Does mercaptopurine expire?
The printed date covers the sealed pack. Once mercaptopurine is opened, mixed or diluted, its label sets a second and usually much shorter limit — quoted below, per product.
Shortest limit on any mercaptopurine label: 8 weeks
“Advise patients and caregivers to use mercaptopurine oral suspension within 8 weeks and properly discard remaining mercaptopurine oral suspension after 8 weeks.”
That applies to the product it is printed on, not to every form of mercaptopurine — check which one you have against the list below.
What the labels say
“Advise patients and caregivers to use mercaptopurine oral suspension within 8 weeks and properly discard remaining mercaptopurine oral suspension after 8 weeks.”
On the label for MERCAPTOPURINE · DailyMed
“Advise patients and caregivers to use MERCAPTOPURINE within 8 weeks and properly discard remaining MERCAPTOPURINE after 8 weeks.”
On the label for MERCAPTOPURINE · DailyMed
How the label says to keep mercaptopurine
Storage is the other half of the question: the stability behind any date assumes these conditions, and a medicine kept outside them ages faster than the calendar says.
- “16 HOW SUPPLIED/STORAGE AND HANDLING Mercaptopurine Oral Suspension is supplied as 2,000 mg/100 mL (20 mg/mL) pink to brown viscous liquid in amber glass multiple-dose bottles.”
- “Store Mercaptopurine Oral Suspension at 20º to 25ºC (68º to 77ºF) [see USP Controlled Room Temperature].”
- “Store in a dry place.”
- “Train patients or caregivers on proper handling, storage, administration, disposal and clean-up of accidental spillage prior to initiation of mercaptopurine oral suspension and during each visit to the clinic.”
- “Store the oral dispensing syringe in a hygienic place with mercaptopurine oral suspension.”
- “16 HOW SUPPLIED/STORAGE AND HANDLING Mercaptopurine Tablets, USP 50 mg supplied as pale yellow, biconvex tablets, with product identification “54 420” on one side and a score on the other side.”
- “Store at 20°C to 25°C (68°F to 77°F).”
- “16 HOW SUPPLIED/STORAGE AND HANDLING MERCAPTOPURINE oral suspension is supplied as 2,000 mg/100 mL (20 mg/mL) pink to brown viscous liquid in amber glass multiple-dose bottles.”
Frequently asked questions
Does mercaptopurine expire?
Two different clocks apply and only one of them is the printed date. The date on a sealed pack is the manufacturer's guarantee for the unopened product. Once it is opened, mixed or diluted, the label imposes its own limit — as tight as 8 weeks on some mercaptopurine products, and that is the number quoted on this page.
Can I still use mercaptopurine after the date on the box?
This page cannot tell you that, and nor can any page. The FDA's own shelf-life programme found 88% of tested lots stayed within specification at least a year past expiry — and concluded in the same breath that lot-to-lot variation means this can only be confirmed by testing each lot. What you can check at home is the in-use limit above and whether the product has been stored as the label requires. Ask a pharmacist about a specific pack; they will also dispose of what you no longer need.
Why do different mercaptopurine products have different limits?
Because they are different formulations. A suspension that gets mixed with water, a pen that gets carried at room temperature, and a sealed tablet do not behave alike, so each manufacturer's label sets its own limit and each is shown here with the product it belongs to. We never merge them into one number for the molecule.
More on mercaptopurine
Quoted from FDA labels for reference, not medical advice, and not a suggestion to use anything past its limit. If you are unsure whether a pack is still good, a pharmacist can tell you and can dispose of it safely.