The rate and efficacy of absorption of a drug depends on the following

1. Route of drug administration: The intravenous (IV) route is most effective.
2. Blood flow: Highly vascularized organs such as the small intestine have the greatest absorbing ability.
3. Surface area available: Absorption of a drug is directly proportional to the surface area available.
4. Solubility of a drug: The ratio of hydrophilic to lipophilic properties (partition coefficient) that a drug has will determine whether the drug can permeate cell membrane.
5. Drug-drug interactions: When given in combination, drugs can either enhance or inhibit one another’s absorption.
6. pH: A drug’s acidity or alkalinity affects its charge, which affects absorption.