Local antibiotic delivery is able to deliver high doses of local antibiotic with low risk of systemic toxicity.
Bone and joint infections are localized infections and systemic antibiotics alone cannot be sufficient especially when the infected wound has poorly perfused areas or dead space. Therefore local antibiotic delivery may be required in cases of bone and joint infections.
There ARE three methods of local antibiotic delivery
1. PMMA antibiotic composites
2. Biodegradable implant composites
3. Local delivery with a pump
General principles of Local Antibiotic Delivery
Local antibiotic therapy has the potential for reducing morbidity associated with prolonged antibiotic administration. For successful delivery, the affected area must be managed with appropriate surgical procedures. The pathogenic organism must be sensitive to antibiotic being used and the antibiotic must reach the entire area.
Polymethyl Methacrylate For Local Antibiotic Delivery
It is the most commonly used method for local antibiotic delivery. PMMA antibiotic depots are made in form of beads. The beads are prepared by mixing powdered antibiotics with PMMA polymer. The beads are implanted after thorough debridement and the wound is closed. Beads are removed 3-6 weeks after implantation. Following bead removal, the defect is filled with autogenous cancellous bone graft or soft tissue transfer.
The primary disadvantage of PMMA as an antibiotic carrier is that it must be removed by a surgical procedure which leaves a dead space An alternative is blocks of bioabsorbable material impregnated with antibiotics. These producsts are still in developmental phase.
Biodegradable bone cement and biodegradable bone cement are few of used materials.
Local Antibiotic Delivery With a Pump
The pump is surgically implanted in the subcutaneous area and the site can differ depending upon the affected area.
The pump consists of two chambers separated by collapsible titanium bellows. One chamber is filled with drug and other with charging fluid. As the charging fluid expands, it compresses the drug chamber and drives drug out of the outflow catheter.
The pump holds about50 ml of the drug and delivers 5-7 ml of drug per 24 hours. The pump can be refilled through the inlet septum at weekly intervals reexpanding the drug chamber. Amikacin is the most commonly used drug in this method.
Problems associated with this method are pump or catheter infection, pump displacement and migration of outflow catheters.