The effect of an enteral nutrient formula (Osmolite) on the absorption of a single oral dose of sustained-release theophylline (Slo-bid) was studied in healthy men. In a randomized, crossover design, subjects received the enteral nutrient diet (2,400 ml/day) or food diet (F) of similar caloric, fat, carbohydrate, protein, and sodium content for 7 days. On day 6 of each diet, volunteers received a single oral dose (600 mg) of sustained-release theophylline (SRT) after fasting or with hourly oral boluses (100 ml) of enteral nutrient formula (ENF). Serial blood samples were collected for 48 h and serum concentrations were analyzed by enzyme multiplied immunoassay. Slight differences (p < 0.01; pairedttest) inCmax(7.1 \pm 1.2 versus 8.2 \pm 1.3 mg/L) andTmax, (10.7 \pm 2.4 vs. 7.1 \pm 1.1 h) were observed between the ENF and F diets, respectively. However, areas under the curve values were similar (215 \pm 72 versus 211 \pm 70 mg h/L). This study suggests that ENF does not affect the extent of absorption of SRT when administered as a single oral dose.