finasteride

Action and Spectrum

The actions of finasteride are primarily related to its ability to selectively inhibit the enzyme 5-alpha-reductase, which converts testosterone to dihydrotestosterone (DHT), a more potent androgen. Finasteride can produce several beneficial effects by reducing DHT levels in the prostate gland, scalp, and other tissues. 

The spectrum of actions of finasteride includes: 

• Treatment of benign prostatic hyperplasia (BPH): finasteride is FDA-approved for the treatment of BPH, a condition in which the prostate gland becomes enlarged, causing urinary symptoms such as hesitancy, frequency, and urgency. By reducing DHT levels in the prostate gland, finasteride can help to shrink the gland and relieve these symptoms. 

• Treatment of male pattern baldness: finasteride is also used off-label to treat androgenetic alopecia, also known as male pattern baldness. By reducing DHT levels in the scalp, finasteride can slow or reverse the progression of hair loss and, in some cases, promote hair regrowth. 

• Potential role in preventing of prostate cancer: Some studies have suggested that finasteride may reduce the risk of developing prostate cancer by up to 25%, although the absolute risk reduction is slight. 

Drug Interaction

Adverse Reaction

Frequency defined 

1-10% 

Erectile dysfunction 

Decreased libido 

Ejaculation disorder 

Breast disorders 

<1% 

Breast tenderness 

Rash 

Black Box Warning

None 

Contraindication / Caution

Contraindication/Caution: 

Contraindications: 

• Hypersensitivity: finasteride is contraindicated in individuals with known hypersensitivity or allergy to the medication or its components. 

• Pregnancy: finasteride is contraindicated in pregnant women or may become pregnant, as it may cause harm to a developing fetus. Pregnant women should avoid handling crushed or broken tablets. 

Precautions: 

• Liver disease: finasteride is metabolized in the liver and excreted primarily in the feces, so caution is advised in patients with liver disease or impaired liver function. 

• Prostate cancer: finasteride may reduce the levels of prostate-specific antigen (PSA), a prostate cancer marker, making it more difficult to detect prostate cancer. Therefore, men taking finasteride should have regular PSA tests and prostate exams. 

• Breast cancer: There have been rare reports of breast cancer in men taking finasteride, so patients should be aware of any breast lumps, changes, or discharge and notify their healthcare provider if any of these symptoms occur. 

• Pediatric use: finasteride is not approved for use in children, as its safety and efficacy have not been established in this population. 

• Drug interactions: finasteride may interact with other medications, particularly those metabolized by the liver. Patients should inform their healthcare provider of all medications, including over the counter and herbal products. 

Pregnancy / Lactation

Pregnancy consideration:  

Not recommended to be used in women 

Breastfeeding warnings:  

Not recommended to be used in women 

Pregnancy category: 

• Category A: Satisfactory and well-controlled studies show no risk to the fetus in the first or later trimester. 

• Category B: No evidence shown of risk to the fetus found in animal reproduction studies, and there are not enough studies on pregnant women. 

• Category C: Adverse effects on the fetus found with evidence in animal reproduction  studies and no adequate evidence for a human product; Pregnant women must take care of the potential risks. 

• Category D: There is adequate data with sufficient evidence of human fetal risk from various platforms. However, despite potential dangers may be used only in emergencies for potential benefits. 

• Category X: Drugs listed in this category outweigh risks over benefits. The drug is not for pregnant women. 

• Category N: No data is available for the drug under this category. 

Pharmacology

Pharmacology: 

finasteride is a medication primarily used to treat benign prostatic hyperplasia (BPH) and male pattern baldness. It works by inhibiting the enzyme 5-alpha-reductase, which converts testosterone to dihydrotestosterone (DHT), an essential hormone in developing BPH and male pattern baldness. 

Pharmacodynamics: 

The pharmacodynamics of finasteride is related to its action mechanism, which inhibits the enzyme 5-alpha-reductase. This enzyme is responsible for converting testosterone to dihydrotestosterone (DHT). This more potent androgen plays a role in developing benign prostatic hyperplasia (BPH) and androgenetic alopecia, also known as male pattern baldness. 

finasteride selectively inhibits the type II isoform of the 5-alpha-reductase enzyme, which is primarily located in the prostate gland, scalp, and other tissues. By reducing DHT levels in these tissues, finasteride helps to shrink the prostate gland and prevent further growth, as well as slow or reverse the progression of male pattern baldness. 

• After several months of treatment, the inhibition of 5-alpha-reductase by finasteride decreases serum DHT levels, typically by about 70-80%. This reduction in DHT levels can lead to a variety of pharmacodynamic effects, including: 

• Reduction in prostate volume and improvement in symptoms of BPH, such as urinary hesitancy, frequency, and urgency. 

• Prevention or slowing of hair loss and in some cases, regrowth of hair in men with male pattern baldness. 

• Alteration of the hormonal environment in the body, including changes in the levels of other androgens and estrogen. 

Pharmacokinetics: 

Absorption 

The bioavailability is 65% 

The time of onset of action is 6 months (BPH); and >3 months (hair loss) 

Peak plasma concentration is achieved in 2-6 hours 

Distribution 

The protein-bound is 90% 

The volume of distribution is 76 L 

Metabolism 

The drug is metabolized hepatically by CYP3A4 

The metabolites formed are t-butyl side chain monohydroxylate and active monocarboxylic acid metabolite. 

Elimination and Excretion 

The half-life is 6 hours 

The drug is excreted (57%) in feces and (39%) in urine 

Adminstartion

finasteride is available as an oral tablet that is typically taken once daily, with or without food. The dosage and duration of treatment may vary depending on the specific indication and the patient’s response to the medication. 

For the treatment of benign prostatic hyperplasia (BPH), the recommended dose of finasteride is 5 mg once daily. It may take several months of treatment to improve symptoms, and the medication may need to be continued long-term to maintain the benefits. 

For treating male pattern baldness, the recommended dose of finasteride is 1 mg once daily. It may take several months of treatment to see a visible improvement in hair growth, and the medication may need to be continued long-term to maintain the benefits. 

It’s essential to take finasteride precisely as prescribed by a healthcare provider. Missing a dose or stopping the medication abruptly may reduce the effectiveness of treatment. 

finasteride is metabolized in the liver and excreted primarily in the feces, so caution is advised in patients with liver disease or impaired liver function. The medication should also be used with caution in pregnant women, as it may cause harm to a developing fetus. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: finasteride 

Pronounced: Fi-nas-te-ride 

Why do we use finasteride? 

finasteride is used for several medical purposes, primarily related to its ability to inhibit the enzyme 5-alpha-reductase, which converts testosterone to dihydrotestosterone (DHT), a more potent androgen. By reducing DHT levels in the body, finasteride can produce several beneficial effects, including: 

• Treatment of benign prostatic hyperplasia (BPH): finasteride is FDA-approved for treating BPH, a condition in which the prostate gland becomes enlarged, causing urinary symptoms such as hesitancy, frequency, and urgency. By reducing DHT levels in the prostate gland, finasteride can help to shrink the gland and relieve these symptoms. 

• Treatment of male pattern baldness: finasteride is also used off-label to treat androgenetic alopecia, also known as male pattern baldness. By reducing DHT levels in the scalp, finasteride can slow or reverse the progression of hair loss and in some cases, promote hair regrowth. 

• Potential role in preventing prostate cancer: Some studies have suggested that finasteride may reduce the risk of developing prostate cancer by up to 25%. However, the absolute risk reduction is slight. 

• Treatment of hirsutism: finasteride can be used off-label to treat hirsutism, a condition where women develop excess hair growth on their face, chest, and other body areas. By reducing DHT levels, finasteride can help slow or stop unwanted hair growth.