Penicillin G Treatment in Infective Endocarditis Patients - Does Standard Dosing Result in Therapeutic Plasma Concentrations?

Penicillin G is frequently used to treat infective endocarditis (IE) caused by streptococci, penicillin-susceptible staphylococci and enterococci. Appropriate antibiotic exposure is essential for survival and reduces the risk of complications and drug resistance development. We determined penicillin G plasma concentration [p-penicillin] once weekly in 46 IE patients. The aim was to evaluate whether penicillin G 3 g every 6 hr (q6 h) resulted in therapeutic concentrations and to analyse potential factors that influence inter- and intra-individual variability, using linear regression and a random coefficient model. [P-penicillin] at 3 hr and at 6 hr was compared with the minimal inhibitory concentration (MIC) of the bacteria isolated from blood cultures to evaluate the following PK/PD targets: 50% fT > MIC and 100% fT > MIC. [P-penicillin] varied notably between patients and was associated with age, weight, p-creatinine and estimated creatinine clearance (eCLcr). Additionally, an increase in [p-penicillin] during the treatment period showed strong correlation with age, a low eCLcr, a low weight and a low p-albumin. Of the 46 patients, 96% had [p-penicillin] that resulted in 50% fT > MIC, while 71% had [p-penicillin] resulting in 100% fT > MIC. The majority of patients not achieving the 100% fT > MIC target were infected with enterococci. Streptococci and staphylococci isolated from blood cultures were highly susceptible to penicillin G. Our results suggest that penicillin G 3 g q6 h is suitable to treat IE caused by streptococci and penicillin-susceptible staphylococci, but caution must be taken when the infection is caused by enterococci. When treating enterococci, therapeutic drug monitoring should be applied to optimize penicillin G dosing and exposure.

Moxifloxacin pharmacokinetic profile and efficacy evaluation in empiric treatment of community-acquired pneumonia.

When antimicrobials are used empirically, pathogen MICs equal to clinical breakpoints or epidemiological cutoff values must be considered. This is to ensure that the most resistant pathogen subpopulation is appropriately targeted to prevent emergence of resistance. Accordingly, we determined the pharmacokinetic (PK) profile of moxifloxacin at 400 mg/day in 18 patients treated empirically for community-acquired pneumonia. We developed a population pharmacokinetic model to assess the potential efficacy of moxifloxacin and to simulate the maximal MICs for which recommended pharmacokinetic-pharmacodynamic (PK-PD) estimates are obtained. Moxifloxacin plasma concentrations were determined the day after therapy initiation using ultra-high-performance liquid chromatography. Peak drug concentrations (Cmax) and area under the free drug concentration-time curve from 0 to 24 h (fAUC0-24) values predicted for each patient were evaluated against epidemiological cutoff MIC values for Streptococcus pneumoniae, Haemophilus influenzae, and Legionella pneumophila. PK-PD targets adopted were a Cmax/MIC of ≥12.2 for all pathogens, an fAUC0-24/MIC of >34 for S. pneumoniae, and an fAUC0-24/MIC of >75 for H. influenzae and L. pneumophila. Individual predicted estimates for Cmax/MIC and fAUC0-24/MIC as well as simulated maximal MICs resulting in target attainment for oral and intravenous administration of the drug were suitable for S. pneumoniae and H. influenzae but not for L. pneumophila. These results indicate that caution must be taken when moxifloxacin is used as monotherapy to treat community-acquired pneumonia caused by L. pneumophila. In conclusion, this report reveals key information relevant to the empirical treatment of community-acquired pneumonia while highlighting the robust and flexible nature of this population pharmacokinetic model to predict therapeutic success. (Clinical Trials Registration no. NCT01983839.).