Jennifer Norman

Determinants of Rifampin, Isoniazid, Pyrazinamide, and Ethambutol Pharmacokinetics in a Cohort of Tuberculosis Patients

ABSTRACT Evaluation of sources of pharmacokinetic variation can facilitate optimization of tuberculosis treatment regimens by identification of avoidable sources of variation and of risk factors for low or high drug concentrations in patients. Our objective was to describe the pharmacokinetics of rifampin, isoniazid, pyrazinamide, and ethambutol in a cohort of tuberculosis patients established on first-line treatment regimens and to evaluate the determinants of pharmacokinetic variation. Plasma concentration-time profiles were determined for each of the drugs in 142 patients with drug-sensitive pulmonary tuberculosis after 2 months of daily treatment in hospital. Pharmacokinetic measures were described by noncompartmental analysis. Multiple linear regression was used to evaluate the patient and the treatment factors associated with variation of the area under the concentration-time curve from 0 to 8 h. Several factors independently associated with variations in antituberculosis drug concentrations were identified: human immunodeficiency virus infection was associated with 39% and 27% reductions for rifampin and ethambutol, respectively; formulation factors were determinants of rifampin and isoniazid bioavailability; female patients had increased rifampin and isoniazid concentrations but reduced ethambutol concentrations; older patients had higher levels of isoniazid and ethambutol; patients with a history of previous antituberculosis treatment had lower ethambutol concentrations; and the dose per kilogram of body weight was associated with the concentrations of all four agents. Further studies are required to assess the implications of variations in antituberculosis drug concentrations for efficacy and safety before decisions are made to change the dosing strategy in patients at risk.

Pharmacokinetics of Ofloxacin and Levofloxacin for Prevention and Treatment of Multidrug-Resistant Tuberculosis in Children

ABSTRACT Limited data on fluoroquinolone pharmacokinetics and cardiac effects in children exist. Among 22 children receiving drug-resistant tuberculosis prophylaxis or treatment, serum concentrations following oral doses of levofloxacin (15 mg/kg of body weight) and ofloxacin (20 mg/kg) were lower than those expected from existing pediatric data, possibly due to differences in the formulations (crushed tablets). Drug exposures were lower than those in adults following standard doses and below the proposed pharmacodynamic targets, likely due to more rapid elimination in children. No QT prolongation was observed.

A liquid-liquid LC/MS/MS assay for the determination of artemether and DHA in malaria patient samples.

A solvent extraction method was developed and validated for the determination of the antimalarial drug, artemether and its active metabolite dihydroartemisinin (DHA) in malaria patient plasma samples. An AB Sciex 4000 triple quadrupole mass spectrometer in the multiple reaction monitoring (MRM) mode was used for detection in the positive ionisation mode. Liquid-liquid extraction was followed by PFP liquid chromatography and tandem mass spectrometry. Stable isotope labelled artemether and DHA was used as internal standards. The calibration range was between 2.00 and 500 ng/ml for both artemether and DHA during the original validation and the upper limit was lowered to 200 ng/ml during a re-instatement validation, prior to sample analysis. The assay was used to measure artemether and DHA in human plasma samples, which were generated from a safety and efficacy clinical trial in Mbarara, Uganda; as well as for a pharmacokinetic interaction study between the antimalarial combination artemether/lumefantrine and combination antiretroviral therapy including nevirapine in HIV-infected adults.

Antimalarial and anticancer activities of artemisinin-quinoline hybrid-dimers and pharmacokinetic properties in mice

Malaria, one of the three most important life-threatening infectious diseases, is recommended to be treated with ACT (artemisinin combination therapy) against which Plasmodium falciparum already displayed resistance. Two artemisinin-4-amino-quinoline hybrid-dimers (1 and 2), previously synthesized, possessed low nanomolar in vitro antiplasmodial activity, while poorly toxic against mammalian cells. They are here investigated to ascertain whether this antimalarial activity would be carried on in vivo against Plasmodium vinckei. During the four day treatment, parasitemia of less than 1% were observed on day 5 after doses from 2.5 mg/kg ip and 50 mg/kg po for hybrid-dimer 1, and from 7.5 mg/kg ip and 25 mg/kg po for hybrid-dimer 2. Snapshot pharmacokinetic analysis demonstrated that the antiplasmodial activity of these C-10-acetal artemisinin dimers may be due to active metabolites, which were confirmed by in silico findings. Hybrid-dimer 1 also displayed potent in vitro activity against tumor cells and was found to be more active than etoposide against TK10, UACC62 and MCF7 cell lines (TGI values 3.45 vs. 43.33 μM, 2.21 vs. 45.52 μM and 2.99 vs. >100 μM, respectively). The 1,3-diaminopropane linker, present in hybrid-dimer 1, was therefore identified as the optimum linker.

Synthesis and in Vitro and in Vivo Pharmacological Evaluation of New 4-Aminoquinoline-Based Compounds

A new class of 4-aminoquinolines was synthesized and evaluated in vitro for antiplasmodial activity against both the chloroquine-sensitive (3D7) and -resistant (K1 and W2) strains. The most active compounds 3c-3e had acceptable cytotoxicity but showed strong inhibition toward a panel of cytochrome P450 enzymes in vitro. Pharmacokinetic studies on 3d and 3e in mice showed that they had moderate half-life (4-6 h) and low oral bioavailability. The front runner compound 3d exhibited moderate inhibition of the malaria parasite on P. berghei infected mice following oral administration (5 mg/kg), achieving reduction of parasitemia population by 47% on day 7.

An LC-MS/MS method for the determination of ofloxacin in 20 μl human plasma.

A sensitive and selective liquid chromatography-tandem mass spectrometry method was developed and validated for the determination of ofloxacin in 20 μl human plasma over the concentration range of 0.078-20 μg/ml. Sample preparation was achieved by protein precipitation with acetonitrile and methanol containing the internal standard (Gatifloxacin). Chromatographic separation was achieved on a Luna 5 μm PFP (110 A, 50 × 2 mm) column with acetonitrile and water containing 0.1% formic acid (50:50, v/v) as the mobile phase, at a flow rate of 400 μl/ml. The within-day and between-day precision determinations for ofloxacin, expressed as the percentage coefficient of variation, were lower than 7% at all test concentrations. Recovery of ofloxacin was greater than 70% and reproducible at the low, medium and high end of the dynamic range. No significant matrix effects were observed for the analyte or internal standard. The assay was successfully used to examine the pharmacokinetics of ofloxacin as part of a study to characterize the pharmacokinetics of a number of anti-tuberculosis drugs utilized in the treatment of multi-drug resistant tuberculosis (MDR-TB).

Nevirapine Concentrations in Preterm and Low Birth Weight HIV-Exposed Infants: Implications for Dosing Recommendations

World Health Organisation guidelines recommend nevirapine 2 mg/kg/d for HIV-exposed infants <2 kg, but 4–6 mg/kg/d for infants >2 kg. In 116 low birth weight infants, nevirapine 2 mg/kg/d until 14 days, and 4 mg/kg/d thereafter, was safe (1 mild possibly related rash) and achieved target plasma concentrations. Concentrations decreased with treatment duration. Routine dose increase at 14 days should be considered.

Pharmacokinetics of the First-Line Antituberculosis Drugs in Ghanaian Children with Tuberculosis with or without HIV Coinfection

ABSTRACT Although human immunodeficiency virus (HIV) coinfection is the most important risk factor for a poor antituberculosis (anti-TB) treatment response, its effect on the pharmacokinetics of the first-line drugs in children is understudied. This study examined the pharmacokinetics of the four first-line anti-TB drugs in children with TB with and without HIV coinfection. Ghanaian children with TB on isoniazid, rifampin, pyrazinamide, and ethambutol for at least 4 weeks had blood samples collected predose and at 1, 2, 4, and 8 hours postdose. Drug concentrations were determined by validated liquid chromatography-mass spectrometry methods and pharmacokinetic parameters calculated using noncompartmental analysis. The area under the concentration-time curve from 0 to 8 h (AUC0–8), maximum concentration (Cmax), and apparent oral clearance divided by bioavailability (CL/F) for each drug were compared between children with and without HIV coinfection. Of 113 participants, 59 (52.2%) had HIV coinfection. The baseline characteristics were similar except that the coinfected patients were more likely to have lower weight-for-age and height-for-age Z scores (P < 0.05). Rifampin, pyrazinamide, and ethambutol median body weight-normalized CL/F values were significantly higher, whereas the plasma AUC0–8 values were lower, in the coinfected children than in those with TB alone. In the multivariate analysis, drug dose and HIV coinfection jointly influenced the apparent oral clearance and AUC0–8 for rifampin, pyrazinamide, and ethambutol. Isoniazid pharmacokinetics were not different by HIV coinfection status. HIV coinfection was associated with lower plasma exposure of three of the four first-line anti-TB drugs in children. Whether TB/HIV-coinfected children need higher dosages of rifampin, pyrazinamide, and ethambutol requires further investigation. (This study has been registered at ClinicalTrials.gov under identifier NCT01687504.)

Relative bioavailability of bedaquiline tablets suspended in water: Implications for dosing in children

Bedaquiline is an important novel drug for treatment of multidrug‐resistant tuberculosis, but no paediatric formulation is yet available. This work aimed to explore the possibility of using the existing tablet formulation in children by evaluating the relative bioavailability, short‐term safety, acceptability and palatability of suspended bedaquiline tablets compared to whole tablets.

The determination of capreomycin in human plasma by LC-MS/MS using ion-pairing chromatography and solid-phase extraction

A bioanalytical method was developed and validated for the quantification of capreomycin (Cm) analogs, Cm IA and Cm IB, in human plasma. This implemented ion-pairing solid phase extraction, followed by ion-pairing high-performance liquid chromatography, with tandem mass spectrometry detection. Chromatographic separation was achieved using a Discovery C18 , 5 μm, 4.6 × 50 mm analytical column. An isocratic mobile phase consisting of water and acetonitrile with 0.1% formic acid and 4mm heptafluorobutyric acid (80:20; v/v) was used at a flow-rate of 500 μL/min. An AB Sciex API 3000 mass spectrometer at unit resolution, in multiple reaction monitoring mode, was used for detection. Electrospray ionization was used for ion production. The method was successfully validated for the range 469-30,000 ng/mL for Cm IA and for Cm IB, with cefotaxime as the internal standard. The within- and between-day precision determinations for Cm IA and IB, expressed as the percentage coefficient of variation, were < 20.0% at the lower limit of quantification (LLOQ) and < 8.2% at all other test concentrations. Recovery of both analogs was > 72.3% and reproducible at the low, medium and high end of the calibration range. No significant matrix effects were observed for the analyte. The assay performed well when applied to clinical samples generated from children in a clinical multidrug resistant tuberculosis research study in South Africa.