Browsing by Author "Muchohi, Simon N."

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    Chloramphenicol Pharmacokinetics in African children with severe malaria
    (Journal of tropical pediatrics, ) Kokwaro, G.; Muchohi, Simon N.; Ogutu, Benhards R.; Newton, Charles RJC
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    Determination of ciprofloxacin in human plasma using high-performance liquid chromatography coupled with fluorescence detection: Application to a population pharmacokinetics study in children with severe malnutrition
    (Journal of Chromatography B, ) Kokwaro, G.; Muchohi, Simon N.; Thuo, Nahashon; Karisa, Japhet; Muturi, Alex; Maitland, Kathryn
    Clinical pharmacokinetic studies of ciprofloxacin require accurate and precise measurement of plasma drug concentrations. We describe a rapid, selective and sensitive HPLC method coupled with fluorescence detection for determination of ciprofloxacin in human plasma. Internal standard (IS; sarafloxacin) was added to plasma aliquots (200uL) prior to protein precipitation with acetonitrile. Ciprofloxacin and IS were eluted on a Synergi Max-RP analytical column (150mm×4.6mm i.d., 5um particle size) maintained at 40 ◦C. The mobile phase comprised a mixture of aqueous orthophosphoric acid (0.025 M)/methanol/acetonitrile (75/13/12%, v/v/v); the pH was adjusted to 3.0 with triethylamine. A fluorescence detector (excitation/emission wavelength of 278/450 nm) was used. Retention times for ciprofloxacin and IS were approximately 3.6 and 7.0 min, respectively. Calibration curves of ciprofloxacin were linear over the concentration range of 0.02–4ug/mL, with correlation coefficients (r2)≥0.998. Intraand inter-assay relative standard deviations (SD) were <8.0% and accuracy values ranged from 93% to 105% for quality control samples (0.2, 1.8 and 3.6ug/mL). The mean (SD) extraction recoveries for ciprofloxacin from spiked plasma at 0.08, 1.8 and 3.6ug/mL were 72.8±12.5% (n = 5), 83.5±5.2% and 77.7±2.0%, respectively (n = 8 in both cases). The recovery for IS was 94.5±7.9% (n = 15). The limits of detection and quantification were 10 ng/mL and 20 ng/mL, respectively. Ciprofloxacin was stable in plasma for at least one month when stored at −15 ◦C to −25 ◦C and −70 ◦C to −90 ◦C. This method was successfully applied to measure plasma ciprofloxacin concentrations in a population pharmacokinetics study of ciprofloxacin in malnourished children.
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    Population pharmacokinetics of a single daily intramuscular dose of gentamicin in children with severe malnutrition
    (Journal of Antimicrobial Chemotherapy, ) Kokwaro, G.; Seaton, Claire; Ignas, James; Muchohi, Simon N.; Maitland, Kathryn; Thomson, Alison
    Objectives: The World Health Organization recommends that all children admitted with severe malnutrition should routinely receive parenteral ampicillin and gentamicin; despite this, mortality remains high. Since this population group is at risk of altered volume of distribution, we aimed to study the population pharmacokinetics of once daily gentamicin (7.5 mg/kg) in children with severe malnutrition and to evaluate clinical factors affecting pharmacokinetic parameters. Methods: Thirty-four children aged 0.5–10 years were studied. One hundred and thirty-two gentamicin concentrations (median of four per patient), drawn 0.4–24.6 h after administration of the intramuscular dose, were analysed. The data were fitted by a two-compartment model using the population package NONMEMw. Results: Gentamicin was rapidly absorbed and all concentrations measured within the first 2 h after administration were >8 mg/L (indicating that satisfactory peak concentrations were achieved). Ninetyeight percent of samples measured more than 20 h after the dose were <1 mg/L. The best model included weight, and it was found that high base deficit, high creatinine concentration and low temperature (all markers of hypovolaemic shock) reduced clearance (CL/F). Weight influenced volume of the central (V1/F) and peripheral (V2/F) compartments, and high base deficit reduced V2/F and intercompartmental CL (Q/F). Interindividual variability in CL was 26%, in V1/F 33% and in V2/F and Q/F was 52%. Individual estimates of CL/F ranged from 0.02 to 0.16 (median 0.10) L/h/kg and those of Vss/F from 0.26 to 1.31 (median 0.67) L/kg. Initial half-lives had a median of 1.4 h and elimination half-lives and a median of 14.9 h. Excessive concentrations were observed in one patient who had signs of renal impairment and shock. Conclusions: Although a daily dose of 7.5 mg/kg achieves satisfactory gentamicin concentrations in the majority of patients, patients with renal impairment and shock may be at risk of accumulation with 24 hourly dosing. Further studies of gentamicin pharmacokinetics in this group are now needed to inform future international guideline recommendations.