TOPICAL gastrointestinal

The H2 Receptor and Its Ligands. The discovery of H2 receptors and antagonists occurred in 1972. This topic, including therapeutic implications, is considered in more detail elsewhere (see GASTROINTESTINAL AGENTS). 

Compounds in animal diets can exert their effects in the gastrointestinal tract or after absorption through the gut epithelial tissue into the bloodstream, or both. On some occasions the administered compounds may be applied topically (Table 1). 

Goldenseal Hydrastis canadens s Antiseptic for skin (topical), astringent for mucous membranes (mouthwash), wash for inflamed eyes, sinus infections, peptic ulcers, colitis, gastritis Large doses may cause dry or irritated mucous membranes and injury to the gastrointestinal system may reduce the beneficial bacteria in the intestines. Siould not be taken for more than 3-7 days. 

Animal experiments into the effect of ingestion of chryso-tile asbestos demonstrated an accumulation of cellular debris within the lumen of the ileum and colon consistent with cytotoxic changes of the mucosal lining cells (Jacobs etal., 1978). The question as to whether asbestos causes tumours in the gastrointestinal tract in humans is a topic of concern, however, the evidence remains equivocal (Levine, 1985). 

See Chap. 117, Gastrointestinal Infections and Enterotoxigenic Poisonings, authored by Steven Martin and Rose Jung, for a more detailed discussion of this topic. 

Gentamicin is an aminoglycoside. As aminoglycosides are not absorbed from the gastrointestinal tract, gentamicin is only presented for parenteral or topical use (as eye/ear drops). 

Topical anesthesia Local use of drugs of this kind on the mucous membranes of the nose, mouth, larynx, tracheobrachial tree, eyes, urinary tract, and gastrointestinal tract causes superficial anesthesia. 

Mucocutaneous infections caused primarily by the fungus Candida albicans occm in regions of moist skin and mucous membranes (i.e. gastrointestinal tract, perianal, and vulvovaginal areas). Amphotericin B, miconazole, clotrimazole, and nystatin are used topically to treat such infections. For chronic infections, ketoconazole is taken orally. 

Topical formulations of nystatin and of amphotericin B are useful in the management of Candida albicans infections of the skin. Both antibiotics are ineffective against dermatophytes. The use of nystatin is limited to topical treatment of cutaneous and mucosal Candida infections because of its narrow spectrum and its negligible absorption from the gastrointestinal tract. Hypersensitivity reactions are rare. It is not known whether topical nystatin can cause fetal harm when used by a pregnant woman. Amphotericin B has broader antifungal activity but its topical use is restricted to Candida. Topical use of amphotericin B has shown minimal absorption through the skin and is well tolerated. Limited human surveillance data do not indicate any harm to mother or fetus, but relative safety is still unknown. 

Bethanechol should not be used in patients with possible mechanical obstruction of the bladder or gastrointestinal tract or when contraction of smooth muscles in these tissues may be harmful (e.g., recent intestinal resection). It is also contraindicated in patients with bronchial asthma, peptic ulcer disease, coronary artery disease, gastrointestinal hypermotility or inflammatory disease, hypotension or marked bradycardia, hyperthyroidism, parkinsonism, or epilepsy. Care should be exercised in administering pilocarpine to elderly patients because it can enter the CNS and affect memory and cognition, even when applied topically to the eye. 

Bacitracin is primarily a topical antibiotic. Previously, it was administered intramuscularly, but the toxicity associated with its parenteral administration has precluded systemic use. The bacitracins are not absorbed from the gastrointestinal tract following oral administration. 

Ineffective topically, griseofulvin is administered orally but has poor gastrointestinal absorption absorp-... 

Fluorouracil is used in several combination regimens in the treatment of breast cancer. It also has palliative activity in gastrointestinal adenocarcinomas, including those originating in the stomach, pancreas, liver, colon, and rectum. Other tumors in which some antitumor effects have been reported include carcinomas of the ovary, cervix, oropharynx, bladder, and prostate. Topical 5-fluorouracil cream has been useful in the treatment of premalignant keratoses of the skin and superficial basal cell carcinomas, but it should not be used in invasive skin cancer. 

Nystatin is a polyene macrolide much like amphotericin B. It is too toxic for parenteral administration and is only used topically. Nystatin is currently available in creams, ointments, suppositories, and other forms for application to skin and mucous membranes. It is not absorbed to a significant degree from skin, mucous membranes, or the gastrointestinal tract. As a result, nystatin has little toxicity, although oral use is often limited by the unpleasant taste. 

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