Can a patient on Keflex (Cephalexin) for cellulitis be treated with Bactrim (Trimethoprim/Sulfamethoxazole) for a urinary tract infection (UTI)?

Concurrent Use of Keflex and Bactrim for Cellulitis and UTI

Yes, a patient can safely take Keflex (cephalexin) for cellulitis and Bactrim (trimethoprim-sulfamethoxazole) for a urinary tract infection concurrently, as they have different mechanisms of action and target different pathogens. 1

Rationale for Concurrent Use

• Keflex (cephalexin) is a first-generation cephalosporin that is appropriate for treating non-purulent cellulitis, which is primarily caused by streptococci 1
• Bactrim (trimethoprim-sulfamethoxazole) is recommended for UTIs when local resistance rates are below 20% and is effective against many common uropathogens 1
• The two antibiotics have different mechanisms of action and different side effect profiles, making concurrent use generally safe 2
• There is no significant drug interaction between cephalexin and trimethoprim-sulfamethoxazole that would preclude their concurrent use 3

Treatment Considerations for Cellulitis

• For non-purulent cellulitis, a 5-6 day course of antibiotics active against streptococci, such as cephalexin, is recommended 1
• Cephalexin is typically dosed at 500 mg four times daily for cellulitis 4
• Beta-lactams like cephalexin are appropriate for non-purulent cellulitis when MRSA is not suspected 1
• Adding trimethoprim-sulfamethoxazole to cephalexin for cellulitis has not been shown to improve outcomes in uncomplicated cellulitis per clinical trials 4

Treatment Considerations for UTI

• For UTIs, trimethoprim-sulfamethoxazole is recommended when local resistance rates are below 20% 1
• Typical dosing for Bactrim in UTIs is one double-strength tablet (160mg/800mg) twice daily for 3 days in uncomplicated cystitis 1
• For complicated UTIs, treatment duration may need to be extended to 7-14 days 1
• Urine culture and susceptibility testing should be performed to guide therapy, especially for complicated UTIs 1

Monitoring and Precautions

• Monitor for potential side effects of both medications, including:

  • Gastrointestinal disturbances (nausea, vomiting, diarrhea) 2
  • Allergic reactions (especially with cephalexin in patients with penicillin allergy) 1
  • Skin rashes or photosensitivity (more common with Bactrim) 3
  • Electrolyte disturbances or renal effects (more common with Bactrim) 3

• Ensure adequate hydration while taking both antibiotics to reduce the risk of crystalluria with Bactrim and to help manage the UTI 2

• If the patient develops worsening symptoms of either infection despite appropriate therapy, reevaluation is necessary 1

Special Considerations

• For patients with renal impairment, dosage adjustments may be needed for both medications 2
• In patients with a history of adverse reactions to either class of antibiotics, alternative regimens should be considered 1
• For elderly patients or those on multiple medications, be vigilant for potential drug interactions beyond the two antibiotics 3

Conclusion

Concurrent use of Keflex for cellulitis and Bactrim for UTI is appropriate and follows guideline recommendations for each infection individually. The combination provides targeted coverage for the different pathogens causing each infection without significant overlapping toxicity.