Gastrointestinal tract treatment, topical

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. 

Nystatin [nye STAT in] is a polyene antibiotic its structure, chemistry, mode of action, and resistance resemble those of amphotericin B. Its use is restricted to topical treatment of Candida infections because of its systemic toxicity. The drug is negligibly absorbed from the gastrointestinal tract, and it is never used par-enterally. It is administered as an oral agent ( swish and swallow ) for the treatment of oral candidiasis. Excretion in the feces is nearly quantitative. Adverse effects are rare because of its lack of absorption, but occasionally nausea and vomiting occur. 

Terbinafine interferes with ergosterol biosynthesis, and thereby with the formation of the fungal cell membrane. It is absorbed from the gastrointestinal tract and undergoes extensive metabolism in the liver (tj 14 h). Terbinafine is used topically for dermatophyte infections of the skin and orally for infections of hair and nails where the site (e.g. hair), severity or extent of the infection render topical use inappropriate (see p. 315). Treatment (250 mg/d) may need to continue for several weeks. It may cause nausea, diarrhoea, dyspepsia, abdominal pain, headaches and cutaneous reactions. 

Carbachol is a quaternary ammonium compound that shares both the muscarinic and nicotinic actions of acetylcholine but is much more slowly deactivated. Carbachol has been used topically in ophthalmology and systemically (subcutaneously, for example in doses of 2 mg/day) for urinary retention. Severe cholinergic effects can result. In one instance they primarily involved the gastrointestinal tract and the patient died of esophageal rupture (1). In other cases patients have experienced extreme bradycardia with hypotension, requiring treatment with intravenous atropine. As carbachol is not destroyed by cholinesterase, a cumulative effect is possible in patients who receive regular doses at short intervals in one case, hypotension only developed on the third treatment day (2). 

Interest in the adhesion of dosage forms to epithelial surfaces has heen aroused hy the possihility of deliberate contact between oral dosage forms and the gut wall to retard the rate of transit down the gastrointestinal tract, but also by the possibility of dosage forms accidentally adhering to the oesophagus or other epithelial surfaces. Adhesive preparations have been formulated for diverse tasks such as the topical treatment of stomatitis and the administration of insulin. The adhesive nature of transdermal patches is important, as is the adhesion of film coats to tablet surfaces. Adhesion of erythrocytes and bacterial cells to polymer surfaces is also of importance in the understanding, respectively, of blood compatibility of polymers and bacterial infection mediated by catheters. 

Polymyxin B is also commonly used in topical preparations to treat local infections. Like bacitracin A, it is also not absorbed by the gastrointestinal tract, so oral administration is ineffective except in treatment of intestinal infections. Bacitracin A and polymyxin B target different bacteria and are therefore commonly mixed together in topical preparations, such as Neosporin. 

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