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→Distribution
* Transcellular Fluid (2%)
* Transcellular Fluid (2%)
* Fat (20%)
* Fat (20%)
Many drugs are bound to proteins with acidic drugs binding to albumin and basic drugs binding to globulin. The extent of the binding is dynamic and the bound drug and free drug exist in equilibrium. Normally only the free drug has the capability of crossing the vascular endothelium. Though if damage occurs protein-bound drugs can enter the circulations.
The '''Volume of Distribution (V<sub>d</sub>)''' is a measure of the volume of fluid needed tocontain the total amount of drug at its plasma concentration.
V<sub>d</sub> depends upon the ability of a drug to enter plamsa and interstitial fluid and to cross cell membranes and gives a good indication of the extent of drug distribution.
* Very low (0.005-0.1l/kg) - drug confined to plasma compartment
* Low (02l/kg) - drug confined to plasma and interstitial space
* Intermediate (0.6l/kg) - drug enters total body water
* Very High (>1l/kg) - concentrated in a body fluid other than plasma and there may be bound residues eg i fat
Lipid-soluble drugs reach all compartments and can accumulate in fat. Whilst lipi-insoluble drugs are mainly contained in plasma and interstitial fluids; they are usually incapable of crossing the blood-brain barrier.
==Metabolism==