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5a-Reductase Inhibitor

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5a-Reductase Inhibitor, Finasteride, Proscar, Propecia, Dutasteride, Duagen, Avodart

  • Indications
  1. Benign Prostatic Hyperplasia
    1. BPH-Associated Gross Hematuria
    2. Large Prostate size >40 ml (see PSA to estimate Prostate size)
  2. Androgenic Alopecia in males (Finasteride)
    1. Adjunct to hair Transplantation
  • Mechanism
  1. Inhibits Testosterone to Dihydrotestosterone conversion
    1. Competitive Inhibition of enzyme 5a-reductase
    2. Finasteride inhibits Type II 5a reductase
    3. Dutasteride inhibits both Type I and II 5a reductase
  2. Reduces volume of Prostate
  3. Improves urine Blood Flow
  • Preparations
  1. Finasteride (Propecia, Proscar)
  2. Dutasteride (Avodart)
  • Dosing
  1. Alopecia
    1. Finasteride 1 mg orally daily (or one quarter tablet daily of the 5 mg tablet)
  2. Benign Prostatic Hyperplasia (typically used in combination with Tamsulosin or Terazosin)
    1. Finasteride 5 mg orally daily
    2. Dutasteride 0.5 mg orally daily
  • Advantages
  • Finasteride
  1. Alopecia
    1. Increases Hair Growth and reduces Hair Loss
    2. Effective on vertex and anterior mid-scalp
    3. Side effects uncommon
  2. Benign Prostatic Hyperplasia
    1. May be more effective in men with large Prostate
  • Disadvantages
  • Finasteride
  1. Alopecia
    1. Improvements take 6-12 months
    2. Any benefits are lost when medication is stopped
    3. Finasteride 1 mg tablet is much more expensive then 5 mg tablet
      1. Consider quartering the 5 mg tablet (generic, cheap) which drops the cost considerably
  2. Benign Prostatic Hyperplasia
    1. Increased urine flow not evident for 6-12 months
    2. Mediocre effects on obstructive symptoms and urine flow (better in Prostate size >40 ml)
      1. Less effective than alpha blockers (e.g. Hytrin)
      2. Less effective than surgery
      3. Only as effective as Saw Palmetto
    3. Highly effective in reducing BPH-related Gross Hematuria (80%)
      1. Kearney (2002) J Urol 167:2489-91 [PubMed]
  • Adverse Effects
  1. Suicidal Ideation
    1. Irwig (2012) J Clin Psychiatry 73(9):1220-3 +PMID: 22939118 [PubMed]
  2. Decreased Libido or Erectile Dysfunction (2%)
    1. Longterm Erectile Dysfunction may persists even after stopping Finasteride in up to 0.1% of patients
    2. Irwig (2012) J Sex Med 9(11): 2927-32 [PubMed]
  3. Lowers Prostate Specific Antigen (PSA) Values by 30-50%
    1. Obtain PSA baseline prior to starting Finasteride
    2. Double the actual PSA to determine work-up
    3. Obtain baseline Digital Rectal Exam
  4. Longterm use associated with high grade Prostate Cancer
    1. Thompson (2003) N Engl J Med 349:215-24 [PubMed]
  • References
  1. (1992) Med Lett Drugs Ther 34:83 [PubMed]
  2. Nickel (1996) CMAJ 155:1251-9 [PubMed]
  3. Guess (1996) J Urol 155:3-9 [PubMed]