Drug Elimination – USMLE exams

by / Monday, 23 August 2010 / Published in Pharmacology

There are two types of drug elimination: Zero Order and 1st Order

Drug Clearance = Rate of elimination / Plasma Drug Concentration

1st Order Elimination – In 1st order elimination, the rate of drug elimination is proportional to the plasma concentration (Cp) of drug.  Thus with more drug concentration there is more drug elimination, if there is less drug concentration there is less drug elimination.  Most drugs are eliminated by 1st order elimination.

Zero Order Elimination – In Zero order elimination, the fraction of drug elimination remains constant, no matter how high the drug concentration.  There are less drugs eliminated with zero-order elimination, two examples are alcohol and aspirin.

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