Background and importance The combination of perphenazine, a typical antipsychotic, with propranolol, a beta adrenergic antagonist, increases the concentrations of both drugs by pharmacokinetic interaction.¹ The main effect of the interaction is potentiation of the hypotensive effect. Typical antipsychotics have an anticholinergic and antihistamine effect that can cause drowsiness, but also have structural similarities with benzodiazepines.

Aim and objectives To describe the clinical case of a patient with drug poisoning and the interaction between perphenazine and propranolol and its haemodynamic and CNS depressant effects.

Material and methods The patient was a 64-year-old woman who was found at home by the emergency ambulance service with a Glasgow coma scale (GCS) score of 3. Anamnesis showed autolytic attempt. Home treatment was letrozole 2.5 mg every 24 hours orally, perphenazine 8 mg every 12 hours orally, losartan 50 mg/hydrochlorothiazide 12.5 mg every 24 hours orally, propranolol 10 mg every 6 hours orally and paracetamol 325 mg/tramadol 37.5 mg every 8 hours orally.

During transfer to hospital, flumazenil 1 mg was administered intravenously (IV) and GCS changed to 9–10. The patient was admitted to the intensive care unit due to a decreased level of consciousness and haemodynamic instability. Drug tests (toxicology screens) on blood and urine were requested. Endotracheal intubation and gastric lavage were performed. Pinkish content came out and it was thought to be traces of propranolol tablets.

For haemodynamic control, dobutamine was administered at 5 µg/kg/min IV perfusion and antidotes to possible pharmacological intoxication were given: glucagon was administered at 0.03 mg/kg/hour perfusion IV (beta blockers), flumazenil bolus 1 mg IV (benzodiazepines) and naloxone 0.4 mg bolus IV (opioids).

Results Drug tests showed positive urine and blood levels of 84.1 g/L for benzodiazepines. In the anamnesis she did not take benzodiazepines. Dobutamine, glucagon and naloxone were stopped because of the test results and haemodynamic improvement. Flumazenil 1 mg bolus IV was administered again and an infusion of flumazenil was started at 0.5 mg/hour IV until the level of consciousness was regained and the patient answered verbal orders on what happened 4 hours later.

Conclusion and relevance Perphenazine can produce possible false positives for benzodiazepines. The interaction between perphenazine and propranolol can trigger haemodynamic instability and CNS depression, which can be successfully managed with dobutamine, glucagon and flumazenil.

References and/or acknowledgements 1. Lexicomp: Interactions. Perphenazine–propranolol. Available at: https://online.lexi.com/lco/action/interact

No conflict of interest.