11-12-2012, 04:03 PM
Non Linear Pharmacokinetics
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Difference between Linear and non linear pharmacokinetics
Linear pharmacokinetics
Change in plasma concentration due to ADME process is proportional to dose of drug administered (single or multiple)
Follow First order kinetics
Semilog plot for concentration vs time is super imposable (Principle of superimposition)
No change in F, Ka, Ke, Vd, Clearance etc.
Nonlinear Pharmacokinetics
Rate process of ADME are dependent on carrier or enzymes having definite capacity and subjected to saturation.
Change in concentration is no more proportional to dose administered during the total process of ADME.
Follow First order + Zero order kinetics
Change in different pharmacokinetic parameters.
Causes of Nonlinearity
During absorption
Absorption is solubility or dissolution rate limited eg. Griseofulvine
Absorption involve carrier mediated transportation eg. Riboflavin, ascorbic acid
Hepatic metabolism attain saturation eg. Propranolol, hydralazine
During Metabolism
Capacity limited metabolism due to enzyme or cofactor saturation eg. Alcohol, Phenytoin.
Enzyme induction eg. Carbamazepine