Metabolism also called biotransformation is the

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Metabolism, also called biotransformation, is the process by which a drug is altered and broken down into smaller substances, known as metabolites. the cytochrome P450 (CYP450) system, a set of microsomal enzymes usually found in the liver, is important in the metabolism of a drug. There are more than
50 enzymes, but most of the metabolism occurs in only a few of them. The functioning of these enzymes is influenced by drugs and other chemical substances A drug–drug interaction can occur if one drug inhibits an enzyme system, causing another drug to become toxic. The PI will inform the nurse which drugs should not be given together in order to prevent a drug–drug interaction. Excretion refers to the removal of drugs from the body either unchanged or as metabolites. Clearance refers to the total volume of blood, serum, or plasma from which a drug is completely removed per unit of time to account for the excretion. The half-life of a drug provides a measure of the expected rate of clearance. Half- life refers to the time required for plasma concentrations of the drug to be reduced by 50%. Lithium and gabapentin, mood stabilizers, are notable examples of renal excretion. Any impairment in renal function or renal disease may lead to toxic symptoms. Dosing refers to the administration of medication over time so that therapeutic levels may be achieved or maintained without reaching toxic levels steady state, occurs when absorption equals excretion and the therapeutic level plateaus TABLE 11.4 FACTO RS AFFECTING DISTRIBUTION OF A DRUG Factor Effect on Drug Distribution Size of the organ Larger organs require more drug to reach a concentration level equivalent to other organs and tissues. Blood flow to the organ The more blood flow to and within an organ (perfusion), the greater the drug concentration. The brain has hi The brain has high perfusion. Solubility of the drug The greater the solubility of a drug within a tissue, the greater its concentration. Plasma protein binding If a drug binds well to plasma proteins, particularly to albumin, it will stay in the body longer but have a slow on. slower distribution. Anatomic barriers Both the gastrointestinal tract and the brain are surrounded by layers of cells that control the passage or uptak uptake of substances. Lipid readily absorbed and pass the blood–brain barrier. Pharmacokinetics is significantly altered at the extremes of the life cycle. Gastric absorption changes as individuals age. Gastric pH increases, and gastric emptying decreases.
Pharmacogenomics is the study of how a person’s genetic makeup affects his or her response to drugs. ethnopsychopharmacology, the study of how culture and genetic differences in human groups determine and influence the response to medications.

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