Food and guar decrease absorption of trimethoprim.

Absorption of trimethoprim suspension 3 mg/kg has been studied in 12 healthy adult volunteers when given alone, with food or with food and guar, using a randomised Latin-squares study design. Serum and urine trimethoprim concentrations were followed for 24 h. The mean peak serum concentration was higher when fasting subjects were treated (mean: 2.35, 1.84 and 1.97 micrograms/ml for the fasting, food and food + guar groups, respectively; ANOVA p less than 0.001 for the difference between fasting and non-fasting values). The times of the peak serum concentrations did not differ. Food ingestion decreased the area under the curve by 22.2%, as did food + guar. For maximal efficacy trimethoprim should be administered between meals.