**Core Concept**
Ivermectin is an anthelmintic medication used to treat various parasitic infections, including strongyloidiasis, onchocerciasis, and lymphatic filariasis. It works by inhibiting the neurotransmitter release from invertebrate nerve cells, leading to muscle paralysis and ultimately, the death of the parasite.

**Why the Correct Answer is Right**
Ivermectin's mechanism of action involves binding to glutamate-gated chloride channels in invertebrate nerve cells, which leads to an influx of chloride ions and subsequent hyperpolarization of the cell membrane. This results in muscle paralysis and death of the parasite. Ivermectin's effectiveness against a wide range of parasites is due to its ability to target these specific ion channels.

**Why Each Wrong Option is Incorrect**
**Option A:** Ivermectin is not a macrolide antibiotic, which is a class of antibiotics that target bacterial protein synthesis.
**Option B:** Ivermectin does not work by inhibiting the synthesis of purine nucleotides, which is a characteristic of certain antimicrobial agents.
**Option C:** Ivermectin is not primarily used as an antihistamine, which is a type of medication used to treat allergic reactions.

**Clinical Pearl / High-Yield Fact**
Ivermectin should be used with caution in patients with neurologic disorders, as it can cause neurotoxicity in high doses or when used in patients with pre-existing neurologic conditions.

**Correct Answer:** D.