GUANABENZ ACETATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GUANABENZ ACETATE (GUANABENZ ACETATE).
Central alpha-2 adrenergic agonist; reduces sympathetic outflow from the brainstem, decreasing peripheral vascular resistance and heart rate.
| Metabolism | Primarily hepatic via glucuronidation and oxidation; CYP450 involvement minimal. |
| Excretion | Renal: ~75% as unchanged drug and metabolites; biliary/fecal: ~25%. |
| Half-life | Terminal elimination half-life is 7-12 hours; requires twice-daily dosing for stable antihypertensive effect. |
| Protein binding | Approximately 90% bound to albumin and α1-acid glycoprotein. |
| Volume of Distribution | 2-3 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral: ~85% (well absorbed, minimal first-pass metabolism). |
| Onset of Action | Oral: 30-60 minutes. |
| Duration of Action | 6-12 hours; clinical effect may persist for up to 24 hours with chronic dosing due to long half-life. |
4 mg orally twice daily, titrated up to 8-16 mg twice daily; maximum 32 mg twice daily.
| Dosage form | TABLET |
| Renal impairment | GFR 30-59 mL/min: reduce dose by 50%; GFR <30 mL/min: avoid use or use with extreme caution. |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B: reduce dose by 50%; Class C: avoid use. |
| Pediatric use | Not recommended; safety and efficacy not established in children. |
| Geriatric use | Initiate at lower dose (2 mg twice daily) and titrate slowly due to increased risk of orthostatic hypotension and sedation. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for GUANABENZ ACETATE (GUANABENZ ACETATE).
| Breastfeeding | Present in breast milk; M/P ratio unknown. Risk of neonatal hypotension and bradycardia. Avoid breastfeeding or use with caution under medical advice. |
| Teratogenic Risk | First trimester: Limited human data; animal studies show no teratogenicity at clinically relevant doses. Second and third trimesters: Risk of fetal bradycardia, hypotension, and decreased placental perfusion due to alpha-2 agonist activity. Avoid use unless benefit outweighs risk. |
| Fetal Monitoring |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to guanabenz; concurrent use with MAOIs.
| Precautions | Rebound hypertension upon abrupt discontinuation; sedation; orthostatic hypotension; syncope; use caution in hepatic impairment. |
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| Monitor maternal blood pressure and heart rate. Fetal heart rate monitoring after maternal dosing. Assess for signs of neonatal withdrawal (e.g., irritability, poor feeding) postpartum. |
| Fertility Effects | No evidence of adverse effects on fertility in animal studies or human data. Reversible hyperprolactinemia reported, which may impair fertility. |