Name of the A-Adrenoceptor Antagonists (Blockers) Drugs
- Doxazosin
- Prazosin
- Tamsulosin
- Alfuzosin
Mechanism of Action:
These drugs block the effect of sympathetic nerves on blood vessels by binding to alpha-adrenoceptors on the vascular smooth muscle. Most of these drugs act as competitive antagonists to the binding of norepinephrine that is released by sympathetic nerves synapsing on smooth muscle.
Selective α- 1 blockers inhibits α-1 adrenoceptors in arterioles, thereby reducing the tone of Vascular smooth muscle and reducing total peripheral resistance.
| Doxazosin |
| Dosage: 1mg, 2mg, 4mg,8mg tablets Extended-release tablets : 4mg, 8mg |
| Administration and handling: PO • Give without regard to food. • Do not break, crush, dissolve, or divide extended-release tablet. • Immediate release tablets given morning or evening; extended-release tablets given with morning meal. |
| Hypertension: Usual dosage 1-2 mg/day. may titrate by doubling daily dose up to 16 mg/day based on BP. Extended release is not recommended for hypertension. |
| BPH: 1mg PO/Day; may titrate by doubling daily dose at 1–2-week intervals to maximum 8 mg/day Extended release: 4 mg PO/Day; may titrate based on response and tolerability every 3-4 weeks to 8 mg PO/Day. |
| if therapy is discontinued for several days, initiate dose at 1 mg/Day and titrate using initial dosing regimen |
| Dosing Modifications :Hepatic impairment, Renal impairment |
| Dosing Considerations: Give first dose and increase at bedtime to avoid syncope |
| Prazosin |
| Dosage: capsule1mg,2mg,5mg |
| Hypertension : Initial: 1 mg PO q8-12hr Maintenance: 6-15 mg/day divided 2 or 3 times daily; alternatively, 1-5 mg PO BID; may increase dose to 20 mg/day in divided doses; some patients may benefit from up to 40 mg/day in divided doses. |
| PTSD-Related Nightmares & Sleep Disruption (Off-label) Initial: 1 mg PO/HS Maintenance: 1 mg PO/HS initially; may increase dose to 2 mg/HS; adjust dose based on response and tolerability in 1-2 mg increments q7days; not to exceed 15 mg/day |
| Benign Prostate Hypertrophy (Off-label) Initial: 0.5 mg PO/12hr :Maintenance: 2 mg PO q12hr |
| Raynaud Phenomenon (Off-label) 0.5-1 mg PO/Day (HS) or 0.5 mg PO BID; adjust dose based on response and tolerability up to 12 mg/day divided BID/TID |
| Administration Give first dose and subsequent increases at bedtime to avoid syncope; Okay with food |
| Tamsulosin |
| Dosage: capsule 0.4mg |
| Administration and handling: PO • Give at same time each day, 30 min after the same meal. • Do not break, crush, or open capsule. |
| Benign Prostatic Hypertrophy : 0.4 mg PO/Day; take 30 minutes after same meal each day; If inadequate response after 2-4 weeks, may increase to 0.8 mg/Day. If therapy interrupted or discontinued for several days, resume at 0.4 mg/day and increase if needed. |
| Bladder Outlet Obstruction (Off-label) : Relief of symptoms ; 0.4 mg PO/Day |
| Ureteral Stones (Off-label) : Facilitation of kidney stone expulsion 0.4 mg PO/Day; discontinued after successful expulsion (average, 1-2 weeks) |
| Dosing Modifications : Renal impairment, Hepatic impairment. |
| Alfuzosin |
| Dosage Forms & Strengths : tablet, extended release 10mg Pediatric : Safety & efficacy not established |
| Benign Prostatic Hyperplasia (BPH) : 10 mg PO/ Day taken after same meal |
Indications:
- Hypertension
- Benign Prostatic Hyperplasia
Cautions & Contraindications:
- Caution in patients with a susceptibility to heart failure & angina.
- Pregnancy & breast feeding
Side Effects
- Postural Hypotension
- Dizziness
- Weakness and fatigue
- Reflex Tachycardia
- Palpitations
- Anxiety
- CNS Depression
- Blurred vision
- Urinary frequency
- Incontinence
Metabolism And Half Life:
Variable- e.g., Doxazosin (t ½ 22hr) extensively metabolized by the liver; Alfuzosin (t ½ 3- 5hr) partially metabolized.
Monitoring:
- May cause severe first-dose hypotension, therefore, need to start at low dose and warn the patient of side-effects.
- Monitor for side effects and evaluate for the therapeutic response: blood pressure control.
Drug Interactions:
Enhanced Hypotensive effect with antihypertensives and alcohol.
Important points:
- Centrally acting α2- adrenoceptor agonists (e.g., clonidine, methyldopa) also have an antihypertensive effect (mediated via suppression of the vasomotor centre in the brain).
- These agents are rarely used due to infrequent but potentially severe adverse effects (methyldopa may cause hepatitis). Methyldopa continues to be used for hypertension in pregnancy.
Nursing considerations & client education:
- Baseline assessment of vital signs and weight
- Orthostatic blood pressure assessment
Client Education:
- Explain how the medication helps to control blood pressure.
- Take consistently and don’t abruptly stop the medication as it may cause rebound hypertension.
- Take 1st dose at bedtime. It helps to avoid severe orthostatic hypotension & syncope.
- Orthostatic hypotension can occur throughout treatment. Hence, sit down if feeling dizziness.
- Make position changes slowly.
- Contact healthcare provider if it persists.
- Avoid alcohol.
- Check with healthcare provider before taking any over the counter medications.
- Teach the client how to take blood pressure at home
1) desired blood pressure values
2) those that require medical attention.
Lifestyle Modifications:
1.Maintain healthy weight
2.Smoking cessation
3.Reduce sodium intake
4.Increase physical activity
REFERENCES
- Robert Kizior, Keith Hodgson, Saunders Nursing Drug handbook,1st edition 2024, Elsevier Publications. ISBN-9780443116070
- McGraw Hill- Drug Handbook, Seventh Edition, 2013, McGraw Hill Education Publications,9780071799430.
- April Hazard, Cynthia Sanoski, Davi’s Drug Guide for Nurses -Sixteenth Edition 2019, FA Davis Company Publications,9780803669451.
- Jones and Bartlet, Pharmacology for Nurses, Second Edition, 2020, Jones and Bartlet Learning Publications, ISBN 9781284141986.
- Nursebro.com, Search – Nursebro
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