A 62-year-old woman with multiple myeloma is given pamidronate calcium biphosphonates. This treatment has been shown to do what?
**Core Concept**
Pamidronate calcium biphosphonates are a class of medications used to treat hypercalcemia of malignancy, including that caused by multiple myeloma. They work by inhibiting osteoclast-mediated bone resorption, thereby reducing the release of calcium into the bloodstream.
**Why the Correct Answer is Right**
Pamidronate binds to hydroxyapatite in bone, causing a localized effect on osteoclasts. This binding disrupts the normal osteoclast function, leading to a decrease in bone resorption and subsequent reduction in serum calcium levels. The mechanism of action is primarily through the inhibition of farnesyl pyrophosphate synthase, an enzyme crucial for the mevalonate pathway involved in prenylation of small GTPases, which are essential for osteoclast function.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because pamidronate does not primarily stimulate osteoblast activity, which would increase bone formation. Instead, it reduces bone resorption.
**Option B:** This option is incorrect because pamidronate does not directly stimulate parathyroid hormone (PTH) production, which would increase serum calcium levels. In fact, pamidronate is used to treat hypercalcemia, a condition associated with elevated PTH levels.
**Option C:** This option is incorrect because pamidronate does not primarily act through the reduction of vitamin D levels, which would decrease calcium absorption from the gut. Pamidronate's mechanism of action is more localized to bone tissue.
**Clinical Pearl / High-Yield Fact**
Bisphosphonates like pamidronate can cause osteonecrosis of the jaw (ONJ), a serious side effect that may occur in patients with prolonged exposure to these medications. This risk is increased in patients with dental disease or those undergoing dental procedures.
**Correct Answer: C. Reduces bone resorption and subsequently decreases serum calcium levels.**