Longitudinal association between polypharmacy and development of pruritus: a Nationwide Cohort Study in a Japanese Population.

BACKGROUND: Although polypharmacy is known to cause side-effects due to drug-drug interactions, dermatological symptoms triggered by polypharmacy are not fully addressed. OBJECTIVE: To investigate whether polypharmacy is associated with the risk of pruritus. METHOD: A cohort study was performed to examine cross-sectional and longitudinal relationships between polypharmacy and pruritus in a general population. Data were collected from the Norm Study conducted in 2016 and 2017, which is a nationwide survey based on a self-administered questionnaire with Japanese representative participants aged 16-84 years. Presence of polypharmacy which was defined as concurrent use of ≥5 prescribed drugs. Primary outcomes were the presence of severe pruritus at baseline for the cross-sectional analysis and the development of severe pruritus after one year for the longitudinal analysis. Multivariable modified Poisson regression analyses were performed to estimate risk ratios (RRs) and 95% confidence intervals (95%CIs) with adjustment for potential confounders (age, gender, smoking habits, drinking habits, depressive symptoms, moderate activities based on IPAQ score and presence of 11 comorbid conditions including skin disease). RESULTS: The study included 3126 participants (mean age, 48.7 years); nearly half (49.8%) were male. In all, 332 participants (10.3%) had polypharmacy in the cross-sectional analysis. Participants with polypharmacy were more likely to present with severe pruritus at baseline than those who were not using drugs (adjusted RR = 1.52 [95%CI 1.15-2.01, P = 0.003]). The longitudinal analysis (n = 1803) was limited to those without severe pruritus at baseline; participants with polypharmacy at baseline were more likely to develop severe pruritus after a one-year follow-up period than those not using drugs (adjusted RR = 1.46 [95%CI 1.14-1.87, P = 0.002]). CONCLUSION: Polypharmacy was associated with the presence of pruritus at baseline and may predict the future risk of developing pruritus.