Background The antibiotic lock therapy (ALT) technique that involves the instillation of a highly concentrated antimicrobial solution with additives such as anticoagulants into the catheter lumen, is an option for treatment of catheter-related bloodstream infections when the central venous catheter is retained. An important limitation is the frequent incompatibility between the components, causing great controversy in the literaure. The ALT with gentamicin is one of the most requested ALT for treating bacteriemias by Gram(-). The anticoagulant that is studied more is unfractioned heparin. It can be used in haemodialysis patients, however, other anticoagulants such as citrate whose data are limited regarding compatibility should be used for patients with a history of heparin-induced trombocytopenua (HIT) or active HIT.

Purpose To study the stability of the catheter lock solution that combines gentamicin 2.5 mg/ml and heparin 2500UI/mL or citrate 2% as anticoagulant.

Material and methods Eight solutions of catheter lock were prepared at fixed concentrations: four solutions of gentamicin 2.5 mg/ml+heparin 2500UI/ml (A1,B1,C1,D1) and four of gentamicin 2.5 mg/ml+citrate 2% (A2,B2,C2,D2). Physical and chemical stability were measured on days 0 (A1,A2), 2 (B1,B2), 3 (C1,C2) and 7 (D1,D2) after the preparation. Two aliquots were prepared from solutions B1, B2 and C1, C2. One aliquot of each one (B1a,B2a,C1a,C2a) were stored in the refrigerator (2°C–8°C) to test the stability of the preparation of ALT extemporaneously prior to its use, and another (B1b,B2b,C1b,C2b) in the oven (35°C–37°C) to simulate the temperatures that are reached once installed in the catheter. Chemical stability was defined as concentrations of gentamicin at least 90% measured by the colourimetric technique. For the analysis the samples were diluted to a gentamycin concentration of 5 mcg/ml. Physical stability was considered as the absence of precipitate or appearance of particles.

Results None of the ALT precipitated during the study nor did they showed variations in colour. The concentrations of gentamicin were stable in the different selected storage conditions: A1:5.31 mcg/mL; A2:5.46 mcg/mL; B1a:5.88 mcg/mL; B1b:5.8 mcg/mL; B2a:5.1 mcg/mL; B2b:4.97 mcg/mL; C1a:5.9 mcg/mL; C1b:5.47 mcg/mL; C2a:5.08 mcg/mL; C2b:5.21 mcg/mL; D1:5.46 mcg/mL; and D2:5.04 mcg/mL. The mean was 5.39±0,32 mcg/mL.

Conclusion The ALT with gentamicin 2.5 mg/ml and heparin 2500UI/ml or citrate 2% are chemically and physically stable. More studies are needed to address areas of uncertainty of great clinical relevance, such as the stability of ALT with other concentrations of gentamicin and ALT that combines other antibiotic with citrate.

No conflict of interest