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IC16 PK of male endocrine drugs Flashcards

1
Q

tamsulosin drug type

A

Reversible α-1 receptor antagonist

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2
Q

tamsulosin MOA

A
  • Reduces vasoconstriction induced by endogenous catecholamines
  • Blocking of α-adrenoreceptors on smooth muscle of prostate, prostatic urethra & bladder neck → Relaxation of SM → increases max urinary flow rate ⇒ relieving obstruction
  • Improves symptoms related to bladder instability & tension of SM of lower urinary tract
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3
Q

tamsulosin MOA
selectivity

A

Greater for α1A; better blockade for α1A (prostate & BV) than α1B (BV & heart) receptors
* Hence lesser effect of tamsulosin on BP & better for BPH

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4
Q

tamsulosin effects

benefits; time for improvement

A
  • Effects on urinary stage & voiding symptoms maintained during long term therapy
    Can hold & pass urine better ⇒ reduces pain
  • Delays need for surgery/ catheterisation
  • Improvement in urinary flow rate after a few hours/ days after administration
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5
Q

tamsulosin PK
absorption

A

Well absorbed orally (take 0.4 mg OD)

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6
Q

tamsulosin PK
distribution

A

Highly bound to plasma protein (> 90%)
Not readily distributed to tissues ⇒ Small Vd (0.2L/ kg)

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7
Q

tamsulosin PK
metabolism

enzymes involved, t1/2

A
  • By CYPs (ie: CYP3A4, CYP2D6)
    Take note: do not take drug with grapefruit juice → affects liver enzymes
  • t1/2 ~ 20-25 hour ⇒ hence OD dosing
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8
Q

tamsulosin PK
excretion

A

~10% excreted unchanged in urine
* Requires dose adjustment for renal impairment

Metabolites more soluble in urine (~90%)

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9
Q

tamsulosin AE

A

Abnormal ejaculation
Back pain

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10
Q

tamsulosin c/i

A

Concurrent use of another α1 adrenoceptor antagonist (CVS patients)

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11
Q

finasteride drug type

A

5α-reductase inhibitor

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12
Q

finasteride MOA

A
  • Competitive inhibition of 5α-reductase
    No conversion of testosterone to DHT, esp in male genitalia
  • Hence decreases prostate size (with higher dose, 5mg)
    Also increases hair growth (with lower dose, 1mg)
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13
Q

finasteride clinical effects

A

improved urine flow, reduces frequency of acute retention of urine & the need to surgical procedures

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14
Q

finasteride clinical treatment

time for effects, serum prostate-specific Ag

A

May take up to 6 months to see clinical effects after initiating treatment

Serum prostate-specific Ag levels decreases with finasteride

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15
Q

finasteride PK
absorption

F

A

Well absorbed orally (5 mg OD)
F ~ 0.65

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16
Q

finasteride PK
distribution

Vd

A

High plasma protein bound (~90%) ⇒ Small Vd

17
Q

finasteride PK
metabolism

t1/2

A

By liver (CYP3A4)
t1/2 ~ 6 hr

18
Q

finasteride PK
excretion

A

50% unchanged in faeces
metabolites in urine & faces

19
Q

finasteride dose adjustments

A

Not required for liver failure, renal insufficiency & elderly patients

20
Q

finasteride AE

A

Loss of libido & sexual potency
Gynaecomastia (rare)

21
Q

finasteride c/i

A

Women & children; pregnancy

22
Q

sildenafil: drug type

A

PDE5 inhibitor

23
Q

sildenafil: MOA

A
  • Inhibits phosphodiesterase type-5 (PDE5) in penis
  • No conversion of cGMP to 5’GMP

Outcomes
(4) Increases cGMP levels in response to NO-release by sexual stimulation
(5) causes SM relaxation
(6) increased BF to corpora cavernosa
(7) erection

23
Q

sildenafil: MOA
specificity of drug

expression of PDE5

A

PDE5 highly expressed in Corpora cavernosa of penis & vasculature; poorly in myocardium ⇒ tissue specificity to compound

23
Q

sildenafil: initiation of dose

A

Ideally lowest recommended dose possible, especially for >65 years old

23
Q

sildenafil: PK
distribution

A

Widely distributed ⇒ large Vd

23
Q

sildenafil: PK
absorption

onset, F, duration of action

A
  • well absorbed orally (5mg OD)
  • Onset: 30-60 mins
  • F ~0.4
  • Duration of action (max): ~12 hours
23
Q

sildenafil: PK
metabolism

t1/2

A

By liver: CYP3A4 (major), CYP2C9 (minor)
t1/2 ~4 hours

23
Q

sildenafil: PK
excretion

A

Metabolites largely excreted in faeces (80%) & lesser in urine (13%)
Remaining unchanged in urine

24
Q

sildenafil: dose adjustment requirments

A

Not required for liver failure, renal insufficiency & elderly patients

24
Q

sildenafil: AE

A
  • Headache, dizziness, flushing, dyspepsia
  • Blur vision → blue-green tinting of vision (due to blockage of retinal PDE6)
  • Priapism (similar feeling to BPH)
25
Q

sildenafil: c/i

A

Cardiac patients on GTN (generates NO; accumulates cGMP)
* Potentiates vasodilation effect on GTN due to increased cGMP; due to concomitant blockade of cGMP degradation by sildenafil
* Have potential marked vasodilation & hypotension

endo y3s1 (16 decks)

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