Potassium Channel Openers

POTASSIUM CHANNEL OPENERS


POTASSIUM CHANNEL OPENERS

General MOA

  • Mainly vasodilators:
  • Causes vasodilation (mainly arterioles, negligible effect on venules) by opening potassium channels.

Adverse effect (Major):

  • Reflex tachycardia – Due to vasodilation.
  • Headache – Due to dilation of cerebral blood vessels.
  • Sodium & fluid retention – Due to compensatory mechanisms.

Important drugs:

  • Hydralazine, minoxidil, diazoxide, nicorandil & dalfampridine.

1. Hydralazine:

  • MOA:
    • Acts by vasodilation.
    • By releasing nitric oxide (NO) from endothelium.
    • NO release requires intact endothelium.
  • Metabolism:
    • Metabolized by acetylation.
    • Effect determined genetically due to presence of slow & fast acetylators.
  • Adverse effect: 
    • Drug-induced lupus erythematosus (on prolonged administration).

2. Minoxidil:

Metabolism:

  • Prodrug.
  • Activated in liver producing minoxidil sulfate (by phase II reaction).
  • MOA:
    • Minoxidil sulphate opens potassium channels.
    • Its levels unaltered in renal disease – Indicated even for chronic renal failure.
  • Uses & adverse effect:
    • As an anti-hypertensive drug.
    • Cause abnormal hair growth in females (hirsutism) – Utilized for alopecia (Alopecia areata) treatment in males.

3. Combination of Minoxidil & hydralazine:

  • Given orally for severe hypertension.

4. Diazoxide:

  • Thiazide derivative.
  • During hypertensive emergencies, as rapid i.v. injection.
  • Adverse effect:
    • Hyperuricemia.
    • Hyperglycemia (by inhibiting insulin release from pancreatic beta cells) –> leading to insulinoma.

5. Nicorandil

  • Cardioprotective potassium channel opener.
    • Causes ischemic preconditioning & coronary dilation – By activating myocardial ATP sensitive K+ channels.
    • Also possesses NO-releasing property.
  • Useful in angina.

6. Dalfampridine:

  • An oral potassium channel blocker.
  • Indication:
    • Improves walking ability in people with multiple sclerosis.

Exam Important

POTASSIUM CHANNEL OPENERS

  • Potassium channel openers are mainly vasodilators (mainly arterioles) by opening potassium channels.
  • Important potsssium channel openers include, Hydralazine, minoxidil, diazoxide, nicorandil & dalfampridine.
  • Hydralazine acts both by vasodilatation & also by releasing nitric oxide (NO) from intact endothelium.
  • On prolonged hydralazine administration, causes drug-induced lupus erythematosus.
  • Minoxidil is a prodrug activated in liver forming “minoxidil sulfate”.
  • Minoxidil sulfate opens potassium channels.
  • Minoxidil is a safer anti-hypertensive drug for chronic renal failure cases.
  • Minoxidil is useful as an anti-hypertensive drug & for alopecia treatment in males.
  • By causing abnormal hair growth as an adverse effect in females (hirsutism), minoxidil is utilized for alopecia treatment (Alopecia areata) in males.
  • Combination of Minoxidil & hydralazine is given orally for severe hypertension.
  • Diazoxide as rapid i.v injection is useful during hypertensive emergencies.
  • Nicorandil is a cardioprotective potassium channel opener, by ischemic preconditioning & coronary dilation.
  • Nicorandil activates myocardial ATP sensitive K+ channels & result in coronary dilation.
  • Dalfampridine is an oral potassium channel opener which helps improve walking ability in people with multiple sclerosis.

 

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