Which Medications Treat Influenza?

Several antivirals shorten illness and reduce complications when started early, especially for people at high risk or with severe disease. The main options are neuraminidase inhibitors — oseltamivir (oral), zanamivir (inhaled), peramivir (intravenous) — and the cap‑dependent endonuclease inhibitor baloxavir (oral, single dose).

Quick Takeaways

• Start as soon as possible; best within 48 hours of symptom onset. Treat regardless of timing in hospitalized, severe, or high‑risk patients.
• Oseltamivir is first‑line for most patients, including during pregnancy.
• Zanamivir is inhaled and can trigger bronchospasm — avoid in asthma/COPD.
• Peramivir (IV) is useful when oral meds can’t be taken/absorbed; not typically used for prophylaxis.
• Baloxavir is single‑dose oral; avoid coadministration with polyvalent cations (e.g., calcium/iron). Not preferred in pregnancy due to limited data.

How These Drugs Work

• Neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) block the viral neuraminidase enzyme, preventing the release of newly formed virions from infected cells and limiting spread to uninfected cells.
• Baloxavir inhibits the viral polymerase acidic (PA) endonuclease, halting viral mRNA synthesis and replication.

These agents don’t “kill” all virus directly; they curb replication so the immune system can clear infection. They shorten symptoms by about 1–3 days and reduce complications (e.g., otitis media in children, pneumonia, hospitalization) when used appropriately.

Who Should Receive Antivirals?

• Anyone hospitalized or with severe/progressive disease.
• People at higher risk of complications: adults ≥65, infants/young children, pregnant/postpartum, chronic heart/lung/kidney/liver/metabolic/neurologic disease, immunocompromised, residents of long‑term care, and people with obesity.
• Consider for otherwise healthy outpatients if treatment can start within 48 hours of onset.

Drug‑by‑Drug Highlights

Oseltamivir (oral)
– Typical adult treatment: 75 mg twice daily for 5 days; weight‑based dosing for children.
– Dose adjustment needed in renal impairment. Generally preferred in pregnancy and breastfeeding.
– Adverse effects: nausea/vomiting (take with food); rare neuropsychiatric events reported, mainly in children/adolescents.
– Post‑exposure prophylaxis is an option for close contacts at high risk per local guidance.

Zanamivir (inhaled powder)
– Typical adult treatment: 10 mg (two 5‑mg inhalations) twice daily for 5 days.
– Avoid in asthma/COPD or those with reactive airway disease due to risk of bronchospasm; not for nebulization.
– Age authorizations and prophylaxis indications vary by region; check local labeling.

Peramivir (intravenous)
– Typical adult treatment: single 600 mg IV dose for uncomplicated cases; some severe cases may need daily dosing per protocols.
– Useful when oral therapy isn’t possible or absorption is unreliable (e.g., GI bleeding, malabsorption, gastric retention). Adjust dose in renal impairment.
– Not generally used for prophylaxis.

Baloxavir (oral, single dose)
– Single weight‑based dose; effective for early, uncomplicated influenza in eligible age groups.
– Avoid with products containing polyvalent cations (e.g., Ca/Fe/Mg/Al, zinc, some antacids, certain supplements) due to reduced absorption.
– Limited data in pregnancy and severe disease; not preferred for these groups. Some resistance concerns have been reported, particularly in children.

Timing Matters

Start treatment as early as possible. Benefit is greatest when initiated within 48 hours, but hospitalized or severe cases still benefit when started later.

What Antivirals Do Not Do

• They are not antibiotics and don’t treat bacterial infections. Use antibiotics only if bacterial coinfection is suspected (e.g., secondary pneumonia).
• Supportive care remains essential: hydration, antipyretics/analgesics (avoid aspirin in children/teens due to Reye syndrome), and monitoring.

Post‑Exposure Prophylaxis (PEP)

For high‑risk close contacts or institutional outbreaks, PEP with oseltamivir or (in some regions) baloxavir may be considered. Follow local public health guidance for eligibility, timing, and dosing.

Special Populations

• Pregnancy/postpartum: oseltamivir is preferred.
• Renal impairment: adjust oseltamivir and peramivir dosing.
• Chronic lung disease: avoid zanamivir.

Educational information only and not a substitute for medical care. Follow local guidelines and consult a clinician for individualized decisions.