formulating a hypothesis about the effect of absorption rates

Classical explanations of the rate and extent of drug absorption have been based on the pH-partition hypothesis. According to this hypothesis, weakly acidic drugs are largely unionized and lipid soluble in acid medium, and hence should be absorbed best by the stomach.

The predictive absorption models are used to determine the rate and extent of oral drug absorption, facilitate lead drug candidate selection, establish formulation development strategy, and support the development of regulatory policies.

The rate determining steps in absorption of orally administered drugs are: II.Rate of dissolution III.Rate of drug permeation through the biomembrane.

It shows how a simple analytical solution for the fraction of a dose absorbed (Fa equation) can offer a theoretical base to tie together the various concepts, and discusses how this solution relates to the rate-limiting cases of oral drug absorption.

Drug absorption is determined by the drug’s physicochemical properties, formulation, and route of administration. Dosage forms (eg, tablets, capsules, solutions), consisting of the drug plus other ingredients, are formulated to be given by various routes (eg, oral, buccal, sublingual, rectal, parenteral, topical, inhalational).

Several mechanisms of drug absorption have been identified, including passive diffusion, carrier-mediated membrane transport such as active and facilitated diffusion, and other nonspecific drug transporters, such as P-glycoprotein. Different factors can affect drug absorption; these factors can be classified as drug-specific and patient-specific.

Drug absorption involves the mass transfer of a drug from the site of absorption to systemic circulation, and all the processes that the drug molecules undergo during such transfer. The extent and rate of drug absorption depend on several factors, including physicochemical features of the drug, the features of the pharmaceutical dosage form ...

The absorption of drugs depends on physicochemical factors, including formulation factors (eg, rates of disintegration and rates of drug release from polymeric dosage forms), drug factors (eg, solubility and lipophilicity), and biological factors (eg, stomach-emptying rate and GI membrane permeability).

3 Altmetric. Abstract. Most drugs are prescribed as oral preparations or extravascular injections (other than intravenous injections) for the treatment of systemic diseases. These drugs must therefore be absorbed in order to be transported to the target tissues to produce their pharmacological actions.

The well known Lipinski rules ( 6) can help in anticipating drug absorption hurdles and more recently, some quantitative structure bioavailability relationships (QSBR) were proposed leading to a more refined estimate of the drug absorption ( 7 – 15 ).