Lack of effect of influenza vaccine on theophylline levels and warfarin anticoagulation in the elderly.

Steady state theophylline concentrations were prospectively measured in 13 elderly institutionalized individuals following influenza vaccination. Vaccine-mediated increase in concentrations could not be identified. In seven individuals receiving warfarin, no change in prothrombin or partial thromboplastin times occurred following vaccination. No adverse drug reactions were observed. The following year 14 individuals receiving theophylline and 12 receiving warfarin were vaccinated without adverse drug reactions noticed. These data fail to support previous reports of influenza vaccine inhibition of theophylline metabolism or vaccine-enhanced anticoagulation and are consistent with recent reports on younger subjects.