Bioavailability refers to the rate and extent to which an active drug reaches systemic circulation from its site of administration. It depends on pharmaceutical factors like dosage form, particle size, salt form, and excipients. Pharmacological factors such as gastric emptying, gastrointestinal diseases, food, and drug interactions also influence bioavailability. Bioavailability can vary between individuals due to pharmacogenetic reasons. The bioavailability of orally administered drugs is usually lower than intravenous routes due to first-pass metabolism in the liver.

1. BIOAVAILABILITY
By
Dr. Darshan j c
Dpt of pharmacy practice

2. BIOAVAILABILITY
• The rate and extend to which the active concentration of a drug
is available at the desired site of action (or bloodstream).
or
• The therapeutic effectiveness of a drug depends upon the
ability of dosage form to deliver the medicament to its site of
action at a rate and attribute of a dosage form.

4. • In pharmacology, bioavailability (BA or F) is a subcategory
of absorption and is the fraction of an administered dose of
unchanged drug that reaches the systemic circulation one of
the principal pharmacokinetic properties of drugs.
• when a medication is administered intravenously its
bioavailability is 100%.However, when a medication is
administered via other routes(such as orally), its bioavailability
generallydecreases may vary from patient to patient.
• Bioavailability is one of the essential tools in
pharmacokinetics, as bioavailability must be considered when
calculating dosages for non-intravenous routes of
administration

5. • Bioavailability depends upon three major factor.
• Pharmaceuticalfactor
• Patient related factor
• Rout of administration If two or more, similar dosage forms of
the same drug reach the blood circulation at the same relative
rate and extend, those are BIOEQUIVALENT
• preparations of that generic drug.
• Difference in bioavailability is usually seen with ORAL
dosage forms,
• bioavailability of I.V is 100%, I.M and S.C are assumed to be
close to 100

6. Chemical Equivalence
• If two or more dosage forms of the same drug contains the
samelabeled quantities of the drug as specified in
Pharmacopoeia, these are Chemical Equivalent drugs.
Pharmaceutical Equivalence
• If the two or more Chemical Equivalent drug’s dosage forms
also contains other similar ingredients, e.g. excipients
(binders), those dosage forms are considered to be
Pharmaceutical Equivalent.

7. Therapeutic Equivalence
• – If they provide an identical in vivo pharmacological
response, as measured by control of symptoms or disease and
safety profile.
Clinical Equivalence
• – If one structurally different drug can provide the same
clinical response as another mechanically related drug, they
are considered to exhibit clinical equivalence.

8. • Types of Bioavailability
• Absolute Bioavailability :-
• absolute bioavailability is the bioavailability
in which whole quantity of administered drug
reaches the blood circulation.
• It is possible only by iv route

9. • Relative Bioavailability :-
Relative bioavailability is the bioavailability in
comparison with reference standards

10. • What are the factors influencing
BIOAVAILABILITY?
• Pharmaceutical factors
• Pharmacological factors

11. It is expected that, bioavailability of drugs to be in this decreasing
order-
• Solutions > Suspension > Capsule > Tablet > Coated Tablet

12. • Factors affecting bioavailability
– Particle Size
• • The rate at which a drug is dissolved can be increased by
increasing its surface area by decreasing its PARTICLE SIZE.
• Tablet contain large aggregates of medicaments takes more
time to disintegrate even on prolonged exposure to gastric and
intestinal juice.
– Salt Form
• •The rate at which a particular salt dissolves differs from its
parent compound.
.

13. • Salts of weakly acidic drugs are highly water soluble, free
acidic drugs is precipitated from these salts is micro
crystalline form, which has a faster dissolution rate and
increases bioavailability
• Crystal Forms: The rate of absorption and bioavailability of a
drug also depends on its crystalline form.
• This is because amorphous forms dissolve faster compared to
crystalline forms, because no energy is needed to break up the
crystalline lattice, thus increasingtheir bioavailability.

14. Nature of Excipients and Adjuvants
• These pharmacologically inert substances , (e.g starch,
lactose, calcium sulfate,gum) which are added as filling
material or as binding agents or to obtain proper granular size,
have tremendous effects on bioavailability of drugs.
• Some of these excipients are wetting agents, which enhance
solvent penetration and ensures faster dissolution and in turn
absorption.
• We should be particularly careful in drugs which follows zero
order or mixed order kinetics or have a low margin of safety.

15. • Degree of Ionisation:
Non-ionised, lipid soluble drugs are better absorbed,
increasing their bioavailabilitycompared to strongly acidic or
strongly basic drugs or highly ionised drugs.
• Concentration:
• High concentration of active medicaments favours rapid
absorption resulting in high bioavailability.

16. • Manufacturing variables:
• Addition of various excipients in the process of
manufacture of a dosage form may affects
the bioavaolability from a given dosage form.
• Eg : addition of lubricants which are
hydrophobic in nature wetting of drug
particles this reduces dissolution.

17. • Firstpass metabolism:
• Orally administered drug go to the systemic
circulation through hepatic portal system
which first penetrates the drug to the liver. The
drug if rapidly metabolized in the liver, a
small fraction will reach the systemic
circulation.

19. • The Pharmacological factors include:
• – Gastric Emptying and Gastrointestinal Motility
• • Factors that accelerate gastric emptying increases the
bioavailability.
• • This is because the drug is exposed to the larger surface area
of the small intestine.
• – Gastrointestinal Diseases
• • There are many gastrointestinal diseases which have an effect
on drug absorption,
• the outcome of Coeliac disease is complex, it increases the
absorption of cephalexin, whereas reduces of amoxycillin.

20. • In case of Crohn’s disease, there is disproportionate
absorption of individualcomponents of cotrimoxazole,
increases absorption of sulfamethoxazole, decreases of
trimethoprim
• – Food and Other Substances
• In general, GI absorption rate is reduced after ingestion of
food, although it has no effect on extend of absorption.
• Both rate and extend of absorption of certain antibiotics like
rifampicin is reduced after meals.

21. • Presence of food in GIT reduces the drug absorption of
amoxicillin and ampicillin. While presence of food side effects
of some drugs like iron such as irritaton, vomiting nausea can
be reduced.
• Interaction with GI components:
• Bile salt with antibacterial inactivate them-less absorption
• Insuli is inactivated by acid- bioavailability zero
• Bile salt increases dissolution of poorly soluble drug

22. • Absorption of tetracyclines is reduced if taken with milk
because it forms poorly absorbed complexes with calcium.
Vit. C increases absorption of iron because it keeps it in it’s
ferrous form.
• – Drug-Drug Interactions: also cause difference in
bioavailability.
• • Liquid paraffin decreases the bioavailability of fat soluble
vitamins as it emulsifies fat.
• • Antacids reduces bioavailability of tetracyclines because it
forms chelated complex.

23. • Pharmacogenetic Factors
• • Large difference in bioavailability often occurs among
humans due to pharmacogenetic reasons.
• Slow and fast acetylators show increased and decreased
bioavailability of isoniazid respectively.
• – Miscellaneous Factors
• • Area of Absorptive Surface
• • State of Circulation at the Site of Absorption (shock, where
tissue perfusion decreases)
• • Route of Administration