• Dennis Swearingen, Michael Pennick, Amir Shojaei, Andrew Lyne, and Kimberly Fiske.
• MDS Pharma Services, Phoenix, Arizona 85044, USA. dennis.swearingen@mdsps.com
• Clin Ther. 2007 Apr 1; 29 (4): 617-25.

BackgroundGuanfacine is an alpha(2)-adrenoreceptor agonist used to treat children and adults with attention-deficit/hyperactivity disorder. An extended-release formulation of guanfacine is currently under development.ObjectiveThe objective of this study was to assess the single-dose pharmacokinetic properties and dose proportionality of guanfacine extended-release (GXR) tablets after oral administration in healthy adults.MethodsThis was a Phase I, randomized, open-label, single-dose, crossover trial of GXR 1-, 2-, and 4-mg tablets in healthy adults. In the lead-in period (period 1), subjects received a single GXR 1-mg tablet, and then were randomized to receive single GXR 2- or 4-mg tablets during 4 separate weekly visits. Vital signs were monitored, blood samples were obtained, and subjects underwent electrocardiography (ECG) before dose administration and at regular intervals over 96 hours. The pharmacokinetic parameters of CmaX, AUC(0-t), and AUC(0-infinity) were determined after each dose of GXR in all subjects. Summary statistics for the concentration-time data were analyzed to assess between-dose linearity. An analysis-of-variance model was constructed to test the concentration-time data for dose proportionality. Tolerability was assessed at each visit through the analysis of standard serology tests; urinalysis/drug screen reports; and physical examination, including height and weight measurements; vital-sign data; and ECG findings.ResultsThe total study enrollment was 52 subjects, including 28 men (53.8%) and 24 (46.2%) women. The subjects had a mean (SD) age of 32.9 (10.3) years (range, 18-54 years) and a mean (SD) body weight of 73.4 (15.7) kg (range, 49.6-120.0 kg). Forty (76.9%) subjects were Hispanic, 7 (13.5%) were white, and 5 (9.6%) were black. Three subjects were discontinued by the study investigators because of noncompliance with study procedures or use of concomitant medications. Forty-nine subjects completed the study. Mean (SD) values for guanfacine plasma concentrations with GXR 1, 2, and 4 mg, respectively, were 0.98 (0.26), 1.57 (0.51), and 3.58 (1.39) ng/mL for C(max); 29.3 (8.84), 54.5 (17.7), and 119.1 (42.3) ng/mL . h(-1) for AUC(0-t); and 32.4 (8.78), 58.0 (18.9), and 124.1 (45.1) ng/mL . h(-1) for AUC(0-infinity) . Mean (SD) t((1/2)) values were 17.5 (3.8), 16.6 (3.8), and 16.7 (4.90) hours for GXR 1, 2, and 4 mg, respectively. The geometric mean ratios for C(max), AUC(0-t), and AUC(0-infinity) were proportional to dose between GXR 1 and 2 mg, 1 and 4 mg, and 2 and 4 mg, except for the increase in C(max) between GXR 1 and 2 mg. All treatment-emergent adverse events (AEs) were assessed as mild or moderate and resolved without treatment with the exception of headache in 3 subjects and 1 case of lower back discomfort, which resolved with therapy. Left rib pain was reported in 1 subject, but it is unknown if it had resolved, since the subject was lost to followup. No subjects withdrew from participation or were discontinued by the study investigators as a result of AEs. The most common treatment-emergent AE, somnolence, occurred in 33 (63.5%) of 52 subjects. All mean vital-sign measurements and mean ECG parameters remained within normal limits after dosing and no marked changes from baseline measurements were noted. Mean values for all test results of hematology and serum chemistry panels were within the reference range at completion of the study, with no significant changes from baseline.ConclusionsIn these 49 healthy adult subjects, the single-dose pharmacokinetic properties of GXR 1-, 2-, and 4-mg tablets appeared to be statistically linear; that is, increases in mean C(max), AUC(0-t), and AUC(0-infinity) of guanfacine were proportional to dose, with the exception of the increase in mean C(max) between GXR 1 and 2 mg. All doses appeared to be well tolerated, with no serious AEs or withdrawal or discontinuation from study participation due to AEs reported.

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