RIMANTADINE HYDROCHLORIDE
Clinical safety rating: safe
Animal studies have demonstrated safety
Rimantadine is a tricyclic amine antiviral that inhibits influenza A virus replication by blocking the M2 proton ion channel, preventing viral uncoating and release of viral RNA into host cells.
| Metabolism | Hepatic primarily via cytochrome P450 (CYP) enzymes, mainly CYP3A4, with renal excretion of unchanged drug and metabolites. |
| Excretion | Renal: 75% unchanged; fecal: <10%; biliary: minimal. Total clearance 2.5 mL/min/kg. |
| Half-life | 25.4 hours (range 13–65 h); prolonged in elderly (38 h) and severe renal impairment (CrCl <10 mL/min: up to 130 h). |
| Protein binding | 40% bound to alpha-1-acid glycoprotein and albumin. |
| Volume of Distribution | 17 L/kg; extensive tissue distribution, high lung concentrations (10-fold plasma). |
| Bioavailability | Oral: 75–95%; no intravenous formulation available. |
| Onset of Action | Oral: ~2–4 days for clinical response (influenza A prophylaxis/treatment). |
| Duration of Action | 14 days (prophylaxis); treatment duration 5–7 days. Once-daily dosing maintains therapeutic levels. |
| Molecular Weight | 215.76 Da |
100 mg orally twice daily for 7 days; initiate within 48 hours of symptom onset.
| Dosage form | TABLET |
| Renal impairment | CrCl 30-50 mL/min: 100 mg orally once daily; CrCl <30 mL/min or hemodialysis: 100 mg orally every 48 hours. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: 100 mg orally once daily; Child-Pugh Class C: 100 mg orally every 48 hours. |
| Pediatric use | Children ≥10 years: 5 mg/kg/day orally in 2 divided doses, max 150 mg/day; children <10 years: 5 mg/kg/day orally in 2 divided doses, max 150 mg/day. |
| Geriatric use | Patients ≥65 years: 100 mg orally once daily due to age-related decline in renal function; monitor for CNS effects. |
| 1st trimester | Animal studies have shown embryotoxicity and teratogenicity at high doses. Use only if potential benefit justifies risk. |
| 2nd trimester | Limited human data. Avoid use unless no alternative. |
| 3rd trimester | May cause CNS effects in neonate if given near term. Use with caution. |
Clinical note
Acetaminophen and aspirin may decrease rimantadine levels Can cause CNS side effects like insomnia and dizziness.
| Placental transfer | Crosses placenta; levels in fetal plasma approximate maternal levels. |
| Breastfeeding | Excreted into breast milk in small amounts; potential for infant CNS effects. Use with caution, especially in neonates. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Common Effects | Insomnia |
| Serious Effects |
Hypersensitivity to rimantadine or adamantanes
| Precautions | Use with caution in patients with hepatic impairment, renal impairment, seizure disorders, or elderly patients due to increased risk of central nervous system effects., May cause CNS side effects such as nervousness, anxiety, insomnia, and difficulty concentrating. Caution in activities requiring alertness., Resistance can develop during treatment; not effective against influenza B., Reduce dose in severe hepatic impairment or severe renal impairment (CrCl < 50 mL/min). |
| Food/Dietary | No significant food interactions. Administer with or without food. Avoid alcohol due to potential worsening of CNS adverse effects. |
Loading safety data…
| L3 - Moderately Safe |
| Teratogenic Risk | Adequate studies in pregnant women are not available. Rimantadine is embryotoxic and teratogenic in animal studies at doses 3x the human recommended dose. Use only if potential benefit justifies potential risk. First trimester: avoid unless essential. Second and third trimesters: limited data, weigh risks. |
| Fetal Monitoring | Monitor maternal renal and hepatic function. Monitor for CNS effects (insomnia, dizziness, headache) and gastrointestinal intolerance. Fetal monitoring: ultrasound for growth and development if exposed during first trimester. |
| Fertility Effects | No human data on fertility. In animal studies, rimantadine did not impair fertility at doses up to 3x human dose. Effects on reproductive function are unknown. |
| Clinical Pearls | Rimantadine is active against influenza A only; not effective against influenza B. Resistance can emerge rapidly, especially in immunocompromised patients. Dose adjustment required for CrCl < 50 mL/min and severe hepatic impairment. Caution in elderly due to increased risk of CNS effects (anxiety, insomnia, seizures). Administer within 48 hours of symptom onset for optimal efficacy. |
| Patient Advice | Take exactly as prescribed; do not skip doses. · Start medication as soon as possible after flu symptoms appear. · May cause dizziness or drowsiness; avoid driving if affected. · Report any confusion, hallucinations, or seizures immediately. · Avoid alcohol as it may increase CNS side effects. · Complete the full course even if symptoms improve. |