Propranolol and folic acid absorption were studied separately in healthy subjects, non-coeliac patients and patients with treated and untreated coeliac disease. 2. The surface pH of jejunal biopsy samples was measured with a pH electrode. 3. When compared with values found in healthy subjects, plasma propranolol levels were elevated in coeliac disease and, in contrast, serum folic acid levels were depressed after oral administration of the drug. Jejunal surface pH was more alkaline in the coeliac groups than in the healthy and non-coeliac subjects. 4. Pharmacokinetic analysis of the plasma drug levels allowed evaluation of the rate constants associated with absorption and elimination. The absorption rate constant was decreased for folic acid in the coeliac group, but increased for propranolol. These changes correlated with variation in surface pH. 5. Although the changes in drug disposition in treated and untreated coeliac disease are the result of several factors, it is suggested that jejunal surface pH may affect the rate of absorption and therefore the plasma concentration-time profile of drugs which undergo dissociation.
