Market penetration of new drugs in one United Kingdom region: implications for general practitioners and administrators.

OBJECTIVE--To determine the use of new drugs in one United Kingdom region. DESIGN--Examination of data on prescribing of angiotensin converting enzyme inhibitors, new broad spectrum antibiotics, and H2 receptor antagonists. Calculation of number of defined daily doses prescribed each month. SETTING--All general practices in Northern Ireland. MAIN OUTCOME MEASURES--Drug use index and market share of each drug. RESULTS--During 1988-91 prescribing of angiotensin converting enzyme inhibitors increased by 126%, of H2 receptor antagonists by 46%, and of new antibiotics by 207%. The first drug on the market usually retained the largest market share. Use of oral antibiotics increased threefold irrespective of the reporting policy of the general practitioners' local laboratory. CONCLUSIONS--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. This suggests that the profession has not instituted effective checks to ensure that the legitimate promotion of new products does not lead to inappropriate and wasteful use.