Intended for healthcare professionals

Endgames Statistical Question

What is an open label trial?

BMJ 2014; 348 doi: (Published 23 May 2014) Cite this as: BMJ 2014;348:g3434
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}

Researchers assessed the effectiveness of prazosin combined with scorpion antivenom in assisting recovery from scorpion sting. An open label randomised controlled trial study design was used. The control treatment was prazosin alone. The setting was a hospital and research centre in Mahad, a region of India. Participants were patients with grade 2 scorpion envenomation, older than 6 months, and with no cardiorespiratory or central nervous system abnormalities. In total, 70 patients were recruited and allocated to treatment (35 to prazosin and scorpion antivenom, and 35 to prazosin alone) by block randomisation.1

The primary endpoint was resolution of the clinical syndrome within 10 hours of treatment, as assessed by the researchers. The secondary endpoints included the time needed for complete resolution of the clinical syndrome. The proportion of patients who showed complete resolution of the clinical syndrome within 10 hours of treatment was significantly greater in the prazosin plus antivenom group than in the prazosin alone group (91.4% v 22.9%; difference 68.5%, 95% confidence interval 51.8% to 85.2%; P<0.001). The mean time needed for complete resolution of the clinical syndrome was significantly shorter in the antivenom plus prazosin group (8 v 17.7 h; difference −9.7 h, −6.9 to −12.4); P<0.001). The researchers concluded that recovery from a scorpion sting was hastened by simultaneous administration of scorpion antivenom plus prazosin compared with prazosin alone.

Which of the following statements, if any, are true?

  • a) After randomisation, participants were aware which treatment they had been allocated to

  • b) The trial was liable to …

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