Effects of Garlic Supplements on Opioids in Healthy Volunteers

OBJECTIVES:

• To determine whether CYP3A (Cytochrome P450 3A) and/or P-glycoprotein mediated interactions exist between garlic supplements and oxycodone (a commonly used oral opioid analgesic) in healthy volunteers.

OUTLINE:

This is a single-blind, randomized, crossover study. Participants are randomized to 1 of 2 arms. Each arm entails two 30-day treatment periods, with a washout of at least 4 weeks in between.

• Arm I: In Period 1, participants receive oral garlic powder twice daily on days 1-28 and oral oxycodone on day 28. In Period 2, participants receive oral placebo twice daily on days 1-28 and oral oxycodone on day 28.
• Arm II: In Period 1, participants receive oral placebo twice daily on days 1-28 and oral oxycodone on days 28. In Period 2, participants receive oral garlic powder twice daily on days 1-28 and oral oxycodone on day 28.

In both periods of each arm, participants receive a combination of oral midazolam and oral digoxin for CYP3A and P-glycoprotein phenotyping on day 29. Blood samples are collected periodically and analyzed by liquid chromatography-mass spectrometry (LC-MS).

Blood and urine samples are collected after receiving oxycodone for pharmacokinetic characterization. Plasma concentrations of oxycodone and its metabolites are measured by LC-MS.

Response to experimentally induced pain by the Cold Pressor Test (CPT) is assessed at baseline and periodically after oxycodone treatment. Subjective ratings of opioid side effects are assessed by validated questionnaires for somatic side effects and cognitive function impairments.

Inclusion criteria

• Healthy volunteer
• Body mass index 20-32

Exclusion criteria

• Not pregnant
• No history of cardiopulmonary, liver, renal, endocrine, neurologic, or psychiatric disease
• No anemia
• No known adverse reactions to opioids, benzodiazepines, cardiac glycosides, or garlic supplements
• No known allergy or hypersensitivity to sulfur-containing food or drugs
• No significant gastrointestinal intolerance to lactose in dairy products
• No recent history of alcohol or substance abuse
• No history of or concurrent heavy daily consumption of allium vegetables (i.e., garlic, shallots, leeks, and chives)
• No handicaps due to visual and hearing impairments
• No resting heart rate < 50 beats per minutes
• No abnormal cardiac rhythm by EKG
• No unusually sensitive response or resistance to pain stimulation (Cold Pressor Test)
• Must be right handed
• No color blindness
• No history of learning disabilities or dyslexia
• Must be literate and proficient in English
• Must be a nonsmoker
• No concurrent medication except oral contraceptives
• No concurrent grapefruit or grapefruit juice
• No other concurrent over-the-counter herbal products or herbal tea