View source for WBR0462

 {{WBRQuestion
|QuestionAuthor= {{YD}} (Reviewed by  {{AJL}} and  {{YD}})
|ExamType=USMLE Step 1
|MainCategory=Pharmacology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|Prompt=A 62-year-old man presents to the physician’s office with complaints of abnormal vision. The patient explains that he has been seeing yellow-green halos ever since he was administered a new drug whose name he cannot recall. The patient’s past medical history is significant for latent tuberculosis, advanced cardiac disease, and erectile dysfunction. Which of the following medications most likely induced this patient’s symptoms?
|Explanation=[[Digitalis]] is a cardiac glycoside. It is a direct [[Na/K/ATPase inhibitor]] that indirectly inhibits the [[Na/Ca exchanger]] by hindering the formation of a sodium gradient. This mechanism of action results in increased inotropy by augmenting levels of intracellular calcium.  Also, [[digitalis]] has [[cholinomimetic]] effects due to its vagal activation. Digitalis administration results in an increase in the [[PR interval]], delay in [[AV node]] conduction, and decrease the [[QT interval]]. [[Digitalis]] is frequently administered to patients with advanced [[congestive heart failure]] and atrial fibrillation. Because digitalis has a narrow therapeutic index, the risk of toxicity with digitalis is quite high, especially in the elderly population. Risk factors for digitalis toxicity include hypokalemia, hypomagnesemia, renal impairment, and concomitant use of other medications that interact with digitalis (eg. quinidine, amiodarone, and calcium channel blockers). Digitalis toxicity may manifest as non-specific GI symptoms, including nausea and vomiting, headaches, anorexia, or confusion. Visual distortion is also a common manifestation of digitalis toxicity; patients often report blurring, central scotomas, glare and halo effects, and green-yellow visual disturbance. Although other color disturbances have been reported, green-yellow discoloration remains the most common color alteration among patients who are administered digitalis.
|AnswerA=Sildenafil
|AnswerAExp=[[Sildenafil]], a [[phosphodiesterase]] (PDE) 5 inhibitor, maintains elevated cGMP and nitrous oxide (NO) levels. Sildenafil is associated with color disturbances that usually manifest as a blue-colored vision, rather than a green-yellow visual disturbance.
|AnswerB=Tadalafil
|AnswerBExp=[[Tadalafil]], a long-acting PDE 5 inhibitor, is not frequently associated with visual color changes.
|AnswerC=Digitalis
|AnswerCExp=Visual distortion is a manifestation of digitalis toxicity; patients often report blurring, central scotomas, glare and halo effects, and green-yellow visual disturbance.
|AnswerD=Ethambutol
|AnswerDExp=[[Ethambutol]], an anti-tuberculous agent, is associated with green-red visual changes and optic neuritis, both of which are reversible following discontinuation of the medication. [[Ethambutol]] is not administered in latent tuberculosis (TB), but rather in active TB.
|AnswerE=Rifampin
|AnswerEExp=[[Rifampin]] is not associated with visual color changes. Classically, rifampin is associated with red-orange discoloration of body fluids.
|EducationalObjectives=[[Digitalis]] is a cardiac glycoside. It is a direct [[Na/K/ATPase inhibitor]] that indirectly inhibits the [[Na/Ca exchanger]] by hindering the creation of a sodium gradient. Visual distortion is a common manifestation of digitalis toxicity; patients often report blurring, central scotomas, glare and halo effects, and green-yellow visual disturbance.
|References=Lawrenson JG, Kelly C, Lawrenson AL, et al. Acquired colour vision deficiency in patients receiving digoxin maintenance therapy. Br J Ophthalmol. 2002;86(11):1259-61.<br>
First Aid 2014 page 301
|RightAnswer=C
|WBRKeyword=digitalis, vision, sildenafil, tadalafiil, ethambutol, side effect, adverse drug reaction, tuberculosis, medication, optic
|Approved=Yes
}}