Transcript Pharmacokinetic Models

Pharmacokinetics
Dr. Muslim Suardi, MSi., Apt.
School of Pharmacy, Faculty of Science
University of Andalas
Pharmacokinetic
ABSORPTION
DISTRIBUTION
METABOLISM
EXCRETION
Pharmacokinetic Models
• Oversimplified but useful mathematical
models for describing the pharmacokinetic
behavior of a drug in the body.
• Depict the body as a single compartment
or a series of compartments.
• These compartments do not necessarily
have any anatomical or physiological
reality.
Single Compartment Model
Can be most readily applied to drugs that
rapidly distribute between blood and tissue
after absorption
ABSORPTION
“Transfer of drug from the administration site
to the systematic circulation”
a. Barriers of Absorption
b. Mechanisms of Absorption
Mechanisms of Absorption
1. Passive Diffusion: Most of drugs.
2. Active Transport: Eg. Levodopa.
3. Facilitated Diffusion
4. Pores
5. Pinocytosis
6. Electrochemical diffusion
Bioavailability
“A measure relative to some standard of
the rate & amount of drug which reaches
the systemic circulation unchanged
following the administration of a suitable
dosage form”
(BA)
Rate of Absorption
“Important for rapid onset of effect”
Methods for Estimating Rate of Absorption:
- Time of peak plasma level
- Determine ka - Method of residuals
- Percent of unabsorbed - For plots
(Large ka - rapid absorption).
Extent of Absorption
• Absolute Vs Relative BA
• Methods for Estimating Extent of
Absorption
• Plasma levels
• Eg. Trapeziodal role
• Urinary recovery (if largely excreted
unchanged)
• (Xu = total amount of unchanged drug
excreted in urine)
Examples
Drug F (oral) %
• Ampicillin
50
• Digoxin
50-90
• Warfarin
100
• Penicillin G <30
• Doxycycline 100
Factors Influencing Bioavailability