxicity (decreased embryofetal/offspring viability, growth, and functional development) was observed at clinically relevant doses [see Data]. Based on these results, women should be advised of a possible risk to the fetus associated with use of riluzole during pregnancy.
Oral administration of riluzole (3, 9, or 27 mg/kg/day) to pregnant rats during the period of organogenesis resulted in decreases in fetal growth (body weight and length) at the high dose. The mid dose, a no-effect dose for embryofetal developmental toxicity, is approximately equal to the recommended human daily dose (RHDD, 100 mg) on a mg/m 2 basis. When riluzole was administered orally (3, 10, or 60 mg/kg/day) to pregnant rabbits during the period of organogenesis, embryofetal mortality was increased at the high dose and fetal body weight was decreased and morphological variations increased at all but the lowest dose tested. The no-effect dose (3 mg/kg/day) for embryofetal developmental toxicity is less than the RHDD on a mg/m 2 basis. Maternal toxicity was observed at the highest dose tested in rat and rabbit.
When riluzole was orally administered (3, 8, or 15 mg/kg/day) to male and female rats prior to and during mating and to female rats throughout gestation and lactation, increased embryofetal mortality and decreased postnatal offspring viability, growth, and functional development were observed at the high dose. The mid dose, a no-effect dose for pre-and postnatal developmental toxicity, is approximately equal to the RHDD on a mg/m 2 basis.
It is not known if riluzole is excreted in human milk. Riluzole or its metabolites have been detected in milk of lactating rat. Women should be advised that many drugs are excreted in human milk and that the potential for serious adverse reactions in nursing infants from riluzole is unknown.
In rats, oral administration of riluzole resulted in decreased fertility indices and increases in embryolethality [see Nonclinical Toxicology ( 13.1)] .
Safety and effectiveness of riluzole tablets in pediatric patients have not been established.
In clinical studies of riluzole tablets, 30% of patients were 65 years and over. No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.
Patients with mild [Child-Pugh’s (CP) score A] or moderate (CP score B) hepatic impairment had increases in AUC compared to patients with normal hepatic function. Thus, patients with mild or moderate hepatic impairment may be at increased of adverse reactions. The impact of severe hepatic impairment on riluzole exposure is unknown.
Use of riluzole tablets is not recommended in patients with baseline elevation of elevations of serum aminotransferases greater than 5 times upper limit of normal or evidence of liver dysfunction (e.g., elevated bilirubin) [Clinical Pharmacology ( 12.3)] .
Japanese patients are more likely to have higher riluzole concentrations. Consequently, the risk of adverse reactions may be greater in Japanese patients [see Clinical Pharmacology ( 12.3)] .
Reported symptoms of overdose following ingestion of riluzole ranging from 1.5 to 3 grams (30 to 60 times the recommended dose) included acute toxic encephalopathy, coma, drowsiness, memory loss, and methemoglobinemia.
No specific antidote for the treatment of riluzole overdose is available. For current information on the management of poisoning or overdosage, contact the National Poison Control Center at 1-800-222-1222 or www.poison.org.
Riluzole is a member of the benzothiazole class. The chemical designation for riluzole is 2-amino-6-(trifluoromethoxy)benzothiazole. Its molecular formula is C 8 H 5 F 3 N 2 OS, and its molecular weight is 234.2. The chemical structure is:
Riluzole is a white to slightly yellow powder that is very soluble in dimethylformamide, dimethylsulfoxide, and methanol; freely soluble in dichloromethane; sparingly soluble in 0.1 N HCl; and very slightly soluble in water and in 0.1 N NaOH.
Each film-coated tablet for oral use contains 50 mg of riluzole and the following inactive ingredients: dibasic calcium phosphate anhydrous, microcrystalline cellulose, colloidal silicon dioxide, magnesium stearate, croscarmellose sodium, hypromellose, lactose monohydrate, titanium dioxide, triacetin, citric acid monohydrate.
The mechanism by which riluzole exerts its therapeutic effects in patients with ALS is unknown.
The clinical pharmacodynamics of riluzole has not been determined in humans.
Table 2 displays the pharmacokinetic parameters of riluzole.
Compared with healthy volunteers, the AUC of riluzole was approximately 1.7-fold greater in patients with mild chronic hepatic impairment (CP score A) and approximately 3-fold greater in patients with moderate chronic hepatic impairment (CP score B). The pharmacokinetics of riluzole have not been studied in patients with severe hepatic impairment (CP score C) [see Use in Specific Populations ( 8.6)] .
The clearance of riluzole was 50% lower in male Japanese subjects than in Caucasian subjects, after normalizing for body weight [see Use in Specific Populations ( 8.7)] .
The mean AUC of riluzole was approximately 45% higher in female patients than male patients.
The clearance of riluzole in tobacco smokers was 20% greater than in nonsmokers.
Geriatric Patients and Patients with Moderate to Severe Renal Impairment
Age 65 years or older, and moderate to severe renal impairment do not have a meaningful
effect on the pharmacokinetics of riluzole. The pharmacokinetics of riluzole in patients
undergoing hemodialysis are unknown.
Drug Interaction Studies
Drugs Highly Bound To Plasma Proteins
Riluzole and warfarin are highly bound to plasma proteins. In vitro, riluzole did not show
any displacement of warfarin from plasma proteins. Riluzole binding to plasma proteins was
unaffected by warfarin, digoxin, imipramine and quinine at high therapeutic concentrations
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