Hypocalcemia is seen with which of the following:September 2008
**Core Concept**
Hypocalcemia refers to a condition where the calcium levels in the blood are lower than normal. This can be caused by various factors including impaired calcium absorption, increased excretion, or redistribution of calcium from the extracellular to the intracellular space.
**Why the Correct Answer is Right**
One of the primary causes of hypocalcemia is the administration of certain medications that interfere with vitamin D metabolism or calcium absorption. Phenytoin, a commonly used antiepileptic medication, falls into this category. Phenytoin can induce the hepatic enzyme CYP2C9, which is responsible for metabolizing vitamin D and its active forms. This leads to a decrease in the levels of 1,25-dihydroxyvitamin D, a crucial hormone that regulates calcium absorption in the intestine. As a result, patients on phenytoin therapy may develop hypocalcemia due to impaired calcium absorption.
**Why Each Wrong Option is Incorrect**
* **Option A:** While certain medications can cause hypocalcemia, the primary mechanism of phenytoin is through vitamin D metabolism, not direct action on calcium channels.
* **Option B:** Phenytoin's effect on calcium levels is not directly related to its action on the parathyroid glands.
* **Option C:** Phenytoin is not primarily used as a treatment for hypercalcemia; rather, it can cause hypocalcemia as a side effect.
**Clinical Pearl / High-Yield Fact**
When treating patients on long-term antiepileptic medications like phenytoin, it is essential to monitor their calcium levels regularly to prevent hypocalcemia.
**Correct Answer: A. Phenytoin**