KEA-1010, a ketamine ester analogue, retains analgesic and sedative potency but is devoid of Psychomimetic effects

Non-NMDA Mechanisms of Analgesia in Ketamine Analogs

Despite 50 years of clinical use and experimental endeavor the anesthetic, analgesic, and psychomimetic effects of ketamine remain to be fully elucidated. While NMDA receptor antagonism has been long held as ketamine's fundamental molecular action, interrogation of bespoke ketamine analogs with known absent NMDA binding, yet profound anesthetic and analgesia fingerprints, suggests alternative targets are responsible for these effects. Herein we describe experimental findings utilizing such analogs as probes to explore ketamine-based analgesic molecular targets. We have focused on two-pore potassium leak channels, identifying TWIK channels as a rational target to pursue further. While the totality of ketamine's mechanistic action is yet to be fully determined, these investigations raise the intriguing prospect of separating out analgesia and anesthetic effects from ketamine's undesirable psychomimesis—and development of more specific analgesic medications.

Dissociative and analgesic properties of ketamine are independent and unaltered by sevoflurane general anesthesia

Ketamine-induced dissociation and analgesia are independent and robust to general anesthesia neural circuit alterations, suggesting that ketamine can be refined into a targeted pain therapeutic.

Introduction:

Ketamine, an anesthetic adjunct, is routinely administered as part of a balanced general anesthetic technique. We recently showed that the acute analgesic and dissociation properties of ketamine are separable to suggest that distinct neural circuits underlie these states.

Objective:

We aimed to study whether this finding is robust to the substantial neural circuit alterations associated with general anesthesia.

Methods:

We conducted a single-site, open-label, randomized controlled, cross-over study of sevoflurane and sevoflurane-plus-ketamine (SK) general anesthesia in healthy subjects (n = 12). Before and after general anesthesia, we assessed precalibrated cuff pain intensity and nociceptive pain quality as well as dissociation using the Clinician-Administered Dissociative States Scale (CADSS). For statistical inference, we ran a variation of backward elimination repeated-measures analysis of covariance. Models with CADSS as a covariate term were used to assess whether dissociation mediated the effect of ketamine on pain intensity and quality.

Results:

Sevoflurane-plus-ketamine general anesthesia was associated with a significant (P = 0.0002) pain intensity decline of 3 (SE, 0.44). There was an order effect for dissociation such that SK was associated with a significant (P = 0.0043) CADSS increase of 17.8 (3.2) when the SK treatment came first. When the pain intensity model was reanalyzed with CADSS as an additional covariate, the effect of CADSS was not significant. These results were also conserved for pain quality.

Conclusions:

Our findings suggest that the analgesic and dissociation properties of ketamine remain separable despite general anesthesia. Thus, ketamine may be used as a probe to advance our knowledge of dissociation independent pain circuits.

Sex-related differences in intravenous ketamine effects on dissociative stereotypy and antinociception in male and female rats

Ketamine, a multimodal dissociative anesthetic drug, is widely used to treat various conditions including acute pain and treatment-resistant depression. We previously reported that subanesthetic doses of intravenous (i.v.) ketamine produced transient dissociative stereotypy and antinociception in male rats. However, sex-related differences in the effects of i.v. ketamine on these measures are not well characterized. Adult male and female Sprague-Dawley rats (10 weeks old) received an i.v. bolus saline or ketamine (2 and 5 mg/kg), and dissociative stereotypy (head weaving, ataxia, and circling) and natural behaviors (horizontal activity, rearing, and grooming) were quantified over a 10-min period. Ten minutes after the behavioral observation, antinociception was measured using a tail flick test. The i.v. ketamine administration increased head weaving, ataxia, circling, and horizontal activity while decreasing rearing and grooming behaviors in male and female rats. Following 5 mg/kg ketamine administration, ataxia was greater in female rats, while head weaving was greater in male rats. Among the female rats, head weaving was greater in the low estrogen group (diestrus phase) as compared to the high estrogen group (proestrus/estrus phase). Ketamine doses (2 and 5 mg/kg) produced antinociception in male and female rats, and female rats were more sensitive to the antinociceptive effects of 2 mg/kg ketamine. The current findings suggest that i.v. ketamine administration, a clinically relevant route of administration, may produce sex-related differences in dissociative behaviors and analgesia between males and females.