Skip to main content

Renin Angiotensin Mechanism.

Volume of Distribution.

 

  • Drug distribution: The reversible transfer of a drug between the blood and the extravascular fluids and tissues of the body.

  •  Volume of Distribution: A hypothetical volume of body fluid into which a drug is distributed. 

  • The Volume of distribution (VD), also known as the apparent volume of distribution, is used to quantify the distribution of a drug between plasma and the rest of the body after oral or parenteral dosing. 

  • It is called the Apparent Volume because all parts of the body equilibrated with the drug do not have equal concentration.

  • It is defined as the volume in which the amount of drug would be uniformly distributed to produce the observed blood concentration.

  • The apparent volume of distribution is a proportionality constant relating the plasma concentration to the total amount of drug in the body.

    • XαC

    • X = VdC

    • Vd = X/C

    • Apparent volume of distribution = amount of drug in the body/ plasma drug concentration.

    • It is expressed in liters or liters /kg body weight.

    • Apparent volume of distribution is dependent on concentration of the drug in plasma.

    • Drugs with a large apparent volume are more concentrated in extravascular tissues and less concentrated intravascular.

Applications of volume of distribution:

  1. Vd provides qualitative information. 

  2. Amount of drug in the body, DB can be determinedIn case the target C1 is known, dosage regimen can be fixed for therapy.

  3. Loading dose required to achieve steady stage C1 can be estimated. 

  4. Dose required for individual patients can be calculated. 

  5. Drug – drug interaction can be explained. 

  6. Total body clearance can be calculated.

Commonly Asked Question.

  1. Write a note on the volume of distribution.

  2. Define Volume of Distribution. Describe the importance of volume of distribution in detail.
Labels:

Popular posts from this blog

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called ...
Read more

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and ...
Read more

Flash Distillation.

  Principle: When a hot mixture is allowed to enter from a high-pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization .  During this process, the chamber is cooled.  The less volatile fraction is condensed and the more volatile component remains in the vapor phase .  This process requires time, hence liquid and vapor are kept in intimate contact until equilibrium is achieved. Flash distillation is also called equilibrium distillation because separation of two liquids takes place when liquid and vapor phases are at equilibrium. Equipment used for Flash Distillation: Construction: It consists of a pump, which is connected to a feed reservoir.  Pumps help in pumping the feed into the heating chamber.  The heating chamber is heat supplied by steam.  The other end of the pipe is directly introduced into the vapor-liquid separator through a reducing valve.  The vapor outlet...
Read more