Amantadine, oseltamivir and zanamivir for the treatment of influenza

Amantadine (Lysovir, Symmetrel, Alliance Pharmaceuticals) acts against influenza A virus by blocking viral replication. It has a UK marketing authorisation for the treatment of people who have signs and symptoms of infection caused by influenza A virus. The summary of product characteristics (SPC) states that treatment should be started as early as possible, and within 48 hours of symptom onset. The recommended dosage of amantadine is 100 mg daily for 4 to 5 days. Amantadine is administered orally as syrup (Symmetrel) or 100-mg capsules (Lysovir) for the treatment of influenza.

The adverse effects associated with amantadine are often mild and transient. The most commonly reported effects are gastrointestinal disturbances such as anorexia and nausea, and central nervous system effects such as loss of concentration, dizziness, agitation, nervousness, depression, insomnia, fatigue, weakness and myalgia. Central nervous system effects are most common in older people. For full details of adverse effects and contraindications, see the SPC.

Amantadine costs £2.40 for five capsules (100 mg each), £4.80 for 14 capsules and £5.55 for 150 ml syrup (50 mg per 5 ml; excluding VAT; BNF edition 55). Costs may vary in different settings because of negotiated procurement discounts.

Oseltamivir (Tamiflu, Roche Products) is a neuraminidase inhibitor that is active against influenza A and B viruses. It prevents viral release from infected cells and subsequent infection of adjacent cells. It has a UK marketing authorisation for the treatment of influenza in people 1 year of age or older who present with symptoms typical of influenza, when influenza virus is circulating in the community. The SPC states that treatment should be started as soon as possible within the first 48 hours of the onset of influenza symptoms. The recommended dosage of oseltamivir for adolescents (13 to 17 years of age) and adults is 75 mg twice daily for 5 days. For infants older than 1 year and children 2 to 12 years of age, the recommended dose of oseltamivir is adjusted according to body weight. Oseltamivir is given orally as syrup or capsules.

Adverse effects associated with oseltamivir include gastrointestinal symptoms, bronchitis and cough, dizziness and fatigue and neurological symptoms such as headache, insomnia and vertigo. Skin rashes and allergic reactions and, rarely, disorders of the hepatobiliary system have been reported. Convulsions and neuropsychiatric disorders, mainly in children and adolescents, have also been reported but a causal link has not been established. For full details of adverse effects and contraindications, see the SPC.

Oseltamivir costs £16.36 for a 5-day course for an adult (excluding VAT; BNF edition 55). Costs may vary in different settings because of negotiated procurement discounts.

Zanamivir (Relenza, GlaxoSmithKline) is a neuraminidase inhibitor that is active against influenza A and B viruses. It prevents viral release from infected cells and subsequent infection of adjacent cells. It has a UK marketing authorisation for the treatment of influenza in people older than 5 years who present with symptoms typical of influenza, when influenza is circulating in the community. The SPC states that treatment should begin as soon as possible, within 48 hours of symptom onset for adults and within 36 hours of symptom onset for children. The recommended dosage of zanamivir for people older than 5 years is 10 mg twice daily for 5 days. Zanamivir is taken by oral inhalation, using a Diskhaler device.

Adverse effects associated with zanamivir are rare. They include bronchospasm and allergic phenomena. For full details of adverse effects and contraindications, see the SPC.

The price of zanamivir was reduced during the course of the appraisal from £24.55 (excluding VAT; BNF edition 55) to £16.36 (excluding VAT; BNF edition 56) for a 5-day course. Costs may vary in different settings because of negotiated procurement discounts.