Since 2007, antimicrobial prophylaxis for dental procedures has been recommended to prevent viridans group streptococcal infective endocarditis only for patients at highest risk of an adverse outcome. Limiting use to such patients does not appear to have led to an increased incidence of infective endocarditis or increased mortality due to infective endocarditis.

Most respiratory tract infections are caused by viruses. Bacterial respiratory tract infections are usually treated empirically with antibiotic therapy that targets the most probable causative pathogens. Recommended antibiotic regimens for outpatient treatment of some common respiratory tract infections are listed in Table 1 for adults and Table 2 for children.

This article includes recommendations for management of most sexually transmitted infections (STIs) other than HIV and viral hepatitis. Some of the indications and dosages recommended here have not been approved by the FDA (see Table 1).

Lyme disease in the US is caused by the spirochete Borrelia burgdorferi, which is transmitted to humans by Ixodes scapularis (blacklegged [deer] tick) and I. pacificus (western blacklegged tick). Most cases of Lyme disease occur in late spring and early summer in northeastern and mid-Atlantic states, the upper Midwest, and in northern California. B. mayonii, which is also transmitted by I. scapularis, has been shown to cause a similar illness in the upper Midwest.

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.

The FDA has approved cefiderocol (Fetroja – Shionogi), a new IV cephalosporin antibiotic, for treatment of complicated urinary tract infections (UTI) caused by susceptible gram-negative bacteria in adults who have limited or no alternative treatment options.

Eravacycline (Xerava – Tetraphase), a new synthetic tetracycline antibiotic, has been approved by the FDA for IV treatment of complicated intra-abdominal infections (cIAIs) in adults. Eravacycline is structurally similar to tigecycline (Tygacil, and generics), a broad-spectrum tetracycline approved by the FDA for IV treatment of complicated skin and skin structure infections, complicated intra-abdominal infections, and community-acquired pneumonia. A higher rate of mortality has been reported with use of tigecycline compared to other antibacterial drugs; it should be used only when no suitable alternative is available.

The FDA has warned that use of the macrolide antibiotic clarithromycin (Biaxin, and generics) may increase the risk of cardiovascular morbidity and mortality in patients with heart disease.

The FDA has approved delafloxacin (Baxdela – Melinta), an anionic fluoroquinolone antibiotic, for oral and parenteral treatment of adults with acute bacterial skin and skin structure infections (ABSSSIs), including those caused by methicillin-resistant Staphylococcus aureus (MRSA). It is the first fluoroquinolone to be approved for treatment of MRSA.

Bacterial infections in adults are generally treated empirically, with the antibiotic covering most, but not all, of the potential causative pathogens. For some infections, culture and sensitivity testing can guide treatment, allowing for use of narrower-spectrum antibiotics. The recommended dosages and durations of antibiotic treatment for common respiratory, skin, and urinary tract infections are listed in Tables 1-3. Infectious disease experts now recommend shorter treatment durations for many infections to reduce the development of antimicrobial resistance and minimize adverse effects.

The text and tables that follow include recommendations for management of sexually transmitted infections (STIs) other than HIV and viral hepatitis. Some of the indications and dosages recommended here have not been approved by the FDA.

The FDA has announced that it is requiring changes in the labeling of systemic fluoroquinolones to warn that the risk of serious adverse effects, including tendinitis, peripheral neuropathy and CNS effects, generally outweighs their benefit for the treatment of acute sinusitis, acute exacerbations of chronic bronchitis, and uncomplicated urinary tract infections. For these infections, the new labels will recommend reserving fluoroquinolones for patients with no other treatment options.

The FDA has approved ceftolozane/tazobactam (Zerbaxa – Cubist), a combination of a new cephalosporin antibiotic and a beta-lactamase inhibitor, for intravenous treatment of complicated urinary tract and intra-abdominal infections in adults.

The FDA has approved oritavancin (Orbactiv – The Medicines Company), a long-acting lipoglycopeptide antibiotic given as a single intravenous (IV) dose, for treatment of acute bacterial skin and skin structure infections caused by susceptible gram-positive bacteria in adults. It is the third lipoglycopeptide antibiotic to be marketed in the US; telavancin (Vibativ) and dalbavancin (Dalvance) were approved earlier.

Many infections can be transmitted during sexual contact. The text and tables that follow include recommendations for management of sexually transmitted infections (STIs) other than HIV, viral hepatitis, and enteric infections. Some of the indications and dosages recommended here have not been approved by the FDA.

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.

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 Medical Letter reader has asked us to review the safety of the fluoroquinolone antibiotic levofloxacin (Levaquin – Ortho-McNeil-Janssen), which has just been approved for generic use by the FDA and has been at the center of some recent lawsuits regarding the adequacy of its safety warnings.

The FDA has approved an extended-release formulation of amoxicillin (Moxatag – MiddleBrook) for once-daily treatment of pharyngitis or tonsillitis caused by Streptococcus pyogenes in adults and children ≥12 years old. Approval was based on an unpublished study that found once-daily treatment with Moxatag 775 mg for 10 days non-inferior to penicillin V 250 mg four times a day for 10 days in eradication of S. pyogenes.

For decades, the drug of choice for oral treatment of streptococcal pharyngitis in adolescents and adults has been penicillin V 250 mg taken three or four times a day.1 Amoxicillin is equally effective, but penicillin is generally recommended because of its narrower spectrum. In adults, immediate-release amoxicillin is usually dosed 375-500 mg two to three times a day, but giving it in a higher dose (750-1000 mg) once a day appears to be equally effective for treatment of strep throat.2-4

Each Moxatag tablet contains 775 mg of amoxicillin divided into one immediate-release and two delayedrelease components. Compared to a similar dose of immediate-release amoxicillin suspension, absorption of amoxicillin from the new formulation is slower, resulting in a lower peak serum concentration, but the elimination half-life and amoxicillin exposure (AUC) are similar. S. pyogenes is susceptible to these serum concentrations, but they may be too low to treat other types of infections.

A 10-day supply of Moxatag is expected to cost about $100 compared to $4 for a similar course of penicillin V or immediate-release amoxicillin.5 There is no good reason to prescribe Moxatag.

1. A Bisno et al. Practice guidelines for the diagnosis and management of group A streptococcal pharyngitis. Infectious Disease Society of America. Clin Infect Dis 2002; 35:113.
2. P Shvartzman et al. Treatment of streptococcal pharyngitis with amoxycillin once a day. BMJ 1993; 306:1170.
3. HM Feder Jr. et al. Once-daily therapy for streptococcal pharyngitis with amoxicillin. Pediatrics 1999; 103:47.
4. HW Clegg et al. Treatment of streptococcal pharyngitis with once-daily compared with twice-daily amoxicillin: a noninferiority trial. Pediatr Infect Dis J 2006; 25:761.
5. Retail cost at one Walgreens pharmacy. February 27, 2009.

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Antimicrobial prophylaxis can decrease the incidence of infection, particularly surgical site infection, after certain procedures. Recommendations for prevention of surgical site infection are listed in this article.

Two types of oral contraceptives are available in the USA: combination oral contraceptives that contain both an estrogen and a progestin, and progestin-only contraceptives, or "mini-pills."Used as directed, all oral contraceptives marketed in the USA are similarly effective in preventing pregnancy.

Lyme disease is caused by the spirochete Borrelia burgdorferi and transmitted to humans by Ixodes ticks. These ticks may also carry other pathogens; co-transmission of Babesia and Ehrlichia species has been reported.

Cefdinir (Omnicef - Parke-Davis), a third-generation oral cephalosporin, has been approved by the FDA for treatment of acute sinusitis, otitis media, acute exacerbations of chronic bronchitis, pharyngitis, community-acquired pneumonia and skin infections. Other drugs available for these indications are reviewed in The Medical Letter Handbook of Antimicrobial Therapy, 1998.

Now that US Secretary of Defense has decided to vaccinate more than 2 million memebers of the US armed forces against anthrax, US physicians may be asked to answer some questions about the vaccine and the disease.

Results of recently completed clinical trials have led to some changes in recommendations for treatment of human immunodeficiency virus (HIV) and other infections associted with AIDS.

A growing number of clinical trials now permits some consensus on the treatment of human immunodeficiency virus (HIV) and other infections associated with acquired immune deficiency syndrome (AIDS) in adults.

Ofloxacin (Floxin - McNeil, Ortho), a new fluoroquinolone antibacterial agent, was recently marketed in the USA for oral treatment of various infections caused by susceptible microorganisms. Ofloxacin is the third fluoroquinolone to become available in this country. Norfloxacin (Noroxin - Medical Letter, 29:25, 1987) is marketed only for treatment of urinary tract infections. Ciprofloxacin (Cipro - Medical Letter, 30:11, 1988), like ofloxacin, is approved for use in a variety of infections.

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.