Primary Outcome Measures:
- Subjects' pain ratings using the visual analog scale (VAS) (0-100 mm) from pre-drug through 6 hours post-drug
Secondary Outcome Measures:
- Subject ratings of allodynia severity to 3 strokes with a foam brush, the surface areas of greatest pain and allodynia, side effect scores, and a Category Pain Relief Scale rating from 0 (pain worsened) to 5 (complete pain relief)
The varicella zoster virus (VZV) is the smallest of the double-stranded DNA herpes viruses, and the only one capable of producing two different diseases, varicella (chickenpox) and herpes zoster (acute herpes zoster [AHZ], shingles). The incidence of AHZ, and the secondary VZV infection, is strongly age-dependent and reaches 1% per year by age 80 and there are between 300,000 and 1 million new cases of AHZ each year in the US. AHZ is almost always painful, and the pain can be of disabling severity, rendering some sufferers bed-bound and too incapacitated to carry out normal activities, leading to weight loss and dehydration sufficient to require inpatient therapy. The elderly are especially likely to suffer severe pain.
The most common complication of AHZ is development of postherpetic neuralgia (PHN). Although the overall incidence of PHN after AHZ is about 10%, the incidence has been reported to rise as high as 80% in those over the age of 80. In all published studies, age and greater severity of initial zoster pain are each found to significantly increase the risk of developing PHN. Severe zoster pain is believed to correlate with a more severe cutaneous outbreak, more severe inflammation of the nerve trunk, and possibly greater injury to primary afferent nerve fibers.
There are two separate issues to address when discussing the pain of AHZ. The first is managing the AHZ pain itself, because the burden of suffering is so high. The second is reducing the incidence of PHN. Both issues need to be considered in trial design, in part because severe AHZ pain is itself a risk factor for PHN. Studies of the analgesic effect of pregabalin suggest an analgesic profile similar to that of gabapentin. We would therefore predict, that pregabalin would reduce the pain associated with AHZ and possibly prevent development of PHN.