Erythema multiforme, allergic drug reaction

Unithiol has been reported to have a low overall incidence of adverse effects (< 4%). Self-limited dermatologic reactions (drug exanthems or urticaria) are the most commonly reported adverse effects, although isolated cases of major allergic reactions, including erythema multiforme and Stevens-Johnson syndrome, have been reported. Because rapid intravenous infusion may cause vasodilation and hypotension, unithiol should be infused slowly over an interval of 15-20 minutes. 

Salicylism and death have occurred following topical application. In an adult, 1 g of a topically applied 6% salicylic acid preparation will raise the serum salicylate level not more than 0.5 mg/dL of plasma the threshold for toxicity is 30-50 mg/dL. Higher serum levels are possible in children, who are therefore at a greater risk for salicylism. In cases of severe intoxication, hemodialysis is the treatment of choice (see Chapter 58). It is advisable to limit both the total amount of salicylic acid applied and the frequency of application. Urticarial, anaphylactic, and erythema multiforme reactions may occur in patients who are allergic to salicylates. Topical use may be associated with local irritation, acute inflammation, and even ulceration with the use of high concentrations of salicylic acid. Particular care must be exercised when using the drug on the extremities of patients with diabetes or peripheral vascular disease. 

Allergic skin reactions have been described with all sulfonylureas. They include pruritic rashes, erythema nodosum, urticaria, blisters (100), erythema multiforme, exfoliative dermatitis, Quincke s edema, erythroderma, and itching, while lichenoid drug reactions with ulceration have occurred after chlorpropamide and tolazamide (124). More generalized hypersensitivity reactions may prove fatal, but rarely. 

Adverse effects associated with ocular drugs are not imcommon, bnt serious reactions are extremely rare. These adverse reactions are nsnally manifestations of drug hypersensitivity (allergy) or toxicity. The allergic or toxic reaction usually occurs locally in the ocular tissues. Occasionally, as in erythema multiforme potentiated by sulfonamide agents, adverse reactions can manifest as a systemic response. 

Allergic skin reactions occur in 1-2% of patients who take nitrofurantoin and comprise about 21% of all adverse reactions to nitrofurantoin (5,71). They often occur with other reactions, such as drug fever, lung, or hver reactions. The lesions can present as pruritus, as macular, maculopapular, or vesicular rashes, urticaria, angioedema, or erjdhema multiforme (72). The frequency of serious cutaneous reactions (erythema multiforme, Stevens-Johnson syndrome, or toxic epidermal necrolysis) after nitrofurantoin has been estimated to be 7 cases per 100 000 exposed individuals (71). 

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