Two different drugs or formulations of the same drug are called bioequivalent if they are absorbed into the blood and become available at the drug action site at about the same rate and concentration. Bioequivalence studies is usually studied by administering dosages to subjects and measuring concentration of the drug in the blood just before and at set times after the administration. These data are then used to determine if the drugs are absorbed at the same rate.
Bioequivalence studies are a surrogate marker for clinical effectiveness and safety data as it would not normally be practical to repeat clinical studies for generic products. It is accepted that if plasma concentrations of the active ingredient of the generic and innovator medicines are the same, then their concentration at the site of action and therefore their safety and effectiveness will be the same. In addition to being bioequivalent, a generic medicine must conform to high quality standards in terms of the method of manufacture and the purity of the final pharmaceutical form.
– Both bioavailability and bioequivalence focus on measuring the absorption of the drug into systemic circulation.
– Bioavailability is a comparison of the drug product to an IV formulation, a solution or a suspension, where as bioequivalence is a comparison with predetermined bioequivalence limits.
– The bioequivalence is said to exist when the bioavailability of a drug with different formulation is same.
Equivalence – Equivalence is more relative term that compares one drug product with another or with a set of established standards.
Equivalence may be defined in several ways:
– Chemical equivalence indicates that two or more dosage forms contain the labelled quantities of drug.
– Clinical equivalence occurs when the same drug from two or more dosage forms gives identical in vivo effects as measured by a pharmacological response or by control of a symptom or a disease.
– Therapeutic equivalence implies that one structurally different chemical can yield the same clinical result as another chemical.
– Bioequivalence indicates that drug in two or more similar dosage forms reaches the general circulation at the same relative rate and the same relative extent.
Need for BIOEQUIVALENCE
– Bioequivalence studies provide a link between the pivotal and early clinical trial formulation.
– Bioequivalence studies are for determination of the therapeutic equivalence between the pharmaceuticall equivalencegeneric drug product and a corresponding reference listed drug.
– Bioequivalence studies provide information on product quality and performance when there are changes in components,compositionand method of manufacture after approval of the drug product.
Limitation of Bioavailability and Bioequivalence
– A cross over design may be difficult for drugs with a long elimination half life.
Highly variable drugs may require a far greater number of subjects to meet the FDA bioequivalence characteristics.
– Certain characteristics in the biotransformation of drugs make it difficult to evaluate the bioequivalence of such drugs. For example, for drugs that are stereoisomer with a different rate of biotransformation and a different pharmacodynamic response, the measurement of individual isomers may be difficult for analytical reasons.
– Drugs that are administered by routes other than the oral route drugs/dosage forms that are intended for local effects have minimal systemic bioavailability. E.g. ophthalmic, dermal, intranasal and inhalation drug products.
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