Constipation as an adverse effect of drug use in nursing home patients: an overestimated risk

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Abstract
Aims To investigate whether results from case control and cross sectional studies which suggest an association between laxative use and other drug use could be confirmed in a cohort study of nursing home patients. Methods A prospective cohort study of 2355 nursing home patients aged 65 years and over was performed to estimate the incidence relative risk of constipation associated with drug use. The study was conducted with prescription sequence analysis of each resident's detailed pharmacy records and data on morbidity and mobility. Results Use of drugs, which according to the summaries of product characteristics (SPC) and the literature on adverse drug effects have moderately to strongly constipating properties, was associated with a relative risk of 1.59 (95% CI 1.24–2.04) for the occurrence of constipation during exposure time. Use of drugs with mildly to moderately constipating effects was not associated with laxative use (RR 1.13; 95% CI 0.93–1.38). Stratification on the level of age, gender, type of nursing (psychogeriatric or somatic), morbidity, number of medications taken and mobility showed no confounding effects of these variables on outcome measurements. These variables all acted as effect modifiers. Effect of age and number of medications taken on the relative risk was nonlinear. Conclusions Although an association between drugs that exhibit moderately to strongly constipating effects and occurrence of constipation was found, the risk was not as high as seen in previous studies. The high prevalence of constipation in nursing home patients is only partly due to adverse drug effects.