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Comfrey root extract ointment in the treatment of acute upper or lower back pain: results of a double-blind, randomised, placebo-controlled, multicenter trial
The objective was to show the superiority of Comfrey root extract ointment (Kytta-Salbe® f; Merck Selbstmedikation GmbH) to placebo ointment in patients with acute upper or low back pain. The double-blind, multi-centre, randomised clinical trial with parallel group design was conducted over a period of 5 days±1 day. The 120 patients were treated with verum or placebo ointment 3 times a day, 4g ointment per application. The trial included four visits.
The primary efficacy variable was the area-under-the-curve (AUC) of the Visual Analogue Scale (VAS) on active standardised movement values at visits 1 to 4. The pain intensity on VAS was assessed at performance of standardised, muscle group specific tests. The secondary objectives of the trial were back pain at rest using assessment by patient on VAS, pressure algometry (pain-time curve; AUC over 5 days), global assessment of efficacy by the patient and the investigator, consumption of analgesic medication, and functional impairment measured with the Oswestry Disability Index.
There was a significant treatment difference between Comfrey extract and placebo regarding the primary variable. In the course of the trial the pain intensity on active standardised movement decreased on average (median) about 95.2% in the Comfrey extract group and 37.8% in the placebo group. After one hour the pain intensity was already decreased about 33.0% in the Comfrey extract group (104.8 to 60.4 (mean VAS sum)) and 12.0% in the placebo group (100.00 to 86.5 (mean VAS sum)) indicating an early onset of the treatment effect.
The results of this clinical trial were clear-cut and consistent across all primary and secondary efficacy variables. Comfrey root extract showed a remarkably potent effect in reducing acute back pain. Reduction of pain and impaired movement was fast and correlated with each other. For the first time a fast-acting effect of the ointment (1 hour) was also witnessed in this trial.