Absorption Through the Skin
Substances that are lipid-soluble can penetrate the epidermis, although rather slowly. On reaching the dermis, the substance is absorbed into the circulation. Administering a brief pulse of electricity can speed penetration. The electrical pulse creates channels in the stratum corneum by changing the position of cells.
As a result of slow absorption, drugs are often ad-ministered via the skin, producing slow and pro-longed action over several days. Nicotine patches, an aid used by smokers to quit smoking, use this type of transdermal administration. By slow and continuous administration of nicotine, the craving for smoking is reduced. Gradually, the dosage of nicotine in the patch can be tapered. Dimethyl sulfoxide (DMSO) is a drug given for treatment of joint and muscle in-juries. Other drugs dissolved in DMSO are easily ab-sorbed through the skin. Estrogen, for the treatment of menopause, and vasodilator drugs, for increasing the coronary blood flow, are examples of transder-mally administered drugs.
Systemic adverse effects can be produced if drugs are administered transdermally for prolonged periods. For example, corticosteroids used to treat chronic in-flammation can be absorbed through the skin and pro-duce symptoms of corticosteroid excess or Cushing’s syndrome.