Unacyn (Erythromycin and Sulfisoxazole) Dosage Regimen for Bacterial Infections
The typical dosage regimen for Unacyn (erythromycin and sulfisoxazole) in adults is erythromycin 250 mg orally four times daily with sulfisoxazole at appropriate doses, while children should receive erythromycin 40 mg/kg/day in divided doses every 6 hours. 1
Adult Dosing
- Erythromycin component: 250 mg orally four times daily (or erythromycin ethylsuccinate 400 mg four times daily) 1
- For specific infections such as community-acquired cutaneous anthrax: erythromycin 250 mg orally every 6 hours 1
- For more severe infections requiring parenteral therapy: erythromycin lactobionate 15-20 mg/kg IV in divided doses every 6 hours (maximum 4g daily) 1
Pediatric Dosing
- Erythromycin component: 40 mg/kg/day divided into four doses 1
- Sulfisoxazole component: 100-150 mg/kg/day (based on clinical evidence in treating otitis media) 2
- Not recommended for children under 2 months of age due to risk of kernicterus from the sulfisoxazole component 2
Duration of Therapy
- For skin and soft tissue infections: approximately 7 days, depending on clinical response 1
- For otitis media due to ampicillin-resistant Haemophilus influenzae: 10 days 2
- For more severe infections: duration may be extended to 10-14 days 1
Clinical Applications
- Particularly effective for respiratory tract infections and skin/soft tissue infections 1
- Useful for treating infections caused by ampicillin-resistant Haemophilus influenzae, especially in otitis media 2
- The combination provides broader coverage than erythromycin alone due to the addition of sulfisoxazole 2
Monitoring and Precautions
- Monitor for gastrointestinal side effects, which are common with erythromycin 1
- Use with caution in patients with liver disease as erythromycin is primarily metabolized by the liver 1
- Avoid in patients with known hypersensitivity to macrolides or sulfonamides 1
- Be aware of potential drug interactions, particularly with drugs metabolized by CYP3A4 1
Special Considerations
- In patients with renal impairment, dose adjustment may be necessary, particularly for the sulfisoxazole component 1
- For patients unable to tolerate oral medications, consider alternative parenteral therapy 1
- Some strains of Staphylococcus aureus and Streptococcus pyogenes may be resistant to erythromycin 1
The combination of erythromycin and sulfisoxazole provides synergistic activity against many common pathogens, making it particularly useful for mixed infections or when broader coverage is needed than what erythromycin alone would provide 2.