• Matilda Bäckberg, Olof Beck, Karl-Henrik Jönsson, and Anders Helander.
• Swedish Poisons Information Centre , Stockholm , Sweden.
• Clin Toxicol (Phila). 2015 Jan 1; 53 (7): 609-17.

BackgroundThe supply of unregulated "new psychoactive substances" (NPS) has shown a steady increase over the past six years. This report from the Swedish STRIDA project describes analytically confirmed non-fatal intoxications involving butyrfentanyl (butyrylfentanyl) or 4-fluorobutyrfentanyl (para-fluorobutyrfentanyl), two fentanyl analogues recently introduced as NPS opioids.Study DesignObservational case series of consecutive patients with suspected acute NPS exposure and requiring hospital care from all over Sweden.Patients And MethodsFrom May 2014 to January 2015, blood and urine samples were obtained from four intoxication cases involving butyrfentanyl and one case involving 4-fluorobutyrfentanyl (men, 19-30 years) presenting in emergency departments (ED) or intensive care units (ICU). Laboratory analysis of serum and/or urine samples was performed by multi-component liquid chromatography-mass spectrometry methods. Data on clinical features were collected during consultations with the Poisons Information Centre and retrieved from medical records.Case DetailsOf the five patients, two were discharged home from the ED and three were admitted to the ICU, of whom two required intubation and mechanical ventilation. Clinical features included typical opioid symptoms such as unconsciousness, respiratory depression, and apnea. In one case, naloxone successfully countered the effects. All patients were discharged the same or the following day. Butyrfentanyl was detected in two serum (0.6 and 0.9 ng/mL) and three urine (2.0-65.6 ng/mL) samples from three of four cases; three cases also contained fentanyl. In the 4-fluorobutyrfentanyl case, the substance was detected in serum (∼15 ng/mL) and urine (∼10 ng/mL). In four cases, other NPS and/or classical drugs were also detected. Analysis of two "butyrfentanyl" NPS products (nasal spray and powder) brought to hospital by patients showed that the 10-fold more potent fentanyl was the main active ingredient (∼7.5-10-fold higher amount) in both.ConclusionTypical and potentially life-threatening opioid toxicity was seen in acute intoxications involving butyrfentanyl, 4F-butyrfentanyl, and fentanyl. The incorrect labelling of butyrfentanyl NPS products which instead mainly contained fentanyl is alarming, given the narrow range between a safe and a lethal dose for opioids.

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