Can vaccines interact with drug metabolism?

Vaccines are safe and efficacious in reducing the burden of several serious infections affecting children and adults. Due to their efficacy, vaccines are often administered in patients with chronic diseases, likely to be under poly-therapy. Because of several case reports indicating changes in drug metabolism after vaccination, the hypothesis of an interaction between vaccines and specific drugs has been put forward. These interactions are conceivably of great concern, especially in patients treated with molecules characterised by a narrow therapeutic index. Herein, we review and systematise the available evidence on vaccine-drug interactions. The picture that emerges indicates that reduction in the activity of specific CYPs following vaccination may occur, most likely via interferon γ overproduction, and for specific drugs such as anticonvulsivant and theophylline may have significant clinical relevance. Clinical interaction between vaccines and drugs that are metabolised by cytochromes uninfluenced by INFγ levels, such as warfarin, are instead unlikely to happen. Further studies are however needed to gain a complete picture of vaccine-drug interactions and define their relevance in terms of possible negative clinical impact.