A randomized controlled study of the effect of ifenprodil on alcohol use in patients with alcohol dependence

Advancements in addressing drug dependence: A review of promising therapeutic strategies and interventions

Substance dependence represents a pervasive global concern within the realm of public health. Presently, it is delineated as a persistent and recurrent neurological disorder stemming from drug-triggered neuroadaptations in the brain's reward circuitry. Despite the availability of various therapeutic modalities, there has been a steady escalation in the mortality rate attributed to drug overdoses. Substantial endeavors have been directed towards the exploration of innovative interventions aimed at mitigating cravings and drug-induced repetitive behaviors. Within this review, we encapsulate the most auspicious contemporary treatment methodologies, accentuating meta-analyses of efficacious pharmacological and non-pharmacological approaches: including gabapentin, topiramate, prazosin, physical exercise regimens, and cerebral stimulation techniques.

Quinolone bioisosteres of phenolic GluN2B-selective NMDA receptor antagonists

Cyclopenta[g]quinolones of type 4 were designed with the aim to bioisosterically replace the phenol of potent GluN2B ligands such as ifenprodil and Ro 25-6981 by the quinolone system and to restrict the conformational flexibility of the aminopropanol substructure in a cyclopentane system. The designed ligands were synthesized in an eight-step sequence starting with terephthalaldehyde (5). Key steps pf the synthesis were the intramolecular Friedel-Crafts acylation of propionic acids 10 to yield the cyclopenta[g]quinolinediones 11 and the Mannich reaction of diketone 11a followed by conjugate addition at the α,β-unsaturated ketone 12a. Although the quinolones 13a, 15a, and 16a contain an H-bond donor group (secondary lactam) as ifenprodil and Ro 25-6981, they show only moderate GluN2B affinity (Ki > 410 nM). However, the introduction of lipophilic substituents at the quinolone N-atom resulted in more than 10-fold increased GluN2B affinity of the benzyl and benzyloxymethyl derivatives cis-13c (Ko = 36 nM) and 13e (Ko = 27 nM). All compounds are selective over the phencyclidine (PCP) binding site of the N-methyl-D-aspartate (NMDA) receptor. The benzyl derivative 13c showed six- and threefold selectivity over σ1 and σ2 receptors, respectively.

Indazole as a Phenol Bioisostere: Structure-Affinity Relationships of GluN2B-Selective NMDA Receptor Antagonists

Negative allosteric modulation of GluN2B subunit-containing NMDA receptors prevents overstimulation, resulting in neuroprotective effects. Since the phenol of prominent negative allosteric modulators is prone to rapid glucuronidation, its bioisosteric replacement by an indazole was envisaged. The key step in the synthesis was a Sonogashira reaction of non-protected iodoindazoles with propargylpiperidine derivatives. Modification of the alkynyl moiety allowed the introduction of several functional groups. The synthesized indazoles showed very high GluN2B affinity but limited selectivity over σ receptors. Molecular dynamics simulations revealed the same molecular interactions with the ifenprodil binding site as the analogous phenols. In two-electrode voltage-clamp experiments, enantiomeric 3-(4-benzylpiperidin-1-yl)-1-(1H-indazol-5-yl)propan-1-ols (S)-10a and (R)-10a displayed higher inhibitory activity than ifenprodil. In contrast to phenolic GluN2B antagonists, the indazoles were not conjugated with glucuronic acid. It can be concluded that the phenol of potent GluN2B antagonists can be replaced bioisosterically by an indazole, retaining the high GluN2B affinity and activity but inhibiting glucuronidation.

Chemical, pharmacodynamic and pharmacokinetic characterization of the GluN2B receptor antagonist 3-(4-phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepine-1,7-diol - starting point for PET tracer development

GluN2B-NMDA receptors play a key role in several neurological and neurodegenerative disorders. In order to develop novel negative allosteric GluN2B-NMDA receptor modulators, the concept of conformational restriction was pursued, i.e. the flexible aminoethanol substructure of ifenprodil was embedded into a more rigid tetrahydro-3-benzazepine system. The resulting tetrahydro-3-benzazepine-1,7-diol (±)-2 (WMS-1410) showed promising receptor affinity in receptor binding studies (K _i = 84 nM) as well as pharmacological activity in two-electrode-voltage-clamp experiments (IC ₅₀ = 116 nM) and in cytoprotective assays (IC ₅₀ = 18.5 nM). The interactions of (R)-2 with the ifenprodil binding site of GluN2B-NMDA receptors were analyzed on the molecular level and the "foot-in-the-door" mechanism was developed. Due to promising pharmacokinetic parameters (logD_7.4 = 1.68, plasma protein binding of 76-77%, sufficient metabolic stability) F-substituted analogs were prepared and evaluated as tracers for positron emission tomography (PET). Both fluorine-18-labeled PET tracers [¹⁸F]11 and [¹⁸F]15 showed high brain uptake, specific accumulation in regions known for high GluN2B-NMDA receptor expression, but no interactions with σ ₁ receptors. Radiometabolites were not observed in the brain. Both PET tracers might be suitable for application in humans.

The metabotropic glutamate receptor 5 as a biomarker for psychiatric disorders

The role of glutamate system in the etiology and pathophysiology of psychiatric disorders has gained considerable attention in the past two decades, including dysregulation of the metabotropic glutamatergic receptor subtype 5 (mGlu5). Thus, mGlu5 may represent a promising therapeutic target for psychiatric conditions, particularly stress-related disorders. Here, we describe mGlu5 findings in mood disorders, anxiety, and trauma disorders, as well as substance use (specifically nicotine, cannabis, and alcohol use). We highlight insights gained from positron emission tomography (PET) studies, where possible, and discuss findings from treatment trials, when available, to explore the role of mGlu5 in these psychiatric disorders. Through the research evidence reviewed in this chapter, we make the argument that, not only is dysregulation of mGlu5 evident in numerous psychiatric disorders, potentially functioning as a disease "biomarker," the normalization of glutamate neurotransmission via changes in mGlu5 expression and/or modulation of mGlu5 signaling may be a needed component in treating some psychiatric disorders or symptoms. Finally, we hope to demonstrate the utility of PET as an important tool for investigating mGlu5 in disease mechanisms and treatment response.

GIRK Channels as Candidate Targets for the Treatment of Substance Use Disorders

Substance use disorders (SUDs) are chronic, lifelong disorders that have serious consequences. Repeated substance use alters brain function. G-protein-activated inwardly rectifying potassium (GIRK) channels are expressed widely in the brain, including the reward system, and regulate neuronal excitability. Functional GIRK channels are identified as heterotetramers of GIRK subunits (GIRK1–4). The GIRK1, GIRK2, and GIRK3 subunits are mainly expressed in rodent brain regions, and various addictive substances act on the brain through GIRK channels. Studies with animals (knockout and missense mutation animals) and humans have demonstrated the involvement of GIRK channels in the effects of addictive substances. Additionally, GIRK channel blockers affect behavioral responses to addictive substances. Thus, GIRK channels play a key role in SUDs, and GIRK channel modulators may be candidate medications. Ifenprodil is a GIRK channel blocker that does not have serious side effects. Two clinical trials were conducted to investigate the effects of ifenprodil in patients with alcohol or methamphetamine use disorder. Although the number of participants was relatively low, evidence of its safety and efficacy was found. The present review discusses the potential of GIRK channel modulators as possible medications for addiction. Therapeutic agents that target GIRK channels may be promising for the treatment of SUDs.

Off-label and investigational drugs in the treatment of alcohol use disorder: A critical review

Compounds known to be successful in the treatment of alcohol use disorder include the aversive agent, Disulfiram, the glutamatergic NMDA receptor antagonist, Acamprosate, and the opioid receptor antagonists, Naltrexone and Nalmefene. Although all four are effective in maintaining abstinence or reduction of alcohol consumption, only a small percentage of patients receive pharmacological treatment. In addition, many other medications have been investigated for their therapeutic potential in the treatment of alcohol use disorder. In this review we summarize and compare Baclofen, Gabapentin, Topiramate, Ondansetron, Varenicline, Aripiprazole, Quetiapine, Clozapine, Antidepressants, Lithium, Neuropeptide Y, Neuropeptide S, Corticotropin-releasing factor antagonists, Oxytocin, PF-05190457, Memantine, Ifenprodil, Samidorphan, Ondelopran, ABT-436, SSR149415, Mifepristone, Ibudilast, Citicoline, Rimonabant, Surinabant, AM4113 and Gamma-hydroxybutyrate While some have shown promising results in the treatment of alcohol use disorder, others have disappointed and should be excluded from further investigation. Here we discuss the most promising results and highlight medications that deserve further preclinical or clinical study. Effective, patient-tailored treatment will require greater understanding provided by many more preclinical and clinical studies.

Phenol-benzoxazolone bioisosteres of GluN2B-NMDA receptor antagonists: Unexpected rearrangement during reductive alkylation with phenylcyclohexanone

Negative allosteric modulators of N-methyl- d-aspartate receptors containing the GluN2B subunit represent promising drug candidates for the treatment of various neurological disorders including stroke, epilepsy, and Parkinson's disease. To increase the bioavailability and GluN2B affinity, the phenol of the potent benzazepine-based inhibitor, WMS-1410 (3), was replaced bioisosterically by a benzoxazolone moiety and the phenylbutyl side chain was conformationally restricted in a phenylcyclohexyl substituent. A four-step, one-pot procedure transformed the oxazolo-benzazepine 7 into the phenylcyclohexyl derivative 11. The same protocol was applied to the methylated analog 12, which unexpectedly led to ring-contracted oxazolo-isoquinolines 18. This rearrangement was explained by the additional methyl moiety in the 8-position inhibiting the formation of the planar intermediate iminium ion with phenylcyclohexanone. The allyl protective group of 11 and 18 was removed with RhCl₃ and HCl to obtain the tricyclic compounds 5 and 19 without substituent at the oxazolone ring. The structures of the rearranged products 18 and 19 were elucidated by X-ray crystal structure analysis. The oxazolo-isoquinoline trans-18 with allyl moiety (K_i  = 89 nM) and the oxazolo-benzazepine 5 without substituent at the oxazolone ring (K_i  = 114 nM) showed GluN2B affinity in the same range as the lead compound 3. In two-electrode voltage clamp measurements, 5 displayed only weak inhibitory activity.

Negative allosteric modulators of NMDA receptors with GluN2B subunit: Alanine-derived benzoxazolone bioisosteres of 2-methyl-3-benzazepine-1,7-diols

Inspired by besonprodil, the phenol of potent negative allosteric modulators of GluN2B-N-methyl-d-aspartate (NMDA) receptors was replaced by a benzoxazolone system. To increase the similarity to the lead compounds, an additional methyl moiety was installed in the 8-position of tricyclic oxazolobenzazepines, resulting in compounds 6. The additional methyl moiety originates from alanine, which was introduced by a Mitsunobu reaction of benzoxazolylethanol 7 with N-triflyl-protected alanine methyl ester. A crucial feature of the synthesis was the protection of the oxazolone ring by an allyl moiety, which was cleaved off at the end of the synthesis by RhCl₃ -catalyzed isomerization. Due to the additional methyl moiety, the intramolecular Friedel-Crafts acylation of acid 10 to afford ketone 11 required careful optimization to minimize the formation of the side product tetrahydroisoquinoline 16. Alkylation or reductive alkylation of secondary amine 13 led to diastereomeric oxazolobenzazepines cis-14 and trans-14, which were separated by flash chromatography. Phenylbutyl derivatives cis-6a and trans-6a revealed twofold higher GluN2B affinity than analog 5a without 8-CH₃ group. The methylated oxazolobenzazepines 6 and 14 did not interact with the phencyclidine binding site of NMDA receptors and σ₂ receptors. However, the σ₁ receptor preferred cis-configured oxazolobenzazepines. The highest σ₁ receptor affinities were obtained for cis-14a (K_i  = 26 nM) and cis-6b (K_i  = 30 nM).

Phenol-Benzoxazolone bioisosteres: Synthesis and biological evaluation of tricyclic GluN2B-selective N-methyl- d-aspartate receptor antagonists

Tricyclic tetrahydrooxazolo[4,5-h]-[3]benzazepin-9-ols 22 were designed as phenol bioisosteres of tetrahydro-3-benzazepine-1,7-diols. Key features of the synthesis are the introduction of the trifluoromethylsulfonyl and allyl protective groups at the heterocyclic N-atoms. Two methods were developed to convert the triflyl-protected ketone 16 into tricyclic alcohols 21 bearing various N-substituents. According to the first method, trifluoromethanesulfinate was removed by K₂ CO₃ . Following the selective reduction of the imino moiety of 17 with NaBH(OAc)₃ afforded the aminoketone 18, which was reductively alkylated and reduced. According to the second method, both the imine and the ketone of the iminoketone 17 were reduced with NaBH₄ to yield the aminoalcohol 20, which was alkylated or reductively alkylated to form tertiary amines 21f-21r. In the last step, the allyl protective group of 21 was removed with RhCl₃ and HCl to obtain oxazolones 22. In receptor binding studies using [³ H]ifenprodil as radioligand ketone, 22m showed the highest GluN2B affinity (K_i  = 88 nM). However, a reduced affinity toward GluN2B subunit-containing N-methyl- d-aspartate (NMDA) receptors was observed for oxazolones 22 compared to bioisosteric 3-benzazepine-1,7-diols. High selectivity of 22m for the ifenprodil binding site of GluN2B-NMDA receptors over the 1-(1-phenylcyclohexyl)piperidine binding site and σ₂ receptors was observed, but only negligible selectivity over σ₁ receptors. In two-electrode voltage clamp experiments, the 4-phenylbutyl derivative 22d (K_i  = 422 nM) demonstrated 80% inhibition of ion flux at a concentration of 1 µM. The differences in GluN2B affinity and inhibitory activity are explained by docking studies. In conclusion, 22d is regarded as a novel scaffold of highly potent GluN1/GluN2B antagonists.

Synthesis of oxazolo-annulated 3-benzazepines designed by merging two negative allosteric NMDA receptor modulators

To improve the metabolic stability and receptor selectivity of ifenprodil (1), the benzoxazolone moiety of besonprodil (2) and the 3-benzazepone moiety of WMS-1410 (3) were merged to obtain oxazolobenzazepines of type 4. The 5-(hydroxyethyl)benzoxazolone 7 representing the first key intermediate was prepared in four steps starting with the 4-(2-hydroxyethyl)phenol (8). Mitsunobu reaction of primary alcohol 7 with N-sulfonylated glycine esters established the necessary side chain. The intramolecular Friedel-Crafts acylation of acid 12a containing the N-tosyl protective group led upon decarbonylation exclusively to the tricyclic tetrahydroisoquinoline 14. Protection of the amino moiety by the stronger electron-withdrawing triflyl group resulted in the desired 3-benzazepine 15 without the formation of analogous isoquinoline. The triflyl protective group was cleaved off by K₂ CO₃ -induced elimination of trifluoromethanesulfinate. In a one-pot three-step procedure, various oxazolobenzazepinediones 15 were obtained, which were reduced to afford the desired secondary alcohols 18.

Ifenprodil for the treatment of methamphetamine use disorder: An exploratory, randomized, double‐blind, placebo‐controlled trial

Aim

No effective pharmacological interventions have been developed for patients with methamphetamine use disorder. Ifenprodil is a blocker of G protein‐activated inwardly rectifying potassium channels, which play a key role in the mechanism of action of addictive substances. We conducted a randomized, double‑blind, exploratory, dose‐ranging, placebo‐controlled trial to examine the clinical efficacy of ifenprodil for the treatment of methamphetamine use disorder.

Methods

Participants were assigned to three groups: placebo, 60 mg/d ifenprodil, or 120 mg/d ifenprodil. The drug administration period was 84 days. The primary outcome was the use or nonuse of methamphetamine during the drug administration period in the placebo group vs 120 mg/d ifenprodil group. We also assessed drug use status, relapse risk based on the Stimulant Relapse Risk Scale (SRRS), drug craving, and methamphetamine in urine as secondary outcomes. We further evaluated drug use status and SRRS subscale scores in patients who were not taking addiction medications during the study.

Results

Ifenprodil did not affect the primary or secondary outcomes. However, the additional analyses showed that the number of days of methamphetamine use during the follow‐up period and scores on the emotionality problems subscale of the SRRS improved in the 120 mg/d ifenprodil group. The safety of ifenprodil was confirmed in patients with methamphetamine use disorder.

Conclusion

The present findings did not confirm the efficacy of ifenprodil for methamphetamine use disorder treatment based on the primary or secondary outcomes, but we found evidence of its safety and efficacy in reducing emotionality problems.

Clinical trial registration

The study was registered at the University Hospital Medical Information Network Clinical Trial Registry (no. UMIN000030849) and Japan Registry of Clinical Trials (no. jRCTs031180080). The main registration site is jRCT (https://jrct.niph.go.jp/).

We conducted an exploratory, randomized, double‐blind, placebo‐controlled trial to investigate the clinical safety and efficacy of ifenprodil for the treatment of methamphetamine use disorder in Japanese patients. Our findings confirmed the safety of ifenprodil, and ifenprodil at the highest dose exerted slight efficacy.

New approved and emerging pharmacological approaches to alcohol use disorder: a review of clinical studies

introduction: The number of medications approved for AUD is small and they generally have limited efficacy. We need new pharmacotherapies for the management of AUD.Areas covered: In this review, the authors aim to synthesise literature for new approved and emerging pharmacotherapies for AUD. Recently approved medications include nalmefene, which was approved in Europe and Australia for the purposes of controlled drinking. Baclofen has also been approved in France but not in other countries. Off label medications including topiramate and gabapentin have received significant attention with multiple RCTs and meta-analyses and have widespread use in several countries including the USA. Several novel medications have emerged over the last decade but further work is required to determine their efficacy and safety for the widespread management of AUD.Expert opinion: Despite significant advances in our understanding of the neurobiological basis of factors that contribute to the development and maintenance of AUD, there have been few new AUD medications approved for almost 20 years. There are many challenges to the development and introduction of new pharmacotherapies for AUD. Strategies for improving the translational pipeline include drug repurposing and utilisation of human acute laboratory models.

Therapeutic potential of targeting G protein-gated inwardly rectifying potassium (GIRK) channels in the central nervous system

G protein-gated inwardly rectifying potassium channels (Kir3/GirK) are important for maintaining resting membrane potential, cell excitability and inhibitory neurotransmission. Coupled to numerous G protein-coupled receptors (GPCRs), they mediate the effects of many neurotransmitters, neuromodulators and hormones contributing to the general homeostasis and particular synaptic plasticity processes, learning, memory and pain signaling. A growing number of behavioral and genetic studies suggest a critical role for the appropriate functioning of the central nervous system, as well as their involvement in many neurologic and psychiatric conditions, such as neurodegenerative diseases, mood disorders, attention deficit hyperactivity disorder, schizophrenia, epilepsy, alcoholism and drug addiction. Hence, GirK channels emerge as a very promising tool to be targeted in the current scenario where these conditions already are or will become a global public health problem. This review examines recent findings on the physiology, function, dysfunction, and pharmacology of GirK channels in the central nervous system and highlights the relevance of GirK channels as a worthful potential target to improve therapies for related diseases.

Ifenprodil Stereoisomers: Synthesis, Absolute Configuration, and Correlation with Biological Activity

Ifenprodil (1) is a potent GluN2B-selective N-methyl-d-aspartate (NMDA) receptor antagonist that is used as a cerebral vasodilator and has been examined in clinical trials for the treatment of drug addiction, idiopathic pulmonary fibrosis, and COVID-19. To correlate biological data with configuration, all four ifenprodil stereoisomers were prepared by diastereoselective reduction and subsequent separation of enantiomers by chiral HPLC. The absolute configuration of ifenprodil stereoisomers was determined by X-ray crystal structure analysis of (1R,2S)-1a and (1S,2S)-1d. GluN2B affinity, ion channel inhibitory activity, and selectivity over α, σ, and 5-HT receptors were evaluated. (1R,2R)-Ifenprodil ((1R,2R)-1c) showed the highest affinity toward GluN2B-NMDA receptors (K_i = 5.8 nM) and high inhibition of ion flux in two-electrode voltage clamp experiments (IC₅₀ = 223 nM). Whereas the configuration did not influence considerably the GluN2B-NMDA receptor binding, (1R)-configuration is crucial for elevated inhibitory activity. (1R,2R)-Configured ifenprodil (1R,2R)-1c exhibited high selectivity for GluN2B-NMDA receptors over adrenergic, serotonergic, and σ₁ receptors.

Absence of methamphetamine-induced conditioned place preference in weaver mutant mice

Aims

G protein‐activated inwardly rectifying potassium (GIRK) channels are related to rewarding effects of addictive drugs. The GIRK2 subunit is thought to play key roles in the reward system. Weaver mutant mice exhibit abnormal GIRK2 function and different behaviors that are caused by several addictive substances compared with wild‐type mice. However, mechanisms of reward‐related alterations in weaver mutant mice remain unclear. The present study investigated changes in the rewarding effects of methamphetamine (METH) in weaver mutant mice.

Methods

The rewarding effects of METH (4.0 mg/kg) were investigated using the conditioned place preference (CPP) paradigm. Extracellular dopamine level in the nucleus accumbens (NAc) was measured by in vivo microdialysis. To identify brain regions that were associated with these changes in rewarding effects, METH‐induced alterations of Fos expression were investigated by immunohistochemical analysis.

Results

Weaver mutant mice exhibited a significant decrease in METH‐induced CPP and dopamine release in the NAc. Methamphetamine significantly increased Fos expression in the posterior NAc (pNAc) shell in wild‐type but not in weaver mutant mice.

Conclusions

Methamphetamine did not induce rewarding effects in weaver mutant mice. The pNAc shell exhibited a significant difference in neuronal activity between wild‐type and weaver mutant mice. The present results suggest that the absence of METH‐induced CPP in weaver mutant mice is probably related to an innate reduction of dopamine and decreased neural activity in the pNAc shell that is partially attributable to the change of GIRK channel function. GIRK channels, especially those containing the GIRK2 subunit, appear to be involved in METH dependence.

Methamphetamine did not induce rewarding effects in weaver mutant mice that possess a mutation in the GIRK2 subunit. The posterior nucleus accumbens shell exhibited a significant difference in neuronal activity between wild‐type and weaver mutant mice.

[Clinical study of GIRK channel inhibitors as candidate medicines for drug dependence]

Recently, topics related to substance dependence and behavioral addiction have been reported through the media. Therapeutic treatment for substance dependence and behavioral addiction is one of the challenges in a clinical practice. This is because there is no therapeutic treatment for a complete cure, and reuses and repetitive hospitalization occur in patients. Therefore, it is an urgent need to develop new treatments for substance dependence and behavioral addiction. In the present review, we outline associations between dependence and G-protein-activated inwardly rectifying potassium (GIRK) channels which we focus on as therapeutic targets, and introduce ongoing clinical study using an inhibitor of GIRK channels. Previous studies including animals and patients have accumulated the results that GIRK channels have a key role for mediating signals from addictive substances. GIRK channels are expressed in various rodent brain regions including the reward system. The activation of G protein-coupled receptors (GPCRs) that activates GIRK channels through G-protein βγ subunits and activated GIRK channels contribute to control of neuronal excitability. Pretreatment with ifenprodil that is one of the GIRK channel blockers suppressed addictive substance-induced behaviors in animals. Ifenprodil is safe and broadly used as a cerebral circulation/metabolism ameliorator that is covered by medical insurance in Japan. The authors reported that ifenprodil treatment for 3 months decreased alcohol use scores in patients with alcohol dependence compared with patients who received the control medication. We currently conduct a clinical trial to investigate the outcomes of ifenprodil treatment for methamphetamine dependence. In the future, we will expand clinical studies using ifenprodil for patients with other substance dependence and behavioral addiction.

Anticraving therapy for alcohol use disorder: A clinical review

Aim

In this review, the author focused on anticraving therapy for alcohol use disorder (AUD) defined by DMS‐5. A comprehensive review was carried out on the available published papers on anticraving drugs for treating AUD patients.

Methods

The author described all drugs with anticraving benefits for treating AUD patients approved by the Food and Drug Administration of the United States (US FDA) and European Medicines Agency of the European Union. Then, the commonly prescribed anticraving drugs and those under development were also described.

Results

The US FDA‐approved anticraving drugs included acamprosate and naltrexone, and those approved by European Medicines Agency were gamma‐hydroxybutyrate and nalmefene. The author also highlighted topiramate, gabapentin, ondansetron, LY196044, ifenprodil, varenicline, ABT‐436, mifepristone, citicoline, and baclofen. The putative mechanisms of action of and the use in clinical practice of those anticraving drugs were also described.

Conclusion

Although slowly developing, the field of anticraving drugs is getting into shape as a promising entity of a pharmaceutical class of drugs. Then, the author addressed on the underused issues of those recommended, and suggested anticraving drugs by the practice guideline of the American Psychiatric Association. The author urges that clinicians should be more “adventurous” in prescribing those promising drugs because benefits of those anticraving drugs are far‐outweighing the possible side effects of anticraving drugs, or the harms of untreated AUD itself.

Prospects for pharmacotherapies to treat alcohol use disorder: an update on recent human studies

PURPOSE OF REVIEW

The aim of this study was to provide an update on medication development efforts for alcohol use disorder (AUD) by reviewing recently published (past 2 years) human studies that evaluated medications' effects on alcohol-related outcomes.

RECENT FINDINGS

Forty-five publications were found suitable for this review. A variety of compounds have been tested in the past 2 years as potential pharmacological options for AUD, including medications that act on multiple targets (topiramate, aripiprazole, quetiapine), calcium channels (gabapentin), gamma-Aminobutyric acid receptors (baclofen, diazepam), glutamate receptors (ifenprodil, memantine, glycine), nicotinic acetylcholine receptors (varenicline, mecamylamine), α1 adrenergic receptors (prazosin, doxazosin), neuroendocrine pathways (oxytocin, a vasopressin receptor 1b antagonist, a ghrelin receptor inverse agonist) and others (samidorphan, ibudilast, N-acetylcysteine, citoline). Important findings and limitations regarding the effects of these medications on alcohol-related outcomes are discussed.

SUMMARY

There is a critical need to increase the armamentarium of medications for AUD. Human laboratory studies may help screen and prioritize promising targets and compounds before running large clinical trials. Given the complexity of AUD and the heterogeneity of afflicted patients, future studies should also investigate potential moderators and predictors of response to each pharmacological intervention.

Study of effects of ifenprodil in patients with methamphetamine dependence: Protocol for an exploratory, randomized, double-blind, placebo-controlled trial

Aims

Pharmacotherapy for methamphetamine dependence has not yet been developed in Japan or elsewhere in the world. Ifenprodil is a blocker of G protein‐activated inwardly rectifying potassium channels that play a key role in the mechanism of action of addictive substances. Our aim is to examine the safety, efficacy, and outcomes of ifenprodil for the treatment of methamphetamine dependence in a randomized, double‐blind, placebo‐controlled trial.

Methods

The recruitment of outpatients with methamphetamine dependence began in January 2018. The patients will be randomized into three arms: placebo, 60 mg/d ifenprodil, or 120 mg/d ifenprodil. Placebo or ifenprodil will be taken for 84 days. We will use Cerocral fine granule 4%^® (ifenprodil tartrate). Follow‐up assessments will be conducted for 84 d after the drug administration period. All of the patients will be assessed by self‐administered questionnaires and urine tests. The primary outcome will be the presence or absence of methamphetamine use during the 84‐day administration period in the 120 mg/d ifenprodil and placebo groups. Secondary outcomes will include the number of days and percentage of days of abstinence from methamphetamine use, positive urine for methamphetamine, relapse risk, and drug craving.

Discussion

This study is the first clinical trial of ifenprodil treatment for methamphetamine dependence and is designed as an intervention test with off‐label drug use. The present study is expected to provide evidence of the effects of ifenprodil treatment on methamphetamine dependence.

Trial registry

This trial was registered in the UMIN clinical trial registry (UMIN000030849; date of registration: January 17, 2018).

This study is the first clinical trial of ifenprodil treatment for methamphetamine dependence and is designed as an intervention test with off‐label drug use. The present study is expected to provide evidence of the effects of ifenprodil treatment on methamphetamine dependence.

A randomized controlled study of the effect of ifenprodil on alcohol use in patients with alcohol dependence

Aim

This prospective, randomized, controlled, rater‐blinded study investigated the effect of G protein‐activated inwardly rectifying potassium (GIRK) channel inhibitor ifenprodil on alcohol use in patients with alcohol dependence.

Methods

The participants were 68 outpatients with alcohol dependence who were assigned to an ifenprodil group (administered 60 mg ifenprodil per day for 3 months) or control group (administered 600 mg ascorbic acid and calcium pantothenate per day for 3 months). The participants completed a questionnaire that included the frequency of alcohol drinking and presence of heavy drinking before the study period (time 1) and 3 months after the start of the study period (time 2). The alcohol use score was calculated using these two items.

Results

Valid data were obtained from 46 participants (25 in the ifenprodil group and 21 in the control group). The alcohol use score at time 2 in the ifenprodil group was significantly lower than that in the control group after adjusting for the score at time 1 and some covariates. The intention‐to‐treat analysis of multiply imputed datasets indicated similar results. Group differences in the frequency of alcohol drinking were significant in the multiply imputed datasets but not in 46 participants. The ifenprodil group had a significantly lower rate of heavy drinking at time 2 than the control group.

Conclusions

This study found an inhibitory effect of ifenprodil on alcohol use in patients with alcohol dependence. The results support the hypothesis that GIRK channel inhibitors ameliorate alcohol dependence.

Trial registry

This trial was registered in the UMIN clinical trial registry (UMIN000006347).

The present prospective, randomized, controlled, rater‐blinded study investigated the effect of G protein‐activated inwardly rectifying potassium (GIRK) channel inhibitor ifenprodil on alcohol use in patients with alcohol dependence. This study found an inhibitory effect of ifenprodil on alcohol use in patients with alcohol dependence. The results support the hypothesis that GIRK channel inhibitors ameliorate alcohol dependence.