From the Research
Introduction to Volume of Distribution
The volume of distribution is a pharmacokinetic property that describes the distribution of a drug throughout the body. It is an apparent volume that gives a mathematical measure of the extent of tissue distribution of the drug into the body 1.
Factors Affecting Volume of Distribution
Several pathophysiological factors can alter the fraction of circulating drug bound to albumin and hence its body distribution, including age, pregnancy, renal insufficiency, and drug interactions 1.
Volume of Distribution of Hydroxyzine
Hydroxyzine is an antihistaminic with sedative properties used in the control of anxiety and emesis 2. The volume of distribution of hydroxyzine is relatively large, exceeding 4 L/kg, indicating extensive distribution into body tissues 3.
Pharmacokinetic Properties of Hydroxyzine
Hydroxyzine has an elimination half-life of about 20 hours, and its total body clearance is generally in the range of 5 to 12 ml/min/kg 3.
Treatment and Dosing Information
Hydroxyzine can be administered once daily to adults due to its relatively long half-life 3. The dosing frequency of hydroxyzine may be influenced by its volume of distribution, which is a major determinant of half-life and dosing frequency of a drug 4.
Caveats and Considerations
The interpretation of pharmacokinetic data for hydroxyzine is complex due to the presence of metabolites and the use of radioimmunoassay methods 3. Additionally, the volume of distribution of hydroxyzine may be affected by pathophysiological factors such as age, pregnancy, and renal insufficiency 1.
Differential Diagnosis and Considerations
In patients with liver disease or renal insufficiency, the elimination half-life of hydroxyzine may be increased, requiring adjustments to the dosing regimen 3. In children, the elimination half-lives of hydroxyzine are shorter than in adults, and dosing regimens may need to be adjusted accordingly 3.