**Question:** Dilated pupil with coma is seen in which poisoning -

A. Organophosphate poisoning
B. Carbon monoxide poisoning
C. Cyanide poisoning
D. N-methyl-D-aspartate (NMDA) receptor antagonist poisoning

**Core Concept:**
The question is asking about a specific type of poisoning that presents with dilated pupils and coma. These symptoms are indicative of a disruption in the central nervous system (CNS) function. Poisoning can affect the CNS in various ways, such as by interfering with neurotransmitter function, neurotransmitter receptors, or by causing respiratory depression.

**Why the Correct Answer is Right:**
The correct answer, **N-methyl-D-aspartate (NMDA) receptor antagonist poisoning**, is the correct option because it results in a syndrome characterized by diffuse cerebral edema, seizures, and a characteristic "target" or "hare-lip" pupils that are typically dilated. NMDA receptors are glutamate receptors found on neurons and play a crucial role in excitatory neurotransmission.

**Why Each Wrong Option is Incorrect:**

A. **Organophosphate poisoning** typically presents with respiratory depression, mydriasis (dilated pupils), and muscle weakness rather than coma. Organophosphates inhibit acetylcholinesterase, leading to increased acetylcholine levels, causing excessive stimulation of the postganglionic parasympathetic neurons, which results in mydriasis and other symptoms.

B. **Carbon monoxide poisoning** is characterized by impaired consciousness, seizures, and respiratory depression due to the binding of carbon monoxide to hemoglobin, forming carboxyhemoglobin, which reduces oxygen delivery to vital organs. Mydriasis is less common in carbon monoxide poisoning, and coma is less common than in N-methyl-D-aspartate receptor antagonist poisoning.

C. **Cyanide poisoning** presents with severe respiratory depression, cyanosis, and altered levels of consciousness, but not coma and mydriasis. Cyanide poisoning inhibits mitochondrial cytochrome c oxidase, leading to impaired cellular respiration and causing hypoxia.

**Clinical Pearl:**

In poisoning cases, it is essential for medical professionals to differentiate between different types of poisoning to initiate proper treatment promptly. Organophosphates, carbon monoxide, and cyanide poisonings result in specific presentations, whereas NMDA receptor antagonist poisoning presents with the combination of coma and dilated pupils (mydriasis) due to inhibition of NMDA receptors, leading to excitotoxicity and cerebral edema.