Pharmacokinetics

Volume of Distribution Vd

TRSanal Dağılım Hacmi
Also known as:Apparent volume of distribution · Vd

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.

Formula

Vd = Amount in body / Cp LD = Ctarget × Vd / F t½ = 0.693 × Vd / CL

In depth

Vd is not a physiological space. Drugs that are highly bound to plasma proteins or confined to plasma, such as heparin and warfarin, have small volumes close to plasma or extracellular fluid volume, whereas drugs extensively bound to or sequestered in tissues, such as amiodarone, chloroquine and digoxin, have volumes many times total body water.

For multi-compartment drugs, the central volume (Vc), the volume at steady state (Vss) and the terminal volume (Vz) are distinguished. Vd determines the loading dose (LD) needed to reach a target concentration (Ctarget) and, with clearance, the half-life; changes in Vd due to oedema, ascites or obesity can change the half-life without changing clearance, whereas altered protein binding also changes the clearance of low-extraction drugs.

Clinical pearl

Drugs with a very large Vd, such as tricyclic antidepressants and digoxin, are poorly removed by haemodialysis because only a small fraction of the body load is present in plasma.

Example drugs

Heparin Warfarin Amiodarone Chloroquine Digoxin
TRIn Turkish

Sanal Dağılım Hacmi

İlacın plazmaya göre vücut dokularına ne ölçüde dağıldığını gösteren teorik hacim; ilacın kan dolaşımından dokulara geçiş miktarını belirtir.

Vd fizyolojik bir boşluk değildir. Heparin ve varfarin gibi plazma proteinlerine yüksek oranda bağlanan veya plazmada kalan ilaçların hacmi küçüktür ve plazma ya da hücre dışı sıvı hacmine yakındır; amiodaron, klorokin ve digoksin gibi dokulara yoğun biçimde bağlanan veya dokularda tutulan ilaçların hacmi ise toplam vücut suyunun katlarca üzerindedir.

Çok kompartmanlı ilaçlarda santral hacim (Vc), kararlı durum hacmi (Vss) ve terminal hacim (Vz) birbirinden ayrılır. Vd, hedef konsantrasyona (Ctarget) ulaşmak için gereken yükleme dozunu (LD), klirensle birlikte de yarılanma ömrünü belirler; ödem, asit veya obeziteye bağlı Vd değişiklikleri klirensi değiştirmeden yarılanma ömrünü değiştirebilir; protein bağlanmasındaki değişiklikler ise ekstraksiyonu düşük ilaçlarda klirensi de değiştirir.

Trisiklik antidepresanlar ve digoksin gibi Vd'si çok büyük ilaçlar, vücuttaki toplam miktarın yalnızca küçük bir kısmı plazmada bulunduğundan hemodiyalizle etkin biçimde uzaklaştırılamaz.

Diğer adları:Görünür dağılım hacmi · Vd
Updated 24.09.2026 12 views Educational reference — verify against current sources before clinical use.

Read next

DistributionDağılım

The reversible transfer of a drug from the bloodstream into the interstitial and intracellular fluids and tissues of the body after it has reached the systemic circulation.

 Loading DoseYükleme Dozu

An initial dose, or series of doses, larger than the maintenance dose, given to reach the target plasma concentration rapidly instead of waiting 4–5 half-lives for accumulation.

 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.

 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.

 Plasma Protein BindingPlazma Proteinlerine Bağlanma

The reversible binding of a drug to plasma proteins, chiefly albumin for acidic drugs and α1-acid glycoprotein for basic drugs, which determines the fraction of drug that is free to distribute and act.

 Enhanced EliminationEliminasyonun Hızlandırılması

Measures that increase the removal of an already absorbed drug or toxin from the body beyond its intrinsic clearance, used in selected poisonings to shorten exposure and reduce toxicity.