Fatal serotonin syndrome: a systematic review of 56 cases in the literature

Content analysis of Reddit posts about coadministration of selective serotonin reuptake inhibitors and psilocybin mushrooms

RATIONALE

Treatments with the serotonergic psychedelic psilocybin are being investigated for multiple neuropsychiatric disorders. Because many patients with these disorders use selective serotonin reuptake inhibitors (SSRIs), understanding interactions between psilocybin and SSRIs is critical for evaluating the safety, efficacy, and scalability of psilocybin-based treatments. Current knowledge about these interactions is limited, as most clinical psilocybin research has prohibited concomittant SSRI use.

OBJECTIVES

We aimed to explore potential interactions between psilocybin and SSRIs by characterizing peoples' real-world experiences using psilocybin mushrooms and SSRIs together.

METHODS

We conducted a systematic search of Reddit for posts describing psilocybin mushroom and SSRI coadministration. We identified 443 eligible posts and applied qualitative content analysis to each.

RESULTS

8% of posts reported negative physical or psychological effects resulting from coadministration. These included 13 reports that may reflect serotonin toxicity, and 1 concerning for a psychotic/manic episode. 54% of posts described reduced intensity of the acute psilocybin experience, but 39% reported unchanged intensity with SSRI coadministration.

CONCLUSIONS

Psilocybin's interactions with SSRIs are likely complex and may depend on multiple factors. Prospective studies are needed to evaluate whether psilocybin treatments are reliably safe and effective in the setting of SSRI use.

Management of serotonin syndrome (toxicity)

Serotonin syndrome (toxicity), resulting from an excessive accumulation of serotonin in the central nervous system, it can occur due to various factors such as the initiation of medication, overdose or drug interactions. Diagnosing serotonin toxicity presents challenges as there are no definitive criteria. This review delves into the pathophysiology, incidence, clinical assessment and management of serotonin toxicity, stressing the significance of promptly recognizing and managing severe cases. Diagnosis relies primarily relies on clinical assessment due to the absence of specific laboratory tests. The Hunter Serotonin Toxicity criteria are commonly utilized but have only been validated in the overdose setting. Assessing the severity of toxicity is crucial for guiding management decisions. Supportive care, discontinuation of causative agents and symptomatic treatment are prioritized in management. Mild toxicity often requires withdrawal or reduction of the serotonergic agent, while more severe toxicity requires more aggressive resuscitative and supportive care. Severe serotonin toxicity characterized by hyperthermia and rigidity requires aggressive supportive measures, including benzodiazepines, intubation, paralysis and active cooling. Animal studies suggest potential benefits of 5-HT2A receptor antagonists in preventing hyperthermia and fatalities, but only at high doses. Their clinical effectiveness remains uncertain, and evidence is predominately from case series and case reports. Although commonly used, serotonin antagonists like cyproheptadine lack conclusive evidence of efficacy. Other serotonin antagonists such as chlorpromazine and olanzapine have been explored but evidence is limited to case reports. Hence, the cornerstone of treating severe cases does not lie in 'antidote' administration or even diagnosis but in effective early resuscitative and supportive care.

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.

A Case Series on Serotonin Syndrome from Concomitant use of linezolid With Methadone, Buprenorphine, and/or Dextroamphetamine

Background and Objectives: The risk of serotonin syndrome (SS), especially when linezolid is used concomitantly with methadone, buprenorphine, and/or dextroamphetamine, remains widely unstudied and may limit the options for antimicrobial therapy in these patient populations. Methods: We reviewed all adult encounters on linezolid with concomitant methadone, buprenorphine, and/or dextroamphetamine from April 2016 to June 2022. The primary outcomes included characterizing prescribing preferences and prevalence of confirmed and possible serotonin syndrome using ICD-10 diagnosis codes, cyproheptadine administration, and electronic medical record chart review using the Hunter Serotonin Toxicity Criteria. Results: Overall, 194 encounters were evaluated. 16.5%, 17.8%, and 7.1% were on high dose methadone, buprenorphine, and dextroamphetamine, respectively. Mean duration of overlap with linezolid was 4.6, 3.3, and 7 days respectively. One confirmed and two possible cases of serotonin syndrome were identified. Conclusion: Linezolid may be considered in patients who are concomitantly on methadone, buprenorphine, and/or dextroamphetamine. In our analysis of 194 encounters, one definitive case and two possible cases of SS were identified. Additional real-world studies are necessary to identify if exposure and/or duration may be correlated with an increased risk of serotonin syndrome.

Cyproheptadine in serotonin syndrome: A retrospective study

Objective

Serotonin syndrome (SS) is an iatrogenic life-threatening condition caused by serotonergic agents. The treatment for SS involves the administration of a serotonin antagonist (cyproheptadine). However, the dosing schedule for cyproheptadine is not uniform in the literature.

Methods

We retrospectively evaluated 23 adult patients (>18 years) admitted to the Neurology Department and met the Hunter criteria for SS.

Results

The mean age was 35.2 years, and 52% were female. Ten patients were managed in the intensive care unit (ICU), whereas thirteen patients were admitted to the ward. Hyperreflexia was the most common clinical feature (100%), followed by clonus (91%), tachycardia (83%), and tremor (83%). Other common clinical features were rigidity (65%), increased bowel sound (61%), diaphoresis (48%), fever (43%), hypertension (39%), and myoclonus (30%). All but one patient received two or more serotonergic drugs. Tramadol was the most common serotonergic agent (39%), followed by sodium valproate (21%), and amitriptyline (21%). Cyproheptadine was administered to all patients. All patients admitted in the ICU received a loading dose of 12 mg followed by 2 mg every 2 h for at least 24 h. All patients admitted to the ward were given 4 mg of cyproheptadine three times each day. Every patient showed at least some response to cyproheptadine within 24 h. The total doses of cyproheptadine and the length of treatment differed between patients.

Conclusion

Any response to cyproheptadine at a therapeutic dose within 24 h, even a partial one, could be a diagnostic indicator of the existence of SS.

Serotonin syndrome: A pharmacovigilance comparative study of drugs affecting serotonin levels

BACKGROUND

Serotonin syndrome is a rare and potentially fatal adverse drug reaction caused by serotonergic drugs and is due to an increase in serotonin concentration or activation of the 5-HT receptor in the central nervous system. We analysed adverse events in the US Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) data set to investigate the main drug classes related to reports of serotonin syndrome and the reporting risk in relation to age and sex.

METHODS

We analysed data from the FAERS database to evaluate the main drug classes related to reports of the serotonin syndrome, and the reporting risk in relation to age and sex.

RESULTS

We found 8,997 cases of serotonin syndrome; selective serotonin reuptake inhibitors (SSRIs) was the class of drugs with most reports, followed by opioids and other antidepressants. The highest Reporting Odds Ratios (ROR) for drug classes was for monoamine oxidase (MAO) inhibitors (45.99, 95% confidence interval (CI): 41.21-51.33) and SSRIs (32.66, 95% CI: 31.33-34.04), while the ten active substances with the highest ROR were moclobemide, isocarboxazid, oxitriptane, tranylcypromine, melitracen, phenelzine, linezolid, amoxapine, reboxetine and tryptophan; with values of ROR ranging from 44.19 (95% CI: 25.38-76.94) of tryptophan to 388.36 (95% CI: 314.58-479.46) of moclobemide. The ROR for the most commonly involved drugs was higher in the group of older adults (65 > years old), and higher in males.

CONCLUSION

Prescribers need to be vigilant about drugs that can raise serotonin concentration or influence serotonergic neurotransmission, also when using drugs with less well-known risk for serotonin syndrome, like linezolid and triptans.

Recognition and Management of Serotonin Toxidrome in the Emergency Department-Case Based Review

Serotonin syndrome (SS) is a clinical toxidrome with high variability in clinical practice. It develops due to increased serotonin levels in the central nervous system. With an underestimated frequency, SS can develop following an overdose, a therapeutic dose increase, or drug to drug interaction of at least one serotonergic agent. It can present with autonomic signs, neuromuscular changes and an altered mental status. However, history and clinical examination are key features to formulate the diagnosis. Treatment options consist of supportive measures, discontinuation of the offending agent and certain therapeutic agents previously reported to improve outcomes. Physicians have limited experience with SS, partially due to the lack of its identification in clinical practice. Therefore, we have integrated, in a narrative review, the case of a young male with SS following an atypical antipsychotic overdose superimposed on chronic treatment with agents previously known to produce SS.

High risk and low prevalence diseases: Serotonin syndrome

INTRODUCTION

Serotonin syndrome is a rare, frequently misdiagnosed, serious condition with high morbidity.

OBJECTIVE

This review highlights the pearls and pitfalls of serotonin syndrome, including diagnosis, initial resuscitation, and management in the emergency department (ED) based on current evidence.

DISCUSSION

Serotonin syndrome is a potentially deadly toxidrome marked by excess serotonin receptor activity or neurotransmission. Features of serotonin syndrome include 1) neuromuscular excitation such as tremor, hyperreflexia, and clonus; 2) autonomic dysfunction such as tachycardia, hypertension/hypotension, and hyperthermia; and 3) altered mental status such as agitation, delirium, and coma. Although serotonin syndrome may be more obvious in patients who have overdosed on serotonergic agents such as serotonin reuptake inhibitors (SSRIs), multiple other medications may also cause serotonin syndrome. Alternative diagnoses such as sepsis, neuroleptic malignant syndrome, and decompensated hyperthyroidism should be considered. The primary components of therapy include stopping the offending agent and supportive care, which focuses on agitation control, monitoring for and treating hyperthermia, and managing autonomic instability.

CONCLUSIONS

An understanding of serotonin syndrome can assist emergency clinicians in diagnosing and managing this disease.

Defensive and Emotional Behavior Modulation by Serotonin in the Periaqueductal Gray

Serotonin 5-hydroxytryptamine (5-HT) is a key neurotransmitter for the modulation and/or regulation of numerous physiological processes and psychiatric disorders (e.g., behaviors related to anxiety, pain, aggressiveness, etc.). The periaqueductal gray matter (PAG) is considered an integrating center for active and passive defensive behaviors, and electrical stimulation of this area has been shown to evoke behavioral responses of panic, fight-flight, freezing, among others. The serotonergic activity in PAG is influenced by the activation of other brain areas such as the medial hypothalamus, paraventricular nucleus of the hypothalamus, amygdala, dorsal raphe nucleus, and ventrolateral orbital cortex. In addition, activation of other receptors within PAG (i.e., CB1, Oxytocin, µ-opioid receptor (MOR), and γ-aminobutyric acid (GABA_A)) promotes serotonin release. Therefore, this review aims to document evidence suggesting that the PAG-evoked behavioral responses of anxiety, panic, fear, analgesia, and aggression are influenced by the activation of 5-HT_1A and 5-HT_2A/C receptors and their participation in the treatment of various mental disorders.

Antidepressant-induced serotonin syndrome in older patients: a cross-sectional study

BACKGROUND

Widespread prescription of antidepressants and their resulting role in serotonin syndrome (SS) are of great importance for clinical practice in the elderly. This study aims to investigate possible associations of antidepressant drug-induced SS with related variables in these patients.

METHODS

A total of 238 older adults using antidepressants were included. Patients who fulfilled the Hunter Serotonin Toxicity Criteria (HSTC) for SS were considered as the clinical groups (mild, moderate, or severe), and those who did not as the control group. We recorded all patients' demographic and clinical characteristics, including age, gender, comorbidity index, number of medications, daily equivalent dose of the relevant antidepressant according to fluoxetine per day, electrocardiogram test results, laboratory results, and management.

RESULTS

The mean age of all patients was 75.4 ± 7.6 years and 63.4% were female. Sixty patients had SS, while 178 patients did not. There was a significant difference between those with and without SS in terms of gender, frequency of combination antidepressant therapy, and daily equivalent antidepressant dose (P < 0.05). The most common diagnostic findings in SS patients were tremor and hyperreflexia and 31.7% was mild, and moderate in 68.3% with higher median age and number of medications (P < 0.041). Antidepressants were discontinued in all patients regardless of severity, of whom 71.7% were treated with benzodiazepines and 36.7% with cyproheptadine. After adjusting for age and sex, association with use of SSRI + SNRI, use of any combination therapy, and daily equivalent dose remained significant.

CONCLUSIONS

The widespread single or combined use of antidepressants in older adults represents an increased clinical concern for SS and physicians should be aware of this drug-related complication in older patients.

Serotonin syndrome

The serotonin syndrome is a life-threatening adverse drug reaction resulting from excess serotonergic agonism due to interactions between multiple drugs, poisoning, or less commonly due to therapeutic action of a single drug. The central triad of features in serotonin syndrome are altered mental state, autonomic hyperactivity, and neuromuscular abnormalities in the context of a patient with new/altered serotonergic therapy, although not all these features are consistently present in all patients. The severity of serotonin syndrome can be assessed clinically based on the number and severity of features. Severe serotonin syndrome warrants more careful management on a high-dependency unit. In case of temperature exceeding 38.5°C, urgent cooling measures and sedation should be employed, progressing to rapid sequence intubation and paralysis if cooling measures are ineffective.

Exposure to immediate-release tramadol in children 6 years and under - a nationwide French poison control center study

INTRODUCTION

Data regarding immediate-release (IR)-tramadol exposures in children remain sparse. We aimed to investigate the incidence of IR-tramadol exposures in ≤6-year-old children, to describe the characteristics and resulting outcome of ingestions involving IR-tramadol alone, and to estimate a clinically relevant toxic dose in this population.

METHODS

Retrospective analysis of IR-tramadol exposures in ≤6-year-old children, collected by the French Poison Control Centers (PCCs) in 2003-2019. The incidence was estimated using IR-tramadol prescription data from the Health Improvement Network database (the French version of THIN). The Poison severity score (PSS) was used to grade severity.

RESULTS

We found 1260 IR-tramadol exposures in ≤6-year-old children. The number of cases per 100,000 IR-tramadol-treated patients increased over time (p < .0001). One hundred forty-five cases involving IR-tramadol alone were analyzed. The median age was 3.0 years (IQR: 1.9, 4.0), the M/F ratio was 1.5 and the median dose was 5.0 mg/kg (IQR 3.3-11.1). Half of the children (49.7%) remained asymptomatic (PSS0) while 29.6% and 14.5% developed minor (PSS1) or moderate-to-severe (PSS2-PSS3) neurological symptoms, respectively. Twelve children developed respiratory depression. No seizures and no fatality were reported. All symptomatic children recovered within 24 h. The ingested IR-tramadol dose was positively correlated with the PSS (p < .0001). Using a receiver operating characteristic (ROC) curve approach (area under the curve, 0.92; p < .001), ingestion of ≥7.4 mg/kg IR-tramadol was appropriate to recommend hospital referral (sensitivity, 100% [95% confidence interval (CI), 85-100]; specificity, 73% [95% CI, 64-80]; predictive positive value, 39% [95% CI, 35-57]; negative predictive value, 100% [95% CI, 96-100]). Children who ingested <7.4 mg/kg IR-tramadol developed no (n = 68) or minor (n = 22) neurological symptoms.

CONCLUSIONS

Despite increasing tramadol prescriptions in adults during the study period in France, oral exposure to IR-tramadol in ≤6-year-old children was rare but possibly responsible for severe toxicity. Children with no underlying disease and concomitant medication ingesting <7.4 mg/kg IR-tramadol alone could be observed at home. However, given the observed variability in the onset of seizures after tramadol ingestion, which can occur at ingested tramadol doses below 7.4 mg and even at therapeutic doses, parents or guardians should be specifically warned about the risk of seizures.

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.

Coexistence of serotonin syndrome and neuroleptic malignant syndrome: does it exist?

We report a 21-year-old man with bipolar disorder who was on a stable dose of escitalopram and risperidone. Tramadol and cough syrup (dextromethorphan) were added for his recent attack of upper respiratory tract infection. However, he developed various neurological symptoms. Haloperidol and ondansetron were added after hospitalisation. However, his condition deteriorated. A diagnosis of serotonin syndrome (SS) was made, and cyproheptadine was started. Cyproheptadine provided relief in most of the symptoms within 48 hours except for the presence of fever and rigidity. The addition of bromocriptine provided a complete resolution of the symptoms. We considered the presence of both SS and neuroleptic malignant syndrome (NMS) in this case. There are four similar cases in the literature. We discussed a diagnostic and therapeutic approach for patients who are on both serotonergic agents and neuroleptics and develop SS-like or NMS-like clinical features.

Antiepileptic drugs and serotonin syndrome- A systematic review of case series and case reports

Serotonin syndrome (SS) is a drug‑induced, potentially fatal, clinical syndrome resulting from drugs that have serotonergic properties. Several antiepileptic drugs (AEDs) are known to have serotonergic properties and it can be hypothesized that such AEDs can cause SS. This study aims to review the literature on SS in patients receiving AEDs. We performed a systematic review of Scopus and MEDLINE/PUBMED for case reports and case series of SS where patients had received at least one AED at the onset of symptoms. The cases published in the English literature between 1 January 1991 and 1 April 2021 were included. Initial search identified 1263 articles of which 63 (76 patients) were included in the final analysis. Most of the included cases (53 cases, 70%) have been published in the last 10 years. The mean age of the 76 patients was 40.6 ± 17.8 years, and 51% of cases were females. These patients had been exposed to a total of 8 different types of AEDs. Valproic acid was the most common drug (29, 38%), followed by lamotrigine (22, 29%), gabapentin (16, 21%), pregabalin (seven, 9%), topiramate (five, 7%) and carbamazepine (two, 3%). There has been one case each with phenytoin and oxcarbazepine. Seven (9%) patients received more than one AEDs. Most patients (67, 88%) also received other serotoninergic agents. Only nine (12%) patients were on AEDs alone. The most common clinical condition for using AEDs was psychiatric disorders (36 patients, 47.3%), followed by migraine (17, 22.4%), other painful conditions (15, 19.7%), epilepsy (7, 9.2%), and perioperative conditions (8, 10.5%). Death was reported in two patients. We suggest that AEDs, because of their serotonergic properties, may induce SS, especially in patients who are on another serotonergic agent.

Chronic serotonin syndrome: A retrospective study

BACKGROUND

Serotonin syndrome (SS) is an underdiagnosed drug-induced clinical syndrome resulting from the excess intrasynaptic concentration of serotonin. Very limited information is available about chronic SS.

AIM

To evaluate the epidemiological, clinical, and other aspects of the insidious onset SS.

METHODS

We retrospectively evaluated 14 consecutive adult patients (> 18 years) who had complaints for more than 6 wk at the time of consultation and met the Hunter criteria for SS.

RESULTS

The mean age was 41.1 years (range: 21-61 years), with a male preponderance (64%). Although tremors were observed in all patients, this was a presenting complaint in only 43% of patients. Generalized body pain, insomnia, and restlessness were common presenting features (50% each). Other common clinical features were stiffness of the limbs (43%), diaphoresis (43%), gait disturbances (36%), bowel disturbances (36%), dizziness (29%), sexual dysfunctions (21%), incoordination (14%), and fatigue (14%) The mean duration of symptoms before the diagnosis of SS was 13.5 ± 5.8 wk (range: 6-24 wk). Amitriptyline was the most common drug (n = 6, 43%), followed by tramadol (n = 5, 36%) and sodium valproate (n = 5, 36%). All patients received cyproheptadine, a 5- hydroxytryptamine2A antagonist, as treatment and noted an excellent response over the course of 4-14 d.

CONCLUSION

This study represents the largest study on chronic SS. We suggest that patients receiving serotonergic drugs should be physically examined for the presence of SS upon the development of new symptoms.