Keys To Addressing MRSA In The Diabetic Foot

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Suhad Hadi, DPM, FACFAS, and Randy Garr, DPM

Current Insights On Treating MRSA With IV Antibiotics

Vancomycin. While vancomycin is commonly perceived as the “gold standard” antibiotic and is often a first-line therapy for at-risk patients with MRSA, there have been reports of increased resistance or decreased efficacy.6 This resistance is often described as a “creeping resistance” given that isolates are still susceptible but require higher concentrations of vancomycin (therefore demonstrating higher minimum inhibitory concentrations). Vancomycin is a glycopeptide, bactericidal antibiotic and requires slow infusion over two hours. One must monitor peaks and troughs, and dose accordingly. Renal function is a concern and clinicians must carefully assess this when considering vancomycin. Tissue penetration is variable depending upon the extent of the inflammatory process present and the presence/absence of bone involvement.

   Quinupristin/dalfopristin (Synercid, Pfizer). Both of these drug components have a synergistic effect in protein synthesis at the 50S ribosomal subunit. While both components are bacteriostatic, the combination of the two demonstrates bactericidal properties to the bacterial wall. There are no renal or hepatic adjustments with the dosing of Synercid but one should still monitor patients with these comorbid risks.
Clinicians commonly use this drug for vancomycin-resistant Staph aureus (VRSA) and as a combination agent for severe MRSA infections. Risks of the medication include arthralgia, myalgia and nausea. Cautious use and prescribing of this agent are recommended in an attempt to avoid the future risks of resistance.

   Tigecycline (Tygacil, Pfizer). Tigecycline, a glycylcycline bacteriostatic agent, demonstrates excellent soft tissue penetration and researchers have shown it to be effective against many resistant organisms, including MRSA.7 One advantage is its efficacy against gram-negative bacteria, giving clinicians a broad spectrum coverage option. Researchers have shown tigecycline to be equivalent to vancomycin in battling skin and soft tissue infections.7

   However, clinicians should use caution in regard to monitoring sensitivities in the presence of polymicrobial infections involving Pseudomonas. There is no required renal or hepatic adjustment in adults but again, monitoring in high-risk populations is recommended.

   Daptomycin (Cubicin, Cubist Pharmaceuticals). Daptomycin is a lipopetide that acts by disrupting cell membrane function via calcium dependent binding. It is bacteriostatic and concentration dependent. There is required renal adjustment to dosing with CrCl levels <30 mL/min. Risks include muscle weakness or pain, and one should monitor patients. Researchers have noted that dosing of greater than 4 mg/kg/day is associated with increased levels of creatine phosphokinase.8 Daptomycin is approved by the FDA for SSTI and is active against MRSA and VRE.

Case Study One: When A Patient With Diabetes Presents With A Recurrent Ulcer

A 59-year-old African-American male with a history of diabetes for 15 years presented to the clinic with a recurrence of an ulcer to the plantar aspect of his left foot at the level of the fifth metatarsal base. He has had the ulcer on and off for the past year as the ulcer would heal fully but then recur. For the last month, the patient had been self-treating the wound with antibiotic ointment (bacitracin) that he had left over from previous prescriptions. He has not had any pain in the area but is concerned that the ulcer is worse than before as it is “blowing out” of the top and side as well. The patient did notice a creamy discharge when it blew out but that has ceased since then.

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