A comparison of two methods for measuring anti-hypertensive drug use: concordance of use with South African standard treatment guidelines

Abstract

To assess prescriber adherence to standard anti-hypertensive treatment guidelines in South Africa, determine if supply data are useful indicators of drug use, and assess the cost implications of not complying with the guidelines. We undertook two studies: an analysis of records of the anti-hypertensive drugs supplied to all 54 public-sector hospitals with a hypertension clinic in KwaZulu-Natal, and a direct-observation survey of anti-hypertensive drug prescriptions presented to pharmacies in a subset of 16 of the 54 hospitals. We calculated the relative use of each anti-hypertensive drug group as a proportion of all anti-hypertensive drugs supplied or prescribed. We ranked drug groups in order of use for comparison with recommended South African standard treatment guidelines, and we compared the proportions derived from supply data with those derived from the prescription survey. Supply data showed that, in line with treatment guidelines, diuretics and angiotensin-converting enzyme inhibitors were the most frequently supplied medicines (42% and 27%, respectively). However, methyldopa - not included in the treatment guidelines - represented 10% of all anti-hypertensives supplied, but the proportion varied widely between hospitals (0-37%). Reserpine, second choice in the treatment guidelines, was used in high amounts by only two hospitals. Calcium channel blockers and beta blockers represented a small proportion of the anti-hypertensive drugs supplied: 6% each. Results from the prescription survey were in concordance with supply data for the most frequently prescribed drugs but gave slightly different estimates of the use of others. Supply data, the most available source of information about drug use in developing countries, are (with some provisos) a reliable data source for the evaluation of adherence to treatment guidelines. Our results showed substantial non-adherence to standard treatment guidelines.