Review Question - QID 109908

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Drug Reactions and Side Effects Medication Reactions QID: 109908 (M1.PH.18.4872)

QID 109908 (Type "109908" in App Search)

A 56-year-old man was brought to the emergency department by his wife when he passed out for 5 seconds after dinner at home. He says that he recalls feeling lightheaded moments prior to passing out and also had some palpitations. Otherwise, he has been feeling fatigued recently and has had some shortness of breath. His previous medical history is significant for diabetes that is well controlled on metformin. An EKG is obtained showing fast sawtooth waves at 200/min. He is administered a medication but soon develops ringing in his ears, headache, flushed skin, and a spinning sensation. The medication that was most likely administered in this case has which of the following properties?

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Decreased rate of phase 0 depolarization and increased action potential duration

49%

95/193

Decreased rate of phase 0 depolarization and normal action potential duration

11%

22/193

Normal rate of phase 0 depolarization and decreased action potential duration

15%

29/193

Normal rate of phase 0 depolarization and increased action potential duration

13%

26/193

Normal rate of phase 0 depolarization and normal action potential duration

2/193

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This patient with atrial flutter who subsequently developed tinnitis, headache, and vertigo after treatment was most likely given quinidine, which acts by decreasing the rate of phase 0 depolarization and increasing action potential duration.

Class I antiarrhythmics work by blocking sodium channels in the heart and preferentially act on cells that are frequently depolarized. This drug class can be further divided into three subclasses based on how they change the action potential profile in the heart. Class Ia antiarrhythmics decrease the rate of phase 0 depolarization and increase the action potential duration. Quinidine is a class Ia antiarrhythmic with a unique side effect profile because it can cause cinchonism, which is characterized by headache, flushing, tinnitus, and vertigo.

Incorrect Answers:
Answer 2: Decreased rate of phase 0 depolarization and normal action potential duration is characteristic of class Ic antiarrhythmics but these do not cause cinchonism as a side effect.

Answer 3: Normal rate of phase 0 depolarization and decreased action potential duration is characteristic of class Ib antiarrhythmics but these do not cause cinchonism as a side effect.

Answer 4: Normal rate of phase 0 depolarization and increased action potential duration is characteristic of class III antiarrhythmics but these do not cause cinchonism as a side effect.

Answer 5: Normal rate of phase 0 depolarization and normal action potential duration is characteristic of class II antiarrhythmics, which work instead by decreasing the slope of phase 4 depolarization. These antiarrhythmics do not cause cinchonism as a side effect.

Bullet Summary:
Cinchonism is a side effect of quinidine, which works by decreasing the rate of phase 0 depolarization and increasing the action potential duration.

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