THE USE OF NITRATES, CALCIUM-CHANNEL BLOCKERS AND ACE-INHIBITORS IN PRIMARY-CARE IN THE NORTHERN REGION - A PHARMACOEPIDEMIOLOGIC STUDY

1 Prescribing rates for cardiovascular drugs have substantial local variation. The objectives of this study were to determine the prescribing prevalence of nitrates, calcium channel blockers and angiotensin-converting enzyme inhibitors in general practice, to examine the indications recorded for these prescriptions, and to identify which therapeutic areas contribute to the variation in prescribing. 2 Anonymised patient-specific prescription data were taken from computerised records in 41 VAMP research practices in the Northern Region (total population 330,749). All patients who received any prescription for calcium channel blockers, nitrates or angiotensin-converting enzyme (ACE) inhibitors during a 12 month period were included. Prescribing rates were determined in terms of patients per 1,000 population within age, sex and diagnostic groups. 3 Overall, 4.3% of the study population were prescribed one or more of the drugs. There was virtually no prescribing for patients under the age of 35 years, but thereafter the prevalences rose steeply to peak at ages 65-74 years for calcium channel blockers (91 per 1,000 population) and ACE inhibitors (34 per 1,000), and at ages 75-84 years for nitrates (100 per 1,000). Prescribing prevalence amongst the over 85's was less than half the peak rate for each drug group. Rates for men and women were comparable, except for nitrates where men had higher rates. 4 Recorded indication rates for patients with ischaemic heart disease and treated with any of these drugs reached 112 per 1,000 population in the 75-84 age group, and were higher in men than women, at all ages. Hypertension indication rates were substantially higher in women over 65; across the genders the peak rate was 88 per 1,000 for those aged 65-74 years. Cardiac failure rates had an older age profile with a much lower peak of 40 per 1,000 population at ages 75-84 years. 5 For patients with IHD the relative use of calcium channel blockers in preference to cheaper nitrates, declined with age. For patients with hypertension the use of ACE inhibitors relative to calcium channel blockers showed a similar decline. 6 Whilst practices had similar profiles of prescribing with respect to patient age and gender, absolute prescribing rates varied substantially for hypertension and IHD, but less so for cardiac failure indications. This variability suggests that treatment guidelines for hypertension are not uniformly adopted or interpreted in primary care.