To the Editor.—We read with inter[ill] the recent article by Powell et al1 garding the effects of ranitidine [ill] cimetidine on theophylline meta[ill] lism. A number of reports have b[ill] published regarding cimetidine's teraction with theophylline,2,3 ranitidine has yet to undergo as ext[ill] sive an investigation of this poten[ill] problem.
Breen and colleagues,4 using me[ill] odologies similar to those employed Powell et al,1 demonstrated a 9% crease in the systemic clearance theophylline and a slightly long mean elimination half life in subje[ill] pretreated with ranitidine compa[ill] with a control period. They, howe[ill] employed only a single dose of ophylline and therefore were unable report on a steady-state regimen of [ill]o drugs. One might expect to see an centuation of any effects in the [ill]eady-state condition. Breen et al also [ill]int out that the molar ratio of [ill]netidine and ranitidine was 4.2:1 and [ill]ggest that it