Subjects

We enrolled eighteen patients with PHN, which was defined as pain that was present for more than three months after healing of the skin rash. The inclusion criteria were the presence of mechanical allodynia and ongoing burning pain of at least 40 mm on a visual analogue scale (VAS, 0 mm=no pain, 100 mm=maximum pain). Those patients with hypersensitivity to lidocaine or who had undergone neurolytic therapy for PHN were excluded from the study. Other exclusion criteria were additional pain of another origin and a decreased compliance with the study protocol due to other disorders.

Method

Study drugs and vehicles

The lidocaine patches (Lidoderm®; Endo Phar­maceuticals Chadds Ford, Pa) contained an adhesive of 5% lidocaine base (700 mg/patch), water, glycerin, D-sorbitol, polyacrylate, sodium carboxymethylcel- lulose, propylene glycol and other ingredients on a non-woven polyester felt backing and this was covered with a polyethylene terephthalate film release liner. The vehicle patches are identical ex­cept for the absence of lidocaine. The size of a single patch were 10 X 14 cm. viagra plus

Study design

The three study sessions were of two types. Each subject underwent two treatment sessions with lidocaine patches and one session with the vehicle patch in a randomized order. During the lidocaine sessions, the subjects applied up to three lidocaine patches directly to the most painful area for 12 hours within a 24-hour period (i.e., 12 hours on, followed by 12 hours off) and they repeated the application once more the next day. During the vehicle patch session, subjects used the same protocol as for the lidocaine patch application. The subjects kept a daily pain diary throughout the study in which they recorded their overall pain level for that day. The sessions were at least 7 days apart. If a subject experienced prolonged relief from one of the sessions, the next sessions were delayed until the pain returned to at least 90% of their average pain level prior to entering the new session. If skin irritation occurred after the application, the next sessions were delayed until the skin irritation completely resolved.

Any kind of topical therapies such as capsaicin and steroids were discontinued at least two weeks prior to the first study session. During the study, subjects were not allowed to use any topical medications on the area affected by the PHN. The subjects were permitted to continue a constant dose of oral medications for controlling the PHN pain, but they were not permitted to start new oral medication during the study.

Pain ratings

Pain intensity was assessed of using a horizontal 100 mm visual analogue scale (VAS). The subject indicated the severity of his or her pain with a mark placed along the line between 0 (=no pain) and 100 (= worst pain) imaginable. The VAS scores were obtained prior to the patch application. After applying the patch, the VAS scores were obtained at 12 hr, 24 hr, 48 hr, 72 hr and 96 hr. Pain relief was assessed using a six-item pain relief scale (0 = worse pain, l=no change, 2 = slight relief, 3 = moderate relief, 4 = a lot of relief, 5= complete relief). As the scale was designed to assess change, the baseline pre-application rating was assumed to be no change (score 1). After applying the patch, the category relief scores were obtained at 12 hr, 24 hr, 48 hr, 72 hr and 96 hr.
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Statistical analysis

The effectiveness end point was the change of the average VAS scores and the 6-item pain relief scales from baseline to the 4th day of the lidocaine and vehicle sessions. The correlation between the lido­caine patch and the vehicle patch results were analyzed using the Mann-Whitney test. The correla­tion between the baseline and each treatment were analyzed using the Wilcoxon signed rank test. Statistical significance was assigned at the p=0.05 level. The data was presented as means + SD. All the analyses were performed using the SPSS package for windows 12.0.