Pharmacokinetics

Pharmacokinetics PK

TRFarmakokinetik

The branch of pharmacology that describes what the body does to a drug: the time course of its absorption, distribution, metabolism and excretion (ADME) and the resulting concentrations in plasma and tissues.

Formula

t½ = 0.693 × Vd / CL Css,avg = F × Dose / (CL × τ)

In depth

Pharmacokinetics links dose to concentration, whereas pharmacodynamics links concentration to effect. Its two primary parameters are clearance (CL), which sets the average steady-state concentration (Css,avg) for a given dosing rate, and volume of distribution (Vd), which sets the loading dose; together they determine the half-life (t½). Bioavailability (F) is the fraction of an extravascular dose that reaches the systemic circulation, and τ is the dosing interval.

Parameters are estimated from serial concentration–time data by non-compartmental analysis (AUC, Cmax, Tmax, t½) or by compartmental and population models. They underpin dose selection, choice of dosing interval, dose adjustment in organ impairment and the interpretation of drug interactions and therapeutic drug monitoring.

Clinical pearl

Most dose individualisation rests on two parameters: clearance determines the maintenance dose and volume of distribution the loading dose; organ impairment, age, pregnancy and interacting drugs act mainly by changing them.

TRIn Turkish

Farmakokinetik

Vücudun ilaca ne yaptığını inceleyen farmakoloji dalıdır; ilacın absorpsiyon, dağılım, metabolizma ve atılımının (ADME) zaman içindeki seyrini ve bunun sonucunda plazma ile dokularda oluşan konsantrasyonları tanımlar.

Farmakokinetik dozu konsantrasyona, farmakodinamik ise konsantrasyonu etkiye bağlar. İki temel parametre, belirli bir doz hızında ortalama kararlı durum konsantrasyonunu (Css,avg) belirleyen klirens (CL) ile yükleme dozunu belirleyen dağılım hacmidir (Vd); yarılanma ömrünü (t½) bu ikisi birlikte belirler. Biyoyararlanım (F), damar dışı yoldan verilen dozun sistemik dolaşıma ulaşan kesri, τ ise doz aralığıdır.

Parametreler, ardışık konsantrasyon–zaman verilerinden kompartmandan bağımsız (non-kompartmantal) analizle (AUC, Cmax, Tmax, t½) ya da kompartman ve popülasyon modelleriyle hesaplanır. Bu parametreler doz seçiminin, doz aralığının belirlenmesinin, organ yetmezliğinde doz ayarlamasının ve ilaç etkileşimleri ile terapötik ilaç izlemi sonuçlarının yorumlanmasının temelini oluşturur.

Doz bireyselleştirmesi büyük ölçüde iki parametreye dayanır: idame dozunu klirens, yükleme dozunu dağılım hacmi belirler; organ yetmezliği, yaş, gebelik ve etkileşen ilaçlar etkilerini esas olarak bu parametreleri değiştirerek gösterir.

Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

Read next

PharmacodynamicsFarmakodinamik

The branch of pharmacology that studies what a drug does to the body: the biochemical and physiological effects of drugs, their mechanisms of action and the relationship between drug concentration and response.

 ClearanceKlirens

The rate at which a drug is removed from the body, primarily by the liver and kidneys, representing the volume of plasma cleared of the drug per unit time.

 Volume of DistributionSanal Dağılım Hacmi

A theoretical volume that describes the extent to which a drug is distributed throughout the body tissues relative to the plasma, indicating how much the drug leaves the bloodstream to enter tissues.

 BioavailabilityBiyoyararlanım

The fraction of an administered dose that reaches the systemic circulation unchanged, and the rate at which it does so; by definition, bioavailability is 1 (100%) for an intravenous dose.

 Elimination Half-LifeEliminasyon Yarı Ömrü

The time required for the plasma concentration of a drug to decrease by 50% during the elimination phase, reflecting how long the drug remains active in the body.

 Population PharmacokineticsPopülasyon Farmakokinetiği

The study of the sources and magnitude of variability in drug concentrations among individuals in a target patient population, using data pooled from many patients, often with only a few samples each.