A case of pulmonary edema due to guanfacine intoxication with measurement of serum guanfacine concentrations.

Guanfacine hydrochloride extended-release (GXR) is used to treat attention deficit hyperactivity disorder. It is a selective α2A-adrenorecepor agonist that was reported to cause QT prolongation and hypotension in the event of overdosing. We report the case of a 17-year-old man who took 226 tablets of GXR 3 mg for attempted suicide. He was found complaining of dyspnea, and emergency medical services were called. When the patient was transferred to our hospital, his Glasgow coma scale was 12 (E4V3M5). He was agitated and hypoxemic. He was intubated for invasive mechanical ventilation under sedation. His chest X-ray and computed tomography scan showed pulmonary edema. Transthoracic echocardiography showed markedly reduced cardiac function. His serum guanfacine concentration peaked on day 3 after admission. His pulmonary edema improved quickly after a decrease in serum guanfacine concentration, but cardiac decompensation persisted for about 1 month. This case reveals that the decline in cardiac function after guanfacine intoxication is prolonged even after its serum concentration has decreased.

Population pharmacokinetic and exposure-response analyses of guanfacine in Japanese pediatric ADHD patients.

Guanfacine hydrochloride extended-release tablet (GXR) is approved for child and adolescent patients with attention-deficit/hyperactivity disorder (ADHD). The aims of this study were to develop a population pharmacokinetic model of guanfacine after administration of GXR and to evaluate factors influencing the pharmacokinetics of guanfacine in pediatric ADHD patients. A population pharmacokinetic analysis was performed using 3231 plasma concentration data items of guanfacine for pediatric ADHD patients aged 6-17 years obtained from clinical studies in Japan and the US. In addition, the relationship of the ADHD Rating Scale IV (ADHD RS-IV, efficacy endpoint) total score with exposure to guanfacine was assessed for Japanese pediatric ADHD patients. A one-compartment model with first-order absorption and lag time well described the plasma concentration data of guanfacine in pediatric ADHD patients. Body weight was selected as a covariate of apparent total body clearance and apparent volume of distribution. There was no pharmacokinetic difference between Japanese and non-Japanese pediatric ADHD patients. The results suggested a tendency of exposure-dependent reduction in the ADHD RS-IV total score, whereas the reduction was observed even at low plasma exposure levels compared with the placebo group.

A thorough QT study of guanfacine.

OBJECTIVES: Guanfacine extended- release (GXR) is approved for the treatment of attention-deficit/hyperactivity disorder in children and adolescents. As part of the clinical development of GXR, and to further explore the effect of guanfacine on QT intervals, a thorough QT study of guanfacine was conducted (ClinicalTrials. gov identifier: NCT00672984). METHODS: In this double-blind, 3-period, crossover trial, healthy adults (n = 83) received immediaterelease guanfacine (at therapeutic (4 mg) and supra-therapeutic (8 mg) doses), placebo, and 400 mg moxifloxacin (positive control) in 1 of 6 randomly assigned sequences. Continuous 12-lead electrocardiograms were extracted, and guanfacine plasma concentrations were assessed pre-dose and at intervals up to 24 hours post-dose. QT intervals were corrected using 2 methods: subject-specific (QTcNi) and Fridericia (QTcF). Time-matched analyses examined the largest, baseline-adjusted, drug-placebo difference in QTc intervals. RESULTS: In the QTcNi analysis, the largest 1-sided 95% upper confidence bound (UCB) through hour 12 was 1.94 ms (12 hours postdose). For the 12-hour QTcF analysis, the largest 1-sided 95% UCB was 10.34 ms (12 hours post-supratherapeutic dose), representing the only 1-sided 95% UCB > 10 ms. Following the supra-therapeutic dose, maximum guanfacine plasma concentration was attained at 5.0 hours (median) post-dose. Assay sensitivity was confirmed by moxifloxacin results. Among guanfacine-treated subjects, most treatment-emergent adverse events were mild (78.9%); dry mouth (65.8%) and dizziness (61.8%) were most common. CONCLUSIONS: Neither therapeutic nor supra-therapeutic doses of guanfacine prolonged QT interval after adjusting for heart rate using individualized correction, QTcNi, through 12 hours postdose. Guanfacine does not appear to interfere with cardiac repolarization of the form associated with pro-arrhythmic drugs.

Population pharmacokinetic/pharmacodynamic modeling of guanfacine effects on QTc and heart rate in pediatric patients.

Using a previously developed population pharmacokinetic model, an exposure-response (ER) model was successfully developed to describe guanfacine plasma concentrations and changes in heart rate (HR) and the QT interval. Guanfacine exposure was associated with small decreases in HR and a small prolongation of the population-corrected QT (QTcP) interval. Based on the final ER model for effect of guanfacine on HR, the estimated population typical decrease in HR would be 2.3% (2.1-2.7%) of the baseline circadian HR for every 1 ng/mL of guanfacine exposure. A QTcP was developed for the analysis using the sampled population. An effect of sex on baseline-corrected QT (BQTP) was the only covariate effect in the final ER model for QTcP, its inclusion resulting in a typical baseline QTcP estimate that is 9 (5-13) ms higher for females. There was no evidence of QT-RR hysteresis. A linear model was used to relate guanfacine plasma concentrations to QTcP. The typical (95% confidence interval) slope parameter was estimated to be 0.941 (0.62-1.25) ms/ng/mL. The final model predicted an approximate 1-ms increase from baseline for every 1 ng/mL of guanfacine in plasma. The main predictor of QTcP prolongation was guanfacine exposure, which decreased with body weight and increased with dose.

Development and validation of a simple, sensitive and accurate LC-MS/MS method for the determination of guanfacine, a selective α2A -adrenergicreceptor agonist, in plasma and its application to a pharmacokinetic study.

A simple, practical, accurate and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and fully validated for the quantitation of guanfacine in beagle dog plasma. After protein precipitation by acetonitrile, the analytes were separated on a C18 chromatographic column by methanol and water containing 0.1% (v/v) formic acid with a gradient elution. The subsequent detection utilized a mass spectrometry under positive ion mode with multiple reaction monitoring of guanfacine and enalaprilat (internal standard) at m/z 246.2 → 159.0 and m/z 349.2 → 205.9, respectively. Good linearity was obtained over the concentration range of 0.1-20 ng/mL for guanfacine in dog plasma and the lower limit of quantification of this method was 0.1 ng/mL. The intra- and inter-day precisions were <10.8% relative standard deviation with an accuracy of 92.9-108.4%. The matrix effects ranged from 89.4 to 100.7% and extraction recoveries were >90%. Stability studies showed that both analytes were stable during sample preparation and analysis. The established method was successfully applied to an in vivo pharmacokinetic study in beagle dogs after a single oral dose of 4 mg guanfacine extended-release tablets.

Semi-automated direct elution of dried blood spots for the quantitative determination of guanfacine in human blood.

BACKGROUND: Direct analysis of dried blood spot (DBS) samples was investigated using a prototype semi-automated robotic device that allows the direct elution of sample spots from a DBS paper card to an online SPE cartridge. The eluted SPE samples were analyzed with high-performance LC-MS/MS. RESULTS: A LLOQ of 0.01 ng/ml was achieved with a linear calibration range from 0.01 to 25 ng/ml. Optimal performance data were obtained from spotting the internal standard solution on the card before blood spotting. Internal standard addition from the system injector loop produced intra-assay inaccuracy of -9.0-7.3% and precision of 1.3-8.2%, and inter-assay inaccuracy of -3.5-3.9% and precision of 4.4-8.7%. CONCLUSION: Results demonstrated the feasibility of a semi-automated online rapid direct elution method that avoids manual extraction for DBS sample analysis using the online DBS-SPE system coupled to LC-MS/MS.

The use of a membrane filtration device to form dried plasma spots for the quantitative determination of guanfacine in whole blood.

RATIONALE: A two-layered polymeric membrane is employed for the formation of separated dried plasma spots from whole blood as an alternative to the direct analysis of whole dried blood spots (DBS). This dried plasma spot (DPS) analysis procedure precludes potential issues of hematocrit differences in whole blood samples while providing pharmokinetic data from plasma rather than whole blood. The described procedure is also semi-automated thus providing a simpler work flow for LC/MS/MS bioanalysis procedures. METHODS: Molecular filtration of red blood cells (RBC) from applied microsamples of whole blood fortified with guanfacine and its stable isotope internal standard was accomplished with a two-layer polymeric membrane substrate. The lower membrane surface containing the separated plasma spot was physically separated from the upper membrane followed by semi-automated direct elution of the sample to an online solid-phase extraction (SPE) cartridge followed by liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS). RESULTS: A two-layer membrane sample preparation substrate produced plasma from whole blood without centrifugation which could be directly eluted for semi-automated LC/MS/MS bioanalysis. Standard curves were constructed by plotting peak area ratios between the analyte and the stable isotope labeled internal standard (SIL-IS) versus the nominal concentration in whole blood. A weighted 1/x(2) linear regression was applied to the data from DPS samples. Standard curves were linear over the range 0.25-250 ng/mL human whole blood. The representative regression equation was y = 0.0142x + 0.00248 (R(2) = 0.995) for the described DPS assay. CONCLUSIONS: The described work demonstrates proof-of-principle using membrane sample preparation techniques to form DPS samples from whole blood for subsequent bioanalysis by LC/MS/MS. This approach has the potential to eliminate the hematocrit issues from the current controversy surrounding validation of DBS assays.

Dried blood spots as a sampling technique for the quantitative determination of guanfacine in clinical studies.

BACKGROUND: Dried blood spot (DBS) technology was evaluated for the quantitative determination of guanfacine in human blood in clinical studies. A very sensitive DBS assay has been developed using HPLC coupled with an AB Sciex 5500 QTRAP® (Applied Biosystems/MDS Sciex, ON, Canada) MS system (LC-MS/MS) with a linear calibration range of 0.05 to 25 ng/ml. High-resolution MS using an Exactive Orbitrap® (ThermoFisher, LLC., CA, USA) was compared with the QTRAP using extracted exact mass ion current profiles for guanfacine and its stable-isotope-incorporated internal standard. The sample preparation employed liquid-liquid extraction with methyl t-butyl ether of 5 mm punched DBS card disks, followed by reversed-phase HPLC separation coupled with either MS/MS or high-resolution MS. Routine experiments were performed to establish the robustness of the DBS assay, including precision, accuracy, linearity, selectivity, sensitivity and long-term stability of up to 76 days. In addition, several factors that potentially affect quantitation were investigated, including blood volume for DBS spotting, punch size and punch location. RESULTS: A sensitive research assay with a LLOQ of 0.05 ng/ml was developed and subjected to several components of a method validation common to a regulated bioanalysis procedure employing DBS. This method development and partial validation study determined that spot volume, punch size or punch location do not affect assay accuracy and precision. The DBS approach was successfully applied to a clinical study (a Phase I, randomized, double-blind, placebo-controlled, crossover study to assess the effect of varying multiple oral doses of guanfacine on the pharmacokinetic, pharmacodynamic, safety, and tolerability profiles in healthy adult subjects). The pharmacokinetic profiles for 12 volunteers generated from the DBS assay and from a previously validated plasma assay were compared and were found to be comparable. DBS incurred samples collected from finger prick blood and directly applied to the DBS cards were also analyzed for comparison. CONCLUSION: From a bioanalytical perspective, DBS sample collection and analysis is a potentially viable alternative for guanfacine determination in clinical studies, utilizing approximately 100 µl of blood per subject profile compared with a few millilitres of blood drawn for conventional plasma bioanalysis.