Amoxicillin shares the uses of other aminopenicillins and is used principally for the treatment of infections caused by susceptible gram-negative bacteria (e.g., Haemophilus influenzae, Escherichia coli, Proteus mirabilis, Salmonella). Amoxicillin also is used for the treatment of infections caused by susceptible gram-positive bacteria (e.g., Streptococcus pneumoniae, enterococci, nonpenicillinase-producing staphylococci, Listeria); however, like other aminopenicillins, amoxicillin generally should not be used for the treatment of streptococcal or staphylococcal infections when a natural penicillin would be effective.
Acute Otitis Media
Amoxicillin is used for the treatment of acute otitis media (AOM) caused by S. pneumoniae, H. influenzae, or M. catarrhalis. Amoxicillin usually is considered the drug of first choice for initial treatment of AOM, unless the patient has severe illness (moderate to severe otalgia or fever 39°C or higher) or the infection is suspected of being caused by β-lactamase-producing H. influenzae or M. catarrhalis, in which case amoxicillin and clavulanate potassium is recommended for initial treatment. The American Academy of Pediatrics (AAP), American Academy of Family Physicians (AAFP), US Centers for Disease Control and Prevention (CDC), and others state that, despite the increasing prevalence of multidrug-resistant S. pneumoniae and presence of β-lactamase-producing H. influenzae or M catarrhalis in many communities, amoxicillin remains the anti-infective of first choice for treatment of uncomplicated AOM since it is highly effective, has a narrow spectrum of activity, is well distributed into middle ear fluid, is well tolerated, has an acceptable taste, and is inexpensive. Amoxicillin (when given in a dosage of 80-90 mg/kg daily) usually is effective in the treatment of AOM caused by S. pneumoniae, including infections involving strains with intermediate resistance to penicillins, and also usually is effective in the treatment of AOM caused by most strains of H. influenzae.
Alternatives for initial treatment of AOM in patients with a history of non-type I hypersensitivity reactions to penicillins include oral cephalosporins (cefdinir, cefpodoxime, cefuroxime axetil) or parenteral ceftriaxone. Alternatives for patients with type I penicillin hypersensitivity include oral macrolides (azithromycin, clarithromycin, fixed combination of erythromycin and sulfisoxazole), oral co-trimoxazole, or oral clindamycin (especially in those with infections known or presumed to be caused by penicillin-resistant S. pneumoniae).
AAP, AAFP, and others recommend that patients who fail to respond to an initial amoxicillin regimen (given in a dosage of 80-90 mg/kg daily) within 48-72 hours should be retreated using a regimen of amoxicillin and clavulanate potassium (90 mg/kg of amoxicillin and 6.4 mg/kg of clavulanate daily in 2 divided doses). Alternatively, a 3-day regimen of IM or IV ceftriaxone can be used for retreatment in those who fail to respond to an initial amoxicillin regimen, especially in those who have severe illness (moderate to severe otalgia or fever 39°C or higher) and in those who are vomiting or cannot otherwise tolerate an oral regimen.
For additional information regarding treatment of AOM, including information on diagnosis and management strategies, anti-infectives for initial treatment, duration of initial treatment, and anti-infectives for retreatment and for information on current recommendations regarding management of otitis media with effusion (OME), .
Amoxicillin is used as an alternative agent for postexposure prophylaxis following exposure to Bacillus anthracis spores, 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), and for the treatment of cutaneous anthrax. Strains of B. anthracis with naturally occurring penicillin resistance have been reported rarely, and there are published reports of B. anthracis strains that have been engineered to have penicillin and tetracycline resistance as well as resistance to other anti-infectives (e.g., macrolides, chloramphenicol, rifampin). Therefore, it has been postulated that exposures to B. anthracis that occur in the context of biologic warfare or bioterrorism may involve bioengineered resistant strains and this concern should be considered when selecting initial therapy for the treatment of anthrax that occurs as the result of bioterrorism-related exposures or for postexposure prophylaxis following such exposures. For additional information on treatment of anthrax and recommendations for postexposure prophylaxis following exposure to anthrax spores,
Ciprofloxacin or doxycycline generally are considered the initial drugs of choice for postexposure prophylaxis following suspected or confirmed exposure to aerosolized B. anthracis spores that occurs in the context of biologic warfare or bioterrorism. If exposure is confirmed and results of in vitro testing indicate that the organism is susceptible to penicillin, then postexposure prophylaxis may be switched to a penicillin (e.g., oral amoxicillin, oral penicillin V). IM penicillin G procaine also has been recommended as an alternative for postexposure prophylaxis. Although monotherapy with a penicillin is not recommended for the treatment of clinically apparent inhalational anthrax when high concentrations of the organism are likely to be present, penicillins may be considered an option for anti-infective prophylaxis when ciprofloxacin and doxycycline are contraindicated, since the likelihood of β-lactamase induction resulting in an increase in penicillin MICs is lower when only a small number of vegetative cells are present.
Although the CDC and other experts recommend that postexposure prophylaxis in children be initiated with ciprofloxacin or doxycycline, if exposure has been confirmed and in vitro tests indicate that the organism is susceptible to penicillin, the postexposure prophylaxis regimen in children may be switched to oral amoxicillin or oral penicillin V.
The possible benefits of postexposure prophylaxis against anthrax should be weighed against the possible risks to the fetus when choosing an anti-infective for postexposure prophylaxis in pregnant women. The CDC and other experts state that ciprofloxacin should be considered the drug of choice for initial postexposure prophylaxis in pregnant women exposed to B. anthracis spores and that, if in vitro studies indicate that the organism is susceptible to penicillin, then consideration can be given to changing the postexposure regimen to amoxicillin. Women who become pregnant while receiving anti-infective prophylaxis should continue the existing regimen and consult with a healthcare provider or public health official to discuss whether an alternative regimen might be more appropriate.
Although natural penicillins (e.g., oral penicillin V, IM penicillin G benzathine, IM penicillin G procaine) generally have been considered drugs of choice for the treatment of mild, uncomplicated cutaneous anthrax caused by susceptible strains of B. anthracis that occurs as the result of naturally occurring or endemic exposure to anthrax, the CDC recommends use of oral ciprofloxacin or oral doxycycline for the treatment of cutaneous anthrax that occurs following exposure to B. anthracis spores in the context of biologic warfare or bioterrorism. Therapy may be changed to oral amoxicillin if results of in vitro susceptibility testing indicate that the organism is susceptible to the drug and the patient is improving. Use of a multiple-drug parenteral regimen is recommended for the initial treatment of cutaneous anthrax when there are signs of systemic involvement, extensive edema, or lesions on the head and neck.
For young children (i.e., younger than 2 years of age), initial therapy for cutaneous anthrax should be IV rather than oral, and combination anti-infective therapy should be considered since it currently is not known whether infants and young children are at increased risk of systemic dissemination of cutaneous anthrax.
For more specific information on the uses of amoxicillin, see Uses in the Aminopenicillins General Statement 8:12.16.08.
For information on the uses of amoxicillin in fixed-ratio combinations with clavulanic acid, see Amoxicillin and Clavulanate Potassium 8:12.16.08.