Magazine article Drug Topics

Skin Testing Works for Reactions When Reagents Are Lacking

Magazine article Drug Topics

Skin Testing Works for Reactions When Reagents Are Lacking

Article excerpt

It's now possible to screen patients for allergic reactions to several antimicrobial agents by simple skin tests, according to re searchers at the University of Texas Southwestern Medical Center.

Raquel Empedrad, M.D., and colleagues said this is important because few diagnostic reagents exist for most of these antimicrobials, which can spot potential IgE drug-specific immediate hypersensitivity reactions in patients. She added that, except for penicillin, antimicrobial agents are typically not immunogenic in their native form and that clinically relevant antigenic determinants formed via degradation or metabolism are unknown. That's why reagents have not been developed so far, she noted.

Empedrad's group, trying to sort out patients who might be vulnerable to allergic reactions, developed a series of intradermal skin tests that can be used to determine whether a particular antimicrobial would cause a reaction in a particular patient.

Nonirritating concentrations of antimicrobials were tested in 15 patients with no known drug allergies, Empedrad said. Each drug was reconstituted on the day of testing, and about 0.02 cc of each was injected intradermally. Wheals were measured right away and then 15 minutes later. If the wheal increased by 2 mm or more, that concentration was considered imitative, she said, and a greater dilution was tried.

The study showed that agents that are nonirritative at a 10-fold dilution were cefazolin (Ancef fox injection, SmithKline Beecham), cefuroxime (Zinacef, Glaxo Welcome), cefotaxime (Claforan, Aventis), ceftriaxone (Rocephin injectable, Roche), ceftazidime (Ceptaz and Fortaz, Glaxo; Tazicef for injection, SmithKline; Tazidime vials, Lilly), clindamycin (Cleocin, Pharmacia & Upjohn), tobramycin (Nebcin vials, Lilly; Tobramycin Sulfate Injection, Lederle Standard), and ticarcillin (Ticar for Injection and disodium, Smith-Kline). Agents nonirritative at a 100-fold dilution were trimethoprim-sulfamethoxazole (Elkins-Sinn and Lederle Standard) and gentamicin (Garamycin injectable, Schering, and Garamycin sulfate injection, Elkins Sinn).

Agents that were nonirritative at a 1,000-fold dilution were erythromycin (base filmtab and delayed-release tablets, Abbott), levofloxacin (Levaquin injection and Levaquin tablets, McNeil Pharmaceutical), and aztreonam (Azactam for injection, Dura Pharmaceuticals). …

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