Bioavailability can be measured through pharmacokinetic and pharmacodynamic methods. Pharmacokinetic methods involve measuring drug concentrations in blood or amount excreted in urine over time to determine parameters like Cmax, Tmax, and AUC. Pharmacodynamic methods involve measuring acute pharmacological responses or long-term therapeutic responses to a drug. The most common pharmacokinetic method is to collect serial blood samples after drug administration and measure drug concentrations to generate a plasma concentration-time curve from which various pharmacokinetic parameters can be derived. Relative bioavailability is calculated as the ratio of AUCs for a test and reference formulation, while absolute bioavailability is calculated as the ratio of AUCs for an oral and intravenous dose.

1. Bioavailability
Measurement of bioavailability
Presented by,
Pradip.L.Ghori
M-Pharm 1st year
Dept. of Pharmaceutics
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2. Measurement of bioavailability
 Pharmacokinetic methods ( indirect )
1. Blood analysis
2. Urinary excretion data
 Pharmacodynamic methods ( direct )
1. Acute pharmacological response
2. Therapeutic response
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3. 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 & concentration of drug in the plasma.
 Serial blood samples are taken after drug administration
& analyzed for drug concentration.
 A typical blood level curve obtained after oral
administration of drug.
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5. Parameters determined
Pharmacokinetic parameters
 Peak Plasma Concentration (Cmax)
 Time of Peak concentration (tmax).
 Area Under Curve (AUC)
Pharmacodynamics parameters
 Minimum Effective Concentration (MEC) / Minimum
Inhibitory Concentration (MIC).
 Maximum Safe Concentration (MSC) / Maximum Safe
Dose (MSD).
 Duration of action
 Onset of action.
 Intensity of action.
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6.  AUC or Extent of absorption can be measured by 3
methods…
1.Planimeter
Instrument for mechanically measuring the area
2. Cut & weigh method
AUC is cut & weighed on analytical balance. The weight
obtained is converted to proper unit by dividing it by
the wt of a unit area of same paper.
3. Trapezoidal method
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7. 3. Trapezoidal method
AUC = ½ ( C1 + C2) (t2 – t1) + ½ (C2 + C3) (t3 – t2) +…….
½ (C n-1 + C n ) (tn – tn-1 )
C = Concentration
t = time
subscript= sample number
AUC = Area Under Curve
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8. Relative bioavailability
F rel = ( AUC) drug . (Dose) standard
(AUC) standard .(Dose) drug
Absolute bioavailability
Fab = (AUC)drug . (Dose) IV
(AUC)IV . (Dose) drug
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9. Urinary 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 drug
absorption.
 The rate of drug excretion is directly proportional to
rate of systemic drug absorption.
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10. Advantages
 Useful when there is lack of sufficiently sensitive
analytical techniques to measure concentration of drug
in plasma.
 Noninvasive method therefore better subject
compliance.
 Convenience of collecting urine samples in comparison to
drawing of blood periodically.
 If any case the urine drug concentration is low, assaying
of larger sample volume is relatively more.
 Direct measurement of bioavailability, both absolute &
relative is possible without the necessity of fitting the
data to the mathematical model.
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12.  Bioavailability is determined by….
F= (U ) oral .D IV
(U ) IV .D oral
U = Cumulative amt of unchanged drug excreted in
urine
D IV = IV dose
D oral = oral dose
F = absolute bioavailability
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13.  When equal doses are administered Intravenously &
Orally…..
F = (U ) oral
(U ) IV
F = (U ) test
(U ) standard
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14.  When drug A was administered IV to a group of volunteers, 80%
of the 500mg dose was recovered unchanged in the urine. When
the same drug was administered to the same volunteers
orally.280 mg was recovered unchanged in urine. What is the
absolute bioavailability of Drug A following oral administration.
Absolute bioavailability = (cumulative amt.of drug excreted) sample
(cumulative amt.of drug excreted)IV
= 280
400
= 0.7 or 70%
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15. Acute pharmacological response
 Bioavailability can be determined from the acute
pharmacologic effect – time curve as well as from
dose response graph.
 DISADVANTAGE is that pharmacological response
tends to more variable & accurate correlation
between the measured response & drug available
from the formulation is difficult.
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16. Therapeutic response
 This method is based on the observing the clinical
response to a drug formulation given to a patients
suffering from disease for which it is intended to be
used.
 Ex …for anti inflammatory drugs, the reduction in the
inflammation is determined.
 The major DRAWBACK is …quantification of observed
response is too improper to allow for reasonable
assessment of relative bioavailability between two
dosage forms of a same drug.
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17. References
 “Biopharmaceutics & pharmacokinetics”, D.M.
Brahmankar & Sunil B. Jaiswal, Vallabh prakashan.
 “Text book of Biopharmaceutics & pharmacokinetics”,
Dr.Shobharani R. Hiramath.
 “Applied Biopharmaceutics & pharmacokinetics”, Leon
Shargel & Andrew B.C.
 www.google.com
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18. Thank you…….!!!
Any
questions….?
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