The P-I-E-N-O Parkinsn's List Drug Database
finasteride / ProscarTM
SYMPTOMATIC BENIGN PROSTATIC HYPERPLASIA:
Description: Finasteride is a relatively new drug that is used in the treatment of symptomatic benign prostatic hyperplasia (BPH), a condition found in the majority of men over the age of 50. Finasteride has been shown to increase and maintain maximum urine flow rate in men with BPH, although not all men show improvement despite the reduction in prostate size. A concern with finasteride therapy is that its reduction of serum prostatespecific antigen (PSA) levels can mask the detection of prostate carcinoma. Finasteride was approved by the FDA in June 1992.
Mechanism of Action: Finasteride is a synthetic 4-aza analog of testosterone that acts as an inhibitor of 5-›-reductase, an intracellular enzyme responsible for converting testosterone to the potent androgen 5-›-dihydrotestosterone (DHT). DHT is the androgen primarily responsible for the development of prostate tissue. As the enzymatic conversion from testosterone to DHT is inhibited, a desirable reduction in prostate hypertrophy is achieved, and urine flow should be improved.
Pharmacokinetics: A single 5 mg dose rapidly reduces serum DHT concentrations by as much as 70%, with the maximum reduction occurring at about 8 hours. The effect lasts for at least 24 hours, so qd dosing is appropriate. However, actual clinical effects are not realized for 3-6 months after beginning therapy.
The bioavailability following a single dose of finasteride is only 63%, and the presence of food further decreases oral absorption. Approximately 90% is bound to plasma proteins, yet the drug does cross the blood-brain barrier. This is not problematic, since finasteride generally does not affect other hormones. Daily dosing causes accumulation to occur, with plasma concentrations increasing by 50% over levels observed from a single dose. After oral dosing, about half of the unchanged drug is excreted in the feces, and one-third is metabolized in the liver to the 17carboxylic acid, which is then excreted in the urine. The plasma half-life is 5-17 hours.
CONTRAINDICATIONS/PRECAUTIONS: Finasteride is pregnancy risk category X and is therefore absolutely contraindicated during pregnancy. It is not for use in women.
Finasteride is also contraindicated for use in children.
DRUG INTERACTIONS: In one small study, concurrent use of theophylline and finasteride resulted in an increase in theophylline clearance, with a decrease in theophylline half-life. These changes were not clinically significant.
Finasteride is a synthetic analog of testosterone and inhibits an intracellular enzyme responsible for converting testosterone to the potent androgen 5-›-dihydrotestosterone (DHT). Although finasteride appears to interfere with the activation of testosterone to a more active form, presumably blocking the effects of testosterone, it would be illogical to administer finasteride concurrently with testosterone or other androgens.
No drug-drug interactions were demonstrated when finasteride was used with antipyrine, digoxin, propranolol, or warfarin. Although no specific drug interaction studies were conducted, finasteride was administered with ›-blockers, ACE inhibitors, analgesics, anticonvulsants, benzodiazepines, œ-blockers, calcium channel blockers, diuretics, HA-blockers, HMG-CoAreductase inhibitors, nitrates, NSAIDs, and quinolone antibiotics without significant interactions.
ADVERSE REACTIONS: During a 12-month trial of finasteride, the only clinically significant adverse reactions were impotence, libido decrease, and decreased ejaculate volume, all of which were reported by about 3% of patients.
PATIENT INFORMATION:
What do finasteride tablets do?
Finasteride (ProscarTM ) can reduce the size of the prostate gland in men with a non-cancerous condition called benign prostatic hyperplasia (BPH). The prostate is a part of the male reproductive system that produces a milky fluid for sperm. Over the age of 50 most men develop an enlarged prostate. As the prostate gets bigger it can restrict the flow of urine. Finasteride can help to reduce symptoms caused by BPH such as a weak or interrupted urine flow; a feeling that the bladder is not completely empty; a need to pass urine more often, especially at night; an urgent feeling that you must pass urine right away; a delay or hesitation when you start to urinate. Generic finasteride tablets are not yet available.
What should my doctor, dentist, or pharmacist know before I take finasteride?
They need to know if you have any of these conditions: (finasteride is not for use in women)
How should I take this medicine?
Take finasteride tablets by mouth. Follow the directions on the prescription label. Swallow the tablets with a drink of water. You can take this medicine with or without food. Take your doses at regular intervals. Do not take your medicine more often than directed.
Special precautions for use in children:
This medicine is not for use in children.
What if I miss a dose?
If you miss a dose, take it as soon as you can. If you do not remember until the next day, take only that day's dose. Do not take double or extra doses.
What other medicines can interact with finasteride?
What side effects may I notice from taking finasteride? Side effects from finasteride are generally mild and do not last; they include:
Let your doctor know about these side effects if they do not go away or if they annoy you.
What do I need to watch for while I take finasteride?
Contact your doctor if there is no improvement in your symptoms. You may need to take finasteride for 6 to 12 months to get the best results.
Women who are pregnant or may get pregnant must not handle broken or crushed finasteride tablets; the active ingredient could harm the unborn baby. If a pregnant woman comes into contact with finasteride she should check with her doctor.
If your sexual partner is pregnant or wants to get pregnant, you should use a condom. Finasteride will be present in your semen and could harm the unborn child.
Finasteride can interfere with PSA laboratory tests for prostate cancer. If you are to have a lab test for prostate cancer, tell your doctor that you are taking finasteride.
Where can I keep my medicine?
Keep out of the reach of children in a container that small children cannot open. Store at room temperature between 15 and 30C (59 and 86F). Protect from light. Keep container tightly closed. Throw away any unused medicine after the expiration date.
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