IJPI’s Journal of Pharmaceutics and Cosmetology Visit www.ijpijournals.com ISSN 2229 – 6832 Importance of Bioavailability of Drugs with Reference to Dosage Form and Formulation 1 Waqar Hussein, 2 Shanza Waqar, 3 Shumula Khalid, * 4 Safila Naveed 1 Faculty of Pharmacy Hamdard University 2 CHK, Dow University Health Sciences, Karachi 3 Department of Pharmacology & Therapeutics, D.M.C, DUHS, Karachi 4 Jinnah University for Women Karachi, PAKISTAN Corresponding author: Safila Naveed Email address: safila117@gmail.com ABSTRACT: Drug availability i.e. efficiency of dosage form as drug delivery system is a top issue to pharmacy and many terms as blood level or significant concentration of drug in the blood stream for distribution process at the site of action through membrane or amount of metabolite or drug excreted unchanged are used to describe the phenomena. The absorption depends on the designing of the formation with appropriate ingredient or excipient, particle size, solubility, dissociation constant pK a, lipid solubility and pH at the absorption site. The additive e.g. diluents, binder, lubricant, suspending agent, surface active agent often may alter absorption of a therapeutic agent from a dosage form. Dissolution i.e. release of drug from the solid dosage form after disintegration is the primary importance for absorption and is rate limiting approved by FDA. Physicians assume drug administered orally or parenterally reach the general circulation in their pharmacologically active form to be distributed throughout the body and exert therapeutic effect at the site of action. It is not true. Complete entry into the general circulation can achieve by intravenous injection. Keywords: Bioavailability, drug formulations, drug dissolution.