Influenza vaccine drug interactions

No formal drug interaction studies of oseltamivir have been performed. Oseltamivir and its carboxylate metabolite do not interact with the cytochrome P450 system. Although probenecid decreases the elimination of oseltamivir, dosage adjustment is not required during coadministration of these drugs because of oseltamivir s margin of safety. Oseltamivir does not interfere with antibody production in response to the influenza vaccine. 

Zanamivir is contraindicated in individuals with severe or decompensated chronic obstructive lung disease or asthma because it has not been shown to be effective in these individuals and can cause serious adverse pulmonary reactions. Individuals with mild to moderate asthma may have a decline in lung function when taking zanamivir. The safety and efficacy of this medication have not been determined in individuals with severe renal insufficiency. No clinically significant drug interactions have been reported. Zanamivir does not decrease the effectiveness of the influenza vaccine. 

Indinavir levels are raised by interleukin-2, but not affected by influenza vaccine or quinidine. Protease inhibitors are predicted to increase quinidine levels. Nelfinavir does not appear to interact with pancreatic enzyme supplements. In one case report, the combination of ritonavir/saquinavir and fusidic acid raised plasma levels of all three drugs. 

Drug-drug interactions Coadministration of tramadol with vitamin K antagonists increases INR [81 ]. Findings were confirmed by a case-control trial assessing patients on tramadol who were placed on a vitamin K antagonist [82 ]. Patients on rifampicin experienced decreased oral bioavailability of lOO-mg tramadol and decreased durabon of acHon of intravenous 50-mg tramadol [83 -]. A case series of two elderly women on 100-mg oral tramadol demonstrated acute onset of hallucinations after administration of influenza vaccine [84 ]. 

After influenza immunization there was a reduction in blood theophylline concentrations in patients and healthy volunteers (58). The authors concluded that flu vaccine may influence the pharmacokinetics of several drugs, and a second group found that theophylline oxidation was significantly reduced at 1 day, but not at 7 days, after immunization (57). However, others did not confirm these effects (55,59). The lack of a clinical interaction with theophylline has also been confirmed by a report of the US Immunization Practices Advisory Committee (9). 

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