pharmacokinetics

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pharmacokinetics

 [fahr″mah-ko-kĭ-net´iks]
the study of the movement of drugs in the body, including the processes of absorption, distribution, localization in tissues, biotransformation, and excretion. adj., adj pharmacokinet´ic.

phar·ma·co·ki·net·ics

(far'mă-kō-ki-net'iks),
Movements of drugs within biologic systems, as affected by uptake, distribution, binding, elimination, and biotransformation; particularly the rates of such movements.
[pharmaco- + G. kinēsis, movement]

pharmacokinetics

/phar·ma·co·ki·net·ics/ (fahr″mah-ko-kĭ-net´iks) the action of drugs in the body over a period of time, including the processes of absorption, distribution, localization in tissues, biotransformation, and excretion.pharmacokinet´ic

pharmacokinetics

(fär′mə-kō-kə-nĕt′ĭks, -kī-)
n. (used with a sing. verb)
1. The process by which a drug is absorbed, distributed, metabolized, and eliminated by the body.
2. The study of this process.

phar′ma·co·ki·net′ic adj.

pharmacokinetics

[fär′məkōkinet′iks]
Etymology: Gk, pharmakon + kinesis, motion
the study of the action of drugs within the body, which can, in many respects, be envisioned more accurately as the actions of the body on an administered drug. It includes studies of the mechanisms of drug absorption, distribution, metabolism, and excretion; onset of action; duration of effect; biotransformation; and effects and routes of excretion of the metabolites of the drug.

pharmacokinetics

(1) The formal study of the processes of absorption, distribution, metabolism and excretion (ADME) of medicinal products.
(2) The processes of absorption, distribution, biotransformation and metabolism, binding and elimination/excretion of a drug or vaccine, which corresponds to the movement of a therapeutic though a biological system, as related to the rates at which these events occur.

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

phar·ma·co·ki·net·ics

(fahr'mă-kō-ki-net'iks)
Study of the movement of drugs within biologic systems, as affected by absorption, distribution, metabolism, and excretion; particularly the rates of such movements.
[pharmaco- + G. kinēsis, movement]

pharmacokinetics

The study of how DRUGS are absorbed into, distributed and broken down in, and excreted from, the body.

pharmacokinetics

study of drug uptake rates, distribution, elimination and transformation within biological systems (i.e. what the body does to a drug); pharmacokinesis is reduced in the elderly due to their reduced kidney function

pharmacokinetics (farˈ·m·kō·k·neˑ·tiks),

n the division of pharmacology that studies the absorption, distribution, and localization of drugs in the body.

phar·ma·co·ki·net·ics

(fahr'mă-kō-ki-net'iks)
Movements of drugs within biologic systems; particularly rates of such movements.
[pharmaco- + G. kinēsis, movement]

pharmacokinetics

the study of the movement of drugs in the body, including the processes of absorption, distribution, localization in tissues, biotransformation and excretion.