Empirical Study On The Antibacterial Activity And Mechanical Properties Of Composite Antibiotic-loaded Bone Cements

Background:Postoperative infection following artificial joint replace- ments can be a significant problem for patients.Using antibiotic-loaded bone cements is one of the primary anti-infective means.However,several issues must be noted.The local antibiotic concentration should surpass the minimum inhibitory concentration.Antibiotic-loaded bone cements must have a relatively high drug concentration in initial stage,and may continue releasing the antibiotics locally in the following days or weeks.In addition, the mechanical properties of bone cements can not be ignored when fixing the artificial joint.Preventing or curing infection are two of the purpose for the application of antibiotic-loaded bone cements in the surgical field of artificial joints.Smaller dose of antibiotics added to the bone cement is enough for preventing infection,meanwhile the mechanical properties of bone cements should pledge the effective fixation of the prosthesis.But higher dose of antibiotics is needed for curing infection,usually with modality of temporary joint spacer or antibiotic beads.In this case,the mechanical properties of bone cements has permission of larger impairment.Staphylococcus aureus is one of the major pathogenic bacteria in post- operative infection following artificial joint replacements,but its drug re- sistance to commonly used antibiotics such as penicillins and aminoglycol- side (gentamicin, tobramycin, etc) is increasing. vancomycin acts as the choice drug to resist the methicillin-resistant Staphylococcus aureus, having powerful bactericidal action to Gram-positive cocci,but the greater adverse reaction and unceasing reports of new drug-resistant strains interrupt its clinical application.Composite antibiotics added to bone cements(PMMA) has impotant meaning for expansion of antibacterial spectrum and reducing drug resistance.Amikacin sulfate,one of the semisynthetic aminoglycoside, posseses high performance to the pseudomonas aeruginosa, suitable for treatment of the infection caused by gram-negative bacilli,especially those strains drug-resistant to kanamycin,gentamicin or tobramycin.And as one of the third generation cephalosporins,semisynthetic ceftazidime has strong antibacterial effect on gram-negative bacilli,also synergistic antibacterial effects on the staphylococcus aureus and enterococcus combined with vancomycin,and similar synergistic effect on the pseudomonas aeruginosa and some E.coli combined with the aminoglycosides.Objective:To evaluate the impact on antibacterial activity and mecha- nical properties of composite antibiotics (vancomycin,ceftazidime, amik- acin)added to domestic bone cements,so as to provide experimental basis for clinical application.Methods:1.Mechanical experiments of antibiotic-loaded bone cements Composite antibiotic powders (vancomycin+ceftazidime,ceftazidime+ amikacin) of distinct matching are divided into 6 groups,dose of 0.5g, 1.0g, and 2.0g added to bone cements per 40g each matching, bone cements without antibiotics incorporation as control, for total 7 groups.Compressive stress with velocity of 20 mm/min are exerted on the standard test pieces (5 per group), cylindrical made from stainless steel, in the universal testing machine. And data of the maximum load, offset, stress, straining, etc, are automatic discharged by the hardware when damage of the sample appears.2.Susceptibility test of antibiotic-loaded bone cements Composite antibiotic powders (vancomycin, vancomycin+ceftazidime, ceftazidime+ amikacin)of distinct matching are divided into 9 groups,dose of 0.5g,1.0g,and 2.0g added to bone cements per 40g each matching. Standard test pieces(5 per group), cylindrical made from stainless steel,are prepared,and then cultured in the agar plates containing the staphylococcus aureus,E.coli,and pseudomonas aeruginosa respectively.Successive observa- tion are performed for six days,recording the circle size due to bacteriosta- sis. 3.Methods of statistical researchMeasurement data are demonstrated by format of means±standard deviation( x±s),one-way ANOVA for statistical analysis,q test for couple comparision,and P<0.05 for significant difference.Results:1.Mechanical experiments of bone cementsLevel of the load and compressive strength of antibiotic-loaded bone cements decreased with the dose increasing of composite antibiotics(ie, 0.5g→1.0g→2.0g),significantly when more than 2.0g,however,no statistical discrepancy between dose of 0.5g(Vancomycin0.25g+Cefta- zidime0.25g; Ceftazidime0.25g+Amikacin0.25g) and 1.0g(Vancomycin0.5g+Ceftazidime 0.5g;ceftazidime0.5g+Amikacin0.5g).2.Susceptibility test of bone cementsAgainst gram-negative bacteria(Escherichia coli,Pseudomonas aeru- ginosa):With dosage increasing(ie,0.5g→1.0g→2.0g)of composite antibi- otics(ceftazidime+amikacin),the antibacterial activity of antibiotic-loaded bone cements gradually increased,circle size due to bacteriostasis increas ing for at least 6 days.GroupⅨ(Ceftazidime1.0g+Amikacin1.0g) has the largest circle, with significant differences comparing to other groups (P<0.05). Against Gram-positive bacteria (Staphylococcus aureus):The largest circle due to bacteriostasis occurs in GroupⅢ(Vancomycin2.0g) and GroupⅥ(Vancomycin1.0g+Ceftazidime1.0g), with significant differences com- paring to other groups (P<0.05),while no statistical difference for couple comparision(P> 0.05).GroupⅦ(Ceftazidime0.25g+Amikacin0.25g)has the smallest circle.Circle size due to bacteriostasis in all groups can extend more than 6 days.Conclusion:1.With dosage increasing of composite antibiotics into bone cements, the mechanical properties may reducing gradually. 40g domestic cement added to 2.0g of the compound the following antibiotics will not affect the mechanical properties of bone cement.2.Composite antibiotics (Vancomycin+Ceftazidime;Ceftazidime+Ami- kacin) incorporating into bone cements can be effectively released and play role of antibacterial.3.As to the choice of antibiotics,Vancomycin+Ceftazidime can be used in infections mainly of Gram-positive bacteria;while Ceftazidime+Ami- kacin used in infections mainly of Gram -negative bacteria.