The anaesthetist, opioid analgesic drugs, and serotonin toxicity: a mechanistic and clinical review

Most cases of serotonin toxicity are provoked by therapeutic doses of a combination of two or more serotonergic drugs, defined as drugs affecting the serotonin neurotransmitter system. Common serotonergic drugs include many antidepressants, antipsychotics, and opioid analgesics, particularly fentanyl, tramadol, meperidine (pethidine), and methadone, but rarely morphine and other related phenanthrenes. Symptoms of serotonin toxicity are attributable to an effect on monoaminergic transmission caused by an increased synaptic concentration of serotonin. The serotonin transporter (SERT) maintains low serotonin concentrations and is important for the reuptake of the neurotransmitter into the presynaptic nerve terminals. Some opioids inhibit the reuptake of serotonin by inhibiting SERT, thus increasing the plasma and synaptic cleft serotonin concentrations that activate the serotonin receptors. Opioids that are good inhibitors of SERT (tramadol, dextromethorphan, methadone, and meperidine) are most frequently associated with serotonin toxicity. Tramadol also has a direct serotonin-releasing action. Fentanyl produces an efflux of serotonin, and binds to 5-hydroxytryptamine (5-HT)_1A and 5-HT_2A receptors, whilst methadone, meperidine, and more weakly tapentadol, bind to 5-HT_2A but not 5-HT_1A receptors. The perioperative period is a time where opioids and other serotonergic drugs are frequently administered in rapid succession, sometimes to patients with other serotonergic drugs in their system. This makes the perioperative period a relatively risky time for serotonin toxicity to occur. The intraoperative recognition of serotonin toxicity is challenging as it can mimic other serious syndromes, such as malignant hyperthermia, sepsis, thyroid storm, and neuroleptic malignant syndrome. Anaesthetists must maintain a heightened awareness of its possible occurrence and a readiness to engage in early treatment to avoid poor outcomes.

Toxicity of tapentadol: a systematic review

BACKGROUND

Tapentadol is a novel atypical opioid. Anecdotal evidence suggests that tapentadol has a lower toxicity than conventional opioids.

OBJECTIVES

To evaluate all single-drug mortality due to tapentadol and assess serious adverse events caused by tapentadol.

METHODS

The Preferred Reporting Items for Systematic review and Meta-Analysis Protocols (PRISMA-P) reporting guidelines, an evidence-based minimum set of items for reporting in systematic reviews, were followed in this systematic review.

RESULTS

 24 peer-reviewed papers were identified. They indicate that tapentadol toxicity can cause mortality and serious adverse effects.

CONCLUSION(S)

At least four confirmed fatalities, and serious adverse effects have been documented for individuals abusing or using tapentadol as prescribed. Serious adverse effects of tapentadol use may include respiratory depression, confusion, coma, hallucination/delusion, seizures, tachycardia, hypertension, agitation, tremor, miosis, hypotension, dyspnea, electrolyte abnormality, atrial fibrillation or severe upper abdominal pain. Tapentadol is unlikely to cause serotonin syndrome. The toxicity of tapentadol is significantly less than pure mu opioids, such as oxycodone.