Tamiflu ( Oseltamivir ) and Relenza ( Zanamivir ) are both neuraminidase enzyme inhibitors. They act by inhibiting entry of influenza virus into uninfected cells and preventing the release of recently formed virus particles from infected cells.
Tamiflu is given orally ( capsules and solution ) and Relenza is given by inhalation ( Diskhaler system ).
Tamiflu
Side effects
The most common side effects of Tamiflu are nausea, vomiting, diarrhoea, abdominal pain, and headache. These may usually occur after the first dose and will usually stop as treatment continues. The frequency of these effects is reduced if Tamiflu is taken with food.
More-serious side effects are very rare.
The product information for Tamiflu lists neuropsychiatric disorders ( reports of convulsions and delirium ) in the side-effects section. These events were added to the product information as a precautionary measure; a causal association between Tamiflu and the reported events is uncertain.
Drug interactions
Clinically important drug interactions with Tamiflu are unlikely, including those involving competition for renal tubular secretion. However, care should be taken when prescribing Tamiflu for patients who are taking co-excreted medicines with a narrow therapeutic margin ( eg, Chlorpropamide or Methotrexate ).
No dose adjustment is required when coadministering with Probenecid in patients with normal renal function. Coadministration of Probenecid, a potent inhibitor of the anionic pathway of renal tubular secretion, results in an approximate two-fold increase in exposure to the active metabolite of Oseltamivir.
Renal impairment
Dose adjustment is recommended for adults with severe renal insufficiency ( ie, creatinine clearance: less than or equal to 30 mL/min ).
Tamiflu is not recommended for patients with a creatinine clearance of less than or equal to 10 mL/min or in those undergoing dialysis.
Relenza
Side effects
Recognised side effects to Relenza are very rare, but may include allergic-type reactions such as swelling of the face, mouth, or throat; skin rash; or hives. Acute bronchospasm or serious decline in respiratory function ( or both ) have been seen in patients with a history of asthma or chronic obstructive pulmonary disease ( COPD ), and in those without a history of respiratory disease.
The product information for Relenza also lists neuropsychiatric disorders as a possible side effect of the medicine. As with Tamiflu, these events were added to the product information as a precautionary measure and a causal association with Relenza is uncertain.
Drug interactions
Clinically significant drug interactions with Relenza are unlikely.
Patients with asthma or COPD
Patients with severe asthma should not receive Relenza unless close medical monitoring and appropriate clinical facilities are available, in case of bronchoconstriction.
In patients with persistent asthma or severe COPD, management of the underlying disease should be optimised during Relenza treatment.
If Relenza is considered appropriate for any patient with asthma or COPD, the patient should be informed of the potential risk of bronchospasm and should have a fast-acting bronchodilator available. Patients on maintenance inhaled bronchodilating therapy should be advised to use their bronchodilators before taking Relenza.
Source: Drug Safety Update – MRCA, 2009
XagenaMedicine2009
Link: Xapedia - Medical Encyclopedia