Local drug therapy

Local anesthetics produce loss of sensation and make it possible for many surgical procedures to be performed without a general anesthetic. Barring any complications, the need for the patient to remain overnight in the hospital is obviated. Local anesthetics are also used to anesthetize specific peripheral nerves or larger nerve trunks. These nerve blocks can provide relief in painful conditions like rib fractures, but they are most frequently used to anesthetize an extremity during hand or foot surgery. Spinal anesthesia and epidural anesthesia, in which a local anesthetic is injected into the subarachnoid or epidural space of the lumbar (lower back) area of the spinal canal, provide pain relief during childbirth or surgery that involves the pelvic area yet lack the problems associated with a general anesthetic. Topical anesthetics, a type of local anesthetic, are also used on the skin, in the eye’s conjunctiva and cornea, and in the mucous membranes of the nose, mouth, larynx, vagina, or urethra.

Medications prescribed for dermatologic disorders account for a large amount of local drug therapy, whether it be a substance to stimulate hair growth or to soothe a burning and itching rash. Many different corticosteroid preparations are available to treat eczema, allergic reactions to substances like poison ivy, or seborrheic dermatitis. Sunblocks are used to protect the skin against ultraviolet rays and prevent skin cancer that can result from exposure to such radiation. Acne is controlled with skin cleansers, keratolytics to promote peeling, and topical antibiotics to prevent or treat infection. Physicians use various wet dressings, lotions, gels, creams, and ointments to treat acutely inflamed weeping and crusting sores and to moisturize and protect dry, cracked, and scaling skin. Burns heal more rapidly and with less scarring when treated appropriately with topical preparations like silver sulfadiazine. Candida infections of the mucous lining of the mouth (i.e., thrush) or the vagina respond to nystatin or one of the imidazole drugs. The traditional treatment of genital warts has been the topical application of podophyllin, a crude resin. The emergence of new technologies in the latter part of the 20th century, however, made possible the development of interferon-α, which is effective in the majority of patients when injected into the lesion itself or subcutaneously below it.

Most ophthalmic drugs are local—eye drops to treat glaucoma, steroid-antibacterial mixtures to treat infection, artificial tears for dry-eye syndromes, or mydriatics (drugs causing dilation of the pupil), like atropine, that facilitate refraction and internal examination of the eye.

Chemotherapy

Chemotherapy is the treatment of disease using chemical agents that are intended to eliminate the causative organism without harming the patient. In the strict sense, this applies to the use of antibiotics to treat such invading organisms as bacteria, viruses, fungi, or parasites. The term is commonly used, however, to describe the use of drugs to treat cancer, in which case the target is not a causative organism but abnormally multiplying cells. The purpose of the therapy is to selectively kill tumour cells and to leave normal cells unharmed—a very difficult task because most drugs have a narrow therapeutic zone beyond which they harm normal cells as well as cancer cells.

Anticancer drugs are only relatively selective for cancer cells, and the toughest task for the physician is to select a drug that will destroy the most cancer cells, leave normal cells unharmed, and cause the fewest unpleasant and undesirable side effects. The therapeutic goal is to favourably balance the risk-benefit ratio in which the morbidity of the treatment is weighed against its potential benefits. If a treatment causes patients to be miserable and has only a slight chance of prolonging life, many patients will forego further treatment. However, if the potential for significantly prolonging survival by aggressive therapy exists, the patient may decide to continue with the therapy.

The effectiveness of chemotherapy depends on the highest possible concentration of the drug being at the tumour site sufficiently long to kill the tumour cells. The maximal opportunity for a cure exists in the early stage of the disease, when the tumour is small and localized. The larger and more disseminated the tumour, the more difficult it is to eradicate. The stage the tumour is in will also determine the route of administration, which can be oral, intravenous, intra-abdominal, intrathecal (into the subarachnoid space of the spinal cord), or intra-arterial—specifically, into the artery feeding the tumour.

Suppression of bone marrow activity, which results in a decrease in blood cell production, represents the most limiting factor in chemotherapy. Because chemotherapy is most effective when used at the highest nontoxic dose, the interval between treatments may need to be prolonged to prevent complete bone marrow suppression. Supportive measures undertaken when bone marrow suppression occurs include repeated platelet transfusions (to combat bleeding caused by diminished platelet production) and white blood cell transfusions (to control infection).

Adjuvant chemotherapy is the use of drugs to eradicate or suppress residual disease after surgery or irradiation has been used to treat the tumour. This is necessary because distant micrometastases often occur beyond the primary tumour site. Adjuvant chemotherapy reduces the rate of recurrence of some cancers, especially ovarian cancer, osteogenic sarcoma, colorectal cancer, and nephroblastoma. The antiestrogen drug tamoxifen has been effective in selected patients with breast cancer.