Study provides first evidence-based colchicine dosing recommendations

Colchicine, a widely used drug for the prevention and treatment of gout flares, interacts dangerously with many commonly prescribed pharmaceuticals, such as antibiotics, antihypertensive drugs, antifungals, immunosuppressants, and protease inhibitors, according to a study published in the August issue of Arthritis & Rheumatism. However, most patients can take colchicines safely with these medications as long as the dose is adjusted, the study indicated.

To develop evidence-based colchicine-dosing algorithms with improved safety, a series of drug-drug interaction (DDI) studies was performed to assess the concomitant treatment of colchicine with known inhibitors of cytochrome P450 3A4 (CYP3A4)/P-glycoprotein (cyclosporine, ketoconazole, ritonavir, clarithromycin, azithromycin, verapamil ER [extended release]), and diltiazem ER).

In all, there were 7 studies. All were open-label, non-randomized, single-center, 1-sequence, 2-period DDI experiments, using two 0.6-mg doses of colchicine, separated by a minimum 14-day washout period, followed by administration of the approved on-label regimen of known CYP3A4/P-glycoprotein inhibitors.

Each of the drugs, except for azithromycin, was found to interact significantly with standard colchicine dosing regimens; in some cases more than doubling levels of colchicine in the blood and increasing the risk of serious toxicities. Cyclosporine and clarithromycin in particular increased peak colchicine blood levels by nearly 300%.

The authors recommended that colchicine doses be reduced between of 33% to 66% for the treatment of acute gout and 50% to 75% for prophylaxis, when used as concomitant therapy with each of the drugs studied with the exception of azithromycyin where no dose adjustments were necessary.

Specific dosing recommendations resulting from the study are as follows:

Drug

Acute Flare Dosing Recommendations

Flare Prophylaxis Dosing Recommendations

Familial Mediterranean Fever Dosing Recommendations

cyclosporine

0.6 mg (1 tablet) X 1 dose

0.3 mg once a day, or 0.3 mg every other day

Maximum daily dose of 0.6 mg (or 0.3 mg twice a day)

clarithromycin, ketoconazole, ritonavir

0.6 mg (1 tablet) X 1 dose, followed by 0.3 mg (half tablet) 1 hour later

0.3 mg once a day, or 0.3 mg every other day

Maximum daily dose of 0.6 mg (or 0.3 mg twice a day)

diltiazem, verapamil

1.2 mg (2 tablets) X 1 dose

0.3 mg twice a day (or 0.6 mg once a day), or 0.3 mg once a day

Maximum daily dose of 1.2 mg (or 0.6 mg twice a day)

azithromycin

No dose reduction required

No dose reduction required

No dose reduction required

The studies were among the 17 clinical trials conducted by URL Pharma that led to FDA approval of Colcrys.

“Despite the fact that colchicine has been used for decades in the prevention and treatment of gout flares and for FMF, the pharmacokinetics and metabolism of colchicine have not been extensively studied, until now,” said Robert A. Terkeltaub, MD, interim division chief and professor of medicine at the University of California San Diego and the VA Medical Center, and the paper’s lead author. “The results of these studies form the foundation of evidence-based dosing guidance for colchicine in the presence of CYP3A4 or P-gp inhibitors that help achieve optimal therapeutic benefit while avoiding dangerous and unnecessary safety risks.”