Knowledge of Pharma

METHODS  FOR  ASSESSING  BIOAVAILABILITY: Direct and indirect methods may be used to assess drug bioavailability. The in-vivo bioavailability of a drug product is demonstrated by the rate and extent of drug absorption, as determined by comparison of measured parameters, eg, concentration of the active drug ingredient in the blood, cumulative urinary excretion rates, or pharmacological effects.  For drug products that are not intended to be absorbed into the bloodstream, bioavailability may be assessed by measurements intended to reflect the rate and extent to which the active ingredient or active moiety becomes available at the site of action. The design of the bioavailability study depends on the objectives of the study, the ability to analyze the drug (and metabolites) in biological fluids, the pharmacodynamics of the drug substance, the route of drug administration, and the nature of the drug product.  Pharmacokinetic and/or pharmacodynamic parameters as well as clinical

INTRODUCTION A multisource drug product is a drug product that contains the same active drug substance in the same dosage form and is marketed by more than one pharmaceutical manufacturer.  Single-source drug products are drug products for which the patent has not yet expired or has certain exclusivities so that only one manufacturer can make it. Single-source drug products are usually brand-name (innovator) drug products. After the patent and other exclusivities for the brand-name drug expires, a pharmaceutical firm may manufacture a generic drug product that can be substituted for the branded drug product.   Since the formulation and method of manufacture of the drug product can affect the bioavailability and stability of the drug, the generic drug manufacturer must demonstrate that the generic drug product is bioequivalent and therapeutically equivalent to the brand-name drug product.   Drug product selection and generic drug product substitution are major responsibilities fo

Physiologic Factors Related to Drug Absorption:   The systemic absorption of a drug is dependent on   The physicochemical properties of the drug,   The nature of the drug product, and   The anatomy and physiology of the drug absorption site.  1. Membrane Physiology A. Nature of Cell Membrane  The fluid mosaic model, proposed by , explains the transcellular diffusion of polar molecules.   According to this model, the cell membrane consists of globular proteins embedded in a dynamic fluid, lipid bilayer matrix. These proteins provide a pathway for the selective transfer of certain polar molecules and charged ions through the lipid barrier.  As shown in , transmembrane proteins are interdispersed throughout the membrane. Two types of pores of about 10 nm and 50 to 70 nma were inferred to be present in membranes based on capillary membrane transport studies. These small pores provide a channel through which water, ions, and dissolved solutes such as urea may move acros

Definitions Pharmacokinetics o    Evaluate the way in which a drug interacts with various barriers within a biological system Pharmacodynamics o    Study of the relationship between systemic exposure of a drug and it’s biological effects on tissue o    Absorption can be defined as the movement of active drug (or prodrug) from the site of administration across biologic barriers into a site where it is measured in the blood. This site of measurement is not specified. o    Bioavailability can be defined as the fraction of administered drug that reaches the systemic circulation. o    Note the difference in endpoint measurement sites    PHARMACEUTICAL FACTORS: It include factors relating to the- A.     Chemical Factors o    A variety of chemical options can be used to improve the stability and systemic availability of drugs. o    For example, esters can be prepared of both acids and bases to produce more stable derivatives, which hydrolyse to the act