• Michael Dörks, Guido Schmiemann, and Falk Hoffmann.
• Department of Health Services Research, Carl von Ossietzky University Oldenburg, Ammerländer Heerstrasse 140, 26111, Oldenburg, Germany. michael.doerks@uni-oldenburg.de.
• Eur. J. Clin. Pharmacol. 2016 Aug 1; 72 (8): 995-1001.

PurposeInjudicious pro re nata (PRN) or as needed prescribing can lead to polypharmacy, potentially harmful drug interactions and total drug doses exceeding the maximum recommended. Despite the known risks and the widespread administration, there is a paucity of current research examining the use of PRN drugs in nursing homes. Therefore, we examined characteristics of PRN drug use and potential predictors in nursing homes.MethodsThe multicentre cross-sectional study included a heterogeneous sample of 21 nursing homes in Northwestern Germany comprising 852 residents. Descriptive statistics and multivariable regression models were used to analyse and present the collected data.ResultsNearly three quarters (74.9 %) of all residents were treated with at least one PRN medication. On average, each resident was prescribed 2.5 ± 2.3 PRN drugs. On average, residents with no PRN prescriptions stayed since 2.4 ± 2.9 years in the nursing home. Residents with five and more PRN prescriptions were on average since 4.8 ± 4.3 years in the nursing home. In a multivariable analysis, length of stay above the median of 2.1 years (OR 2.4; 95 % CI 1.8, 3.2) and polypharmacy with five or more long-term drugs (OR 2.1; 95 % CI 1.5, 2.9) were associated with a higher number of PRN prescriptions. Most commonly used PRN drug was acetaminophen, which was prescribed to 289 (33.9 %) residents.ConclusionsThe high prevalence of PRN medication should be taken into account when considering polypharmacy and inappropriate drug prescribing or using screening tools like the STOPP/START (screening tool of older persons' potentially inappropriate prescriptions/screening tool to alert doctors to right) criteria in nursing homes. Physicians should regularly reconsider the need of each PRN drug on the medication schedule. Moreover, the high prevalence of PRN medication and the association with length of stay highlights the importance of an accurate documentation.

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