Dextromethorphan Effect on Central Sensitization to Pain in Healthy Volunteers

This is a cross-over group, double-blind, randomized clinical trial in healthy volunteers comparing dextromethorphan and inactive control on freeze-induced hyperalgesia, experimental pain, diffuse noxious inhibitory control (DNIC), pupillary reaction and reaction time.

The influence of CYP3A4 and MDR1 polymorphism on the dextromethorphan analgesic efficacy will be measured.

The study design is divided in two study sequences and each subject participates in the two study sequences and receive the two treatments (dextromethorphan and placebo).

Each study sequence consists of 3 assessment days (Day -1, Day 0 = first treatment administration and Day 1).

Inclusion criteria

• Healthy male volunteers
• Aged between 18 and 45 years
• CYP2D6 Extensive and Intermediate metabolizers
• Body mass index (BMI) between 19 and 30 kg/m2
• Systolic blood pressure between 100 and 150 mmHg, diastolic blood pressure between 50 and 90 mmHg, heart rate between 45 and 90 beats per minute
• Without treatment during the 7 days before inclusion specially no use of analgesic and anti-inflammatory drugs
• Cooperation and understanding enough to conform to the study obligations
• Having given free informed written consent
• Affiliated to the French Social Security
• Inscription or acceptation of inscription in the national register of volunteers involved in trials.

Exclusion criteria

• Hypersensitivity to the active substance or to any of the excipients
• Lactose intolerance
• Hypertension
• History of stroke
• Severe heart failure
• Severe hepatic impairment
• Shortness of breath
• Congenital galactosemia, glucose-galactose malabsorption, lactase deficiency
• Association with linezolid
• Pre-existence or history of peripheral neuropathy due to a cause different from neurotoxic chemotherapy
• Diabetes (type I and II)
• CYP2D6 Poor and Ultra-rapid metabolizers
• AST, ALT, total bilirubin twice the average
• Dextromethorphan intake during the 7 days before inclusion
• Medical and surgical history incompatible with the study
• Disease progression during inclusion
• Excessive consumption of alcohol (> 50g/day), tobacco (≥ 10 cigarettes/day), coffee, tea or drinks with caffeine (equivalent to more than 4 cups a day) or any addiction to drugs
• Subject lacking concentration during tests training and low test results reproducibility
• Subject does not meet the selection criteria for its ability to discriminate sensations to noxious stimuli during psychometric tests
• Subject exclusion period, or the total allowable compensation exceeded
• Subject undergoing a measure of legal protection (guardianship, supervision