“It is the study of factors influencing the rate (Kinetics) & amount of drug that reaches the systemic circulation and the use of this information to optimize the efficacy of the drug products”.

“Bioavailability is the rate (Kinetics) and extent

(amount) of drug absorption”.

Any alteration in the drug’s bioavailability is reflected in its pharmacological effects.

“Pharmacokinetics is the study of time course of drug ADME and their relationship with its therapeutic and toxic effects of the drugs”.

OR

“Pharmacokinetics is the ‘kinetics of ADME’ or KADME”

Pharmacokinetic processes

Four Phases of Drug administration and Therapy:

1. Pharmaceutical Phase

2. Pharmacokinetic Phase

3. Pharmacodynamic Phase

4. Therapeutic Phase.

1. Pharmaceutical Phase: Concerned with Physicochemical properties of drugs, and Design and manufacture of effective drug

product for administration by a suitable means.

2. Pharmacokinetic Phase: ADME of drugs and its relationship with -

Dose, Dosage form, Dosing frequency and Route of administration.

3. Pharmacodynamic Phase: Concerned with Biochemical and Physiological

effects of drugs, and its mechanism of action. Concentration of drug at the site of action and its

relation to the magnitude of effects observed.

In comparison – Pharmacokinetics is the study of what the body

does to the drug, whereas, Pharmacodynamics is the study of what the drug does to the body.

4. Therapeutic Phase: Concerned with the pharmacological effects of

the drug.

Drug in dosage formReleaseRelease

Drug particles in body fluids

Dissolution

Drug in solutionDegradation

Absorption

Liver

Excretion

GI

Central Compartment

Free Bound

Distribution

PeripheralTissues

Pharmacologic effect

Processes involved in Drug Therapeutics

Drug in dosage form

ReleaseRelease

Drug particles in body fluidsDissolution

Drug in solution Degradation

Absorption

Liver

Excretion

GI

Central Compartment

Free Bound

Distribution

PeripheralTissues

Pharmacologic effect

Pharmacodynamics

Pharmaceutics

Pharmacokinetics

Therapeutic Phase

Relationship between drug Product and its Pharmacological action

Drug Release & Dissolution

Drug in Tissues

Drug in Systemic Circulation

Excretion & Metabolism

Pharmacological or

Clinical Effects

Absorption

Elimination

Different Transport Mechanisms

Stomach Small Intestine

Large Intestine

Rectum

pH range 1-3 5-7.5 6-8 6-8

Length (cm) 20 300-500 110 20

Diameter (cm) 15 2.5 5 2.5

Surface area (sq.m) 0.1-0.2 200 0.15 0.02

Blood flow (L/min.) 0.15 1.0 0.02 -

Transit time (hrs) 1-5 3-6 6-12 6-12

Absorptive role Lipophilic, acidic &

neutral drugs

All types of drugs

Some drugs, water &

electrolytes

All types of drugs

Absorption mechanism

Passive diffusion,

convective transport

All absorption

mechanisms

Passive diffusion,

convective transport

Passive diffusion,

convective transport,

Endocytosis

Anatomical & Functional differences between important regions of GIT

• Systemic distribution: 1. Plasma 3L2. Extra-cellular 15 L3. Intra-cellular 4L

• Binding to blood proteins

• Uneven distribution in body organs:1. Deposition in fat tissue2. Deposition in liver/kidneys3. Deposition in target organ

• Internal barriers-Blood brain barrier/Placenta

Drug Distribution

20%

80%

Amount of drug adsorption

Influenced by:• Release of the active

substance from the formulation

• Solubility of the active component

• Enzymatic degradation prior to adsorption

• Transport over the biological barrier