Part 2 · Treating a flare
Colchicine dosing & safety
Colchicine treats a gout flare at low doses but has a narrow safety margin, and a few common drugs can push its blood level up several-fold. Pick an interacting drug and press play to watch ten days of prophylaxis, then compare the published flare and prophylaxis schedules, the organs that are watched, and the kidney and liver rules.
Dosing for any person is set by their own clinician. This module reports what the US labels (COLCRYS tablets, MITIGARE capsules), EULAR 2016 and the ACR guidelines publish. It is a study aid, not a dosing guide. 117,124,135,203,331
Interactions can be fatal
Strong CYP3A4 inhibitors (such as clarithromycin, ketoconazole, itraconazole, ritonavir) and P-glycoprotein inhibitors (such as cyclosporine) stop the body clearing colchicine. The US label contraindicates them with colchicine in people with kidney or liver impairment, because fatal toxicity has occurred at therapeutic doses. EULAR 2016 says not to give colchicine with strong P-gp and/or CYP3A4 inhibitors. 117,331
1 · The exposure window
Schematic. The curve heights come from the label's single-dose (0.6 mg) AUC studies in healthy volunteers, scaled to twice-daily dosing with a half-life of about 29 hours; inhibition is modelled as a mix of higher absorption and slower clearance. That 29 hours sits inside the label's repeated-dose range of 26.6–31.2 hours, but a study after an intravenous dose found 57.8 hours, so the curve would be flatter or steeper with other values. 117,132 The zone boundaries are illustrative: there is no sharp line between safe and toxic levels. 133 0.6 mg twice daily is the top of the label's prophylaxis range, chosen for the picture.
| Added drug or food | Label group | Mean colchicine AUC change (single 0.6 mg dose) | Label flare dose if there is no alternative | Label prophylaxis dose (if 0.6 mg twice daily was intended) |
|---|---|---|---|---|
| Ritonavir (and most protease inhibitors) | Strong CYP3A4 inhibitor | +296% | 0.6 mg, then 0.3 mg 1 h later; not repeated within 3 days | 0.3 mg once daily |
| Clarithromycin | Strong CYP3A4 inhibitor | +282% | 0.6 mg, then 0.3 mg 1 h later; not repeated within 3 days | 0.3 mg once daily |
| Cyclosporine (and ranolazine) | P-gp inhibitor | +259% | 0.6 mg once; not repeated within 3 days | 0.3 mg once daily |
| Ketoconazole (itraconazole listed with it) | Strong CYP3A4 inhibitor | +212% (ketoconazole) | 0.6 mg, then 0.3 mg 1 h later; not repeated within 3 days | 0.3 mg once daily |
| Verapamil | Moderate CYP3A4 inhibitor | +103% | 1.2 mg once; not repeated within 3 days | 0.3 mg twice daily or 0.6 mg once daily |
| Diltiazem | Moderate CYP3A4 inhibitor | +93% | 1.2 mg once; not repeated within 3 days | 0.3 mg twice daily or 0.6 mg once daily |
| Azithromycin | Not in the label's adjustment lists | +57% | None listed | None listed |
| Grapefruit juice | Moderate CYP3A4 inhibitor | −2% in the label's own study | 1.2 mg once; not repeated within 3 days | 0.3 mg twice daily or 0.6 mg once daily |
| Statins, fibrates | Added muscle toxicity | Not quantified in our sources | Warning: myopathy and rhabdomyolysis | |
Sources: COLCRYS label interaction studies and dose table; the adjustments also apply within 14 days of stopping the interacting drug. The 3-day interval appears only in this table. 117 Other moderate inhibitors in the same label row include erythromycin, fluconazole and aprepitant. 117
The clarithromycin study
10.2% vs 3.6%In a retrospective study, 9 of 88 inpatients (10.2%) given clarithromycin and colchicine at the same time died, versus 1 of 28 (3.6%) given them one after the other. A longer overlap (RR 2.16), baseline kidney impairment (RR 9.1) and pancytopenia (RR 23.4) predicted death. 172
Pharmacokinetic studies support no adjustment with azithromycin. 407
How big are the cuts?
33–66% · 50–75%A dose-reduction algorithm built from pharmacokinetic studies supports cutting the flare dose by 33–66% and the prophylaxis dose by 50–75% with most CYP3A4 or P-gp inhibitors. 407
Statins and fibrates
The concern here is muscle. Statins, fibrates and cyclosporine can potentiate colchicine myopathy and rhabdomyolysis, and older people and people with kidney dysfunction are at higher risk. 117
Grapefruit: a label paradox
The label lists grapefruit juice in its table of moderate CYP3A4 inhibitors, with the matching dose cuts, yet its own interaction study found colchicine AUC changed by −2%. Both sit in the same document, and it does not resolve the conflict. 117
Two products, two wordings
COLCRYS contraindicates P-gp or strong CYP3A4 inhibitors in renal or hepatic impairment. MITIGARE contraindicates drugs that inhibit both P-gp and CYP3A4 in renal or hepatic impairment, and use at all in combined renal and hepatic impairment. 117,124
2 · Published gout schedules
Each schedule is drawn as published, not as a dose for anyone; a dose for a person is set by their clinician. Tablet size shows the mg taken; the line shows the running total over the first 48 hours.
What the US label publishes
- Flare: 1.2 mg at the first sign, then 0.6 mg 1 hour later; maximum 1.8 mg over 1 hour. "Higher doses have not been found to be more effective." 117
- Prophylaxis (adults and adolescents over 16): 0.6 mg once or twice daily, maximum 1.2 mg/day. 117
- Flare during prophylaxis: up to 1.2 mg, then 0.6 mg 1 hour later; wait 12 hours, then resume the prophylactic dose. 117
- Repeat flare courses: safety and efficacy have not been evaluated. 117
- MITIGARE capsules are labelled for prophylaxis only. 124
What guidelines add
- EULAR 2016: 1 mg, then 0.5 mg 1 hour later on day 1, within 12 hours of onset; prophylaxis 0.5–1 mg/day for the first 6 months of urate lowering, reduced in kidney impairment. 331
- ACR 2012: colchicine only if the flare began 36 hours or less earlier; after the loading doses, 0.6 mg once or twice daily from 12 hours until the flare resolves. 203
- ACR 2020: low-dose over high-dose colchicine (strong recommendation); prophylaxis for 3–6 months rather than less than 3 when starting urate lowering. 135
- Hong Kong 2023: prophylaxis 0.5 mg once or twice daily for 3–6 months. 440
Why the low dose won
6.2 vs 6.8 ng/mLThe low-dose flare schedule (1.8 mg over 1 hour) reached a mean peak of 6.2 ng/mL; the old high dose (4.8 mg over 6 hours) reached 6.8 ng/mL. 117 In a Cochrane review, high dose gave no extra benefit but more adverse events (number needed to harm 2). 419
Prophylaxis works
0.52 vs 2.91mean flares with colchicine 0.6 mg twice daily vs placebo while starting allopurinol, in a trial of 43 people (P = 0.008). Months 3–6: 0 vs 1.05 flares. 26 The label says prophylaxis "may be beneficial for at least the first six months" of urate lowering. 117
3 · Toxicity and what is watched
Click an organ or a button. Schematic body map.
Narrow margin, serious overdose. Colchicine has a narrow therapeutic index, with no clear line between non-toxic, toxic and lethal doses; the lowest reported lethal oral doses are 7–26 mg. 133 In a review of 150 overdoses in the label, people who took under 0.5 mg/kg survived with mostly gut effects, 0.5–0.8 mg/kg caused severe reactions such as myelosuppression, and over 0.8 mg/kg was fatal in every case. 117
How toxicity unfolds. Acute toxicity typically begins within 24 hours with abdominal pain, nausea, vomiting and diarrhoea; multi-organ failure follows at 24–72 hours. Gut symptoms are often the first sign. 117,124
4 · Kidneys and liver
Creatinine clearance (CrCl) in mL/min. Categories and rules follow the COLCRYS label's gout sections.
Liver impairment
COLCRYS label (gout): no dose change in mild to moderate hepatic impairment, with close monitoring. In severe impairment, consider a lower prophylaxis dose, and repeat flare courses no more than once every 2 weeks. ACR 2012 lists hepatic disease as a limit for colchicine, NSAIDs and COX-2 inhibitors. 117,203
5 · Pregnancy and breastfeeding
What a 2023 guideline says
The British Society for Rheumatology says colchicine "may be considered during pregnancy" and "may be used in breastfeeding". It rests on a meta-analysis of 550 exposed pregnancies, mostly in FMF at 1–2 mg/day, against 1263 unexposed, with no rise in malformations or miscarriage. 176,356