Sweatman - BPH Flashcards
1
Q
What is BPH?
A
- Originates in transition zone of the prostate, surrounding the proximal urethra
- Untreated enlargement can block urine flow and cause bladder, urinary tract, or kidney problems
2
Q
What are the 2 short-acting selective alpha-1 blockers?
A
- Prazosin
- Alfuzosin
3
Q
What are the 2 long-acting selective alpha-1 blockers?
A
- Terazosin
- Doxazosin
4
Q
What are the alpha-1 partially selective blockers?
A
- Tamsulosin
- Silodosin
5
Q
What are the drug targets for BPH and lower urinary tract symptoms (image)?
A
6
Q
Why is the alpha-receptor hierarchy important?
A
- Sub-divided by structure and, when expressed in the target tissue, can represent potential therapeutic advantage for specifically targeted drugs
-
Alpha-1a overwhelmingly predominant in the normal human prostatic stroma
1. Alpha-1d present to a lesser extent
7
Q
Where in the urinary tract/prostate do alpha-1a and alpha-1d predominate (image)?
A
- Alpha-1a: predominates in lower GI tract
- Alpha-1d: predominates in detrussor muscle of the urinary bladder
- NOTE: alpha-1 blockers cause relaxation of the smooth muscle in the prostatic and penile urethra, permitting easier urination
8
Q
Describe the metab/elim, half-life, and bioavailability of the 6 alpha-1 blockers.
A
- All oral drugs with extensive CYP metabolism, so there is always an issue for drug-drug interactions
- Generally have a long duration of action, so less frequent dosing and better compliance
1. Except Prazosin: great variability from pt to pt, so dose titration necessary (Q12h dosing) - Tamsulosin: DEC bioavailability with food
- REMEMBER: Tamsulosin (9-18%), Silodosin (<=28%) partially selective
9
Q
What are the issues with the alpha-1 blockers?
A
- All have comparable efficacy, and common AE’s include: GI (xerostomia, nausea), CNS (dizziness, somnolence, asthenia, headache, insomnia)
- Selective (alpha-1a) agents:
1. Advantage: no need for dose titration (diminished effects on CV func)
2. Disadvantage: abnormal (retrograde, or no) ejaculation, block of Dopa and other regulatory CNS transmitters - Floppy iris syndrome
10
Q
What is the best alpha blocker currently available for treating BPH? Why?
A
- Alfuzosin 10mg
- Achieves clinically significant improvements in LUTS and has no significant effects on dizziness, asthenia, and ejaculatory dysfunction
- NOTE: this is just the conclusion in one paper
11
Q
What is floppy iris syndrome?
A
- Occasional AE during cataract sx in pts on alpha-1 blockers (mechanism unknown)
- Characteristics: flaccid iris that billows in response to intraoperative irrigation
1. Progressive intraoperative miosis (excessive constriction of pupil) despite dilation with std mydriatic drugs
2. Potential prolapse of the iris toward pharmacoemulsification incisions - No apparent benefit of stopping alpha-1 blocker therapy prior to cataract surgery
- May necessitate possible modifications to sx technique
12
Q
Describe the molecular pathway PDE5 is involved in. What do PDE5 INH do?
A
- NOS produces NO, which is released from endo cells and cavernous nerves in the smooth muscle of the urethra
- NO stimulates guanylyl cyclase, leading to INC levels of cGMP
- Subsequent phosphorylation of cellular mem proteins via PKG results in efflux of Ca, and smooth muscle relaxation, vasodilation of penile arteries and sinus, and erection
- PDE5 INH DEC breakdown of cGMP by INH of PDE5, resulting in prolonged high levels of cGMP necessary for erections
13
Q
Tadalafil use, metab, AEs
A
- Relief of BPH via smooth muscle relaxation -> comparable to corpus cavernosum effect in erectile dysfunction
- Hepatic metabolism (3A4); mainly fecal elim
- Well tolerated, and AE’s uncommon: headache, nausea, indigestion, nasopharyngitis, URTIs
1. RARE: non-arteritic ischemic optic neuropathy, retinal artery occlusion, hearing loss -
Contraindication: concurrent organic nitrates
1. Profound hypotension
2. Exacerbated by alcohol consumption - This is the ONLY PDE5 INH approved for this use (probably due to its long duration of action: <35-hr half-life)
14
Q
What is the role of 5-alpha reductase in smooth muscle tone? INH?
A
- Catalyzes conversion of T to DHT, which binds the AR w/higher affinity, and activates gene expression more efficiently
1. Type 1: predominantly in non-genital skin, liver, and bone
2. Type 2: mainly in urogenital tissue in men, and genital skin in men and women - 5-alpha reductase INH reduce DHT-driven proliferation of the prostate, providing relief for urinary evacuation
15
Q
Finasteride, Dutasteride
A
- Finasteride: type 2 (comparable drugs, outside of this difference in specificity)
- Dutasteride: types 1 and 2 -> competitive, long binding time, slow reversal (extensive 3A4 hepatic metabolism)
- Both Cat X, but not carried in semen
- Well tolerated; low incidence of AE’s: ejaculation and erectile dysfunction, DEC libido, gynecomastia
1. DEC PSA levels: problem if being used to monitor prostate cancer, INC rate of prostate cancer reported (1.8 vs. 1.1%)
18
Q
What is the MOA of Alprostadil?
A
- Synthetic mimic of naturally occurring PDE1
- Activates adenylate cyclase, which synthesizes cAMP from ATP
- cAMP acts as a 2nd messenger, activating PKA
- Efflux of IC Ca -> SM. M. RELAXATION and erection
19
Q
What are the options for delivery of Alprostadil?
A
- Intra-urethral suppository: placed to dissolve in residual urine and be absorbed across urethral wall
- Direct injection into the corpus cavernosum, avoiding the top and bottom of the penis (to avoid systematization via deep and dorsal arteries of penis)
- Minimal systematization
21
Q
Compare the pharmacology of the PDE5-INH.
A
- Oral drugs, w/peak plasma levels achieved quickly
- Hepatically processed, so drug-drug interactions possible
- Common and rare AE’s similar, with HEADACHE being the most common
- All are associated with: CV issues, and sudden loss of hearing and sight
-
THINGS TO NOTE:
1. Sildenafil/Vardenafil bioavailability DEC by high-fat meals
2. No CV effects listed for Sildenafil
3. Avanafil has fewest AE’s listed
4. Resp effects only listed for Tadalafil - Remember: Tadalafil used for BPH (probably due to long 1/2-life)
