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Thread: Biopharmaceutics

  1. #1

    Default Biopharmaceutics kit

    Biopharmaceutics is the study of the physicochemical properties of the drug and the drug product, in vitro, on the bioavailability of the drug, in vivo, to produce a desired therapeutic effect.

    Physiochemical Factors that Affect Drug Absorption include:

    1.Drug disintegration (rate-limiting step)
    2.Drug dissolution (rate-limiting step)
    3.Drug across the cell membrane (rate-limiting step)
    4.Drug stability (loss of drug due to decomposition)
    5.Drug particle size (drug particle surface area, affecting dissolution)
    6.Drug polymorphism (affecting dissolution)
    Last edited by CheneyHsiung; Fri 26th February '16 at 10:44pm.
    Clinical Pharmacy Specialist - Hematology

  2. #2

    Default

    Bioavailability refers to the measurement of the rate and extent of active drug that becomes available at the site of action.

    Because the systemic blood circulation delivers therapeutically active drug to the tissues and to the site of action of the drug, changes in bioavailability affect changes in the pharmacodynamics and toxicity of a drug.
    Clinical Pharmacy Specialist - Hematology

  3. #3

    Default Rate-Limiting Steps in Drug Absorption

    Systemic drug absorption from a drug product consists of a succession of rate processes.

    For solid oral, immediate-release drug products, the rate processes include 1.disintegration of the drug, 2.dissolution of the drug in an aqueous environment, and 3.absorption across cell membranes into the systemic circulation.

    In the above processes, the rate at which drug reaches the circulatory system is determined by the slowest step in the sequence and the slowest step in a series of kinetic processes is called the rate-limiting step.

    Except for controlled-release products, disintegration of a solid oral drug product is usually more rapid than drug dissolution and drug absorption.

    For drugs that have very poor aqueous solubility, the rate at which the drug dissolves is often the slowest step and therefore exert a rate-limiting effect on drug bioavailability. In contrast, for a drug that has a high aqueous solubility, the dissolution rate is rapid, and the rate at which the drug crosses or permeates cell membranes is the slowest or rate-limiting step.
    Clinical Pharmacy Specialist - Hematology

  4. #4
    PharmD Year 1 TomHsiung's Avatar
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    Default Biopharmaceutics Properties Indicating Variability in Bioavailability/Bioequivalence

    1.The active drug ingredient has low solubility in water


    2.The dissolution rate of one or more such products is slow


    3.The particle size and/or surface area of the active drug ingredient is critical in determining its bioavailability


    4.Certain structural forms of the active drug ingredient dissolve poorly, thus affecting absorption


    5.Drug products that have a high ratio of excipients to active ingredients


    6.Specific inactive ingredients either may be required for absorption of the active drug or may interfere with such absorption


    7.The active drug ingredient, or its precursor is absorbed mostly in a particular segment of the GI tract or is absorbed from a localized site


    8.The degree of absorption of the therapeutic moiety or its precursor is poor, even when it is administered in pure form


    9.There is rapid metabolism of the therapeutic moiety in the intestinal wall or liver during the absorption process, so that the rate of absorption is unusually important in the therapeutic effect and/or toxicity of the drug product


    10.The therapeutic moiety is rapidly metabolized or excreted, so that rapid dissolution and absorption are required for effectiveness


    11.The active drug ingredient or therapeutic moiety is unstable in specific portions of the GI tract and requires special coatings or formulations to ensure adequate absorption


    12.The drug product is subject to dose-dependent kinetics in or near the therapeutic range, and the rate and extent of absorption are important in establishing bioequivalence
    Last edited by TomHsiung; Tue 5th January '16 at 2:55pm.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

  5. #5
    PharmD Year 1 TomHsiung's Avatar
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    Default The pH-Partition Hypothesis

    If the pH on one side of a cell membrane differs from the pH on the other side of the membrane, then:

    1.The drug (weak acid or base) will ionize to different degrees on respective sides of the membrane;

    2.The total drug concentrations (ionized plus nonionized drug) on either side of the membrane will be unequal;

    3.The compartment in which the drug is more highly ionized will contain the greater total drug concentration.

    For this reason, a weak acid will be rapidly absorbed from the stomach, whereas a weak base will be poorly absorbed from the stomach.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

  6. #6
    PharmD Year 1 TomHsiung's Avatar
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    Default Re: Biopharmaceutics

    Several types of modified-release oral drug products are recognized:

    1.Extended-release drug products. A dosage form that allows at least a twofold reduction in dosage frequency as compared to that drug presented as an immediate-release (conventional) dosage form. Examples of extended-release dosage forms include controlled-release, sustained-release, and long-acting drug products.

    2.Delayed-release drug products. A dosage form that releases a discrete portion or portions of drug at a time other than promptly after administration. An initial portion may be released promptly after administration. Enteric-coated dosage forms are common delayed-release products (e.g., enteric coated aspirin and other NSAID products).

    3.Targeted-release drug products. A dosage form that releases drug at or near at the intended physiologic site of action. Targeted-release dosage forms may have either immediate- or extended-release characteristics.

    4.Orally disintegrating tablets (ODT). ODT have been developed to disintegrate rapidly in the saliva after oral administration. ODT may be used without the addition of water. The drug is dispersed in saliva and swallowed with little or no water.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

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