Ascorbic Acid inhibits development of tolerance and dependence to opiates in mice: possible glutamatergic or dopaminergic modulation

Vitamin C, Pain and Opioid Use Disorder

Vitamin C (ascorbic acid, AA) is an essential nutrient in humans. It is vital to a multitude of metabolic pathways, including those affecting mental health, stress response, and pain perception. This paper provides a review of the literature and a theoretical perspective on the potential roles of AA in the treatment of pain and opioid use disorder (OUD). A powerful antioxidant and anti-inflammatory agent involved in glutathione recycling, AA is a cofactor in adrenal steroidogenesis and catecholamine biosynthesis. AA supports the synthesis of serotonin, modulates synaptic dopamine and glutamate, and may also enhance the synthesis of endomorphins and endorphins. In animal models, AA reduces and prevents opioid drug tolerance and physical dependency. It irreversibly inactivates opioid stereospecific binding, while increasing the antinociceptive effects of pain medications. In clinical trials, AA has been proven safe and effective in acute and chronic pain relief, including ambulatory, surgical, and oncological settings. AA may temper the need for opioids, which raises the question of whether it can help reduce the risk of OUD onset. High, frequent doses of AA may also abort cravings and opioid withdrawal symptoms in those with OUD and has better tolerability than other OUD treatments. Further clinical trials on the potential of AA in the prevention and treatment of OUD are warranted.

An open-label pilot study of oral vitamin C as an opioid-sparing agent in patients with chronic pain secondary to cancer

PURPOSE

The purpose of this study is to assess the efficacy of oral Vitamin C as an opioid-sparing agent when used in conjunction with opioids and standard adjuvant therapy in the management of chronic cancer pain.

METHODS

An open-label pilot study of patients ≥18 years of age with chronic pain secondary to cancer and/or its treatment and a Brief Pain Inventory average pain score of ≥3/10. In addition to opioid analgesia, patients received 1 g of vitamin C twice daily over 3 days (total daily dose of 2 g). Patients' usual medications, including breakthrough medications, were continued throughout the study period. The primary endpoint was total daily opioid use during vitamin C administration compared with that immediately prior to study.

RESULTS

Thirty-four patients were enrolled in the study. Seven failed to complete the trial. Across the 17 evaluable patients, the median daily opioid consumption was 360 mg oral morphine equivalents (OME) on the days prior to vitamin C and 390 mg when administered with vitamin C.

CONCLUSION

This study failed to demonstrate any clinically significant benefit from vitamin C in conjunction with opioids in cancer-related pain and does not provide support for embarking on a larger randomised trial to determine efficacy.

Ascorbic Acid interaction with analgesic effect of morphine and tramadol in mice

Background:

Combining different analgesic drugs for improvement of drug efficacy is a recommended strategy intended to achieve the optimal therapeutic effects.

Objectives:

The purpose of the present study was to assess the nature of the interaction between ascorbic acid and two analgesic drugs, morphine and tramadol.

Materials and Methods:

The analgesic activity was assessed by the acetic acid writhing test in male Naval Medical Research Institute (NMRI) mice. The results were obtained using four to six animals in each group. All the drugs were injected intraperitoneally. The effective doses (ED) that produced 20%, 50%, and 65% antinociception (ED₂₀, ED₅₀ and ED₆₅) were calculated from the dose-response curve of each drug alone as well as co-administration of ascorbic acid and tramadol or morphine. The interaction index was calculated as experimental ED/theoretical ED. For each drug combination, ED₅₀, ED₂₀ and ED₆₅ were determined by linear regression analysis of the dose-response curve, and they were compared to theoretical ED₅₀, ED₂₀ and ED₆₅ using t-test.

Results:

The antinociceptive effects of all drugs were dose-dependent (ED₅₀was 206.1 mg/kg for ascorbic acid, 8.33 mg/kg for tramadol, and 0.79 mg/kg for morphine). The interaction index demonstrated additive effects at ED₅₀ and ED₆₅ for co-administration of ascorbic acid and tramadol or morphine. However, at ED₂₀, combination of ascorbic acid and tramadol or morphine showed synergic effects. The interaction index values of the combinations demonstrated the potency ratio of ascorbic acid/morphine to be lower than ascorbic acid/tramadol.

Conclusions:

This study demonstrated the results of interactions between ascorbic acid and tramadol or morphine. The results showed that the interaction effects on antinociception may be synergistic or additive, depending on the level of effect.