The red wine maximization test: drinking histamine rich wine induces a transient increase in plasma diamine oxidase activity in healthy volunteers

Are adverse effects of sildenafil also caused by inhibition of diamine oxidase?

BACKGROUND

Sildenafil citrate (Viagra), a drug used to treat erectile dysfunctions, causes adverse reactions such as headache, flushing or nasal congestion. Sildanefil's potency as inhibitor of diamine oxidase was investigated, as side effects may also be induced by histamine itself due to an impaired histamine metabolism.

METHODS

Placental diamine oxidase inhibition experiments were performed with consecutive dilutions of sildenafil citrate (10(-5) to 10(-9) mol/l). In 9 male volunteers in vivo diamine oxidase inhibition was investigated after taking 100 mg sildenafil (Viagra).

RESULTS

Sildenafil citrate did not inhibit placental diamine oxidase either in vitro or in vivo. However, infusion of 300 mg of cimetidine inhibited diamine oxidase activity by 27 +/- 7% 15 min after infusion, demonstrating that drugs may inhibit diamine oxidase in vivo.

CONCLUSION

As side effects of sildenafil are not caused due to inhibition of diamine oxidase, sildenafil citrate seems to be harmless for patients suffering from histamine intolerance.