Medication use and multiple myeloma risk in Los Angeles County.

Background: The role of medication use in multiple myeloma (MM) risk remains unclear.
Methods: The Los Angeles County Multiple Myeloma Case-Control Study, comprising 278 MM cases and individually matched neighborhood controls, provided data to assess associations between medication use and MM risk. Odds ratios (OR) and 95 % confidence intervals (CI) were estimated using conditional logistic regression.
Results: Erythromycin (ever) use was associated with increased MM risk (OR 1.85, 95 % CI 1.13-3.03). This association was restricted to men (OR 3.77, 95 % CI 1.72-8.29) and was especially apparent among men who took two or more courses of erythromycin (OR 4.68, 95 % CI 1.70-12.87).
Conclusions: Compared to females, males have lower levels of cytochrome P450 3A4 (CYP3A4), for which erythromycin is both a substrate and inhibitor. Use of CYP3A4-inhibiting drugs such as erythromycin in men may thus result in even lower levels of CYP3A4 and, consequently, higher levels of CYP3A4-metabolized substances. These results could potentially provide clues to explain discrepancies in MM incidence by sex. Consortial efforts to confirm these associations are warranted.