Which one of the following is the shortest acting intravenous analgesic –
**Core Concept**
The question is testing the pharmacokinetics and pharmacodynamics of intravenous analgesics. Specifically, it's asking about the duration of action of these medications, which is a critical factor in managing pain.
**Why the Correct Answer is Right**
Fentanyl is a potent opioid analgesic with a rapid onset and short duration of action. It acts as a μ-opioid receptor agonist, producing analgesia by activating these receptors in the central nervous system. Fentanyl's short duration of action is due to its rapid metabolism by the liver enzyme CYP3A4, which converts it into inactive metabolites. This makes it an ideal choice for short procedures or when a rapid recovery from analgesia is desired.
**Why Each Wrong Option is Incorrect**
**Option A:** **Morphine** has a longer duration of action compared to fentanyl due to its slower metabolism and longer half-life.
**Option B:** **Pethidine** (meperidine) has a longer duration of action and is also known for its active metabolite normeperidine, which can cause CNS toxicity.
**Option C:** **Sufentanil** is another potent opioid analgesic, but it has a longer duration of action compared to fentanyl, making it less suitable for short procedures.
**Clinical Pearl / High-Yield Fact**
When using short-acting opioids like fentanyl, remember that their duration of action can be influenced by factors like patient age, liver function, and concurrent use of CYP3A4 inhibitors.
**Correct Answer: D. Fentanyl**