A reader who took the online continuing medical education (CME) exam for issue 1406 (Med Lett Drugs Ther 2012; 54:101) pointed out that the first question assumed that a rash following oral administration of ampicillin would be due to allergy. Perhaps we should have mentioned in our article on penicillin allergy that late-appearing maculopapular rashes associated with oral ampicillin or amoxicillin are generally considered non-allergic and need not preclude subsequent administration of ampicillin or amoxicillin.

Only a small minority of patients who say they are allergic to penicillin will have a reaction if they take a penicillin.

A penicillin is the drug of choice for treatment of many infections, but allergic reactions to these drugs occur frequently and, rarely, can be fatal. From 5% to 20% of patients have a history of a rash or some other reaction while taking a penicillin, but maculopapular rashes with ampicillin or amoxicillin, especially in children with infectious mononucleosis, are probably not allergic.

Treatment of community-acquired pneumonia (CAP) is usually empiric, with selected antibiotic regimens directed against some of the most common causative pathogens. Recommended empiric regimens are listed in Table 2; recommended antibiotic dosages for treatment of CAP are listed in Tables 3 and 4. Joint guidelines for treatment of CAP by the American Thoracic Society and the Infectious Diseases Society of America (ATS/IDSA) were updated in 2019.

Many physicians believe that antimicrobial prophylaxis before procedures that may cause transient bacteremia can prevent endocarditis and prosthetic joint infection in patients at increased risk for these disorders. The effectiveness of this common practice has never been established by controlled trials in humans.

Piperacillin/tazobactam (Zosyn - Lederle), an antibiotic combination product, has been approved by the US Food and Drug Administration for intravenous treatment of intra-abdominal, pelvic, skin, and skin-structure infections and for community-acquired pneumonia of moderate severity.

Tigecycline (Tygacil - Wyeth), a derivative of minocycline, is a new intravenous (IV) antibiotic approved for treatment of complicated intra-abdominal and skin and skin-structure infections.

Antimicrobial prophylaxis can decrease the incidence of postoperative surgical site infection after some procedures. Since the last Medical Letter article on this subject, consensus guidelines have been published. Recommendations for prophylaxis in specific surgical procedures are listed in Table 1.

The FDA has approved ceftaroline fosamil (Teflaro – Forest), an intravenous (IV) cephalosporin, for treatment of acute bacterial skin and skin structure infections, including those caused by methicillin-resistant Staphylococcus aureus (MRSA), and for treatment of community-acquired bacterial pneumonia in adults. It is the first beta-lactam antibiotic approved for treatment of MRSA.

The text that follows reviews some common bacterial infections and their empiric treatment pending the results of culture and susceptibility testing. The recommendations made here are based on the results of susceptibility studies, clinical trials, and the opinions of Medical Letter reviewers. Tables 1 and 2 list the usual dosages of antibacterial drugs.