Silodosin

Generic name: silodosin
Brand name: Rapaflo
Dosage form: oral capsule (4 mg; 8 mg)
Drug class: Alpha-adrenoreceptor antagonists

Medically reviewed by A Ras MD.

What is silodosin used for?

Silodosin is a prescription medicine that is used to treat the signs of an enlarged prostate. It may be given to you for other reasons.

Description

Silodosin is a selective antagonist of alpha-1 adrenoreceptors. The chemical name of silodosin is 1-(3-Hydroxypropyl)-5-[(2R)-2-({2-[2-(2,2,2-trifluoroethoxy)phenoxy]ethyl}amino)propyl]-2,3-dihydro-1H-indole-7-carboxamide and the molecular formula is C25H32F3N3O4 with a molecular weight of 495.53. The structural formula of silodosin is:

Silodosin is a white to pale yellow powder that melts at approximately 105 to 109°C. It is freely soluble in acetic acid, freely soluble in alcohol and very slightly to practically soluble in water.

Each silodosin capsules 4 mg capsule for oral administration contains 4 mg silodosin, and the following inactive ingredients: pregelatinized starch, sucrose, sodium lauryl sulfate and magnesium stearate. The size #3 hard gelatin capsules contain gelatin and titanium dioxide. The capsules are printed with edible gold ink containing shellac, propylene glycol and iron oxide yellow.

Each silodosin capsules 8 mg capsule for oral administration contains 8 mg silodosin, and the following inactive ingredients: pregelatinized starch, sucrose, sodium lauryl sulfate and magnesium stearate. The size #1 hard gelatin capsules contain gelatin and titanium dioxide. The capsules are printed with edible green ink containing shellac, propylene glycol, iron oxide yellow FD&C Blue No. 1 Aluminum Lake.

Mechanism of Action

Silodosin is a selective antagonist of post-synaptic alpha-1 adrenoreceptors, which are located in the human prostate, bladder base, bladder neck, prostatic capsule, and prostatic urethra. Blockade of these alpha-1 adrenoreceptors can cause smooth muscle in these tissues to relax, resulting in an improvement in urine flow and a reduction in BPH symptoms.

An in vitro study examining binding affinity of silodosin to the three subtypes of the alpha-1 adrenoreceptors (alpha-1A, alpha-1B, and alpha-1D) was conducted. The results of the study demonstrated that silodosin binds with high affinity to the alpha-1A subtype.

Before taking silodosin, tell your doctor:

If you are allergic to silodosin; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
If you have any of these health problems: Kidney disease or liver disease.
If you take any drugs (prescription or OTC, natural products, vitamins) that must not be taken with silodosin, like certain drugs that are used for HIV, infections, or depression. There are many drugs that must not be taken with silodosin. Your doctor or pharmacist can tell you if you are taking a drug that must not be taken with silodosin.
If you are taking or will be taking another drug like this one.

This is not a list of all drugs or health problems that interact with silodosin.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take silodosin with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take silodosin?

Tell all of your health care providers that you take silodosin. This includes your doctors, nurses, pharmacists, and dentists.
Avoid driving and doing other tasks or actions that call for you to be alert until you see how silodosin affects you.
To lower the chance of feeling dizzy or passing out, rise slowly if you have been sitting or lying down. Be careful going up and down stairs.
If you are having cataract surgery or other eye procedure, talk with your doctor.
Have blood work checked as you have been told by the doctor. Talk with the doctor.
Check your blood pressure as you have been told.
Have a rectal exam (to check prostate gland) and blood work (PSA test). Talk with your doctor.
Talk with your doctor before you drink alcohol.
This medicine is not approved for use in children. Talk with the doctor.
This medicine is not approved for use in women. If you are a woman using silodosin, talk with your doctor if you are pregnant, plan on getting pregnant, or are breast-feeding.

How is silodosin best taken?

Use silodosin as ordered by your doctor. Read all information given to you. Follow all instructions closely.

Take with a meal.
You may sprinkle contents of capsule on applesauce. Do not chew. Swallow right away and follow with cool water.
If mixing on applesauce, the applesauce should not be warm. Do not sprinkle on other liquids or foods.

What do I do if I miss a dose?

Take a missed dose as soon as you think about it, with a meal.
If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
Do not take 2 doses at the same time or extra doses.

What are the side effects of silodosin that I need to call my doctor about immediately?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
Very bad dizziness or passing out.

What are some other side effects of silodosin?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

Orgasm with less or no semen.
Dizziness.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

If overdose is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out silodosin?

Store at room temperature.
Protect from light.
Store in a dry place. Do not store in a bathroom.
Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.