Can Bactrim (sulfamethoxazole/trimethoprim) and clindamycin be taken together orally?

Co-administration of Bactrim and Clindamycin

Bactrim (sulfamethoxazole/trimethoprim) and clindamycin can be administered together orally as this combination is specifically recommended in clinical guidelines for certain infections, particularly in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections.

Evidence for Combined Use

The 2015 European Society of Cardiology (ESC) guidelines for infective endocarditis specifically mention the combination of cotrimoxazole (sulfamethoxazole/trimethoprim) with clindamycin as an alternative therapy for Staphylococcus aureus infections, including both methicillin-susceptible and methicillin-resistant strains 1. The recommended dosage is:

• Sulfamethoxazole 4800 mg/day and Trimethoprim 960 mg/day (in 4-6 doses)
• Clindamycin 1800 mg/day IV in 3 doses

Clinical Applications

MRSA Infections

The combination is particularly useful for:

• Skin and soft tissue infections caused by MRSA
• Osteomyelitis where the Infectious Diseases Society of America guidelines recommend TMP-SMX in combination with other agents 1
• Alternative therapy when first-line agents cannot be used

Dosing Considerations

When administering these medications together:

1. Standard adult dosing for Bactrim: 1-2 double-strength tablets twice daily (each containing 800mg sulfamethoxazole/160mg trimethoprim) 1
2. Standard adult dosing for clindamycin: 300-450mg orally three times daily 1

Important Pharmacological Interactions

While the medications can be used together, there are some important considerations:

1. Pharmacodynamic Interaction: Research has shown that the combination of clindamycin and trimethoprim demonstrates indifference (neither synergy nor antagonism) against most staphylococcal strains, though antagonism was observed in some cases 2. This means the combination doesn't provide enhanced killing but remains useful for polymicrobial infections.

2. Rifampin Consideration: If rifampin is added to this regimen (as sometimes done for biofilm-associated infections), be aware that rifampin significantly decreases oral clindamycin bioavailability - in such cases, intravenous clindamycin would be preferred 3.

Potential Side Effects and Monitoring

When using these medications together, monitor for:

• Gastrointestinal effects (both medications can cause diarrhea)
• Increased risk of Clostridioides difficile infection
• Skin reactions (both medications can cause rash)
• Blood dyscrasias (particularly with long-term Bactrim use)
• Renal function (Bactrim dosage should be adjusted when creatinine clearance is <30 ml/min) 4

Contraindications

Avoid this combination in patients with:

• History of severe allergic reactions to either medication
• Significant hepatic impairment
• Megaloblastic anemia due to folate deficiency
• Pregnancy near term (risk of kernicterus with Bactrim)

Conclusion

The combination of Bactrim and clindamycin is supported by clinical guidelines, particularly for MRSA infections. While there is no significant synergistic effect between these agents, they can be safely administered together to provide coverage against a broad spectrum of organisms including aerobic gram-positive, some gram-negative, and anaerobic bacteria.