Finasteride

Finasteride is widely used to treat both benign prostatic hyperplasia (BPH) and hair loss. It is particularly effective for early stages of male pattern baldness, known as androgenetic alopecia. The drug was first approved in 1992 at a 5 mg dose for BPH treatment and later received approval in 1997 at a lower 1 mg dose specifically for male pattern hair loss. Beyond its approved uses, finasteride is also prescribed off-label to address hyperandrogenism-related symptoms such as hirsutism. Additionally, it is used in transgender women, typically in combination with estrogen, for its anti-androgenic properties.

BRAND NAMES:

Proscar - Proscar contains 5mg of finasteride as a main active ingredient and available as oral tablets.

Propecia - Propecia is available as oral tablets containing finasteride as the main active ingredient with 1mg drug composition.

MECHANISM OF ACTION:

Finasteride acts as a competitive inhibitor of the type II and III isoenzymes of 5-alpha reductase, effectively reducing the conversion of testosterone into dihydrotestosterone (DHT). It has a low binding affinity for the type I isoenzyme. Type I 5-alpha reductase is predominantly located in sebaceous and sweat glands, dermal papilla cells, and in both epidermal and follicular keratinocytes. In contrast, type II is mainly found in the outer root sheath of hair follicles, as well as in the epididymis, vas deferens, seminal vesicles, and prostate.

PHARMACOKINETICS:

Absorption: The bioavailability of finasteride is approximately 65%.

Distribution: Finasteride exhibits around 90% protein binding, has a steady-state volume of distribution of 76 liters, and is capable of crossing the blood-brain barrier.

Metabolism: Finasteride is extensively metabolized in the liver by the cytochrome P450 enzyme system, primarily by CYP3A4, producing two active metabolites that possess less than 20% of finasteride’s original activity.

Excretion: Finasteride has a serum elimination half-life of approximately 5 to 6 hours, with a range of 3 to 6 hours. It is excreted in the form of metabolites, with 57% eliminated via the feces and 39% through the urine.

DOSAGE AND ADMINISTRATION:

Finasteride is available in tablet form in dosages of 1 mg and 5 mg. The recommended dosage varies based on the patient's age and the severity of the condition:

For benign prostatic hyperplasia, the recommended dose is 5 mg once daily.
For androgenic alopecia, 1 mg once daily is advised.
For hirsutism, the recommended dosage is either 5 mg once daily or 2.5 mg twice daily.
The Endocrine Society recommends a dose of either 2.5 mg or 5 mg once daily for premenopausal women.

DRUG INTERACTIONS:

Certain medications should be avoided when taking finasteride, as their interactions can lead to severe adverse effects. Below is a list of some drugs to avoid while using finasteride.

BPH agents - Dutasteride.

CONTRAINDICATIONS:

Finasteride is contraindicated in those with hypersensitivity to any of its components or formulation.

ADVERSE EFFECTS: