Moclobemide poisoning: toxicokinetics and occurrence of serotonin toxicity

Serotonin syndrome controversies: A need for consensus

Serotonin syndrome (SS) is a drug-induced clinical syndrome resulting from increased serotonergic activity in the central nervous system. Although more than seven decades have passed since the first description of SS, it is still an enigma in terms of terminology, clinical features, etiology, pathophysiology, diagnostic criteria, and therapeutic measures. The majority of SS cases have previously been reported by toxicology or psychiatry centers, particularly in people with mental illness. However, serotonergic medications are used for a variety of conditions other than mental illness. Serotonergic properties have been discovered in several new drugs, including over-the-counter medications. These days, cases are reported in non-toxicology centers, such as perioperative settings, neurology clinics, cardiology settings, gynecology settings, and pediatric clinics. Overdoses or poisonings of serotonergic agents constituted the majority of the cases observed in toxicology or psychiatry centers. Overdose or poisoning of serotonergic drugs is uncommon in other clinical settings. Patients may develop SS at therapeutic dosages. Moreover, these patients may continue to use serotonergic medications even if they develop mild to moderate SS due to several reasons. Thus, the clinical presentation (onset, severity, and clinical features) in such instances may not exactly match what toxicologists or psychiatrists observe in their respective settings. They produce considerable diversity in many aspects of SS. However, other experts discount these new developments in SS. Since SS is a potentially lethal illness, consensus is required on several concerns related to SS.

Predicting serotonin toxicity in serotonin reuptake inhibitor overdose

AIMS

We aimed to investigate the frequency of serotonin toxicity following overdose of antidepressants that inhibit serotonin reuptake and the factors that influence the probability of serotonin toxicity occurring.

METHODS

This was a retrospective cohort study of overdoses that included selective serotonin reuptake inhibitors (SSRIs) (70%) and serotonin norepinephrine reuptake inhibitors (SNRIs) (30%) admitted to a tertiary toxicology unit over 23 years. A multivariate mixed effects logistic regression model using NONMEM (7.2.0) was used to determine factors that influenced the probability of serotonin toxicity occurring.

RESULTS

There were 1978 overdoses in 1520 patients; median age 33 y (range: 13-86 years) and 64% female. Median defined daily dose equivalent (DDD) was 15 (1-420). Co-ingestants were taken in 1678/1978 (85%) overdoses: 11 co-ingested the monoamine oxidase-A inhibitor (MAOI) moclobemide, 99 (5%) co-ingested olanzapine, 58 (3%) co-ingested risperidone and 417 co-ingested a benzodiazepine (21%). Serotonin toxicity occurred in 269 overdoses (13.6%). The probability of serotonin toxicity increased slightly per 10 DDD units dose [OR, 1.01; 95% confidence intervals (CIs): 0.93-1.10], increased for an SNRI vs. an SSRI [OR, 1.07; 95% CI: 0.99-1.15], and markedly increased with co-ingestion of moclobemide [OR, 33.12; 95% CI: 7.5-147]. The probability decreased per 10 y age [OR, 0.84; 95% CI: 0.74-0.95], and with co-ingestion of the serotonin 2 A receptor (5-HT_2A) antagonists olanzapine [OR, 0.40; 95% CI: 0.17-0.94] or risperidone [OR, 0.13; 95% CI: 0.02-0.99]. The probability of serotonin toxicity was 12.5% at 1 DDD (therapeutic), 12.7% at 15 DDDs and 19% at 420 DDDs. In overdoses of the median dose of 15 DDDs, co-ingestion of moclobemide increased the probability to 83%, and co-ingestion of olanzapine or risperidone decreased it to 5.5% and 1.8%, respectively.

CONCLUSIONS

Serotonin toxicity is common following SSRI/SNRI overdose. Although dose increases probability, this was only a small effect. Co-ingestion with olanzapine or risperidone reduced the risk 2-6-fold, and moclobemide increased the risk 5-fold.

The serotonin toxidrome: shortfalls of current diagnostic criteria for related syndromes

INTRODUCTION

Serotonin syndrome (toxicity) describes adverse drug effects from toxic amounts of intra-synaptic central nervous system serotonin. A wide range of drugs have been implicated to cause serotonin toxicity, not all justifiably. The plausible agents all have a final common pathway resulting in a substantial increase in central nervous system serotonergic neurotransmission. Serotonin toxicity is characterized by neuromuscular excitation, mental status changes, and autonomic dysregulation. Signs and symptoms represent a spectrum of toxicity (mild to life-threatening) related to increasing serotonin concentrations. As there is no consensus on the threshold for "toxicity" or diagnostic criteria, the true incidence of serotonin toxicity is unknown. The incidence in overdose is easier to quantify and is reasonably common in serotonergic antidepressant overdoses. In a large case series of overdoses, moderate serotonin toxicity occurred in 14% of poisonings with a selective serotonin reuptake inhibitor. While half those ingesting a monoamine oxidase inhibitor in combination with a serotonergic agent in overdose exhibit at least moderately severe serotonin toxicity. In contrast, the incidence of serotonin toxicity in those on therapeutic serotonergic agents appears to be very low.

OBJECTIVES

To provide a narrative review of the current diagnostic criteria, utilizing case reports of fatalities to evaluate how many meet the various diagnostic criteria and propose practical solutions to resolve controversies in diagnosis.

METHODS

A review of serotonin toxicity diagnostic criteria in the English literature was completed by searching Embase and PubMed from January 1990 to July 2021 for the keywords "serotonin syndrome/toxicity" paired with "diagnostic criteria" or "diagnosis." Also, fatal cases of serotonin toxicity identified from a recent systematic review were independently examined to determine what diagnostic criteria were met and whether serotonin toxicity or another cause was most likely.

REVIEW OF DIAGNOSIS CRITERIA

Serotonin toxicity is a clinical diagnosis, four diagnostic criteria (Sternbach, Serotonin Syndrome Scale, Radomski, and Hunter) have been proposed. However, the Serotonin Syndrome Scale has not been validated in patients with serotonin toxicity and only utilized in those on a serotonergic agent. The remaining three criteria are utilized more widely but have undergone little refinement or validation.

REVIEW OF FATAL CASES

Shortfalls with diagnostic criteria can be illustrated by examining case fatalities. Of 55 fatal cases reviewed, 12 (22%) were unlikely to be serotonin toxicity. Sternbach and Radomski criteria were met by 25 (45%), 20 (36%) had insufficient data reported and 10 (18%) met an exclusion criterion. Few had sufficient information reported to determine whether Hunter Criteria were met, with only 13 (24%) documented as meeting the criteria, the remaining 42 (76%) had insufficient data.

RESOLVING SHORTFALLS IN CURRENT DIAGNOSTIC CRITERIA

As serotonin toxicity is a clinical diagnosis, issues arise when basing the diagnosis on symptom criteria alone, without considering whether the drug/s ingested increase central nervous system serotonin or whether there is an alternative diagnosis. This has resulted in case reports and government warnings for drugs that cannot plausibly cause significant serotonin toxicity (e.g., ondansetron and antipsychotics). We propose when assessing for a serotonin toxidrome, both the causative agent(s) and clinical scenario is considered to determine the likelihood of serotonin toxicity. Then the clinical features assessed, those with a moderate to high prior probability (e.g., serotonergic drug-drug interaction, overdose, recent initiation or increase in dose of serotonergic agent/s) could be diagnosed based on the Hunter criteria. However, those with a low probability (e.g., stable therapeutic doses of a serotonergic agent) require more specific and stringent criteria. Finally, we propose a minimum dataset for case reports/series of serotonin toxicity.

CONCLUSIONS

More complete and accurate reporting of serotonin toxicity cases is required in the future, to avoid further misleading associations that are physiologically implausible.

Monoamine oxidase A inhibition by toxic concentrations of metaxalone

Context: Serotonin toxicity is a reported complication associated with both therapeutic use and overdose of metaxalone while on therapeutic doses of serotonergic drugs such as serotonin reuptake inhibitors. Monoamine oxidase A (MAO-A) inhibition by metaxalone has been proposed as the etiology of this toxicity. Metaxalone concentrations reported with cases of serotonin toxicity range from 31 to 61 mcg/ml (140-276 µM). We investigated the effect of metaxalone on MAO-A activity using an in vitro model.Methods: Metaxalone at concentrations ranging from 1.56 to 400 µM were incubated with a proprietary MAO substrate and recombinant human MAO-A for 1 h. After that, an esterase and luciferase were added and luminescence measured. Clorgyline, a known MAO-A inhibitor, was used as a positive control. Luminescence was measured using a Biotek Synergy HT microplate reader.Results: Metaxalone demonstrated significant dose-related inhibition of MAO-A activity. Four-parameter logistic regression analysis demonstrated a strong dose-response relationship at increasing concentrations.Conclusions: Our in vitro model shows that at toxic concentrations similar to those reported in case reports metaxalone shows significant MAO-A inhibition. Clinicians should be aware of this mechanism and understand the potentially lethal interactions metaxalone can have when prescribed with other serotonergic drugs and consider this as a potential cause of serotonin toxicity, especially in overdose scenarios.

The hot patient: acute drug-induced hyperthermia

Drugs can cause dysregulation of the hypothalamic–pituitary–adrenal axis which can result in a rise in core temperature This type of hyperthermia is unresponsive to antipyretics and can be complicated by rhabdomyolysis multi-organ failure and disseminated intravascular coagulation

Organic causes of fever such as infection must be ruled out Syndromes associated with drug-induced fever include neuroleptic malignant syndrome and anticholinergic sympathomimetic and serotonin toxicity

The class of offending drugs as well as the temporal relationship to starting or stopping them assists in differentiating between neuroleptic malignant syndrome and serotonin toxicity

Immediate inpatient management is needed The mainstay of management is stopping the drug and supportive care often in the intensive care unit

Restarting antidepressant and antipsychotic medication after intentional overdoses: need for evidence-based guidance

Intentional drug overdoses with antidepressant and antipsychotic medications are an increasingly common problem. Currently, there is little guidance with regard to reintroduction of these medications after intentional overdoses. We have used published toxicological and pharmacokinetic data to obtain factors which control the recovery from overdoses. From such data, we have proposed guidance regarding their reintroduction, provided there are no adverse effects or contraindications. Tentatively, we suggest that when adverse effects from the overdose are lost, treatment could recommence after a further mean half-life of elimination. Most antidepressant and antipsychotic drugs are metabolized by cytochrome P450 enzymes and, where cytochrome P450 inhibitors are co-ingested, serial plasma concentrations should optimally be obtained in order to assess a suitable time for reintroduction of the psychoactive drugs. We hope the proposals presented will stimulate research and discussion that lead to better guidance for clinicians concerning reintroduction of psychoactive medication after intentional overdose.

Potential Roles of microRNAs in the Regulation of Monoamine Oxidase A in the Brain

Monoamine oxidase A (MAO-A) is an enzyme that regulates the levels of monoamine neurotransmitters, such as serotonin, noradrenaline and dopamine and it has been used as a therapeutic target for depression. However, MAO-A inhibitors, which directly acts on MAO-A protein, have limited use due to their adverse effects. microRNAs (miRNAs) are 18-22 nucleotide long, small non-coding RNAs, which have recently emerged as regulators of protein levels that could potentially be new therapeutic targets for psychiatric disorders. This review article aims to discuss the current status of the treatment for depression with MAO-A inhibitors and the regulatory factors of MAO-A. Further, the review also proposes possible regulatory mechanisms of MAO-A by miRNAs, which leads to better understanding of the pathology of depressive disorders and their potential use as therapeutic agents.

Methylene blue and its analogues as antidepressant compounds

Methylene Blue (MB) is considered to have diverse medical applications and is a well-described treatment for methemoglobinemias and ifosfamide-induced encephalopathy. In recent years the focus has shifted to MB as an antimalarial agent and as a potential treatment for neurodegenerative disorders such as Alzheimer's disease. Of interest are reports that MB possesses antidepressant and anxiolytic activity in pre-clinical models and has shown promise in clinical trials for schizophrenia and bipolar disorder. MB is a noteworthy inhibitor of monoamine oxidase A (MAO-A), which is a well-established target for antidepressant action. MB is also recognized as a non-selective inhibitor of nitric oxide synthase (NOS) and guanylate cyclase. Dysfunction of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) cascade is strongly linked to the neurobiology of mood, anxiety and psychosis, while the inhibition of NOS and/or guanylate cyclase has been associated with an antidepressant response. This action of MB may contribute significantly to its psychotropic activity. However, these disorders are also characterised by mitochondrial dysfunction and redox imbalance. By acting as an alternative electron acceptor/donor MB restores mitochondrial function, improves neuronal energy production and inhibits the formation of superoxide, effects that also may contribute to its therapeutic activity. Using MB in depression co-morbid with neurodegenerative disorders, like Alzheimer's and Parkinson's disease, also represents a particularly relevant strategy. By considering their physicochemical and pharmacokinetic properties, analogues of MB may provide therapeutic potential as novel multi-target strategies in the treatment of depression. In addition, low MAO-A active analogues may provide equal or improved response with a lower risk of adverse effects.

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BACKGROUND

Methylene blue is used in medical practice for various reasons. Recent findings point to a potential interaction with serotonin reuptake inhibitors (SRIs) that could lead to serotonergic toxicity.

OBJECTIVE

To describe the risk of serotonergic toxicity associated with the interaction between methylene blue and SRIs.

DATA SOURCES

Relevant publications were searched systematically via MEDLINE (1946 to March 21, 2013) and Embase (1974 to 2013, week 11) with the following search terms: "methylene blue", "methylthioninium", "monoamine oxidase inhibitors", "serotonin reup-take inhibitors", and "serotonin syndrome". No restrictions were applied in relation to the indication for methylene blue or the language of publication. The reference lists of identified articles were also searched.

STUDY SELECTION AND DATA EXTRACTION

Eighteen case reports and 2 case series were identified for inclusion. To date, no randomized controlled trials have been published.

DATA SYNTHESIS

The first case report indicating suspicion of an interaction between methylene blue and SRIs was published in 2003. Seventeen other case reports describing the same type of interaction have been published since then. The 2 case series provided data from about 325 parathyroidectomies in which methylene blue was used for staining. The 17 patients who experienced central nervous system toxicity were all taking SRIs in the preoperative period.

CONCLUSION

When administered in combination with SRIs, methylene blue may lead to serotonergic toxicity at doses as low as 0.7 mg/kg. Methylene blue would seem to have monoamine oxidase A inhibitory properties. Precautions should be taken to avoid this interaction. [Publisher's translation].

Serotonin Syndrome: Analysis of Cases Registered in the French Pharmacovigilance Database

BACKGROUND

More information would be required for a better understanding of the actual circumstances of serotonin syndrome (SS) occurrence in routine clinical practice.

AIM

The objective of the study was to analyze characteristics of SS French pharmacovigilance reports, especially involved drugs and nature of drug-drug interactions (DDIs).

METHOD

We performed a retrospective analysis of SS registered in the French pharmacovigilance database between January 1, 1985 and May 27, 2013. Only cases whose clinical symptoms fulfilled Sternbach, Radomski, or Hunter SS diagnostic criteria were retained for the analysis.

RESULTS

Most of the 125 (84.0%) analyzed cases were associated with a recent change in a serotonergic drug (introduction, increasing the dose or overdose). Antidepressants were the most often involved serotonergic drugs, mostly serotonin reuptake inhibitors (SRIs, 42.1%) and to a lesser extent serotonin-noradrenalin reuptake inhibitors (9.1%, mainly venlafaxine), tricyclic antidepressants (8.6%, mainly clomipramine), and some monoamine oxidase inhibitors (6.2%, mainly moclobemide). Nonpsychotropic medications were also involved, generally opioids (14.8%, mainly tramadol). Most of the cases (59.2%) resulted from pharmacodynamic DDIs, most often involving SRIs + opioids (mostly paroxetine + tramadol). However, SS also occurred with a single serotonergic drug in a significant number of cases (40.8%), most often SRIs (mainly fluoxetine) or venlafaxine at usual doses. Lastly, a major pharmacokinetic DDI could have played a role in 1/5 (20.8%) of cases.

CONCLUSIONS

This is the first study about SS based on a large pharmacovigilance database and published in English. Our results reveal not only the frequent involvement of antidepressants and tramadol, the importance of DDIs (both pharmacodynamic and pharmacokinetic), but also the significant risk of SS even with a single serotonergic drug used at normal dose.

Mild serotonin syndrome: A report of 12 cases

Serotonin syndrome (SS) is an under diagnosed and under reported condition. Mild SS is easily overlooked by physicians. Every patient with mild SS is a potential candidate for developing life-threatening severe SS because of inadvertent overdose or the addition of the second serotonergic drug. Herein, we describe 12 patients with mild SS observed over 12 months in neurology outpatient clinic. It is a retrospective chart review of 12 consecutive patients who had hyperreflexia with tremor (defined as mild SS Hunter's criteria) and had received serotonergic agents in the past 5 weeks. Only four patients (33%) reported tremor as a presenting or main feature. The presenting features in another eight patients were: Dizziness, generalized body pain, headache, and seizure. Five patients responded to the removal of the offending agents and got a complete response in 2-7 days. There were no or minimal responses in another seven patients to the removal of the serotonergic drugs. Cyproheptadine was started in these patients, at the dose of 8 mg three times daily. Response started within 1-3 days of initiation of the drug and the complete responses were noted in 5-14 days. There were no side effects from cyproheptadine in any patient. We suggest that any patient on serotonergic drug developing new symptoms should be examined for the presence of tremor, hypertonia, hyperreflexia, and clonus to look for mild SS. In addition, every patient on any serotonergic drug should be examined for the presence of mild SS before escalating the dose or before adding a new one.

Serotonin toxicity

Serotonin toxicity is a potentially life-threatening condition associated with a range of psychotropic medications, co-administration of specific combinations of agents and overdose of certain drugs. It is associated with a wide diversity of clinical signs and symptoms, including cognitive, autonomic and somatic effects, as well as serious complications, including possible death. Diagnosis is often challenging and requires a high index of suspicion. Differential diagnosis includes syndromes such as neuroleptic malignant syndrome. Management depends on the causal agent and urgency of clinical presentation. Treatment may involve discontinuing the causal agent and providing supportive measures, or emergency intervention to preserve vital functions (airway, breathing, circulation), amongst other measures. Further research is needed to clarify the incidence of serotonin toxicity, issues related to differential diagnosis, optimal management of the condition, and treatment of mood problems following serotonin toxicity.

Antidepressant overdose-induced seizures

Treating patients with psychiatric problems can present numerous challenges for clinicians. The deliberate self-ingestion of antidepressants is one such challenge frequently encountered in hospitals throughout the United States. This review focuses on 1) the classes of antidepressants, their pharmacologic properties, and some of the proposed mechanism(s) for antidepressant overdose-induced seizures; 2) the evidence for seizures caused by antidepressants in overdose; 3) management strategies for patients who have intentionally or unintentionally overdosed on an antidepressant, or who have experienced an antidepressant overdose-induced seizure.

Antidepressant drugs

Therapeutic Reviews aim to provide essential independent information for health professionals about drugs used in palliative and hospice care. Additional content is available on www.palliativedrugs.com. Country-specific books (Hospice and Palliative Care Formulary USA, and Palliative Care Formulary, British and Canadian editions) are also available and can be ordered from www.palliativedrugs.com. The series editors welcome feedback on the articles (hq@palliativedrugs.com).

Antidepressant overdose-induced seizures

Antidepressants are the most commonly prescribed class of medications in the United States. The clinician should be mindful of the many antidepressants that can produce seizures following an accidental exposure or an overdose. A broader understanding of the seizure potential of antidepressants, combined with the ability to recognize individuals at risk for a seizure after an overdose, can aid clinicians in determining the need for inpatient monitoring, and help facilitate their treatment decisions.

CNS toxicity involving methylene blue: the exemplar for understanding and predicting drug interactions that precipitate serotonin toxicity

Methylene blue has only recently been noted to cause severe central nervous system toxicity. Methylene blue is used for various conditions, including, intravenously, in methemoglobinemia, vasoplegia and as an aid to parathyroidectomy (at doses of 1-7.5 mg kg(-1)). This review of the current evidence concludes that 13 of 14 of the reported cases of CNS toxicity were serotonin toxicity that met the Hunter Serotonin Toxicity Criteria. That has important preventative and treatment implications. Serotonin toxicity is precipitated by the monoamine oxidase inhibitor (MAOI) property of methylene blue interacting with serotonin reuptake inhibitors. Serotonin toxicity is reviewed, using the lessons inherent in the methylene blue story and experience, to illustrate how the mechanisms and potency of serotonergic drugs interact to determine severity. Recent human data showed that an intravenous dose of only 0.75 mg kg(-1) of methylene blue produced a peak plasma concentration of 500 ng ml(-1) (1.6 µM), indicating that the concentration in the central nervous system reaches a level that inhibits monoamine oxidase A. That is consonant with the actual occurrence of severe serotonin toxicity in humans at the dose of only 1 mg kg(-1). It seems that all proposed uses of methylene blue entail levels that block monoamine oxidase, so cessation of serotonin reuptake inhibitors should be very carefully considered before using methylene blue.

Risk of severe serotonin toxicity following co-administration of methylene blue and serotonin reuptake inhibitors: an update on a case report of post-operative delirium

In a previous case report, published in this journal, we described a postoperative delirium in a patient during recovery from parathyroidectomy. We noted that the delirium resembled serotonin toxicity and that the patient had been taking paroxetine until 2 days before surgery. We offered several tentative explanations for this event, including an adverse interaction between paroxetine and other agent(s) used in the course of the anaesthesia. Recent developments in characterisation of serotonin toxicity have prompted us to re-examine the clinical details surrounding this life-threatening event. It is now known to be important that the patient was given methylene blue, pre-operatively, to enable visualisation of the parathyroid glands. Methylene blue has been found to be a potent inhibitor of monoamine oxidase (MAO), and several cases of serotonin toxicity have been reported recently following its administration. All these cases are consistent with the well-known risk of serotonin toxicity when drugs that augment serotonergic transmission are given in combination with an MAO inhibitor. Methylene blue is used in a variety of surgical settings as well as for treatment of various types of hypotensive shock and methemoglobinaemia. It is also being studied for treatment of Alzheimer's disease and malaria. In this paper, we outline the pharmacology of methylene blue and the aetiology of serotonin toxicity to help prevent further unintentional co-administration of drugs that risk precipitating this life-threatening drug interaction.

Triptans, serotonin agonists, and serotonin syndrome (serotonin toxicity): a review

The US Food and Drug Administration (FDA) have suggested that fatal serotonin syndrome (SS) is possible with selective serotonin reuptake inhibitors (SSRIs) and triptans: this warning affects millions of patients as these drugs are frequently given simultaneously. SS is a complex topic about which there is much misinformation. The misconception that 5-HT1A receptors can cause serious SS is still widely perpetuated, despite quality evidence that it is activation of the 5-HT2A receptor that is required for serious SS. This review considers SS involving serotonin agonists: ergotamine, lysergic acid diethylamide, bromocriptine, and buspirone, as well as triptans, and reviews the experimental foundation underpinning the latest understanding of SS. It is concluded that there is neither significant clinical evidence, nor theoretical reason, to entertain speculation about serious SS from triptans and SSRIs. The misunderstandings about SS exhibited by the FDA, and shared by the UK Medicines and Healthcare products Regulatory Agency (in relation to methylene blue), are an important issue with wide ramifications.

Serotonin toxicity caused by moclobemide too soon after paroxetine-selegiline

Serotonin toxicity is an iatrogenic complication of serotonergic drug therapy. It is due to an overstimulation of central and peripheral serotonin receptors that lead to neuromuscular, mental and autonomic changes. Moclobemide is a reversible inhibitor of monoamine oxidase (MAO)-A, selegiline is an irreversible selective inhibitor of MAO-B, and paroxetine is a selective serotonin reuptake inhibitor. Combined use of these agents is known to cause serotonin toxicity. A 53-year-old woman had been treated with paroxetine and selegiline. After moclobemide was prescribed in place of paroxetine without a washout period, she quickly developed confusion, agitation, ataxia, diaphoresis, tremor, mydriasis, ocular clonus, hyperreflexia, tachycardia, moderately elevated blood pressure and high fever, symptoms that were consistent with serotonin toxicity. Discontinuation of the drugs, hydration and supportive care were followed by remarkable improvement of baseline status within 3 days. This case demonstrates that serotonin toxicity may occur even with small doses of paroxetine, selegiline and moclobemide in combination. Physicians managing patients with depression must be aware of the potential for serotonin toxicity and should be able to recognize and treat or, ideally, anticipate and avoid this pharmacodynamically-mediated interaction that may occur between prescribed drugs.

Drug-induced serotonin syndrome: a review

Serotonin syndrome, or serotonin toxicity (ST), is a clinical condition that occurs as a result of an iatrogenic drug-induced increase in intrasynaptic serotonin levels primarily resulting in activation of serotonin(2A) receptors in the central nervous system. The severity of symptoms spans a spectrum of toxicity that correlates with the intrasynaptic serotonin concentration. Although numerous drugs have been implicated in ST, life-threatening cases generally occur only when monoamine oxidase inhibitors are combined with either selective or nonselective serotonin re-uptake inhibitors. The triad of clinical features consists of neuromuscular hyperactivity, autonomic hyperactivity and altered mental status, which may present abruptly and progress rapidly. The awareness of ST is crucial not only in avoiding the unintentional lethal combination of therapeutic drugs but also in recognizing the clinical picture when it occurs so that treatment can be promptly initiated. In this review, the pathophysiology, clinical features, implicated drugs, diagnosis and treatment of ST are discussed.

Serotonin toxicity: a practical approach to diagnosis and treatment

Excess serotonin in the central nervous system leads to a condition commonly referred to as the serotonin syndrome, but better described as a spectrum of toxicity - serotonin toxicity. Serotonin toxicity is characterised by neuromuscular excitation (clonus, hyperreflexia, myoclonus, rigidity), autonomic stimulation (hyperthermia, tachycardia, diaphoresis, tremor, flushing) and changed mental state (anxiety, agitation, confusion). Serotonin toxicity can be: mild (serotonergic features that may or may not concern the patient); moderate (toxicity which causes significant distress and deserves treatment, but is not life-threatening); or severe (a medical emergency characterised by rapid onset of severe hyperthermia, muscle rigidity and multiple organ failure). Diagnosis of serotonin toxicity is often made on the basis of the presence of at least three of Sternbach's 10 clinical features. However, these features have very low specificity. The Hunter Serotonin Toxicity Criteria use a smaller, more specific set of clinical features for diagnosis, including clonus, which has been found to be more specific to serotonin toxicity. There are several drug mechanisms that cause excess serotonin, but severe serotonin toxicity only occurs with combinations of drugs acting at different sites, most commonly including a monoamine oxidase inhibitor and a serotonin reuptake inhibitor. Less severe toxicity occurs with other combinations, overdoses and even single-drug therapy in susceptible individuals. Treatment should focus on cessation of the serotonergic medication and supportive care. Some antiserotonergic agents have been used in clinical practice, but the preferred agent, dose and indications are not well defined.

Urinary serotonin level is associated with serotonin syndrome after moclobemide, sertraline, and citalopram overdose

INTRODUCTION

Altered mental status, autonomic dysfunction, and neuromuscular abnormalities are a characteristic triad of serotonin syndrome. No laboratory tests confirm the diagnosis of serotonin syndrome.

CASE REPORT

A 35-year-old woman took moclobemide, sertraline, and citalopram in a suicide attempt. She was conscious with mild tachycardia, hypertension, and tachypnea one hour after ingestion. In the second hour after ingestion diaphoresis, mydriasis, horizontal nystagmus, trismus, hyperreflexia, clonus, and tremor appeared. She became agitated and unresponsive. In the third hour after ingestion she became comatose and hyperthermic. She was anesthetized, paralyzed, intubated, and ventilated for 24 hours. Serum moclobemide, sertraline, and citalopram levels were above therapeutic levels. The serum serotonin level was within normal limits and the urinary 5-hydroxyindoleacetic acid:creatinine ratio was below the average daily value. The urinary serotonin:creatinine ratio was increased on arrival (1 mg/g).

DISCUSSION AND CONCLUSION

The urinary serotonin level is increased in serotonin syndrome due to a monoamine oxidase inhibitor and selective serotonin-reuptake inhibitors overdose. It is possible that urinary serotonin concentration could be used as a biochemical marker of serotonin syndrome.

High-performance liquid chromatographic method for the determination of moclobemide and its two major metabolites in human plasma

A selective, sensitive, and simple high-performance liquid chromatographic (HPLC) method was developed for the determination of moclobemide and its two major metabolites, Ro 12-5637 and Ro 12-8095, in human plasma. Sample preparation (0.5 ml of plasma) involved solid-phase extraction (SPE) using Speedisk H(2)O-Philic DVB columns. Separations were performed on a Waters XTerra RP18 column (5 microm, 150 mm x 4.6 mm). The mobile phase consisted of 10 mM KH(2)PO(4) with 1% triethylamine (pH 3.9) and acetonitrile (83:17, v/v), and a flow-rate was 1.2 ml/min. The total run time was 13 min. UV detection was performed at 240 nm. Mean absolute recoveries were > or =90% and the limit of quantification (LOQ) for all analytes was 0.02 mg/l. Calibration curves were linear (r>0.995) over a wide range of the analyte concentrations in plasma; thus, the method is suitable for different clinical studies when large variations in the drug/metabolites concentrations are observed. During a 5-day assay validation procedure the accuracy and precision were tested and proven (relative errors (RE)< or =13%; intra-day coefficient of variation (CV)< or =7%; inter-day CV< or =13%). Many drugs frequently used in the target patient population were evaluated for potential interference in order method selectivity to be ensured. The assay has been used in a clinical pharmacokinetic study to assess steady-state pharmacokinetics of moclobemide and two metabolites in depressive patients on mono- and combined therapy.

A review of serotonin toxicity data: implications for the mechanisms of antidepressant drug action

Data now exist from which an accurate definition for serotonin toxicity (ST), or serotonin syndrome, has been developed; this has also lead to precise, validated decision rules for diagnosis. The spectrum concept formulates ST as a continuum of serotonergic effects, mediated by the degree of elevation of intrasynaptic serotonin. This progresses from side effects through to toxicity; the concept emphasizes that it is a form of poisoning, not an idiosyncratic reaction. Observations of the degree of ST precipitated by overdoses of different classes of drugs can elucidate mechanisms and potency of drug actions. There is now sufficient pharmacological data on some drugs to enable a prediction of which ones will be at risk of precipitating ST, either by themselves or in combinations with other drugs. This indicates that some antidepressant drugs, presently thought to have serotonergic effects in animals, do not exhibit such effects in humans. Mirtazapine is unable to precipitate serotonin toxicity in overdose or to cause serotonin toxicity when mixed with monoamine oxidase inhibitors, and moclobemide is unable to precipitate serotonin toxicity in overdose. Tricyclic antidepressants (other than clomipramine and imipramine) do not precipitate serotonin toxicity and might not elevate serotonin or have a dual action, as has been assumed.

Differentiation of hippocampal stem cells into functional neurons: evolving our understanding of monoamine oxidase-A inhibition

Depression affects many millions of people worldwide and much is still unknown with respect to the mode of action of antidepressant drugs. The hippocampus has been associated with many psychiatric disorders, including clinical depression. Recently, stem cells have also been shown to reside within discrete regions of the hippocampus and can differentiate under a variety of conditions into neural cells. In this issue, Chiou et al. have elegantly demonstrated that cells isolated from the rat hippocampus, and treated with the antidepressant moclobemide, may be differentiated in vitro into neural cells exhibiting features to those of serotoninergic neurons. They have also suggested that this process was mediated, in part, through the expression of specific antiapoptotic genes (Bcl-2 and Bcl-XL) and via activation of extracellular-regulated kinase. This work raises the attractive possibility that the use of antidepressants, such as moclobemide, may exert neuroprotective and potentially neurogenerative effects not just in vitro, but also in vivo, through the selected differentiation of stem cells into functional neurons. The exact mechanisms by which such antidepressants differentiate neural stem cells still remains to be fully elucidated.

A systematic review of the serotonergic effects of mirtazapine in humans: implications for its dual action status

A systematic review of published work concerning mirtazapine was undertaken to assess possible evidence of serotonergic effects or serotonin toxicity (ST) in humans, because drug toxicity and interaction data from human over-doses is an useful source of information about the nature and potency of drug effects. There is a paucity of evidence for mirtazapine having effects on any indicator of serotonin elevation, which leads to an emphasis on ST as an important line of evidence. Mirtazapine is compared with its analogue mianserin, and other serotonergic drugs. Although mirtazapine is referred to as a dual-action 'noradrenergic and specific serotonergic drug' (NaSSA) little evidence to support that idea exists, except from initial microdialysis studies in animals showing small effects; those have not subsequently been replicated or substantiated by independent researchers. Also, new data indicate its affinity for Alpha 2 adrenoceptors is not different to mianserin. It appears to exhibit no serotonergic symptoms or toxicity in over-dose by itself, nor is there evidence that it precipitates ST in combination with monoamine oxidase inhibitors, as would be expected if it raises intra-synaptic serotonin levels. Mirtazapine has no demonstrable serotonergic effects in humans and there is insufficient evidence to designate it as a dual-action drug.

The pathophysiology of serotonin toxicity in animals and humans: implications for diagnosis and treatment

Serotonin toxicity (or serotonin syndrome) has become an increasingly common and important clinical problem in medicine over the last 15 years with the introduction of many new antidepressants that can cause increased levels of serotonin (5-HT) in the central nervous system (CNS). Severe and life-threatening cases are almost exclusively a result of combinations of antidepressants (usually monoamine oxidase inhibitors and selective serotonin reuptake inhibitors). Unfortunately, the term serotonin syndrome has a number of quite different meanings, and many people writing on this subject have failed to differentiate them. This has led to false conclusions regarding the 5-HT receptor subtypes responsible for the life-threatening effects in animal and human toxicity, and suggestions of ineffective treatment strategies. This review primarily addresses the serotonin receptor subtypes that underlie the clinical manifestations of excess CNS serotonin in humans and animals, and their implications for diagnosis and treatment. More specific diagnostic criteria for serotonin toxicity are required to identify situations when specific antidotes are likely to be useful. However, the mainstay of treatment of severe cases is good supportive care and early intubation and paralysis in life-threatening serotonin toxicity.

A chronopharmacological diagnostic test and treatment for bipolar disorder and depression: Nitric oxide release during sleep causes it to become depressogenic in a subset of patients

In some patients sleep can have a depressogenic effect and sleep reduction can result in mania. The hypothesis on which this model is based postulates that it is nitric oxide release during sleep that causes it to become depressogenic in a subset of patients. That subset is comprised of patients with genetic polymorphisms in nitric oxide genes and/or in serotonin and melatonin genes. The nature of the dynamic equilibrium between nitric oxide, on the one hand, and serotonin and melatonin, on the other, determines whether or not sleep is likely to have a depressogenic effect. Changes throughout the sleep cycle thereby impart a chronological factor to the dynamic equilibrium. Other writers have postulated, but not defined, a certain so-called "critical period" during the sleep cycle when sleep can become particularly depressogenic. This model assumes that in fact there is such a critical period and that it is stage IV sleep. In addition to the chronological influences on the dynamic equilibrium, the aging process also exerts an influence. The increased sleep fragmentation associated with the aging process causes stage IV sleep to become increasingly more depressogenic because of a concept called delta rebound. Delta rebound results in deeper sleep intensity. It is associated with increased nitric oxide production and the concomitant serotonin suppression that is associated with it. The chronopharmacological test that is proposed challenges the dynamic equilibrium between nitric oxide, on the one hand, and serotonin and melatonin on the other. It consists of melatonin taken at bedtime and the antidepressant moclobemide, taken as close to the onset of stage IV sleep as possible. If there is a noticeable lessening of depressive symptoms the following morning, then drug treatments that increase serotonin and/or melatonin are appropriate and drugs that suppress or block serotonin or melatonin, or that increase nitric oxide, are not.

A chronopharmacological preventive treatment for sleep-related migraine headaches and chronic morning headaches: Nitric oxide supersensitivity can cause sleep-related headaches in a subset of patients

Frequent and recurrent migraine headaches can, over time, pose the additional risks of stroke, brain damage, heart failure and attention deficit. This is why prevention should always be a part of the treatment. Nitric oxide supersensitivity is the hypothesis upon which this model is based. Its role in causing migraine headaches and chronic morning headaches can be triggered by both normal and abnormal characteristics of the sleep cycle and more specifically by the release of nitric oxide that occurs towards the end of the sleep cycle. Stress and the age-related loss of sleep continuity, together with the corresponding increase in cortisol levels, potentiate delta rebound. Delta rebound results in deeper sleep intensity. It is associated with increased nitric oxide production. Increased delta rebound then causes an increase in the amount and duration of nitric oxide release at night. Migraineurs are susceptible to migraine headaches because they are supersensitive to nitric oxide. The diurnal pattern of the incidence of sleep-related headaches in a subset of the general population is caused by the effect of nitric oxide supersensitivity during the sleep cycle. The proposed treatment is for both sleep-related migraine headaches and chronic morning headaches. It consists of melatonin and moclobemide taken during the night, close the end of the sleep cycle so as to achieve the maximum concentrations. Both melatonin and moclobemide affect three important aspects of sleep-related headaches: nitric oxide supersensitivity, stress system dysfunction and sleep pathology. Both melatonin and moclobemide have demonstrated effectiveness in preventing migraine headaches. Additionally, both melatonin and moclobemide are compatible with most of the other therapeutic agents used to prevent migraine headaches and with at least 1 therapeutic agent that is used to treat migraine headaches.

Antidepressants and seizures: emphasis on newer agents and clinical implications

Seizures are a known, relatively rare, consequence of antidepressant treatment. Risk estimates vary depending on the study, source of data and patient population, predisposed vs. nonpredisposed. For newer antidepressants (e.g. selective serotonin reuptake inhibitors, bupropion, mirtazepine, etc.), the risk is generally considered to be low (0.0%-0.4%) and not very different from the incidence of first seizure in the general population (0.07%-0.09%). Risk with tricyclic antidepressants at effective therapeutic doses is relatively high (0.4% to 1-2%). Seizure following overdose is a significant and relatively frequent event for some antidepressants. Patients being considered for antidepressant treatment should be screened for predisposition to seizures. Predisposed patients should receive antidepressants cautiously. The seizure potential of antidepressants in patients without a predisposition is low, especially for newer antidepressants. Seizure risk, along with other drug-related considerations, e.g. weight gain, sexual dysfunction and sedation, should be considered when prescribing an antidepressant.

Monoamine oxidase inhibitors, opioid analgesics and serotonin toxicity

Toxicity resulting from excessive intra-synaptic serotonin, historically referred to as serotonin syndrome, is now understood to be an intra-synaptic serotonin concentration-related phenomenon. Recent research more clearly delineates serotonin toxicity as a discreet toxidrome characterized by clonus, hyper-reflexia, hyperthermia and agitation. Serotonergic side-effects occur with serotonergic drugs, and overdoses of serotonin re-uptake inhibitors (SRIs) frequently produce marked serotonergic side-effects, and in 15% of cases, moderate serotonergic toxicity, but not to a severe degree, which produces hyperthermia and risk of death. It is only combinations of serotonergic drugs acting by different mechanisms that are capable of raising intra-synaptic serotonin to a level that is life threatening. The combination that most commonly does this is a monoamine oxidase inhibitor (MAOI) drug combined with any SRI. There are a number of lesser-known drugs that are MAOIs, such as linezolid and moclobemide; and some opioid analgesics have serotonergic activity. These properties when combined can precipitate life threatening serotonin toxicity. Possibly preventable deaths are still occurring. Knowledge of the properties of these drugs will therefore help to ensure that problems can be avoided in most clinical situations, and treated appropriately (with 5-HT(2A) antagonists for severe cases) if they occur. The phenylpiperidine series opioids, pethidine (meperidine), tramadol, methadone and dextromethorphan and propoxyphene, appear to be weak serotonin re-uptake inhibitors and have all been involved in serotonin toxicity reactions with MAOIs (including some fatalities). Morphine, codeine, oxycodone and buprenorphine are known not to be SRIs, and do not precipitate serotonin toxicity with MAOIs.

QTc abnormalities in deliberate self-poisoning with moclobemide

BACKGROUND

Several medications have been found to prolong the QT interval in overdose. This can predispose to torsade de pointes-type ventricular tachycardia.

AIMS

To analyse the effects of moclobemide deliberate self-poisoning on the length of both QT and corrected QT (QTc) intervals.

METHODS

Electrocardiograms (ECG) of all patients presenting to a regional toxicology service with moclobemide ingestion were reviewed. Cases where a cardiotoxic agent was coingested were excluded. QT and QTc parameters were compared with a comparison group of patients ingesting paracetamol or benzodiazepines.

RESULTS

Of 75 patients where ECG were available, the median ingested dose was 4.5 g (interquartile range (IQR): 2.4-7.5; range: 0.6-18 g) and the median age was 34 years (IQR: 26-44). The mean QT interval was 415 ms (standard deviation (SD): 51 ms) with a mean QTc of 459 ms (SD: 44 ms), and were prolonged compared with the comparison group. Twelve female patients had a QTc > 500 ms and in seven of these causality was established based on a pre- or post-ECG with a QTc < 500 ms. Only 10% of the moclobemide cases had a heart rate (HR) > 100 beats per minute, making overcorrection of HR by Bazett's formula an unlikely cause of the findings. No cardiac arrythmias were observed other than one case of first-degree heart block.

CONCLUSIONS

Moclobemide prolongs the QT and QTc intervals in overdose and a 12-lead ECG should be done on all moclobemide deliberate self-poisonings. Continuous cardiac monitoring for what is otherwise a relatively benign overdose would appear to be an inappropriate use of resources but can be considered in patients with a QTc > 500 ms or with known risks for QT prolongation.