Pharmacodynamics, also described as “making the drug to the body”, includes receptor binding effects following receptor binding (postreceptor effects) and chemical interactions. The pharmacokinetics of drugs intended onset, duration and intensity of drug action. Formulas that put these processes in relation to each other, grasp the pharmacokinetic behavior of most drugs together (s. Formulas define the basic pharmacokinetic parameters).

Pharmacokinetics, sometimes described as “what the body does with the drug” refers to the way a drug into, through and out of the body – the time course of absorption, bioavailability, distribution, metabolism and excretion of the drug. Pharmacodynamics, also described as “making the drug to the body”, includes receptor binding effects following receptor binding (postreceptor effects) and chemical interactions. The pharmacokinetics of drugs intended onset, duration and intensity of drug action. Formulas that put these processes in relation to each other, grasp the pharmacokinetic behavior of most drugs together (s. Formulas define the basic pharmacokinetic parameters). Formulas defining basic pharmacokinetic parameters category parameter Formula Resorptionsratenkonstante absorption rate of absorption of the drug for absorption ÷ remaining amount of drug bioavailability amount of the absorbed drug ÷ given drug dose distribution Apparent volume of distribution of the amount in the body befindl cozy medicament ÷ plasma concentration of the drug unbound fraction plasma concentration of unbound drug ÷ total plasma concentration of the drug elimination (metabolism and excretion) Elimination rate Renal excretion + extrarenal (usually metabolic) Elimination clearance rate of elimination of the drug ÷ plasma concentration of the drug or elimination rate constant Renal × apparent volume of distribution Clearance Rate of renal excretion of a drug ÷ plasma concentration of the drug metabolic clearance rate of metabolism of the drug ÷ plasma concentration of the drug excreted unchanged fraction rate of renal excretion of the drug ÷ elimination of the drug elimination rate constant rate of elimination of the drug ÷ amount of drug clearance located in the body ÷ volume of distribution Biological half-life 0693 ÷ elimination rate constant (for elimination of the first order – Drug Metabolism Rate) The pharmacokinetics of a drug depends on both patient-related factors as well as on the chemical properties of the drug. Some patient-related factors (eg. As renal function, genetic predisposition, gender, age) can be used to predict the pharmacokinetic parameters of a population. For example, may be the half-life of some drugs of considerable duration in the elderly, especially when both the metabolism and the excretion depends (comparison of pharmacokinetic results for diazepam in a younger (A) and an older man (B).). So physiological changes of aging affect many aspects of the pharmacokinetics (pharmacokinetics in the elderly and pharmacokinetics in children). Other factors are related to the individual physiology. The impact of some individual factors (eg. As renal failure, obesity, liver failure, dehydration) can be fairly well predicted, however, other factors are idiosyncratic and therefore have unforeseen consequences. Because of individual differences, the administration of drugs to the need of each patient must be based – in the traditional way by empirical dose adjustment until the therapeutic goal is reached. This approach is often inadequate because it may delay the optimum reaction or lead to undesired effects. Knowledge of pharmacokinetic principles helps the prescriber to adjust the dosage more accurate and faster. By therapeutic drug monitoring the application of pharmacokinetic parameters in individual pharmaceutical therapy is called. Comparison of pharmacokinetic results for diazepam in a younger (A) and an older man (B). Diazepam is metabolized in the liver by P450 enzymes to desmethyldiazepam. Desmethyldiazepam is an active sedative, which is excreted through the kidneys. Half-life of elimination is inversely proportional to the terminal slopes of the curves; flat slopes corresponding to long half-lives. 0 = time of delivery. (After Greenblatt DJ, Allen MD, Harmatz JS, Shader RI: diazepam dispositional determinants Clinical Pharmacology and Therapeutics. 27: 301-312, 1980.)

Health Life Media Team

Leave a Reply