Should I give an intramuscular benzathine penicillin G injection to my 8‑year‑old who is already on oral amoxicillin for streptococcal pharyngitis but now has a runny nose, cough, and fever?

Do Not Give the Benzathine Penicillin G Injection

This child is already on appropriate oral amoxicillin therapy for streptococcal pharyngitis and does not require an intramuscular benzathine penicillin G injection. The new symptoms of runny nose, cough, and fever are most likely a concurrent viral upper respiratory infection, not a treatment failure of the strep throat.

Why the Injection is Not Indicated

The Patient is Already on Effective Therapy

• Oral amoxicillin is the preferred first-line treatment for streptococcal pharyngitis in children, with proven efficacy equivalent to or superior to penicillin V 1.
• The child has only been on treatment for 2 days—patients are considered non-contagious after just 24 hours of appropriate antibiotic therapy 1.
• A full 10-day course is required for maximal pharyngeal eradication and rheumatic fever prevention, but clinical improvement typically occurs within the first few days 1.

Benzathine Penicillin G Has Specific Indications

According to the American Heart Association guidelines, intramuscular benzathine penicillin G should be reserved for specific situations 1:

• Patients unlikely to complete a 10-day oral course
• Personal or family history of rheumatic fever or rheumatic heart disease
• Environmental risk factors (crowded living conditions, low socioeconomic status)

None of these indications appear to be present in this case, as the child is already taking oral medication and there is no mention of compliance concerns or high-risk factors.

The New Symptoms Suggest Viral Co-Infection

• Runny nose and cough are not typical symptoms of streptococcal pharyngitis, which classically presents with sore throat, fever, tonsillar exudates, and anterior cervical lymphadenopathy 1.
• These symptoms appearing on day 2 of appropriate antibiotic therapy strongly suggest a concurrent viral upper respiratory infection, not treatment failure.
• True treatment failure would be assessed by persistent streptococcal symptoms (sore throat, fever without upper respiratory symptoms) after 48-72 hours of therapy 2.

Risks of Unnecessary Intramuscular Injection

The FDA label for benzathine penicillin G warns of serious complications 3:

• Severe neurovascular damage including transverse myelitis with permanent paralysis
• Gangrene requiring amputation
• Nicolau syndrome with tissue necrosis
• Quadriceps femoris fibrosis and atrophy with repeated injections
• The injection is extremely painful, particularly in children

Appropriate Management

Continue Current Oral Amoxicillin

• Ensure the full 10-day course is completed to prevent rheumatic fever, regardless of symptom resolution 1, 2.
• Standard pediatric dosing is 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) 4, 2.

Manage the Viral Symptoms Supportively

• Provide symptomatic treatment for the runny nose and cough (likely viral).
• Reassess if streptococcal symptoms (throat pain, fever without URI symptoms) persist beyond 48-72 hours of antibiotic therapy 2.

When to Consider Treatment Modification

True treatment failure would warrant consideration of alternative therapy, but this would be indicated by 1, 4:

• Persistent positive throat culture with same serotype after completing therapy
• Documented chronic carrier state after multiple treatment courses
• In such cases, amoxicillin/clavulanate (40 mg/kg/day of amoxicillin component, maximum 2000 mg/day) for 10 days would be the next step, not benzathine penicillin G 1, 4.

Critical Pitfall to Avoid

Do not confuse concurrent viral illness with streptococcal treatment failure. The timing (day 2 of therapy) and symptom pattern (URI symptoms rather than persistent pharyngitis) make viral co-infection far more likely than treatment failure. Adding an unnecessary painful injection exposes the child to significant risks without clinical benefit 3.