LOW, SINGLE DAILY DOSES OF GUANFACINE IN THE AMBULATORY TREATMENT OF HYPERTENSION

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.

Effect of guanfacine on ambulatory blood pressure and its variability in elderly patients with essential hypertension

The effect of guanfacine (2 mg once daily) on ambulatory blood pressure was studied with the Remler M 2000 recorder in 16 elderly hypertensive patients during a randomized, double-blind, placebo-controlled, balanced, cross-over study. Guanfacine significantly reduced heart rate and systolic and diastolic ambulatory blood pressure. The antihypertensive effect was maintained over the whole recording period. Systolic and diastolic blood pressure variability was not changed by guanfacine, neither when defined as standard deviation or variation coefficient of the mean, nor when defined as the range between the highest and lowest ambulatory blood pressure, suggesting that blood pressure variability is unrelated to sympathetic nervous system activity.

A multicenter, randomized, double-blind dose-response evaluation of step-2 guanfacine versus placebo in mild to moderate hypertension

Guanfacine, an alpha-adrenoceptor agonist, may exhibit distinct dose-related curves for efficacy and adverse effects in the step-2 therapy of essential hypertension. To determine the lowest clinically effective safe dose, 462 newly or previously diagnosed subjects were admitted to a 5-week prerandomization phase at 8 centers. Patients were weaned from any current antihypertensive drugs and placed on 25-mg chlorthalidone, daily, in the morning. At the end of the 5-week weaning period, 362 patients with seated diastolic blood pressures (BPs) between 95 and 114 mm Hg qualified for the 12-week postrandomization phase. Subjects were randomized to receive either an indistinguishable placebo or 0.5, 1, 2 or 3 mg of guanfacine. Chlorthalidone was changed to bedtime administration and taken with the study medications. Guanfacine was started at the lowest dose in all subjects and increased (if scheduled, according to the randomization code) to the next higher dose at biweekly intervals. Of the 362 randomized patients, 278 completed the study. The 1-mg guanfacine dosage produced a 14/13 mm Hg decrease in BP (p less than 0.0125 compared with placebo). Doses of guanfacine at 2 and 3 mg/day were not more effective than the 1 mg/day dose; 0.5 mg/day was not better than placebo. There was an increase in the frequency of side effects possibly or probably associated with 2 and 3 mg/day guanfacine. Only 3.2% of the patients in the 1 mg/day group dropped out of the study because of side effects. We conclude that when added to a diuretic, 1 mg/day guanfacine at bedtime is the lowest safe and therapeutically effective dose.