Serotonin syndrome: history and risk

Clinically Relevant Drug Interactions with Monoamine Oxidase Inhibitors

Monoamine oxidase inhibitors (MAOI) are a class of drugs that were originally developed for the treatment of depression but have since been expanded to be used in management of affective and neurological disorders, as well as stroke and aging-related neurocognitive changes. Ranging from irreversible to reversible and selective to non-selective, these drugs target the monoamine oxidase (MAO) enzyme and prevent the oxidative deamination of various monoamines and catecholamines such as serotonin and dopamine, respectively. Tyramine is a potent releaser of norepinephrine (NE) and is found in high concentrations in foods such as aged cheeses and meats. Under normal conditions, NE is unable to accumulate to toxic levels due to the presence of MAO-A, an enzyme that degrades neurotransmitters, including NE. When MAO-A is inhibited, the capacity to handle tyramine intake from the diet is significantly reduced causing the brain to be vulnerable to overstimulation of postsynaptic adrenergic receptors with as little as 8-10 mg of tyramine ingested and can result in life-threatening blood pressure elevations. In addition to adverse reactions with certain foods, both older and newer MAOIs can negatively interact with both sympathomimetic and serotonergic drugs. In general, patients on a MAOI want to avoid two types of medications: those that can elevate blood pressure via sympathomimetic actions (e.g., phenylephrine and oxymetazoline) and those that can increase serotonin levels via 5-HT reuptake inhibition (e.g., dextromethorphan, chlorpheniramine, and brompheniramine). Illicit drugs that stimulate the central nervous system such as ecstasy (MDMA, 3,4-methylenedioxymethamphetamine) act as serotonin releasers. Patient involvement is also crucial to ensure any interaction within the healthcare setting includes making other providers aware of a MAOI prescription as well as avoiding certain OTC medications that can interact adversely with MAOIs.

Chronic Serotonergic Overstimulation Mimicking Panic Attacks in a Patient with Parkinson's Disease Receiving Additional Antidepressant Treatment with Moclobemide

Background

The pharmacological treatment options of Parkinson's disease (PD) have considerably evolved during the last decades. However, therapeutic regimes are complicated due to individual differences in disease progression as well as the occurrence of complex nonmotor impairments such as mood and anxiety disorders. Antidepressants in particular are commonly prescribed for the treatment of depressive symptoms and anxiety in PD. Case Presentation. In this case report, we describe a case of a 62-year-old female patient with PD and history of depressive symptoms for which she had been treated with moclobemide concurrent with anti-Parkinson medications pramipexole, rasagiline, and L-DOPA+benserazide retard. An increase in the dosage of moclobemide 12 months prior to admission progressively led to serotonergic overstimulation and psychovegetative exacerbations mimicking the clinical picture of an anxiety spectrum disorder. After moclobemide and rasagiline were discontinued based on the hypothesis of serotonergic overstimulation, the patient's psychovegetative symptoms subsided.

Conclusions

The specific pharmacological regime in this case probably caused drug-drug interactions resulting in a plethora of psychovegetative symptoms. Likely due to the delayed onset of adverse effects, physicians had difficulties in determining the pharmacologically induced serotonin toxicity. This case report emphasizes the complexity of pharmacological treatments and the importance of drug-drug interaction awareness in the treatment of PD patients with complicating nonmotor dysfunctions such as depression.

Rare case of severe serotonin syndrome leading to bilateral compartment syndrome

The term 'serotonin syndrome' describes a constellation of symptoms caused by serotonergic overstimulation. Its characteristic clinical presentation consists of encephalopathy, neuromuscular signs and autonomic hyperactivity. After removal of the offending agent, the clinical course is usually self-limited but can occasionally lead to severe symptoms. We report the case of a 68-year-old woman who presented emergently with encephalopathy. Home medications included paroxetine and dextroamphetamine/amphetamine. Physical examination revealed tachycardia, tachypnoea, diaphoresis, rigidity, hyperreflexia and clonus. Given the fast onset of symptoms, a diagnosis of serotonin syndrome was made. Laboratory studies showed acute-on-chronic kidney injury and elevated creatine kinase. The patient's mental status quickly returned to baseline with supportive care. Her rhabdomyolysis, however, persisted and led to acute compartment syndrome in her lower extremities. After bilateral leg fasciotomies and treatment of a severe wound infection with intravenous antibiotics, the patient has now recovered with complete resolution of her symptoms.

Serotonin Syndrome Induced by Fluvoxamine and Oxycodone

Objective:

To report a case of severe serotonergic symptoms following the addition of oxycodone to fluvoxamine.

Case Summary:

A 70-year-old woman developed severe serotonergic features, including confusion, nausea, fever, clonus, hyperreflexia, hypertonia, shivering, and tachycardia, following the addition of oxycodone 40 mg twice daily to fluvoxamine 200 mg/day, easily fulfilling diagnostic criteria for serotonin syndrome. Discontinuation of the offending drugs resulted in resolution of her symptoms over 48 hours, and no other cause of the syndrome was identified. Use of the Naranjo probability scale indicated a probable relationship between the serotonergic symptoms and the addition of oxycodone to fluvoxamine therapy.

Discussion:

Serotonin syndrome is a serious adverse reaction usually due to interactions with serotonergic drugs. There have been only 3 previous reports involving oxycodone. Most previous reports of serotonin syndrome involving analgesics have been associated with meperidine, dextromethorphan, and tramadol. Unlike these synthetic opioids, however, oxycodone does not inhibit the reuptake of serotonin. In addition, there are a number of other possible pharmacologic mechanisms for the interaction we observed.

Conclusions:

Monitoring for serotonergic adverse events should be done when oxycodone is given to patients receiving serotonin-reuptake inhibitors.

Serotonin Syndrome in a Patient on Trazodone and Duloxetine Who Received Fentanyl following a Percutaneous Liver Biopsy

Serotonin syndrome is a rare but potentially life-threatening adverse drug reaction resulting from the use or overuse of serotonergic medications alone or in combination. Mild symptoms, overlapping features with similar conditions and clinician lack of awareness are the major reasons for an often missed diagnosis. Not surprisingly, this condition is significantly underreported as a potential complication of endoscopy if serotonergic medications are used periprocedurally for sedation and analgesia. Here we report the case of a patient with relapsed chronic hepatitis C on antidepressant medications who developed signs and symptoms of serotonin syndrome after a percutaneous liver biopsy. Review of the patient's medication list suggested a possible interaction between her home antidepressants and the post-procedure use of fentanyl for abdominal pain. The patient required monitoring in the medical intensive care unit and stabilized after the administration of benzodiazepines and temporary discontinuation of her home medications. We propose that clinicians need to be aware of the increased risk of serotonin syndrome in the outpatient endoscopy setting, particularly with the wider use of serotonergic antidepressants now available and the repeated number of liver biopsies being performed for management of patients with chronic liver disease.

The murine serotonin syndrome - evaluation of responses to 5-HT-enhancing drugs in NMRI mice

In humans, the ingestion of the combination of two or more serotonin (5-HT)-enhancing drugs but also of a single drug in overdose can induce serious adverse effects, which are characteristics of the serotonin syndrome (SS). In mice, acute administration of direct and indirect 5-HT agonists also leads to behavioral and autonomic responses, but in literature different responses are thought to be essential. In order to detect common behavioral SS responses induced by 5-HT-enhancing drugs with different mechanisms of action, we investigated the effects of the 5-HT precursor 5-hydroxy-l-tryptophan (5-HTP), the selective serotonin reuptake inhibitor (SSRI) fluoxetine (FLX), and the monoaminooxidase (MAO) inhibitor tranylcypromine (TCP) in male NMRI mice. The drugs were administered alone or in combination to investigate additive effects or drug potentiation. Moreover, we compared the 5-HT responses to the effects induced by the dopamine, noradrenaline, and cholinergic agonists, apomorphine (APO), atomoxetine (ATO), and oxotremorine (OXO). Our results show that the studied 5-HT-enhancing drugs induced a different number of concomitant responses. The following five responses consistently and dose-dependently occurred in NMRI mice: flat body posture, hindlimb abduction, piloerection, tremor, and decreased rearings. Like in humans, the combination of 5-HT-enhancing drugs leads to a potentiation of drug effects. With the exception of flat body posture the responses are not specific for serotonergic hyperactivity. The findings demonstrate that the SS in NMRI mice is a suitable animal model for preclinical research, if it is taken into account that the spectrum of typical responses to 5-HT enhancing drugs may differ depending on drug and mouse strain and that some responses might be evoked by activation of other transmission systems, too.

Serotonin syndrome: is it a reason to avoid the use of tramadol with antidepressants?

BACKGROUND

There is a warning associated with all serotonergic antidepressants and its concomitant use with tramadol due to the concern for a drug-drug interaction resulting in serotonin syndrome (SS). The prescribing of antidepressants with tramadol may be unnecessarily restricted due to fear of causing this syndrome.

OBJECTIVES

There are 3 objectives of this review. To (1) review case reports of SS associated with the combination of tramadol and antidepressant drugs in recommended doses, (2) describe the mechanisms of the drug interaction, and (3) identify the potential risk factors for SS.

METHODS

Case reports of SS associated with tramadol and antidepressants were identified via Cochrane Library, PubMed, and Ovid (through October 2012) using search terms SS, tramadol, antidepressants, fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram, escitalopram, venlafaxine, desvenlafaxine, duloxetine, mirtazapine, milnacipran, trazodone, vilazodone, and bupropion. Cases involving monoamine oxidase inhibitors (MAOIs) and tricyclic antidepressants were excluded.

RESULTS

Nine articles were identified describing 10 cases of suspected SS associated with therapeutic doses of tramadol combined with an antidepressant. Mechanisms of the drug-drug interactions involve pharmacodynamic, pharmacokinetic, and possible pharmacogenetic factors.

CONCLUSIONS

Review of the available case reports of tramadol combined with antidepressant drugs in therapeutic doses indicates caution in regard to the potential for SS but does not constitute a contraindication to their use. Tramadol is only contraindicated in combination with MAOIs but not other antidepressants in common use today. These case reports do suggest several factors associated with a greater risk of SS, including increased age, higher dosages, and use of concomitant potent cytochrome P450 2D6 inhibitors. Tramadol can be safely combined with antidepressants; however, monitoring and counseling patients are prudent when starting a new serotonergic agent or when doses are increased.

Animal models of the serotonin syndrome: a systematic review

The serotonin syndrome (SS) is a potentially life-threatening disorder in humans which is induced by ingestion of an overdose or by combination of two or more serotonin (5-HT)-enhancing drugs. In animals, acute administration of direct and indirect 5-HT agonists also leads to a set of behavioral and autonomic responses. In the current review, we provide an overview of the existing versions of the animal model of the SS. With a focus on studies in rats and mice, we analyze the frequency of behavioral and autonomic responses following administration of 5-HT-enhancing drugs and direct 5-HT agonists administered alone or in combination, and we briefly discuss the receptor mediation of these responses. Considering species differences, we identify a distinct set of behavioral and autonomic responses that are consistently observed following administration of direct and indirect 5-HT agonists. Finally, we discuss the importance of a standardized assessment of SS responses in rodents and the utility of animal models of the SS in translational studies, and provide suggestions for future research.

Rediscovering catatonia: the biography of a treatable syndrome

OBJECTIVE

Catatonia, a disorder of movement and mood, was described and named in 1874. Other observers quickly made the same recognition. By the turn of the century, however, catatonia was incorporated as a type within a conjured syndrome of schizophrenia. There, catatonia has lain in the psychiatric classification for more than a century.

METHOD

We review the history of catatonia and its present status. In the 1970s, the tie was questioned when catatonia was recognized among those with mood disorders. The recognition of catatonia within the neuroleptic malignant syndrome offered effective treatments of high doses of benzodiazepines and electroconvulsive therapy (ECT), again questioning the tie. A verifying test for catatonia (the lorazepam sedation test) was developed. Soon the syndromes of delirious mania, toxic serotonin syndrome, and the repetitive behaviors in adolescents with autism were recognized as treatable variations of catatonia.

RESULTS

Ongoing studies now recognize catatonia among patients labeled as suffering from the Gilles de la Tourette's syndrome, anti-NMDAR encephalitis, obsessive-compulsive disease, and various mutisms.

CONCLUSION

Applying the treatments for catatonia to patients with these syndromes offers opportunities for clinical relief. Catatonia is a recognizable and effectively treatable neuropsychiatric syndrome. It has many faces. It warrants recognition outside schizophrenia in the psychiatric disease classification.

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).

A venlafaxine and mirtazapine-induced serotonin syndrome confirmed by de- and re-challenge

CASE DESCRIPTION

A 85 year old woman with a history of severe depression treated with mirtazapine and venlafaxine was admitted to the hospital twice after progressive deterioration of her general condition evolving to unconsciousness. Clinicians diagnosed a metabolic encephalopathy caused by a urinary tract infection which was treated appropriately. Although mirtazapine was stopped during the first hospitalization, the patient's general practitioner restarted mirtazapine four days before readmission. During rehospitalization, she developed extreme restlessness, hyperreflexia and an increased tone in the lower limbs. She was hypertensive and tachycardic. Excessive sweating, elevated creatine kinase levels and bilateral mydriasis were noticed. Urinary analysis showed positive levels of mirtazapine and venlafaxine and both drugs were withdrawn. Symptoms resolved within 48 h after discontinuation of her antidepressants. Conclusion To our knowledge, this is the first case of the serotonin syndrome confirmed by a positive challenge, de-challenge and re-challenge.

Psychotropic drug-related problems in the elderly

Almost any drug therapy has the potential to cause iatrogenic complications for older people, but the risk is particularly significant for those being treated for major psychiatric illnesses. In the past, focus was centered mostly upon relatively obvious forms of drug-related harm, such as adverse drug reactions and drug interactions, but it is clear that this approach substantially under-represents the extent of the problem. Other, more inclusive categorization systems can be used to capture a broader representation of the profile and severity of medication-related problems, and these can provide insight into more subtle concerns. Analysis of psychotropic drug-related problems in the elderly provides a basis for individual interventions to lessen the impact of iatrogenic harm, as well as systematic approaches that can be used in the clinical setting to diminish the likelihood of preventable problems in a vulnerable patient population.

Pharmacokinetic drug interactions and adverse consequences between psychotropic medications and pharmacotherapy for the treatment of opioid dependence

BACKGROUND

Psychiatric comorbidities among opioid-dependent patients are common. Many medications used to treat both conditions are metabolized through complimentary cytochrome P450 isoenzymes. When medication-assisted treatment for opioid dependence is concurrently used with psychotropic medications, problematic pharmacokinetic drug interactions may occur.

METHODS

We reviewed relevant English language articles identified through the MedLine, Scopus, and Embase databases from 1950 to December 2009 using the specific generic names of medications and keywords such as pharmacokinetics and drug interactions with buprenorphine, methadone, and naltrexone. Selected references from these articles were reviewed. Additionally, a review was conducted of abstracts and conference proceedings from national and international meetings from 1990 to 2009. A total of 60 studies were identified and reviewed.

RESULTS

Clinical case series and carefully controlled pharmacokinetic interaction studies have been conducted between methadone, buprenorphine, or naltrexone and some psychoactive medications. Important pharmacokinetic drug interactions have been demonstrated within each class of medications affecting either methadone and buprenorphine or psychoactive drugs. Few studies, however, have been conducted with naltrexone.

CONCLUSIONS

Several interactions between methadone, buprenorphine, or naltrexone and psychoactive medications are described and may have important clinical consequences. To optimize care, clinicians must be alerted to these interactions.

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.

Neuroleptic malignant syndrome: mechanisms, interactions, and causality

This review focuses on new data from recent publications concerning how compounding interactions between different thermoregulatory pathways influence the development of hyperthermia and/or neuroleptic malignant syndrome (NMS), and the fundamental issue of the presumed causal role of antipsychotic drugs. The formal criteria for substantiating cause-effect relationships in medical science, established by Hill, are applied to NMS and, for comparison, also to malignant hyperthermia and serotonin toxicity. The risk of morbidities related to hyperthermia is reviewed from human and experimental data: temperatures in excess of 39.5°C cause physiological and cellular dysfunction and high mortality. The most temperature-sensitive elements of neural cells are mitochondrial and plasma membranes, in which irreversible changes occur around 40°C. Temperatures of up to 39°C are "normal" in mammals, so, the term hyperthermia should be reserved for temperatures of 39.5°C or greater. The implicitly accepted presumption that NMS is a hypermetabolic and hyperthermic syndrome is questionable and does not explain the extensive morbidity in the majority of cases, where the temperature is less than 39°C. The thermoregulatory effects of dopamine and acetylcholine are outlined, especially because they are probably the main pathways by which neuroleptic drugs might affect thermoregulation. It is notable that even potent antagonism of these mechanisms rarely causes temperature elevation and that multiple mechanisms, including the acute phase response, stress-induced hyperthermia, drugs effects, etc., involving compounding interactions, are required to precipitate hyperthermia. The application of the Hill criteria clearly supports causality for drugs inducing both MH and ST but do not support causality for NMS.

The serotonin syndrome-the need for physician's awareness

Background

Serotonin syndrome is a potentially life-threatening adverse drug reaction that results from therapeutic drug use, usually of selective serotonin reuptake inhibitors (SSRIs), intentional excessive use or interactions between various drugs.

Case presentation

A 16-year-old Caucasian boy presented to our emergency department (ED) with alteration in his mental status for 6 h prior to arrival. On physical examination in our ED, he was combative and disoriented to time, place and person. He was febrile, hypertensive and tachycardic as well. He had intermittent rigid extremities with myoclonus of both lower extremities. A diagnosis of serotonin syndrome (SS) was made based on history of intake of fluoxetine and clinical signs, which included presence of inducible clonus and agitation. The child received supportive care involving intravenous fluids and intravenous lorazepam. The child was back to his baseline mental status and had a normal neurological exam by 24 h and was discharged home later for follow-up with a psychiatrist.

Conclusions

SS occurs with increasing frequency, and most cases resolve with prompt recognition and supportive care. Failure to make an early diagnosis and to comprehend adverse pharmacological effects of therapy can lead to adverse outcomes.

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.

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.

The dark side of ecstasy: neuropsychiatric symptoms after exposure to 3,4-methylenedioxymethamphetamine

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is a known neurotoxin in animals. This review discusses the history, pattern of use, pharmacology, acute and long-term effects of MDMA. Emphasis is given to the concern that MDMA may induce long-term cognitive and psychiatric effects. MDMA is an illegal substance, and investigations of the effects of exposure in human beings have limitations and weaknesses. There are numerous studies suggesting a correlation between MDMA exposure and psychopathology, and that the psychotropic effects may be long-lasting or permanent. However, it is not possible to conclude that there is a causal relationship between exposure and the increased psychopathology observed in MDMA users. Longitudinal studies are needed to assess whether MDMA causes persistent cognitive impairment and/or psychiatric symptoms in human beings.

Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction

BACKGROUND AND PURPOSE

Monoamine oxidase inhibitors (MAOI) are known to cause serotonin toxicity (ST) when administered with selective serotonin reuptake inhibitors (SSRI). Methylene blue (methylthionium chloride, MB), a redox dye in clinical use, has been reported to precipitate ST in patients using SSRI. MB was assessed for MAO inhibition and so for its potential to precipitate ST.

EXPERIMENTAL APPROACH

Inhibition of purified human MAO was quantified using kinetic assays and visible spectral changes to study the interactions of MB with MAO A.

KEY RESULTS

MB was a potent (tight binding) inhibitor for MAO A. It also inhibited MAO B but at much higher concentration. Interactions of MB with the active site of MAO A were confirmed by its action both as an oxidising substrate and as a one-electron reductant.

CONCLUSIONS AND IMPLICATIONS

MB is a potent reversible inhibitor of MAO A with implications for gut uptake of amines when administered orally. At concentrations reported in the literature after intravenous administration, MAO B would be partially inhibited but MAO A would be completely inhibited. This inhibition of MAO A would be expected to lead to perturbations of 5-hydroxytryptamine metabolism and hence account for ST occurring when administered to patients on SSRI treatment.

Behavioral effects of dipropyltryptamine in rats: evidence for 5-HT1A and 5-HT2A agonist activity

These studies investigated the role of serotonin-1A (5-HT1A) and 5-HT2A receptors in the behavioral effects of dipropyltryptamine (DPT). Eight rats discriminated 0.56 mg/kg 2,5-dimethoxy-4-methylamphetamine (DOM) from saline and responded under a fixed ratio 5 schedule of food presentation; 12 other rats were used for observational studies. DOM and DPT increased responding on the DOM lever with 3.2 mg/kg DPT producing greater than 95% responding on the DOM lever; this effect of DPT was antagonized by the 5-HT2A receptor antagonist MDL100907. In another study, the 5-HT1A and 5-HT7 receptor agonist 8-OH-DPAT produced lower-lip retraction and, at larger doses, flat body posture; DPT alone produced flat body posture and not lower-lip retraction; MDL100907 alone did not produce either effect. Pretreatment with DPT blocked 8-OH-DPAT-elicited lower-lip retraction, suggesting antagonist activity of DPT at 5-HT1A receptors; however, in the presence of MDL100907 DPT produced not only flat body posture but also lower-lip retraction, suggesting that agonist activity of DPT at 5-HT2A receptors masked agonist activity at 5-HT1A receptors. Lower-lip retraction and flat body posture by DPT in the presence of MDL100907 were attenuated by the 5-HT1A receptor antagonist WAY100635. These findings suggest that DPT has agonist activity at 5-HT1A and 5-HT2A receptors and that effects at 5-HT2A receptors mask effects at 5-HT1A receptors.

Tricyclic antidepressant pharmacology and therapeutic drug interactions updated

New data on the pharmacology of tricyclic antidepressants (TCAs), their affinities for human cloned CNS receptors and their cytochrome P450 enzyme inhibition profiles, allow improved deductions concerning their effects and interactions and indicate which of the TCAs are the most useful. The relative toxicity of TCAs continues to be more precisely defined, as do TCA interactions with selective serotonin reuptake inhibitors (SSRIs). TCA interactions with monoamine oxidase inhibitors (MAOIs) have been, historically, an uncertain and difficult question, but are now well understood, although this is not reflected in the literature. The data indicate that nortriptyline and desipramine have the most pharmacologically desirable characteristics as noradrenaline reuptake inhibitors (NRIs), and as drugs with few interactions that are also safe when coadministered with either MAOIs or SSRIs. Clomipramine is the only available antidepressant drug that has good evidence of clinically relevant serotonin and noradrenaline reuptake inhibition (SNRI). These data assist drug selection for monotherapy and combination therapy and predict reliably how and why pharmacodynamic and pharmacokinetic interactions occur. In comparison, two newer drugs proposed to have SNRI properties, duloxetine and venlafaxine, may have insufficient NRI potency to be effective SNRIs. Combinations such as sertraline and nortriptyline may therefore offer advantages over drugs like venlafaxine that have fixed ratios of SRI/NRI effects that are not ideal. However, no TCA/SSRI combination is sufficiently safe to be universally applicable without expert knowledge. Standard texts (e.g. the British National Formulary) and treatment guidelines would benefit by taking account of these new data and understandings.

Choreoathetosis, an unusual presentation of serotonin syndrome

We describe a 63 year old male with serotonin syndrome, presenting with choreoathetosis. Differentiating this syndrome from neuroleptic malignant syndrome remains a challenge. It is important to be aware of drugs that can potentially precipitate this syndrome.

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.

Serotonin toxicity associated with the use of linezolid: a review of postmarketing data

BACKGROUND

Linezolid is the first oxazolidinone antimicrobial marketed in the United States. It exhibits monoamine oxidase (MAO) type A and MAO type B inhibitory effects. The concomitant administration of nonselective MAO inhibitors or MAO-A inhibitors with drugs that increase serotonin concentrations is associated with serotonin toxicity.

METHODS

We requested from the US Food and Drug Administration all postmarketing adverse event reports regarding linezolid that included serotonin toxicity or any report describing cognitive or behavioral symptoms and autonomic and neuromuscular excitability. We assessed the case summaries obtained from the Adverse Event Reporting System database for serotonin toxicity. A case of serotonin toxicity was defined as having the following: (1) linezolid as the primary suspect drug; (2) concurrent administration of > or =1 secondary suspect drug known to increase serotonin concentrations in the central nervous system; and (3) serotonin toxicity, as defined by the modified Hunter Serotonin Toxicity Criteria or by the reporter.

RESULTS

Twenty-nine cases were classified as serotonin toxicity. Patients' ages ranged from 17-83 years, and the ratio of females to males was 1:1. The most common class of drugs received concurrently with linezolid was selective serotonin reuptake inhibitors (26 of 43 patients). Thirteen patients required an intervention to prevent permanent impairment or required hospitalization for the adverse event.

CONCLUSION

The use of linezolid with medications that increase concentrations of serotonin in the central nervous system may result in serotonin toxicity. Prescribers must weigh risks and benefits of this combination. Patients and prescribers should be cognizant of signs and symptoms of serotonin toxicity and should initiate appropriate measures if such symptoms develop.

Drug interactions and fluoxetine: a commentary from a clinician's perspective

This commentary suggests that clinicians require an additional perspective to that expressed in Wernicke's review. Clinicians must consider the relative risks, because even small differences may be a reason to adjust usage of a particular drug. As early as 1993, reviews noted a 'serious' interaction potential. Also, the product information requires supplementation because it does not provide the emphasis on predictable interactions that clinicians require. An extensive basis in experimental pharmacology provides the foundations for our knowledge of cytochrome P450 interactions which predict the effects on the levels of other drugs. This work has been confirmed in human studies. Adverse outcomes related to fluoxetine interactions are relatively frequent and sometimes fatal. Patients may suffer serious and irreversible ill-effects from the increased risk of many manifestations of toxicity, and the cost of resultant medico-legal settlements is considerable. A clinician who balances risks may use fluoxetine less frequently.

Ecstasy: are animal data consistent between species and can they translate to humans?

The number of 3,4-methylenedioxymethamphetamine (ecstasy or MDMA) animal research articles is rapidly increasing and yet studies which place emphasis on the clinical significance are limited due to a lack of reliable human data. MDMA produces an acute, rapid release of brain serotonin and dopamine in experimental animals and in the rat this is associated with increased locomotor activity and the serotonin behavioural syndrome in rats. MDMA causes dose-dependent hyperthermia, which is potentially fatal, in humans, primates and rodents. Subsequent serotonergic neurotoxicity has been demonstrated by biochemical and histological studies and is reported to last for months in rats and years in non-human primates. Relating human data to findings in animals is complicated by reports that MDMA exposure in mice produces selective long-term dopaminergic impairment with no effect on serotonin. This review compares data obtained from animal and human studies and examines the acute physiological, behavioural and biochemical effects of MDMA as well as the long-term behavioural effects together with serotonergic and dopaminergic impairments. Consideration is also given to the role of neurotoxic metabolites and the influence of age, sex and user groups on the long-term actions of MDMA.

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.

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.

Drug-induced movement disorders in children and adolescents

The use of psychotropic medication among children and adolescents is increasing with a concomitant increase in the incidence of drug-related movement disorders. This class of adverse reactions to medications can be divided into those that are acute in onset, others that are continuous as long as the offending drug is administered, and a final category consisting of symptoms that are persistent, even after the causative agent has been discontinued. Within these three categories, this review discusses the epidemiology, risk factors, clinical features and treatment of acute dystonic reactions, drug-induced parkinsonism, neuroleptic malignant syndrome, serotonin syndrome, acute akathisia, and the tardive syndromes. In addition, drugs that commonly cause tremor, chorea, or myoclonus are included.

Serotonin Syndrome Induced by a Combination of Bupropion and SSRIs

Serotonin syndrome (SS) is a potentially fatal complication of the combined use of agents that enhance serotonin activity. Bupropion inhibits noradrenaline and dopamine reuptake with milder effects on serotonergic activity. Although regarded as a potential causative agent for SS, no cases have been reported in the medical literature. A 62-year-old woman treated with therapeutic dosages of bupropion and sertraline for depression for the previous 3 weeks presented with upper extremity myoclonic jerks, clumsiness, and gait difficulties with fluctuating symptoms of confusion, forgetfulness, and the alternation of agitation and lethargy. Symptoms were interpreted as an aggravation of depression and venlafaxine was added. The clinical picture progressed to alteration of consciousness and dysautonomia. After admission, medications were discontinued and she was started on cyproheptadine and clonazepam with gradual improvement and complete resolution of symptoms. This is a rare report of SS related to the association of bupropion and selective serotonin reuptake inhibitors (SSRIs). It also illustrates the potential for misinterpretation of the earliest manifestations of SS as signs of aggravation of the patient's underlying condition. The role of bupropion in SS is possibly related to its well-established specific inhibition of the cytochrome P450 2D6 pathway, increasing blood levels of SSRIs and tricyclic antidepressants.