Type II 5 Alpha-reductase Inhibitor
Action And Clinical Pharmacology: Finasteride is a competitive and specific inhibitor of Type II 5 alpha-reductase, an intracellular enzyme that converts the androgen testosterone into dihydrotestosterone (DHT). Two distinct isozymes of 5 alpha-reductase are found in mice, rats, monkeys, and humans: Type I and II. Each of these isozymes is differentially expressed in tissues and developmental stages. In humans, Type I 5 alpha-reductase is predominant in the sebaceous glands of most regions of skin, including scalp and liver. Type I 5 alpha-reductase is responsible for approximately one-third of circulating DHT. The Type II 5 alpha-reductase isozyme is primarily found in prostate, seminal vesicles, epididymides and hair follicles as well as liver, and is responsible for two-thirds of circulating DHT.
In humans, the mechanism of action of finasteride is based on its preferential inhibition of the Type II isozyme. Using native tissues (scalp and prostate), in vitro binding studies examining the potential of finasteride to inhibit either isozyme revealed a 100-fold selectivity for the human Type II 5 alpha-reductase over Type I isozyme (IC50=500 and 4.2 nM for Type I and II, respectively). For both isozymes, the inhibition by finasteride is accompanied by reduction of the inhibitor to dihydrofinasteride and adduct formation with NADP+. The turnover for the enzyme complex is slow (t1/2 approximately 30 days for the Type II enzyme complex and 14 days for the Type I complex).
Finasteride has no affinity for the androgen receptor and has no androgenic, antiandrogenic, estrogenic, antiestrogenic, or progestational effects. Inhibition of Type II 5 alpha-reductase blocks the peripheral conversion of testosterone to DHT, resulting in significant decreases in serum and tissue DHT concentrations. Finasteride produces a rapid reduction in serum DHT concentration, reaching 65% suppression within 24 hours of oral dosing with a 1 mg tablet.
In men with male pattern hair loss (androgenetic alopecia), the balding scalp contains miniaturized hair follicles and increased amounts of DHT compared with hairy scalp. Administration of finasteride decreases scalp and serum DHT concentrations in these men. By this mechanism, finasteride interrupts a key factor in the development of androgenetic alopecia in those patients genetically predisposed.
In a study in 15 healthy male subjects, the mean bioavailability of finasteride 1 mg tablets was 65% (range, 26 to 170%), based on the ratio of AUC relative to a 5 mg i.v. dose infused over 60 minutes. Following the i.v. infusion, mean plasma clearance was 165 mL/min (range, 70 to 279 mL/min) and mean steady-state volume of distribution was 76 L (range, 44 to 96 L). In a separate study, the bioavailability of finasteride was not affected by food.
Approximately 90% of circulating finasteride is bound to plasma proteins. Finasteride has been found to cross the blood-brain barrier.
Indications And Clinical Uses: For the treatment of male pattern hair loss (androgenetic alopecia) in men who have mild to moderate scalp hair loss of the vertex and anterior mid-scalp. Clinical studies were conducted in men between 18 to 41 years of age.
Not indicated for use in women or children.
Contra-Indications: Pregnancy: Use in women when they are or may potentially be pregnant (see Warnings and Precautions, Exposure to Finasteride – Risk to Male Fetus).
Hypersensitivity to any component of this product.
Not indicated for use in women or children.
Manufacturers’ Warnings In Clinical States: Pregnancy and Lactation: Finasteride is not indicated for use in women. Women should not handle crushed or broken finasteride tablets when they are or may potentially be pregnant (see Contraindications). Because of the ability of Type II 5 alpha-reductase inhibitors such as finasteride to inhibit conversion of testosterone to dihydrotestosterone, finasteride may cause abnormalities of the external genitalia of a male fetus when administered to a pregnant woman. It is not known whether finasteride is excreted in human milk.
Precautions: General: Caution should be used in the administration of finasteride in patients with liver function abnormalities, as finasteride is metabolized in the liver.
Other causes of alopecia should be ruled out prior to prescribing finasteride. Efficacy and duration of treatment should be assessed periodically by the treating physician.
Exposure to Finasteride – Risk to Male Fetus: Women should not handle crushed or broken tablets of finasteride when they are or may potentially be pregnant because of the possibility of absorption of finasteride and the subsequent potential risk to a male fetus (see Warnings, Pregnancy and Lactation). Finasteride tablets are coated and will prevent contact with the active ingredient during normal handling, provided that the tablets have not been broken or crushed.
Geriatrics: Clinical studies with finasteride have not been conducted in elderly men with male pattern hair loss.
Children: Finasteride is not indicated for use in children.
Drug Interactions: No drug interactions of clinical importance have been identified. Finasteride does not appear to affect significantly the cytochrome P450-linked drug metabolizing enzyme system. Compounds which have been tested in man have included antipyrine, digoxin, glyburide, propranolol, theophylline and warfarin, and no interactions were found. However, patients on medication with narrow therapeutic indices, such as phenytoin, should be carefully monitored when treatment with finasteride is initiated.
Other Concomitant Therapy: Although specific interaction studies were not performed, in clinical studies finasteride doses of 1 mg or more were used concomitantly with ACE inhibitors, acetaminophen, alpha blockers, benzodiazepines, beta blockers, calcium-channel blockers, cardiac nitrates, diuretics, H2 antagonists, HMG-CoA reductase inhibitors, prostaglandin synthetase inhibitors (NSAIDs), and quinolones, without evidence of clinically significant adverse interactions.
Drug/Laboratory Test Interactions : In clinical studies with finasteride in men 18 to 41 years of age, the mean value of serum prostate-specific antigen (PSA) decreased from 0.7 ng/mL at baseline to 0.5 ng/mL at month 12. When fina-steride is used in older men who have benign prostatic hyperplasia (BPH), PSA levels are decreased by approximately 50%. Until further information is gathered in men >41 years of age without BPH, consideration should be given to doubling the PSA level in men undergoing this test while taking finasteride.
Information to be Provided to the Patient: Patients should be advised that: finasteride is to be used by men only and should be taken daily as prescribed.
In general, daily use for 3 months or more is necessary before hair growth is increased and/or further hair loss is prevented.
The clinical benefits of finasteride can only be maintained with continuous use of finasteride.
A small number of men may experience less desire to have sex and/or difficulty in achieving an erection. In clinical studies, these side effects disappeared in men who stopped taking finasteride and in most men who continued treatment.
If the patient experiences sustained impairment in sexual function or any other unintended effect, the patient should be advised to consult with the prescribing physician regarding continuation of the medication.
As with all other medications, it is important that any other treating physician(s) be aware of the patient’s use of fina-steride.
Women who are or may potentially be pregnant must not use finasteride. They should not handle crushed or broken tablets of finasteride.
Adverse Reactions: Finasteride for male pattern hair loss has been evaluated for safety in clinical studies involving more than 3 200 men and is generally well tolerated. In 3 12-month, placebo-controlled, double-blind, multicenter studies of comparable design, the overall safety profiles of finasteride and placebo were similar. Discontinuation of therapy due to any clinical adverse experience occurred in 1.7% of 945 men treated with finasteride and 2.1% of 934 men treated with placebo.
In these studies, the following drug-related adverse experiences were reported in ³1% of men treated with finasteride or placebo, respectively: decreased libido (1.8%, 1.3%), erectile dysfunction (1.3%, 0.7%) and ejaculation disorder (1.2%, 0.7%; primarily decreased volume of ejaculate:[0.8%, 0.4%]). Integrated analysis of clinical adverse experiences showed that during treatment with finasteride, 36 (3.8%) of 945 men had reported one or more of these adverse experiences as compared to 20 (2.1%) of 934 men treated with placebo (p=0.04).
Resolution of these adverse reactions occurred in men who discontinued therapy with finasteride and in 58% who continued therapy. In a separate study, the effect of finasteride on ejaculate volume was measured and was not different from that seen with placebo.
A sexual function questionnaire was self-administered by patients participating in the 2 vertex baldness trials to detect more subtle changes in sexual function. At month 12, statistically significant differences were found in 3 of 4 domains (sexual interest, erections, and perception of sexual problems) when compared to placebo. However, no significant difference was seen in the question on overall satisfaction with sex life.
The adverse reactions profile for 547 patients who continued on finasteride for up to 24 months was similar to that observed in the 12-month controlled studies.
Finasteride is also in use for the treatment of older men with BPH at 5 times the dosage recommended for male pattern hair loss. Additional adverse reactions that have been reported at the 5 mg dosage in men with BPH are: breast tenderness and enlargement, and hypersensitivity reactions, including lip swelling and rash. In the clinical studies with finasteride, the incidence of these events was not different from placebo.
Laboratory Tests: No difference in standard laboratory parameters was observed between patients treated with placebo or finasteride.
Symptoms And Treatment Of Overdose: Symptoms and Treatment: Patients have received single doses of finasteride up to 400 mg and multiple doses of finasteride up to 80 mg/day for 3 months without adverse reactions.
No specific treatment for overdosage with finasteride is recommended.
Dosage And Administration: The recommended dosage is one 1 mg tablet daily. Finasteride may be taken with or without food.
In general, daily use for 3 months or more is necessary before hair growth is increased and/or further hair loss is prevented. Continued use is recommended to obtain maximum benefit. Withdrawal of treatment leads to reversibility of effect within 12 months.
Dosage in Renal Insufficiency: Adjustments in dosage are not necessary in patients with varying degrees of renal insufficiency (creatinine clearances as low as 0.15 mL/s [9 mL/min]) as pharmacokinetic studies did not indicate any change in the disposition of finasteride.
Availability And Storage: Each tan-colored, 8-sided, film-coated convex tablet, with the code MSD 71 on one side and PROPECIA 1 on the other, contains: finasteride 1 mg. Nonmedicinal ingredients: docusate sodium, hydroxypropylcellulose, lactose monohydrate, magnesium stearate, methylhydroxypropylcellulose, microcrystalline cellulose, pregelatinized starch, red ferric oxide, sodium starch glycolate, talc, titanium dioxide and yellow ferric oxide. Blister packages of 28. Store at room temperature 15 to 30°C and protect from moisture.
PROPECIA® MSD Finasteride Type II 5 Alpha-reductase Inhibitor
Posted by RxMed