Dosing and uses of Wytensin (guanabenz)
Adult dosage forms and strengths
tablet
- 4mg
- 8mg
Hypertension
Initial dose: 4 mg PO q12hr intially; may increase dose by 4-8 mg/day at 1-2 week intervals
Maintenance dose range is typically 4-16 mg PO q12hr
Not to exceed 32 mg PO q12hr
Pediatric dosage forms and strengths
Safety and effectiveness not established
Geriatric dosage forms and strengths
Adverse CNS effects; may cause bradycardia and orthostatic hypotension; not recommended as routine treatment for hypertension (Beers criteria)
Not drug of choice in elderly because of CNS effects
Hypertension
4 mg PO qDay, gradually increase q1-2weeks
Wytensin (guanabenz) adverse (side) effects
>10%
Sedation/somnolence (20-50%)
Dry mouth (12-37%)
Dizziness (12-17%)
1-10%
Weakness (4%)
Chest pain (3%)
Edema (3%)
Palpitations (3%)
Anxiety (3%)
Ataxia (3%)
Depression (3%)
Pruritus (3%)
Rash (3%)
Gynecomastia (3%)
Abdominal pain (3%)
Constipation (3%)
Diarrhea (3%)
Nausea (3%)
Vomiting (3%)
Myalgia (3%)
Blurred vision (3%)
Dyspnea (3%)
Nasal congestion (3%)
Frequency not defined
Rebound HTN with abrupt discontinuance
Warnings
Contraindications
Hypersensitivity to guanabenz
Cautions
Avoid abrupt withdrawal (rebound hypertension)
CVD, recent MI, sedation, severe coronary insufficiency liver disease, renal impairment
Avoid during breast-feeding
Pregnancy and lactation
Pregnancy category: C
Lactation: excretion in milk unknown; use with caution
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Wytensin (guanabenz)
Mechanism of action
Central sympatholytic via alpha-2-agonist activity resulting in decreased PVR and Hr
Absorption
Bioavailability: 75%
Onset: initial effect: 60 min; max effect: 2-4 hr
Peak plasma time: 2-5 hr
Duration: 10-12 hr
Distribution
Protein binding: 90%
Vd: 7.4-13.4 L/kg
Metabolism
Liver
Metabolites: para-hydroxy guanabenz; 2,6-dichlorobenzaldehyde azine (inactive)
Elimination
Half-Life: 6 hr
Dialyzable: HD: No, PD: No
Excretion: Feces 16%, urine <1%
