Clinical meaning
Serotonin syndrome results from excessive serotonergic activity at 5-HT1A and 5-HT2A receptors in the central and peripheral nervous systems, caused by combinations of serotonergic medications such as SSRIs with tramadol, triptans, MAOIs, or linezolid, producing a triad of altered mental status, autonomic instability, and neuromuscular hyperactivity. Neuroleptic malignant syndrome (NMS) involves dopamine D2 receptor blockade primarily in the hypothalamus and basal ganglia, most commonly triggered by antipsychotic medications, manifesting as lead-pipe rigidity, hyperthermia exceeding 40 degrees Celsius, altered mental status, and markedly elevated creatine kinase. QT prolongation occurs when medications block the hERG potassium channel (IKr current), delaying ventricular repolarization and increasing the risk of torsades de pointes, a potentially fatal polymorphic ventricular tachycardia. Drug-drug interactions through CYP450 inhibition or induction alter the metabolism of co-administered drugs, leading to either toxicity from elevated drug levels or therapeutic failure from accelerated clearance.