Two medicines, side by side
Azathioprine vs sulfasalazine
Azathioprine and sulfasalazine are both labeled for rheumatoid arthritis. Drugs@FDA records approvals of azathioprine since 1968 and of sulfasalazine since 1950. Pharmacies paid $0.124 per azathioprine 50 mg tablet and $0.199 per sulfasalazine 500 mg tablet (NADAC, October 7, 2026); the strengths differ, so the two prices are not like for like. In FDA's classes, azathioprine is a purine antimetabolite and sulfasalazine an aminosalicylate.
Check it at the source: the azathioprine FDA label on DailyMed (effective November 8, 2025); the sulfasalazine FDA label on DailyMed (effective May 29, 2026).
Highlights of the azathioprine record
Azathioprine (Imuran) · label of November 8, 2025
MALIGNANCY Chronic immunosuppression with IMURAN, a purine antimetabolite increases risk of malignancy in humans. Reports of malignancy include post-transplant lymphoma and hepatosplenic T-cell lymphoma (HSTCL) in patients with inflammatory bowel disease. Physicians using this drug should be very familiar with this risk as well as with the mutagenic potential to both men and women and with possible hematologic toxicities. Physicians should inform patients of the risk of malignancy with IMURAN.
Used for
From the label: indicationsIMURAN is indicated as an adjunct for the prevention of rejection in renal homotransplantation. It is also indicated for the management of active rheumatoid arthritis to reduce signs and symptoms. Renal Homotransplantation: IMURAN is indicated as an adjunct for the prevention of rejection in renal homotransplantation. […]
On the market
- Earliest approval on file
- March 20, 1968
- Generic labelers
- 17 labelers
- Pharmacy cost
- $0.124 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 1
Highlights of the sulfasalazine record
Sulfasalazine (Azulfidine) · label of May 29, 2026
Used for
From the label: indicationsAZULFIDINE Tablets are indicated: • in the treatment of mild to moderate ulcerative colitis, and as adjunctive therapy in severe ulcerative colitis; and • for the prolongation of the remission period between acute attacks of ulcerative colitis.
On the market
- Earliest approval on file
- June 20, 1950
- Generic labelers
- 5 labelers
- Pharmacy cost
- $0.199 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 0
Source: FDA drug labels via openFDA (Azathioprine label of November 8, 2025, Sulfasalazine label of May 29, 2026); NDC Directory, Drugs@FDA, NADAC, FDA shortages and recalls (October 8, 2026)
How do azathioprine and sulfasalazine differ on the record?
In FDA's classes, azathioprine is a purine antimetabolite and sulfasalazine an aminosalicylate.
Half-life, in each label's words: Azathioprine, “Maximum serum radioactivity occurs at 1 to 2 hours after oral 35 S-azathioprine and decays with a half-life of 5 hours.”; Sulfasalazine, “The observed plasma half-life for intravenous sulfasalazine is 7.6 ± 3.4 hours.”
Only the azathioprine label carries a boxed warning.
Generics: azathioprine since 1995; sulfasalazine since 1973 (Drugs@FDA).
| Azathioprine | Sulfasalazine | |
|---|---|---|
| Labeled for | Organ transplant rejection, Rheumatoid arthritis | Crohn's disease and ulcerative colitis, Rheumatoid arthritis |
| Pharmacologic class | Purine Antimetabolite | Aminosalicylate |
| How it works (label) | n/a | n/a |
| Half-life (label) | Maximum serum radioactivity occurs at 1 to 2 hours after oral 35 S-azathioprine and decays with a half-life of 5 hours. | The observed plasma half-life for intravenous sulfasalazine is 7.6 ± 3.4 hours. |
| Earliest approval on file (Drugs@FDA) | March 20, 1968 | June 20, 1950 |
| First generic approved | March 31, 1995 | November 12, 1973 |
| Generic labelers (NDC) | 17 labelers | 5 labelers |
| Pharmacy cost (NADAC, each one's most listed form; strengths differ) | $0.124 per tablet (Azathioprine 50 mg tablet) | $0.199 per tablet (Sulfasalazine 500 mg tablet) |
| 12-month price change | -10% | +10% |
| Boxed warning | Yes | No |
| Shortage now | No current entry | No current entry |
| Recalls recorded | 1 | 0 |
| FAERS reports (a report is not proof of cause; counts follow how widely a medicine is used) | 89,586 | 77,784 |
| DEA schedule | none | none |
Source: Drugs@FDA, FDA NDC Directory, CMS NADAC of October 7, 2026, FDA shortages and recalls, FAERS via openFDA (FDA files October 8, 2026)
What next?
- Alternatives to azathioprine
- every medicine labeled for the same conditions