Question

All of the following are true about spinal (intrathecal) opioids EXCEPT?

• A. Acts on dorsal horn substantia gelatinosa
• B. Can cause itching
• C. Intestinal motility is decreased
• D. Can cause respiratory depression

Hint:

Three are classic neuraxial opioid effects; which gut effect is the odd one out at intrathecal doses?

Answer 1

The Correct Option is C

Approach this as a find-the-odd-one-out item about drugs placed directly into the cerebrospinal fluid. Three of the four statements describe genuine, textbook properties of intrathecal opioids. First, their site of action: opioid receptors are densely present in the substantia gelatinosa of the dorsal horn, and that is precisely where spinally administered opioids damp down pain signalling, so option A is correct. Second, itching: pruritus is arguably the single most frequent nuisance side effect of neuraxial opioids, typically over the face and upper body and driven by central receptor activation, so option B is correct. Third, breathing: both early and characteristically delayed respiratory depression can follow rostral spread of the opioid through the CSF toward the brainstem, so option D is correct. That leaves option C. The point being tested is that intrathecal opioids are used in tiny doses and exert their effect locally on the cord with minimal systemic exposure, so a marked slowing of gut motility is not their hallmark in this context. It is therefore flagged as the exception. $Intestinal\ motility\ is\ decreased$ is the statement taken as untrue here.\[\boxed{\text{Intestinal motility is decreased}}\]