A novel use of Naloxone as a treatment for Eucalyptus oil induced central nervous system depression

To the Editor:

Eucalyptus oil is readily available and commonly used as an inhalation for upper respiratory tract infections. We report a case of an elderly woman who accidentally ingested eucalyptus oil. This is the first reported use of naloxone for reversal of eucalyptus oil induced central nervous system (CNS) depression.

A 74 year old woman was brought in by ambulance to the Emergency Department (ED) of a tertiary care centre three hours after an accidental ingestion of eucalyptus oil. She mistook it for her cough syrup and ingested approximately 20 to 30 mL of 100% pure eucalyptus oil. The contents of the cough syrup were guaiphenesin, glucose, treacle, sucrose, sodium benzoate and sodium bisulphate. Her only co-morbidities were hypertension and hypercholesterolemia for which she was prescribed perindopril, clopidogrel and atorvastatin. She was not known to have any allergies. The patient felt drowsy and lethargic on pre-hospital assessment by paramedics.

On initial assessment in the ED, she was maintaining her airway. Respiratory effort was weak with a rate of 14 breaths/min but with good air entry on auscultation. Her oxygen saturation was 98% on a venturi mask at 60% inspired oxygen concentration. Her pulse rate was 70 beats/min with a blood pressure of 169/88 mm Hg. Glasgow coma scale (GCS) was 14 and she appeared drowsy and lethargic. Bilaterally pupils were size 2 (miosis) and sluggishly reactive to light. Her blood sugar was 8.2 mmol/L (reference range 3.0–7.8 mmol/L) and venous blood gas was suggestive of lactic acidosis with pH 7.31 (reference range 7.34–7.45) and lactate 3.58 mmol/L (reference range 0.70–2.50 mmol/L). Otherwise her full blood count, electrolytes, liver function tests and renal function tests were within normal range. Urine toxicology screen did not show presence of opiates or any other substance. A strong smell of eucalyptus oil was present on her breath and in her nasogastric aspirate.

Over the next hour, she continued to get increasingly drowsy and her GCS dropped to 13 and the respiratory rate reduced to 9 breaths/min with an oxygen saturation of 90%. She was given intravenous naloxone 400 microgram as a bolus. Within three minutes, her GCS improved to 15 and she was talking normally. Her respiratory rate increased to 16 breaths/min and oxygen saturation improved to 100%. Half an hour after the naloxone, she started to get drowsy and her respiratory rate dropped again. She was given a second dose of intravenous naloxone 400 microgram with an excellent effect.

A further deterioration in her respiratory effort and level of consciousness occurred 20 min later. A decision was made to commence her on a therapeutic trial of a naloxone infusion. Resolution of her symptoms and signs occurred within 15 min, and she remained well for the duration of the infusion. The infusion was started at 0.4 mg/h for 4 h, and then reduced to 0.2 mg/h for a further 2 h prior to cessation. After six hours, the naloxone infusion was stopped and she was observed overnight in the ED short stay unit. She did not have any adverse effects secondary to naloxone treatment and was discharged the following morning without any sequelae. One month later, it is known by telephonic enquirythat she has continued to remain well.

Toxic doses of Eucalyptus oil can range from 0.6–5 mL in children and 5–10 mL in adults (with respect to a 100% oil preparation) however there is no correlation between the amount ingested and the presence of symptoms. Symptom onset can be rapid but in some cases may be delayed for several hours. Initially these symptoms may include headache, dizziness, and nasal and epigastric burning. This can progress to vomiting and gastrointestinal distress, miosis, headache, ataxia, seizures, hypoventilation and coma. Respiratory distress and pneumonia can also be associated with aspiration of the oil.^1,2

There has been no effective antidote reported in the literature. Due to our patients’ hypoventilation, drowsiness and miosis a test dose of naloxone was administered. This proved to be very effective. Naloxone is described as a pure antagonist that reverses the effects of both exogenous and endogenous opioids including endorphins, encephalins and dynorphins.³ Hence naloxone can also partially reverse CNS depression due to a number of other non-opioid drugs and a variety of pathological states. The mechanism of CNS depression by volatile oils is unclear.

This is the first reported case of eucalyptus oil induced CNS depression that responded to naloxone. There was no adverse event and our patient made a complete recovery. Further case reports are required to establish its routine use.

Declaration of Interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper.