Serotonin syndrome caused by overdose with paroxetine and moclobemide

Adjunctive 5-Hydroxytryptophan Slow-Release for Treatment-Resistant Depression: Clinical and Preclinical Rationale

Serotonin transporter (SERT) inhibitors treat depression by elevating brain extracellular 5-hydroxytryptamine (5-HT_Ext). However, only one-third of patients respond adequately. Treatment-resistant depression (TRD) is a major unmet need. Interestingly, elevating 5-HT_Ext beyond what is achieved by a SERT inhibitor appears to treat TRD. Adjunctive administration of 5-hydroxytryptophan (5-HTP) safely elevates 5-HT_Ext beyond the SERT inhibitor effect in humans; however, 5-HTP cannot be a clinically viable drug because of its poor pharmacokinetics. A slow-release (SR) delivery mode would be predicted to overcome the pharmacokinetic limitations of 5-HTP, substantially enhancing the pharmacological action and transforming 5-HTP into a clinically viable drug. Animal studies bear out this prediction. Thus, adjunct 5-HTP SR could be an important new treatment for TRD. Here, we review the clinical and preclinical evidence for this treatment.

Serotonin syndrome due to an overdose of moclobemide?

Serotonin syndrome, a triad of autonomic instability, altered mental status and neuromuscular abnormalities, is usually attributed to serotonergic overdoses. Moclobemide is a new selective monoamine oxidase inhibitor (MAOI) that generally causes mild, self-limited gastrointestinal and central nervous system effects after ingestion. We present a case of serotonin syndrome that occurred after moclobemide overdose, and discuss the recognition and treatment of this important condition. Serotonin syndrome may become increasingly common because of the liberal use of selective serotonin reuptake inhibitors, new MAOIs and other agents such as codeine and meperidine, which have the potential for harmful interaction.

Anticipating potential linezolid-SSRI interactions in the general hospital setting: an MAOI in disguise

Linezolid, a novel antimicrobial with activity against gram-positive bacteria including pathogens resistant to traditional antimicrobials, also inhibits monoamine oxidase. This latter property can cause potentially lethal adverse interactions with antidepressant medications. Long known to psychiatrists, monoamine oxidase inhibitors (MAOIs) and complications of their use may be unfamiliar to medical and surgical practitioners who may thus unwittingly precipitate a hypertensive crisis or serotonin syndrome. We review the pharmacology of MAOis and describe 3 clinical situations In which linezolid-selective serotonin inhibitor (SSRI) interactions, actual or potential, figured prominently.

Paroxetine overdose

Paroxetine is a commonly used antidepressant with a safe side-effect profile. A case of paroxetine overdose (560 mg) is reported in an 18-year-old female who attempted suicide and recovered without any sequelae, requiring only supportive treatment. This report highlights a case of pure paroxetine overdose and the safety profile of paroxetine in overdose.

Comparative Toxicity of Citalopram and the Newer Antidepressants After Overdose

OBJECTIVE

To compare the toxicity of citalopram, venlafaxine, mirtazapine, and nefazadone after overdose.

METHODS

Two-year retrospective review of consecutive patients admitted to the toxicology unit of Edinburgh Royal Infirmary. Outcome measure included physiological variables, ECG recordings, peak creatine kinase, development of arrhythmias, seizure, tremor or agitation, and the need for admission to a critical care facility.

RESULTS

A total of 225 patients were studied. Venlafaxine was associated with a significantly higher pulse rate (p < 0.0001) and tremor (p = 0.007) than other antidepressants. Citalopram was associated with a significantly longer QT interval on ECG recording (p < 0.0001) but mean QTc durations were not significantly different between all drugs studied. No arrhythmias were recorded. Only venlafaxine and citalopram caused seizures and were associated with the need for admission to Intensive Care, but there was no significant difference between them.

CONCLUSIONS

Mirtazapine and nefazadone appear safe in overdose and were associated with minimal features of neurological or cardiovascular toxicity. Citalopram is more likely to cause QT prolongation but other features of cardiovascular toxicity were uncommon. Both citalopram and venlafaxine are proconvulsants. Venlafaxine also causes more frequent features of the serotonin syndrome.

Moclobemide poisoning: toxicokinetics and occurrence of serotonin toxicity

AIMS

To investigate the spectrum of toxicity of moclobemide overdose, the occurrence of serotonin toxicity, and to estimate toxicokinetic parameters.

METHODS

All moclobemide overdoses presenting over a 10-year period to the Hunter Area Toxicology Service were reviewed. Clinical features, complications, length of stay (LOS) and intensive care (ICU) admission rate were extracted from a standardized, prospectively collected database. Comparisons were made between moclobemide alone and moclobemide with a serotonergic coingestant poisoning. Serotonin toxicity was defined by a combination of Sternbach's criteria and a clinical toxicologist's diagnosis. In five patients serial moclobemide concentrations were measured. Time to maximal plasma concentration (Tmax), peak plasma concentration (Cmax) and terminal elimination half-lives were estimated.

RESULTS

Of 106 included patients, 33 ingested moclobemide alone, 21 ingested moclobemide with another serotonergic agent (in some cases in therapeutic doses) and 52 ingested moclobemide with a nonserotonergic agent. Eleven (55%) of 21 patients coingesting a serotonergic drug developed serotonin toxicity, which was significantly more than one (3%) of 33 moclobemide-alone overdoses (odds ratio 35, 95% confidence interval 4, 307; P < 0.0001). In six of these 21 cases severe serotonin toxicity developed with temperature >38.5 degrees C and muscle rigidity requiring intubation and paralysis. The 21 patients had a significantly increased LOS (34 h) compared with moclobemide alone overdoses (12 h) (P < 0.0001) and a significantly increased ICU admission rate of 57% vs. 3% (P < 0.0001). Time to peak plasma concentration was delayed in two patients where prepeak samples were obtained. Cmax increased slightly with dose, but all three patients ingesting > or = 6 g vomited or had charcoal. The mean elimination half-life of moclobemide in the five patients in whom serial moclobemide concentrations were measured was 6.3 h and elimination was first order in all cases. There was no evidence of a dose-dependent increase in half-life.

CONCLUSIONS

The effects of moclobemide alone in overdose are minor, even with massive ingestions. However, moclobemide overdose in combination with a serotonergic agent (even in normal therapeutic doses) can cause severe serotonin toxicity. The elimination half-life is prolonged by two to four times in overdose, compared with that found in healthy volunteers given therapeutic doses. This may be a result of wide interindividual variation in overall elimination, also seen with therapeutic doses, but appears not to be due to saturation of normal elimination pathways.

What to do if an initial antidepressant fails?

OBJECTIVE

To provide family physicians with practical ways of managing depressed patients responding insufficiently to initial antidepressant treatment.

QUALITY OF EVIDENCE

A search of MEDLINE and relevant bibliographies showed most studies could be categorized as level III evidence. Few well controlled studies (eg, level I evidence) specify treatment of next choice in rigorously defined treatment-refractory depression (TRD).

MAIN MESSAGE

Failure to achieve and sustain full symptom remission affects relatively few treated depressed patients. Most chronically depressed people are not absolutely resistant but are relatively resistant to treatment; they fail to achieve the goals of treatment because of improper diagnosis or insufficient treatment application. The literature on TRD has largely focused on medication strategies; fewer studies investigated psychosocial approaches. The best established augmentation strategies are lithium salts and triidothyronine (T3). Combination antidepressants have become clinical psychiatrists' preferred treatment, despite limited evidence. Electroconvulsive therapy (ECT) remains a feasible option for TRD, but response rates are poor among people with TRD. High relapse rates after ECT remain a serious and common clinical dilemma.

CONCLUSION

Family physicians should familiarize themselves with some new strategies to modify inadequate response to initial antidepressant treatment.

Moclobemide: therapeutic use and clinical studies

Moclobemide is a reversible inhibitor of monoamine-oxidase-A (RIMA) and has been extensively evaluated in the treatment of a wide spectrum of depressive disorders and less extensively studied in anxiety disorders. Nearly all meta-analyses and most comparative studies indicated that in the acute management of depression this drug is more efficacious than placebo and as efficacious as tricyclic (or some heterocyclic) antidepressants or selective serotonin reuptake inhibitors (SSRIs). There is a growing evidence that moclobemide is not inferior to other antidepressants in the treatment of subtypes of depression, such as dysthymia, endogenous (unipolar and bipolar), reactive, atypical, agitated, and retarded depression as with other antidepressants limited evidence suggests that moclobemide has consistent long-term efficacy. However, more controlled studies addressing this issue are needed. For patients with bipolar depression the risk of developing mania seems to be not higher with moclobemide than with other antidepressants. The effective therapeutic dose range for moclobemide in most acute phase trials was 300 to 600 mg, divided in 2 to 3 doses. While one controlled trial and one long-term open-label study found moclobemide to be efficacious in social phobia, three controlled trials subsequently revealed either no effect or less robust effects with the tendency of higher doses (600 - 900 mg/d) to be more efficacious. Two comparative trials demonstrated moclobemide to be as efficacious as fluoxetine or clomipramine in patients suffering from panic disorder. Placebo-controlled trials in this indication are, however, still lacking. A relationship between the plasma concentration of moclobemide and its therapeutic efficacy is not apparent but a positive correlation with adverse events has been found. Dizziness, nausea and insomnia occurred more frequently on moclobemide than on placebo. Due to negligible anticholinergic and antihistaminic actions, moclobemide has been better tolerated than tri- or heterocyclic antidepressants. Gastrointestinal side effects and, especially, sexual dysfunction were much less frequent with moclobemide than with SSRIs. Unlike irreversible MAO-inhibitors, moclobemide has a negligible propensity to induce hypertensive crisis after ingestion of tyramine-rich food ("cheese-reaction"). Therefore, dietary restrictions are not as strict. However, with moclobemide doses above 900 mg/d the risk of interaction with ingested tyramine might become clinically relevant. After multiple dosing the oral bioavailability of moclobemide reaches almost 100%. At therapeutic doses, moclobemide lacks significant negative effects on psychomotor performance, cognitive function or cardiovascular system. Due to the relative freedom from these side effects, moclobemide is particularly attractive in the treatment of elderly patients. Moclobemide is a substrate of CYP2C19. Although it acts as an inhibitor of CYP1A2, CYP2C19, and CYP2D6, relatively few clinically important drug interactions involving moclobemide have been reported. It is relatively safe even in overdose. The drug has a short plasma elimination half-life that allows switching to an alternative agent within 24 h. Since it is well tolerated, therapeutic doses can often be reached rapidly upon onset of treatment. Steady-state plasma levels are reached approximately at one week following dose adjustment. Patients with renal dysfunction require no dose reduction in contrast to patients with severe hepatic impairment. Cases of refractory depression might improve with a combination of moclobemide with other antidepressants, such as clomipramine or a SSRI. Since this combination has rarely been associated with a potentially lethal serotonin syndrome, it requires lower entry doses, a slower dose titration and a more careful monitoring of patients. Combination therapy with moclobemide and other serotonergic agents, or opioids, should be undertaken with caution, although no serious adverse events have been published with therapeutic doses of moclobemide to date. On the basis of animal data the combined use of moclobemide with pethidine or dextropropoxyphene should be avoided. There is no evidence that moclobemide would increase body weight or produce seizures. Some preclinical data suggest that moclobemide may have anticonvulsant property.