The effect of ethanol and pH on the adsorption of drugs from simulated gastric fluid onto activated charcoal.

The effect of ethanol and pH on the adsorption of acetaminophen (ACET), phenobarbital (PHB), phenytoin (PHY), salicylic acid (SA), and theophylline (THEO) from simulated gastric fluid onto activated charcoal was studied. For the ethanol study, each drug was prepared at a concentration of 10 g/L in ethanol; in hydrochloric acid (HCl), 1.2 mol/L; and in HCl, 1.2 mol/L, containing 75% ethanol, 50% ethanol, and 25% ethanol (v/v), respectively. For the pH study, each drug was prepared at a concentration of 10 g/L in HCl, 1.2 mol/L, pH 1.0, and in buffers of pH 1.7, 3.0, 4.0, 4.8, 5.8, 6.5, 7.4, and 9.4. After the addition of 1 g of activated charcoal to 10 mL of each solution, it was incubated for one hour at 37 degrees C. For comparison, in each experiment a blank consisting of the solution without charcoal was also incubated. With increasing concentrations of ethanol, there were substantial decreases in the adsorption of ACET, PHB, and PHY to charcoal. Ethanol-induced decreases in the adsorption of SA and THEO were less pronounced. Changes in pH did not affect the adsorption of ACET, PHB, PHY, or THEO. However, the adsorption of SA was decreased slightly at pH 1.0 and 3.0.