Q 2-23.
Absorption and Action of Topical Medicine; In General:
What about rise and drop in blood concentration of topical medicine?
A 2-23.
Topical medicine is used in a solution, ointment, tape and patch preparation.
Topical medicine is absorbed through the skin. The drug goes into capillary vessels and lymphatic flow at the dermal layer. Then it enters systemic circulation. The drug is not metabolized nor inactivated in the liver before it is distributed to the whole body.
Blood concentration of the drug rises to the therapeutic level in 15-30 minutes, usually. There is a difference in the absorption time between drugs.
Human skin absorbs medicine well while skin is kept wet. Absorption of a topical drug will be stopped after the skin is dried. The residual medicine on the scalp may cause contact dermatitis afterwards.
Medicine on an adhesive tape and patch keeps stable blood concentration for 12-14 hours while the tape is applied on the skin.
When we want to cancel the effect of topical medicine in an undesired situation, we can stop absorption of the drug by wiping off the solution and ointment, or by peeling off the tape. Blood concentration of the drug will drop shortly after that.
