Patients who have received amoxicillin in the last 30 days should be treated with Amoxicillin-clavulanate.
Otitis media is the most common reason antibiotic are prescribed in children. Most infections are mixed with both viral and bacterial pathogens. The most common bacterial pathogens are Streptococcus pneumoniae, nontypeable Haemophilus influenzae, and Moraxella catarrhalis. Group A streptococcus is less commonly seen.
Beta-lactam antibiotics such as cephalosporins and penicillins target cell wall proteins called penicillin binding proteins. Streptococcus pneumoniae can develop resistance to beta-lactams through modification of this protein. Most strains remain susceptible to high dose oral amoxicillin.
Around half of H influenzae isolates from otitis media cases produce a beta-lactamase making them resistant to amoxicillin. These strains would be covered by Amoxicillin-clavulanate or a second or third generation cephalosporin.
M catarrhalis uniformly produces a beta-lactamase creating resistance to amoxicillin though the natural history of M catarrhalis is less severe than other pathogens.
Amoxicillin is typically first line as at high dose it covers most pneumococcus and about half of H influenzae however Amoxicillin-clavulanate should be used in those who have received amoxicillin in last 30 days.
Lieberthal AS, Carroll AE, Chonmaitree T, Ganiats TG, Hoberman A, Jackson MA, Joffe MD, Miller DT, Rosenfeld RM, Sevilla XD, Schwartz RH, Thomas PA, Tunkel DE. The diagnosis and management of acute otitis media. Pediatrics. 2013 Mar;131(3):e964-99. PMID: 23439909