PHARMACOLOGY

 DISTRIBUTION OF DRUGS ::

After a drug is absorbed it is distributed into intestinal cellular or transcellular fluids The rate extent and pattern of distribution are determined by : (1) Physiochemical characteristics of drug (2) Cardiac output and (3) Regional blood flow 

        In general : (1) Lipid soluble drugs that can cross the membranes are easily distributed throughout the body more promptly into the heart brain liver kidney and other highly perfused tissues but less rapidly into the muscle and more slowly into the fat 

(2) Those drugs which are not freely permeable through cell membrance are distributed to the extracellular fluid compartment and have restricted site of action 

        The distribution is influenced by : 1.pH and lipid solubility 2.Active transport 3. Protein binding 4. Tissue bindings 

pH and Solubility ::

The difference between intracellular and extracellular pH is very small (7.0: 7.4) In general this factor does not influence the distribution of drugs to a great extent However weak acids are concentrated more extracellularly while weak bases are concentrated more intracellularly Alteration in pH of extracellular or intracellular fluid can change distribution of the drug 

Active Transport ::

Some drugs are distributed by this mechanism here the distribution is unequal eg. adrenergic neurone blockers