Objectives: To investigate the mechanisms of these effects.

Methods: The study group included 106 long-term care stable geriatric inpatients. Diet and drugs were kept stable. The study lasted 5 weeks; during the first 2 weeks 100 mg aspirin was administered once a day. Clinical and laboratory follow-up were performed at baseline and weekly for the next 3 weeks. The glomerular filtration rate was estimated by creatinine clearance measured in 24 hour urine and serum creatinine, and by the Cockcroft-Gault formula (C-G) equation. Uric acid clearance (Cu acid) was determined from serum concentrations and 24 hour excretion of uric acid. Patients with serum creatinine > 1.5 mg/dl were not included.

Results: After 2 weeks on low dose aspirin, measured creatinine and uric acid clearances decreased significantly compared with the initial values in 70% and 62% of the patients, respectively, with mean decreases of 19% and 17%, respectively (P < 0.001). Blood urea nitrogen increased by 17% while serum creatinine and uric acid concentrations increased by 4% (P < 0.05 for all). The C-G[1] values decreased by 3% (P < 0.05). After withdrawal of aspirin all parameters improved. However, 67% of the patients remained with some impairment in their measured Ccr[2], compared to baseline. Patients who reacted adversely to low dose aspirin had significantly better pre-study renal function (Ccr), lower hemoglobin and lower levels of serum albumin.

Conclusions: Short-term low dose aspirin affected renal tubular creatinine and uric acid transport in the elderly, which may result in a prolonged or permanent deterioration of the renal function. It is suggested that renal functions be monitored even with the use of low dose aspirin in elderly patients.