OBJECTIVES: Polypharmacy puts older adults at increased risk of adverse drug reactions because of the compromised drug metabolism. Cutaneous adverse drug reaction (CADR), a major class of ADRs frequently reported, is a mild health condition that affects skin, but has potential to inflict serious lesions when left unattended. This study thus aimed to determine the association of CADR risk with polypharmacy exposure among older adults.

METHODS: Within a cohort of 10% random sample of older adults 65 or older in South Korea, new cases of CADR were identified based on primary and secondary diagnosis codes in the year of 2013 excluding those who had records of CADR in previous two years. Controls were those older adults who had no records of CADR. Each case was matched to 5 controls based on the disease risk scores of CADR among the polypharmacy-unexposed. Conditional logistic regression was used to test odds ratio of CADR risk for different definitions of polypharmacy.

RESULTS: The number of new cases of CADR identified within the cohort was 431 with the matched (1:5) controls being 2,155. Of the different periods of polypharmacy, only the 1-month polypharmacy significantly explained the risk of CADR; i.e., the 1-year polypharmacy did not significantly explain the risk variation of CADR (p=.404). Furthermore, compared to the polypharmacy less than 3 drugs per month, only the polypharmacy of having 6 to 8 drugs per month was significantly associated with the increased risk of CADR (OR=1,415, p<0.01).

CONCLUSIONS: CADR, a mild skin reaction, is more likely to be reported for immediate-term polypharmacy exposure than for long-term exposure. It is also more likely for the polypharmacy of 6-8 drugs per month rather than for the number greater than 8. Healthcare provider should watch for CADR occurrence when older patients begin to take 6-8 drugs per month.