1. The document discusses bioavailability and bioequivalence studies, which are important for determining the rate and extent of drug absorption from different formulations. 2. Key aspects of bioavailability studies include absolute and relative bioavailability, factors affecting bioavailability, and methods of measuring bioavailability through pharmacokinetic and pharmacodynamic approaches. 3. Bioequivalence studies aim to show that two products have identical plasma concentration time profiles and are therefore interchangeable. Different study designs like randomized and crossover designs are used to evaluate bioequivalence.

1. RATNAM INSTITUTE OF PHARMACY
BIOAVAILABILITY (BA)
AND
BIOEQUIVALANCE (BE) STUDIES
By,
MR. CH.PRAVEEN KUMAR M.Pharm., (Ph.D)
ASSOCIATE PROFESSOR
DEPARTMENT OF PHARMACEUTICS

2. BA & BE Studies
BIOAVAILABILITY:
"Bioavailability means the rate and the extent to which the active drug
ingredient of therapeutic moiety is absorbed from a drug product and
becomes available at the site of action.
"The rate at which, and the extent to which the drug substance and/or its
active metabolites reach(es) the systemic circulation."
Bioavailable fraction: The dosage which is available at the site of
absorption. F=bio available dose/administered dose
2

3. 3
OBJECTIVES OF BIOAVAILABILITY STUDIES:
It is important in the
 Primary stages of development of dosage form of newdrug entity to find
its therapeutic utility.
 Determination of influence of excipients on absorption.
 Development of new formulations of existing drugs.
 Control of quality of drug products and influence of processing factors,
storage and stability onabsorption.
 Comparison of drug in different dosage forms or same dosage form
of differentmanufacturer.
BA & BE Studies

4. 4
ABSOLUTE BIOAVAILABILITY:
The systemic availability of a drug administered orally is determined in
comparison to its iv administration.
Characterization of a drug's absorption properties from thee.v. site.
Intravenous dose is selected as a standard due to its100% bioavailability
If the drug is poorly water soluble, intramuscular dose canbe taken as
standard.
Its determination is used to characterize a drug’s inherent absorption
properties from extravascularsite.
Absolute bioavailability (F):
Dose (iv) x [AUC] (oral)
F = ------------------------------- X 100
Dose (oral) x [AUC] (iv)
BA & BE Studies
Absolute bioavailability (F):

5. 5
RELATIVE BIOAVAILABILITY:
 The availability of a drug product as compared to another dosage form or
product of the same drug given in thesame dose.
 Characterization of absorption of a drug fromits formulation.
The standard is a pure drug evaluated in a crossoverstudy. Its determination
is used to characterize absorption ofdrug from its formulation.
Both F and Fr are expressed as percentage
Relative bioavailability (Frel)
BA & BE Studies
Relative bioavailability (Fr):
Dose (std) x [AUC] (test)
Fr = ------------------------------- X 100
Dose (test) x [AUC] (std)

6. 6
FACTORS AFFECTING BIOAVAILABILITY :
BIOAVAILABILITY
BA & BE Studies

7. 7
MEASUREMENT OF BIOAVAILABILITY
Pharmacokinetic
(Indirect )
Plasma level
time studies
Urinary
excretion
studies
Pharmacodynamic
(Direct )
Acute
pharmacological
response
Therapeutic
response
BA & BE Studies

8. 8
Pharmacokinetic methods
 These are indirect methods
 Assumption that –pharmacokinetic profile reflects the therapeutic
effectiveness of a drug.
Advantages: - Accurate, Reliable,Reproducible
A. Plasma / blood level time profile.
 Time for peak plasma (blood) concentration (t max)
 Peak plasma drug concentration (C max)
 Area under the plasma drug concentration–time curve (AUC)
B. Urinary excretion studies.
 Cumulative amount of drug excreted in the urine (D u)
 Rate of drug excretion in the urine (dD u/dt)Time for maximum urinary
excretion (t)
C. Other biological fluids
BA & BE Studies

9. 9
Pharmacodynamic methods
Involves direct measurement.
(measurement of pharmacologic or therapeutic end point)
Disadvantages:- High variability- Difficult to measure- Limited choices- Less
reliable- More subjective- Drug response influenced by several physiological
& environmental factors
 Maximum pharmacodynamic effect (E max)
 Time for maximum pharmacodynamic effect
 Area under the pharmacodynamic effect–time curve
 Onset time for pharmacodynamic effect
They involve determination of bioavailability from:
A. Acute pharmacological response.
B. Therapeutic response.
BA & BE Studies

10. 10
In-vitro dissolution studies
 Closed compartment apparatus
 Open compartment apparatus
 Dialysis systems.
Clinical observations
 Well-controlled clinical trials
BA & BE Studies

11. 11
PLASMA LEVEL TIME STUDIES
 This is the most reliable method of choice comparison to urine data
method
 Single dose: serial blood samples collection – 2-3 half lifes
Plasma concentration vs time Curve
 For I.V. Sampling started within 5 min and subsequent samples at 15
min intervals
 For oral dose at least 3 points taken on absorption curve (ascending
part)
 Parameters considered important in plasma level time studies for
determining bioavailability.
a) Tmax
b) Cmax
c) AUC
BA & BE Studies

12. 1. Cmax : It is peak plasma concentration. It increases with dose as
well as increase in rate of absorption.
2. Tmax: The peak time at which Cmax atended.
3. AUC: Area under curve explains about amount of drug.
relF
12
BA & BE Studies
(Css, max)test .Dose std . Ƭtest
=
(Css, max)std .Dose test. Ƭstd
F=
(AUC)oral .Dose iv
(AUC)iv .Dose oral
Fr=
(AUC)test. Dose std
(AUC)std .Dose test
F
=
(AUC)test .Dose std . Ƭtest
(AUC)std .Dose test. Ƭstdrel

13. 13
In multiple dose
study:
BA & BE Studies
Multiple dosing up to steady state

14. 14
URINARY EXCRETION STUDIES
 This method is based on the principle that the urinary excretion of
unchanged drug is directly proportional to the plasma concentration of
drug.
 It can be performed if
At least 20% of administered dose is excreted unchanged in urine.
 The study is useful for
Drugs that extensively excreted unchanged in urine eg. Thiazide diuetics
Drugs that have urine as site of action eg. Urinary antiseptics like
nitrofurantoin and hexamine
BA & BE Studies

15. 15
Steps involved: Collection of urine at regular intervals for 7 half lifes.
 Analysis of unchanged drug in collected sample.
 Determination of amount of drug at each interval and cumulative as
well.
Criteria's must be followed
 At each sample collection total emptying of bladder is necessary.
 Frequent sampling is essential in the beginning to compute correct
rate of absorption.
 The fraction excreted unchanged in urine must remain constant.
BA & BE Studies
URINARY EXCRETION STUDIES

16. (dXu/dt)max:
Maximun urinary excretion rate(Because most drugs are eliminated by a
first- order rate process, the rate of drug excretion is dependent on the
first-order elimination rate constant k and the concentration of drug in the
plasma Cp.)
(tu)max:
Time for maximum excretion rate(its value decreases as the absorption rate
increases.)
Xu∞:
Cumulative amount of drug excreted in the urine.(It is related to the AUC of
plasma level data and increases as the extent of absorption increases.)
16
Important parameters in urinary excretion
studies
BA & BE Studies

17. 17
OTHER BIOLOGICAL FLUIDSBioavailability can also be determined using other biological fluids like
 Plasma
 Urine
 Saliva
 CSF
 Bile
Examples : Theophylline → salivary fluid,
Cephalosporin → CSF and bile fluids, etc.
BA & BE Studies

18. 18
PHARMACODYNAMIC METHODS
Acute pharmacological response:
When bioavailability measurement by pharmacokinetic methods is difficult,
inaccurate or non reproducible this method is used. Such as ECG, EEG,
Pupil diameter etc.
It can be determined by dose response graphs.
Responses measure for at least 3 half lifes.
Disadvantages:
- Pharmacological response is variable and accurate correlation drug
and formulation is difficult.
-Observed response may be due to active metabolite.
BA & BE Studies

19. 19
Therapeutic response:
This method is based on observing clinical response in patients.
Drawbacks:
- Quantitation of observed response is too improper.
-The physiological status of subject assumed that does not change
significantly over duration of study.
-If multiple dose protocols are not involved. Patient
receive only single dose for few days or a week
-The patient s receiving more than one drug treatment may be
compromised due to drug-drug interaction.
BA & BE Studies

20. 20
IN VITRO DISSOLUTION STUDY
 Drug dissolution studies may under certain conditions give an indication of drug
bioavailability. Ideally, the in-vitro drug dissolution rate should correlate with in-vivo
drug bioavailability.
 The best available tool which can at least quantitatively assure about the biological
availability of a drug from its formulation.
 The aim of these tests are to predict in vivo behavior to such an extent that in
vivo bioavailability test need not be performed.
BA & BE Studies

21. 21
A. Closed compartment apparatus : Non sink condition
B. Open compartment apparatus : perfect sink condition
C. Dialysis system - This method is useful for very poorly aqueous soluble drugs for
which maintenance of sink condition would require large volume of dissolution
fluid.
BA & BE Studies
Apparatus Name Formulation tested
Apparatus-1 Rotating basket Tablets
Apparatus-2 Rotating paddle Tablets, Capsules, Suspensions
Apparatus-3 Reciprocating cylinder Tablets, CR formulations
Apparatus-4 Flow-through cell Implants & Microparticulates
Apparatus-5 Paddle over disc Transdermals
Apparatus-6 Cylinder type Transdermals
Apparatus-7 Reciprocating Disc CR and Transdermal formulations

22. 22
BA & BE Studies Representation of official USP apparatus

23. 23
BA & BE Studies
Dissolution acceptance criteria

24. 24
IN VITRO- IN VIVO CORRELATION (IVIVC):
It is defined as the predictive mathematical model that describes the relationship
between in vitro property ( rate & extent of dissolution) and in vivo response
(plasma drug concentration).
The main objective of developing and evaluating IVIVC is to use dissolution
test to serve as alternate for in vivo study in human beings.
IVIVC Levels:
Level A: The highest category of correlation. It represents point to point
correlation between in vitro dissolution and in vivo rate of absorption.
Advantages: serves as alternate for in vivo study, change in manf. Procedure or
formula can be justified without human studies.
Level B:
The mean in vitro dissolution time is compare with mean in vivo residence time. It is not
point to point correlation . Data can be used for quality control standards.
Level C: It is single point correlation. e.g. t50%, Tmax, Cmax. This level is only useful as
guide for formulation development or quality control.
.
BA & BE Studies

25. 25
BIOEQUIVALENCE
A relative term which denotes that the drug substance in two or more
dosage forms, reaches the systemic circulation at the same relative rate
and to the same relative extent i.e., their plasma concentration time profiles
will be identical without significant statistical difference.
It’s commonly observed that there are several formulations of the same
drug, in the same dose, in similar dosage form and meant to be given by
the same route, in order to ensure clinical performance of such drug
products, bioequivalence studies should be performed.
BA & BE Studies

26. 26
BIOEQUIVALENCE STUDY:
 Surrogate for therapeutic equivalence to enable “switchability”
 An appropriate measure for the quality control of the product in vivo
“Bioequivalence Studies” Conducted
 When a generic formulation is tested against an innovator brand
 Where a proposed dosage form is different from that used in a pivotal
clinical trial
 When significant changes are made in the manufacture of the
marketed formulation
BA & BE Studies

27. 27
TYPES OF EQUIVALENCE:
1.Chemical Equivalence:
When 2 or more drug products contain the same labeled chemical
substance as an active ingredient in the same amount.
2.Pharmaceutical Equivalence:
When two or more drug products are identical in strength, quality, purity,
content uniformity, disintegration and dissolution characteristics; they may
however differ in excipients.
3. Bioequivalance:
A relative term which denotes that the drug substance in two or more
dosage forms, reaches the systemic circulation at the same relative rate
and to the same relative extent i.e., their plasma concentration time
profiles will be identical without significant statistical difference.
BA & BE Studies

28. 28
4.Clinical Equivalence:
When the same drug from 2 or more dosage forms gives identical in vivo effects
as measured by pharmacological response or by control over a symptom or a
disease.
5.Therapeutic Equivalence:
When two or more drug products that contain the same therapeutically active
ingredient, elicit identical pharmacologic response and can control the
disease to the same extent.
BA & BE Studies

29. 29
6. Therapeutic Equivalence:
Drug products are considered to be therapeutic equivalents only if
they are pharmaceutical equivalents and if they can be expected to
have the same clinical effect and safety profile when administered to
patients under the conditions specified in the labeling.
Therapeutic Equivalence = Bioequivalence +Pharmaceutical Equivalence
BA & BE Studies

30. 30
DIFFERENT METHODS OF STUDYING
BIOEQUIVALENCE:
In vivo bioequivalence studies: Criteria,
1. Oral immediate release product with systemic action
-Indicated for serious conditions requiring assured
response.
-Narrow therapeutic window.
- complicated pharmacokinetic, absorption <70%, presystemic
elimination>70%, nonlinear kinetics.
2. Non-oral immediate release products
3. Modified release products with systemic action.
BA & BE Studies

31. 31
In vitro bioequivalence studies: If none of the above criteria
is applicable comparative in vitro dissolution studies can be
done.
Biowaivers: In vivo studies can be exempted under certain
In vitro bioequivalence studies: Criteria,
1.Drug product only differ in strength of drugprovided,
- Their pharmacokinetics are linear, Drug & excipient ratiois same,
- both products manufactured by same manuf. at samesite.
- BA/BE study done for original product, dissolution rate is same
under same conditions.
2. The method of production slightly modified in a way that not affect
bioavailability
3. The drug product meet following requirements: The product is in
solubilised form,no excipients affecting absorption, Topical use, Oral but
not absorbed, inhalationas gas or vapour.
BA & BE Studies

32. 32
BIOEQUIVALENCE EXPERIMENTAL STUDY DESIGNS
Completely
randomized
designs
Randomized
block
designs
Repeated
measures,
cross over
designs
Latin square
designs
BA & BE Studies

33. 33
1.COMPLETELY RANDOMIZED DESIGNS:
All treatments are randomly allocated among all experimental subjects.
e.g. If there are 8 subjects, number from 1 to 8. randomly select non repeating
numbers among these labels for the first treatment. And then repeat for all other
treatments .
Advantages:
Easy to construct, can accommodate any number of treatment and subjects,
Simple to analyze.
Disadvantages:
 Although can be used for number of treatments, but suited for few treatments.
 All subjects must be homogenous or random error will occur.
BA & BE Studies

34. 34
2.RANDOMIZED BLOCK DESIGNS:
First subjects are sorted in homogenous groups, called blocks and then treatments
are assigned at random within blocks.
Advantages:
 Systematic grouping gives more precise results.
 No need o equal sample size, any number of treatments can be followed,
statistical analysis is simple, block can be dropped , variability can be
introduced.
Disadvantages:
Missing observations in a block require more complex analysis.
Degree f freedom is less.
BA & BE Studies

35. 35
3.REPEATED MEASURES, CROSS OVER
DESIGNS:
It is a kind of randomized block design where same subject serves as a block.
 Same subject utilized repeatedly so called as repeated measure
design.
 The administration of two or more treatments one after the other in a specified
or random order to the same group of patients is called cross-over designs.
Advantages:
 Good precision, Economic, can be performed with few subjects, useful in
observing effects of treatment over time in the same subject.
Disadvantages:
 Order effect due to position in treatment order.
 Cary over effect due to preceding treatment.
 Wash out period necessary – 10 elimination half lifes.
BA & BE Studies

36. 36
4.LATIN SQUARE DESIGNS:
 All other above designs are continuous trial. Howeverin Latin square design each
subject receives each treatmentduring the experiment.
 It is a two factor design (Rows=Subjectsand Columns=Treatments ).
 Carry –over effects are balanced.
Advantages: minimize variability of plasma profiles and carry-over effects. Small
scale experiments can be carried out for pilotstudies. Possible to focus on
formulation variables.
Disadvantages: Less degree of freedom, randomization iscomplex, long time
study, more formulations more complex study, subject dropout rates are high.
BA & BE Studies

37. 37
BA & BE Studies
BIOAVAILABILITY STUDY PROTOCOL

38. 38
LIMITATIONS OF BA/BE STUDIES :
 Difficult for drugs with a long elimination half life.
 Highly variable drugs may require a far greater number of subjects
 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.
 Biotransformation of drugs make it difficult to evaluate the
bioequivalence of such drugs e.g. stereoisomerism
BA & BE Studies

39. 39
REFERENCES
 Biopharmaceutics and pharmacokinetics – A Treatise , D. M. Brahmankar, Sunil
B.Jaiswal. Vallabh prakashan IInd edition, pp- 315-366.
 Basics of Pharmaokinetics, Leon Shargel, fifth edition, willeypu blications, pp- 453-
490.
 Shargel L., Andrew B.C., Fourth edition “Physiologic factors related to drug
absorption” Applied Biopharmaceutics and Pharmacokinetics, Prentice Hall
International, INC., Stanford 1999. Page No. 99-128.
 Internet sources.
BA & BE Studies

40. 40
Thank you