The Future of Trimethoprim

Abstract

From a dissertation read before the Society on 11th February, 1981.

Co-trimoxazole became available for medical use towards the end of 1968 and represented a successful marriage of the old and the new, being a combination of a sulphonamide and a new drug called trimethoprim. Today it is one of the most widely prescribed drugs in the United Kingdom, and is used extensively in urinary and respiratory tract infections. More recently, however, trimethoprim has been released for use on its own, and this has raised considerable controversy as to which is the drug of choice.

Three original claims for co-trimoxazole

Simple laboratory tests suggest that a combination of trimethoprim and a sulphonamide will inhibit bacterial growth at concentrations lower than either drug on its own. More formal assays which compare the drugs over a range of concentrations confirm that the antibacterial effect of the combination greatly exceeds a purely additive response. The drugs' interaction is said to be synergistic, although no single definition of the term synergy has ever been universally accepted.