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The in vitro interaction between trimethoprim and some adsorptive materials was investigated; the kinetics and extent of adsorption of the drug were determined. Adsorption studies with trimethoprim powder using three antacids viz; magnesium trisilicate, aluminium hydroxide, magnesium hydroxide as well as edible clay were carried out. Trimethoprim tablets were formulated and their physicochemical properties were evaluated. The effects of the antacids and edible clay on the tablet disintegration time and dissolution were determined. The physicochemical parameters of the tablets (mass, disintegration time, friability, hardness and content of active) met official BP specifications. The adsorption of trimethoprim onto the antacids and edible clay increased as the concentration of the adsorbents increased. Adsorption of the drug by the adsorbents followed the rank order; magnesium trisilicate > aluminium hydroxide > edible clay > magnesium hydroxide. There was no significant increase in the disintegration times of the tablets, and retardation of dissolution in the presence of the antacids and the edible clay followed the same rank order; magnesium trisilicate > aluminium hydroxide > magnesium hydroxide > edible clay. Co-administration of trimethoprim with adsorptive antacid formulations and concomitant consumption of edible clay with trimethoprim needs to be strongly discouraged.