drug distribution
TRANSCRIPT
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 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