Zuranolone

Introduction Since the last edition of the Black Book, several innovative agents have been approved or are poised to be approved in the coming year. These include novel antidepressants, the first muscarine agonist for the treatment of schizophrenia, the first psychedelic which may be approved for the treatment of PTSD (Post Traumatic Stress Disorder), and the first disease modifying drug for the treatment of Alzheimer's disease. Three new antidepressants have come to the market in the past 18 months. The first of those, Auvelity, the combination of bupropion and dextromethorphan, takes advantage of a pharmacokinetic and pharmacodynamic synergism between the two drugs.⁸⁵ Dextromethorphan has several pharmacodynamic properties including actions on the NMDA receptor and the Sigma 1 receptor, adding to the indirect norepinephrine agonist properties of bupropion. How Dextromethorphan is rapidly metabolized via the CYP2D6 isoenzyme to dextrophan that may have mu opioid agonist properties. The combination with bupropion, a CYP2D6 inhibitor, inhibits the metabolism of dextromethorphan allowing for more consistent therapeutic levels. The combination of dextromethorphan 45 mg twice per day and bupropion SR 105 mg twice daily appears to be more effective than an equivalent dose of bupropion alone both in speeding up antidepressant response and achieving remission. However, it's not clear at this time how the combination would compare with a more typical dose of bupropion of 300-450 milligrams a day range. The phase III program for Auvelity, showed that the drug was well tolerated with the most common side effects being dizziness, headache, and dry mouth.⁸⁶ Another novel antidepressant agent approved in 2023 is zuranolone (Zurzuvae). Zuranolone is an oral analog of IV brexanalone, and like brexanolone, was approved for the treatment of post-partum depression.⁸³ The advantages of zuranolone over brexanalone are many. While brexanolone is a 60-hour intravenous infusion that must be administered in a health care facility, zuranolone is a once/day oral medication that is usually taken at home. Like brexanolone, and unlike most antidepressants, zuranolone has a short course of treatment, lasting just 14 days. Zuranolone's, as does brexanolone, is thought to act primarily as allosteric modulator of the GABA-a receptors. Despite only 14 days of treatment, zuranolone produced in depression in post-partum patients a clinically and significantly meaningful improvement at day 15 and continued to day 45 or 1 month past the end of treatment. Zuranolone is a schedule IV drug. The most common side effect in clinical trials was somnolence with 36% of participants reporting this side effect vs only 6% of those on placebo.⁸⁴ Other common side effects included dizziness, diarrhea and fatigue. While the FDA declined to approve zuranolone as monotherapy or as an adjunctive treatment to standard antidepressants in major depression itself, there are positive studies in non-post-partum major depression albeit with smaller effect sizes and less consistent duration of activity. It is likely that zuranolone will continue to be studied in other depressive syndromes such as depression with anxious distress. The third "new" antidepressant approved late 2023 was gepirone (Exxua). Gepirone is not exactly a new or novel antidepressant and originally sought approval in the US about 20 years ago.⁸⁸ There had been two positive studies of gepirone during the original NDA application but also a number of failed, negative, or non-informative studies as well. Thus, the FDA declined to originally approve the drug. However, failed and negative trials are common with antidepressants and after much internal debate, the FDA ultimately agreed to approve the drug based on the positive trials and a relatively favorable side effect profile. Gepirone, like buspirone, is a partial agonist of the 5HT1a receptor and a 5HT2 antagonist. As such, gepirone does not tend to be associated with sexual side effects, weight gain, or sedation. The most common side effects are dizziness, nausea, and insomnia which tend to improve in many patients over time. Second generation antipsychotics (SGAs) continue to be the only class of agents [other than esketamine (Spravato)] approved in adjunctive treatment of resistant major depression. In addition to olanzapine (combined with fluoxetine; Symbyax), aripiprazole (Abilify), quetiapine (Seroquel), brexpiprazole (Rexulti), cariprazine (Vraylar) became the latest SGA to be approved in 2022.⁹⁰ Adjunctive cariprazine at 1.5 mg daily was significantly more effective than adjunctive placebo in patients with MDD who had failed to achieve an adequate response with an antidepressant alone after 6 weeks of treatment. Interestingly, a 3 mg dose of cariprazine was less consistently effective.⁹¹ The major advantage of cariprazine over some of the other approved adjunctive SGA's is easy dosing, with the starting 1.5 mg dose being the optimal therapeutic dose for most people, and a lower metabolic side effect burden with most subjects having limited or no weight gain in short term trials. The most common side effect were akathisia/restlessness, fatigue, and nausea. Lumateperone (Caplyta) is also has positive phase III data in the adjunctive treatment of major depression and is expective file for approval in late 2024. Another recent major development in psychopharmacology is the reemergence of psychedelics in the treatment of psychiatric disorders. The first of these is MDMA (phenethylamine 3,4-methylenedioxymethamphetamine) assisted psychotherapy for the treatment of PTSD. A New Drug Application (NDA) was accepted by the FDA for MDMA in the treatment of PTSD in late 2023.⁸⁷ Because the drug is being fast tracked as a "breakthrough" treatment by the FDA, it was expected to see approval in the summer of 2024. The phase II and III data for MDMA assisted psychotherapy in the treatment of PTSD have been quite consistent and impressive. However, independent reviews have pointed to significant deficiencies in these studies including the bias introduced because of functional unblinding; virtually all patients in psychedelic studies can guess whether they got the active drug or placebo. The functional unblinding, the lack of standardization of adjunctive psychotherapy as well as the abuse potential of MDMA, may delay an FDA approval. The typical regimen in these trials included 3 preparatory psychotherapy sessions followed by once/month dosing sessions (lasting about 8 hours) and using doses of 120-160 mg in a split dose. There were typically 3 monthly dosing sessions, each followed by 3 integrative psychotherapy sessions to help subjects process and understand their experiences during the dosing sessions. In the most recent phase 3 trials, over 70% of subjects no longer met criteria for PTDS compared to 46% of those treated with psychotherapy and placebo alone.⁸⁹ The only approved medications for treating PTSD are two SSRIs, paroxetine and sertraline. These drugs effect only some dimensions of PTSD with only 20-30% achieving a remission level response with these drugs. Thus, MDMA assisted psychotherapy appears to achieve much higher levels of remission and response than has been true for the SSRIs. Since MDMA is not taken continuously, side effects from MDMA tend to be short lived. Side effects have included muscle tightness, nausea, diminished appetite, excessive sweating, feeling cold and dizziness among others. Since MDMA is currently a schedule I drug, it is likely that a rigorous Risk Evaluation Mitigation (REMs) program will be put in place and a limited number of centers and clinicians will be designated to perform MDMA assisted psychotherapy for PTSD. In addition to MDMA, psilocybin-assisted psychotherapy is in phase 3 trials for treating resistant depression but unlikely to be available before late 2025 at the earliest. An argument can be made that there has not been a truly novel antipsychotic since the introduction of clozapine in the US in 1990. All first-generation antipsychotics have been dopamine 2 antagonists and second-generation drugs have involved some ratio of 5HT2 antagonism to D2 blockade. In 2023, the FDA accepted the application of xenomaline/tropsium (KarXT) which may become the first muscarinic M1M4 agonist approved for the treatment of schizophrenia.^82,83 Tropsium is added as a muscarine antagonist to block the peripheral cholinergic effects of a muscarine agonist. Xenomaline/tropsium appears to be effective in treating both positive and negative symptoms of schizophrenia. In a phase 3 study of 407 patients with schizophrenia, xenomaline/tropsium at doses of xenomaline/50 mg/tropsium 20 mg twice daily up to 125 mg/30 mg twice daily was significantly more effective than placebo in treating both and negative symptoms over 5 weeks of treatment. As would be expected, the side effect profile of xenomaline/tropsium is very different that all currently available antipsychotics. There is no risk of EPS as it is not a dopamine antagonist, and xenomaline/tropsium is not associated with significant metabolic effects. The side effects are cholinergic in nature and include constipation, dry mouth, and nausea. A decision is expected in September of 2024. The year 2023 also saw the approval of the first disease modifying drug in the treatment of Alzheimer's disease, lecanemab (Lequembi). While acetylcholinesterase inhibitors and memantine have been available for decades, these drugs modestly improve cognition in Alzheimer's disease patients and do not alter the progressive course of the illness. Lecanemab is an IV monoclonal antibody that targets the removal of beta-amyloid in the brain as well proto-fibrils that are also known to be toxic to neuronal tissue. When given early in the course of the illness, patients treated with Lecanemab showed 27% less decline on some measures of cognition and function than did patients treated with a placebo over 18 months (about 1 and a half years). It is not known whether treatment for longer than 18 months would show lesser or greater decline over time. However, there are simulation studies that suggest that Lecanemab may modestly reduce the number of patients who progress to severe Alzheimer's disease and require institutional care. The standard dose is 10 mg/kg given via IV over one hour every 2 weeks for 18 months. Lecanemab is typically administered in an infusion center so that side effects can be monitored. The most serious side effects of Lecanemab are amyloid related imaging abnormalities (ARIA) that are associated with brain edema and microhemorrhages. ARIA can occur in up to 15% of patients. More common side effects are headache and nausea. While it remains to be seen how useful these new agents will be in clinical practice, they do represent an approach to treating neuropsychiatric disorders that are a notable departure from the pharmacotherapy of the past half century. It seems likely that some patients who have not been able to respond to or tolerate traditional pharmacotherapy will find hope in these new medications.