6.4.9-10 - Alpha Blockers

Front 1

Nonselective Alpha Blockers
- Drugs in class (name at least 1)
- Indication
- Mode of action

Back 1

Phentolamine & Phenoxybenzamine

Phaeochromocytoma

Block alpha 1: vasodilation of arteries and veins

Block alpha 2: increased NA release and enhances reflex tachycardia

Results in a orthostatic drop in BP which is the goal.
Often used with BB to reduce tachycardia

Front 2

Compare phentolamine with phenoxybenzamine

Back 2

Phenoxybenzamine is irreversible, and lasts about 3-4 days. It is orally available. It can be used long term if inoperable, or before surgery

Phentolamine is only IV, competitive not irreversible, and can be used during surgery to control surges in BP. ALSO USED WITH PAPAVERINE and/or ALPROSTADIL for erectile dysfunction (but no commercial product available)

Front 3

Selective Alpha Blockers
- Drugs in class
- MOA
- Indication

Back 3

Prazosin, Tamsulosin, Terazosin
Inhibit post-synaptic alpha-1 adrenoreceptors, causing ARTERIAL AND VENOUS vasodilation
Less likely to cause reflex tachycardia because of lack of alpha-2 block - N.B. blockage increases symptathetic tone & HR

Hypertension
Symptomatic relief of BPH

Front 4

Selective Alpha Blockers
- CI (1)
- Conditions where orthostatic hypotension may be worsened?
- When might first dose hypotension be worsened?
- Preg / BF

Back 4

- HF due to mechanical obstruction such as aortic stenosis (CI)
Worse O.H:
- dehydration
- elderly

First dose hypotension
- BB, CCB, DIURETICS > ACEIs
- RI: may have profound RDH

- Preg: avoid, no data
- BF: Caution; ltd data

Front 5

Selective alpha blockers
- Drug interactions

Back 5

1. Antihypertensives: lower BP and first dose hypotension
2. PDE-5: symptomatic hypotension; use only if stable on alpha blocker, space 4 hours apart (or 6hr for vardenafil), and use low doses of PDE5 inhibitor

Front 6

Selective alpha blockers
- Adverse effects

Back 6

Common
- orthostatic hypotension, nasal congestion, urinary urgency, fatigue/weakness

Front 7

Selective alpha blockers
- Management of first dose hypotension

Back 7

1. bedtime
2. low dose
3. withhold diuretics for a few days first
4. correct hypovolaemia
5. increase dose slowly:
(a) 3-7/7 - prazosin
(b) 7/7 - terazosin
(c) at 2 week intervals if very concerned

**Extra extra caution if there is
1. elderly
2. renal impairment
3. fluid depletion
4. other antihypertensives
If possible, withhold diuretics for a few days before starting alpha blockers

It is suggested that patients re-titrate if have missed several days dosing (genitourinary)

Front 8

Prazosin
- brands
- dose forms
- dosing

Back 8

Minipress, Pressin,
1mg.100, 2mg.100, 5mg.100

Hypertension:
Start low on e.g. 0.5mg bd
Increase over 3-7/7 or longer prn
Maintain on 1.5-10mg bd
BPH:
0.5mg bd --> increase after 3-7/7 according to clinical response up to 2mg bd

Front 9

Terazosin
- brands
- dose forms
- dosing

Back 9

Hytrin
1mg.7, 2mg.7 = Hytrin Starter Pack
2mg.28, 5mg.28, 10mg.28

HTN: 1mg d, increase after 7/7 to 2mg d; Max 20mg d
BPH: as for HTN, but max 10mg mane

Front 10

Tamsulosin
- brands
- dose forms
- dosing
- why only for BPH

Back 10

Flomaxtra
400mcg.28 tabs
BPH only: 400mcg d
Because selective for alpha receptor subtypes in the bladder and prostate

Front 11

PBS considerations for alpha blockers

Back 11

- Only prazosin is on the PBS
- Terazosin is RPBS-A
- Tamsulosin is RPBS-A

Front 12

Which alpha blockers should be chosen?

Back 12

All good
Prazosin is bd, others are d

Front 13

Special counselling points

Back 13

1. L16 & take the first dose at bedtime & be careful if you get up at night
**HW, normally take morning, because it can cause increased urination
2. Tamsulosin should be taken with food

Front 14

How long does it take to work?

Back 14

BPH: Trial for 4-6 weeks at maximal dose and then discontinue if no effect.

Front 15

When is it appropriate to use alpha blockers for hypertension?

Back 15

THIRD LINE (n.b. alpha-2 blockers are second lind)
Because one of the old derivatives increased rate of HF