title: Serum theophylline concentrations are not affected by coadministration of doxycycline.
abstract: Doxycycline (D) is often administered during respiratory infections to asthmatic patients, many of them treated by theophylline (T) as well. We therefore investigated a possible interaction between D and T. Steady-state basal T levels were measured on two successive days before and after three and four days of D administration in ten stable asthmatic patients. Mean T levels before D were 9.9 +/- 3.1 micrograms/mL and after D 10.1 +/- 2.9 micrograms/mL, which are not significantly different. But T levels in four patients increased and in two patients, T levels decreased. We conclude that in some patients, T concentrations may be affected by D. This may require determination of T blood levels and T dose adjustment in some patients treated by T and D.
mesh_terms: D000293:Adolescent; D000328:Adult; D001249:Asthma / Q000188:drug therapy; D002648:Child; D004318:Doxycycline / Q000008:administration & dosage*; D004359:Drug Therapy, Combination; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013806:Theophylline / Q000008:administration & dosage* / Q000097:blood*
chemical_list: D013806:Theophylline; D004318:Doxycycline