WARNINGS
Liver Injury / Monitoring Liver Chemistries
RILUTEK should be prescribed with care in patients with current evidence or history of abnormal liver function indicated by significant abnormalities in serum transaminase (ALT/SGPT; AST/SGOT), bilirubin, and/or gamma-glutamate transferase (GGT) levels (see PRECAUTIONS and DOSAGE AND ADMINISTRATION sections). Baseline elevations of several LFTs (especially elevated bilirubin) should preclude the use of RILUTEK.
RILUTEK, even in patients without a prior history of liver disease, causes serum aminotransferase elevations. Experience in almost 800 ALS patients indicates that about 50% of riluzole-treated patients will experience at least one ALT/SGPT level above the upper limit of normal, about 8% will have elevations > 3 × ULN, and about 2% of patients will have elevations > 5 × ULN. A single non-ALS patient with epilepsy treated with concomitant carbamazepine and phenobarbital experienced marked, rapid elevations of liver enzymes with jaundice (ALT 26 × ULN, AST 17 × ULN, and bilirubin 11 × ULN) four months after starting RILUTEK; these returned to normal 7 weeks after treatment discontinuation.
Maximum increases in serum ALT usually occurred within 3 months after the start of riluzole therapy and were usually transient when < 5 times ULN. In trials, if ALT levels were < 5 times ULN, treatment continued and ALT levels usually returned to below 2 times ULN within 2 to 6 months. Treatment in studies was discontinued, however, if ALT levels exceeded 5 × ULN, so that there is no experience with continued treatment of ALS patients once ALT values exceed 5 times ULN. Treatment should be discontinued if ALT levels are ≥ 5 × ULN or if clinical jaundice develops (see PRECAUTIONS: Laboratory Tests). There were rare instances of jaundice and hepatitis. Serum aminotransferases including ALT levels should be measured before and during riluzole therapy. Serum ALT levels should be evaluated every month during the first 3 months of treatment, every 3 months during the remainder of the first year, and periodically thereafter. Serum ALT levels should be evaluated more frequently in patients who develop elevations. (see PRECAUTIONS).
Neutropenia
Among approximately 4000 patients given riluzole for ALS, there were three cases of marked neutropenia (absolute neutrophil count less than 500/mm3), all seen within the first 2 months of riluzole treatment. In one case, neutrophil counts rose on continued treatment. In a second case, counts rose after therapy was stopped. A third case was more complex, with marked anemia as well as neutropenia and the etiology of both is uncertain. Patients should be warned to report any febrile illness to their physicians. The report of a febrile illness should prompt treating physicians to check white blood cell counts.
PRECAUTIONS
Use in Patients with Concomitant Disease
RILUTEK should be used with caution in patients with concomitant liver insufficiency (see WARNINGS, CLINICAL PHARMACOLOGY). In particular, in cases of RILUTEK-induced hepatic injury manifested by elevated liver enzymes, the effect of the hepatic injury on RILUTEK metabolism is unknown.
Special Populations
Riluzole should be used with caution in elderly patients whose hepatic function may be compromised due to age. Also, female patients and Japanese patients may possess a lower metabolic capacity to eliminate riluzole compared to males and Caucasian subjects, respectively (see CLINICAL PHARMACOLOGY: Special Populations).
Information for the Patient
Patients should be advised to report any febrile illness to their physicians (see WARNINGS: Neutropenia).
Patients and caregivers should be advised that RILUTEK should be taken on a regular basis and at the same time of the day (e.g., in the morning and evening) each day. If a dose is missed, take the next tablet as originally planned (see DOSAGE AND ADMINISTRATION).
Patients should be warned about the potential for dizziness, vertigo, or somnolence and advised not to drive or operate machinery until they have gained sufficient experience on RILUTEK to gauge whether or not it affects their mental and/or motor performance adversely.
Whether alcohol increases the risk of serious hepatotoxicity with RILUTEK is unknown; therefore, patients being treated with RILUTEK should be discouraged from drinking excessive amounts of alcohol.
Patients should also be made aware that RILUTEK should be stored at temperatures between 20°–25°C (68°–77°F) and protected from bright light.
RILUTEK must be kept out of the reach of children.
Laboratory Tests
As noted in the WARNINGS Section, there is no experience with continued treatment of patients once ALT exceeds 5 × ULN. Treatment should be discontinued if ALT levels are ≥ 5 × ULN or if clinical jaundice develops. Because there is no experience with rechallenge of patients who have had RILUTEK discontinued for ALT > 5 × ULN, no recommendations about restarting RILUTEK can be made.
In the two controlled trials in patients with ALS, the frequency with which values for hemoglobin, hematocrit, and erythrocyte counts fell below the lower limit of normal was greater in RILUTEK-treated patients than in placebo-treated patients; however, these changes were mild and transient. The proportions of patients observed with abnormally low values for these parameters showed a dose-response relationship. Only one patient was discontinued from treatment because of severe anemia. The significance of this finding is unknown.
Drug Interactions
There have been no clinical studies designed to evaluate the interaction of riluzole with other drugs.
As with all drugs, the potential for interaction by a variety of mechanisms is a possibility.
Hepatotoxic Drugs
The clinical trials in ALS excluded patients on concomitant medications which were potentially hepatotoxic, (e.g., allopurinol, methyldopa, sulfasalazine). Accordingly, there is no information about the safety of administering RILUTEK in conjunction with such medications. If the practitioner chooses to prescribe such a combination, caution should be exercised.
Drugs Highly Bound To Plasma Proteins
Riluzole is highly bound (96%) to plasma proteins, binding mainly to serum albumin and to lipoproteins. The effect of riluzole (up to 5 mcg/mL) on warfarin (5 mcg/mL) binding did not show any displacement of warfarin. Conversely, riluzole binding was unaffected by the addition of warfarin, digoxin, imipramine and quinine at high therapeutic concentrations.
Effect of Other Drugs On Riluzole Metabolism
In vitro studies using human liver microsomal preparations suggest that CYP 1A2 is the principal isozyme involved in the initial oxidative metabolism of riluzole and, therefore, potential interactions may occur when riluzole is given concurrently with agents that affect CYP 1A2 activity. Potential inhibitors of CYP 1A2 (e.g., caffeine, phenacetin, theophylline, amitriptyline, and quinolones) could decrease the rate of riluzole elimination, while inducers of CYP 1A2 (e.g., cigarette smoke, charcoal-broiled food, rifampicin, and omeprazole) could increase the rate of riluzole elimination.
Effect of Riluzole On the Metabolism of Other Drugs
CYP 1A2 is the principal isoenzyme involved in the initial oxidative metabolism of riluzole; potential interactions may occur when riluzole is given concurrently with other agents which are also metabolized primarily by CYP 1A2 (e.g., theophylline, caffeine, and tacrine). Currently, it is not known whether riluzole has any potential for enzyme induction in humans.
Drug Laboratory Test Interactions
None known
Carcinogenesis, Mutagenesis, Impairment of Fertility
Riluzole was not carcinogenic in mice or rats when administered for 2 years at daily oral doses up to 20 mg/kg and 10 mg/kg, respectively, which are approximately equivalent to the maximum human dose on a mg/m2 basis.
The genotoxic potential of riluzole was evaluated in the bacterial mutagenicity (Ames) test, the mouse lymphoma mutation assay in L5178Y cells, the in vitro chromosomal aberration assay in human lymphocytes and the in vivo rat cytogenetic assay and in vivo mouse micronucleus assay in bone marrow. There was no evidence of mutagenic or clastogenic potential in the Ames test, the mouse lymphoma assay, or the in vivo assays in the mouse and rat. There was an equivocal clastogenic response in the in vitro human lymphocyte chromosomal aberration assay, which was not reproduced in a second assay performed at equal or higher concentrations; riluzole was therefore considered non-clastogenic in the human lymphocyte assay.
N-hydroxyriluzole, the major active metabolite of riluzole, caused chromosomal damage in the in vitro mammalian mouse lymphoma assay and in the in vitro micronucleus assay that used the same mouse lymphoma cell line, L5178Y. N-hydroxyriluzole was not mutagenic in this cell line when tested in the HPRT gene mutation assay, and was negative in the Ames bacterial gene mutation assay (with and without rat or hamster S9), the in vitro UDS assay in rat hepatocytes, the chromosomal aberration test in human lymphocytes, and the in vivo mouse bone marrow micronucleus test.
Riluzole impaired fertility when administered to male and female rats prior to and during mating at an oral dose of 15 mg/kg or 1.5 times the maximum daily dose on a mg/m2 basis (see PRECAUTIONS: "Pregnancy" for effects on fertility).
Pregnancy
Pregnancy category C
Oral administration of riluzole to pregnant animals during the period of organogenesis caused embryotoxicity in rats and rabbits at doses of 27 mg/kg and 60 mg/kg, respectively, or 2.6 and 11.5 times, respectively, the recommended maximum human daily dose on a mg/m2 basis. Evidence of maternal toxicity was also observed at these doses.
When administered to rats prior to and during mating (males and females) and throughout gestation and lactation (females), riluzole produced adverse effects on pregnancy (decreased implantations, increased intrauterine death) and offspring viability and growth at an oral dose of 15 mg/kg or 1.5 times the maximum daily dose on a mg/m2 basis.
There are no adequate and well-controlled studies in pregnant women. Riluzole should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Nursing Women
In rat studies, 14C-riluzole was detected in maternal milk. It is not known whether riluzole is excreted in human breast milk. Because many drugs are excreted in human milk, and because the potential for serious adverse reactions in nursing infants from RILUTEK® is unknown, women should be advised not to breast-feed during treatment with RILUTEK.
Geriatric Use
Age-related compromised renal and hepatic function may cause a decrease in clearance of riluzole (see CLINICAL PHARMACOLOGY: Special Populations). In controlled clinical trials, about 30% of patients were over 65. There were no differences in adverse effects between younger and older patients.
Pediatric Use
The safety and the effectiveness of RILUTEK in pediatric patients have not been established.
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