New prescriptions of spironolactone associated with angiotensin-converting- enzyme inhibitors and/or angiotensin receptor blockers and their laboratory monitoring from 2001 to 2008 : a population study on older people living in the community in Italy

Purpose: To analyse, in older community-dwelling people living in Italy's Lombardy region, 8-year trends in new users of spironolactone co-prescribed with angiotensin-converting-enzyme inhibitors (ACE-Is) and/or angiotensin receptor blockers (ARBs); blood test monitoring; and independent predictors of appropriate blood test monitoring. Methods: The region's administrative health database from 2001 to 2008 was used to retrieve yearly frequencies of subjects aged 65+ who started this co-prescription. Multivariate analyses were adjusted for age, sex, local health unit, treatment with beta-blockers, drugs for diabetes, and polypharmacy (i.e., exposure to five or more different drugs). Results: Only new users of spironolactone co-prescribed with ARBs increased from 2001 to 2008 (P < 0.001). In the 6 months before starting the co-prescriptions 96 to 100% of patients measured serum creatinine (mean 99.3%), sodium (97.3%) and potassium (98.6%). Within 3 months of starting the co-prescriptions 96 to 99% of patients measured serum sodium (mean 97.3%) and potassium (98.6%), but on average only 48% of them (range 43 to 53%) measured serum creatinine, with an increase over time (odds ratio [change in regression per year] = 1.03, 95% CI 1.02-1.05, P < 0.001). At multivariate analysis polypharmacy was found to be the only independent predictor of such creatinine monitoring (P < 0.001). Conclusions: Our results support the need for greater awareness within the medical community of the potential renal toxicity of the association of spironolactone with ACE-Is and/or ARBs. Adequate short-term monitoring of serum creatinine in all older community-dwelling people who receive such co-prescription is necessary in order to ensure safe usage of these medications.