True about first order kinetics is/are:
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 7th/ed, p30,31Explanation# Clearance (CL): defined as "the theoretical volume of plasma from which the drug is completely removed in unit time".# CL = rate of elimination/plasma 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 kinetics)Zero 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 1/2 remains constant because CL does not change with dose.* V/2 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 1/2 related but not recalled.
Very few drugs follow it
Option not recalled but was related to tl/2
Salicylates follow it throughout therapeutic ranges
Rate of elimination increases with increase in concentration of drug and decreases with decrease in concentration of drug
General Pharmacology