Signs and symptoms of overdose may include hypotension, initial hypertension, bradycardia, lethargy, and respiratory depression. Haemodynamic instability has also been associated with a guanfacine overdose 3 times the recommended daily dose. Management of Guanfacine Extended-Release overdose should include monitoring for and treatment of these signs and symptoms.
Paediatric patients (children and adolescents 6-17 years old inclusive) who develop lethargy should be observed for the development of more serious toxicity including coma, bradycardia, and hypotension for up to 24 hours, due to the possibility of delayed onset of these symptoms.
Treatment of overdose may include gastric lavage if it is performed soon after ingestion. Activated charcoal may be useful in limiting the absorption. Guanfacine is not dialysable in clinically significant amounts (2.4%).
Not applicable.
Summary of the safety profile
In the data set from controlled, doubled blinded and open-label clinical studies with Guanfacine Extended-Release the most frequently reported adverse reactions (very common) include somnolence (40.6%), headache (27.4%), fatigue (18.1%), abdominal pain upper (12.0%), and sedation (10.2%). Serious adverse reactions commonly reported include hypotension (3.2%), weight increase (2.9%), bradycardia (1.5%) and syncope (uncommon) (0.7%). The adverse reactions somnolence and sedation occurred predominantly at the start of treatment and may typically last for 2-3 weeks and longer in some cases.
Tabulated list of adverse reactions
The following table presents all adverse reactions based on clinical trials and spontaneous reporting. All adverse reactions from post-marketing experience are italicised.
The following definitions apply to the frequency terminology used hereafter:
Very common (>1/10)
Common (>1/100 to <1/10)
Uncommon (>1/1,000 to <1/100)
Rare (>1/10,000 to <1/1,000)
Very rare (<1/10,000)
Not known (cannot be estimated from the available data).
|
Table 4. Adverse Drug Reactions Reported with Guanfacine Extended-Release | ||
| System/Organ Class Adverse Drug Reaction | Incidence Category | |
| Immune system disorders | ||
| Hypersensitivity | Uncommon | |
| Metabolism and nutrition disorders | ||
| Decreased appetite | Common | |
| Psychiatric disorders | ||
| Depression | Common | |
| Anxiety | Common | |
| Affect lability | Common | |
| Insomnia | Common | |
| Middle insomnia | Common | |
| Nightmare | Common | |
| Agitation | Uncommon | |
| Hallucination | Uncommon | |
| Nervous system disorders | ||
| Somnolence | Very common | |
| Headache | Very common | |
| Sedation | Common | |
| Dizziness | Common | |
| Lethargy | Common | |
| Convulsion | Uncommon | |
| Syncope/loss of consciousness | Uncommon | |
| Dizziness postural | Uncommon | |
| Hypersomnia | Rare | |
| Cardiac disorders |
| |
| Bradycardia | Common | |
| Atrioventricular block first degree | Uncommon | |
| Tachycardia | Uncommon | |
| Sinus arrhythmia | Uncommon | |
| Vascular disorders | ||
| Hypotension | Common | |
| Orthostatic hypotension | Common | |
| Pallor | Uncommon | |
| Hypertension | Rare | |
| Hypertensive encephalopathy | Very rare | |
| Respiratory, thoracic, and mediastinal disorders | ||
| Asthma | Uncommon | |
| Gastrointestinal disorders | ||
| Abdominal pain | Very common | |
| Vomiting | Common | |
| Diarrhoea | Common | |
| Nausea | Common | |
| Constipation | Common | |
| Abdominal/stomach discomfort | Common | |
| Dry mouth | Common | |
| Dyspepsia | Uncommon | |
| Skin and subcutaneous tissue disorders | ||
| Rash | Common | |
| Pruritus | Uncommon | |
| Renal and urinary disorders | ||
| Enuresis | Common | |
| Pollakiuria | Uncommon | |
| Reproductive system and breast disorders | ||
| Erectile dysfunction | Not known | |
| General disorders | ||
| Fatigue | Very common | |
| Irritability | Common | |
| Asthenia | Uncommon | |
| Chest pain | Uncommon | |
| Malaise | Rare | |
| Investigations | ||
| Blood pressure decreased | Common | |
| Weight increased | Common | |
| Blood pressure increased | Uncommon | |
| Heart rate decreased | Uncommon | |
| Alanine aminotransferase increased | Uncommon | |
Description of selected adverse reactions
Somnolence/sedation, hypotension, bradycardia and syncope
In the overall pool of guanfacine-treated patients, somnolence occurred in 40.6% and sedation in 10.2% of guanfacine-treated patients. Bradycardia occurred in 1.5%, hypotension in 3.2% and syncope occurred in 0.7% of all guanfacine-treated patients. The occurrence of somnolence/sedation and hypotension was most prominent in the first few weeks of treatment and diminished gradually thereafter.
Effects on height, weight and body Mass index (BMI)
Careful follow-up for weight suggests that children and adolescents who took Guanfacine Extended-Release in the study (i.e., treatment for 7 days per week throughout the year) have demonstrated by an age- and sex-normalised mean change from baseline in BMI percentile, 4.3 over 1 year (average percentiles at baseline and 12 months were 68.3 and 73.1, respectively). Consequently, as part of routine monitoring height, weight and BMI should be monitored at the start of treatment and every 3 months during the first year, then 6 monthly taking in to consideration clinical judgement with maintenance of a growth chart.
Thorough QT /QTc study
The effect of 2 dose levels of immediate-release guanfacine (4 mg and 8 mg) on QT interval was evaluated in a double-blind, randomised, placebo- and active-controlled, cross-over study in healthy adults. An apparent increase in mean QTc was observed for both doses. This finding has no known clinical relevance.
In phase II-III randomised double-blind monotherapy studies respective increases in QTc interval prolongation that exceeded change from baseline greater than 60 ms Fridericia-correction and Bazett-correction were 0 (0.0%) and 2 (0.3%) among placebo and 1 (0.1%) and 1 (0.1%) among Guanfacine Extended-Release patients. The clinical relevance of this finding is uncertain.
Blood pressure and heart rate increase upon discontinuation of Guanfacine Extended-Release
Blood pressure and pulse may increase following discontinuation of Guanfacine Extended-Release. In post-marketing experience, hypertensive encephalopathy has been very rarely reported upon abrupt discontinuation of Guanfacine Extended-Release.
In a maintenance of efficacy study in children and adolescents, increases in mean systolic and diastolic blood pressure of approximately 3 mmHg and 1 mmHg, respectively, above original baseline were observed upon discontinuation of Guanfacine Extended-Release. However, individuals may have larger increases than reflected by the mean changes. The increases in blood pressure were observed in some individuals at the end of the follow up period which ranged between 3 and 26 weeks post final dose.
Adult patients
Guanfacine Extended-Release has not been studied in adults with ADHD.
Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the national reporting system:
United Kingdom:
Yellow Card Scheme
Website: www.mhra.gov.uk/yellowcard
Ireland:
HPRA Pharmacovigilance
Earlsfort Terrace
IRL - Dublin 2
Tel: +353 1 6764971
Fax: +353 1 6762517
Website: www.hpra.ie
e-mail: [email protected]
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.
Guanfacine Extended-Release is indicated for the treatment of attention deficit hyperactivity disorder (ADHD) in children and adolescents 6-17 years old for whom stimulants are not suitable, not tolerated or have been shown to be ineffective.
Guanfacine Extended-Release must be used as a part of a comprehensive ADHD treatment programme, typically including psychological, educational and social measures.
Pharmacotherapeutic group: Antihypertensives, antiadrenergic agents, centrally acting ATC code: C02AC02.
Mechanism of action
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 alpha 2- adrenergic receptors.
Pharmacodynamic effects
Guanfacine is a known antihypertensive agent. By stimulating alpha 2A-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.
Clinical efficacy and safety
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
Atomoxetine
Placebo | 114
112
111 | 43.1 (5.5)
43.7 (5.9)
43.2 (5.6) | -23.9 (12.4)
-18.6 (11.9)
-15.0 (13.1) | -8.9 (-11.9, -5.8) 0.8 -3.8 (-6.8, -0.7) 0.3 NA | 64.3%
55.4%
42.3% | 21.9% (9.2 ; 34.7)
13.0% (0.0 ; 26.0)
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 Guanfacine Extended-Release, 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).
Co-administration with Psychostimulants
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.
ADHD with Oppositional Symptoms Study
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.
Absorption
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 Guanfacine Extended-Release was taken together with a high fat meal, compared to intake in the fasted state.
Distribution
Guanfacine is moderately bound to plasma proteins (approximately 70%), independent of drug concentration.
Biotransformation
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.
Transporters
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.
Elimination
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.
Special populations
There have been no studies performed in children with ADHD under the age of 6 years with Guanfacine Extended-Release.
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 Guanfacine Extended-Release.
Hypotension, bradycardia and syncope
Guanfacine Extended-Release can cause syncope, hypotension and bradycardia. Syncope may involve risks of falls or accidents, which could result in serious harm.
Prior to initiation of treatment, patient's cardiovascular status including heart rate and blood pressure parameters, family history of sudden cardiac death /unexplained death, should be assessed to identify patients at increased risk of hypotension, bradycardia, and QT-prolongation/risk of arrhythmia. Monitoring of heart rate and blood pressure parameters should continue on a weekly basis during dose titration and stabilisation and at least every 3 months for the first year, taking into consideration clinical judgement. 6 monthly monitoring should follow thereafter, with more frequent monitoring following any dose adjustment.
Caution is advised when treating patients with Guanfacine Extended-Release who have a history of hypotension, heart block, bradycardia, or cardiovascular disease, or who have a history of syncope or a condition that may predispose them to syncope, such as hypotension, orthostatic hypotension, bradycardia, or dehydration. Caution is also advised when treating patients with Guanfacine Extended-Release who are being treated concomitantly with antihypertensives or other medicinal products that can reduce blood pressure or heart rate or increase the risk of syncope. Patients should be advised to drink plenty of fluid.
Blood pressure and heart rate increase upon discontinuation
Blood pressure and pulse may increase following discontinuation of Guanfacine Extended-Release. In post-marketing experience, hypertensive encephalopathy has been very rarely reported upon abrupt discontinuation of Guanfacine Extended-Release. To minimise the risk of an increase in blood pressure upon discontinuation, the total daily dose of Guanfacine Extended-Release should be tapered in decrements of no more than 1 mg every 3 to 7 days. Blood pressure and pulse should be monitored when reducing the dose or discontinuing Guanfacine Extended-Release.
QTc interval
In phase II-III randomised double-blind monotherapy studies respective increases in QTc interval prolongation that exceeded change from baseline greater than >60 ms Fridericia-correction and Bazett-correction were 0 (0.0%) and 2 (0.3%) among placebo and 1 (0.1%) and 1 (0.1%) among Guanfacine Extended-Release patients. The clinical relevance of this finding is uncertain.
Guanfacine should be prescribed with caution in patients with a known history of QT prolongation, risk factors for torsade de pointes (e.g., heart block, bradycardia, hypokalaemia) or patients who are taking medicinal products known to prolong the QT interval. These patients should receive further cardiac evaluation based on clinical judgement.
Sedation and somnolence
Guanfacine Extended-Release may cause somnolence and sedation predominantly at the start of treatment and could typically last for 2-3 weeks and longer in some cases. It is therefore recommended that patients will be closely monitored weekly during dose titration and stabilisation , and every 3 months during the first year, taking into consideration clinical judgement. Before Guanfacine Extended-Release is used with any other centrally active depressants (such as alcohol, sedatives, phenothiazines, barbiturates, or benzodiazepines) the potential for additive sedative effects should be considered. Patients should not drink alcohol whilst taking Guanfacine Extended-Release. Patients are advised against operating heavy equipment, driving or cycling until they know how they respond to treatment with Guanfacine Extended-Release.
Suicidal ideation
Patients with emergent suicidal ideation or behaviour during treatment for ADHD should be evaluated immediately by their physician. Treatment of an underlying psychiatric condition may be necessary and consideration should be given to a possible change in the ADHD treatment programme.
Effects on height, weight and Body Mass index (BMI)
Children and adolescents treated with Guanfacine Extended-Release may show an increase in their BMI. Therefore, monitoring of height, weight and BMI should be done prior to initiation of therapy and then every 3 months for the first year, taking into consideration clinical judgement. 6 monthly monitoring should follow thereafter, with more frequent monitoring following any dose adjustment.
Excipients
Guanfacine Extended-Release contains lactose. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicinal product.
Guanfacine Extended-Release can cause dizziness and somnolence. These effects occur predominantly at the start of treatment and may occur less frequently as treatment continues. Syncope has also been observed. It may have a moderate to severe influence on the ability to drive, use machines or cycling. Patients should be warned of these possible effects and be advised that if affected, they should avoid these activities.
Treatment must be initiated under the supervision of an appropriate specialist in childhood and/or adolescent behavioural disorders.
Pre-treatment screening:
Prior to prescribing, it is necessary to conduct a baseline evaluation to identify patients at increased risk of somnolence and sedation, hypotension and bradycardia, QT-prolongation arrhythmia and weight increase/risk of obesity. This evaluation should address a patient's cardiovascular status including blood pressure and heart rate, documenting comprehensive history of concomitant medications, past and present co-morbid medical and psychiatric disorders or symptoms, family history of sudden cardiac/unexplained death and accurate recording of pre-treatment height and weight on a growth chart.
Posology
Careful dose titration and monitoring is necessary at the start of treatment with Guanfacine Extended-Release since clinical improvement and risks for several clinically significant adverse reactions (syncope, hypotension, bradycardia, somnolence and sedation) are dose- and exposure-related. Patients should be advised that somnolence and sedation can occur, particularly early in treatment or with dose increases. If somnolence and sedation are judged to be clinically concerning or persistent, a dose decrease or discontinuation should be considered.
For all patients, the recommended starting dose is 1 mg of guanfacine, taken orally once a day.
The dose may be adjusted in increments of not more than 1 mg per week. Dose should be individualised according to the patient's response and tolerability.
Depending on the patient's response and tolerability for Guanfacine Extended-Release the recommended maintenance dose range is 0.05-0.12 mg/kg/day. The recommended dose titration for children and adolescents is provided below (see tables 1 and 2). Dose adjustments (increase or decrease) to a maximum tolerated dose within the recommended optimal weight-adjusted dose range based upon clinical judgement of response and tolerability may occur at any weekly interval after the initial dose.
Monitoring during titration
During dose titration, weekly monitoring for signs and symptoms of somnolence and sedation, hypotension and bradycardia should be performed.
Ongoing monitoring
During the first year of treatment, the patient should be assessed at least every 3 months for:
- Signs and symptoms of:
o somnolence and sedation
o hypotension
o bradycardia
- weight increase/risk of obesity
It is recommended clinical judgement be exercised during this period. 6 monthly monitoring should follow thereafter, with more frequent monitoring following any dose adjustments.
Table 1
| Dose Titration Schedule for Children Aged 6-12 years | ||||
| Weight Group | Week 1 | Week 2 | Week 3 | Week 4 |
| 25 kg and up Max Dose= 4 mg | 1 mg | 2 mg | 3 mg | 4 mg |
Table 2
| Dose Titration Schedule for Adolescents (Aged 13-17 Years) | |||||||
| Weight Groupa | Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 |
| 34-41.4 kg Max Dose= 4 mg | 1 mg | 2 mg | 3 mg | 4 mg | |||
| 41.5-49.4 kg Max Dose= 5 mg | 1 mg | 2 mg | 3 mg | 4 mg | 5 mg |
|
|
| 49.5-58.4 kg Max Dose= 6 mg | 1 mg | 2 mg | 3 mg | 4 mg | 5 mg | 6 mg |
|
| 58.5 kg and above Max Dose= 7 mg | 1 mg | 2 mg | 3 mg | 4 mg | 5 mg | 6 mg | 7 mgb |
a Adolescent subjects must weigh at least 34 kg.
b Adolescents weighing 58.5 kg and above may be titrated to a 7 mg/day dose after the subject has completed a minimum of 1 week of therapy on a 6 mg/day dose and the physician has performed a thorough review of the subject's tolerability and efficacy.
The physician who elects to use guanfacine for extended periods (over 12 months) should re-evaluate the usefulness of guanfacine every 3 months for the first year and then at least yearly based on clinical judgement , and consider trial periods off medication to assess the patient's functioning without pharmacotherapy, preferably during times of school holidays.
Downward titration and discontinuation
Patients/caregivers should be instructed not to discontinue guanfacine without consulting their physician.
When stopping Guanfacine Extended-Release, the dose must be tapered with decrements of no more than 1 mg every 3 to 7 days, and blood pressure and pulse should be monitored in order to minimise potential withdrawal effects, in particular increases in blood pressure and heart rate.
In a maintenance of efficacy study, upon switching from guanfacine to placebo, 7/158 (4.4%) subjects experienced increases in blood pressure to values above 5 mmHg and also above the 95th percentile for age, sex and stature.
Missed dose
In the event of a missed dose, Guanfacine Extended-Release dosing can resume the next day. If two or more consecutive doses are missed, re-titration is recommended based on the patient's tolerability to guanfacine.
Switching from other formulations of guanfacine
Immediate-release guanfacine tablets should not be substituted on a mg/mg basis, because of differing pharmacokinetic profiles.
Special populations
Adults and elderly
The safety and efficacy of guanfacine in adult and the elderly with ADHD has not been established and therefore should not be used in this group.
Hepatic impairment
Guanfacine is cleared both by the liver and the kidneys, and at least 50% of the clearance of guanfacine is hepatic. Dose reduction may be required in patients with different degrees of hepatic impairment.
The impact of hepatic impairment on the pharmacokinetics of guanfacine in paediatric patients (children and adolescents 6-17 years old) was not assessed.
Renal impairment
Guanfacine is cleared both by the liver and the kidneys, with approximately 30% of an intact medicinal product excreted with urine. Dose reduction may be required in patients with severe renal impairment (GFR 29-15 ml/min) and an end stage renal disease (GFR<15 ml/min) or requiring dialysis. The impact of renal impairment on the pharmacokinetics of guanfacine in paediatric patients (children and adolescents 6-17 years old) was not assessed.
Children under 6 years
Guanfacine Extended-Release should not be used in children under the age of 6 years because efficacy and safety in this patient population has not been studied.
Patients treated with CYP3A4 and CYP3A5 inhibitors/inducers
CYP3A4/5 inhibitors have been shown to have a significant effect on the pharmacokinetics of guanfacine when co-administered. Dose adjustment is recommended with concomitant use of moderate/strong CYP3A4/5 inhibitors (e.g., ketoconazole, grapefruit juice), or strong CYP3A4 inducers (e.g., carbamazepine). In case of concomitant use of strong and moderate CYP3A inhibitors, a 50% reduction of the guanfacine dose is recommended. Due to variability in interaction effect, further dose titration may be needed (see above). If guanfacine is combined with strong enzyme inducers, a retitration to increase the dose up to a maximum daily dose 7 mg , may be considered if needed. If the inducing treatment is ended, retitration to reduce the guanfacine dose is recommended during the following weeks.
Method of administration
Oral use.
Guanfacine Extended-Release is taken once daily either morning or evening. Guanfacine Extended-Release should not be crushed, chewed or broken before swallowing because this increases the rate of guanfacine release.
Treatment is recommended only for children who are able to swallow the tablet whole without problems.
Guanfacine Extended-Release can be administered with or without food but should not be administered with high fat meals, due to increased exposure.
Guanfacine Extended-Release should not be administered together with grapefruit juice.
Any unused medicinal product or waste material should be disposed of in accordance with local requirements.
