*2.7.1 Selection criteria for subjects*

The studies should be performed on healthy adult volunteers with the aim to minimize variability between the study drugs. Subjects may be males or females; however, the choice of gender should be consistent with usage and safety criteria of the drug. To minimize intra and intersubject variation, the study design should be standardized as much as possible and acceptable.

#### *2.7.2 Fasting and fed state considerations*

Generally, a single dose study should be conducted after an overnight fast (at least 10 hours) and subsequent fasting of 4 hours after administration dosing. For multiple dose studies, 2 hours of fasting before and after the dose are acceptable. Estimation of Cmax and Tmax for the modified release products or drug is given with food in such case fed state studies also been carried out in addition to the normal fasting state bioavailability studies [22]. During fed state studies, the consumption of a high fat breakfast of 950–1000 KCals is required before dosing. The food intake containing at least 50% of these calories must come from fat, 15–20% calories from proteins, and the remaining from carbohydrates. A single standard diet should be followed taking into consideration of all the Indian subcontinent people. The high fat breakfast must be consumed approximately 15 minutes before dosing in fed state condition.

#### **2.8 Study conditions**

Study conditions such as study environment, diet, fluid intake, post dosing postures, exercise, sampling schedules, etc. are monitored during studies. These conditions are stated in the protocol, and at the end of the study, these should be complied, to assure that all variability factors involved in the study to minimize the products to be tested. Least 48 hours before commencement, the study subjects abstain from smoking, drinking alcohol, xanthine containing foods, coffee, tea and beverages, and fruit juices.

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their metabolite.

bioavailability [23].

*Bioavailability and Bioequivalence Studies DOI: http://dx.doi.org/10.5772/intechopen.85145*

Steady state study is considered in the following conditions:

fluctuation in plasma drug concentration at steady state.

6.For drugs that exhibit nonlinear, that is, dose or time dependent

9.For enteric coated preparations where the coating is innovative.

7.For combination products where the ratio of plasma concentration of the

Ideally, the biological samples collected as per the sampling procedure have to be analyzed immediately after the study but most of the times the samples are stored for several days before subjected to analysis. During storage, the drug may undergo a chemical degradation, adsorption on the walls of the container, etc., so storage of plasma samples is an important aspect of bioavailability studies. The analytical method used for the estimation of the active ingredient responsible for the therapeutic efficacy must be selective and sensitive. Drugs, that undergo the first pass effect exhibit different unchanged drug/metabolite ratio depending on the rate of absorption. In the analysis of blood and urine, the major problem is to extract quantitatively and then separate the intact drug from its major metabolites or even to separate a mixture of two or more drugs from

Pharmacokinetic methods are used for the assessment of bioavailability of drug products that exists as a linear relation between the drug level in the biological fluid and therapeutic response. Therefore, these methods are also known indirect methods. Because therapeutically active drug can be accurately measured in biological fluids, plasma and urine data give the most objective information on

5.Where the drug is likely to accumulate in the body.

8.For those drug which induce their own metabolism

2.Blood concentrations after a single dose cannot be achieved for a sufficient

3.For drugs, which are toxic or have adverse effects that are ethically should not be administered to patients but they are a necessary part of therapy

4.For modified release products or sustained release products which assess the

1.The drug has a long terminal elimination half-life

**2.9 Steady state studies**

time.

(cytotoxics).

pharmacokinetics.

individual drugs is important.

**2.10 Analysis of biological samples**

**2.11 Methods of assessment of bioavailability**
