Mechanism of Action (Pharmacodynamics)
The drug's site of action is the early stage of viral replication within the host cell. Under physiological conditions, virus entry involves acidification of the endosomal interior. Hydrogen ions enter the viral particle through specific ion channels formed by the viral M2 protein.
The drop in pH triggers deproteinization—the dissociation of ribonucleoproteins from the matrix protein. As a result, the viral RNA is released from the capsid into the cytoplasm for subsequent transport to the nucleus (viral "uncoating").
Rimantadine acts as an M2 ion channel blocker. It prevents proton transport into the virion, blocking the acidification of its internal environment. Consequently, ribonucleoprotein dissociation is disrupted, making the release of the viral genome into the cytoplasm impossible.
Additional mechanism: There is evidence suggesting an effect on late stages of replication, which is associated with conformational changes in viral hemagglutinin.
Spectrum of Activity and Indications
The drug has a narrow spectrum of activity: it is active only against influenza A virus. It has no effect on influenza B because influenza B genetically lacks the M2 protein.
Indications for use:
- Prophylaxis: During influenza epidemics (proven efficacy is 70–90%).
- Treatment: Strictly at the initial stage of the disease. Early administration alleviates clinical symptoms and accelerates recovery.
Pharmacokinetics
The drug is administered orally after meals. It has high bioavailability (over 90%). An important clinical feature is its ability to cross the blood-brain barrier (BBB) and the placenta.
Unlike its predecessor (amantadine), Rimantadine undergoes extensive hepatic metabolism (about 75%) and has a significantly longer elimination half-life ($T_{1/2}$ of 24–36 hours).
Adverse Effects and Safety Profile
Because the drug is lipophilic and readily crosses the BBB, major adverse reactions involve the Central Nervous System (CNS). Patients may experience:
- Insomnia;
- Ataxia (impaired coordination of movements);
- Impaired concentration.
Compared to amantadine, adverse effects associated with rimantadine occur less frequently and are less severe.
Place in Therapy and Prescribing Guidelines
When choosing influenza therapy, it is important to distinguish M2 channel blockers from other drug classes. For example, oseltamivir (a neuraminidase inhibitor) disrupts the release of new virions from the cell, while kagocel stimulates the production of endogenous interferons. Drugs like enfuvirtide (a fusion inhibitor) are specific for HIV and are ineffective against influenza.
Formulation: Tablets (including coated tablets) of 0.05 g. The therapeutic oral dose range is 0.05–0.1 g.
Prescription example: `Rp.: Tab. Remantadini 0,05` `D.t.d. N. 20` `S. Oral, 1-2 tablets per schedule.`