💊 Oseltamivir

Oseltamivir is an antiviral drug belonging to the class of neuraminidase inhibitors. It is specifically used for the treatment and prophylaxis of influenza A and B infections.

Oseltamivir is a prodrug that is metabolised to its active form, oseltamivir carboxylate. This active metabolite selectively inhibits viral neuraminidase, an enzyme crucial for the release of new virions from infected cells and their spread within the respiratory tract. By inhibiting neuraminidase, oseltamivir prevents the budding and dissemination of influenza virus.

Oseltamivir is indicated for the treatment of influenza in adults and children who present with symptoms typical of influenza when influenza virus is circulating in the community. It is also used for post-exposure prophylaxis of influenza in individuals aged 1 year or older following contact with a clinically diagnosed influenza case. Pre-exposure prophylaxis may be considered in specific high-risk situations.

Hypersensitivity to oseltamivir or any component of the formulation is an absolute contraindication. Caution is advised in patients with severe renal impairment, as dose adjustments are necessary. There is limited data on its use in patients with chronic cardiac or respiratory disease, or in immunocompromised individuals.

Common adverse effects include nausea, vomiting, and abdominal pain, which can often be reduced by taking the drug with food. Headache and insomnia are also reported. Rarely, neuropsychiatric events such as delirium, hallucinations, and self-injury have been observed, particularly in children and adolescents, though a causal link is not fully established.

No routine laboratory monitoring is typically required for oseltamivir. However, patients should be monitored for any unusual behavioural changes or neuropsychiatric symptoms, especially in younger individuals. Renal function should be assessed in patients with pre-existing renal impairment to guide dose adjustment.

Always check for known allergies to oseltamivir. Drug interactions are generally uncommon, but always review the patient's full medication list. Counsel patients on the importance of taking the medication as prescribed and to report any unusual behavioural changes. Advise taking with food to minimise gastrointestinal upset.

High-yield facts include its specific action against influenza A and B by inhibiting neuraminidase. Remember the '48-hour window' for optimal treatment efficacy. Its role in both treatment and prophylaxis is important. Be aware of the potential for neuropsychiatric side effects, especially in younger patients.

SBA questions often revolve around the timing of oseltamivir administration for treatment (within 48 hours of symptom onset) and its role in prophylaxis. Questions might also explore its mechanism of action (neuraminidase inhibition) or differentiate it from other antivirals. Awareness of potential neuropsychiatric side effects, particularly in children, is a common theme.