An antibiotic delivery device is a medical implant designed to administer medication directly to a specific location within the body. Unlike a one-time injection, these devices are engineered to release a controlled, sustained dose of antibiotics over an extended period, from several days to many weeks. The primary function is to target an infection at its source, such as in bone or surrounding a surgical implant. This allows clinicians to manage and treat infections that are otherwise difficult to reach.
Purpose of Localized Antibiotic Delivery
The purpose of a localized delivery device is to achieve a high concentration of medication at the infection site while minimizing exposure to the rest of the body. When antibiotics are taken orally or intravenously, they are distributed systemically through the bloodstream. This approach can struggle to deliver a sufficient dose to areas with poor blood supply, like infected bone. A localized device releases the drug directly into the affected tissue, reaching concentrations over one hundred times higher than what is safe with systemic administration.
This targeted method reduces the risk of side effects associated with systemic antibiotics. Because the drug is largely contained within a specific area, there is less impact on the body’s organs and healthy microbial flora. This makes it a safer option for patients with impaired kidney or liver function or who are intolerant to certain systemic drugs.
Localized delivery is effective for treating infections involving bacterial biofilms. A biofilm is a protected colony of bacteria that adheres to a surface, such as a metal joint replacement or a piece of dead bone. These structures are highly resistant to systemic antibiotics, which have difficulty penetrating the film’s protective layer. Placing a device directly adjacent to the biofilm allows the high antibiotic concentration to break down these defenses and eliminate the bacteria.
Common Types of Antibiotic Delivery Devices
Antibiotic delivery devices are categorized as either non-biodegradable or biodegradable. The most common non-biodegradable material is polymethyl methacrylate (PMMA), also known as bone cement. Surgeons mix powdered antibiotics, such as gentamicin or tobramycin, directly into the PMMA before it hardens. This mixture is then molded into shapes like beads, rods, or custom spacers used to fill a void in bone.
PMMA devices are implanted during surgery to release their antibiotic load over several weeks. The antibiotic elutes from the surface of the hardened cement into the surrounding tissue, with the release rate typically highest in the first few days before tapering off. Because PMMA is a non-resorbable material, it remains in the body after the antibiotic is depleted and must eventually be removed in a second procedure.
In contrast, biodegradable devices are made from materials the body can absorb over time. This category includes materials like collagen sponges, calcium sulfate pellets, and synthetic polymers such as polylactic acid (PLA). These materials are loaded with antibiotics and degrade at a controlled rate, releasing the medication as they dissolve. A primary benefit is that a second surgery for removal is not required. Some materials also act as a scaffold that supports new tissue growth as they are resorbed.
Medical Applications and Procedures
The most frequent use of these devices is in orthopedic surgery for treating and preventing bone and joint infections. A primary application is managing osteomyelitis, a persistent bone infection. Following a procedure to remove infected bone tissue, a void is often left behind. Surgeons fill this space with antibiotic-loaded PMMA beads or a biodegradable material to eliminate remaining bacteria.
These devices are also used in joint replacement surgeries for the hip and knee. To prevent infection, which can lead to implant failure, surgeons may use antibiotic-impregnated bone cement to secure the new joint. If a joint is already infected, a two-stage revision surgery is common. In the first stage, the infected implant is removed, the area is cleaned, and a temporary spacer made of antibiotic-loaded PMMA is inserted. This spacer delivers antibiotics for several weeks before it is removed in a second surgery and replaced with a new implant.
Beyond orthopedics, these delivery systems are applied in other medical fields. They are used in complex bone fractures, especially open fractures, to reduce infection risk. Similar principles are applied in some dental and maxillofacial surgeries to treat jawbone infections. Another application is managing chronic wounds, like diabetic foot ulcers, by controlling infections that impede healing.
Management and Removal of Devices
The management of an antibiotic delivery device depends on its material. For non-biodegradable devices made from PMMA, removal is part of the treatment plan. Once the drug has been delivered and the infection is resolved, typically after several weeks, the device must be surgically removed.
Leaving a non-biodegradable implant in the body poses a risk. The inert material can act as a foreign body, providing a surface for new bacteria to attach and form a biofilm, which can cause a new infection. A second surgical procedure is required to extract the PMMA beads, rods, or spacers to prevent this.
Biodegradable devices offer a path that avoids subsequent surgery. Materials like collagen sponges or calcium sulfate pellets are designed to be completely resorbed by the body. As the material breaks down, it releases the antibiotic and is gradually replaced by the patient’s own tissue. This eliminates the risks and costs associated with a second surgical procedure.