Review Question - QID 107272

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Toxicology Toxicology Drug Introduction QID: 107272 (M2.PH.17.4678)

QID 107272 (Type "107272" in App Search)

A 66-year-old man presents to his primary care physician with abdominal pain in the setting of progressively worsening constipation. He complains of epigastric pain that waxes and wanes, and expressed concern that he has not defecated for the past 5 days. Upon further questioning, he relates that he has been taking three of his wife's multivitamins each day for the past three weeks to "combat a cold." Vital signs are within normal limits. Physical exam reveals an abdomen with nonspecific tenderness to deep palpation without rebound tenderness, hyperpercussion, or flank tenderness. What is the most likely cause of his symptoms?

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Magnesium overdose

33%

1/3

Iron overdose

33%

1/3

Potassium overdose

33%

1/3

Folic acid overdose

0/3

Zinc overdose

0/3

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This patient's symptoms are associated with significant intake of multivitamins. Among the various mineral overdoses, iron toxicity is most likely in this patient.

In the multivitamin market, women's formulations generally contain more iron than men's, purportedly to replenish loss from menses. Chronic iron overconsumption may present with constipation and manifest as abdominal pain. Severe iron toxicity can cause acute corrosive necrosis of the stomach and liver. In these cases, treatment with the antidote deferoxamine is necessary.

This question challenges the examinee to recall prodromes associated with various toxins. The USMLE exams will provide classic symptom histories for toxicology questions. In this case, only iron is most strongly associated with abdominal pain. The other minerals and nutrients listed among answer choices have their own toxidromes (see below).

Incorrect Answers:
Answer 1: Hypermagnesemia presents with lethargy and neurological symptoms including decreased deep tendon reflexes. Abdominal pain is not a classic presentation.
Answer 3: Potassium is rarely an additional supplement found in multivitamins. Hyperkalemia can cause life-threatening arrhythmias.
Answer 4: Folic acid toxicity in animal studies has been associated with reduced zinc absorption. However, it has not been found to cause significant harm in humans.
Answer 5: Zinc has been associated with decreased duration of common cold symptoms, but overdose is associated with bad taste, nausea, and vomiting. While abdominal pain can result from vomiting, there is no such history provided for this patient.

Part of the issue with iron overdose may be due to prescribing scientifically unfounded doses. A recent randomized controlled trial demonstrated that higher doses of iron were associated with less absorption. In 54 non-anemic women with low ferritin levels, those who took less than 60 mg ferrous sulfate once daily demonstrated greater improvement in iron levels compared to those on the traditionally taught three times daily dosing schedule. (1)