Adjunctive Therapies for Diabetic Foot Infections

F oot infections in patients with diabetes are complex problems that often fail to respond to antimicrobial therapy and surgical procedures. Thus, several adjunctive therapies for these infections have been investigated over the past few years. These include novel antimicrobial delivery systems, larval biotherapy, granulocyte-colony stimulating factor and hyperbaric oxygen.1,2 Long-standing diabetes is associated with accelerated atherosclerosis, especially in the tibial and peroneal arteries between the knee and ankle. Several studies have shown that certain antibiotics have limited penetration to infected diabetic foot tissues. The tissue concentrations of a systemically administered antibiotic may be less than the serum level, sometimes as low as 25%.3-6 Intra-aterial administration of antibiotics could potentially be a method for needed treatment to enter infected areas in patients with limb ischemia. Antibiotics can be injected directly into lower leg arteries, most commonly the femoral artery. Theoretically, this method should result in drug concentrations that are higher and more rapidly delivered via collateral vessels. Current data on this technique is minimal, however, and there are safety issues associated with the technique.7 Another way to provide higher tissue antibiotic levels is to give a pressurized IV injection nearer to the site of infection. One technique is called local transvenous pressure injection in Bier’s arrest. While this method deposits antibiotic in the infected tissue 10 to 20 times that of serum concentrations, there are few literature reports on its efficacy.8,9 Another potential method of delivering high local levels of antibiotic is by a retrograde venous catheter delivery system. The novel experimental TheraPed Catheter (Figure 1) is designed to be threaded through a foot vein, where antibiotic is delivered from a port between two inflated balloons. Limited but promising results using levofloxacin with the catheter in animal studies were presented at the 2002 European Association for the Study of Diabetes meeting.10 Investigators have looked at using biodegradable sponges impregnated with antibiotics to treat diabetic foot infections. Compared to polymethyl-methacrylate or PMMA beads, this method can be used with a wider variety of antibiotics. Biodegradable sponges, including those made of collagen, can also deliver higher tissue levels of antibiotics. The therapeutic levels do not last as long as with beads, and no repeat operation is needed to extract the sponge.11,12