| 释义 |
biotransformation
bi·o·trans·for·ma·tion B0270900 (bī′ō-trăns′fər-mā′shən)n. Chemical alteration of a substance within the body, as by the action of enzymes.bi•o•trans`for•ma•tion (ˌbaɪ oʊˌtræns fərˈmeɪ ʃən)
n. the series of chemical changes occurring in a compound, esp. a drug, as a result of enzymatic or other activity by a living organism. [1950–55] Translationsbiotransformation
biotransformation[¦bī·ō‚tranz·fər′mā·shən] (biochemistry) The series of chemical reactions that occur in a compound, especially a drug, as a result of enzymatic or metabolic activities by a living organism. biotransformation
biotransformation [bi″o-trans″for-ma´shun] the series of chemical alterations of a compound (e.g., a drug) occurring within the body, as by enzymatic activity.bi·o·trans·for·ma·tion (bī'ō-trans'fōr-mā'shŭn), The conversion of molecules from one form to another within an organism, often associated with change (increase, decrease, or little change) in pharmacologic activity; refers especially to drugs and other xenobiotics. Synonym(s): biodegradationbiotransformation (bī′ō-trăns′fər-mā′shən)n. Chemical alteration of a substance within the body, as by the action of enzymes.biotransformation Biochemistry
Bioconversion, see there.
Metabolism
A series of chemical changes in a compound (e.g., a drug), which occur within the body (e.g., by enzymatic activity).
Pharmacology
Drug metabolism, see there.
Physiology
Metabolism, see there.therapeutic drug monitoring Clinical pharmacology The regular measurement of serum levels of drugs requiring close 'titration' of doses in order to ensure that there are sufficient levels in the blood to be therapeutically effective, while avoiding potentially toxic excess; drug concentration in vivo is a function of multiple factors Common TDM drugs Carbamazepine, digoxin, gentamycin, procainamide, phenobarbital, phenytoin, theophylline, tobramycin, valproic acid, vancomycin Therapeutic drug levels in vivo–factors involved Patient compliance Ingestion of drug in the doses prescribed Bioavailability Access to circulation, interaction with cognate receptor(s); ionized and 'free', or bound to a carrier molecule, often albumin Pharmacokinetics Drug equilibrium requires 4-6 half-lives of drug clearance (a period of time for1/2 of the drug to 'clear', either through metabolism or excretion, multiplied by 4-6); the drug is affected by • Interaction with foods or other drugs at the site of absorption, eg tetracycline binding to cations or chelation with binding resins, eg bile acid-binding cholestyramine that also sequesters warfarin, thyroxine and digitoxin or interactions of various drugs with each other, eg digitalis with quinidine resulting in a 3-fold ↓ in digitalis clearance • Absorption may be changed by GI hypermotility or large molecule size • Lipid solubility, which affects the volume of distribution; highly lipid-soluble substances have high affinity for adipose tissue and a low tendency to remain in the vascular compartment, see Volume of distribution. • Biotransformation, with 'first pass' elimination by hepatic metabolism, in which polar groups are introduced into relatively insoluble molecules by oxidation, reduction or hydrolysis; for elimination, lipid-soluble drugs require the 'solubility' steps of glucuronidation or sulfatation in the liver; water-soluble molecules are eliminated directly via the kidneys, weak acidic drugs are eliminated by active tubular secretion that may be altered by therapy with methotrexate, penicillin, probenecid, salicylates, phenylbutazone and thiazide diuretics First order kinetics Drug elimination is proportional to its concentration Zero order kinetics Drug elimination is independent of the drug's concentration Physiological factors • Age Lower doses are required in both infants and the elderly, in the former because the metabolic machinery is not fully operational, in the latter because the machinery is decaying, with ↓ cardiac and renal function, enzyme activity, density of receptors on the cell surfaces and ↓ albumin, the major drug transporting molecule • Enzyme induction, which is involved in a drug's metabolism may reduce the drug's activity; enzyme-inducing drugs include barbiturates, carbamazepine, glutethimide, phenytoin, primidone, rifampicin • Enzyme inhibition, which is involved in drug metabolism, resulting in ↑ drug activity, prolonging the action of various drugs, including chloramphenicol, cimetidine, disulfiram (Antabuse), isoniazid, methyldopa, metronidazole, phenylbutazone and sulfonamides Genetic factors play an as yet poorly defined role in therapeutic drug monitoring, as is the case of the poor ability of some racial groups to acetylate drugs Concomitant disease, ie whether there are underlying conditions that may affect drug distribution or metabolism, eg renal disease with ↓ clearance and ↑ drug levels, or hepatic disease, in which there is ↓ albumin production and ↓ enzyme activity resulting in a functional ↑ in drug levels, due to ↓ availability of drug-carrying proteins bi·o·trans·for·ma·tion (bī'ō-trans'fŏr-mā'shŭn) The conversion of molecules from one form to another within an organism, often associated with change in pharmacologic activity; refers especially to drugs and other xenobiotics.
Synonym(s): biodegradation. biotransformation see BIOCONVERSION.bi·o·trans·for·ma·tion (bī'ō-trans'fŏr-mā'shŭn) The conversion of molecules from one form to another within an organism, often associated with change in pharmacologic activity. |