Special dosage of amoxicillin for endocarditis, anthrax, and chlamydial infections

Special dosage of amoxicillin for endocarditis, anthrax, and chlamydial infections
Prevention of Bacterial Endocarditis
When selecting anti-infectives for the prevention of bacterial endocarditis, the current recommendations published by the American Heart Association (AHA) should be consulted.

When an oral regimen is used for prevention of bacterial endocarditis in patients at high or moderate risk undergoing certain dental procedures or minor upper respiratory tract surgery or instrumentation the AHA, American Dental Association (ADA), and others currently recommend that adults receive a single 2-g dose of oral amoxicillin and children receive a single 50-mg/kg dose of oral amoxicillin given 1 hour prior to the procedure. Pediatric dosage should not exceed adult dosage. Previous recommendations for prophylaxis of bacterial endocarditis in patients undergoing dental or minor upper respiratory tract procedures included use of a 2-dose regimen of amoxicillin (3 g given 1 hour prior to the procedure and 1.5 g given 6 hours later). However, because recent comparisons of these dosing schedules indicate that a single 2-g dose of amoxicillin results in adequate serum concentrations for several hours and causes fewer adverse GI effects than the previously recommended regimen, recommended dosage was lowered and the second dose is no longer considered necessary.

For prevention of enterococcal endocarditis in patients at high or moderate risk undergoing certain GI, biliary tract, or genitourinary tract surgery or instrumentation use of a 2-dose parenteral regimen is recommended for most patients; however, the AHA and others state that a single-dose regimen of parenteral ampicillin or oral amoxicillin can be considered for those with cardiac conditions that put them only at moderate risk of enterococcal endocarditis. If the single-dose amoxicillin regimen is used for prophylaxis of enterococcal endocarditis in patients at moderate risk, the AHA and others recommend that adults receive a single 2-g dose of oral amoxicillin and children receive a single 50-mg/kg dose of oral amoxicillin given 1 hour prior to the procedure. When a 2-dose regimen is used for prophylaxis of enterococcal endocarditis in patients at high or moderate risk, the first dose should consist of IM or IV ampicillin (2 g in adults or 50 mg/kg in children) given in conjunction with IM or IV gentamicin (1.5 mg/kg) and administered within 30 minutes of starting the procedure; the second dose administered 6 hours later can consist of IM or IV ampicillin (1 g in adults or 25 mg/kg in children) or, alternatively, oral amoxicillin (1 g in adults or 25 mg/kg in children). Pediatric dosage should not exceed adult dosage.

Anthrax
If oral amoxicillin is used as an alternative agent for postexposure prophylaxis following suspected or confirmed exposure to aerosolized anthrax spores (inhalational anthrax) or for the treatment of anthrax when a parenteral regimen is not available (e.g., when there are supply or logistic problems because large numbers of individuals require treatment in a mass casualty setting), the CDC and other experts (e.g., US Working Group on Civilian Biodefense) recommend that adults receive 500 mg 3 times daily and that children receive 80 mg/kg daily (maximum 1.5 mg daily) given in 3 divided doses at 8-hour intervals. Anti-infective postexposure prophylaxis should be continued until exposure to B. anthracis has been excluded. If exposure is confirmed, postexposure vaccination with anthrax vaccine (if available) may be indicated in conjunction with prophylaxis. Because of the possible persistence of anthrax spores in lung tissue following an aerosol exposure, the CDC and other experts recommend that postexposure prophylaxis be continued for 60 days.

If oral amoxicillin is used as an alternative for the treatment of mild, uncomplicated cutaneous anthrax caused by susceptible Bacillus anthracis, the CDC and other experts (e.g., US Working Group on Civilian Biodefense) recommend that adults receive 500 mg 3 times daily and that children receive 80 mg/kg daily (maximum 1.5 mg daily) given in 3 divided doses at 8-hour intervals. Cutaneous anthrax in infants and children younger than 2 years of age should be treated initially IV. Although 5-10 days of anti-infective therapy may be adequate for the treatment of mild, uncomplicated cutaneous anthrax that occurs as the result of natural or endemic exposures to anthrax, the CDC and other experts recommend that therapy be continued for 60 days if the cutaneous infection occurred as the result of exposure to aerosolized anthrax spores since the possibility of inhalational anthrax would also exist. Anti-infective therapy may limit the size of the cutaneous anthrax lesion and it usually becomes sterile within the first 24 hours of treatment, but the lesion will still progress through the black eschar stage despite effective treatment.

Chlamydial and Mycoplasmal Infections
For the treatment of chlamydial urogenital infections during pregnancy, the recommended dosage of oral amoxicillin is 500 mg 3 times daily for 7-10 days. Experience with oral amoxicillin therapy in this infection is limited and the drug may not be highly efficacious. Therefore, the CDC recommends that repeat testing (preferably by culture) should be performed 3 weeks after treatment is completed.