Evaluation of the use of partition coefficients and molecular surface properties as predictors of drug absorption: a provisional biopharmaceutical classification of the list of national essential medicines of Pakistan

BACKGROUND AND THE PURPOSE OF THE STUDY Partition coefficients (log D and log P) and molecular surface area (PSA) are potential predictors of the intestinal permeability of drugs. The aim of this investigation was to evaluate and compare these intestinal permeability indicators. METHODS Aqueous solubility data were obtained from literature or calculated using ACD/Labs and ALOGPS. Permeability data were predicted based on log P, log D at pH 6.0 (log D(6.0)), and PSA. RESULTS Metoprolol's log P, log D(6.0,) and a PSA of <65 Å correctly predicted 55.9%, 50.8% and 54.2% of permeability classes, respectively. Labetalol's log P, log D(6.0) and PSA correctly predicted 54.2%, 64.4% and 61% of permeability classes, respectively. Log D(6.0) correlated well (81%) with Caco-2 permeability (P(app)). Of the list of national essential medicines, 135 orally administered drugs were classified into biopharmaceutical classification system (BCS). Of these, 57 (42.2%), 28 (20.7%), 44 (32.6%), and 6 (4.4%) were class I, II, III and IV respectively. CONCLUSION Log D(6.0) showed better prediction capability than log P. Metoprolol as permeability internal standard was more conservative than labetalol.