True about thiopentone-
**Core Concept**
Thiopentone, a barbiturate, is a rapid-acting hypnotic agent used for inducing general anesthesia. It acts by enhancing the inhibitory neurotransmission mediated by GABA (gamma-aminobutyric acid) in the central nervous system.
**Why the Correct Answer is Right**
Thiopentone's mechanism of action involves binding to the GABA_A receptor, a ligand-gated chloride channel. This binding increases the frequency of chloride channel opening, leading to an influx of chloride ions into the neuron, which hyperpolarizes the neuronal membrane and reduces the excitability of neurons. This results in sedation, hypnosis, and eventually, loss of consciousness. The rapid onset of action of thiopentone is due to its ability to cross the blood-brain barrier quickly.
**Why Each Wrong Option is Incorrect**
**Option A:** Thiopentone is a potent anticonvulsant. **Incorrect because** thiopentone can actually lower the seizure threshold and may precipitate seizures, especially in patients with a history of seizure disorders.
**Option B:** Thiopentone is a non-depolarizing muscle relaxant. **Incorrect because** thiopentone does not have significant muscle relaxant properties and should not be used for this purpose.
**Option C:** Thiopentone is metabolized primarily by the liver. **Incorrect because** thiopentone is metabolized mainly by the liver, but it is also partially metabolized by the kidneys, and its metabolites are excreted in the urine.
**Clinical Pearl / High-Yield Fact**
Thiopentone is contraindicated in patients with porphyria, as it can induce an acute attack of the disease. This is an important consideration when selecting an induction agent for patients with a history of porphyria.
**Correct Answer:** None provided. Please provide the correct options and answer for a complete explanation.