Enhanced migration of the ionized forms of acidic drugs from water into chloroform in the presence of phospholipids

The transfer process of various acidic drugs from water into chloroform containing phospholipids has been examined using a nonemulsifying system. The ionized forms of the drugs which have little lipid solubility show a marked increase in transfer to the chloroform phase containing lecithin at the physiological pH of the small intestine. The pH-profiles of salicylic acid, p-aminobenzoic acid and sulphisoxazole transfer are in good agreement with available in situ absorption data. These results suggest a role for phospholipids in the intestinal absorption of ionized acidic drugs which has not been clearly apparent with pH-partition hypothesis alone.