Terazosin

BRAND NAMES

Hytrin and Tezruly.

Terazosin is taken orally and can be administered with or without food.

MECHANISM OF ACTION

Terazosin is an alpha-1 adrenergic receptor antagonist, or alpha-blocker, that works by blocking the alpha-1 adrenoceptors throughout the body. This blockade relaxes the smooth muscles in both blood vessels and the prostate gland. For benign prostatic hyperplasia (BPH), this relaxation eases pressure on the urethra and improves urinary flow. For hypertension, the relaxation of blood vessels reduces overall peripheral resistance, which lowers blood pressure.

PHARMACOKINETICS

Absorption

Terazosin is an alpha-1 adrenergic blocker that is quickly and nearly completely absorbed following oral administration. This high and consistent absorption is a key pharmacokinetic feature that allows for convenient once-daily dosing.

Distribution

The volume of distribution for terazosin is estimated to be between 25 and 30 liters.

Metabolism

Terazosin is extensively metabolized in the liver, with its primary elimination occurring via the biliary system. Only a small amount is eliminated through the urine. Its plasma clearance is about 80 mL per minute, while renal clearance is approximately 10 mL per minute. The average half-life during the beta phase is around 12 hours.

Excretion

Approximately 60% of the total dose is eliminated through the feces, while the remaining 40% is excreted via the urine.

PHARMACODYNAMICS

Terazosin is a long-acting, selective alpha-1 adrenergic receptor antagonist with pharmacodynamic effects that include relaxation of smooth muscles in blood vessels and the prostate. These actions lead to therapeutic effects in both hypertension and benign prostatic hyperplasia (BPH). 

ADMINISTRATION

Terazosin is an oral medication typically taken once daily, often at bedtime, to help minimize the effects of potential low blood pressure. The initial administration involves a low amount, which a doctor gradually adjusts to address high blood pressure or symptoms associated with benign prostatic hyperplasia (BPH). 

DOSAGE AND STRENGTH

Terazosin is available in two oral formulations: capsules and solution.

1 mg

2 mg

5 mg

10 mg 

DRUG INTERACTIONS

Terazosin can cause significant drug interactions, primarily centered around its blood pressure-lowering effect. The most dangerous interactions involve other medications that also decrease blood pressure, which can lead to severe hypotension, dizziness, and fainting. This includes other blood pressure-lowering medications, such as beta-blockers, diuretics, and calcium channel blockers. Combining terazosin with erectile dysfunction medications like sildenafil or tadalafil is also risky for the same reason. 

FOOD INTERACTIONS

You can take terazosin with or without food, though taking it with food can help if you experience stomach upset. While there are no major food interactions, you should be mindful of certain substances and dietary habits. Consuming alcohol can increase dizziness and significantly drop your blood pressure. Some sources also suggest avoiding grapefruit juice and high-sodium or high-cholesterol foods, as they can interfere with the medication's blood pressure-lowering effects. If you experience dizziness, taking your dose at bedtime and rising slowly can help minimize side effects.

CONTRAINDICATIONS

Terazosin and other alpha-1 blockers from the quinazoline family, such as doxazosin and prazosin, should not be used by individuals with a known allergy to any of these drugs. Due to the risk of significant blood pressure changes, it is also not recommended for those with a history of orthostatic hypotension.

SIDE EFFECTS

• Dizziness or lightheadedness.

• Weakness or fatigue.

• Nasal congestion.

• Swelling.

• Nausea.

• Blurred vision.

• Priapism.

• Intraoperative Floppy Iris Syndrome.

• Severe allergic reaction.

• Rapid or irregular heartbeat.

OVER DOSE

• Extreme dizziness or lightheadedness.

• Fainting or passing out.

• Severely low blood pressure (hypotension), which may potentially result in shock.

• Rapid or irregular heartbeat (palpitations).

• Confusion.

• Nausea or vomiting.

• Headache.

• Shortness of breath.

• Prolonged, painful erection (priapism).

TOXICITY

Terazosin toxicity is primarily caused by its pharmacological effects, which are a marked reduction in blood pressure and the relaxation of smooth muscles. An overdose can cause a life-threatening drop in blood pressure (hypotension) and other severe symptoms, requiring immediate medical attention.