A rapid high-performance liquid chromatography method to measure linezolid and daptomycin concentrations in human plasma

Daptomycin and linezolid, recently introduced to treat severe Gram-positive infections, are effective against multidrug-resistant Gram-positive microorganisms such as methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis, and vancomycin-resistant Enterococci bacteria that are less sensitive or frankly resistant, including methicillin-resistant S. aureus. However, alteration of their plasma profile has been described in some patients and this may be associated with toxicities or selection of resistant strains. The measurement of plasma concentrations of both drugs may allow the identification of those subjects at major risk of adverse events. Therefore, a rapid and sensitive high-performance liquid chromatography method for the analysis of daptomycin and linezolid was developed and applied in clinical settings. Drugs were extracted from plasma by adding methanol and, after centrifugation, clear supernatants were injected into the high-performance liquid chromatography system. Isocratic elution (1.5 mL/min) was performed using a mobile phase consisting of ammonium phosphate buffer 40 mM, pH 4.0, acetonitrile (70:30, vol/vol) through a BDS C8 Hypersil stationary phase (250 x 4.6 mm, 5 mum); ultraviolet detection was used at 214 nm. Linezolid and daptomycin eluted within 20 minutes from the injection, and mean recoveries ranged between 95.4% and 112.1%, respectively. The method was linear (coefficient of linearity, 0.998-0.999) over the full range of concentrations assayed, from 0.78125 mg/L (limit of quantitation) to 100 mg/L for both drugs. The Sy.x values were equal to 0.25 +/- 0.10 and 0.29 +/- 0.18 mg/L for daptomycin and linezolid, respectively. Precision values were lower than 20% over the entire range of calibration standard, and accuracy was within the range of 80% to 120% for all concentrations. The present method proved to be sensitive and specific to measure daptomycin and linezolid plasma concentrations in patients affected by severe Gram-positive infections, allowing therapeutic drug monitoring in those patients at major risk of severe adverse events.

Indications:5 patients with staphylococcal infections (2 sepsis, 2 endocarditis, and 1 knee prosthetic arthritis).TypeofStudy:Cubicin plasma and body fluid levels were measured by high performance liquid chromatography in patients with staphylococcal infection. Open study.DosageDuration:Plasma level group: 350-700 mg daily (6-8 mg/kg daily) iv as a 30 minute infusion. Duration: 5 days. Other fluids group: 6 mg/kg (n=1) or 8 mg/kg (n=1) daily. Duration: not stated.Results:Maximum plasma concentrations (Cmax) of Cubicin ranged from 52.8 up to 84.7 mg/L, whereas trough plasma concentrations were 12.5 mg/L, displaying a discrete interpatient variability. The Cmax/minimum inhibitory concentration value required for a bacteriostatic effect against Staphylococcus pneumoniae and Staphylococcus aureus was achieved (range, 106-169), whereas the Cmin value was associated with a reduced risk of creatine phosphokinase elevation in serum. Cubicin reached concentrations of 5.0 mg/l in pleural effusion of 1 patient who received 6 mg/kg daily and 15.8 mg/L in synovial fluid of 1 patient who received 8 mg/kg daily.FreeText:Drugs were extracted from plasma by adding methanol and, after centrifugation, clear supernatants were injected into the high-performance liquid chromatography system. Isocratic elution (1.5 mL/minute) was performed using a mobile phase consisting of ammonium phosphate buffer 40 mM, pH 4.0, acetonitrile; ultraviolet detection was used at 214 nm. Test: Cubicin blood levels.AdverseEffects:No patient had increased creatine phosphokinase levels.AuthorsConclusions:In conclusion, the present study demonstrates that the method described here is robust and reliable and may be useful to measure plasma concentrations of daptomycin and linezolid in plasma and other matrices. At present, the availability of this simple and rapid method in our unit is useful for all of those physicians who are administering daptomycin or linezolid to critically ill patients.Patients:7 patients. Plasma level group: 5 patients, 4 males and 1 female, mean age 54 years. Other fluids group: 2 patients, 1 man aged 61 years and 1 woman aged 80 years.