The document discusses bioavailability and bioequivalence. It defines bioavailability as the rate and extent to which an active drug ingredient is absorbed and available at the site of action. Key factors that can affect bioavailability are discussed, including pharmaceutical factors like drug properties and dosage form characteristics, and patient factors like gastrointestinal pH and disease states. Methods for measuring bioavailability include pharmacokinetic methods like plasma level time studies and urinary excretion studies, and pharmacodynamic methods like measuring acute pharmacological response. The FDA guidelines for bioavailability and bioequivalence testing are also summarized.

1. BIOAVAILABILITY AND
BIOEQUIVALANCE
Presented by: Guided by:
E.Aslesha Dr.SATYABRATA BHANJA
256213886007 M.Pharm,Ph.D

2. CONTENTS
 Definitions
 Objectives of Bioavailability studies
 FDA guidelines for testing of Bioavailability
 Factors effecting bioavailability
 Methods of Bioavailability measurement
--Pharmacokinetic methods:
1. Plasma level time studies
2. Urinary excretion studies
--Pharmacodynamic methods:
1. Acute pharmacological response
2. Therapeutic response
 Bioavailability enhancement
2

3. CONTENTS
 Bioequivalence and Types
 Bioequivalance Protocol
 Bioequivalence experimental study designs
1. Completely randomized designs
2. Randomized block designs
3. Repeated measures, cross over, carry-over
designs
4. Latin square designs
 Statistical interpretation of bioequivalence data
1.Analysis of variance (ANOVA)
2.Confidence interval approach 3

4. BIOAVAILABILITY(BA):
 "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.“( FDA
Official Statement in 1977)
 "The rate at which, and the extent to which the drug
substance and/or its active metabolites reach(es) the
systemic circulation." ( International Consensus
Statement in 1991)
 Bioavailable fraction :The dosage which is available
at the site of absorption
F=bio available dose/administered dose
4

5. OBJECTIVES OF BIOAVAILABILITY
STUDIES:
It is important in the
 Primary stages of development of dosage form of new drug
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 on absorption.
 Comparison of drug in different dosage forms or same
dosage form of different manufacturer.
5

6. FDA GUIDELINES FOR TESTING OF
BIOAVAILABILITY
PART 320 BIOAVAILABILITY AND BIOEQUIVALENCE
REQUIREMENTS
 Subpart A--General Provisions
§ 320.1 - Definitions.
 Subpart B--Procedures for Determining the Bioavailability or
Bioequivalence of Drug Products
§ 320.21 - Requirements for submission of bioavailability and
bioequivalence data.
§ 320.22 - Criteria for waiver of evidence of in vivo bioavailability or
bioequivalence.
§ 320.23 - Basis for measuring in vivo bioavailability or
demonstrating bioequivalence.
§ 320.24 - Types of evidence to measure bioavailability or establish
bioequivalence.
§ 320.25 - Guidelines for the conduct of an in vivo bioavailability
study.
§ 320.26 - Guidelines on the design of a single-dose in vivo
bioavailability or bioequivalence study.
6

7. § 320.27 - Guidelines on the design of a multiple-dose in vivo
bioavailability study.
§ 320.28 - Correlation of bioavailability with an acute
pharmacological effect or clinical evidence.
§ 320.29 - Analytical methods for an in vivo bioavailability or
bioequivalence study.
§ 320.30 - Inquiries regarding bioavailability and
bioequivalence requirements and review of protocols by the Food
and Drug Administration.
§ 320.31 - Applicability of requirements regarding an
"Investigational New Drug Application."
§ 320.32 - Procedures for establishing or amending a
bioequivalence requirement.
§ 320.33 - Criteria and evidence to assess actual or potential
bioequivalence problems.
§ 320.34 - Requirements for batch testing and certification by
the Food and Drug Administration.
§ 320.35 - Requirements for in vitro testing of each batch.
§ 320.36 - Requirements for maintenance of records of
bioequivalence testing.
§ 320.38 - Retention of bioavailability samples.
§ 320.63 - Retention of bioequivalence samples. 7

8. ABSOLUTE BIOAVAILABILITY:
oThe systemic availability of a drug administered orally is
determined in comparison to its iv administration.
oCharacterization of a drug's absorption properties from the e.v.
site.
oIntravenous dose is selected as a standard due to its 100%
bioavailability
o If the drug is poorly water soluble, intramuscular dose can be
taken as standard.
o Its determination is used to characterize a drug’s inherent
absorption properties from extravascular site.
Absolute bioavailability (F):
o Dose (iv) x [AUC] (oral)
o F = ------------------------------- X 100
o Dose (oral) x [AUC] (iv) 8

9. RELATIVE BIOAVAILABILITY:
 The availability of a drug product as compared to another
dosage form or product of the same drug given in the same
dose.
 Characterization of absorption of a drug from its
formulation.
 Fr=AUCA
AUCB
The standard is a pure drug evaluated in a crossover study.
Its determination is used to characterize absorption of drug
from its formulation.
Both F AND Fr ARE EXPRESSED AS PERCENTAGE.
Relative bioavailability (Frel)
Dose (std) x [AUC] (sample)
Frel = ------------------------------- X 100
Dose (sample) x [AUC] (std) 9

10. FACTORS AFFECTING BIOAVAILABILITY :
BIOAVAILABILITY
Patient related
Factors
Pharmaceutic
Factors
Routes of
administration
10

11. A.PHARMACEUTICAL FACTORS:
1.PHYSICOCHEMICAL PROPERTIES OF THE DRUG.
1. Drug solubility& dissolution rate.
2. Particle size& effective surface area.
3. Polymorphism&Amorphism.
Amorphous >metastable > stable
4. Pseudopolymorphism(Hydrates / Solvates )
Anhydrates > hydrates e.g.Theophylline,Ampicillin
Organic solvates > non solvates e.g. fludrocortisone
5. Salt formof the drug.
Weakly acidic drugs – strong basic salt
e.g.barbiturates , sulfonamides.
Weakly basic drugs – strong acid salt
6. Lipophilicity of the drug .
7. pKa of the drug& pH .
8. Drug stability.
11

12. 2) DOSAGE FORM CHARACTERISTICS &
PHARMACEUTIC INGREDIENTS :
1. Disintegration time (tab/cap)
2. Dissolution time.
3. Manufacturing variables.
4. Pharmaceutic ingredients ( excipients / adjuvants )
5. Nature & type of dosage form.
 Solutions> Emulsions> Suspensions> Cap> Tab> Enteric
Coated Tab > Sustained Release
6. Product age & storage conditions.
12

13. B ) PATIENT RELATED FACTORS :
1. Age
2. Gastric emptying time .
3. Intestinal transit time .
4. Gastrointestinal pH .(HCL > Acetic > citric )
5. Disease States .
6. Blood flow through the gastrointestinal tract .
7. Gastrointestinal contents :
a) Other drugs .
b) Food .
c) Fluids
d) Other normal g.i. contents
8. Presystemic metabolism (First – Pass effect ) by :
a) Luminal enzymes .
b) Gut wall enzymes .
c) Bacterial enzymes .
d) Hepatic enzymes . 13

14. C ) ROUTES OF ADMINISTRATION :
Parenteral > Rectal > Oral > Topical
Route Bioavailability (%) Characteristics
Intravenous 100 (by definition) Most rapid onset
(IV)
Intramuscular 75 to ≤ 100 Large volumes often feasible; may be
(IM) painful
Subcutaneous 75 to ≤ 100 Smaller volumes than IM; may be
painful
(SC)
Oral (PO) 5 to < 100 Most convenient; first pass effects may
be significant
Rectal (PR) 30 to < 100 Less first-pass effects than oral
Inhalation 5 to < 100 Often very rapid onset
Transdermal 80 to ≤ 100 Usually very slow absorption; used for
lack of first-pass effects; prolonged
duration of action
14

15. MEASUREMENT OF BIOAVAILABILITY
Pharmacokinetic
(Indirect )
1.Plasma level
time studies
2.Urinary
excretion
studies
Pharmacodynamic
(Direct )
1. Acute
pharmacological
response
2. Therapeutic
response 15

16. 1. 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 16

17. 2. 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. 17

18. 3. In-vitro dissolution studies
 Closed compartment apparatus
 Open compartment apparatus
 Dialysis systems.
4. Clinical observations
 Well-controlled clinical trials
18

19. 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
 Plot concentration vs time
 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.
1. Tmax
2. Cmax
3. AUC
19

20. 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.
ravenous
oral
oral
AUC
F  
int
ravenous
Dose
Dose
AUC
int
STD
TEST
TEST
AUC
F  
rel Dose
STD
Dose
AUC

STD test
CSS
  20
rel Dose t
TEST std
MAX
MAX
Dose t
CSS
F


21. In multiple dose study:
21

22. CALCULATION OF AUC USING THE TRAPEZOIDAL
RULE
Area=1/2 (AB+CD)CM D C
For each trapezoid ,
[AUC] = C n-1 + Cn (tn – tn-1)
2 A M B
[AUC]=C1+C2 (t2-t1)
2
AUC total = AUC extrap + AUC 0-t
where AUC extrap = C last /k el
22

23. 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 nitrofurontoin.
23

24. Steps involved:
o collection of urine at regular intervals for 7 half lifes.
o Analysis of unchanged drug in collected sample.
o Determination of amount of drug at each interval and
cumulative as well.
o Criteria's must be followed
o At each sample collection total emptying of bladder is
necessary.
o Frequent sampling is essential in the beginning to
compute correct rate of absorption.
o The fraction excreted unchanged in urine must remain
constant.
24

25. 1. (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 C p.)
2. (tu)max: Time for maximum
excretion rate(its value
decreases as the absorption rate
increases.)
3. 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.)
25
Parameters considered important in Urinary
excretion studies

26. OTHER BIOLOGICAL FLUIDS
 Bioavailability can also be determined using other
biological fluids like
1. Plasma
2. Urine
3. Saliva
4. CSF
5. Bile
 Examples : Theophylline → salivary fluid,
Cephalosporin → CSF and bile fluids,
etc.
26

27. PHARMACODYNAMIC METHODS
1. 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.
27

28. 2. 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.
28

29. 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. Dissolution
studies are often performed on several test formulations of the same
drug. The test formulation that demonstrates the most rapid rate of
drug dissolution in vitro will generally have the most rapid rate of
drug bioavailability in vivo.
 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.
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.
29

30. 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. 30

31. CLINICAL OBSERVATIONS
 Well-controlled clinical trials in humans establish the safety
and effectiveness of drug products and may be used to
determine bioavailability.
 However, the clinical trials approach is the least accurate,
least sensitive, and least reproducible of the general
approaches for determining in-vivo bioavailability.
 The FDA considers this approach only when analytical
methods and pharmacodynamic methods are not available to
permit use of one of the approaches described above.
 Comparative clinical studies have been used to establish
bioequivalence for topical antifungal drug products (eg,
ketoconazole) and for topical acne preparations.
 For dosage forms intended to deliver the active moiety to the
bloodstream for systemic distribution, this approach may be
considered acceptable only when analytical methods cannot
be developed to permit use of one of the other approaches.
31

32. METHODS FOR ENHANCEMENT OF
BIOAVAILABILITY
Pharmaceutic
Approach
Pharmacokinetic
Approach :
Biologic Approach
32

33. 33

34. 1) PHYSICAL MODIFICATIONS
Particle size reduction: Micronization
Nanosuspension
Sonocrystalisation
Supercritical fluid process
Modification of the crystal habit: Polymorphs
Pseudopolymorphs
Drug dispersion in carriers:Eutectic mixtures
Solid dispersions
Solid solutions
Complexation : Use of complexing agents
Solubilization by surfactants:Microemulsions
Self microemulsifying drug delivery systems
34

35. 2) CHEMICAL MODIFICATIONS
Prodrug
Salt formation
3) OTHER METHODS
pH Adjustment
Cocrystalisation
Cosolvency
Hydrotrophy
Solvent deposition
Selective adsorption on insoluble carrier
Functional polymer technology
Porous microparticle technology
Nanotechnology approaches
35

36. Micronization .
Methods: - spray drying
- air attrition methods.
E.g. : Aspirin
Griseofulvin
Steroidal compounds
Sulfa drugs
Use of surfactants :
1. ‘Surfactants promote wetting & penetration of fluids into solid
drug particles.’
2. Better membrane contact.
3. Enhanced membrane permeability.
-
- Surfactants are used below CMC(critical micelle concentration)
- E.g. Spironolactone
36

37.  Alteration of pH of drug microenvironment:
i. In situ salt formation
ii. Buffered formulation e.g. Aspirin
 Solute-solvent complexation:
- Solvates of drugs with organic solvents ( pseudo
polymorphs) have higher aqueous solubility than their
respective hydrates or original drug .
E.g.1:2 Griseofulvin – Benzene solvate.
 Selective adsorption on insoluble carriers :
- A highly active adsorbent like inorganic clay e.g.
Bentonite, enhance dissolution rate by maintaining
concentration gradient at its maximum.
E.g. Griseofulvin
Indomethacin
Prednisone.
37

38.  Use of salt forms:
E.g. Alkali metal salts of acidic drugs like penicillins
Strong Acid salt of basic drugs like atropine.
 Solid solution( Molecular dispersion/mixed crystals )
- It is a binary system comprising of solid solute
molecularly dispersed in a solid solvent.
- Systems prepared by Fusion method : Melts
- e.g. Griseofulvin-succinic acid
 Solid dispersions (Co evaporators/co precipitates) :
- Both the solute and solid carrier solvent dissolved in
common volatile liquid e.g. Alcohol
- The drug is precipitated out in an amorphous form
as compared to crystalline forms in solid
solutions/eutectics.
E.g. Amorphous sulfathiazole in crystalline urea.
38

39.  Eutectic mixture :
-It is intimately blended physical mixture of two crystalline
components.
- Paracetamol -urea
- Griseofulvin – urea
- Griseofulvin-succinic acid
 Disadvantage :
Not useful in :
a) Drugs which fail to crystallize from mixed melt.
b) Thermo labile drugs
c) Carrier like succinic acid decompose at their
melting point.
39

40.  Use of Metastable Polymorphs :
- more stable than stable polymorph
e.g. Chloramphenicol palmitate .
 Molecular encapsulation with Cyclodextrins :
-β and γ Cyclodextrins have ability to form inclusion
complexes with hydrophobic drug having poor aqueous
solubility.
- These molecules have inside hydrophobic cavity
to accommodate lipophilic drug , outside is hydrophilic.
E.g. Thiazide diuretics
Barbiturates
Benzodiazepines
NSAIDS.
40

41. 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. 41

42. 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
42

43. 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.
FDA considers drug products to be pharmaceutical
equivalents if they meet these three criteria:
 1. they contain the same active ingredient(s)
 2. they are of the same dosage form and route of
administration
 3. they are identical in strength or concentration
43

44. 3.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.
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. 44

45. THERAPEUTIC EQUIVALENCE:
 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
 Drugs are considered to be therapeutic equivalents and thus
suitable for substitution (generic equivalents) if, among other
factors, they are both pharmaceutical equivalents and
bioequivalent.
 It does not encompass a comparison of different therapeutic
agent used in the same condition.
45

46.  The FDA considers drug products to be therapeutically
equivalent if they meet the following criteria:
1. Approved as safe and effective.
2. Pharmaceutically equivalent
3. Bioequivalent
4. Adequately labeled
5. Manufactured in compliance with cGMP.
 Although, they may differ in characteristics like, Shape,
release mechanism, excipients, packaging, minor aspects of
labeling (like the presence of specific pharmacokinetic
information), expiration date/ time, etc.
 The FDA believes that products classified as therapeutically
equivalent can be substituted with the same expectation that
the substituted product will produce the same clinical effect
and safety profile as the prescribed product.
46

47. DIFFERENT METHODS OF STUDYING
BIOEQUIVALENCE:
In vivo bioequivalence studies: when needed,
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. 47

48. 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
conditions.
1.Drug product only differ in strength of drug provided,
- Their pharmacokinetics are linear, Drug & excipient ratio is
same,
- both products manufactured by same manuf. at same site.
- BA/BE study done for original product, disso. rate 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, inhalation as
gas or vapour.
48

49. BIOEQUIVALENCE EXPERIMENTAL STUDY
DESIGNS
Completely
randomized
designs
Randomized
block
designs
Repeated
measures,
cross over
designs
Latin square
designs
49

50. 1.COMPLETELY RANDOMIZED DESIGNS:
 All treatments are randomly allocated among all experimental subjects.
e.g. If there are 20 subjects, number from 1 to 20. 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.
50

51. 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.
51

52. 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.
TYPES
 Replicated designs-Two-formulation, four-period, two-sequence
 Non-replicated designs-Two-formulation, two-period, two-sequence,
crossover design
52

53. 4.LATIN SQUARE DESIGNS:
 All other above designs are continuous trial. However in
 Latin square design each subject receives each treatment during
the experiment.
 It is a two factor design ( Rows=Subjects and
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 pilot studies.
Possible to focus on formulation variables.
Disadvantages: Less degree of freedom, randomization is complex,
long time study, more formulations more complex study, subject
dropout rates are high.
53

54. STATISTICAL INTERPRETATION OF
BIOEQUIVALENCE DATA
 After the data has been collected , statistical methods must be applied
to determine
 The level of significance or any observed difference in rate and /or
extent of absorption to establish bioequivalence between two or more
drug products.
1. Analysis of varience ( ANOVA): It is statistical procedure use to
test data for differences within and between treatment and control
groups. A statistical difference between the pharmacokinetic
parameters obtained from two or more drug products is considered
statistically significant if there is probability of less than 1 in 20 or
0.05 (p≤0.05) . The value of p indicates the level of statistical
significance.
2. Confidence interval approach: It is also called as two one-sided
procedure and used to demonstrate if bioavailability of test product
is too low or too high in comparison to reference product. 90%
confidence interval of two drug products must be within ±20% for
bioavailability parameters such as AUC or Cmax. ( i.e. between 80
to 102 %). For log transformed data 90% confidence interval is set at
80-125%.
54

55. 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 55

56. 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, willey publications, 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.
 Indian Journal of Pharmaceutical sciences.
 Internet sources.
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