Keys To Addressing MRSA In The Diabetic Foot

Start Page: 64
Suhad Hadi, DPM, FACFAS, and Randy Garr, DPM

   Where vancomycin was at one time the mainstay for management of MRSA, there has been increasing concern for resistance to the drug. This is a precise reminder of the rapid virulence of S. aureus. Despite a decline in the development of newer antibiotics, there are currently a number of antibiotic options for the treatment of MRSA and a variety of oral options. It is critical to remember, however, that these antibiotics come with risks. Close monitoring of renal and/or hepatic function is often crucial and one must appropriately adjust the dosing.

A Closer Look At Oral Antibiotics For MRSA

Trimethoprim/sulfamethoxazole (Bactrim, Roche). This is a dihydrofolate reductase inhibitor with a bactericidal, synergistic effect. It is contraindicated in patients with hepatic impairment and requires adjustment for renal dosing with CrCl of 15 to 30 mL/min. Indicated for CA-MRSA, trimethoprim/sulfamethoxazole is effective in deep infections and soft tissue infections with noted purulence. There is a concern for increasing resistance to trimethoprim/sulfamethoxazole. Therefore, cautious use and prescribing of the antibiotic is recommended. It is contraindicated in patients with folate deficiency, glucose-6-phosphate dehydrogenase deficiency, a history of anemia or thrombocytopenia. Exercise caution and make appropriate dosing adjustments when using this in elderly patients with renal insufficiency.

   Doxycycline (Vibramycin, Pfizer). There has been growing use of doxycycline for CA-MRSA and it offers convenient twice per day dosing at 100 mg. There is no required renal adjustment to dosing but one must use caution with the drug and ensure monitoring in patients with hepatic impairment. Multiple reports have demonstrated successful outcomes with the use of doxycycline in SSTI.5 To date, research has shown doxycycline to be an effective monotherapy option in MRSA-associated SSTI.

   Clindamycin (Cleocin, Pfizer). While clindamycin is effective in some MRSA infections, there has been increasing resistance in both the outpatient and hospital settings. It is critical to note that resistance to clindamycin is inducible but inked to macrolide resistance. Therefore, one should avoid clindamycin in patients with erythromycin isolates despite clindamycin sensitivity.

   Clindamycin has bacteriostatic properties and does not require renal or hepatic adjustment in dosing. The manufacturer notes that possible side effects include diarrhea (noted in up to 20 percent of those taking the medication) and a risk of C. difficile. Clindamycin has excellent tissue, bone and abscess penetration. Further testing with the D-zone test is recommended for the detection of resistance although this would result in a one- to two-day delay in final confirmation.

   Linezolid (Zyvox, Pfizer). Linezolid is an oxazolidinone drug that also inhibits the initiation of protein synthesis at the 50S ribosome. It has a specific indication for diabetic foot infections (skin and soft tissue infections) and is effective in targeting both MRSA and vancomycin resistant Enterococcus (VRE). It does not require renal adjustment with dosing and the dosage is 600 mg q12h. It is available as both an oral and parenteral agent with equal bioavailability. Accordingly, oral dosing is more desirable.

   Use caution in all patients as there are associated risks of hematologic toxicity, thrombocytopenia and anemia. Therefore, monitoring of the complete blood cell count is required in patients on prolonged therapy.

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