A Comparison of In vivo and In vitro Tests for the Absorption, Penetration, and Diffusion of Some Medicinals from Silicone and Petrolatum Ointment Bases

Abstract

Five drugs–sulfanilamide, ammoniated mercury, salicylic acid, iodine and sodium radio–iodide (I135), and chlortetracycline–each incorporated into three silicone ointment bases and three petrolatum ointment bases, were tested by in vitro procedures for diffusion of the drug and by in vivo procedures for penetration and absorption of the drug. A modified agar plate method and a chemical procedure were the two in vitro tests used for measuring diffusion. The penetration of the drugs from ointments was determined by applying the ointments to the skin of white rats and subsequently analyzing a biopsy of the inuncted skin. The absorption of the drugs into systemic circulation was measured by analyzing the blood or a “storage organ” for the drugs. Both intact-skin studies and abraded-skin studies were conducted. The results obtained by in vitro diffusion tests did not correlate well with the penetration of the drugs as shown by in vivo tests. With three of the five drugs the in vitro data correlated fairly well with the absorption through abraded skin; whereas there was little correlation between in vitro data and absorption through intact skin. Neither the silicone ointment bases nor the petrolatum ointment bases could be shown to be the universally more efficient vehicles.