Ampicillin for Streptococcal Pharyngitis
Ampicillin is NOT a recommended first-line antibiotic for streptococcal pharyngitis—use penicillin V or amoxicillin instead. While ampicillin is effective against Group A Streptococcus (GAS), it is not included in current treatment guidelines for this indication 1, 2.
Why Ampicillin Is Not Recommended
The major clinical guidelines from both the American Heart Association (2009) and the Infectious Diseases Society of America (2012) do not list ampicillin as a treatment option for streptococcal pharyngitis 1, 2. This omission is significant because:
- Penicillin V and amoxicillin are the established oral penicillins of choice with proven efficacy, narrow spectrum, and decades of clinical experience 1
- Ampicillin has a broader spectrum than necessary, potentially selecting for more resistant organisms
- Amoxicillin is preferred over ampicillin because it has better oral bioavailability and more convenient dosing
FDA-Approved Use for Streptococcal Infections
The FDA label for ampicillin does indicate it can be used for streptococcal infections, stating that "therapy must be sufficient to eliminate the organism (10 days minimum); otherwise the sequelae of streptococcal disease may occur" 3. However, this general statement about streptococcal infections does not make it a preferred agent for pharyngitis specifically.
Key FDA Label Requirements:
- Duration: 10 days minimum to prevent rheumatic fever sequelae 3
- Take with a full glass of water, one-half hour before or two hours after meals 3
- Cultures should be taken after treatment completion to confirm eradication 3
Recommended First-Line Alternatives
For patients without penicillin allergy:
- Penicillin V: 250 mg twice daily (children) or 500 mg twice daily (adults) for 10 days 2
- Amoxicillin: 50 mg/kg once daily (max 1000 mg) or 25 mg/kg twice daily (max 500 mg per dose) for 10 days 2
- Benzathine penicillin G (IM): Single dose of 600,000 U (<27 kg) or 1,200,000 U (≥27 kg) 2
For penicillin-allergic patients (non-anaphylactic):
- First-generation cephalosporins (cephalexin, cefadroxil) for 10 days 2
Clinical Reasoning
The preference for penicillin V and amoxicillin over ampicillin is based on:
- Narrow spectrum: Minimizes disruption of normal flora and reduces selection pressure for resistance 1
- Proven efficacy: GAS has never developed resistance to penicillin 1
- Cost-effectiveness: Both are inexpensive options 1
- Better palatability: Amoxicillin suspension is more palatable than alternatives, improving adherence in children 1
- Once-daily dosing option: Amoxicillin can be given once daily, enhancing compliance 1, 4, 5
Important Caveats
- Do not use ampicillin empirically when guideline-recommended agents are available
- If ampicillin is used for any reason, ensure the full 10-day course is completed to prevent rheumatic fever 3
- Ampicillin is poorly absorbed during labor, making it unsuitable for intrapartum use 3
- Watch for drug interactions, particularly with allopurinol (increased rash risk) and oral contraceptives (reduced effectiveness) 3
The bottom line: Stick with penicillin V or amoxicillin as first-line therapy for streptococcal pharyngitis, reserving ampicillin for other indications where it is specifically indicated.