Sympatholytics Overview and Classification
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Questions and Answers

What is the primary action of prazosin as a selective α1 blocker?

  • Stimulate aldosterone release
  • Increase heart rate
  • Decrease urine retention
  • Cause vasodilation (correct)

Which of the following is NOT a use of prazosin?

  • Inhibition of erectile dysfunction (correct)
  • Heart failure
  • Benign hyperplasia of prostate
  • Hypertension

What adverse effect can occur within 2 hours of the initial dose of prazosin?

  • Increased urine output
  • First dose hypotension (correct)
  • Persistent tachycardia
  • Prostate enlargement

What is the main reason for using small doses of prazosin when starting treatment?

<p>To avoid syncope due to hypotension (A)</p> Signup and view all the answers

Which mechanism enables prazosin to avoid causing tachycardia?

<p>Blocking presynaptic α2 receptors (D)</p> Signup and view all the answers

Which class of drugs includes alpha blockers that inhibit adrenergic responses?

<p>Alpha adrenoceptor blockers (C)</p> Signup and view all the answers

Which of the following drugs is an α1 adrenergic blocker that is specifically mentioned for the treatment of benign prostatic hyperplasia?

<p>Alfuzosin (A)</p> Signup and view all the answers

What is a key characteristic differentiating tadalafil from sildenafil?

<p>Longer duration of action (D)</p> Signup and view all the answers

What is a characteristic of non-selective alpha blockers?

<p>They are irreversible and non-competitive. (A), They affect both alpha 1 and alpha 2 receptors. (B)</p> Signup and view all the answers

Which drug mentioned is a selective α2 blocker that may improve erection in males?

<p>Yohimbine (B)</p> Signup and view all the answers

Which drug is considered a centrally acting alpha-2 agonist?

<p>Clonidine (C)</p> Signup and view all the answers

What effect does prazosin have on peripheral resistance and venous return?

<p>Decreases both (D)</p> Signup and view all the answers

What is a primary use of alpha adrenoceptor blockers in medical practice?

<p>Control of hypertension in pheochromocytoma (D)</p> Signup and view all the answers

What adverse effect is commonly associated with the use of alpha blockers?

<p>Tachycardia (A)</p> Signup and view all the answers

What is the mechanism of action for sildenafil in treating erectile dysfunction?

<p>Inhibition of 5-phosphodiesterase enzyme (B)</p> Signup and view all the answers

Alpha blockers like Phenoxybenzamine have what characteristic regarding their binding?

<p>They bind covalently and irreversibly. (D)</p> Signup and view all the answers

Which of the following is an adrenergic neurone depressant?

<p>Á-methyl dopa (C)</p> Signup and view all the answers

What is a consequence of the use of adrenergic neurone blockers like Guanethidine?

<p>Depletion of noradrenaline stores. (C)</p> Signup and view all the answers

What is the mechanism through which non-selective alpha blockers cause vasodilation?

<p>By blocking alpha 1 receptors. (C)</p> Signup and view all the answers

The Regitine test is used for the diagnosis of what condition?

<p>Pheochromocytoma (D)</p> Signup and view all the answers

Which ergot alkaloid is primarily classified as a full agonist at the D2 receptor?

<p>Ergotamine (C)</p> Signup and view all the answers

What is the primary reason for using Bromocryptine in clinical practice?

<p>To treat prolactin secretory adenomas and acromegaly (C)</p> Signup and view all the answers

Which receptor does Ergotamine act as a partial agonist?

<p>5 HT2 receptor (C)</p> Signup and view all the answers

What effect does Ergometrine primarily have on the uterus?

<p>Induces contractions (A)</p> Signup and view all the answers

Which ergot alkaloid is specifically indicated for the treatment of migraines?

<p>Ergotamine (C)</p> Signup and view all the answers

Which action is characteristic of Dihydroergotamine?

<p>Partial agonist at the 5 HT2 receptor (D)</p> Signup and view all the answers

What is a major therapeutic use of Ergotoxine?

<p>Treatment of cerebral insufficiency (D)</p> Signup and view all the answers

Which alkaloid is known for suppressing lactation by decreasing prolactin levels?

<p>Bromocryptine (A)</p> Signup and view all the answers

Which receptor does Methyl ergometrine have a weak action on?

<p>α1 receptor (B)</p> Signup and view all the answers

What primarily distinguishes semi-synthetic ergot alkaloids from natural ones?

<p>Method of synthesis (B)</p> Signup and view all the answers

Flashcards

Alpha Adrenergic Receptor Blockers

Drugs that block the effects of norepinephrine on alpha receptors, without affecting beta receptors.

Non-selective Alpha Blockers

Alpha blockers that affect both alpha 1 and alpha 2 receptors.

Phenoxybenzamine

A powerful non-selective alpha blocker with irreversible action.

Phentolamine and Tolazoline

Non-selective alpha blockers with reversible action.

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Pheochromocytoma

A tumor of the adrenal gland causing excessive release of norepinephrine.

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Pre-operative use of alpha-blockers

Used to control high blood pressure before surgery, especially in pheochromocytoma patients.

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Irreversible alpha-blockers

Alpha blockers that bind permanently to the receptors.

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Reversible alpha-blockers

Alpha blockers that bind temporarily to the receptors.

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Alpha-methyl dopa

A drug that interferes with the synthesis of noradrenaline.

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Reserpine

A drug that depletes noradrenaline stores.

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Prazosin

A selective alpha-1 blocker used to treat hypertension and other conditions.

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Alpha-1 Blocker Mechanism

Reduces blood pressure by relaxing blood vessels, and reducing tone in bladder neck.

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First-dose Hypotension

A sudden drop in blood pressure after the initial dose of a medication.

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Peripheral Vascular Disease (PVD)

Disorder affecting blood circulation in the extremities.

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Benign Prostatic Hyperplasia (BPH)

A noncancerous enlargement of the prostate gland.

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Alpha-1-adrenergic blockers (BPH treatment)

Drugs that relax bladder muscles and prostate to improve urination.

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5-alpha reductase inhibitors

Drugs that reduce prostate size to ease urination.

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Yohimbine

Selective alpha-2 blocker that increases antidiuretic hormone release, and may improve male impotence.

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Erectile Dysfunction (ED) Treatment

Various drugs and therapies to improve erectile function, such as sildenafil, tadalafil, and others.

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Phosphodiesterase inhibitors

Substances like sildenafil that block the enzyme phosphodiesterase, allowing for increased cGMP levels and resulting in vasodilation.

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Ergot Alkaloid Types

Ergot alkaloids are a group of medicines derived from the fungus Claviceps purpurea, with both semi-synthetic and natural forms. Examples include ergotamine, ergometrine, methysergide, dihydroergotamine, and bromocryptine.

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Ergotamine Action

Ergotamine acts directly on various receptors, powerful vasoconstrictor, partial agonist at 5-HT2 receptors, partial agonist at alpha-1 receptors. It's used for migraine headaches.

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Ergometrine Action

Ergometrine acts on receptors, a powerful oxytocic with effects on the uterus, used to prevent postpartum hemorrhage.

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Bromocryptine Action

Bromocryptine suppresses lactation by reducing prolactin. It also treats prolactin-secreting tumors and Parkinson's disease.

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Ergot Receptor Action

Ergot alkaloids interact with various receptors affecting vessels and nerve centers, like Serotonin 2 (5HT2), alpha-1 adrenegic, dopamine (D2), affecting uterine contractions and central nervous system functions.

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Ergot Alkaloid Uses

Ergot alkaloids are used for migraines, postpartum bleeding control, as per specific receptor targets and to regulate prolactin which has effects on lactation.

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Methyl Ergometrine

Semi-synthetic ergot alkaloid derivative, used to treat postpartum hemorrhages.

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Direct vs. Receptor Actions

Ergot alkaloids can affect organs by directly interacting with vascular receptors, or indirectly impacting receptors on the organ. Such actions affect the dynamic of organs.

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Ergotoxin

Natural ergot alkaloid, with particular effects on peripheral vascular conditions.

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Ergot Alkaloid Dynamics

Ergot alkaloids have different effects based on the receptor type they bind to, and their potency. Such differences influence their range of medical applications.

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Study Notes

Sympatholytics 1

  • Sympatholytics are drugs that depress adrenergic nerve function.
  • Objectives:
    • List sympathetic depressants & classify alpha adrenoreceptor blockers.
    • Recognize the pharmacokinetics, dynamics, uses, and adverse effects of alpha adrenoreceptor blockers.

Sympathetic Depressants

  • These drugs depress adrenergic nerve function.
  • Types of Sympatholytics:
    • 1-Adrenergic Receptor Blockers:
      • Alpha blockers
      • Beta blockers
    • 2- Adrenergic Neurone Depressants:
      • Drugs that interfere with the synthesis of noradrenaline (e.g., α-methyl dopa)
      • Drugs that deplete noradrenaline stores (e.g., Reserpine)
      • Drugs that inhibit the release of NA (e.g., Guanethidine)
    • 3- Ganglion Blockers: Trimethaphan
    • 4- Central sympathetic depressants:
      • Centrally Acting Alpha-2 Agonists: Clonidine
      • V.M.C. Depressants: reserpine

Alpha Adrenoreceptor Blockers

  • These drugs inhibit adrenergic responses mediated through alpha receptors without affecting beta receptors.
  • Types:
    • Non-selective alpha blockers:
      • Imidazolines: Tolazoline, Phentolamine
      • B-Halo alkyl amines: Phenoxybenzamine
    • Selective alpha blockers:
      • α1-blockers: Prazosin, Terazosin, Doxazosin
      • α2-blockers: Yohimbin
    • Other:
      • Ergot alkaloids
      • Labetalol & carvedilol
      • Chlorpromazine
      • TCA as amitriptyline
      • Ketanserine

Dynamics of Non-Selective α Blockers

  • Phenoxybenzamine:
    • Very Powerful alpha blocker
    • Irreversible, non-competitive block
    • Delayed onset (prodrug)
    • Long duration of action
    • Inhibits neuronal uptake I and tissue uptake II of NA.
  • Phentolamine and Tolazoline:
    • Block both post-synaptic α1 and pre-synaptic α2 receptors.
    • Increase release of noradrenaline.
    • Discomfortable tachycardia.
    • Used in pre-operative control of pheochromocytoma (rapid and short acting) and diagnosis of sustained pheochromocytoma (Regitine test)
    • Used in peripheral vascular disease (tolazoline)

Prazosin

  • Selective α1 blocker
  • Vasodilation
  • Inhibits phosphodiesterase enzyme.
  • Increases both cAMP and cGMP.
  • Mixed arterial and venous dilator.
  • Reduces peripheral resistance and afterload.
  • Decreases venous return and preload.
  • Decreases both systolic and diastolic blood pressures.
  • No uncomfortable tachycardia.
  • Used in hypertension, heart failure, peripheral vascular diseases, benign hypertrophy of prostate (BHP).
  • Side effects:
    • Dizziness, headache, drowsiness
    • First-dose hypotension within 2 hours (more severe in salt depleted patients—start at low dose and at bed time to avoid)
    • Salt and water retention

BPH

  • Benign Prostatic Hypertrophy (BPH):
    • Static component (increased size of prostate)
    • Dynamic component (tone of bladder neck muscle increased)
  • Treatment:
    • Alpha-1 adrenergic blockers (prazosin-like) — reduce tone of bladder neck
    • 5-alpha reductase inhibitors (finasteride) — reduce size of prostate
    • Other selective alpha-1 blockers (Terazosin, Alfuzosin, Tamsulosin)

Selective α2 Blockers

  • Yohimbine:
    • Increases release of antidiuretic hormone.
    • Used in erectile dysfunction.

Ergot Alkaloids

  • Natural and semi-synthetic derivatives from Claviceps purpurea

  • Types:

    • Ergotamine
    • Ergometrine
    • Ergotoxine
    • Methyl ergometrine
    • Dihydroergotamine
    • Methysergide
    • Bromocryptine

  • Some are used in migraine, others in suppressing lactation, treating Parkinsonism, infertility etc.

Toxicity and Side Effects of Ergot Alkaloids

  • Dihydroergotamine: similar to ergotamine; potent blocker; used for acute migraine. Methyl Ergometrine (methergine): semi-synthetic, potent oxytocic.
  • Ergot toxicity or ergotism:
    • Cold extremities, tingling
    • Numbness gangrene
    • Hypertension, angina
    • Nausea & vomiting
    • Uterine stimulation and abortion

Direct Action Receptor Interactions

Multiple Choice Questions

  • These are test questions regarding different sympatholytics.
    • e.g. Which one of the following is a selective α1 blocker? (Answer: Prazosin)

Resources and References

  • USMLE step-1 lecture notes pharmacology (Kaplan)
  • Lippincott illustrated review 6th edition

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Sympatholytics1 - Dr. Monira Selim - PDF

Description

This quiz covers the classification and pharmacological effects of sympatholytics, particularly alpha adrenoreceptor blockers. Participants will learn about the types of sympathetic depressants, their uses, pharmacokinetics, dynamics, and potential adverse effects. Ideal for students studying pharmacology or related health sciences.

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