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Old 09-06-2014
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Arrow Practice Question #5

A 38-year-old woman presents to the ER complaining of a 2-day history of fatigue, lethargy and double vision. Physical examination shows a right nystagmus. A detailed history reveals that he recently began treatment for recurrent tonic-clonic seizures.
Laboratory studies show:

Na+: 143 mEq/L
K+: 4.5 mEq/L
Cl-: 103 mEq/L
HCO3-: 26 mEq/L
Blood urea nitrogen: 45 mg/dL
Creatinine: 4.3 mg/dL

Which of the following agents is most likely responsible
for this patientís condition?

(A) Clozapine
(B) Imipramine
(C) Lithium
(D) Phenytoin
(E) Sumatriptan
(F) Valproic acid
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Old 09-06-2014
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Option D phenytoin!
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Old 09-06-2014
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Will take D
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Old 09-06-2014
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Phenytoin --> causes both vertigo and nystagmus.

I found this nice mnemonic online:
P - P-450 inducer
H - Hirsutism
E - enlarged gums (gingival hyperplasia)
N - Nystagmus
Y - yellow-browning of skin
T - teratogenic
O - osteomalacia
I - impaired folate absorp (--> anemia)
N - neuropathies with headache and vertigo
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  #5  
Old 09-06-2014
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Yes!

The correct answer is D.
Phenytoin toxicity can lead to nystagmus, diplopia, lethargy, and ataxia. It can also lead to tubulointerstitial nephritis, which can cause a sharp increase in creatinine levels.
(A)Clozapine is an antipsychotic that possesses extrapyramidal and anticholinergic adverse effects.
(B)Imipramine is a tricyclic antidepressant that can lead to the ď3 CísĒ: Convulsion, Coma, and Cardiotoxicity.
(C)Lithium toxicity presents with tremor, polyuria, slurred speech, and poor coordination.
(E)Sumatriptan is a 5-HT1 agonist used to treat migraines. Sumatriptan toxicity can present with chest discomfort and tingling.
(F)Valproate, an antiepileptic that works primarily by increasing GABA in the CNS, can cause nystagmus. Although it does not cause nephritis, valproate has been known to disrupt the urea cycle, leading to hyperammonemia and cerebral edema. Other adverse effects include rare but severe hepatotoxicity, thrombocytopenia, and alopecia. Valproate can increase phenytoin levels by inhibiting CYP450 metabolism.
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