Ciclacillin is an aminopenicillin antibiotic. Its spectrum of activity is similar to that of ampicillin, although it is less susceptible to beta-lactamases than ampicillin and has much higher bioavailability. A large randomized, double-blind clinical trial published in 1978 also showed that ciclacillin is associated with significantly fewer and milder adverse effects than ampicillin; later studies seemed to confirm this improved tolerability, at least in children. Cloxacillin is a semisynthetic penicillin widely used in nonmethicillin resistant Staphylococcus aureus infections. Several hypersensitivity reactions to cloxacillin have been reported, although IgE-mediated allergic reactions to the drug are rare and there is little information about possible tolerance to other semisynthetic penicillins or cephalosporins in patients with cloxacillin allergy.
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