[Side effects and consequences of frequently used antibiotics in clinical practice].

Oral antimicrobial substances belonging to the beta-lactams, quinolones, macrolides, tetracyclines and the trimethoprim-sulfamethoxazole combination are among the most prescribed classes of drugs in private practice. Knowledge of the potential side effects considered in the light of various patient-associated factors such as genetic makeup, renal and liver function, underlying diseases, drug allergies and coadministered drugs, is important in order to minimize the risk of adverse reactions. This article reviews important side effect patterns and focuses on more recent aspects of antibiotic-associated diarrhea and beta-lactam allergy relevant to the practicing physician. Diarrhea occurring during antibiotic treatment raises the possibility of Clostridium-difficile-associated disease, which may evolve into life-threatening toxic megacolon. Mild cases with resolving symptoms after discontinuation of the antibiotic usually do not require further workup. More severe cases with watery diarrhea, abdominal pain, dehydration and electrolyte abnormalities warrant rapid diagnosis, cessation of antibiotic treatment and specific treatment including oral metronidazole. The use of oral vancomycin as a first line drug is discouraged because of the possibility of selecting vancomycin-resistant enterococci. Hypersensitivity reactions to beta-lactams are the most important type of side effects which can often be prevented. Patients with a history of beta-lactam associated IgE-mediated hypersensitivity (hives, wheezing or hypotension) should undergo penicillin skin testing. The frequently observed maculopapular rash associated with aminopenicillins without hives is in most cases not caused by an IgE-mediated mechanism. Patients with previous life-threatening penicillin allergy such as anaphylaxis or Lyell's syndrome should not undergo skin testing. Currently available tests do not reliably predict cephalosporin hypersensitivity. More recent data suggest that crossreactivity between penicillins and cephalosporins is infrequent. It thus seems safe to administer a cephalosporin to a penicillin-allergic patient, though excluding patients with previous life-threatening penicillin reactions.