Estimation of Bioavailability

**65**

**Chapter 4**

**Abstract**

will be established.

**1. Introduction**

cross over study, area under curve

Studies

*Divvela Hema Nagadurga*

Bioavailability and Bioequivalence

*In vivo* bioavailability studies are performed for new drug to establish essential pharmacokinetic parameters including rate of absorption, extent of absorption, rates of excretion and metabolism and elimination half-life after a single and multiple dose administration. These essential pharmacokinetic parameters are useful in establishing dosage regimens. Bioequivalence used to assess the expected *in vivo* biological equivalence of two proprietary preparations of drug products. If two drugs are bioequivalent, it means that they are expected to be same for all intents and purposes. In determining bioequivalence between two drugs such as a reference drug or brand and potential to be test drug or marketed generic drug. Pharmacokinetic studies are conducted whereby each of the drugs is administered in a cross over study to healthy volunteer's subjects. Plasma is obtained at regular intervals and assayed for parent drug or metabolite concentration to compare the two drugs. For comparison purpose of two formulations, the plasma concentration data are used to assess key pharmacokinetic parameters. If 90% confidence interval for the ratio of the geometric least square means of peak plasma concentration, area under curve of test and reference drugs are within 80–125%, then bioequivalence

**Keywords:** bioavailability, bioequivalence studies, pharmacokinetic parameters,

Bioavailability is defined as relative amount of drug from an administered dosage which enters the systemic circulation and the rate at which the drug appears in the systemic circulation. The bioavailability studies are done by measuring the concentration of the drug in the plasma or blood after administration of drug following systemic protocol of studies and documented over time. The systemic protocol is helpful for clinical trials in the early drug development, and the data obtained are used in subsequent bioequivalence studies. Bioequivalence studies were carried out to distinguish between two pharmaceutical products containing the same active substance. One drug formulated into two different formulations if they show to be therapeutically equivalent to one another in order to be considered interchangeable. Pharmacokinetics of drug deals with the change in drug concentration in plasma and/or its metabolites in the human or animal body with respect to time following administration of the pharmaceutical product. Bioequivalence studies are used to assess the expected *in vivo* biological equivalence of two proprietary preparations of a drug. If two pharmaceutical products are said to be bioequivalent, then they
