The stability of carbapenems before and after admixture to PMMA-cement used for replacement surgery caused by Gram-negative bacteria

BACKGROUND: Prosthetic joint infection (PJI) is a serious complication of orthopedic implant surgery. Treatment often includes the use of an antibiotic-loaded Polymethyl methacrylate (PMMA) bone cement spacer. Several antibiotics are commonly used for the preparation of these spacers, but due to the increasing number of infections with resistant Gram-negative bacteria, there is a need for the use of carbapenem antibiotics such as meropenem and imipenem as drugs of last resort. Unfortunately, the reaction heat generated during the preparation of the bone cement can be a major problem for the stability of these antibiotics. In the present study, the stability of meropenem and imipenem was tested before and after the admixture to PMMA bone cements. METHODS: High-performance liquid chromatography with ion-pairing reversed-phase separation and spectrophotometric detection was used for analysis. Stability tests with meropenem and imipenem were performed with antibiotics in solution and solid form at different temperatures (37 °C, 45 °C, 60 °C, 90 °C) and times (30 min, 60 min, 120 min). To test the stability of both antibiotics in PMMA after exposure to the reaction heat during polymerization, three different bone cements were used to generate specimens that contained defined amounts of antibiotics. Reaction heat was measured. The form bodies were mechanically crushed and aliquots were dissolved in ethyl acetate. Samples were prepared for HPLC DAD analysis. RESULTS: Meropenem and imipenem showed the highest degradation levels after heat stressed in solution, with maximum levels of 75% and 95%, respectively. In solid form, degradation levels decreased dramatically for meropenem (5%) and imipenem (13%). Stability tests of both carbapenems in bone cement showed that they remained largely stable during PMMA polymerization, with retrieved amounts of about 70% in Palacos(®) R and Copal(®) G+V, and between 80 and 90% in Copal(®) spacem. CONCLUSIONS: In contrast to the results of meropenem and imipenem in solution, both antibiotics remain stable in solid form and mostly stable in the cement after PMMA polymerization. The low degradation levels of both antibiotics after exposure to temperatures > 100 °C allow the conclusion that they can potentially be used for an application in PMMA cements.