Drug Interaction Report

Theoretically, coadministration of dapsone with inducers of CYP450 3A4 such as rifamycins, anticonvulsants, barbiturates, and St. John's wort may increase the formation of dapsone hydroxylamine, a metabolite associated with hemolysis. Dose-related hemolysis is the most common adverse event associated with oral dapsone in both patients with or without glucose-6-phosphate dehydrogenase (G6PD) deficiency. While clinical studies have not demonstrated evidence of clinically significant anemia in patients treated with dapsone 5% gel for acne vulgaris, an increased reticulocyte count and a decreased hemoglobin level were noted to be associated in a G6PD-deficient patient. Exposure to dapsone from the recommended topical dose is about 1% of that from a 100 mg oral dose.

GENERALLY AVOID: An isolated case report suggests that foods containing large amounts of tyramine may precipitate a hypertensive crisis in patients treated with St. John's wort. The mechanism of interaction is unknown, as St. John's wort is not thought to possess monoamine oxidase (MAO) inhibiting activity at concentrations achieved in vivo. The case patient was a 41-year-old man who had been taking St. John's wort for seven days prior to presentation at the emergency room with confusion and disorientation. The patient recalled last eating aged cheese and having a glass of red wine approximately 10 hours prior to admission. No other cause of delirium or hypertension could be identified. In addition, alcohol may potentiate some of the pharmacologic effects of St. John's wort. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Until further information is available, patients treated with St. John's wort should consider avoiding consumption of protein foods in which aging or breakdown of protein is used to increase flavor. These foods include cheese (particularly strong, aged or processed cheeses), sour cream, wine (particularly red wine), champagne, beer, pickled herring, anchovies, caviar, shrimp paste, liver (particularly chicken liver), dry sausage, figs, raisins, bananas, avocados, chocolate, soy sauce, bean curd, yogurt, papaya products, meat tenderizers, fava beans, protein extracts, and dietary supplements. Caffeine may also precipitate hypertensive crisis so its intake should be minimized as well. Patients should also be advised to avoid or limit consumption of alcohol.