Usage
Terazosin is prescribed for:
- Benign Prostatic Hyperplasia (BPH): Reduces symptoms like frequent urination, weak stream, and nighttime urination by relaxing smooth muscles in the prostate and bladder neck.
- Hypertension (High Blood Pressure): Lowers blood pressure by relaxing vascular smooth muscle, decreasing peripheral vascular resistance.
Pharmacological Classification: Terazosin is an alpha-1 adrenergic blocker, specifically a postsynaptic alpha-1 antagonist.
Mechanism of Action: Terazosin selectively blocks postsynaptic alpha-1 adrenergic receptors. In BPH, this relaxes smooth muscle in the prostate and bladder neck, improving urine flow. In hypertension, it relaxes vascular smooth muscle, reducing peripheral resistance and lowering blood pressure.
Alternate Names
International/Regional Variations: No significant variations exist. The INN (International Nonproprietary Name) is Terazosin.
Brand Names: Hytrin, Tezruly
How It Works
Pharmacodynamics: Terazosin primarily affects vascular and prostatic smooth muscle by antagonizing alpha-1 adrenergic receptors, leading to vasodilation and reduced urethral resistance.
Pharmacokinetics:
- Absorption: Terazosin is well-absorbed orally. Food can delay but not significantly reduce absorption.
- Metabolism: Extensively metabolized in the liver, primarily by CYP3A4 enzymes.
- Elimination: Excreted primarily in feces (60%) and to a lesser extent in urine (40%). Renal impairment has minimal impact on elimination.
Mode of Action: Terazosin competes with norepinephrine and other alpha-1 agonists for binding at postsynaptic alpha-1 adrenergic receptors on vascular and prostatic smooth muscle. This competitive antagonism inhibits smooth muscle contraction, causing vasodilation and reducing urethral resistance.
Receptor Binding, Enzyme Inhibition, or Neurotransmitter Modulation: Terazosin is a competitive antagonist at postsynaptic alpha-1 adrenergic receptors.
Dosage
Standard Dosage
Adults:
- Hypertension: Initial dose: 1 mg orally at bedtime. Maintenance dose: 1-5 mg orally once a day; titrate slowly, as needed, up to a maximum of 20 mg/day.
- BPH: Initial dose: 1 mg orally at bedtime. Titrate upwards weekly to 2 mg, 5 mg, then 10 mg, as needed, up to a maximum of 20 mg/day. A dose of 10 mg is usually needed for clinical response.
Children: The safety and efficacy of terazosin in children younger than 18 years have not been established. Use is generally not recommended.
Special Cases:
- Elderly Patients: Initial dose: 0.5 mg at bedtime for hypertension. Titrate cautiously, as they are more susceptible to postural hypotension. Use for hypertension is generally avoided in this population.
- Patients with Renal Impairment: No dosage adjustment is necessary.
- Patients with Hepatic Dysfunction: Use with caution. Start with a low dose and titrate cautiously.
Clinical Use Cases
Terazosin’s clinical use is limited to hypertension and BPH. It is not typically used in settings like intubation, surgical procedures, mechanical ventilation, or the ICU.
Dosage Adjustments
Dose adjustments are primarily based on the patient’s blood pressure response (for hypertension) or BPH symptom improvement.
Side Effects
Common Side Effects
Dizziness, headache, asthenia (weakness, tiredness), nasal congestion, peripheral edema, somnolence, nausea, palpitation, postural hypotension.
Rare but Serious Side Effects
Syncope (especially with initial dose or dose increase), priapism.
Long-Term Effects
Not extensively studied.
Adverse Drug Reactions (ADR)
Intraoperative Floppy Iris Syndrome (IFIS) during cataract surgery.
Contraindications
Hypersensitivity to terazosin or other quinazolines, history of micturition syncope.
Drug Interactions
Terazosin interacts with other blood pressure-lowering medications (e.g., other alpha blockers, beta blockers, diuretics, ACE inhibitors, calcium channel blockers), PDE-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil), and CYP3A4 inhibitors and inducers. Concurrent use with these agents can potentiate the hypotensive effects of terazosin.
Pregnancy and Breastfeeding
Pregnancy Safety Category: C. Terazosin should be used during pregnancy only if the potential benefit outweighs the risk to the fetus.
Fetal Risks/Teratogenicity: Animal studies have shown increased fetal resorptions and decreased fetal weight at high doses.
Breastfeeding: It is unknown if terazosin is excreted in breast milk. Caution is advised.
Drug Profile Summary
- Mechanism of Action: Alpha-1 adrenergic blocker.
- Side Effects: Dizziness, headache, asthenia, nasal congestion, postural hypotension, somnolence, nausea. Rarely, syncope and priapism.
- Contraindications: Hypersensitivity, micturition syncope.
- Drug Interactions: Other antihypertensives, PDE-5 inhibitors, CYP3A4 inhibitors/inducers.
- Pregnancy & Breastfeeding: Use with caution if benefits outweigh risks.
- Dosage: Hypertension: 1-20 mg/day; BPH: 1-10 mg/day. Start with 1 mg at bedtime.
- Monitoring Parameters: Blood pressure, BPH symptoms.
Popular Combinations
Terazosin is sometimes used in combination with a 5-alpha reductase inhibitor (e.g., finasteride or dutasteride) for the management of BPH.
Precautions
- Administer the initial dose and dose increases at bedtime to minimize postural hypotension.
- Monitor blood pressure closely, especially during initial titration.
- Caution patients about the risk of dizziness and syncope.
- Patients undergoing cataract surgery should inform their ophthalmologist about terazosin use due to the risk of IFIS.
FAQs (Frequently Asked Questions)
Q1: What is the recommended starting dosage for Terazosin?
A: The recommended starting dosage for both hypertension and BPH is 1 mg orally at bedtime.
Q2: What is the maximum dose of Terazosin?
A: The maximum recommended dose is 20 mg/day.
Q3: When should Terazosin be administered?
A: Terazosin should be administered at bedtime to minimize the risk of postural hypotension and syncope.
Q4: What are the most common side effects of Terazosin?
A: Dizziness, headache, asthenia, nasal congestion, peripheral edema, somnolence, nausea, and palpitations.
Q5: What is the mechanism of action of Terazosin?
A: Terazosin is a selective alpha-1 adrenergic blocker, which leads to relaxation of smooth muscle in the prostate and blood vessels.
Q6: Is Terazosin safe to use in pregnancy?
A: Terazosin is Pregnancy Category C. Use only if the benefits clearly outweigh the risks.
Q7: How should the dosage of Terazosin be adjusted in elderly patients?
A: Start with a lower initial dose (0.5 mg) and titrate more cautiously in elderly patients due to increased sensitivity to postural hypotension. Avoid using for hypertension in the elderly if possible.
Q8: Does Terazosin interact with other medications?
A: Yes, Terazosin can interact with other antihypertensive drugs, PDE-5 inhibitors, and CYP3A4 inhibitors/inducers.
Q9: What should patients be advised about taking Terazosin?
A: Patients should be cautioned about the risk of dizziness and syncope, especially when first starting treatment or increasing the dose. They should avoid activities requiring alertness until they know how the medication affects them.
Q10: What is Intraoperative Floppy Iris Syndrome (IFIS)?
A: IFIS is a complication that can occur during cataract surgery in patients taking or who have taken alpha-1 blockers like terazosin. It can make the surgery more difficult and increase the risk of complications. Patients should inform their ophthalmologist about their terazosin use.
