(1) PHYSICAL STATE : Drugs in the form of liquid or a drug given as watery solution is absorbed faster than when the same is given in solid form or as oily solution. Gases are quickly absorbed through lungs.
(2) PARTICLE SIZE : The rate of absorption is faster when a particle size of drug is smaller. If the particle size is large, the drug is slowly absorbed and hence the action is delayed.
(3) SOLUBILITY : An easily soluble drug is quickly absorbed. Also drug in the form of solutions are quickly absorbed then solids.
(4) CONCENTRATION : Drug given as concentrated solution is absorbed faster than dilute solution.
(5) AREA OF ABSORBING SURFACE : Larger the area of absorbing surface, faster is the absorption of drug. For example, lungs and peritoneal cavity are large surface areas from where drugs can be quickly absorbed.
(6) CIRCULATION TO THE SITE OF ABSORPTION : Increased blood flow to the site of absorption can increase the absorption of a drug. This can be achieved by massage or local application of heat. Vasoconstrictors decrease blood flow and so decrease the absorption of a drug.
(7) ROUTE OF ADMINISTRATION : This affects drug absorption because each route has its own mechanism or pattern of absorption. This is a very important factor which determines drug absorption. Some drugs are absorbed only on parenteral administration and they fail to get absorbed on oral administration. For example, Insulin. So it is necessary to carefully choose the route of administration of drug.
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