Use and overuse of sumatriptan. Pharmacoepidemiological studies based on prescription register and interview data.

Abstract

The serotonin agonist sumatriptan was marketed in Denmark in 1992 for the treatment of acute attacks of migraine and cluster headache. The clinical development program of the drug was impressive. However, knowledge of the long-term use of sumatriptan in unselected patients was lacking. Misuse of sumatriptan was reported in single patients shortly after the introduction of the drug. The aim of the present thesis was, therefore, to provide an epidemiological description of sumatriptan use with particular emphasis on overuse. The author conducted three studies, two of which were exclusively based on population-based data from a regional (Odense Pharmacoepidemiological Database) and a national (Registry of Drug Statistics, Danish Medicines Agency) prescription registry. Both registries record patient-specific information, thus enabling the conduct of longitudinal studies of drug use. The regional registry covers the county of Funen (reimbursable prescription drugs only), while the national registry records information on all prescriptions presented in the entire country. Consumption was described by means of the Defined Daily Dose (DDD) unit. One DDD of sumatriptan amounts to 100 mg orally or 6 mg subcutaneously. Subjects were classified as recipients of single or multiple prescriptions. Individuals in the latter category were characterized by the 30-day period with the most intensive dispensing of sumatriptan (peak use): low (less than 30 DDD/30 days), intermediate (30-59 DDD/30 days) and high-peak users (60 or more DDD/30 days). In 1995, 33,206 users of sumatriptan were identified in Denmark, corresponding to a 1-year period prevalence of use of 7.8 per 1,000 inhabitants (only persons aged > or = 16 years were included). A female-to-male ratio of 3.8:1 was found. Use was most common among women aged 35-54 years and was highest among 45 to 49-year-olds for both sexes. The standardized period prevalence of sumatriptan use varied regionally between the Danish counties from 6.4 to 9.6 per 1,000 inhabitants. The period prevalence of sumatriptan use in the county of Funen was highly comparable with that of the entire nation. Among the 43,389 sumatriptan users presenting prescriptions for sumatriptan in Denmark in 1994 and 1995, 507 (1.1%) and 1726 (4.0%) belonged to the high and intermediate-peak-use group, respectively. Patients belonging to these two groups were responsible for 38% of the total consumption of sumatriptan. For patients in the high-peak-use group the median span between first and last prescription was 693 days while the median quantity of sumatriptan purchased was 648 DDD. Highly comparable patterns of long-term intense sumatriptan use were found in the data from the regional registry, which covered the 27-month period after the introduction of the drug (February 1992). The register data were highly suggestive of overuse, but lacked essential information, e.g., the indication for use. A third study was therefore conducted using a combination of register and interview data. During a 14-day period, current users of sumatriptan were recruited through community pharmacies in the county of Funen. Respondents returned a signed consent form, including their unique personal identification number (CPR), allowing us to retrieve patient-specific data from the regional registry. For each respondent, all available relevant prescription data for the period 1992-96 were retrieved. Subjects were classified into high, intermediate, and low-peak-use groups according to register data from the 4-year period. The register data were used to evaluate representativity after anonymizing nonrespondent data. The response rates were 33% (7/21) in the high-peak-use group, 47% (30/64) in the intermediate-peak-use group, and 56% (196/350) in the low-peak-use group. Respondents and nonrespondents in the three groups were comparable with regard to age and use of other drugs. (ABSTRACT TRUNCATED)