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Updated: Sep 6, 2025

Intracranial Pharmacotherapy and Pain Assays in Rodents
Published on: April 9, 2019
Antinociceptive and Analgesic Effects of (2R,6R)-Hydroxynorketamine
Jonathan G Yost1, Hildegard A Wulf1, Caroline A Browne1
1Neuroscience Graduate Program (J.G.Y., C.A.B., I.L.), Department of Pharmacology and Molecular Therapeutics (H.A.W., C.A.B., I.L.), and Department of Psychiatry (I.L.), Uniformed Services University, Bethesda, Maryland.
(2R,6R)-hydroxynorketamine (HNK), a ketamine metabolite, offers pain relief via AMPA receptors with a better safety profile than ketamine. HNK also effectively treats neuropathic pain, outperforming gabapentin over time.
Area of Science:
- Neuroscience
- Pharmacology
- Pain Management
Background:
- Opioid and ketamine analgesics have limitations including dangerous side effects and limited efficacy.
- Ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) shows potential for pain relief with fewer side effects.
Purpose of the Study:
- Compare antinociception profiles and mechanisms of ketamine and (2R,6R)-HNK.
- Evaluate (2R,6R)-HNK's efficacy against neuropathic pain (mechanical allodynia) compared to gabapentin.
Main Methods:
- Administered ketamine and (2R,6R)-HNK to C57BL/6J mice, assessing antinociception.
- Utilized AMPA receptor antagonist NBQX and opioid receptor antagonist naltrexone to probe mechanisms.
- Tested (2R,6R)-HNK and gabapentin in a spared nerve injury model of neuropathic pain.
Main Results:
- (2R,6R)-HNK induced delayed antinociception (24 hours) dependent on AMPA receptors, unlike ketamine's rapid, short-lived effect.
- (2R,6R)-HNK demonstrated no dystaxia at analgesic doses, indicating a superior safety profile to ketamine.
- (2R,6R)-HNK reversed mechanical allodynia effectively, with short-term efficacy similar to gabapentin but longer duration (24 hours).
Conclusions:
- (2R,6R)-HNK represents a promising non-opioid analgesic candidate with a distinct mechanism involving AMPA receptors.
- The metabolite (2R,6R)-HNK offers advantages over ketamine in safety and over gabapentin in sustained neuropathic pain relief.
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