antagonistas H2
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Questions and Answers

Que fan as "dinas" MA (antagonistas H2)?

Inhiben o receptor H2 na célula parietal, suprimen a secreción estimulada pola comida, baixan a secreción estimulada polo vago, histamina, gastrina, pepsina e colinomiméticos.

Os antagonistas H2 son eficaces para inhibir a secreción nocturna?

True (A)

Onde se metabolizan principalmente os antagonistas H2?

No fígado.

Cal é a biodispoñibilidade dos antagonistas H2?

<p>50%</p> Signup and view all the answers

Como se eliminan os antagonistas H2 do corpo?

<p>A través do fígado e dos riles.</p> Signup and view all the answers

É necesario axustar a dose dos antagonistas H2 en pacientes con insuficiencia renal?

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

Onde se absorben os antagonistas H2?

<p>No intestino.</p> Signup and view all the answers

Cal é a vida media dos antagonistas H2?

<p>1.1 a 4 horas.</p> Signup and view all the answers

Canto tempo tardan en facer efecto os antagonistas H2?

<p>30-60 minutos ou 1-2 horas como máximo.</p> Signup and view all the answers

Canto tempo dura a inhibición producida polos antagonistas H2?

<p>6-10 horas ou ata 20 horas.</p> Signup and view all the answers

Cando se recomenda tomar a dose de antagonistas H2?

<p>1 hora despois de comer ou antes de durmir (C)</p> Signup and view all the answers

Cal é a potencia relativa da cimetidina?

<p>1</p> Signup and view all the answers

Cal é a dose de cimetidina para o tratamento de úlceras?

<p>800mg antes de durmir ou 400mg 2 veces ao día.</p> Signup and view all the answers

Cal é a dose de cimetidina para o tratamento do refluxo?

<p>800mg 2 veces ao día.</p> Signup and view all the answers

Cales son os efectos adversos da cimetidina a longo prazo e en doses altas?

<p>Efectos antiandroxénicos como xinecomastia e impotencia en homes, e galactorrea en mulleres.</p> Signup and view all the answers

A cimetidina pode atravesar a placenta e o leite materno?

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

Que efecto produce o bloqueo da unión da dehidrotestosterona ao seu receptor e a inhibición do metabolismo do estradiol?

<p>Efecto antiandroxénico.</p> Signup and view all the answers

Que significa tomar un medicamento "en erge"?

<p>Profilaxe antes da comida.</p> Signup and view all the answers

Os antagonistas H2 alivian os síntomas da acidez pouco frecuente no 50-60% dos pacientes?

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

Flashcards

Antagonistas H2

Inhiben o receptor H2 na célula parietal. Suprimen a secreción estimulada pola comida.

Acción dos antagonistas H2

Inhibe a secreción estimulada polo vago, histamina, gastrina, pepsina e colinomiméticos.

Efectividade nocturna

Inhiben o 90% da secreción nocturna.

Efecto no pH

Aumentan o pH en xaxún a 4-5.

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Metabolismo

Hepático; biodispoñibilidade do 50%.

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Eliminación

Hepática e renal; requirir diminuír a dose con insuficiencia renal ou hepática.

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Absorción

Intestinal.

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Vida media

1.1 a 4 horas.

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Inicio de acción

30-60 minutos ou 1-2 horas máximo.

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Duración da inhibición

6-10 horas ou ata 20 horas; dose 2x ao día.

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Cimetidina

Potencia relativa: 1; dose: 400-800mg.

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Efectos adversos da cimetidina

A longo prazo e en altas doses causa efectos antiandroxénicos como xinecomastia e impotencia en homes, galactorrea en mulleres.

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Efecto antiandroxénico

Bloqueo da unión da dehidrotestosterona ao seu receptor e inhibición do metabolismo do estradiol.

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Ranitidina

Dose: 150mg; xa non se usa comunmente.

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Nizatidina

Dose: 150mg; úlcera: 300mg antes de durmir ou 150mg 2x ao día; refluxo: 150mg 2x ao día.

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Famotidina

Potencia relativa 20-50; dose: 20mg.

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Uso dos antagonistas H2

Profilaxe antes da comida; alivio sintomático no 50-60% dos pacientes con acidez pouco frecuente.

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Vías de administración antagonistas H2

Via oral, IM, IV

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Dose de cimetidina para úlcera e refluxo.

Úlcera: 800mg antes de durmir ou 400mg 2x ao día; Refluxo: 800mg 2x ao día.

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Dose de ranitidina para úlcera e refluxo.

Úlcera: 300 mg antes de durmir ou 150mg 2x ao día; refluxo: 150mg 2x ao día.

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Dose de nizatidina para úlcera e refluxo.

Úlcera: 300mg antes de durmir ou 150mg 2x ao día; refluxo: 150mg 2x ao día.

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Dose de famotidina para úlcera e refluxo.

úlcera: 40mg antes de durmir ou 20mg 2x al día; refluxo: 20mg 2x al día

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Study Notes

  • H2 antagonists, identified by the suffix "dinas," inhibit H2 receptors on parietal cells.
  • They suppress food-stimulated secretion and reduce secretion stimulated by the vagus nerve, histamine, gastrin, pepsin, and cholinomimetics.
  • H2 antagonists effectively inhibit 90% of nocturnal secretion and increase fasting pH to 4-5.
  • They are available in oral, intramuscular (IM), and intravenous (IV) formulations.
  • H2 antagonists undergo hepatic metabolism and exhibit approximately 50% bioavailability.
  • Elimination occurs through both hepatic and renal pathways. Dosage adjustments are necessary for patients with renal or hepatic impairment.
  • Absorption occurs in the intestine.
  • The half-life ranges from 1.1 to 4 hours.
  • The onset of action occurs within 30-60 minutes, with peak effects observed at 1-2 hours.
  • Inhibition lasts for 6-10 hours or up to 20 hours. The typical dosage is twice daily, administered 1 hour after meals or before sleep.

Cimetidine

  • Cimetidine has a relative potency of 1. Typical doses range from 400-800mg.
  • For ulcers, the dosage is 800mg before sleep or 400mg twice daily. For reflux, the dosage is 800mg twice daily.

Adverse Effects of Cimetidine

  • Long-term use or high doses may lead to anti-androgenic effects such as gynecomastia and impotence in men, and galactorrhea in women.
  • Cimetidine can cross the placenta and is present in breast milk.

Anti-Androgenic Effect

  • This effect involves blocking the binding of dihydrotestosterone to its receptor and inhibiting estradiol metabolism.

Ranitidine

  • Ranitidine, while not commonly used anymore, has a standard dose of 150mg.
  • For ulcers, the dosage is 300mg at bedtime or 150mg twice daily.
  • For reflux, the dosage is 150mg twice daily.

Nizatidine

  • Nizatidine has a standard dose of 150mg. For ulcers, the dosage is 300mg at bedtime or 150mg twice daily.
  • For reflux, the dosage is 150mg twice daily.

Famotidine

  • Famotidine has a relative potency of 20-50. The standard dose is 20mg.
  • For ulcers, the dosage is 40mg at bedtime or 20mg twice daily.
  • For reflux, the dosage is 20mg twice daily.

Use

  • Used as a prophylaxis before meals, providing symptomatic relief in 50-60% of patients with infrequent heartburn.

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