Drug distribution

DRUG DISTRIBUTION IN THE BODY

PREPARED BYBIBHUTI RANJAN GOGOI

ROLL NO: 03 B.Pharm 4th year

DEFINITION

Drug Distribution is defined as the Reversible transfer of drug between one compartment (blood) to another (extra vascular tissue).

Significance

Pharmacological action of drug depends upon its concentration at the site of action.

Thus distribution plays important role in Onset of Action Intensity of Action Duration of Action

STEPS IN DRUG DISTRIBUTION

Permeation of Free Drug through capillary wall & entry in to ECF.

Permeation of drugs from ECF to ICF through membrane of tissue cell.

DISTRIBUTION PROCESS

DISTRIBUTION OF DRUG IS NOT UNIFORM THROUGH OUT THE BODY---- WHY ?

Because tissue receive the drug from plasma at different rates & different extents.

ORGAN PERFUSED ml/100g/min

Brain 55

Liver 20

Kidney 450

Muscle 3

Skin 5

Fat 1

Factors Affecting Drug Distribution

Factor relating to the drug

a. Lipid solubility of the drugsb. Molecular weight of the drugsc. pKa of drug

Factor relating to the protein and other binding component

a) Physicochemical characteristic of the protein or binding component.

b) Concentration of protein or binding component.

Miscellaneous Factors

Agea) Total body waterb) Fat contentc) Skeletal musclesd) Organ compositione) Plasma protein content Pregnancy Obesity Diet Disease states

Volume of Distribution (Vd): Apparent volume of body water that drug appears to distribute into to produce a drug concentration equal to that in the blood.

Volume of Distribution (L) : Expressed as liters of body water.

Vd = Q/CQ = amount of drug in body (g)C = unbound plasma drug concentration (g/liter)

Volume of Distribution (% BW) : Expressed as % of body weight.

Vd = (Q)(100)/(C) (body weight in Kg)

Q = drug dose C = plasma drug level

Reference

Biopharmaceutics and Pharmacokinetics by Brahmankar, page no: 75-88.

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