Clarithromycin is a potent inhibitor of the activity of cytochrome P450 (CYP) 3A4 and P-glycoprotein (P-gp). CYP 3A4 plays a role in the metabolism of colchicine and P-gp is responsible for the efflux of colchicine across membranes. This study will evaluate the effect of clarithromycin-related inhibition of CYP 3A4 and P-gp on the pharmacokinetics of colchicine. It will also evaluate the safety and tolerability of concurrent administration of clarithromycin and a single dose of colchicine.

Clarithromycin is a potent inhibitor of the activity of cytochrome P450 (CYP) 3A4 and P-glycoprotein (P-gp). CYP 3A4 plays a role in the metabolism of colchicine and P-gp is responsible for the efflux of colchicine across membranes. This open-label, one sequence, two-period, drug-drug interaction study will evaluate the effect of clarithromycin-related inhibition of CYP 3A4 and P-gp on colchicine pharmacokinetics in 24 healthy, non-smoking, non-obese (within +/- 15% of ideal body weight), male and female adult volunteers. The safety and tolerability of concurrent administration of clarithromycin and a single dose of colchicine will also be evaluated. During the first period, subjects will be confined to the study unit beginning the afternoon of the day prior to scheduled dosing (Day -1). On the morning of Day 1, after an overnight fast of at least 10 hours, subjects will be administered a single dose of colchicine 0.6 mg tablet with 240 ml of room temperature water. Blood will be drawn at times sufficient to characterize the baseline pharmacokinetics for this group. Following a 20 day washout period on Day 22, all subjects will return to the clinic to receive a supply of clarithromycin 250 mg tablets, which they will take on an outpatient basis twice daily (at 8 a.m. and 8 p.m.) without regard to meals for a total of 14 doses. Clinic staff will make telephone contact daily with subjects during this course to confirm compliance with the clarithromycin dosing regimen, and to monitor for adverse events and use of concomitant medication. On day 28 in the afternoon, subjects will again be confined to the study unit. On the morning of day 29, after an overnight fast of at least 10 hours all subjects will be administered a single dose of colchicine 0.6 mg and the final dose of clarithromycin with 240 ml water. Blood samples will be drawn at times sufficient to determine pharmacokinetic profiles of colchicine in the presence of clarithromycin at steady state. The pharmacokinetic profiles will be compared to determine the extent of drug-drug interaction.

Inclusion Criteria:

• Healthy, non-smoking, adult volunteers, male and female, 18 to 45 years of age, weighing at least 55 kg and within 15% of ideal body weight, with hemoglobin >/=12 g/dL.
• Female volunteers must be sexually abstinent for 14 days prior to the first dose and throughout the study or using acceptable birth control methods (prior to and during the study), including being postmenopausal or surgically sterile (or sexual activity restricted to a partner that is surgically sterile), hormonal contraception, an IUD, or barrier methods with spermicide. Additionally, they will be advised to remain sexually inactive or to keep the same birth control method for at least 14 days following the last dose of colchicine.

Exclusion Criteria:

• Subjects who are pregnant or lactating
• Test positive at screening for human immunodeficiency virus (HIV), hepatitis B surface antigen (HbsAg) or hepatitis C virus (HCV)
• Have history or presence of significant cardiovascular, pulmonary, hepatic, renal, hematologic, gastrointestinal, endocrine, immunologic, dermatologic, neurologic, or psychiatric disease; have used any drugs or substances known to inhibit or induce CYP enzymes and/or P-gp within 30 days prior to the first dose and throughout the study
• Recent (2-year) history of evidence of alcoholism or drug abuse
• Subjects who donated 50-499 ml of blood within 30 days and more than 499 ml within 56 days prior to the first dose; subjects who have donated in excess of 500 ml of blood in 14 days, 1500 ml or blood in 180 days, or 2500 ml of blood in 1 year (through completion of the study)
• Have participated in another clinical trial within 30 days prior to dosing
• Known and documented drug allergies to colchicine or macrolide antibiotics.