The Aminopenicillins:  Ampicillin and Amoxicillin

• Therapeutic Uses

  • Respiratory Tract Infections

    • Upper respiratory tract infections

      • Amoxicillin is a first-line therapy for many upper respiratory infections.

        • In acute otitis media (middle ear infection) and acute bacterial sinusitis, amoxicillin (often at high doses) is typically recommended as first-line treatment.²

          • Amoxicillin covers the primary bacterial causes, Streptococcus pneumoniae (most common) and non-beta-lactamase-producing Haemophilus influenzae, as well as Streptococcus pyogenes and Moraxella catarrhalis (though M. catarrhalis usually produces beta-lactamase, so amoxicillin-clavulanate is preferred if M. catarrhalis is suspected).³

          • Guidelines, such as the IDSA’s sinusitis guideline, endorse amoxicillin (or amoxicillin-clavulanate) as empiric therapy for acute bacterial sinusitis in adults and children.^2,4

          • For streptococcal pharyngitis (strep throat), penicillin V remains the narrow-spectrum drug of choice⁵, but amoxicillin is frequently used interchangeably in pediatrics and adults, given its pleasant taste (as a liquid) and convenient dosing.

           

          Acute Pharyngitis Audio Overview

           

          • Acute Pharyngitis⁵

            "Patient exhibiting redness and edema of the oropharynx, and petechiae." Attribution CDC group A Strept Infection. Clinical Guidance for group A Streptococcal Pharyngitis. Health Care Providers. August 5, 2025. https://www.cdc.gov/group-a-strep/hcp/clinical-guidance/strep-throat.html

          • Amoxicillin effectively eradicates Group A Streptococcus from the tonsillopharynx in pharyngitis when given for 10 days, similar to penicillin.⁵

    • Lower respiratory tract infections

      Community Acquired Pneumonia Audio Overview

      • Aminopenicillins also play a major role in community-acquired pneumonia (CAP) and other lower respiratory infections.

      • Community-acquired pneumonia in otherwise healthy adults is often due to S. pneumoniae, and amoxicillin is now recognized as an appropriate first-line agent for outpatient treatment of mild CAP.

        • Chest X-Ray:  Community Acquired Pneumonia

          Attribution Agrawal, R Community Acquired Pneumonia on Chest X-Ray Dec 19, 20129 https://www.youtube.com/watch?v=XDBO8st8okM Slide Presentation:  https://docs.google.com/presentation/d/1mQaP0-jSG6Dj9LPHk6L5913Lu7yTlVEZjK_t8f9xELg/edit?slide=id.p#slide=id.p

        • The 2019 IDSA/ATS pneumonia guidelines explicitly added high-dose amoxicillin (1 g three times daily) as a preferred empiric option for outpatient CAP in adults without comorbidities.⁶ 

          • Amoxicillin monotherapy covers pneumococcus (including intermediate-resistant strains, if high doses are used)⁷, but it does not cover atypical pneumonia pathogens (Mycoplasma, Chlamydophila, Legionella).

            • If atypical coverage is needed or if the patient has certain risk factors, combination therapy is used^8,9 (e.g. amoxicillin + a macrolide such as azithromycin).

      • For acute bacterial bronchitis or acute exacerbations of chronic bronchitis, aminopenicillins can be used if H. influenzae or Streptococcus species (non-beta-lactamase producing) are the likely cause.¹⁰

      • In pediatric pneumonia, amoxicillin is also the first-line treatment.

        • The WHO recommends oral amoxicillin dispersible tablets as the antibiotic of choice for childhood pneumonia in outpatient settings.¹¹