rimantadine hydrochloride
Flumadine

Available forms
Available by prescription only
Syrup: 50 mg/5 ml
Tablets: 100 mg

Indications and dosages
 Prophylaxis against influenza A virus. Adults and children age 10 and older: 100 mg P.O. b.i.d.; for patients with severe hepatic dysfunction or renal failure (creatinine clearance 10 ml/minute or less) and for elderly patients in communal settings, a dose reduction to 100 mg P.O. daily is recommended.
Children younger than age 10: 5 mg/kg P.O. once daily. Maximum dose, 150 mg.
 Treatment of illness caused by various strains of influenza A virus. Adults: 100 mg P.O. b.i.d. for 7 days from symptom onset; for patients with severe hepatic dysfunction or renal failure (creatinine clearance 10 ml/minute or less) and for elderly patients in communal settings, a dose reduction to 100 mg P.O. daily is recommended.

Pharmacodynamics
Antiviral action: Mechanism of action isn’t fully understood. Drug appears to exert inhibitory effect early in viral replication cycle, possibly inhibiting uncoating of the virus. Genetic studies suggest that a virus protein specified by the virion M₂ gene plays an important role in susceptibility of influenza A virus to inhibition by rimantadine.

Pharmacokinetics
Absorption: Tablet and syrup forms are equally absorbed.
Distribution: Plasma protein-binding is about 40%.
Metabolism: Extensively metabolized in the liver.
Excretion: Less than 25% is excreted in urine as unchanged drug. Elimination half-life of drug is about 25 1/2 to 32 hours. Hemodialysis doesn’t contribute to drug clearance.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug or to amantadine. Use cautiously in pregnant women and patients with impaired renal or hepatic function or seizure disorders (especially epilepsy).

Interactions
Drug-drug. Acetaminophen, aspirin: Reduces rimantadine levels. Monitor patient for drug effect.
Cimetidine: May decrease total rimantadine clearance by about 16%. Monitor patient for adverse effects.

Adverse reactions
CNS: insomnia, headache, dizziness, nervousness, fatigue, asthenia, impaired concentration.
GI: nausea, vomiting, anorexia, dry mouth, abdominal pain.

Effects on lab test results
None reported.

Overdose and treatment
Information specific to rimantadine overdose isn’t available. Overdoses of a related drug, amantadine, have been reported, with reactions ranging from agitation to hallucinations, cardiac arrhythmia, and death.
 As with any overdose, administer supportive care as indicated. Administration of I.V. physostigmine (1 to 2 mg in adults and 0.5 mg in children; repeated as needed but not to exceed 2 mg/hour) may benefit patients with CNS effects from overdose of amantadine.

Special considerations
 ALERT Don’t confuse rimantadine with amantadine.
• For illnesses related to various strains of influenza A, treatment should begin as soon as possible, preferably within 48 hours after onset of signs and symptoms, to reduce duration of fever and systemic symptoms.
• An increased risk of seizures has been observed in some patients with history of seizures who weren’t prescribed an anticonvulsant during rimantadine therapy. If seizures develop, discontinue drug.
• Influenza A-resistant strains can emerge during therapy. Patients taking drug may still be able to spread the disease.
• Because of risk of drug metabolites accumulating during multiple dosing, monitor patient with any degree of renal insufficiency for adverse effects, and adjust dosage as needed.
Breast-feeding patients
• Drug shouldn’t be given to breast-feeding women because of the potential adverse effects to the infant.
Pediatric patients
• Drug is recommended for prophylaxis of influenza A. Safety and efficacy of drug in treating symptomatic influenza infection in children haven’t been established.
• Prophylaxis studies with rimantadine haven’t been performed in children younger than age 1.
Geriatric patients
• Adverse drug reactions occur more often in elderly patients than in the general population. Monitor these patients closely.

Patient education
• Advise patient to take drug several hours before bedtime to prevent insomnia.
• Inform patient that taking drug doesn’t prevent him from spreading the disease and that he should limit contact with others until fully recovered.
• Warn patient that drug may cause adverse CNS effects. Tell him not to drive or perform activities that require mental alertness until these effects are known.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use