Variable linezolid exposure and response and the role of therapeutic drug monitoring: Case series

Two patients with normal renal function, yet each showed unexpected, supra- and subtherapeutic linezolid plasma concentrations resulting in toxicity and ineffective therapy, respectively. TDM helps to early identify and correct such excursions.

Evaluation of treatment options for methicillin-resistant Staphylococcus aureus infections in the obese patient

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major cause of infection in both the hospital and community setting. Obesity is a risk factor for infection, and the prevalence of this disease has reached epidemic proportions worldwide. Treatment of infections in this special population is a challenge given the lack of data on the optimal antibiotic choice and dosing strategies, particularly for treatment of MRSA infections. Obesity is associated with various physiological changes that may lead to altered pharmacokinetic parameters. These changes include altered drug biodistribution, elimination, and absorption. This review provides clinicians with a summary of the literature pertaining to the pharmacokinetic and pharmacodynamic considerations when selecting antibiotic therapy for the treatment of MRSA infections in obese patients.

Sex and body weight are major determinants of venlafaxine pharmacokinetics

We assessed the effect of body weight and BMI on plasma concentrations of venlafaxine (VEN), O-desmethylvenlafaxine (ODVEN), active moiety (AM=VEN+ODVEN), and dose-corrected plasma concentrations (C/D). A database containing concentrations of VEN and ODVEN including 737 of 1594 eligible patients was analyzed. Analyses included sex, body weight, and BMI as well as concentrations of VEN, ODVEN, AM, and C/D. A positive correlation was detected between body weight and daily dosage (rs=0.168, P<0.001). A negative correlation was found between body weight and AM (rs=-0.124, P=0.001) and ODVEN (rs=-0.137, P<0.001). Negative correlations were also found between body weight and C/D ratios (C/D VEN: rs=-0.134, P<0.001, C/D ODVEN: rs=-0.239, P<0.001, C/D AM: rs=-0.256, P<0.001). No correlations were detected between BMI and concentrations for VEN, ODVEN, and AM. Comparing low-BMI (<20 kg/m²), medium-BMI (20-29.9 kg/m²), and high-BMI (≥30 kg/m²) groups, higher values of some pharmacokinetic variables in the lower BMI group did not remain significant after controlling for sex. Women had higher VEN, ODVEN, AM, and C/D values for AM, VEN, and ODVEN than men (P<0.001 for all comparisons). Our results highlight the role of different pharmacokinetically relevant parameters and foremost of sex as mediators for the effect of BMI on VEN metabolism.

Optimization of linezolid therapy in the critically ill: the effect of adjusted infusion regimens

Objectives

Insufficient linezolid levels, which are associated with a poorer outcome, are often observed in ICU patients who receive standard dosing. Although strategies to overcome these insufficient levels have been discussed, appropriate alternative dosing regimens remain to be identified.

Methods

Various infusion regimens (1200-3600 mg/day; q6h, q8h, q12h and continuous) were simulated in 67 000 ICU patients. The probability of attaining pharmacodynamic targets ( T >MIC ≥85%, AUC/MIC ≥100, cumulative fraction of response for Staphylococcus aureus and Enterococcus spp., PTA for an MIC of 0.5-4 mg/L) as well as the avoidance of toxic concentrations and concentrations constantly below the MIC (lack of antibiotic effect) or inside a mutant selection window (resistance development) were evaluated.

Results

Best target attainment according to T >MIC was observed for continuous infusions, followed by q6h, q8h and q12h. A substantially reduced target attainment was observed in patients with acute respiratory distress syndrome (ARDS). In patients without ARDS, 1200 mg/day was insufficient irrespective of the regimen, while a dose of 1400 mg/day administered q6h or by continuous infusions provided an acceptable target attainment (e.g. cumulative fraction of response with regards to T >MIC  ≥93%). Higher rates of potentially toxic trough concentrations (28% versus 12%) and concentrations constantly inside the mutant selection window (15% versus <0.1%) were observed with continuous infusions compared with q6h infusions (1400 mg/day, patients without ARDS).

Conclusions

Irrespective of the regimen, 1200 mg/day linezolid might be insufficient for the treatment of ICU patients. Patients without ARDS might particularly benefit from q6h infusions with increased daily doses (e.g. 1400 mg/day).