Drug metabolism is a series of reaction. Oxidation, hydration, reduction, hydrolysis are different kind of reactions by which a drug is metabolized. Liver is the major organ where a drug is metabolized. It is a pharmacokinetics process; a drug can be a lipid soluble or water soluble and are excreted by various processes. The Drug metabolism rate depends on an individual’s genetic factor and if that individual is diseased.
The liver is the principal site of drug metabolism. Although metabolism typically inactivates drugs, some drug metabolites are pharmacologically active—sometimes even more so than the parent compound. An inactive or weakly active substance that has an active metabolite is called a prodrug, especially if designed to deliver the active moiety more effectively.
Drugs can be metabolized by oxidation, reduction, hydrolysis, hydration, conjugation, condensation, or isomerization; whatever the process, the goal is to make the drug easier to excrete. The enzymes involved in metabolism are present in many tissues but generally are more concentrated in the liver. Drug metabolism rates vary among patients. Some patients metabolize a drug so rapidly that therapeutically effective blood and tissue concentrations are not reached; in others, metabolism may be so slow that usual doses have toxic effects. Individual drug metabolism rates are influenced by genetic factors, coexisting disorders (particularly chronic liver disorders and advanced heart failure), and drug interactions (especially those involving induction or inhibition of metabolism).
For many drugs, metabolism occurs in 2 phases. Phase I reactions involve formation of a new or modified functional group or cleavage (oxidation, reduction, hydrolysis); these reactions are nonsynthetic. Phase II reactions involve conjugation with an endogenous substance (eg, glucuronic acid, sulfate, glycine); these reactions are synthetic. Metabolites formed in synthetic reactions are more polar and thus more readily excreted by the kidneys (in urine) and the liver (in bile) than those formed in nonsynthetic reactions. Some drugs undergo only phase I or phase II reactions; thus, phase numbers reflect functional rather than sequential classification.
For almost all drugs, the metabolism rate in any given pathway has an upper limit (capacity limitation). However, at therapeutic concentrations of most drugs, usually only a small fraction of the metabolizing enzyme’s sites are occupied, and the metabolism rate increases with drug concentration. In such cases, called first-order elimination (or kinetics), the metabolism rate of the drug is a constant fraction of the drug remaining in the body (ie, the drug has a specific half-life).
For example, if 500 mg is present in the body at time zero, after metabolism, 250 mg may be present at 1 hour and 125 mg at 2 hours (illustrating a half-life of 1 hour). However, when most of the enzyme sites are occupied, metabolism occurs at its maximal rate and does not change in proportion to drug concentration; instead, a fixed amount of drug is metabolized per unit time (zero-order kinetics). In this case, if 500 mg is present in the body at time zero, after metabolism, 450 mg may be present at 1 hour and 400 mg at 2 hours (illustrating a maximal clearance of 50 mg/h and no specific half-life). As drug concentration increases, metabolism shifts from first-order to zero-order kinetics.
Last Updated on: Dec 22, 2024List of Open Access Journals View More
Department of Electrical Engineering: Current Research
DEECR welcomes authors to contribute current research and reports, Experimental studies, Review articles, Short communication, Editorial, Letter to Editor, Survey Reports submission of manuscripts related to Signal Processing, Material Science, Microelectronics, Electronic materials, Power System Protection, DC Power Converter, C Power Converter, Electrophysics and its applications, Electromagnetism, etc....View More
Journal of Rehabilitation Research Current Updates
JRRCU publishes original, current research, clinical studies, novel methods, advancing concepts on Orthopaedics, Geriatric, Trauma, Neuropsychological Rehabilitation, Palliative care, psychology, etc....View More
Journal of Environmental and Pollution
JEP is a scholarly open access peer-reviewed journal aim to publish be valuable source of information both experimental and theoretical in the field of environmental issues and Pollution and its applications...View More
Reviews in Pharmacy and Pharmaceutical Sciences
Reviews in Pharmacy and Pharmaceutical sciences is a peer-reviewed scholarly journal that aims to publish high quality research on Pharmacology and Toxicology, Pharmaceutical Chemistry, Pharmaceutical Analysis and Quality Assurance, Pharmaceutics, Hospital and Clinical Pharmacy...View More
Clinical Trials and Medical Case Reports
Clinical trials and Medical Case reports is an open access peer reviewed journal. It publishes Clinical trials, Medical case reports and Medical images from all fields of medicine in all orders by which medicinal services experts, specialists and others can easily understand the disease conditions...View More
Journal of Molecular Genetics and Gene Research
Journal of Molecular Genetics and Gene Research is a peer reviewed scientific journal known for rapid dissemination of high-quality research. It serves the International Scientific Community with its standard research publications. This journal is using Online Manuscript Management system...View More