Opioid-Gabapentinoid Additive CNS Depression — SCE Palliative Medicine MCQ

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ModeratePain ManagementOpioid-Gabapentinoid Additive CNS DepressionSCE Palliative Medicine

A palliative care consultant reviews a patient on both oxycodone and pregabalin for mixed cancer pain. The patient reports dizziness, sedation, and cognitive impairment. What pharmacodynamic interaction is occurring?

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Correct answer: D — Additive CNS depression — both oxycodone (opioid) and pregabalin (gabapentinoid) independently depress CNS function, and their effects summate

Explanation lettering: D = shown as A · E = shown as C · A = shown as D · C = shown as E

The correct answer is A. The UK SmPC for pregabalin explicitly states that it is additive to oxycodone in impairing cognitive and motor function, indicating a pharmacodynamic interaction via CNS depression. MHRA safety data also report increased risk of respiratory failure, coma, and death when gabapentinoids are used with opioids, further supporting additive CNS depression. There is no evidence of oxycodone affecting pregabalin metabolism (ruling out B), nor does pregabalin block opioid analgesia (ruling out C). The temporal relationship to drug therapy and established pharmacology makes cancer-related causes (D) or no interaction (E) implausible.

Reference: MHRA FOI response / eMC SmPC wording (MHRA, recent); GOV.UK Drug Safety Update on pregabalin (2021), https://assets.publishing.service.gov.uk/media/65f23476ff117048966159b9/FOI_23-264_response_redacted.pdf