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Clearance is variable in zero-order kinetics because a constant amount of the drug is eliminated per unit time, but it is constant in first-order kinetics, because the amount of drug eliminated per unit time changes with the concentration of drug in the blood. [3] [4]
Most drugs are eliminated from the blood plasma with first-order kinetics. For this reason, when a drug is introduced into the body at a constant rate by intravenous therapy, it approaches a new steady concentration in the blood at a rate defined by its half-life. Similarly, when the intravenous infusion is ended, the drug concentration ...
First-pass metabolism may occur in the liver (for propranolol, lidocaine, clomethiazole, and nitroglycerin) or in the gut (for benzylpenicillin and insulin). [4] The four primary systems that affect the first pass effect of a drug are the enzymes of the gastrointestinal lumen, [5] gastrointestinal wall enzymes, [6] [7] [8] bacterial enzymes [5] and hepatic enzymes.
Pharmacokinetics (from Ancient Greek pharmakon "drug" and kinetikos "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to describing how the body affects a specific substance after administration. [1]
The AUC (from zero to infinity) represents the total drug exposure across time. AUC is a useful metric when trying to determine whether two formulations of the same dose (for example a capsule and a tablet) result in equal amounts of tissue or plasma exposure. Another use is in the therapeutic drug monitoring of drugs with a narrow therapeutic ...
In first-order (linear) kinetics, the plasma concentration of a drug at a given time t after single dose administration via IV bolus injection is given by; = / where: C 0 is the initial concentration (at t=0)
Drugs are excreted from the kidney by glomerular filtration and by active tubular secretion following the same steps and mechanisms as the products of intermediate metabolism. Therefore, drugs that are filtered by the glomerulus are also subject to the process of passive tubular reabsorption. Glomerular filtration will only remove those drugs ...
Zero-order absorption: rate of absorption is constant. A common example is continuous intravenous infusion. First-order absorption: rate of absorption is proportional to the amount of drug remaining to be absorbed. Representative examples include typical cases of oral administration, subcutaneous injection, and intramuscular injection.