ABSORPTION VIA TOPICAL SITES ::
Absorption of most drugs through the intact skin is poor as the keratinized epidermis behaves like a barrier However the underlying dermis is quite permeable to many drugs and significant absorption can occur if the skin is denuded The extent of absorption through the skin is proportional to the lipid solubility of the drug and the surface area to which the drug is applied Absorption can be enhanced by dissolving the drug in an oily base vigorous massanging of the area occlusive dressing or simultaneously applying a keratin softening agent like salicylic acid
Recently drugs intended for systemic action are being formulated in a way that topical application is utilized as the route of administration For example the nitroglycerin transdermal system patch This drug impregnated patch is applied to the skin of the upper torso in patients of angina pectoris Nitroglycerin is slowly absorbed through the skin to provide consistent and effective plasma levels for 12 to 24 hours Transdermal patches of scopolamine and clonidine are now also available for control of motion sickness and hypertension respectively
Absorption of most drugs through mucous membranes is usually very rapid mainly due to the thin and highly vascular absorbing surface However drugs applied to mucous membranes are generally used for their local action e.g. nasal decongestants or vaginal anti infectives Rather their systemic absorption may result in unwanted side effects Some drugs like ergotamine and vasopressin may be applied to mucous membranes to facilitate their systemic absorption
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