Clinical studies that initiated the use of spinal opioids for the treatment of pain: A new approach to historical review.

Opioids administered into the spinal space by intrathecal or epidural routes can provide potent and prolonged selective analgesia. Compared to the systemic administration of opioids, spinal administration can bring about analgesia with fewer central and systemic adverse effects. For the past 40 years, spinal opioid analgesia has achieved great popularity in various fields of pain treatment. The aim of this work is to identify clinical studies that initiated the use of spinal opioids for the treatment of pain. To determine the historical role of each of the review's studies we used the combination of two factors: the study priority in terms of the time of its publication and the degree of its acknowl-edgement in the form of citation impact. The date of publication was regarded as the primary factor, but only if the count of citations indicated a sufficient acknowledgement by the other authors. The citation impact was assessed as the initial citation count - for period of five years after the year of article publication - and the total count. The selection of studies most important for the introduction of spinal opioids to clinical practice was based on two factors - the study priority in terms of the time of its publication and the degree of acknowledgement in the form of citation impact. The date of publication was regarded as the primary factor, but only if the citation count was indicative of sufficient acknowledgement by other authors. Analysis of the related data shows that the clinical studies initiating the use of spinal opioids for the treatment of pain belong to two groups of authors - Wang et al. and Behar et al. Both studies were published in 1979 and described delivery of morphine into the spinal space, although the techniques of administration were different: Wang et al. injected morphine intrathecally, Behar et al. administered morphine epidurally. The response to these studies was overwhelming -- close to a dozen reports on this topic were published in 1979 and more than a hundred - in 1980-1981. The total citation response to the Wang et al. article reached 699, and that to Behar et al. - 518. Two earlier records (1900-1901) of the use of intrathecal morphine, by Nicolae Racoviceanu-Pitesti and Otojiro Kitagawa, found no following in medical literature for more than three quarters of a century.