Mechanism of Action
Structurally, Oseltamivir and its precursors are sialic acid analogues. The drug's development was based on rational drug design through the study of the neuraminidase complex with its natural substrate.
During replication, new viral particles bud from the host cell membrane. Virion hemagglutinin binds to sialic acid residues on the cell surface, anchoring the virus. The viral enzyme neuraminidase cleaves this bond, facilitating the release of the virion.
Oseltamivir acts as a neuraminidase inhibitor. By blocking this enzyme, the drug disrupts the detachment of new virions from the infected cell and prevents further spread of the infection.
Pharmacokinetics
The substance is administered orally and is well absorbed, with the bioavailability of the active form reaching 80%. By nature, Oseltamivir is a prodrug (prodrug).
Upon entering the body, it is biotransformed by hepatic and intestinal esterases into its active metabolite, oseltamivir carboxylate. This specific form provides the antiviral effect.
Elimination occurs primarily via the kidneys in unchanged form (as the carboxylate). The elimination half-life ($t_{1/2}$) ranges from 6 to 10 hours.
Indications
The drug is prescribed for the specific treatment and prophylaxis of influenza A and B.
It is critically important to initiate therapeutic administration within the first 2 days (48 hours) from the onset of initial disease symptoms. The agent is also used for prophylactic purposes during seasonal epidemics.
Approved for adults and children older than 1 year (for patients under 12 years of age, dosing is calculated individually based on body weight).
Adverse Effects and Safety Profile
The most prominent adverse reactions associated with Oseltamivir involve the Central Nervous System (CNS):
- insomnia;
- ataxia (impaired motor coordination);
- decreased concentration;
- other neuropsychiatric disturbances.
Compared to other drugs in the class (e.g., M2 channel blockers amantadine and rimantadine), neuraminidase inhibitors possess a different tolerability profile and lack cross-resistance with older agents.
Clinical Administration and Dosing
The standard oral capsule formulation contains 75 mg.
Standard dosing regimen: orally, regardless of meals, 75 mg twice daily for a course of 5 days.
Unlike antibiotics or M2 channel blockers (such as rimantadine, which is only effective against influenza A), oseltamivir maintains high specificity for the neuraminidase of both major influenza types and is inactive against other viral infections such as HIV.