Which of the following anaesthetic agent lacks analgesic effect – a) N2Ob) Thiopentonec) Methohexitoned) Ketaminee) Fentanyl

**Core Concept**
Thiopental and methohexital are barbiturate-based general anesthetic agents that primarily induce sedation and hypnosis without significant analgesic effects. Their mechanism of action involves modulating the neurotransmitter activity in the central nervous system, particularly at the GABA receptor, leading to a decrease in neuronal excitability.

**Why the Correct Answer is Right**
Thiopental and methohexital do not possess analgesic properties as they do not activate opioid receptors or other pathways involved in pain modulation. Their primary use is for inducing general anesthesia or sedation, whereas analgesia is achieved through other mechanisms, such as the activation of opioid receptors by agents like fentanyl. These barbiturates can be used in conjunction with analgesics to provide a balanced anesthetic effect.

**Why Each Wrong Option is Incorrect**
**Option A:** N2O (nitrous oxide) is a gas with analgesic and anxiolytic effects, often used in combination with other anesthetics to provide pain relief.

**Option D:** Fentanyl is an opioid analgesic with potent pain-relieving properties, commonly used in anesthesia to provide analgesia.

**Clinical Pearl / High-Yield Fact**
When using barbiturates like thiopental and methohexital, it is essential to combine them with analgesics and other anesthetics to achieve a balanced anesthetic effect, as they do not possess analgesic properties.

**Correct Answer:**
✓ Correct Answer: D. bc. Thiopental and methohexital lack analgesic effects.