In vitro elution studies of amikacin and cefazolin from polymethylmethacrylate

In vitro elution of amikacin, cefazolin, gentamicin, ampicillin/sulbactam, and meropenem from a commercially available calcium sulfate delivery kit

Introduction

The use of implantable antibiotic beads has become a frequent treatment modality for the management of surgical site infections in human and veterinary medicine. The objective of this study is to describe the elution kinetics of five antibiotics from a commercially available calcium sulfate antibiotic delivery kit. A secondary goal was to compare elution concentrations with minimal inhibitory concentrations (MIC) for commonly encountered bacteria from the University of Florida's veterinary microbiology laboratory database.

Methods

Calcium sulfate powder was combined with amikacin, cefazolin, gentamicin, ampicillin/sulbactam, and meropenem. Triplicates of three antibiotic-loaded beads were immersed in 5 mL of phosphate-buffered saline (PBS) and kept at 37°C under constant agitation. Antibiotic-conditioned PBS was sampled at 14 time points from 1-h to 30 days and analyzed by liquid chromatography to determine the antibiotic concentration.

Results

All beads eluted concentrations of antibiotics for the 30-day sampling period, except for ampicillin/sulbactam, with the most antibiotics being eluted within the first week. The concentration of antibiotics within the eluent within the first 3-9 days (3- and 5-mm beads, respectively) was greater than the MIC of common isolates. The 5 mm bead samples were superior in maintaining higher concentrations for a longer period, compared to the 3-mm beads.

Discussion

CSH beads eluted antibiotics over the 30-day course of the study. Most of the antibiotic elution occurred within the first week and was maintained above the MIC of commonly encountered isolates. This information may be useful for clinical decision making for treatment of local infections encountered in practice.

Utilization of Antibiotic Bone Cement in Spine Surgery: Pearls, Techniques, and Case Review

Vertebral osteomyelitis (VO) encompasses a spectrum of spinal infections ranging from isolated mild vertebral osteomyelitis to severe diffuse infection with associated epidural abscess and fracture. Although patients can often be treated with an initial course of intravenous antibiotics, surgery is sometimes required in patients with sepsis, spinal instability, neurological compromise, or failed medical treatment. Antibiotic bone cement (ABC) has been widely used in orthopedic extremity surgery for more than 150 years, both for prophylaxis and treatment of bacterial infection. However, relatively little literature exists regarding its utilization in spine surgery. This article describes ABC utilization in orthopedic surgery and explains the technique of ABC utilization in spine surgery. Surgeons can choose from multiple premixed ABCs with variable viscosities, setting times, and antibiotics or can mix in antibiotics to bone cements themselves. ABC can be used to fill large defects in the vertebral body or disc space or in some cases to coat instrumentation. Surgeons should be wary of complications such as ABC extravasation as well as an increased difficulty with revision. With a thorough understanding of the properties of the cement and the methods of delivery, ABC is a powerful adjunct in the treatment of spinal infections.

Induced membrane technique using bone cement with or without cefazolin in chicken segmental radius defect

The utilization of antibiotic-loaded cement spacer in the induced membrane development has been a debate topic in human medicine. To the best of the author's knowledge, these combinations have not yet been evaluated in birds. Therefore, this study assessed induced membrane formation using radiography and histology, in a segmental defect of a chicken radius, with or without the addition of cefazolin. Thirty 18-month-old healthy chickens were divided into two equal groups: G1-bone defect filled with bone cement; G2-bone defect filled with cefazolin powder-loaded bone cement. Radiographic examinations of the left forearm were taken immediately after surgery and at 7, 15, and 21 postoperative days. For the collection of the induced membranes, five chickens in each group were euthanized at 7, 15, and 21 days after surgery. Radiographically, the bone cement was identified as a radiopaque structure occupying the bone defect in both groups. Mild new bone formation in at least one of the fractured extremities of the bone defect was seen only 21 days after surgery in most chickens. Histologically, there was no difference in the mean thickness of the induced membrane between groups at all time points. Multifocal multinucleated cells differed between groups at 7 (G1 > G2) and 21 (G2 > G1) days after surgery. Mononuclear inflammatory infiltrate differed between groups only on day 21 (G1 > G2). Fibrous tissue proliferation did not differ between groups at all evaluation times. Blood vessel density differed only at 21 days postoperatively (G2 < G1). Multifocal areas of cartilage differed between groups at all time points (G1 > G2). In conclusion, cefazolin mixed with bone cement did not affect thickness of the induced membrane, but did result in a negative effect on some histological aspects, such as fewer vessels, less multifocal areas of cartilage, and persistence of inflammation.

Thermal Stability and in Vitro Elution Kinetics of Alternative Antibiotics in Polymethylmethacrylate (PMMA) Bone Cement

BACKGROUND

Amikacin, meropenem, minocycline, and fosfomycin have potential clinical utility for orthopaedic infections; however, their suitability for use in polymethylmethacrylate (PMMA) is poorly understood. The purpose of this study was (1) to quantify the thermal stability of these antibiotics at clinically relevant temperatures and (2) to determine the elution pharmacodynamics of these alternative antibiotics in vitro from PMMA beads of different sizes.

METHODS

Polymerization temperatures of 10-mm PMMA beads were measured over time to generate a simulated heating curve. Aqueous solutions of tobramycin, amikacin, meropenem, minocycline, and fosfomycin were subjected to the temperature curves, followed by incubation at 37°C. Minimum inhibitory concentrations of each antibiotic were evaluated against Staphylococcus aureus, Escherichia coli, and Acinetobacter baumannii. High-dose 4.5-mm, 6-mm, and 10-mm antibiotic-laden PMMA beads (10% antibiotic by weight) were submerged individually in a phosphate-buffered saline solution and incubated at 37°C. Antibiotic elution was determined with use of high-performance liquid chromatography with mass spectrometry.

RESULTS

Tobramycin, amikacin, and fosfomycin demonstrated thermal stability and maintained antimicrobial activity for 28 days. Minocycline and meropenem lost antimicrobial activity against all 3 organisms after 48 hours and 7 days, respectively. Elution concentrations, rates, and cumulative drug mass for tobramycin, amikacin, and meropenem were orders of magnitude higher than minocycline and fosfomycin at each time point.

CONCLUSIONS

This study identified notable differences in thermal stability and elution among antibiotics used to treat infections. Amikacin exhibited activity similarly to tobramycin. Meropenem demonstrated favorable elution kinetics and thermal stability in the initial 7-day period.

CLINICAL RELEVANCE

Amikacin and meropenem show pharmacologic promise as potential acceptable alternatives for local delivery in PMMA for treatment of orthopaedic infections. Further work to establish clinical relevance and utility is needed.

In vitro Elution of Penicillin, Ampicillin, Tetracycline, Tulathromycin, and Florfenicol From Plaster of Paris Beads

The objectives of this study were to report a recipe for making antibiotic impregnated Plaster of Paris (AI-PoP) beads using penicillin, ampicillin, tetracycline, tulathromycin, and florfenicol and to determine the in vitro elution rates of those antibiotics in the beads. The AI-PoP beads were made using Plaster of Paris powder, antibiotic, and water, cured for 24 h, sterilized by ethylene oxide, and stored up to 5 months before testing. For each antibiotic, 20 beads were combined with bovine serum in sterile tubes and incubated at 37°C on a rocker. Serum was replaced at intervals over the 14 days study period, and antibiotic concentrations were determined by high pressure liquid chromatography with mass spectrometry. Separately, in a proof-of-concept study, the growth of E. coli and T. pyogenes in eluent from 10 beads for each antibiotic was quantified by flow cytometry. Antibiotic was detected in AI-PoP bead eluent for 14 days for all but the ampicillin beads, for which antibiotic was detected for 8 days. The concentration of antibiotic in eluent was greater than the minimum inhibitory concentration (MIC) of tested bacteria for the entire study period for penicillin, tetracycline, tulathromycin, and florfenicol. The concentration of ampicillin remained greater than the MIC of E. coli for 4 days and T. pyogenes for 6 days. The colony forming units (CFU)/ml of live E. coli and T. pyogenes was reduced over a 72-h period by 1-3 log10 CFU, with the exception of tetracycline, which reduced CFU/ml of T. pyogenes by Collapse

Key Words

• Plaster of Paris
• antibiotics
• cattle
• elution
• wound infection

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Affiliation(s)

Paul Merkatoris Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, United States
Jennifer Schleining Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, United States
Adam Krull Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, United States
David Borts Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, United States
Virginia Fajt Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, United States

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In vitro elution of amikacin and Dispersin B from a polymer hydrogel

OBJECTIVE

To characterize the in vitro elution of amikacin and Dispersin B (β-N-acetylglucosaminidase) in a degradable hydrogel.

STUDY DESIGN

In vitro, prospective study.

METHODS

Amikacin (group A; 40 mg/mL), Dispersin B (group D; 70 μg/mL), or combined amikacin and Dispersin B (group AD; 40 mg/mL and 70 μg/mL, respectively) were added to a hydrogel. Ten aliquots per group were incubated in phosphate-buffered saline that was exchanged at 1, 4, 8, 12, and 24 hours and then once daily for 10 days. Eluted amikacin and Dispersin B were quantitated by using an amikacin reagent kit and a Dispersin B enzyme-linked immunosorbent assay kit, respectively. Time point drug concentrations were compared between groups by using repeated-measures analysis of variance, and total drug elution was compared by using an area under the curve calculation.

RESULTS

Amikacin alone, Dispersin B alone, and amikacin and Dispersin B combined together underwent rapid elution in the first 24 hours, followed by a gradual decrease over 10 days. The concentration of Dispersin B eluted in group D was higher at 1 day and lower from day 5 to day 10 compared with that in group AD. The concentration of amikacin eluted in group A was higher at 1, 4, and 8 hours and on day 10 and lower on day 1 compared with that in group AD. The total elution of amikacin was greater from group AD compared with that from group A (P = .02).

CONCLUSION

Combining amikacin and Dispersin B had an affect on the total elution of amikacin but not Dispersin B.

CLINICAL SIGNIFICANCE

The combination of amikacin and Dispersin B in a degradable hydrogel could allow local treatment of complex infections without the requirement for multiple invasive procedures.

Selected Heat-Sensitive Antibiotics Are Not Inactivated During Polymethylmethacrylate Curing and Can Be Used in Cement Spacers for Periprosthetic Joint Infection

BACKGROUND

Antibiotic use in polymethylmethacrylate (PMMA) spacers has historically been limited to those which are "heat-stable" and thus retain their antimicrobial properties after exposure to the high temperatures which occur during PMMA curing.

METHODS

This study examines the requirement of "heat stability" by measuring temperatures of Palacos and Simplex PMMA as they cure inside commercial silicone molds of the distal femur and proximal tibia. Temperature probes attached to thermocouples were placed at various depths inside the molds and temperatures were recorded for 20 minutes after PMMA introduced and a temperature curve for each PMMA product was determined. A "heat-stable" antibiotic, vancomycin, and a "heat-sensitive" antibiotic, ceftazidime, were placed in a programmable thermocycler and exposed to the same profile of PMMA curing temperatures. Antimicrobial activity against Staphylococcus aureus was compared for heat-treated antibiotics vs room temperature controls.

RESULTS

Peak PMMA temperatures were significantly higher in tibial (115.2°C) vs femoral (85.1°C; P < .001) spacers. In the hottest spacers, temperatures exceeded 100°C for 3 minutes. Simplex PMMA produced significantly higher temperatures (P < .05) compared with Palacos. Vancomycin bioactivity did not change against S aureus with heat exposure. Ceftazidime bioactivity did not change when exposed to femoral temperature profiles and was reduced only 2-fold with tibial profiles.

CONCLUSION

The curing temperatures of PMMA in knee spacers are not high enough or maintained long enough to significantly affect the antimicrobial efficacy of ceftazidime, a known "heat-sensitive" antibiotic. Future studies should investigate if more "heat-sensitive" antibiotics could be used clinically in PMMA spacers.

Biomechanical evaluation of polymethyl methacrylate with the addition of various doses of cefazolin, vancomycin, gentamicin, and silver microparticles

Objectives: Numerous studies have examined the biomechanics of polymethyl methacrylate (PMMA) with added antibiotics, but direct comparison between studies is difficult. Our purpose was to evaluate the effects of the addition of antibiotic drugs and silver on compressive and bending strength of PMMA. Our null hypothesis was that there would be no significant difference in the compressive strength or bending strength of PMMA with the addition of silver or varying amounts of antibiotic drugs.

Methods: Polymethyl methacrylate was mixed with cefazolin, gentamicin, vancomycin, or silver; the control was PMMA alone. Antibiotic groups contained 20 g PMMA and 0.5 g, 1 g, 2 g, or 3 g of antibiotic. Silver groups had 0.25 g silver powder alone added to 20 g PMMA or silver with PMMA and 0, 0.5 g or 1 g of antibiotic. Samples underwent four-point bending and compression testing in air at room temperature and prevailing humidity. Pairwise comparisons between groups and to the ASTM and ISO standards were performed.

Results: Compression: All antibiotic and silver groups were weaker than the control. Samples with cefazolin tended to be stronger than other antibiotic groups with equivalent doses of antibiotic. All groups were above the ASTM standard, except 3 g vancomycin. Four-point bending: The addition of antibiotics did not significantly affect bending strength in groups with lower doses of antibiotics. The silver + PMMA group was weaker than the control. No groups were significantly below the ISO standard except the 3 g vancomycin group.

Clinical significance: The addition of antibiotic or silver decreased the biomechanical strength in all samples, but not below the ASTM or ISO standard for most groups. The addition of cefazolin appears to affect strength the least, while high doses of vancomycin alter strength the most.

A review of local antibiotic implants and applications to veterinary orthopaedic surgery

In the face of increasing incidence of multidrug resistant implant infections, local antibiotic modalities are receiving increased attention for both infection prophylaxis and treatment. Local antibiotic therapy that achieves very high antibiotic drug concentrations at the site of the implant may represent an avenue for treatment of biofilmforming bacterial pathogens. Randomized controlled trials in human patients have demonstrated an infection risk reduction when antibiotic-impregnated cement is used for infection prophylaxis in implanted joint prostheses, and when a gentamicin-impregnated collagen sponge is used for infection prophylaxis in midline sternotomy. The other modalities discussed have for the most part yet to be evaluated in randomized controlled trials in veterinary or human patients. In general, the in vivo pharmacokinetics and appropriate dosing profiles for local antibiotic modalities have yet to be elucidated. Toxicity is possible, and attention to the dose applied is warranted.

Elution of Clindamycin and Enrofloxacin From Calcium Sulfate Hemihydrate Beads In Vitro

OBJECTIVE

To compare the in vitro elution characteristics of clindamycin and enrofloxacin from calcium sulfate hemihydrate beads containing a single antibiotic, both antibiotics, and each antibiotic incubated in the same eluent well.

STUDY DESIGN

Experimental in vitro study.

METHODS

Calcium sulfate hemihydrate beads were formed by mixing with clindamycin and/or enrofloxacin to create 4 study groups: (1) 160 mg clindamycin/10 beads; (2) 160 mg enrofloxacin/10 beads; (3) 160 mg clindamycin + 160 mg enrofloxacin/10 beads; and (4) 160 mg clindamycin/5 beads and 160 mg enrofloxacin/5 beads. Chains of beads were formed in triplicate and placed in 5 mL phosphate buffered saline (PBS; pH 7.4 and room temperature) with constant agitation. Antibiotic-conditioned PBS was sampled at 14 time points from 1 hour to 30 days. Clindamycin and enrofloxacin concentrations in PBS were determined using high-performance liquid chromatography.

RESULTS

Eluent concentrations from clindamycin-impregnated beads failed to remain sufficiently above minimum inhibitory concentration (MIC) for common infecting bacteria over the study period. Enrofloxacin eluent concentrations remained sufficiently above MIC for common wound pathogens of dogs and cats and demonstrated an atypical biphasic release pattern. No significant differences in elution occurred as a result of copolymerization of the antibiotics into a single bead or from individual beads co-eluting in the same eluent well.

CONCLUSION

Clindamycin-impregnated beads cannot be recommended for treatment of infection at the studied doses; however, use of enrofloxacin-impregnated beads may be justified when susceptible bacteria are cultured.

Antimicrobial considerations in the perioperative patient

Surgical site infections are among the complications that can be reduced with the timely implementation of appropriate antimicrobial therapy. A 3-D approach to judicious antimicrobial use focuses on the de-escalation of systemic antimicrobial therapy, design of dosing regimens, and decontamination of the surgeon, patient, and environment. De-escalation can be accomplished in part through proper antimicrobial prophylaxis. Dosing regimens should be designed to maximize efficacy and minimize resistance. Decontamination includes disinfection of inanimate surfaces and timely application of appropriate antiseptics at concentrations that maximize efficacy.

Local release of antibiotics for surgical site infection management using high-purity calcium sulfate: an in vitro elution study

BACKGROUND

The aim of this study was to characterize the elution of four antibiotics from pharmaceutical-grade calcium sulfate beads and show that the eluted antibiotics retained efficacy.

METHODS

Calcium sulfate was combined with gentamicin, tobramycin, vancomycin, or rifampicin (ratio: 20 g of calcium sulfate, to 240 mg, 500 mg, 900 mg, and 600 mg of antibiotic, respectively). Three grams of beads were immersed in 4 mL of sterile phosphate-buffered saline (PBS) at 37°C. At each time point (4, 8, 24 h; 2, 7, 14, 28, 42 d), eluates were removed for analysis by liquid chromatography-mass spectrometry. The antimicrobial efficacy of antibiotics combined with calcium sulfate beads after 42 d was tested by a modified Kirby-Bauer disc diffusion assay.

RESULTS

All samples showed a generally exponential decay in the eluted antibiotic concentration. At the first time point, both gentamicin and tobramycin had eluted to a peak concentration of approximately 10,000 mcg/mL. For rifampicin, the peak concentration occurred at 24 h, whereas for vancomycin, it occurred at 48 h. The eluted concentrations exceeded the minimum inhibitory concentration for common periprosthetic joint infection pathogens for the entire span of the 42 study days. Mass spectrometry confirmed all antibiotics were unchanged when eluted from the calcium sulfate carrier. Antimicrobial efficacy was unaltered after 42 d in combination with calcium sulfate at 37°C.

CONCLUSIONS

Pharmaceutical-grade calcium sulfate has the potential for targeted local release of tobramycin, gentamicin, vancomycin, and rifampicin over a clinically meaningful time period.

Sterilization by gamma radiation of antibiotic impregnated polymethylmethacrylate and plaster of Paris beads. A pilot study

INTRODUCTION

Ethylene oxide is currently recommended for sterilization of antibiotic impregnated beads; however this method carries health risks to personnel and is becoming less available.

OBJECTIVE

To perform a pilot study of the effect of radiation for sterilization of polymethylmethacrylate (PMMA) and plaster of Paris (POP) beads impregnated with amikacin, enrofloxacin, and ceftiofur.

HYPOTHESIS

Radiation would effectively sterilize the beads without affecting the efficacy of the antibiotic.

MATERIALS AND METHODS

Beads of PMMA and POP were prepared in a clean but non-sterile manner with one of the three antibiotics (amikacin, enrofloxacin, ceftiofur) or no antibiotic. Beads were then exposed to radiation for a total dose of 0 kiloGray (kGy), 10 kGy and 25 kGy. Beads were incubated on Mueller-Hinton agar plates seeded with Escherichia coli, Staphylococcus aureus or Pseudomonas aeruginosa for 24 hours or cultured in brain-heart infusion broth for 48 hours. Zones of inhibition were measured on the agar plates and statistics were performed on the diameters of the zones of inhibition using an analysis of variance.

RESULTS

There were no differences in the diameters of inhibition for all levels of radiation for all PMMA beads. The same was true with POP beads with the exception of enrofloxacin which had a significantly decreased zone of inhibition with increased levels of radiation, though the clinical significance of this finding was not assessed. Only beads without antibiotics and not exposed to radiation had bacterial growth.

CLINICAL SIGNIFICANCE

Radiation may be an effective method of sterilization for antibiotic impregnated beads.

Octenidine in combination with polymethylmethacrylate: a new option for preventing infection?

BACKGROUND

Orthopedic implant infections represent a serious complication for both patient and surgeon. In order to minimize this risk, it has become standard practice in surgery and orthopedics to add antimicrobial substances to the polymethylmethacrylate (PMMA) bone cement. The aim of this study is to find new options for preventing infection by using alternative adjuvants in combination with PMMA. We hypothesized, that Octenidine, after being combined with PMMA, can be released in vitro and an antimicrobial efficacy of discharged Octenidine can be shown.

METHODS

The release of Octenidine from PMMA was assessed in high pressure liquid chromatography of the supernatant. In order to assess the efficacy of Octenidine on Staphylococcus aureus and Pseudomonas aeruginosa in vitro, a nutrient solution for these bacteria was incubated with a defined number of these bacteria (10(6) colony forming units) and cement pellets containing the antiseptic Octenidine for 24 h. After the incubation the number of bacteria in the solution was determined by counting the colony forming units on blood agar plates.

RESULTS

Octenidine was shown to be released in a concentration-dependent manner from PMMA in the elution experiment. The experimental procedure using S. aureus demonstrated a bactericidal effect for bone cement containing Octenidine. For P. aeruginosa, bone cement containing 5-8% Octenidine was associated with tenfold reduction in bacterial count.

CONCLUSION

These results suggest that Octenidine is released after combining it with PMMA and reaches working concentrations in vitro. These findings suggest a new and effective alternative for prevention of infection in cemented implants. Further investigations on the biocompatibility of this combination is needed.

Total ear canal ablation and lateral bulla osteotomy for treatment of otitis externa and media in a rabbit

CASE DESCRIPTION

A 7-year-old spayed female Miniature Rex European rabbit (Oryctolagus cuniculus) was evaluated because of scratching at the right ear. Physical examination revealed purulent exudate in the right ear canal.

CLINICAL FINDINGS

Microbial culture of the exudate yielded Pseudomonas aeruginosa susceptible to marbofloxacin; however, the infection was refractory to appropriate medical treatment. Computed tomography revealed isoattenuating material within the right tympanic bulla and external ear canal with no enhancement following IV administration of contrast medium. The left tympanic bulla appeared normal.

TREATMENT AND OUTCOME

A total ear canal ablation and lateral bulla osteotomy were performed on the right ear, and polymethylmethacrylate beads containing either gentamicin or cefazolin were placed within the bulla and surrounding tissues. Two weeks after surgery, the patient appeared comfortable with no signs of scratching at the right ear.

CLINICAL RELEVANCE

Total ear canal ablation and lateral bulla osteotomy can be successfully performed for treatment of chronic otitis externa and media in rabbits. Cartilage plates that compose the external ear canal, a bony acoustic duct, lack of a horizontal ear canal, and thickness of the lateral aspect of the tympanic bulla are features unique to rabbits and have not been described in relation to these surgical procedures in rabbits. Rabbits also produce a caseous exudate, and it is difficult to resolve infections of bone and soft tissues. Placement of antimicrobial-impregnated polymethylmethacrylate beads is recommended to minimize the risk of recurrent infection.

In vitro elution of amikacin and ticarcillin from a resorbable, self-setting, fiber reinforced calcium phosphate cement

OBJECTIVE

To determine in vitro elution characteristics of amikacin and ticarcillin from fiber reinforced calcium phosphate beads (FRCP).

SAMPLE POPULATION

Experimental.

METHODS

FRCP beads with water (A), amikacin (B), ticarcillin/clavulanate (C), or both amikacin and ticarcillin/clavulanate (D) were bathed in mL phosphate-buffered saline (PBS) at 37°C, 5% CO(2) and 95% room air. PBS was sampled (eluent) and beads were placed in fresh PBS at time points 1 and 8 hours and 1, 2, 3, 4, 5, 6, 7, 10, 12, 14, 18, 21, 25, 28, 35, 42, 49, and 56 days. Antibiotic concentration and antimicrobial activity of eluent against Escherichia coli, Staphylococcus aureus, and Klebsiella pneumoniae were determined.

RESULTS

Both antibiotics eluted in a bimodal pattern. Beads with a single antibiotic eluted 20.8 ± 2.5% of amikacin and 29.5 ± 0.8% of ticarcillin over 56 days. Coelution of the antibiotics resulted in a lower proportion (AUC(0-∞) ) of antibiotics eluted for both amikacin (9.5 ± 0.2%) and ticarcillin (21.7 ± 0.09%). Bioassay of antimicrobial activity of the eluent (t = 1, 8, and 24 hours) established reduced antimicrobial activity of amikacin from combination beads (D).

CONCLUSIONS

FRCP beads with amikacin or ticarcillin/clavulanate, but not the combination, are suitable carriers for wound implantation.

CLINICAL RELEVANCE

Duration before complete resorption of FRCP beads in vivo should be determined before clinical use as a resorbable depot. The results of this study underscore the importance of testing drug combinations, despite success of the combination systemically, before their use in local applications.

In vitro elution of amikacin and vancomycin from impregnated plaster of Paris beads

OBJECTIVE

To describe in vitro elution characteristics of amikacin and vancomycin from calcium sulfate hemihydrate 98% (plaster of Paris, POP) beads and characterize eluent inhibition of Staphylococcus spp.

STUDY DESIGN

Experimental study.

METHODS

POP beads were impregnated with amikacin or vancomycin alone or in combination and then incubated alone or in combination for 84 days at 37 degrees C in plastic tubes containing sterile phosphate-buffered saline (PBS). Beads containing no antimicrobial served as negative control. Beads were intermittently moved to a new tube containing drug-free PBS. Antimicrobial was measured in the eluent using a polarized fluorescent immunoassay. Eluent inhibition of Staphylococcus spp. was determined at each time point.

RESULTS

Antimicrobial release from beads was characterized by an initial rapid phase then a slower phase. Although antimicrobial release from beads occurred throughout the 84 days, most was in the first 24 hours, except for vancomycin alone. Duration of eluent inhibition of Staphylococcus spp. growth ranged from 0.5 (amikacin alone) to 56 days (vancomycin alone). Control eluent did not inhibit bacterial growth.

CONCLUSIONS

Amikacin elution from POP beads was rapid, inhibiting growth for <24 hours with or without vancomycin. Vancomycin elution was slower and inhibited growth for 56 days alone or for 5 days with amikacin.

CLINICAL RELEVANCE

Vancomycin-impregnated beads appear to be reasonable as a therapeutic option whereas amikacin-impregnated POP beads and amikacin and vancomycin combinations may require further study before considering as a therapeutic option.