Wide variation in serum chlorpropamide concentration in outpatients

Serum chlorpropamide concentrations (s-CPA) were determined and related to clinical findings in 83 outpatients with maturity onset diabetes. The daily doses of CPA (mg/kg) varied six-fold, but s-CPA ranged 18-fold between the patients. There was a significant correlation between dose and s-CPA (r = 0.61), which rose to 0.75 in the 30 patients who had prescribed no other drugs. Patients given other drugs concomitantly were over-represented amongst subjects with extreme values of apparent plasma clearance of CPA. There was no correlation either between serum creatinine or age and s-CPA. Of the 83 patients 40 (48%) had acceptable blood and urinary glucose values according to our criteria; but as 17 were overweight, only 23 patients (28%) had acceptable clinical control. Of the remaining 60 patients, too low a dose was being given to only 12, and dietary failure was the most probable explanation in the others. Thirteen patients (16%) probably did not need CPA. It is likely that this is a partial explanation for the high utilisation of oral antidiabetic drugs in Sweden. There was no general correlation between dose or s-CPA and blood glucose values, but analysis of s-CPA may still be of value in explaining unexpected changes in clinical control.