Market penetration of new drugsBMJ 1994; 308 doi: https://doi.org/10.1136/bmj.308.6925.416 (Published 05 February 1994) Cite this as: BMJ 1994;308:416
- H McGavock,
- G D Johnston,
- C H Webb
- Drug Utilisation Research Unit, Department of Therapeutics and Pharmacology, Queen's University of Belfast, Belfast BT9 7BL.
EDITOR, - Three letters1 comment on our article on the market penetration of new drugs in Northern Ireland.2 J P Griffin attacks our article as flawed in its conclusions without revealing the flaws.1 We did not state that it was “always the first medicine in the field which continues to be…the market leader.” We did not advocate that the search for better products in the same therapeutic class should not be pursued. We described not “modest increases” in drug use but twofold and threefold increases over four years. The clinical need for these drugs, apart from angiotensin converting emzyme inhibitors, is unlikely to have increased over the same period. Our generalisations were not “based on too few data.” They covered all prescribing for 1.6 million people, every month for four years. Finally, the caution of doctors in the United Kingdom in using new drugs is well documented and probably well justified.
In R C Davis's letter the calculations on the estimated use of angiotensin converting enzyme inhibitors in heart failure are simplistic and unlikely to represent the true picture.1 The estimated prevalence of heart failure of 0.4% refers to all patients with symptomatic heart failure. Most patients in Northern Ireland who receive angiotensin converting enzyme inhibitors have grade III or IV disease (New York Heart Association classifications); patients with this grade of disease make up a relatively small percentage of the total. In addition, most of these patients receive captopril, a short acting agent, and only rarely receive one of the longer acting preparations. The increased prescribing of long acting angiotensin converting emzyme inhibitors is therefore mostly due to these drugs' increased use in hypertension.
With regard to Andrew H Watt's letter, because we work in a drug utilization research unit we are well aware of the difficulties of reaching conclusions from prescription pricing data.1 Our paper was cautious, with circumspect language. In the case of the three therapeutic groups that we studied we would remind Watt that our argument is simply that “the increase in prescribing of these drugs seems to be greater than can be accounted for by an increase in patients with specific indications for these drugs.” We would welcome epidemiological or other evidence from Watt that challenges our conclusionss.