This document discusses measurements of bioavailability. It defines bioavailability and bioequivalence. There are two main methods to measure bioavailability - pharmacokinetic and pharmacodynamic. Pharmacokinetic methods include plasma level time studies and urinary excretion studies which measure parameters like Cmax, Tmax, and AUC from plasma data or urinary excretion rate and amount excreted from urine data. Pharmacodynamic methods include measuring acute pharmacological responses or therapeutic responses but have disadvantages like variable individual responses.

1. Measurements of
Bioavailability
Presented by
Naga Chandrika Pallam,
Department of Pharmaceutics
Geethanjali College of Pharmacy,
Cheeryal, Hyd.
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2. Bioavailability
Bioequivalence
Bioavailability means the rate
and extent of drug, which
reaches the systemic circulation
unchanged following the
administration of dosage form.
Bioequivalence is a relative term,
which denotes that the drug
substance in two or more identical
dosage forms reaches the systemic
circulation at the same relative
rate and to same relative extent.
DEFINITIONS
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4. Measurements of Bioavailability
Pharmacokinetic
methods
Plasma level
time studies
Urinary
excretion
studies
Pharmacodynamic
methods
Acute
pharmacological
response
Therapeutic
response
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5. Plasma Level Time Studies
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6. PLASMA LEVEL TIME STUDIES
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 attended.
3. AUC : Area under Curve explains about amount of
drug.
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7. Urinary excretion data studies
1.(dXu/dt)
(maximum
urinary excretion
rate)
• Value increases as the rate
and/or extent of absorption
increases.
• Analogous to C max derived
from plasma studies.
2. (tu)max
(Time for
maximum
excretion rate)
• Value decreases as the
absorption rate increases.
• Analogous to t max derived
from plasma studies.
3. XU:
(cumulative amount
of drug excreted
in urine
• Value increases as the extent of
absorption increases.
• Related to AUC of Plasma level data.
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8. 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.
• It can be determined by dose response graphs.
• DISADVANTAGES:
• Pharmacological response is variable and accurate
correlation drug and formulation is difficult.
• Observed response may be due to active metabolites.
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9. 2. THERAPEUTIC RESPONSES
• This method is based on observing clinical response in
patients.
• Demerits:
• Quantitative of observed response is too improper.
• Physiological variations maybe present between
patients.
• If multiple dose protocols are not involved. Patient
receive only single dose for few days or a weak.
• The patients receiving more than one drug treatment
may be compromised due to drug-drug interactions.
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10. REFERENCES
• Biopharmaceutics and pharmacokinetics A treatise by
D.M. Brahmankar, Sunil B. Jaiswal, second edition,
Vallabh Prakash, pg. no. 315-363.
• Basics of pharmacokinetics, Leon Shargel, fifth
edition, willey publications, pp- 453-490.
• www.google.com
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