Maintenance of high urinary pH is impoant during methotrexate treatment because:
**Core Concept**
Methotrexate is a chemotherapeutic agent that works by inhibiting dihydrofolate reductase (DHFR), an enzyme necessary for DNA synthesis and repair. To minimize its toxic effects, it's essential to maintain a high urinary pH during treatment.
**Why the Correct Answer is Right**
Methotrexate is a weak acid that is primarily excreted by the kidneys. At acidic pH, it can reabsorb in the renal tubules, leading to increased toxicity. By maintaining a high urinary pH, the kidneys can increase the excretion of methotrexate, reducing its reabsorption and minimizing its toxic effects. This is particularly important in patients at high risk of methotrexate toxicity, such as those with renal impairment.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the mechanism of methotrexate toxicity or its excretion.
**Option B:** While hydration is important during methotrexate treatment, it is not the primary reason for maintaining high urinary pH.
**Option C:** This option is not accurate, as the primary mechanism of methotrexate toxicity is not related to its interaction with potassium.
**Clinical Pearl / High-Yield Fact**
To minimize methotrexate toxicity, patients should receive high doses of folic acid or folinic acid, which can bypass the DHFR inhibition caused by methotrexate. This is a critical aspect of methotrexate treatment and is essential for preventing its toxic effects.
**Correct Answer: C.**