Guanfacine Hcl (guanfacine HCl)

Dosage of guanfacine hydrochloride is expressed in terms of guanfacine.

No dosing information is available for this tab.

There is no enhanced messaging for this drug.

There are no contraindication interactions for this drug.

Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

Alpha-2 Agonists/Tizanidine

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Tizanidine is an alpha-2 agonist. Concurrent use with other alpha-2 agonists may result in additive effects on blood pressure.(1)

CLINICAL EFFECTS: Concurrent use of alpha-2 agonists and tizanidine may result in hypotension.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of tizanidine states concurrent use with other alpha-2 agonists is not recommended.(1) Patients receiving concurrent therapy should be monitored for hypotension. The risk of hypotension may be decreased by careful titration of tizanidine dosages and monitoring for hypotension prior to dose advancement. Counsel patients about the risk of orthostatic hypotension.(1)

DISCUSSION: Severe hypotension has been reported following the addition of tizanidine to existing lisinopril therapy.(2-4) Alpha-2 agonists linked include: clonidine, dexmedetomidine, guanabenz, guanadrel, guanethidine, guanfacine, methyldopa, and moxonidine.

Guanfacine/Strong & Moderate Cyp3a4 Inducers

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Strong or moderate inducers of CYP3A4 may induce the metabolism of guanfacine.(1)

CLINICAL EFFECTS: The concurrent administration of a strong or moderate CYP3A4 inducer may result in decreased levels and effectiveness of guanfacine.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: Patients maintained on guanfacine may need dosage adjustments if strong or moderate inducers of CYP3A4 are initiated or discontinued. The manufacturer of extended-release guanfacine recommends a starting dose of extended-release guanfacine initiated at up to double the recommended level of the weight based dosing in patients receiving strong or moderate inducers of CYP3A4. If a patient has been maintained on extended-release guanfacine and is started on a strong or moderate CYP3A4 inducer, the dose of extended-release guanfacine should be increased up to double the recommended weight based dose over 1 to 2 weeks. If a patient has been maintained on extended-release guanfacine and a strong or moderate CYP3A4 inducer, and the strong or moderate CYP3A4 inducer is discontinued, the dose of extended-release guanfacine may need to be decreased to the recommended weight based dose over 1 to 2 weeks. Extended-release guanfacine target dose range for attention deficit hyperactivity disorder is 0.05-0.12 mg/kg/day. Doses above 4 mg/day have not been evaluated in children ages 6-12 years and doses above 7 mg/day have not been evaluated in adolescents ages 13-17 years.(1)

DISCUSSION: Rifampin (dosage not stated), a strong inducer of CYP3A4, decreased the maximum concentration (Cmax) and area-under-curve (AUC) of guanfacine (dosage not stated) by approximately 50%.(1) Strong inducers of CYP3A4 include: apalutamide, barbiturates, carbamazepine, encorafenib, enzalutamide, fosphenytoin, ivosidenib, lumacaftor, mitotane, phenobarbital, phenytoin, primidone, rifabutin, rifampin, rifapentine, and St. John's wort.(1-3) Moderate inducers of CYP3A4 include: belzutifan, bosentan, cenobamate, dabrafenib, efavirenz, elagolix, etravirine, fexinidazole, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, sotorasib, telotristat, thioridazine, and tovorafenib.(1-3)

Guanfacine/Strong & Moderate Cyp3a4 Inhibitors

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Strong or moderate inhibitors of CYP3A4 may inhibit the metabolism of guanfacine.(1)

CLINICAL EFFECTS: The concurrent administration of a strong or moderate CYP3A4 inhibitor may result in elevated levels of guanfacine, which may result in increased adverse effects such as hypotension, bradycardia, loss of consciousness, and drowsiness.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients maintained on guanfacine may need dosage adjustments if strong or moderate inhibitors of CYP3A4 are initiated or discontinued. The manufacturer of extended-release guanfacine recommends a starting dose of extended-release guanfacine initiated at half the recommended level of the weight based dosing in patients receiving strong or moderate inhibitors of CYP3A4. If a patient has been maintained on extended-release guanfacine and is started on a strong or moderate CYP3A4 inhibitor, the dose of extended-release guanfacine should be decreased to half the recommended weight based dose. If a patient has been maintained on extended-release guanfacine and a strong or moderate CYP3A4 inhibitor and the strong or moderate CYP3A4 inhibitor is discontinued, the dose of extended-release guanfacine may need to be increased to the recommended weight based dose based upon patient response. Extended-release guanfacine target dose range for attention deficit hyperactivity disorder is 0.05-0.12 mg/kg/day. Doses above 4 mg/day have not been evaluated in children ages 6-12 years and doses above 7 mg/day have not been evaluated in adolescents ages 13-17 years.(1)

DISCUSSION: Ketoconazole (dosage not stated), a strong inhibitor of CYP3A4, increased the maximum concentration (Cmax) and area-under-curve (AUC) of guanfacine (dosage not stated) by approximately 1.75-fold and 3-fold, respectively.(1) Strong inhibitors of CYP3A4 include: adagrasib, boceprevir, ceritinib, clarithromycin, cobicistat, ensitrelvir, idelalisib, indinavir, itraconazole, josamycin, ketoconazole, levoketoconazole, lonafarnib, lopinavir/ritonavir, mibefradil, mifepristone, nefazodone, nelfinavir, nirmatrelvir/ritonavir, posaconazole, relacorilant, ribociclib, ritonavir, saquinavir, telaprevir, telithromycin, tipranavir, troleandomycin, tucatinib, and voriconazole.(1-3) Moderate inhibitors of CYP3A4 include: amprenavir, aprepitant, atazanavir, avacopan, berotralstat, clofazimine, conivaptan, crizotinib, darunavir, diltiazem, dronedarone, duvelisib, erythromycin, fedratinib, fluconazole, fluvoxamine, fosnetupitant, imatinib, isavuconazonium, lenacapavir, letermovir, netupitant, nilotinib, rilzabrutinib, schisandra, stiripentol, tofisopam, treosulfan and verapamil.(1-3)

Moderate Interaction: Assess the risk to the patient and take action as needed.

Selected Antihypertensives And Vasodilators/Apomorphine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Apomorphine causes dose-dependent decreases in blood pressure. Concurrent use with antihypertensive agents may result in additive effects on blood pressure.(1)

CLINICAL EFFECTS: Concurrent use of antihypertensives and apomorphine may result in orthostatic hypotension with or without dizziness, nausea, or syncope.(1)

PREDISPOSING FACTORS: The risk of orthostatic hypotension may be increased during dose escalation of apomorphine and in patients with renal or hepatic impairment.(1)

PATIENT MANAGEMENT: Patients receiving concurrent therapy should be monitored for hypotension. Counsel patients about the risk of orthostatic hypotension.(1)

DISCUSSION: Healthy volunteers who took sublingual nitroglycerin (0.4 mg) concomitantly with apomorphine experienced a mean largest decrease in supine systolic blood pressure (SBP) of 9.7 mm Hg and in supine diastolic blood pressure (DBP) of 9.3 mm Hg, and a mean largest decrease in standing SBP and DBP of 14.3 mm Hg and 13.5 mm Hg, respectively. The maximum decrease in SBP and DBP was 65 mm Hg and 43 mm Hg, respectively. When apomorphine was taken alone, the mean largest decrease in supine SBP and DBP was 6.1 mm Hg and 7.3 mm Hg, respectively, and in standing SBP and DBP was 6.7 mm Hg and 8.4 mm Hg, respectively.(1)

Guanfacine is contraindicated in patients with known hypersensitivity to the drug.

There are no contraindication contraindications for this drug.

• Bradycardia
• Hypotension
• Suicidal ideation

• Aggressive behavior
• Alcohol intoxication
• Disease of liver
• Drowsy
• Kidney disease with reduction in glomerular filtration rate (GFr)
• Orthostatic hypotension

Common adverse effects in patients receiving guanfacine include dry mouth, somnolence, dizziness, constipation, fatigue, asthenia, impotence, and headache.

Rare or Very Rare

• Atrioventricular block
• Bradycardia
• Chest pain
• Encephalopathy
• Exfoliative dermatitis
• Hypersensitivity drug reaction
• Seizure disorder
• Sinus node dysfunction
• Suicidal
• Suicidal ideation
• Tachycardia

More Frequent

• Acute abdominal pain
• Dizziness
• Drowsy
• Fatigue
• Hypotension
• Insomnia
• Lethargy
• Nausea
• Sedation
• Weight gain
• Xerostomia

Less Frequent

• Acute cognitive impairment
• Anorexia
• Constipation
• Dyspepsia
• Erectile dysfunction
• General weakness
• Headache disorder
• Increased urinary frequency
• Irritability
• Libido changes
• Nightmares
• Palpitations
• Pruritus of skin
• Urinary incontinence
• Vomiting

Rare or Very Rare

• Accidental fall
• Alopecia
• Arthralgia
• Blurred vision
• Conjunctivitis
• Cramps in legs
• Depression
• Dysgeusia
• Dyspnea
• Edema
• Hallucinations
• Malaise
• Myalgia
• Pallor
• Paresthesia
• Raynaud's phenomenon
• Skin inflammation
• Skin rash
• Symptoms of anxiety
• Syncope
• Tremor
• Vertigo

No enhanced messaging available.

Safety and efficacy of guanfacine for the management of hypertension have not been established in children younger than 12 years of age; use in these pediatric patients is not recommended.

Mania and aggressive behavioral changes have been reported in pediatric patients with ADHD receiving guanfacine (as conventional tablets)+; all patients had medical or family risk factors for bipolar disorder. All patients recovered following discontinuance of the drug.

Category B. (See Users Guide.)

Guanfacine is not recommended for the treatment of acute hypertension associated with toxemia of pregnancy.

Guanfacine is distributed into milk in rats; it is not known whether the drug is distributed into human milk. Caution is advised if guanfacine is used in nursing women.

Guanfacine dosage should be selected with caution (usually starting at the low end of the dosing range) because of age-related decreases in hepatic, renal, and/or cardiac function and concomitant disease and drug therapy.

Clinical trial data for patients 65 years of age or older are insufficient to determine whether geriatric patients respond differently than younger adults. Other experience suggests that response is similar to that in younger adults.

Dosage of guanfacine should be selected with caution because of age-related decreases in hepatic, renal, and/or cardiac function and potential for concomitant disease and drug therapy.