Β-lactam antibiotic reactions to any β-lactam antibiotic may occur in up to 10% of patients receiving that agent (a small fraction of which are truly IgE-mediated allergic reactions, see amoxicillin rash). Anaphylaxis will occur in approximately 0.01% of patients. There is perhaps a 5%-10% cross-sensitivity between penicillin-derivatives, cephalosporins, and carbapenems; but this figure has been challenged by various investigators. Nevertheless, the risk of cross-reactivity is sufficient to warrant the contraindication of all β-lactam antibiotics in patients with a history of severe allergic reactions (urticaria, anaphylaxis, interstitial nephritis) to any β-lactam antibiotic. A Jarisch–Herxheimer reaction may occur after initial treatment of a spirochetal
Antibiotic synergy level, the boosted antimicrobial potency provided by synergy allows the body to more rapidly clear infections, resulting in shorter courses of antibiotic therapy. Shorter courses of therapy in turn reduce the effects of dose-related toxicity, if applicable. Additionally, synergy aids in total bacterial eradication, more completely removing an infection than would be possible without synergy. At a higher level, synergistic effects are useful for combating resistant bacterial strains through increased potency and for stalling the spread of bacterial resistance through the total eradication of infections, preventing the evolutionary selection of resistant cells and strains. Current research on antibiotic synergy and