Bioavailability is rate and extent of drug absorption The relative amount of administered dose of drug that reaches to its site of action from the site and dose of administration in an unchanged form. The rate at which this phenomenon occurs is known as BIOAVAILABILITY Here site of action refers to plasma or systemic circulation and unchanged form refers to therapeutically active form Bioavailabile Dose:- Fraction of administered dose of drug which reaches to site of action is bioavailable dose.

1. Seminaron
“BIOAVAILABILITY
AND BIOEQUIVALENCE”
By
Dr. Priyanka Patil
MD(Ayu)
Dept of RS & BK

2. INTRODUCTION:
 In any medical field oral route of drug administration is
considered as a major route and has been practicing widely. A
basic assumption is that a when a drug is administered orally
the dosage form of that releases and absorbs completely and
promptly. But is not so. Many of the drugs are not absorbed to
the desired extent due to the factors related to drug, dosage
form, physiological factors etc. In such cases, concepts of
Bioavailability and Bioequivalence become important
consideration in assuring the optimal and consistent drug
absorption.

3. What Is BIOAVAILABILITY?
 Bioavailability is rate and extent of drug absorption.
 The relative amount of administered dose of drug that reaches
to its site of action from the site and dose of administration in
an unchanged form. The rate at which this phenomenon
occurs is known as BIOAVAILABILITY.
 Here site of action refers to plasma or systemic circulation and
unchanged form refers to therapeutically active form.
 Bioavailabile Dose:- Fraction of administered dose of drug
which reaches to site of action is bioavailable dose.

4. Why do we care for BIOAVAILABILITY?
 True dose of drug is not the drug swallowed but it is the
drug available to exert its effect.
 Bioavailability does not only depend on the dose
administered, but also on the fraction of that is absorbed
and escapes any first pass metabolism and elimination.
Therefore for 100% bioavailability of a drug, entire drug
must move from dosage form to the systemic circulation.

5. Factors Influencing The Bioavailability:
 Food eaten by the patient
 Age of the patient
 Affect of the disease state
 Dosage form
 Instability of the drug in G.I fluids
 Physiochemical characters of the drug
 Method of manufacture
 Size of the dose
 Frequency of the dose
 Route of administration
 Environmental conditions in G.I.T

6. Food and Bioavailability
 Food may increase or decrease or may not affect on
bioavailability.
 It may increase G.I motility and hence increase solubility.
 Complication of a drug (binding of a drug molecule with
food).
 Alter gastric pH and stimulate gastric secretion.
 Food may tend to vomiting which decrease bioavailability.

7. Dosage form and Bioavailability
 In general drugs must be in solution of in G.I fluids before it
gets absorbed.
 Type of dosage form and its manufacture methods can
influence bioavailability thus weather drug is administered in
the form of solution/suspension/solid dosage form can affect
bio availability.
 The stage between administration and absorption are directly
depend on dosage form.
 Hence bioavailability of drug dosage form will be in
following order
Aqueous solution> aqueous suspension > solid dosage form
 Excipients like lubricants, coloring agents, flavoring agents
etc. can also influence bioavailability.

8. Routeof Drug Administrationand Bioavailability
 Rapid and maximum BA of a drug is affected markedly by
route of administration.
 Difference in plasma conc. Of a drug depends on number and
nature of membrane across its must transported before reaches
to plasma.
 Drug administered through I.V is not subjected to any
transport process so that maximum BA is attained immediately
with entire dose

9. Route of Drug Administration And
Bioavailability:
Absorption through I.M, S.C route is less bioavailable
than I.V route since they involve transport across
membrane barrier.
I.M route gives more rapid bioavailability than S.C
route because skeletal muscles have a better blood
supply than S.C tissue.
These routes also provide rapid absorption with little
lose of drug.
It should be kept in mind that the nature of specific
drug may alter the absorption through these routes
because of local binding of the drug.

10. Rectal Route and Bioavailability:
 Only 50% of the drug is absorbed through
rectal route because the drug will undergo first
pass metabolism through liver.
 Trough this route, rate of absorption of the
drug is very rapid because of high vascularity.

11. Oral drug administration and B.A.
 Stages involved:-
 Disintegration:- solid dosage form of the drug break into
individual particles of active form
 Dissolution:- Disintegrated drug will dissolved into aqueous
G.I. fluid
 Absorption:- dissolved drug then absorbed by the G.I.T.
 Bioavailability:- absorbed drug then reaches to systemic
circulation.

12. Effects of Oral drug administration on B.A.
BA may be incomplete through oral route because of,
 Stomach contents
 Environmental conditions in G.I.T.
 Incomplete absorption of drug by the gut
 First pass metabolism in gut wall/liver
 Rapid emptying of intestine
 Instability of drug in G.I fluids.
 Solubility of drug in G.I fluids
 Emesis because of G.I mucosa.

13. Criteria for an Ideal Oral Drug
Ideal oral drug is the one which must be 100% bioavailable i.e.
the entire drug must move from dosage form to systemic
circulation. Hence the drug must be,
 Completely released from dosage form.
 Fully dissolved in G.I fluids.
 Stable in solution in G.I. fluids
 Pass through gastro intestinal barriers into mesenteric
circulation without metabolism.
 Pass through liver unchanged into systemic circulation.

14. Why BA vary in oral drug administration?
 Disintegration:-
 Nature of binders, diluents, lubricants etc
 Manufacturing process (eg:-force used to compress the
tablet)
 Dissolution:-
 Solubility of the drug
 Particle size
 Crystal form etc.
 Absorption
 Poorly soluble and slowly absorbed drugs show
difference in bioavailability.

15. Significance of Variance in BA
 Variability in BA can cause plasma concentration of
the drug too high & hence can cause side effects OR
too low & therefore the drug may be inactive.
 BA variance is more significance for the drugs with
low safety margin or where drug dosage needs precise
control.

16. Why assessment of BA is necessary?
 Measurement of BA gives net results of the effect of the
release of drug into solution in the physiological fluid at the
site of absorption.
 Stability of the drug in the physiological fluid can be
determined.
 Permeability and pre systemic metabolism and rate & extent of
drug absorption is known
 It gives information on other pharmacokinetic parameters such
as distribution, metabolism, and elimination of the drug

17. (contd….)
 Maximum safe concentration of the drug in plasma can be
assumed above which side effects are expected.
 The time required to achieve minimum effective
concentration, peak concentration, duration of the
therapeutic effective period of the drug can be assumed
which is very essential in clinical practice.
 BA study serves as a benchmark for subsequent BE
studies.
 Comparison of BA assessment of 2 or more chemically
equivalent drugs or pharmaceutical alternatives is nothing
but BE study.

18. How to assess BA?
Well controlled animal study.
 Well controlled clinical trials in human.
 Plasma concentration time curve.
 Excretion of drug through urine.

19. Plasma Concentration Time Curve:
 When a single dose of drug is administered to a patient, serial
blood samples are withdrawn for a constant intervals of time
and plasma is assayed for drug and the values are graphically
represented which is known as Plasma Concentration Time
Curve.
 In this curve time taken to reach max concentration of drug is
represented as Tmax
 Peak concentration of the drug in plasma is termed as Cmax

20. Factors effecting Plasma Concentration of the Drug:
• Drug concentration is related to the level of activity of drug.
• Plasma Concentration of the Drug is mainly affected by the
rate at which it is absorbed into plasma and the rate at which
the drug is eliminated by excretion or biotransformation.
• Distribution of the drug between plasma to other tissues also
will affect the plasma concentration of the drug.

21. Determination of BA through Urine:
 The amount of drug eventually excreted in an
unchanged form in urine shows the percentage of the
dose reached to systemic circulation.

22. Absolute Bioavailability
 The fraction or the percentage of the administered
dose of the drug absorbed intact into systemic
circulation is Absolute Bioavailability.
 It can be calculated by comparing the total amount of
intact drug reaches to the systemic circulation after
administration of a known dose of the dosage form
via a route of administration with that of I.V. route
with same dose.
 Here I.V route is considered to be ideal to compare
with other routes because of its 100% bioavailability.

23. Relative Bioavailability
It is a measurement of fraction of drug absorbed
intact into systemic circulation from a dosage form
relative to standard (clinically proven) dosage form
of the drug.
 in case of drugs that can not be administered
through IV route then the relative bioavailability is
determined rather than absolute bioavailability
In such case BA of drug from test dosage form is
compared with same drug administered in a standard
dosage form that is route from which drug is known
to be well absorbed and efficacy is clinically proved.

24. Concept of Equivalence :
 In pharmaceutics Equivalence is a general term that
indicates a comparison of one drug product with another
with an established set of standards.
 It may be defined in several ways….
 Chemical Equivalence:- 2 or more dosage forms contain
same chemical components or labeled quantities of the
drug
 Clinical Equivalence:- the same drug from 2 or more
dosage forms give identical in vivo effects on a symptom
or a disease.
 Therapeutic Equivalence:- 2 brands of a same drug
product are expected to yield same clinical results.

25. Pharmaceutical Equivalence:
 If 2 or more drugs contain the same active ingredients,
identical in strength (concentration), dosage form and route of
administration
Bioequivalence:
o 2 pharmaceutically Equivalent drugs are considered to be
Bioequivalent when the rate and extent of absorption of their
active ingredients are not significantly differ under similar
experimental conditions.

26. How to conduct BE studies?
 In conducting BE study one of the chemically equivalent drug
products which is chemically proven for its therapeutic
efficacy serves as a standard against which the other test
product may be compared.
 Comparison between following parameters must be done.
 Max plasma concentration Cmax
 Time of peak concentration Tmax
 Area under plasma concentration time curve (AUC)
 If there is no significant deference between these parameters
then both the drugs can be considered as bioequivalent.
 If the test product is found to be bioequivalent to the standard
product then it can be expected that the test product is
therapeutically effective as that of standard product.

27. BA Versus BE
Bioequivalence is an extension of the concept of
relative bioavailability, in which the test product is
compared with a standard product for its
Bioavailability.
In other words, Bioequivalence Study is a
comparative Bioavailability Study designed to
establish equivalence between 2 medicinal products,
i.e. test product and clinically proved standard
product.

28. Bioequivalence in terms of Bioavailability
 If 2 medicinal products are bioequivalent, if they are
pharmaceutically equivalent or alternatives and their
bio availabilities are identical in the same dose with
respect to both safety and efficacy.

29. Application of concepts of BA&BE IN rasashastra
 Concept of pratinidhi dravyas. eg:-mukta & mukta shukti
 Bhasma prepared by different procedures. Eg:- kupi & puta
method
 Bhasma prepared by different media. Eg: Gandhaka media,
mulika media, parada media, ariloha marita bhasmas
 Bhasma after several putas. Eg:- abhraka bhasma after 10 puta,
100 puta,1000 puta.

30. Cont…
Comparative BA studies are essential for rasa dravyas
with same chemical components
 Differenet raw meterials. Eg:- abhraka bhasma, loha
bhasma, mandura bhasma, kasisa bhasma. OR all
sudhavargiya drayas
 Different methods of preperation
 Bahuguna gandhaka jarita parada
 Raw material collected from different place

31. Goal of Bioequivalence Study:
BE studies are important in determining whether
chemically equivalent products manufactured by
different companies are therapeutically equivalent
that is produce identical therapeutical response in a
patient.
To establish a new product or formulation which has
same therapeutic equivalence in the rate and extent of
absorption to the reference drug product.

32. Goal of BA & BE studies:
 The ultimate goal of bioavailability and
bioequivalence studies is for the safe and
efficacious drug product.