Sulfasalazine (Azulfidine)
Prodrug cleaved by colonic bacterial azoreductases into 5-aminosalicylic acid (5-ASA, the anti-inflammatory moiety acting locally in the colon) and sulfapyridine (carrier, systemically absorbed and responsible for most AEs). Used for rheumatoid arthritis (DMARD), ulcerative colitis, and Crohn's colitis. Typical dose 1-3 g/day PO divided BID-QID, titrated from 500 mg/day. Parent F~15% (most delivered intact to colon for local activation); parent t1/2 ~6h, sulfapyridine t1/2 ~10h (longer in slow NAT2 acetylators). Common AEs: GI intolerance, headache, reversible oligospermia, hemolysis in G6PD deficiency, rare Stevens-Johnson/DRESS.
Projected serum levels — 1k mg, twice daily
Maintenance schedule: 1k mg twice daily (oral).
Loading schedule: 1.7k mg on day 1, then 1k mg twice daily — reaching therapeutic levels sooner.
Modeled steady state after ~1 days: peak ≈ 125 mg, trough ≈ 79.1 mg body load. Population-based estimate over 15 days for a 1k mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.
Key facts
- Category
- DMARD
- Route modeled
- Oral
- Model confidence
- inferred
- Half-life
- 6 h
- Common dose
- 1k mg
- Suggested maximum
- 3k mg/day
- Reference dose range
- 500–3k mg (single dose)
- Suggested cadence
- twice daily
- Validated against
- 1k mg oral — Cmax 22 mg/L at 6 h
Documented interactions
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danger
Levothyroxine (Synthroid) + Sulfasalazine (Azulfidine)
Sulfasalazine (Azulfidine) may displace Levothyroxine (Synthroid) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free…
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danger
Tacrolimus (Prograf) + Sulfasalazine (Azulfidine)
Sulfasalazine (Azulfidine) may displace Tacrolimus (Prograf) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free…
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danger
Warfarin (Coumadin) + Sulfasalazine (Azulfidine)
Sulfasalazine (Azulfidine) may displace Warfarin (Coumadin) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free…
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warning
Apigenin + Sulfasalazine (Azulfidine)
Apigenin may displace Sulfasalazine (Azulfidine) from plasma protein binding sites, transiently raising free drug concentration.
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warning
Aripiprazole (Abilify) + Sulfasalazine (Azulfidine)
Aripiprazole (Abilify) may displace Sulfasalazine (Azulfidine) from plasma protein binding sites, transiently raising free drug concentration.
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warning
Armour Thyroid (Desiccated Thyroid Extract) + Sulfasalazine (Azulfidine)
Sulfasalazine (Azulfidine) may displace Armour Thyroid (Desiccated Thyroid Extract) from plasma protein binding sites, transiently raising free drug concentration.
Serum checks 176 modeled interaction pairings for sulfasalazine (azulfidine) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.
Research behind this entry
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Clinical pharmacokinetics of sulphasalazine, its metabolites and other prodrug forms of 5-aminosalicylic acid
Foundational PK review: sulfasalazine F~15% parent, colonic azoreduction to 5-ASA + sulfapyridine, NAT2 acetylator status determines sulfapyridine exposure and AE risk.
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Sulfasalazine: a review of its use in the management of rheumatoid arthritis
Clinical review establishing sulfasalazine 2-3 g/day as effective conventional DMARD for RA with clinical and radiographic disease modification.
2 published studies referenced in the app, each with a plain-language summary.