Plasma vitamin C is lower in postherpetic neuralgia patients and administration of vitamin C reduces spontaneous pain but not brush-evoked pain.
OBJECTIVE
Plasma vitamin C concentrations have been suggested to be related to pain modulation in postherpetic neuralgia (PHN), an intractable neuropathic pain syndrome. In this study, we first compared plasma concentrations of vitamin C between healthy volunteers and PHN patients and then designed a symptom-based and mechanism-based approach to assess the analgesic effect of intravenous vitamin C on spontaneous and brush-evoked pain.


METHODS
Study 1 was cross-sectional that enrolled 39 healthy volunteers and 38 PHN patients. Study 2 was a double-blinded, placebo-controlled intervention study, which comprised 41 patients randomly allocated into the ascorbate group and placebo. Each patient received normal saline infusion with or without ascorbate on days 1, 3, and 5 and answered questionnaires that included side effects; numeric rating pain scale (NRS) on spontaneous and brush-evoked pain on days 1, 3, 5, and 7; and patient global impression of change on spontaneous and brush-evoked pain on day 7.


RESULTS
Study 1 revealed that plasma concentrations of vitamin C were significantly lower in patients with PHN than in healthy volunteers (P<0.001). Study 2 showed that ascorbate treatment effectively restored plasma vitamin C concentrations in the patients and decreased spontaneous pain by 3.1 in NRS from baseline to day 7, as compared with a decrease of 0.85 in NRS by placebo treatment (P<0.001). Conversely, ascorbate treatment did not significantly affect brush-evoked pain. Ascorbate treatment also resulted in a better efficacy than placebo in patient global impression of change on spontaneous pain (P<0.001) on day 7 and did not affect brush-evoked pain. No side effects were observed.


CONCLUSIONS
Plasma vitamin C status plays a role in PHN, and intravenous ascorbate helps relieve spontaneous pain in PHN.
Chen
Jen-Yin
JY
Departments of Anesthesiology, Chi-Mei Foundation Hospital, Taichung, Taiwan.
Chang
Chia-Yu
CY
Feng
Ping-Hsun
PH
Chu
Chin-Chen
CC
So
Edmund Cheng
EC
Hu
Miao-Lin
ML
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000975:Antioxidants / Q000627:therapeutic use*; D001205:Ascorbic Acid / Q000097:blood* / Q000627:therapeutic use*; D003430:Cross-Sectional Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D051474:Neuralgia, Postherpetic / Q000097:blood / Q000188:drug therapy / Q000503:physiopathology; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D010812:Physical Stimulation / Q000009:adverse effects; D018709:Statistics, Nonparametric; D013997:Time Factors
D000975:Antioxidants; D001205:Ascorbic Acid