Part 2 · Colchicine
Dosing, safety, interactions
Colchicine works 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 daily dosing, then explore the published dose ranges, the organs that are monitored, and what the guidelines say about kidneys, pregnancy and lifelong use.
Dosing for any person is set by their own clinician. This module reports what EULAR 2016, the 2024 EULAR/PReS update and the US label (COLCRYS) publish. It is a study aid, not a dosing guide. 63,199,203
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 once-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 published half-lives run from about 7 hours to about 58 hours depending on study design, so the curve would be flatter or steeper with other values. 16,63,66 The zone boundaries are illustrative: there is no sharp line between safe and toxic levels. 1.8 mg/day is simply a value inside the label's adult FMF range, chosen for the picture.
| Added drug or food | Label group | Mean colchicine AUC change (single 0.6 mg dose) | Label FMF cap if there is no alternative |
|---|---|---|---|
| Clarithromycin | Strong CYP3A4 inhibitor | +282% | 0.6 mg/day |
| Ketoconazole (itraconazole listed with it) | Strong CYP3A4 inhibitor | +212% (ketoconazole) | 0.6 mg/day |
| Ritonavir (and most protease inhibitors) | Strong CYP3A4 inhibitor | +296% | 0.6 mg/day |
| Cyclosporine | P-gp inhibitor | +259% | 0.6 mg/day |
| Verapamil | Moderate CYP3A4 inhibitor | +103% | 1.2 mg/day |
| Diltiazem | Moderate CYP3A4 inhibitor | +93% | 1.2 mg/day |
| Azithromycin | Not in the cap lists we cite | +57% | None listed in our sources |
| Grapefruit juice | Moderate CYP3A4 inhibitor | No meaningful mean change in the label's own study (Cmax and AUC each moved by under 3%) | 1.2 mg/day; label tells patients to avoid it |
| Statins, fibrates | Added muscle toxicity | Not quantified in our sources | Warning: myopathy and rhabdomyolysis |
Sources: US label interaction studies and dose-adjustment lists; the caps also apply within 14 days of taking the interacting drug. 63,257
The clarithromycin study
10.2% vs 3.6%In a retrospective study, 9 of 88 patients (10.2%) given clarithromycin and colchicine at the same time died, versus 1 of 28 (3.6%) given them one after the other. Baseline kidney impairment, a longer overlap and pancytopenia predicted death. 103
Azithromycin raised colchicine exposure much less and is suggested in reviews as the safer macrolide. 16,257
Statins and fibrates
The concern here is muscle: colchicine and these drug classes can each damage it. The label reports myopathy and rhabdomyolysis when one is added to a stable regimen of the other, and notes that CK monitoring will not necessarily prevent severe myopathy. 63
One review suggests pravastatin or rosuvastatin may be preferred over CYP3A4-metabolized statins; myopathy has still been reported with pravastatin. 16,243
Grapefruit: a label paradox
Both sides of this sit in the same document. The label lists grapefruit juice in its table of moderate CYP3A4 inhibitors, applies the 1.2 mg/day FMF cap to it and tells patients to avoid it. Yet the label's own interaction study (240 mL twice daily for 4 days) found mean Cmax and AUC each moved by under 3%, which is no meaningful change. Neither source we cite resolves the contradiction; the effect may vary with the product and the person. 63,147
2 · Published doses by age
Bars report published ranges, not a dose for anyone; a dose for a person is set by their clinician. Dark lilac: EULAR 2016 starting dose. Light lilac: room for stepwise increases up to the published maximum (red line). The guidelines give the maxima for "children" and "adults" without naming an age cut-off, so age 18 is this app's assumption, not a guideline figure.
What EULAR publishes
- Start colchicine as soon as a clinical diagnosis is made. 199,200
- Starting doses: ≤0.5 mg/day under 5 years, 0.5–1.0 mg/day at 5–10 years, 1.0–1.5 mg/day over 10 years and in adults. 199,200
- Maximum 2 mg/day in children and 3 mg/day in adults; the 2024 update keeps both ceilings. 43,200,203
- Higher starting doses can be used with high disease activity, M694V homozygosity, or complications such as amyloidosis. 199,200
- The maxima are published for "children" and "adults"; no source we cite names the age at which one becomes the other. 199,200,203
Single or divided?
Both EULAR 2016 and the 2024 update allow one daily dose or divided doses, chosen by tolerance and adherence. Dividing can ease gut side effects; once daily can help adherence. 199,200,203
In a 24-week randomized trial (79 children completed it), once-daily dosing was non-inferior to twice-daily for attacks, CRP, ESR and SAA. Diarrhoea was slightly more frequent with once-daily dosing. 213
Steps up and the label
If attacks or subclinical inflammation persist in an adherent patient, the dose is raised stepwise: 0.5 mg/day steps in EULAR 2016, 0.25 or 0.5 mg steps in a German consensus, 0.3 mg/day increments in the US label. CRP or SAA is checked at least every 3 months while escalating. 59,63,199,200,222
US label FMF ranges: 0.3–1.8 mg/day at 4–6 years, 0.9–1.8 at 6–12 years, 1.2–2.4 over 12 years and in adults. A 2007 paediatric consensus put the ceiling at 2.5 mg/day. 59,63,117
A steady-state study across ages 2 to under 16 found broadly similar colchicine exposure in children and adults on standard starting doses, despite the higher mg/kg doses in younger children; exposure ran about 25% higher in the 4 to under 6 year group. 22
3 · Toxicity and monitoring
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. Overdose can be fatal: poisoning moves over days from gut symptoms and fluid loss to multi-organ failure. The 2024 update asks that any intentional or accidental overdose be assessed carefully, and the label advises keeping tablets away from children. 43,63,67,147
What is checked, and how often. EULAR 2016: review response, toxicity and adherence every 6 months (more often in the first year or when inflammatory markers are raised, yearly once stable), with SAA and/or CRP, blood count, liver enzymes, kidney function, CPK and urinalysis. The 2024 update asks for regular monitoring, more often at diagnosis and when disease is uncontrolled, without a fixed interval. 199,203,222
4 · Kidneys and liver
Creatinine clearance (CrCl) in mL/min. Categories follow the US label's FMF section.
Liver impairment
Clearance may be much lower and the half-life longer in chronic liver disease, with wide variation between patients. The label (FMF) advises close monitoring in mild to moderate impairment and considering a dose reduction in severe disease; there are no pharmacokinetic data for Child-Pugh C. In one report the half-life was 2–3 times longer in severe kidney failure and about 10 times longer with kidney failure plus cirrhosis. 16,63
5 · Pregnancy, breastfeeding, fertility
Pregnancy Established
EULAR 2016: colchicine should not be stopped during conception, pregnancy or breastfeeding, and amniocentesis is not justified because of it. The 2024 update keeps both points. 43,199,200
- 179 colchicine-exposed FMF pregnancies vs 197 untreated FMF and 312 healthy: no difference in early or late miscarriage or malformations. 15
- 238 exposed pregnancies (87% FMF): major anomalies 4.5% vs 3.9% in controls (P = 0.648), no cytogenetic anomalies. 53
- 2018 meta-analysis: no increase in miscarriage or major malformations. 107
Breastfeeding
Fetal plasma levels are reported at about 15% of maternal levels; breast-milk levels are similar to maternal serum. 63
In 4 nursing mothers with FMF, milk levels (1.9–8.6 ng/mL) tracked serum levels; the authors judged infant intake small and nursing safe. The label estimates infant exposure at under 10% of the maternal weight-adjusted dose and urges caution. 9,63
Male fertility
EULAR 2016: men generally need not stop colchicine before conception; only rare, proven colchicine-related azoospermia may call for a temporary dose reduction. 199,200
In some FMF men with azoospermia, testicular biopsy showed amyloidosis, so the disease, not the drug, may be the cause. The label calls drug-related male infertility rare and reversible. 10,63,91
6 · Resistance, adherence, lifelong use
Resistance and intolerance
5–10%One review reports non-response at 5–10%; another puts it at up to 5%, plus 2–5% who cannot tolerate the drug; a third gives 5–15% and notes the top figure may be inflated by missed doses. 13,16,200
EULAR 2016: ≥1 attack a month after ≥6 months at the maximum tolerated dose may indicate resistance. A 2021 consensus: ≥1 attack a month over 3 months, or persistent lab inflammation, with adherence checked. The 2024 update: add-on therapy, IL-1 blockers best supported; colchicine usually continues. 59,199,202,203
Adherence
13%of 38 patients in an Israeli clinic filled every prescription in a year; 8% filled none. 13
- 324 Turkish children (MASIF scale): 72.8% poorly adherent. 60
- 104 Turkish adults (MMAS-8): low 28.8%, moderate 45.2%, high 26.0%. 24
Guidelines rule out missed doses before labelling anyone resistant. 59,200
Lifelong, and the 5-year rule
FMF treatment is lifelong, with adherence as the cornerstone of the 2024 principles. 43,200,203
EULAR 2016 allowed a dose reduction to be considered only after more than 5 years without attacks and with normal acute-phase reactants, after expert consultation and with continued monitoring. A 2025 editorial warns that older age or carrying one variant should not automatically lead to dose reduction. 89,199,200