<prompt> True about first order kinetics isare:Very few drugs follow itOption not recalled but was related to tl2Salicylates follow it throughout therapeutic rangesRate of elimination increases with increase in concentration of drug and decreases with decrease in concentration of drug  <response>: Ans. D. Rate of elimination increases with increase in concentration of drug and decreases with decrease in concentration of drugRef: Essentials of Medical Pharmacology by KD Tripathi 7thed, p30,31Explanation Clearance CL: defined as the theoretical volume of plasma from which the drug is completely removed in unit time. CL rate of eliminationplasma concentration ... equation Drug elimination is the sum-total of metabolic inactivation and excretion. Elimination of drug depends on the availability of metabolic or excretion pathway. For majority of drugs, the processes involved in elimination transporters, enzymes, blood flow, etc. are not saturated over the clinically obtained concentrations, thus they follow first order kinetics option a.First order kinetics linear kineticsZero order kinetics nonlinear kinetics Rate of elimination is directly proportional to the drug concentration option d CL remains constant See equation above Rate of elimination remains constant irrespective of drug concentration CL 1 with increase in concentration See equation above Constant fraction of the drug present in the body is eliminated in unit time. Constant amount of the drug is eliminated in unit time. t 12 remains constant because CL does not change with dose. V2 increases with dose because CL progressively decreases as dose is increased. Most drugs follow first order elimination option a Low dose aspirin Example: Alcohol and very few drugs follow this in therapeutic range; e.g.warfarin, theophylline, tolbutamide and phenytoin. Aspirin at high dose option c Relationship between dose rate and steady state plasma concentration Cpss is linear. Increase in dose beyond saturation levels causes an increase in Cpss which is out of proportion to the change in dose rate. Zero order kinetics is also known as capacity limited elimination or Michaelis-Menten elimination. Options c and e were t 12 related but not recalled. 