The therapeutic course as a measure complementary to defined daily doses when studying exposure to antibacterial agents.

Abstract

The defined daily dose (DDD) method may not provide accurate information about exposure to antibacterial agents, owing to their short-term use and the consequently high turnover of subjects. This study was addressed to evaluate whether the number of "therapeutic courses" could offer additional information. Prescription data of antibacterial agents (ATC J01) in Ravenna, Italy (350,000 inhabitants), were studied in 1998. All the prescriptions issued within 10 days were considered as belonging to one therapeutic course (TC). The following measures were compared: DDD/1000 inhabitants/year, number of exposed subjects/1000 inhabitants/year and number of TC/1000 inhabitants/year. In order to compare the number of 10-day TCs with the number of DDDs, the latter was divided by 10 (DDD10). The intensity of drug treatment was also evaluated as the average number of DDDs per TC (therapeutic intensity). Sixty-one percent of the subjects received only one prescription in 1998. Among the second prescriptions, 69% were issued after a time interval greater than 21 days. The overall prevalence of use was 329 per 1000 inhabitants, the TCs were 525 per 1000 inhabitants and DDD10/1000 inhabitants/year were 470. The therapeutic intensity varied with the age classes (being lowest in the elderly) and with the individual antibiotics used. Two or more antibacterials were used within the same TC in 7% of the cases. The measures considered in this study provided different estimates of exposure to antimicrobial agents. The combined analysis of DDDs and TCs may offer a more reliable information about exposure to antimicrobial agents.