Osteomyelitis and periprosthetic joint infections are serious conditions, which lead to significant morbidity, require prolonged treatment and are associated with high rates of recurrence [
1,
2]. Antibiotic-loaded bone cement, or antibiotic-impregnated polymethylmethacrylate (PMMA), has been developed to treat chronic osteomyelitis and periprosthetic infections [
2]. The benefit of antibiotic-impregnated PMMA is its ability to provide a local concentration of antibiotics to eradicate infection [
3], which limits the side effects associated with systemic antibiotics [
4]. Gentamicin is one of the antibiotics commonly used to mix with PMMA [
1]. If physicians require higher concentrations of gentamicin; when preparing handmade PMMA beads or articulating spacers, gentamicin in powder form is normally used for mixing with PMMA. The reason for this is that most of the available, commercial gentamicin-impregnated PMMA, contains only 0.5–1 g of gentamicin in batches of bone cement (40 g) [
5]. However, gentamicin powder is difficult to obtain in some countries where only liquid gentamicin is available [
6]. Another drawback of gentamicin powder is its substantially higher cost compared with liquid gentamicin [
7]. A previous study reported that gentamicin powder costs approximately 10 times more than liquid gentamicin [
2]. Earlier studies have reported the results of gentamicin-impregnated PMMA made with liquid gentamicin [
2,
7], and in both of these reports, the dose of gentamicin mixed with a pack of cement was 480 mg. However, preparing handmade gentamicin-impregnated PMMA with liquid gentamicin, in order to obtain a higher concentration of gentamicin, was precluded. As an example; if a physician wanted to add 2 g of gentamicin to 40 g of PMMA, the procedure requires 50 ml of liquid gentamicin [Gentamicin 80 mg/2 ml], so not all of the liquid gentamicin can be mixed with the liquid monomer and cement powder. This is because the high volume of normal saline, which is solvent in liquid gentamicin, will dilute the liquid monomer and prevent the hardening of PMMA. This means that liquid gentamicin cannot be realistically used to produce high-concentrations gentamicin PMMA.
The lyophilization technique, or freeze drying, is a process of dehydration via the lowering of temperature until water freezes; this enables water to change directly from its solid phase to its gas phase. This process is commonplace in procedures of pharmaceutical formulations [
8]. However, due to availability limitations, and the high cost of gentamicin powder we believe that lyophilized liquid gentamicin could also be used to make gentamicin-impregnated PMMA. Hence, the aim of this study was to evaluate the elution characteristics of gentamicin-impregnated PMMA made with lyophilized liquid gentamicin, as compared to that of PMMA made with commercial gentamicin powder; using the enzyme multiplied immunoassay technique (EMIT) [
9].