Amantadine hydrochloride capsules for influenza A and parkinsonism treatment

Amantadine hydrochloride capsules contain amantadine, which is used to prevent and treat infections caused by influenza A virus strains. Additionally, it is prescribed to treat symptoms of Parkinson's disease and drug-induced extrapyramidal movement disorders. The medication works against influenza A viruses and has neurological effects helpful in certain movement disorders.

Amantadine hydrochloride capsules are approved for the following purposes:

• Prevention (chemoprophylaxis) of signs and symptoms of influenza A virus infection, including during outbreaks and in conjunction with influenza vaccination (for the 2- to 4-week period needed to develop antibody response).
• Treatment of uncomplicated respiratory tract illness caused by influenza A virus strains, especially when given early in the illness.
• Treatment of idiopathic Parkinson’s disease (Paralysis Agitans), postencephalitic parkinsonism, symptomatic parkinsonism following nervous system injury by carbon monoxide poisoning, and parkinsonism associated with cerebral arteriosclerosis in elderly patients.
• Treatment of drug-induced extrapyramidal reactions caused by neuroleptic drugs, with fewer anticholinergic side effects compared to anticholinergic antiparkinson drugs.

It is not effective for viral respiratory illnesses caused by influenza B or other viruses.

Amantadine hydrochloride

Amantadine works by interfering with the replication of influenza A virus. It disrupts the viral M2 protein function, preventing release of infectious viral nucleic acid into host cells and sometimes blocking virus assembly during replication. This action inhibits influenza A virus growth but has little or no effect on influenza B virus.

In Parkinson’s disease and drug-induced extrapyramidal reactions, the exact mechanism is unknown. Amantadine appears to have effects on dopamine neurons and acts as a weak, non-competitive NMDA receptor antagonist. Although not directly anticholinergic in experimental studies, it produces anticholinergic-like side effects such as dry mouth, urinary retention, and constipation in clinical use.

Amantadine hydrochloride capsules are administered orally, commonly in 100 mg capsules. Maximum plasma concentrations increase with doses up to 200 mg/day; doses above 200 mg/day may raise plasma levels disproportionately. The usual dosage and treatment duration depend on the indication and patient-specific factors, particularly kidney function.

Adjustments are needed for patients with impaired renal function due to reduced clearance and longer half-life of the drug. Elderly patients (60 years and older) also show reduced clearance and increased half-life.

Amantadine hydrochloride capsules are contraindicated in patients with known hypersensitivity to amantadine hydrochloride or any of the capsule ingredients.

Serious risks and precautions:

• Overdose can be fatal, with the lowest reported lethal amount being 1 gram. Toxicity may involve anticholinergic effects and damage to heart, kidneys, respiratory system, or CNS.
• Deaths have occurred from drug accumulation in patients with kidney impairment receiving doses too high for their renal function.
• Suicide attempts, some fatal, have been reported in patients treated with amantadine. These may occur with or without prior psychiatric history, and symptoms may include confusion, depression, agitation, hallucinations, paranoia, and other mental changes.
• Caution is advised when treating patients on other CNS-active drugs or those with psychiatric disorders or substance abuse history.
• Monitor patients with a history of seizures closely for increased seizure risk.
• Patients experiencing CNS effects or vision blurring should avoid activities requiring alertness such as driving.
• Patients with congestive heart failure or peripheral edema should be monitored closely, as worsening may occur during amantadine treatment.

Common side effects include anticholinergic-like symptoms such as dry mouth, urinary retention, and constipation. Central nervous system effects such as confusion, dizziness, hallucinations, agitation, and sleep disturbances may also occur. Less common but serious adverse effects include cardiac arrhythmias and congestive heart failure in susceptible individuals.

Caution is advised when using amantadine concomitantly with drugs affecting the central nervous system due to increased risk of adverse psychiatric or neurological effects.

Overdose with amantadine can cause cardiac, respiratory, renal, or CNS toxicity, potentially fatal. The lowest reported lethal dose was 1 gram. Symptoms may include arrhythmias, tachycardia, hypertension, and anticholinergic manifestations. Immediate medical attention is necessary in suspected overdose cases.