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.