PROBENECID AND COLCHICINE
Clinical safety rating
safeIncreases levels of many drugs by inhibiting their renal secretion (eg penicillins methotrexate) Can cause GI upset and nephrotic syndrome.
Probenecid inhibits renal tubular reabsorption of uric acid, increasing its excretion; colchicine binds to tubulin, inhibiting microtubule polymerization and reducing inflammatory response to urate crystals.
| Metabolism | Probenecid: hepatic via glucuronidation and oxidation; colchicine: hepatic via CYP3A4 and P-glycoprotein. |
| Excretion | Probenecid: Renal excretion of unchanged drug and metabolites; approx. 75-95% of dose eliminated in urine, with <5% as unchanged probenecid. Colchicine: Primarily fecal excretion (about 65%) via biliary excretion; renal excretion accounts for about 20-30% of elimination, with enterohepatic recirculation. |
| Half-life | Probenecid: Terminal half-life 6-12 hours (dose-dependent; prolonged at higher doses due to saturable tubular secretion). Colchicine: Terminal half-life 20-40 hours (range 9-30 hours in healthy subjects; prolonged in renal impairment up to 50-60 hours). |
| Protein binding | Probenecid: 85-95% bound to albumin. Colchicine: 30-50% bound to albumin. |
| Volume of Distribution | Probenecid: 0.15 L/kg (indicates distribution primarily in extracellular fluid). Colchicine: 2-8 L/kg (large Vd indicating extensive tissue distribution, particularly into leukocytes and other cells). |
| Bioavailability | Probenecid: Oral bioavailability nearly complete (approx. 100%) with extensive metabolism. Colchicine: Oral bioavailability 25-50% (first-pass metabolism and P-glycoprotein efflux in gut); bioavailability listed for oral route. |
| Onset of Action | Probenecid: Oral, onset of uricosuric effect within 30-60 minutes; peak effect at 2-4 hours. Colchicine: Oral, onset of anti-inflammatory effect for acute gout flares within 12-24 hours; IV (not available in US) onset of action within 6-12 hours. |
| Duration of Action | Probenecid: Uricosuric effect lasts 8-12 hours after oral dose. Colchicine: Duration of symptomatic relief in acute gout is variable; typical course of treatment is 1-2 days for acute flare, with effect persisting for 24-48 hours after cessation. |
| Molecular Weight | Probenecid: 285.36 Da; Colchicine: 399.44 Da |
One tablet (probenecid 500 mg/colchicine 0.5 mg) orally twice daily for 7 days, then one tablet daily thereafter.
| Dosage form | TABLET |
| Renal impairment | GFR 30-50 mL/min: reduce dose to one tablet daily. GFR 10-29 mL/min: one tablet every 2-3 days. GFR <10 mL/min or dialysis: contraindicated. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce colchicine dose by 50%. Child-Pugh C: contraindicated. |
| Pediatric use | Not recommended for pediatric use. For acute gout in adolescents, consider alternative therapy. |
| Geriatric use | Start at lowest dose (one tablet daily), monitor renal function and for toxicity due to age-related decreased renal function. |
| 1st trimester | Avoid due to colchicine teratogenicity (increased risk of chromosomal abnormalities and neural tube defects). Probenecid may affect uric acid levels, but data limited. |
| 2nd trimester | Use only if benefit outweighs risk. Colchicine has potential for fetal toxicity; probenecid safety not well established. |
| 3rd trimester | Avoid near term due to colchicine's antimitotic effects and potential neonatal toxicity; probenecid may cause neonatal hyperuricemia. |
Clinical note
Increases levels of many drugs by inhibiting their renal secretion (eg penicillins methotrexate) Can cause GI upset and nephrotic syndrome.
| FDA category | Animal |
| Placental transfer | Both colchicine and probenecid cross the placenta. Colchicine achieves significant fetal concentrations; probenecid transfer is moderate. |
| Breastfeeding | Both probenecid and colchicine are excreted into breast milk. Colchicine can accumulate in nursing infants; probenecid may cause infant rash or diarrhea. Avoid or use with caution, monitor infant for adverse effects. |
| Lactation Rating | L4 (Possibly Hazardous) |
| Teratogenic Risk | First trimester: Data limited; colchicine is associated with increased risk of chromosomal abnormalities in vitro, but human studies show no consistent pattern of major malformations. Probenecid is not teratogenic in animal studies. Second and third trimesters: No evidence of fetal harm from either drug, but insufficient data. Avoid during pregnancy unless benefit outweighs risk. |
| Fetal Monitoring | Monitor renal function (serum creatinine, BUN) and liver enzymes periodically, especially with prolonged use. In pregnancy, consider fetal ultrasound for growth and anatomy if exposure in first trimester. |
| Fertility Effects | Colchicine may cause reversible oligospermia or azoospermia in males; no evidence of female fertility impairment. Probenecid has no known effects on fertility. |
■ FDA Black Box Warning
None.
| Common Effects | Hyperuricemia |
| Serious Effects |
Hypersensitivity to probenecid, colchicine, or any componentSevere renal impairment (CrCl < 10 mL/min)Blood dyscrasias (e.g., aplastic anemia, agranulocytosis)Active peptic ulcer diseaseGout flare during acute attack (if used prophylactically, not for acute treatment)
| Precautions | Hematologic toxicity (bone marrow suppression), neuromuscular toxicity (especially with renal impairment), severe diarrhea, drug interactions (CYP3A4 and P-gp inhibitors), use caution in elderly and renal/hepatic impairment. |
| Food/Dietary | Limit consumption of high-purine foods (e.g., organ meats, anchovies, sardines, red meat, shellfish) as they can exacerbate gout. Avoid alcohol, particularly beer and liquor, which increase uric acid production and reduce probenecid efficacy. No specific food interaction with colchicine; maintain adequate hydration. |
| Clinical Pearls | Colchicine levels can increase with concurrent use of P-glycoprotein inhibitors (e.g., amiodarone, verapamil, clarithromycin) or CYP3A4 inhibitors (e.g., ketoconazole, ritonavir). Probenecid can raise plasma concentrations of penicillins, cephalosporins, and indomethacin. Monitor for colchicine toxicity (nausea, diarrhea, myopathy) especially in renal impairment; reduce dose in chronic kidney disease. Probenecid may inhibit renal excretion of drugs and can cause uricosuria, so ensure high fluid intake to prevent urate stones. |
| Patient Advice | Take with food or milk to reduce gastrointestinal upset. · Drink plenty of water (at least 8 glasses per day) while taking probenecid. · Colchicine can cause severe diarrhea or vomiting; stop and call your doctor if this occurs. · Avoid alcohol, which can worsen gout and interfere with probenecid's effect. · Do not start new medications (especially antibiotics, antifungal, or heart medications) without consulting your doctor due to drug interactions. · Report unexplained muscle pain, weakness, numbness, or tingling immediately (colchicine myopathy). · Keep this and all medications out of reach of children. |
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