Prosthetic materials

While selection of antimicrobial therapy may be a major consideration in treating infectious diseases, it may not be the only therapeutic intervention. Other important therapies may include adequate hydration, ventilatory support, and other supportive medications. In addition, antimicrobials are unlikely to be effective if the process or source that leads to the infection is not controlled. Source control refers to this process and may involve removal of prosthetic materials such as catheters and infected tissue or drainage of an abscess. Source-control considerations should be a fundamental component of any infectious diseases treatment. It is also important to recognize that there may be many different antimicrobial regimens that may cure the patient. While the following therapy sections... 

It is important to determine (1) whether the isolate is methicillin-susceptible or methicillin-resistant and (2) whether the patient has a prosthetic valve. For patients with no prosthetic material, methicillin-susceptible staphylococci treatment should consist of a penicillinase-resistant penicillin (e.g., nafcillin or oxacillin) with or without gentamicin, and for methicillin-resistant strains, therapy should consist of vancomycin (see Table 71-4). Combination therapy with aminoglycosides, when used in these patients, typically is given only during the first 3 to 5 days of therapy. In the absence of prosthetic material, some treatment guidelines do not recommend combination therapy against MRSA. However, many clinicians may combine either gentamicin or rifampin with vancomycin if the patient is unresponsive to monotherapy. 

TABLE 71-4. Therapy for Endocarditis Caused by Staphylococci in the Absence of Prosthetic Materials... 

Source control Removal of the primary cause of an infection such as contaminated prosthetic materials (e.g., catheters), necrotic tissue, or drainage of an abscess. Antimicrobials are unlikely to be effective if the process or source that led to the infection is not controlled. 

Hench, L.L., Splinter, R.J., Allen, W.C. and Greenlee, T.K. Jr. (1971) Bonding mechanism at interface of ceramic prosthetic materials. Journal of Biomedical Materials Research Symposium, 2, 117-141. 

In patients with endocarditis of prosthetic valves or other prosthetic material caused by viridans streptococci and Streptococcus bovis, treatment courses are extended to 6 weeks (Table 37-5). 

Therapy for Endocarditis of Prosthetic Valves or Other Prosthetic Material Caused by Viridans Group Streptococci and Streptococcus bovis... 

Completely repaired congenital heart defect with prosthetic material or device, whether placed by surgeiy or by catheter intervention, during the first 6 months after the procedure ... 

Except for the conditions listed above, antibiotic prophylaxis is no longer recommended for any other form of CHD Prophylaxis is recommended because endothelialization of prosthetic material occurs within 6 months after the procedure From Wilson W, TaubertFA, CewilzM,etaL Prevention of infective endocarditis. Grculalion 2007 116 1736-1754 with permission Copyright 2007, American Medical Association. 

High-risk procedures include implantation of prosthetic materials and other procedures in which surgical-site infection is associated with high morbidity. 

Prophylactic antibiotics are beneficial in cases involving implantation of prosthetic material (pins, plates, artificial joints). 

Surgical procedures that necessitate the use of antimicrobial prophylaxis include contaminated and clean-contaminated operations, selected operations in which postoperative infection may be catastrophic such as open heart surgery, clean procedures that involve placement of prosthetic materials, and any procedure in an immunocompromised host. The operation should carry a significant risk of postoperative site infection or cause significant bacterial contamination. 

Organopolysiloxanes (silicones) are very important materials for therapeutic applications because of their good physicochemical properties and their inertness to biochemical processes. For example, silicones are employed as ointments (especially for burns), prosthetic materials (e.g. replacement of blood vessels), and plastic surgery (e.g. augmentation of soft tissue or loose skin). 

Corresponding to these fundamental advances (Srinivasan and Sawyer, 1970), it was discovered that prosthetic materials remain free of thrombi if they are negatively charged andhave apotential on the H scale more negative than -0.6 V. This knowledge has significantly influenced the design of prosthetics. 

It is expected that the intermacromolecular complexes display entirely new physical and chemical characteristics different from those of the individual polymer components. So the following applications are, for example, considered membranes for dialysis, ultrafiltration, fuel cells and battery separators, wearing apparel, electrically conductive and antistatic coatings for textiles, medical and surgical prosthetic materials, environmental sensors or chemical detectors, and electrodes modified with specific polymers. 

While the receptors involved in platelet adhesion to the subendothelium have been studied extensively, the receptors involved in platelet adhesion to prosthetic materials are less well identified. The biomaterials adsorb a It er of plasma proteins on their surface tqxm exposure to blood. The content of this protein ItQror varies with time and induces Fg, Ig G, Fn, vWF and vibronectin (18,19) etc.. For which there are specific surface receptors on platelet surface (28). 

Infusion phlebitis presents a problem in parenteral nutrition. Various alternative techniques of administration have been compared in order to identify means of countering this problem (9). Mechanical trauma appears to be a causative factor it can be reduced by hmiting the time of exposure of the vein wall to nutrient infusion and by minimizing the amount of prosthetic material within the vein (10). This is hkely to be even more important in small veins. In one study the addition of heparin (500 U/1) and hydrocortisone (5 micrograms/ml) significantly reduced the risk of thrombophlebitis from 0.43 to 0.11... 

In the last case the strain was identical to eight MRSA isolates obtained from hospitals in the New York City metropolitan area, and all eight isolates, but not control isolates, could be transformed in vitro to develop intermediate resistance to vancomycin. Both the presence of glyco-peptides and environmental factors, as demonstrated by increased resistance of S. aureus to antibiotics in the presence of prosthetic material in animals, can exert selective pressure to develop new resistance mechanisms (93-95). 

Coagulase-negative staphylococci, such as Staphylococcus epidermidis, are the most common causes of catheter-related infections due to their ability to adhere to prosthetic material. Staphylococcus aureus, aerobic gramnegative bacilli, and Candida albicans are also common causes of catheter-related infections. Depending on local susceptibility patterns, methicillin-resistant S. aureus (MRSA) may represent up to 20% of all isolates. In contrast, upward of 80% of S. epidermidis are methicillin-resistant (MRSE). 

B. Equipment and non-medication supplies issued by Pharmacy and Prosthetics/Materials Management Services may be ordered without co-signature of a physician. 

TABLE 109—6. Therapy for Endocarditis Due to Staphylococcus in the Absence of Prosthetic Material ... 

TABLE 1 09—7. Treatment of Staphylococcal Endocarditis in the Presence of a Prosthetic Valve or Other Prosthetic Material... 

Rifampin plays a unique role in the eradication of staphylococcal infection involving prosthetic material (see text) combination therapy is essential to prevent emergence of rifampin resistance. 

Altered immune response Implantation of prosthetic materials... 

Muzzarelli et al. (2000) described a method for coating prosthetic articles with chitosan-oxychitin. Plates of titanium (Ti) and its alloys were plasma sprayed with hydroxyapatite and glass layers, and subsequently a chitosan coat was deposited on the plasma-sprayed layers using chitosan acetate. These layers were treated with 6-oxychitin to form a polyelectrolytic complex. This complex was optionally contacted with l-ethyl-3-(3-dimethylami-nopropyl) carbodiimide at 4°C for 2 hours to form amide links between the two polysaccharides, or acetylation with acetic anhydride in methanol to obtain a chitin film. In all cases, the modified coats were insoluble, uniformly flat, and smooth. Prosthetic materials coated with chitosan-oxychitin were capable of provoking colonization by cells, osteogenesis, and osteointegration. 

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