Gregory Medley

Plasma and tissue pharmacokinetics of cefazolin in patients undergoing elective and semielective abdominal aortic aneurysm open repair surgery.

ABSTRACT Surgical site infections are common, so effective antibiotic concentrations at the sites of infection, i.e., in the interstitial fluid (ISF), are required. The aim of this study was to evaluate contemporary perioperative prophylactic dosing of cefazolin by determining plasma and subcutaneous ISF concentrations in patients undergoing elective/semielective abdominal aortic aneurysm (AAA) open repair surgery. This was a prospective pharmacokinetic study in a tertiary referral hospital. Cefazolin (2 g) was administered as a 3-min slow bolus 30 min prior to incision in 12 enrolled patients undergoing elective/semielective AAA open repair surgery. Serial blood, urine, and ISF (via microdialysis) samples were collected and analyzed using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Cardiac output was determined using pulse waveform contours with Vigileo. The recruited patients had a median (interquartile range) age of 70 (66 to 76) years and weight of 88 (81 to 95) kg. The median (interquartile range) terminal volume of distribution was 0.14 (0.11 to 0.15) liter/kg, total clearance was 0.05 (0.03 to 0.06) liter/h, and minimum observed unbound concentration was 5.7 (5.4 to 8.1) mg/liter. The penetration of unbound drug from plasma to ISF was 85% (78% to 106%). We found correlations present, albeit weak, between cefazolin clearance and cardiac output (r2 = 0.11) and urinary creatinine clearance (r2 = 0.12). In conclusion, we found that a single 2-g dose of cefazolin administered 30 min before incision provides plasma and ISF concentrations in excess of the likely MICs for susceptible pathogens in patients undergoing AAA open repair surgery.

Simple and sensitive liquid chromatography-tandem mass spectrometry methods for quantification of paraquat in plasma and urine: application to experimental and clinical toxicological studies.

Simple, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods have been developed and validated for quantification of paraquat (PQ) in plasma and urine. Plasma and urine sample preparation were carried out by one-step protein precipitation using cold acetonitrile (-20 to -10 °C). After centrifugation, an aliquot of 10 μL of supernatant was injected into a Kinetex™ hydrophilic interaction chromatography (HILIC) column with a KrudKatcher™ Ultra in-line filter. The chromatographic separation was achieved using the mobile phase mixture of 250 mM ammonium formate (with 0.8% aqueous formic acid) in water and acetonitrile at a flow rate of 0.3 mL/min. Detection was performed using an API2000 triple quadrupole tandem mass spectrometer in multiple reaction monitoring (MRM) mode via an electrospray ionization (ESI) source. The calibration curve was linear over the concentration range of 10-5000 ng/mL, with an LLOQ of 10 ng/mL. The inter- and intra-day precision (% R.S.D.) were <8.5% and 6.4% for plasma and urine, respectively with the accuracies (%) within the range of 95.1-102.8%. PQ in plasma and urine samples was stable when stored at -70 °C for three freeze-thaw cycles. The methods were successfully applied to determine PQ concentration in rat and human samples.

Multiphoton microscopy and fluorescence lifetime imaging provide a novel method in studying drug distribution and metabolism in the rat liver in vivo

Multiphoton microscopy has been shown to be a useful tool in studying drug distribution in biological tissues. In addition, fluorescence lifetime imaging provides information about the structure and dynamics of fluorophores based on their fluorescence lifetimes. Fluorescein, a commonly used fluorescent probe, is metabolized within liver cells to fluorescein mono-glucuronide, which is also fluorescent. Fluorescein and its glucuronide have similar excitation and emission spectra, but different fluorescence lifetimes. In this study, we employed multiphoton fluorescence lifetime imaging to study the distribution and metabolism of fluorescein and its metabolite in vivo in rat liver. Fluorescence lifetime values in vitro were used to interpret in vivo data. Our results show that the mean fluorescence lifetimes of fluorescein and its metabolite decrease over time after injection of fluorescein in three different regions of the liver. In conclusion, we have demonstrated a novel method to study a fluorescent compound and metabolite in vivo using multiphoton fluorescence lifetime imaging.

Evaluation of limited sampling strategies for total and free prednisolone in adult kidney transplant recipients

PurposeThe aims of this study were to evaluate the predictive performances of all previously derived limited sampling strategies (LSSs) for total prednisolone, and to derive LSSs for free prednisolone in an independent cohort of adult kidney transplant recipients.MethodsTotal and free prednisolone area under the concentration–time curve profiles from 0 to 12 hours post-dose (AUC0–12) were collected from 20 subjects. All previously published total prednisolone LSSs were identified from the literature. Free prednisolone LSSs were developed using multiple linear regression analyses. AUC predicted by each of the LSSs was compared with AUC0–12. Median percentage prediction error (MPPE) and median absolute percentage prediction error (MAPE) were calculated to evaluate bias and imprecision.ResultsTotal dose-adjusted prednisolone exposure varied 5-fold among study participants, while free dose-adjusted prednisolone exposure varied 3-fold. Correlation (r2) between total and free prednisolone AUC0–12 was 0.79 (p = <0.0001) for the entire study cohort. This correlation was poorer in those early compared with late post-transplant (r2 = 0.42 (p = 0.04) versus r2 = 0.59 (p = 0.009) respectively). Ten previously published LSSs for total prednisolone and 15 derived LSSs for free prednisolone performed with acceptable levels of bias and imprecision (<15%). Of the free prednisolone LSSs, an equation incorporating 0.25-, 2- and 4-h concentrations showed the highest predictive power (AUC0–12 = −17.20 + 1.18 × C0.25 + 2.75 × C2 + 4.45 × C4; MPPE = 0.1%, MAPE = 4.6%).ConclusionsWide between-subject variability in drug exposure suggests a role for TDM. LSSs can accurately estimate both total and free prednisolone AUC0–12. However, given the poor correlation observed between the two parameters, our data suggest that free prednisolone LSSs may be preferable.

Simultaneous quantification of carbamate insecticides in human plasma by liquid chromatography/tandem mass spectrometry

Carbofuran (CFN), carbosulfan (CSN) and fenobucarb (FBC) are carbamate pesticides that are widely used in gardening and agriculture for the control of insects. Human poisoning due to occupational or self-poisoning exposures is also reported, so assays are required to quantify the plasma concentration of these insecticides. An LC-MS/MS method was developed and validated for the simultaneous quantification of these three carbamate insecticides in the plasma of patients with acute intentional self-poisoning. Plasma samples were pretreated by acetonitrile for protein precipitation. Chromatography was carried out on a Luna C18(2) analytical column with gradient elution using a mobile phase containing acetonitrile and water with 10mM ammonium acetate. Mass spectrometric analysis was performed by an Applied Biosystems MDS Sciex API 2000 triple quadrupole mass spectrometer coupled with electrospray ionization (ESI) source in the positive ion mode. The total run time was 7 min. The assay was validated over a concentration range from 10 to 1000 ng/ml for CSN and FBC and 20-2000 ng/ml for CFN. The precision and accuracy for both intra- and inter-day determination of all analytes were acceptable (<15%). No significant matrix effect was observed. Stability of compounds was established for short term bench and autosampler storage as well as freeze/thaw cycles. The method was effectively applied to 270 clinical samples from patients with a history of acute intentional carbamate self-poisoning.

Determination of trovafloxacin and marbofloxacin in sheep plasma samples by HPLC using UV detection

A simple and rapid high performance liquid chromatographic method was developed, validated and applied for the simultaneous determination of marbofloxacin (MBX) and trovafloxacin (TVX) in sheep plasma. Samples were extracted with 20% perchloric acid and MBX and TVX were separated on a C(18) column using a gradient mobile phase system consisting of 17.5mM of NaH(2)PO(4) and 1.5mM of tetrabutylammonium hydroxide aqueous solution, pH 3 (A) and 50% acetonitrile and 50% methanol (B), with UV detection at 293 and 270 nm. The retention times of MBX and TVX were 4.9 and 6.6 min respectively. The detection and quantification limits for MBX and TVX were 2 ng/mL and 10 ng/mL respectively for both compounds. The calibration curves were linear over a concentration range of 10-50,000 ng/mL for both antibiotics. The linearity, precision, accuracy, recovery and stability of the assay were evaluated from spiked sheep plasma. The method was successfully applied to sheep plasma samples obtained from MBX and TVX pharmacokinetic studies.

Isoniazid poisoning: Pharmacokinetics and effect of hemodialysis in a massive ingestion.

Isoniazid is a rare overdose that causes seizures and there is limited evidence to guide treatment. We report a 20‐year‐old female migrant who presented with recurrent seizures after ingesting 25 g of isoniazid. She was treated with activated charcoal, repeated doses of midazolam for the seizures, and given multiple doses of pyridoxine (14 mg), limited by availability. She was admitted to intensive care, and 5.5 hours post‐ingestion, she was commenced on continuous veno‐venous hemodiafiltration (CVVHDF). She was extubated after 24 hours and CVVHDF was ceased 6 hours later (30 hours post‐overdose). Her renal function remained normal and her initial lactate was the highest at 2.3. She made a full recovery. Five plasma samples were collected before, during, and after CVVHDF, and isoniazid was quantified with liquid chromatography‐tandem mass spectrometry. A pharmacokinetic analysis of time‐isoniazid concentration data was fitted to a two‐compartment model with first‐order input (with fixed ka) with the effect of CVVHDF modeled as a time‐dependent covariate. This suggested that there was initially good clearance with CVVHDF (4 times endogenous clearance), which rapidly declined within hours.

Acute intentional self-poisoning with a herbicide product containing fenoxaprop-P-ethyl, ethoxysulfuron and isoxadifen ethyl. A prospective observational study

Background. Herbicides are commonly ingested for self-harm, but relatively little has been published on poisoning with herbicides other than paraquat and glyphosate. We report here a case series of patients with acute exposure to a combination herbicide (brand name Tiller Gold or Whip Super) containing the selective phenoxy herbicide compounds fenoxaprop-P-ethyl and ethoxysulfuron and a safener isoxadifen ethyl. Method. Clinical data on all patients presenting with Tiller Gold or Whip Super poisoning to two General Hospitals in Sri Lanka from 2002–2008 were collected prospectively until discharge. Results. Eighty-six patients with a history of Tiller Gold or Whip Super ingestion were included. The main clinical features were an epigastric burning sensation and vomiting; however, most of those who vomited had received gastric lavage or forced emesis. Eight patients had a reduced level of consciousness on admission (Glasgow coma scale 9–14) that resolved without intervention over several hours. Only symptomatic and supportive care was required. The median hospital stay was 1 day (IQR: 1–2) and the case fatality was zero (95% confidence interval: 0–4.2%). This low case fatality compared favorably with the case fatality of other common herbicides in our cohort: paraquat >40%, propanil >10%, 4-chloro-2-methylphenoxyacetic acid > 5%, and glyphosate >2%. Conclusion. This combination herbicide product appears to be safe in patients with acute self-poisoning, particularly in comparison with other herbicides, and causing few clinical features.

Using deconvolution to understand the mechanism for variable plasma concentration-time profiles after intramuscular injection.

To introduce better antibiotics for the treatment of some infectious diseases in sheep and to expand the range of antibiotics available for veterinary medicine, pharmacokinetics of two antibiotics marbofloxacin (MBX) and trovafloxacin (TVX) were investigated in sheep after intramuscular injection. Variable and irregular plasma concentration-time profiles were observed for TVX but not for MBX. To understand the mechanism of this phenomenon, intravenous studies were performed for both drugs and data were analyzed using a population approach. Deconvolution was then performed using various approaches to obtain absorption profiles of both drugs in sheep after intramuscular injection. The Loo-Riegelman and staircase deconvolution function methods were found to provide more reliable estimates of absorption rate than the Spath-spline and B-spline constraining break points deconvolution methods. The absorption profiles resulting from deconvolution indicated a zero-order absorption process for TVX and a first-order process for MBX. Precipitation of TVX at the injection site was suspected to cause the pseudo zero-order absorption. This hypothesis was supported by the observation of crystalline deposits of TVX in sheep meat after direct injection, using reflectance confocal microscopy.

2-Methyl-4-chlorophenoxyacetic acid and bromoxynil herbicide death

Abstract Case report. We report a fatal case of a 37 year old gentleman who ingested a MCPA/bromoxynil co-formulation herbicide. Although clinically well on initial examination, our patient declined dramatically over his 18 h admission with increasing CO2 production, hyperthermia and metabolic derangement to eventually die from cardiac asystole 20 h post ingestion. Two hours after ingestion the MCPA concentration was 83.9 μg/mL and bromoxynil concentration was 137 μg/mL. Discussion. The patients’ mechanism of death appeared to be uncoupling of oxidative phosphorylation, excess CO2 production and hyperthermia. There is limited knowledge on the acute toxicity of these herbicides, in particular bromoxynil, and this case highlights the relentless progression of severe toxicity in humans.