Population Pharmacokinetics and Pharmacodynamics Modeling of Oral Levofloxacin.

Background: Levofloxacin, a fluoroquinolone, is an isomer of ofloxacin with an extensive spectrum of antimicrobial efficacy. In common with other fluoroquinolones, the main pharmacokinetic/pharmacodynamic (PK/PD) index that correlates with its therapeutic efficacy is the area under the plasma time-concentration curve (AUC)/the minimum inhibitory concentration (MIC) ratios. Objective: To evaluate the population PK and determine the efficacy of various dosage regimens in achieving the probability of target attainment (PTA) and the cumulative fraction of response (CFR) of oral levofloxacin when prescribed as the switching therapy after intravenous levofloxacin treatment. Material and Method: The PK studies were conducted in 45 healthy volunteers who received one 500 mg tablet of levofloxacin and PTAs were determined by using a Monte Carlo simulation. The dosage regimens were predicted to achieve CFR greater than or equal to 90% by referral to the MIC distributions database of the European Committee on Antimicrobial Susceptibility Testing. Results: The population PKs of levofloxacin were; the volume of distribution (V) = 101.71±1.41 L, total clearance (CL) = 8.51±1.43 L/hour and the area under the plasma time-concentration curve from 0 to 24 hours (AUC0-24 ) = 66.19±1.30 mg*hour/L. The predicted CFRs for a target AUC0-24 /MIC ratio of 30 for S. aureus and S. pneumoniae were 83.12% and 92.63%, respectively for 500 mg levofloxacin, and 84.96% and 98.17%, respectively for 750 mg levofloxacin. The predicted CFRs for a target AUC0-24 /MIC ratio of 125 for E. coli and Klebsiella spp. were 84.25% and 88.81%, respectively for 500 mg levofloxacin and 86.00% and 91.34%, respectively for 750 mg levofloxacin. Conclusion: The population PKs of levofloxacin in the present study were similar to the values obtained from the previous study. Both 500 mg qd and 750 mg qd of oral levofloxacin dosage regimens had a high probability of achieving optimal impact against S. pneumoniae, but only the 750 mg qd dosage regimen achieved optimal exposure against Klebsiella spp.

Higher phthalate concentrations are associated with precocious puberty in normal weight Thai girls.

BACKGROUND: The cause of precocious puberty may be associated with genetics and other conditions such as central nervous system (CNS) insults, or the exposure to endocrine disrupting chemicals (EDCs). Phthalates is known to be one of the EDCs and have estrogenic and antiandrogenic activities, and may be associated with advanced puberty. The objective of the study was to determine the association between urinary phthalate metabolites and advanced puberty. METHODS: A cross-sectional study was conducted in patients with precocious puberty (breast onset <8 years, n=42) and early puberty (breast onset 8-9 years, n=17), compared to age-matched controls (n=77). Anthropometric measurements, estradiol, basal and gonadotropin releasing hormone (GnRH)-stimulated follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels, uterine sizes, ovarian diameters and bone ages (BA) were obtained. Urine samples were collected and mono-methyl phthalate (MMP) and mono-ethyl phthalate (MEP) were analyzed by high performance liquid chromatography (HPLC) and adjusted with urine creatinine. RESULTS: The median adjusted-MEP concentration in girls with precocious puberty, was greater than in normal girls (6105.09 vs. 4633.98 µg/g Cr: p<0.05), and had the same trend among early puberty and normal puberty (5141.41 vs. 4633.98 µg/g Cr: p=0.4), but was not statistically significant. CONCLUSIONS: Precocious puberty girls had an association with increased MEP concentration. This is the first report of the association between urinary phthalate levels and precocious puberty in Thai girls.

Population pharmacokinetics and Monte Carlo dosing simulations of meropenem during the early phase of severe sepsis and septic shock in critically ill patients in intensive care units.

Pathophysiological changes during the early phase of severe sepsis and septic shock in critically ill patients, resulting in altered pharmacokinetic (PK) patterns for antibiotics, are important factors influencing therapeutic success. The aims of this study were (i) to reveal the population PK parameters and (ii) to assess the probability of target attainment (PTA) for meropenem. The PK studies were carried out following administration of 1 g of meropenem every 8 h during the first 24 h of severe sepsis and septic shock in nine patients, and a Monte Carlo simulation was performed to determine the PTA of achieving 40% exposure time during which the free plasma drug concentration remains above the MIC (fT>MIC) and 80% fT>MIC. The volume of distribution (V) and total clearance (CL) of meropenem in these patients were 23.7 liters and 7.82 liters/h, respectively. For pathogens with MICs of 4 µg/ml, the PTAs of 40% fT>MIC following administration of meropenem as a 1-h infusion of 1 g every 8 h and a 4-h infusion of 0.5 g every 8 h were 92.52% and 90.29%, respectively. For pathogens with MICs of 2 µg/ml in immunocompromised hosts, the PTAs of 80% fT>MIC following administration of 1-h and 4-h infusions of 2 g of meropenem every 8 h were 84.32% and 94.72%, respectively. These findings indicated that the V of meropenem was greater and the CL of meropenem was lower than the values obtained in a previous study with healthy subjects. The maximum recommended dose, i.e., 2 g of meropenem every 8 h, may be required for treatment of life-threatening infections in this patient population.