Bioavailability is a measure of the amount of drug that reaches systemic circulation after administration. It may be less than 100% due to incomplete absorption and first-pass metabolism by the liver. Factors like pharmaceutical properties, gastrointestinal conditions, food intake, and route of administration can impact bioavailability. There are two types - absolute bioavailability compares systemic availability after oral vs intravenous doses, while relative bioavailability compares oral doses to an oral standard. Bioavailability is assessed indirectly through pharmacokinetic methods like analyzing blood concentrations over time and measuring drug excreted unchanged in urine.

1. Presentation
Pharmacology
Bioavailability

2. What is Bioavailability?
• Bioavailability: It is a measure of the fraction (F )
of administered dose of a drug that reaches the
systemic circulation in the unchanged form.
• bioavailability may be less than 100% for two main
reasons:
• incomplete extent of absorption across the gut
wall and
• first-pass elimination by the liver

3. • In such cases, the dose available to the patient
called as Bioavailable dose. It often less than the
administered dose.
• The amount of drug that reaches the systemic
circulation is called as Systemic availability.
• The term bioavailable Fraction F refers to the
fraction of administered dose that enters the
systemic circulation.

4. TABLE: Routes of administration,
bioavailability, and general characteristics.

5. Factors affecting Bioavailability
• There are various factors which affect
bioavailability.
 Pharmaceutical Factors.
 Pharmacological factors.
 Route of administration.

7. Pharmaceutical factors
Particle size
Salt form
Crystal form
Nature of Excipients
Degree of ionization
Partition coefficient

8. Pharmacological factors include:
• Gastric emptying and gastrointestinal motility.
• Gastrointestinal diseases.
• Food and other substances.
• First pass metabolism.
• Drug-drug interactions.

10. Route of administration
• Parenteral
• Oral
• Topical
• Rectal
• Inhalation.

11. Types of Bioavailability
• There are two types of Bioavailability
1. Absolute Bioavailability
2. Relative Bioavailability

12. Absolute Bioavailability
1.Absolute Bioavailability: when the systemic
availability of a drug administered orally is
comparison to its intravenous administration. Is
known as absolute bioavailability

13. Relative Bioavailability
• The relative Bioavailability is the systemic
availability of a drug administered orally is
determined by doing its comparison with that of
an oral standard of same drug.

14. Conti..
• Range of Biovailability -0 to 1
• It is usually expressed as percentages (%)
• An Absolute Bioavailability of 1 (or 100%)
indicates complete absorption.
• Relative Bioavailability of 1 (or 100%)
implies that the Bioavailability of drug from
both dosage forms is same but does not
indicate the completeness of the systemic
drug absorption.

16. Methods of assessing Bioavailability
• Pharmacokinetic methods (Indirect)
1. Blood analysis.
2. Urinary excretion data

17. Pharmacokinetic method(Indirect)
Blood analysis
• Plasma level time studies or the plasma
concentration - time curve or blood level
curve.
• A direct relationship exists concentration of
drug at the site of action and concentration of
drug in the plasma.

18. • Serial blood samples are taken after drug
administration and analyzed for drug
concentration.
• A typical blood level curve obtained after
oral administration of drug.

19. Urine excretion data
• The method of determination bioavailability
provided that the active ingredient is excreted
unchanged in the significant quantity of
urine.
• The cumulative amount of active drug
excreted in urine is directly proportional to
extent of systemic circulation.
• The rate of drug excretion is directly
proportional to rate of systemic drug
absorption.

20. Pharmacokinetic parameters
• Peak plasma concentration (Cmax).
• Time of peak concentration(Tmax).
• Area under curve (AUC)

22. AUC or extent of absorption
can be measured by 3 methods
•Planimeter: Instrument for mechanically
measuring the area.
•Cut and weigh method:
AUC is cut and weighed on analytical palace.
The weight obtained is converted to proper
unit by dividing it by the weight of a unit area
of same paper.
•Trapeziodal method.