Silodosin

Silodosin is a drug that is used to treat symptoms associated with benign prostatic hyperplasia (BPH). It belongs to the group of alpha-1-adrenoreceptor antagonists.

Benign prostatic hyperplasia (BPH) is a common condition in older men. It occurs when the prostate, a gland below the bladder, increases in size and presses on the urethra. Possible symptoms include difficulty urinating, weak urine flow and frequent urge to urinate.

The exact cause of BPH is not fully understood, but it is thought to be influenced by hormonal changes that occur as men age. It is thought that an increase in the level of dihydrotestosterone (DHT), a hormone derived from testosterone, stimulates the growth of prostate cells. This leads to an enlargement of the prostate and thus to the symptoms of BPH.

Prostatic smooth muscle tone is regulated by the α-adrenoceptor subtype α1A. Silodosin is an α1-adrenoceptor antagonist with the highest selectivity for the α1A-adrenoceptor subtype. By blocking the α1A-adrenoceptor signaling pathway, silodosin promotes smooth muscle relaxation in the prostate and urethra, improving symptoms of BPH. Silodosin also acts on the afferent nerves in the bladder and can also relieve bladder overactivity and congestion symptoms.

Silodosin is metabolized in the liver and rapidly absorbed after oral administration. The bioavailability, i.e. the percentage of the active ingredient available in the blood, is 32%. The half-life, i.e. the time the body needs to excrete half of the active substance, is 13 hours. The maximum plasma concentration (Cmax), i.e. the maximum concentration of the active ingredient in the blood plasma (liquid cell-free part of the blood), is reached after about 3 hours. When taken with high-fat food, the maximum plasma concentration is reduced by about 20 - 40 % and the time to reach this concentration is delayed by about 1 hour.

The apparent volume of distribution is about 50 L. Plasma protein binding is about 97 %. The enzyme mainly responsible for metabolization is UGT2B7. Other enzymes involved in metabolism are alcohol dehydrogenases, aldehyde dehydrogenases and CYP3A4. Slightly more than half of the dose is excreted in the stool, while around 30% is excreted in the urine.

Always take silodosin exactly as described in the package leaflet or as advised by your doctor.

The recommended dosage is 8 mg per day.

Initially, the usual dose is usually 4 mg per day and is increased to 8 mg per day during the course of therapy if necessary.

If kidney function is impaired, a reduced dosage of 4 mg may be necessary.

Silodosin should, if possible, always be taken at the same time and with a meal.

The following side effects may occur:

Very common:

• Ejaculation disorders
• Reduction of sperm count in the ejaculate and reversible impairment of fertility

Frequent:

• Diarrhea
• Dizziness
• Nasal congestion

Occasional:

• Decreased libido
• Tachycardia
• Erectile dysfunction
• Nausea
• Dry mouth
• allergic reactions
• altered liver values
• low blood pressure

Rarely:

• rapid or irregular heartbeat
• fainting spell

Frequency unknown:

• Floppy iris syndrome during cataract surgery

Interactions may occur if the following medicines are taken at the same time:

• Medication that lowers blood pressure
• Medication against fungal infections
• Medication for the treatment of AIDS
• Medication used after organ transplants
• Medication for the treatment of erectile dysfunction
• Medication for the treatment of epilepsy
• Rifampicin

Silodosin must NOT be taken in the following cases

• in case of allergy to silodosin

Silodosin should only be used from the age of 18.

As silodosin is used exclusively in men, no data are available on its use during pregnancy and breastfeeding. Silodosin should not be taken by women.

Silodosin was developed by the Japanese companies Kissei Pharmaceutical and Daiichi Sankyo and was first approved in Japan in 2006. The substance was approved in the USA in 2008. Approvals were granted in the EU and Switzerland in 2010 and 2016 respectively.