What antibiotics can be given together for a patient with conjunctivitis and strep throat?

Antibiotic Selection for Concurrent Conjunctivitis and Strep Throat

For a patient with both bacterial conjunctivitis and strep throat, use topical moxifloxacin (or another fluoroquinolone) eye drops for the conjunctivitis and oral penicillin or amoxicillin for the strep throat—these antibiotics can be safely given together without drug interactions. 1, 2

Treatment Algorithm

For Strep Throat (Group A Streptococcal Pharyngitis)

First-line systemic therapy:

• Penicillin V oral: 50 mg/kg per day in 2-3 divided doses (maximum 500 mg per dose) for 10 days 1
• Amoxicillin oral: 50 mg/kg once daily (maximum 1 g) for 10 days 1
• Penicillin G benzathine IM: Single dose of 600,000 U for patients <27 kg or 1,200,000 U for patients ≥27 kg 1

Alternative options if penicillin-allergic:

• Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days 1
• Cephalexin: 20 mg/kg per dose twice daily (maximum 500 mg per dose) for 10 days (avoid in immediate hypersensitivity to penicillin) 1
• Clindamycin: 7 mg/kg per dose three times daily (maximum 300 mg per dose) for 10 days 1

For Bacterial Conjunctivitis

First-line topical therapy:

• Moxifloxacin 0.5%: 1 drop in affected eye 3 times daily for 7 days 1, 2
• Alternative fluoroquinolones: Levofloxacin, gatifloxacin, ciprofloxacin, or besifloxacin are all effective against common bacterial pathogens including Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus 1, 3

The American Academy of Ophthalmology recommends a 5-7 day course of broad-spectrum topical antibiotic for mild to moderate bacterial conjunctivitis 3, 4

Safety of Concurrent Use

These medications can be safely administered together because:

• Topical fluoroquinolones have minimal systemic absorption and do not interact with oral penicillins or macrolides 1, 2
• Drug interaction studies indicate moxifloxacin does not inhibit cytochrome P450 enzymes (CYP3A4, CYP2D6, CYP2C9, CYP2C19, CYP1A2), making drug interactions unlikely 2
• No contraindications exist for combining topical ophthalmic antibiotics with systemic antibiotics for pharyngitis 1

Important Clinical Considerations

If Using Azithromycin for Strep Throat

You can still use topical fluoroquinolones for conjunctivitis concurrently. While azithromycin has activity against conjunctivitis pathogens, the American Academy of Pediatrics explicitly endorses topical fluoroquinolones as effective therapy for bacterial conjunctivitis, and systemic azithromycin dosed for pharyngitis does not provide adequate ocular coverage 1, 3

Special Situations Requiring Different Approach

Do NOT use this standard approach if:

• Severe purulent discharge with copious exudate suggests possible gonococcal conjunctivitis—requires ceftriaxone 250 mg IM single dose PLUS azithromycin 1 g oral single dose, with daily ophthalmology monitoring 1, 3
• Neonatal conjunctivitis (age <1 month)—requires systemic antibiotics coordinated with pediatrics 1, 3
• Contact lens wearer with conjunctivitis—requires culture and consideration of Pseudomonas coverage 3, 5
• No improvement after 3-4 days of topical therapy—obtain cultures and consider resistant organisms including MRSA 3, 4

Critical Pitfalls to Avoid

• Never use topical corticosteroids (like Tobradex) without definitively ruling out viral conjunctivitis, as steroids can prolong adenoviral infections and worsen HSV infections 3
• Avoid contact lens wear during treatment of bacterial conjunctivitis 2
• Do not use doxycycline or fluoroquinolones systemically in pregnant patients or children <8 years for strep throat—use penicillin, amoxicillin, or azithromycin instead 1
• Geographic resistance patterns matter—macrolide resistance to Group A Streptococcus varies temporally and geographically, making penicillin/amoxicillin preferred first-line agents 1

Dosing Convenience Advantage

The combination of once-daily oral amoxicillin for strep throat plus three-times-daily moxifloxacin eye drops for conjunctivitis provides a practical regimen with good adherence potential 1, 2. Moxifloxacin requires less frequent dosing (TID) compared to older fluoroquinolones like ciprofloxacin or ofloxacin (QID) 4, 2