HYLOREL
Clinical safety rating
cautionComprehensive clinical and safety monograph for HYLOREL (HYLOREL).
Selective alpha-1 adrenergic receptor antagonist; inhibits sympathetic vasoconstriction, reducing peripheral vascular resistance and blood pressure.
| Metabolism | Extensively metabolized in the liver via O-demethylation and conjugation; CYP450 enzymes involved (CYP2D6, CYP3A4). |
| Excretion | Primarily renal (50-60% unchanged) and biliary/fecal (40-50%). |
| Half-life | Approximately 12-15 hours; clinically, steady-state achieved in 2-3 days. |
| Protein binding | 90-95% bound to plasma proteins (albumin and alpha-1-acid glycoprotein). |
| Volume of Distribution | 0.5-0.7 L/kg; indicates distribution into total body water. |
| Bioavailability | 85-90% after oral administration. |
| Onset of Action | 2-4 hours after oral dosing. |
| Duration of Action | 24-48 hours; may require dose adjustment in renal impairment. |
| Molecular Weight | 280.75 |
10 mg orally twice daily, titrated to 20-40 mg twice daily based on blood pressure response.
| Dosage form | TABLET |
| Renal impairment | No adjustment needed for mild to moderate renal impairment (GFR 30-89 mL/min). For severe renal impairment (GFR <30 mL/min), reduce dose by 50% and monitor blood pressure closely. |
| Liver impairment | For Child-Pugh Class A: no adjustment. For Class B: reduce starting dose to 5 mg twice daily, titrate cautiously. For Class C: avoid use due to lack of safety data. |
| Pediatric use | Not recommended in pediatric patients due to lack of safety and efficacy data. |
| Geriatric use | Start at 5 mg twice daily, titrate slowly; monitor for orthostatic hypotension and electrolyte imbalances due to age-related changes in renal function and sympathetic response. |
| 1st trimester | Avoid use; insufficient human data; animal studies show risk. |
| 2nd trimester | Avoid use; may cause fetal harm due to receptor blockade. |
| 3rd trimester | Avoid use; may cause neonatal hypotension, respiratory depression, and feeding problems. |
Clinical note
Comprehensive clinical and safety monograph for HYLOREL (HYLOREL).
| Placental transfer | Crosses placenta in animal studies; human data limited but likely crosses. |
| Breastfeeding | Excreted into breast milk in low amounts; avoid or use with caution due to potential for infant cardiovascular effects. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Pregnancy Category C. First trimester: No adequate studies, but potential for fetal harm based on animal data (skeletal abnormalities, reduced fetal weight at high doses). Second and third trimesters: May cause fetal bradycardia, hypotension, and reduced placental perfusion; avoid use due to risk of oligohydramnios and fetal renal impairment. |
| Fetal Monitoring | Maternal: Blood pressure, heart rate, signs of hypotension (dizziness, syncope), fluid status. Fetal: Ultrasound for amniotic fluid index if used in second/third trimester; fetal heart rate monitoring. Neonatal: Apgar scores, blood pressure, and heart rate for 24-48 hours postpartum if exposed near term. |
| Fertility Effects | Reproductive toxicity studies in animals showed no impairment of fertility at therapeutic doses. In humans, no specific studies; however, alpha2-agonists may theoretically affect libido or erectile function but no conclusive evidence of fertility impairment. |
■ FDA Black Box Warning
None
| Common Effects | Limited data available |
| Serious Effects |
Hypersensitivity to guanadrel or componentsPheochromocytomaMonoamine oxidase inhibitor (MAOI) use within 14 daysCongestive heart failureSevere renal impairment
| Precautions | Syncope and orthostatic hypotension, Priapism, Intraoperative floppy iris syndrome, Use in patients with impaired hepatic function |
| Food/Dietary | Avoid tyramine-rich foods (aged cheeses, cured meats, fermented products) as guanethidine may potentiate pressor effects. Also avoid excessive alcohol consumption due to additive hypotensive effects. Take with food to reduce GI upset. |
| Clinical Pearls | HYLOREL (guanethidine) is a potent adrenergic neuron blocker used primarily for moderate to severe hypertension. Its use is limited due to orthostatic hypotension and dose-related side effects. Initiate at low doses (10 mg/day) and titrate slowly. Avoid in patients with pheochromocytoma or MAOI use within 14 days. Monitor for profound orthostasis, especially upon waking and after exercise. May cause diarrhea due to increased GI motility. Combine with a diuretic to reduce dose requirements and enhance efficacy. |
| Patient Advice | Take exactly as prescribed; do not stop abruptly as this may cause rapid blood pressure increase. · Arise slowly from sitting or lying to prevent dizziness and fainting. Avoid sudden position changes. · Avoid alcohol and over-the-counter cold or allergy medications unless approved by your doctor. · May cause drowsiness; use caution when driving or operating machinery. · Report persistent dizziness, fainting, or severe diarrhea to your healthcare provider. · Maintain adequate fluid intake, but avoid excessive salt unless directed. · Inform all healthcare providers of your use of this medication before any surgery. |
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