Ascending-Dose Study of Controlled-Release Ketamine Tablets in Healthy Volunteers: Pharmacokinetics, Pharmacodynamics, Safety, and Tolerability

Current Perspectives on the Clinical Research and Medicalization of Psychedelic Drugs for Addiction Treatments: Safety, Efficacy, Limitations and Challenges

Mental health disorders and substance use disorders (SUDs) in particular, contribute greatly to the global burden of disease. Psychedelics, including entactogens and dissociative substances, are currently being explored for the treatment of SUDs, yet with less empirical clinical evidence than for other mental health disorders, such as depression or post-traumatic stress disorder (PTSD). In this narrative review, we discuss the current clinical research evidence, therapeutic potential and safety of psilocybin, lysergic acid diethylamide (LSD), ketamine, 3,4-methylenedioxymethamphetamine (MDMA) and ibogaine, particularly in the context of the SUD treatment. Our aim was to provide a balanced overview of the current research and findings on potential benefits and harms of psychedelics in clinical settings for SUD treatment. We highlight the need for more clinical research in this particular treatment area and point out some limitations and challenges to be addressed in future research.

Extended-release ketamine tablets for treatment-resistant depression: a randomized placebo-controlled phase 2 trial

Ketamine has rapid-onset antidepressant activity in patients with treatment-resistant major depression (TRD). The safety and tolerability of racemic ketamine may be improved if given orally, as an extended-release tablet (R-107), compared with other routes of administration. In this phase 2 multicenter clinical trial, male and female adult patients with TRD and Montgomery-Asberg Depression Rating Scale (MADRS) scores ≥20 received open-label R-107 tablets 120 mg per day for 5 days and were assessed on day 8 (enrichment phase). On day 8, responders (MADRS scores ≤12 and reduction ≥50%) were randomized on a 1:1:1:1:1 basis to receive double-blind R-107 doses of 30, 60, 120 or 180 mg, or placebo, twice weekly for a further 12 weeks. Nonresponders on day 8 exited the study. The primary endpoint was least square mean change in MADRS for each active treatment compared with placebo at 13 weeks, starting with the 180 mg dose, using a fixed sequence step-down closed test procedure. Between May 2019 and August 2021, 329 individuals were screened for eligibility, 231 entered the open-label enrichment phase (days 1-8) and 168 responders were randomized to double-blind treatment. The primary objective was met; the least square mean difference of MADRS score for the 180 mg tablet group and placebo was -6.1 (95% confidence interval 1.0 to 11.16, P = 0.019) at 13 weeks. Relapse rates during double-blind treatment showed a dose response from 70.6% for placebo to 42.9% for 180 mg. Tolerability was excellent, with no changes in blood pressure, minimal reports of sedation and minimal dissociation. The most common adverse events were headache, dizziness and anxiety. During the randomized phase of the study, most patient dosing occurred at home. R-107 tablets were effective, safe and well tolerated in a patient population with TRD, enriched for initial response to R-107 tablets. ClinicalTrials.gov registration: ACTRN12618001042235 .

Hydroxynorketamine, but not ketamine, acts via α7 nicotinic acetylcholine receptor to control presynaptic function and gene expression

Ketamine is clinically used fast-acting antidepressant. Its metabolite hydroxynorketamine (HNK) shows a robust antidepressant effect in animal studies. It is unclear, how these chemically distinct compounds converge on similar neuronal effects. While KET acts mostly as N-methyl-d-aspartate receptor (NMDAR) antagonist, the molecular target of HNK remains enigmatic. Here, we show that KET and HNK converge on rapid inhibition of glutamate release by reducing the release competence of synaptic vesicles and induce nuclear translocation of pCREB that controls expression of neuroplasticity genes connected to KET- and HNK-mediated antidepressant action. Ro25-6981, a selective antagonist of GluN2B, mimics effect of KET indicating that GluN2B-containing NMDAR might mediate the presynaptic effect of KET. Selective antagonist of α7 nicotinic acetylcholine receptors (α7nAChRs) or genetic deletion of Chrna7, its pore-forming subunit, fully abolishes HNK-induced synaptic and nuclear regulations, but leaves KET-dependent cellular effects unaffected. Thus, KET or HNK-induced modulation of synaptic transmission and nuclear translocation of pCREB can be mediated by selective signaling via NMDAR or α7nAChRs, respectively. Due to the rapid metabolism of KET to HNK, it is conceivable that subsequent modulation of glutamatergic and cholinergic neurotransmission affects circuits in a cell-type-specific manner and contributes to the therapeutic potency of KET. This finding promotes further exploration of new combined medications for mood disorders.

Ketamine as a therapeutic agent for depression and pain: mechanisms and evidence

Ketamine is an anesthetic drug which is now used to treat chronic pain conditions and psychiatric disorders, especially depression. It is an N-methyl-D-aspartate (NMDA) receptor antagonist with additional effects on α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, opioid receptors, and monoaminergic receptors. This article focuses on ketamine's role in treating depression and pain, two commonly comorbid challenging conditions with potentially shared neurobiologic circuitry. Many clinical trials have utilized intravenous or intranasal ketamine for treating depression and pain. Intravenous ketamine is more bioavailable than intranasal ketamine and both are effective for acute depressive episodes. Intravenous ketamine is advantageous for post-operative analgesia and is associated with a reduction in total opioid requirements. Few studies have treated chronic pain or concurrent depression and pain with ketamine. Larger, randomized control trials are needed to examine the safety and efficacy of intravenous vs. intranasal ketamine, ideal target populations, and optimal dosing to treat both depression and pain.

Chiral Pharmacokinetics and Metabolite Profile of Prolonged-release Ketamine Tablets in Healthy Human Subjects

BACKGROUND

The anesthetic ketamine after intravenous dosing is nearly completely metabolized to R- and S-stereoisomers of the active norketamine (analgesic, psychoactive) and 2,6-hydroxynorketamine (potential analgesic, antidepressant) as well as the inactive dehydronorketamine. Oral administration favors the formation of 2,6-hydroxynorketamines via extensive presystemic metabolism. The authors hypothesized that plasma exposure to 2,6-hydroxynorketamines relative to the psychoactive ketamine is greater after prolonged-release ketamine tablets than it is after intravenous ketamine.

METHODS

Pharmacokinetics of ketamine after intravenous infusion (5.0 mg) and single-dose administrations of 10, 20, 40, and 80 mg prolonged-released tablets were evaluated in 15 healthy white human subjects by means of a controlled, ascending-dose study. The stereoisomers of ketamine and metabolites were quantified in serum and urine by validated tandem mass-spectrometric assays and evaluated by noncompartmental pharmacokinetic analysis.

RESULTS

After 40 mg prolonged-release tablets, the mean ± SD area under the concentrations-time curve ratios for 2,6-hydroxynorketamine/ketamine were 18 ± 11 (S-stereoisomers) and 30 ± 16 (R-stereoisomers) compared to 1.7 ± 0.8 and 3.1 ± 1.4 and after intravenous infusion (both P < 0.001). After 10 and 20 mg tablets, the R-ratios were even greater. The distribution volumes at steady state of S- and R-ketamine were 6.6 ± 2.2 and 5.6 ± 2.1 l/kg, terminal half-lives 5.2 ± 3.4 and 6.1 ± 3.1 h, and metabolic clearances 1,620 ± 380 and 1,530 ± 380 ml/min, respectively. Bioavailability of the 40 mg tablets was 15 ± 8 (S-isomer) and 19 ± 10% (R-isomer) and terminal half-life 11 ± 4 and 10 ± 4 h. About 7% of the dose was renally excreted as S-stereoisomers and 17% as R-stereoisomers.

CONCLUSIONS

Prolonged-release ketamine tablets generate a high systemic exposure to 2,6-hydroxynorketamines and might therefore be an efficient and safer pharmaceutical dosage form for treatment of patients with chronic neuropathic pain compared to intravenous infusion.

EDITOR’S PERSPECTIVE

Influence of formulation and route of administration on ketamine's safety and tolerability: systematic review

PURPOSE

Ketamine has rapid-onset antidepressant effects in patients with treatment-resistant depression. Common side effects include dissociation (a sense of detachment from reality) and increases in systolic and diastolic blood pressure. The objective of this structured review was to examine the effect of ketamine formulation and route of administration on its pharmacokinetics, safety and tolerability, to identify formulation characteristics and routes of administration that might minimise side effects.

METHODS

This was a structured review of published ketamine pharmacokinetics, safety and tolerability data for any ketamine formulation. The ratio of ketamine:norketamine was calculated from reported C_max values, as a measure of first pass metabolism. The effect of formulation and route of administration on safety was evaluated by measuring mean changes in systolic blood pressure and tolerability by changes in dissociation ratings. Data were correlated using Spearman's method.

RESULTS

A total of 41 treatment arms were identified from 21 publications, and included formulation development studies in healthy volunteers, and studies in clinical populations (patients undergoing anaesthesia, or being treated for pain or depression). Ketamine:norketamine ratios were strongly positively correlated with change in dissociation ratings (r = 0.89) and change in blood pressure (r = 0.96), and strongly negatively correlated with ketamine T_max (r = - 0.87; p < 0.00001 for all). Ketamine T_max strongly positively correlated with a change in dissociation ratings (r = - 0.96) and change in blood pressure (r = - 0.99; p < 0.00001 for all).

CONCLUSION

Ketamine formulations that maximize first pass metabolism and delay T_max will be better tolerated and safer than formulations which lack those characteristics.

Safety and efficacy of extended release ketamine tablets in patients with treatment-resistant depression and anxiety: open label pilot study

BACKGROUND

Ketamine's defining side effects are dissociation and increased blood pressure/heart rate. An oral formulation with delayed absorption could minimize these effects. We recently reported safety and tolerability data for an extended release ketamine tablet in healthy volunteers.

METHODS

To assess safety, tolerability, efficacy, and pharmacokinetics of an extended release oral ketamine tablet in patients with treatment-resistant depression/anxiety. This was a multiple dose open-label flexible dose uncontrolled study in seven patients with treatment-resistant depression/anxiety, who had all previously demonstrated mood improvement to subcutaneous ketamine. Assessments included ratings of anxiety, depression and dissociation, safety and tolerability, and blood samples for ketamine pharmacokinetics and brain-derived neurotrophic factor (BDNF) concentrations.

RESULTS

Improvements in anxiety and depression ratings occurred gradually over 96 h; all patients had >50% improvements in mood ratings. Ketamine was safe and well tolerated, with no changes in vital signs, and a single brief report of dissociation. Ketamine may induce its own metabolism, as the ratio of norketamine to ketamine increased out to 96 h. Serum BDNF concentrations did not change during the study.

CONCLUSION

Ketamine's safety/tolerability may be improved with an extended release oral formulation. Onset of mood improvement is slightly delayed compared with parenteral dosing. These data support the further development of extended release ketamine tablets for treatment of resistant depression and anxiety disorders.