Source: European Medicines Agency (EU) Revision Year: 2020 Publisher: Shire Pharmaceuticals Ireland Limited, Block 2 & 3 Miesian Plaza, 50–58 Baggot Street Lower, Dublin 2, IRELAND
Pharmacotherapeutic group: Antihypertensives, antiadrenergic agents, centrally acting
ATC code: C02AC02
Guanfacine is a selective alpha2A-adrenergic receptor agonist in that it has 15-20 times higher affinity for this receptor subtype than for the alpha2B or alpha2C subtypes. Guanfacine is a non-stimulant. The mode of action of guanfacine in ADHD is not fully established. Preclinical research suggests guanfacine modulates signalling in the prefrontal cortex and basal ganglia through direct modification of synaptic noradrenalin transmission at the alpha2-adrenergic receptors.
Guanfacine is a known antihypertensive agent. By stimulating alpha2A-adrenergic receptors, guanfacine reduces sympathetic nerve impulses from the vasomotor centre to the heart and blood vessels. This results in a decrease in peripheral vascular resistance and blood pressure, and a reduction in heart rate.
The effects of guanfacine in the treatment of ADHD has been examined in 5 controlled studies in children and adolescents (6 to 17 years), 3 short-term controlled trials in children and adolescents aged 6 to 17 years, 1 short-term controlled study in adolescents aged 13 to 17 years, and 1 randomised withdrawal trial in children and adolescents aged 6-17 years, all of whom met the DSM-IV-TR criteria for ADHD. The majority of patients achieved an optimised dose between 0.05-0.12mg/kg/day.
Three hundred and thirty-seven patients aged 6-17 years were evaluated in the pivotal Phase 3 Study SPD503-316, to assess safety and efficacy of once-daily dosing (children:1-4mg/day, adolescents: 1-7 mg/day). In this 12-week (6-12 years) or 15-week (13-17 years), randomised, double-blind, parallel-group, placebo- and active-reference (atomoxetine), dose-titration study, guanfacine showed significantly greater efficacy than placebo on symptoms of ADHD based upon investigator ratings on the ADHD Rating Scale (ADHD-RS). The ADHD Rating Scale is a measure of the core symptoms of ADHD. The results with respect to the primary endpoint study are presented in Table 5.
Table 5. Summary of primary efficacy for study SPD503-316: ADHD-RS-IV:
| Treatment groups | N | Baseline ADHD-RS-IV (SD) | Change from baseline (SD) | Difference from placebo (95%CI) Effect size | Responders | Difference from placebo (95%CI) |
|---|---|---|---|---|---|---|
| Guanfacine | 114 | 43.1 (5.5) | -23.9 (12.4) | -8.9 (-11.9, -5.8) 0.8 | 64.3% | 21.9% (9.2 ; 34.7) |
| Atomoxetine | 112 | 43.7 (5.9) | -18.6 (11.9) | -3.8 (-6.8, -0.7) 0.3 | 55.4% | 13.0% (0.0 ; 26.0) |
| Placebo | 111 | 43.2 (5.6) | -15.0 (13.1) | NA | 42.3% | NA |
Results of the secondary endpoints were consistent with that of the primary endpoint. The percentages of subjects who met response criteria (≥30% reduction from baseline in ADHD-RS-IV Total Score and a CGI-I value of 1 or 2) was 64.3% for guanfacine, 55.4% for atomoxetine and 42.3% for placebo. Guanfacine also showed significant improvement in learning, school and family functioning as measured with the (WFIRS-P score).
In addition a 15-week, double-blind, randomised, placebo-controlled, dose-optimisation study (SPD503-312) conducted in adolescents aged 13-17 years (n=314) to confirm the efficacy, safety, and tolerability of guanfacine (1-7 mg/day) in the treatment of ADHD. Guanfacine showed a significantly greater improvement in the ADHD-RS-IV total score compared with subjects receiving placebo. Guanfacine-treated patients were in statistically significantly better conditions on the functional outcome as measured by the clinical global impression of severity (CGI-S) at endpoint compared to placebo-treated patients. Superiority (statistical significance) over placebo on the family and school, and learning domains of the WFIRS-P score was not established in this study.
Study (SPD503-315) was a 41 week long term maintenance of efficacy study which included an open-label phase (up to 13 weeks) followed by double-blind, placebo-controlled, randomised-withdrawal phase (up to 26 weeks), conducted in paediatric patients (children and adolescents aged 6-17 years old inclusive) (n=526 in the open-label phase and n=315 in the double-blind randomised-withdrawal phase) to assess the efficacy, safety, and tolerability of once-daily dosing with guanfacine (children: 1-4 mg/day, adolescents:1-7 mg/day) in the treatment of ADHD. Guanfacine was superior to placebo in the long-term maintenance of treatment in children and adolescents with ADHD as measured by cumulative treatment failures (49.3% for Intuniv, and 64.9% for placebo, p=0.006). Treatment failure was defined as a ≥50% increase in ADHD-RS-IV total score and a ≥2 point increase in CGI-S score compared to the respective scores at the double-blind baseline visit. At the end of their double-blind treatment, a significantly larger proportion of subjects in the guanfacine compared with placebo group were normal or borderline mentally ill as measured by the clinical global impression of severity (CGI-S) that includes assessment of functioning. Superiority (statistical significance) over placebo on the family and school, and learning domains of the WFIRS-P score was not consistently established in this study.
Similar results for the efficacy of guanfacine in the treatment of ADHD were established in 2 randomised, double-blind, placebo-controlled, fixed-dose (range of 1-4 mg/day) monotherapy trials in paediatric patients (children and adolescents 6-17 years old inclusive). Studies SPD503-301 and SPD503-304 were 8 and 9 weeks in duration, respectively, both conducted in the United States. Guanfacine showed significantly greater improvement compared to placebo on the change from baseline to final on treatment assessment in the ADHD Rating Scale (ADHD-RS-IV) score in both studies (placebo-adjusted reduction in LS mean range from 5.4 to 10.0, p<0.02).
Study SPD503-314 was conducted in children aged 6-12 years to assess the efficacy of once daily dosing with guanfacine (1-4 mg) administered either in the morning or the evening. This was a double-blind, randomised, placebo-controlled, dose-optimisation study, 9-weeks in duration conducted in the United States and Canada. Symptoms of ADHD were evaluated as the change from baseline to week 8 (final on treatment assessment) in the ADHD Rating Scale (ADHD-RS-IV) total scores. Guanfacine showed significantly greater improvement compared to placebo regardless of time (AM or PM) of administration (placebo-adjusted LS mean difference of -9.4 and -9.8 for AM and PM dosing, respectively, p<0.001).
The effect of co-administration with psychostimulants was examined in an add-on study in partial responders to psychostimulants. The study was double-blind, randomised, placebo-controlled, multi-centre, dose-optimisation 9-weeks study. It was designed to evaluate the efficacy and safety of guanfacine (1, 2, 3, and 4 mg/day) when co-administered with long-acting psychostimulants (amphetamine, lisdexamphetamine, methylphenidate, dexmethylphenidate) in children and adolescents aged 6-17 years with a diagnosis of ADHD and a suboptimal, partial response to psychostimulants. Suboptimal response was defined as an ADHD-RS-IV total score of ≥24 and a CGI-S score ≥3 at screening and baseline. The primary efficacy assessment was the ADHD-RS-IV total score. The results showed that patients treated with add-on guanfacine improved more on the ADHD-RS-IV compared to those treated with add-on placebo (20.7 (12.6) points vs. 15.9 (11.8); difference: 4.9 95% CI 2.6 , 7.2). No age differences were observed with respect to response to the ADHD-RS-IV.
Study SPD503-307 was a 9-week, double-blind, randomised, placebo-controlled, dose-optimisation study with guanfacine (1-4 mg/day) conducted in children aged 6-12 years with ADHD and oppositional symptoms (n=217). Oppositional symptoms were evaluated as the change from baseline to endpoint in the Oppositional Subscale of the Conners' Parent Rating Scale – revised Long Form (CPRS-R:L) score. Results show statistically significantly (p≤0.05) greater mean reductions at endpoint from Baseline (indicating improvement) in oppositional subscale of CPRS-R:L scores in the guanfacine group compared to placebo (10.9 points vs. 6.8 for guanfacine vs. placebo, respectively) and the effect size was 0.6 (p<0.001). These reductions represent a percentage reduction of 56% vs. 33% for guanfacine vs. placebo, respectively.
Guanfacine is readily absorbed, with peak plasma concentrations reached approximately 5 hours after oral administration in paediatric patients (children and adolescents 6-17 years old inclusive). In adults, the mean exposure of guanfacine increased (Cmax ~75% and AUC ~40%) when Intuniv was taken together with a high fat meal, compared to intake in the fasted state (see section 4.2).
Guanfacine is moderately bound to plasma proteins (approximately 70%), independent of drug concentration.
Guanfacine is metabolised via CYP3A4/5-mediated oxidation, with subsequent phase II reactions of sulphation and glucuronidation. The major circulating metabolite is 3-OH-guanfacine sulphate which lacks pharmacological activity.
Guanfacine is a substrate of CYP3A4 and CYP3A5, and exposure is affected by CYP3A4 and CYP3A5 inducers and inhibitors. In human hepatic microsomes, guanfacine did not inhibit the activities of the other major cytochrome P450 isoenzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4 or CYP3A5); guanfacine is also not expected to be an inducer of CYP3A, CYP1A2 and CYP2B6.
Based on in vitro studies, guanfacine is a substrate of OCT1 and OCT2, but not BCRP, OATP1B1, OATP1B3, OAT1, OAT3, MATE1 or MATE2. Guanfacine is not an inhibitor of BSEP, MRP2, OATP1B1, OATP1B3, OAT1, OAT3, OCT2 or MATE2K, but it is an inhibitor of MATE1 and may be an inhibitor of OCT1 at maximal portal vein concentrations.
Guanfacine is cleared by the kidneys via filtration and active secretion and the liver. Active renal secretion is mediated via OCT2 transporter. Renal excretion is the major elimination pathway (80%) with parent drug accounting for 30% of the urinary radioactivity. The major urinary metabolites were 3-hydroxy guanfacine glucuronide, guanfacine dihydrodiol, 3-hydroxy guanfacine sulphate. The elimination half-life of guanfacine is approximately 18 hours.
The pharmacokinetics of guanfacine is similar in children (aged 6 to 12) and adolescents (aged 13 to 17) ADHD patients, and healthy adult volunteers.
There have been no studies performed in children with ADHD under the age of 6 years with Intuniv.
Systemic exposure to guanfacine is similar for men and women given the same mg/kg dose.
Formal pharmacokinetic studies for race have not been conducted. There is no evidence of any impact of ethnicity on the pharmacokinetics of Intuniv.
No carcinogenic effect of guanfacine was observed in studies of 78 weeks in mice at doses up to 10 mg/kg/day. A significant increase in incidence of adenomas of the pancreatic islet was observed in male rats treated with 5 mg/kg/day guanfacine for 102 weeks but not in female rats. The clinical relevance is unknown.
Guanfacine was not genotoxic in a variety of test models, including the Ames test and an in vitro chromosomal aberration test.
General toxicity observed in animals (rat, dog) upon treatment with guanfacine included prolongation of uncorrected QT interval (heart), atrophic spleen and decreased white blood cells, affected liver – increased bilirubin and ALT levels included, irritated and inflamed intestines, increased creatinine and blood urea nitrogen levels (kidney), corneal clouding (eye) in rat and mouse only, alveolar macrophage infiltration & pneumonitis and reduced spermatogenesis.
No adverse effects were observed in a fertility study in female rats at doses up to 22 times the maximum recommended human dose on a mg/m² basis.
Male fertility was affected at 8 mg/kg/day, the lowest dose tested, equivalent of 10.8 times the maximum recommended human dose of 0.12 mg/kg on a mg/m² basis. Due to lack of proper toxicokinetic data, comparison to human clinical exposure was not possible.
Guanfacine showed embryo foetal developmental toxicity in mice and rats (NOAEL 0.5 mg/kg/day) and in rabbits (NOAEL 3.0 mg/kg/day) in the presence of maternal toxicity. Due to a lack of proper toxicokinetic data, comparison to human clinical exposure was not possible.
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