WYTENSIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for WYTENSIN (WYTENSIN).
Centrally acting alpha-2 adrenergic agonist; reduces sympathetic outflow from the brainstem, decreasing peripheral vascular resistance and heart rate.
| Metabolism | Hepatic metabolism via CYP450 enzymes, primarily CYP2D6; excreted renally and in feces. |
| Excretion | Renal: ~50% unchanged; fecal: ~50% as metabolites and unchanged drug. |
| Half-life | Terminal elimination half-life: 10-12 hours in patients with normal renal function. |
| Protein binding | ~90% bound to serum albumin. |
| Volume of Distribution | 0.5-1.0 L/kg; indicates extensive tissue distribution. |
| Bioavailability | Oral: ~60% (range 50-70%). |
| Onset of Action | Oral: 30-60 minutes for a measurable reduction in blood pressure. |
| Duration of Action | Oral: 12-24 hours; daily dosing provides sustained blood pressure control. |
| Molecular Weight | 448.9 |
Initial 10 mg orally twice daily; titrate to 20-40 mg/day in divided doses; maximum 40 mg/day.
| Dosage form | TABLET |
| Renal impairment | GFR 30-60 mL/min: reduce dose by 50%; GFR <30 mL/min: reduce dose by 75% or use alternative drug. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use. |
| Pediatric use | Not recommended due to lack of safety and efficacy data; alternative antihypertensives preferred. |
| Geriatric use | Start at 5 mg twice daily; titrate slowly due to increased risk of orthostatic hypotension and renal impairment. |
| 1st trimester | Avoid due to embryotoxicity risk from ACE inhibition; second-line agent for hypertension if compelling indication after first trimester. |
| 2nd trimester | Avoid; increased risk of fetal oligohydramnios, renal dysplasia, and skull ossification defects. |
| 3rd trimester | Avoid; risk of fetal/neonatal oligohydramnios, renal failure, hypotension, and hyperkalemia. |
Clinical note
Comprehensive clinical and safety monograph for WYTENSIN (WYTENSIN).
| Placental transfer | Crosses human placenta; detected in fetal plasma (approximately 70-80% of maternal levels). Fetotoxic risk. |
| Breastfeeding | Excreted in breast milk in low amounts; use with caution, especially in premature or low-birth-weight infants. Monitor infant for hypotension and electrolyte disturbances. |
■ FDA Black Box Warning
WYTENSIN (guanabenz) is not associated with a black box warning.
| Serious Effects |
History of angioedema related to ACE inhibitorsPregnancy (particularly second and third trimesters)Hypersensitivity to methyldopa or any component of the formulationActive hepatic disease (e.g., acute hepatitis, cirrhosis)
| Precautions | Rebound hypertension upon abrupt discontinuation, Sedation and drowsiness, Orthostatic hypotension, Hepatic impairment, Renal impairment |
| Food/Dietary | Avoid or limit alcohol as it can enhance the sedative effects. No specific food interactions reported. Maintain a heart-healthy diet low in sodium and saturated fats as part of hypertension management. |
Loading safety data…
| Lactation Rating |
| L3 (Moderately Safe) - Limited data suggests risk of adverse effects in infant but generally acceptable with close monitoring. |
| Teratogenic Risk | First trimester: Limited data; animal studies show no teratogenicity but human risk cannot be excluded. Second and third trimesters: Associated with decreased fetal renal function, oligohydramnios, and skull ossification defects if used after 20 weeks gestational age. Risk of neonatal hypotension, hyperkalemia, and renal impairment if exposed near term. |
| Fetal Monitoring | Monitor maternal blood pressure, serum electrolytes, and renal function. Fetal ultrasound to assess amniotic fluid volume and renal structure if used after 20 weeks. Neonatal monitoring for hypotension and hyperkalemia after delivery if exposed near term. |
| Fertility Effects | No known adverse effects on fertility in animal studies. Human data insufficient to conclude impact on fertility. |
| Clinical Pearls |
| Wytensin (guanabenz acetate) is a centrally acting alpha-2 adrenergic agonist used for hypertension. Avoid abrupt discontinuation to prevent rebound hypertension. Monitor for sedation and dry mouth, especially in elderly. Use with caution in patients with severe coronary insufficiency, recent MI, or cerebrovascular disease. May impair ability to perform hazardous tasks. Dosage adjustment needed in renal impairment. |
| Patient Advice | Take exactly as prescribed, usually twice daily. Do not stop suddenly as this can cause dangerous blood pressure spikes. · This medication may cause drowsiness, dizziness, or dry mouth. Avoid driving or operating machinery until you know how it affects you. · Rise slowly from sitting or lying to minimize dizziness. Limit alcohol intake as it can worsen side effects. · Inform your doctor if you experience heart rate changes, fainting, or persistent headache. · Keep regular appointments for blood pressure monitoring. Do not use over-the-counter cold or weight loss medications without consulting your doctor. |