Drug stability: how long mixed, opened and in-use products last
PTCB topic: Drug stability
- Count the discard date from the day of mixing or first use.
- A discard date is never later than the printed expiration date.
- Amoxicillin-clavulanate suspension: refrigerate, discard after 10 days.
- In use: Lantus 28 days, Tresiba 56 days.
- Opened multiple-dose vials: 28 days unless the manufacturer says otherwise.
Key facts
- Reconstituted amoxicillin suspension: discard after 14 days (refrigeration preferable, not required); amoxicillin-clavulanate: refrigerate, discard after 10 days.
- Reconstituted cefdinir suspension is kept at 68°F to 77°F for 10 days; clarithromycin suspension is used within 14 days and must not be refrigerated.
- In-use Lantus lasts 28 days and in-use Tresiba lasts 56 days; a Victoza pen lasts 30 days after first use.
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- Humulin N at room temperature: 31 days total for the vial and 14 days total for the KwikPen, counting unopened time out of the refrigerator.
- CDC: date an opened multiple-dose vial and discard it within 28 days unless the manufacturer gives another date (Epogen: 21 days after first entry).
- Reconstituted varicella vaccine (Varivax) is discarded if not used within 30 minutes.
- A discard date is never later than the manufacturer's printed expiration date.
Quick check1 question · 2 more at the end
A technician reconstitutes amoxicillin-clavulanate potassium for oral suspension. According to the product label, how is the reconstituted suspension stored, and when is any unused portion discarded?
Correct answer: B.
Each reconstituted suspension has its own storage condition and discard period, printed in sections 2 and 16 of its label. Amoxicillin-clavulanate potassium suspension is refrigerated and discarded after 10 days, while plain amoxicillin suspension is kept 14 days. The technician writes the storage instruction and the discard date on the bottle when mixing it.
A Room temperature and 14 days do not match this label, which calls for refrigeration and a 10-day limit.
B Correct: the label says to store the reconstituted suspension under refrigeration and discard unused suspension after 10 days.
C Refrigeration is right, but 14 days is the limit for plain amoxicillin or cephalexin suspension, not amoxicillin-clavulanate.
D Reconstituted oral antibiotic suspensions are not frozen; no such instruction appears on the label.
Full lesson
Each part starts with its main idea. Open a part when you want the details.
The short answer: Once a product is mixed, opened or first used, a label-specific discard date replaces the printed expiration date if it comes first. Amoxicillin-clavulanate suspension lasts 10 days refrigerated, Lantus 28 days in use, Tresiba 56 days, and opened multiple-dose vials 28 days unless the manufacturer says otherwise. Count the days from the mixing or first-use date.
1 What does drug stability mean for a technician?A product stays potent only for the time and conditions its label allows. 1 min
A product stays potent only for the time and conditions its label allows. The manufacturer's expiration date covers the unopened product stored correctly. Once you mix, open or first use certain products, a shorter discard date (often called a beyond-use date) starts.
- Count the discard date from the day the product is mixed, punctured or first used.
- The discard date can never be later than the printed expiration date.
- The exact period comes from the product label, usually sections 2 and 16.
The 2026 PTCE outline lists drug stability with oral suspensions, insulins, reconstituted products, injectables and vaccines as examples.
2 How long do reconstituted oral suspensions last?Each antibiotic suspension has its own storage condition and day limit, so always read the label of the exact product. 1 min
Each antibiotic suspension has its own storage condition and day limit, so always read the label of the exact product. These examples come from current labels.
| Suspension after mixing | Storage | Use within |
|---|---|---|
| Amoxicillin | Refrigeration preferable, not required | 14 days |
| Amoxicillin-clavulanate | Refrigerate | 10 days |
| Cefdinir | 68°F to 77°F (20°C to 25°C) | 10 days |
| Clarithromycin | 59°F to 86°F; do not refrigerate | 14 days |
| Azithromycin (Zithromax) | 41°F to 86°F (5°C to 30°C) | 10 days |
3 How long can opened insulin and pens be used?Many opened insulins last 28 days, but several products have longer or shorter limits. 1 min
Many opened insulins last 28 days, but several products have longer or shorter limits. Unopened insulin kept in the refrigerator lasts until its expiration date, and insulin that has been frozen is never used.
| Product | In-use period |
|---|---|
| Insulin glargine (Lantus) vial or SoloStar pen | 28 days |
| Insulin degludec (Tresiba) | 56 days (8 weeks) |
| Humulin N vial | 31 days total at room temperature |
| Humulin N KwikPen | 14 days total at room temperature |
| Liraglutide (Victoza) pen, after first use | 30 days |
For Humulin N, the room-temperature total includes time the product sat unopened outside the refrigerator. A Humulin N pen left out for 5 days before the first injection has 9 days left.
4 What about injectable vials and vaccines?Opened vials and mixed vaccines have their own clocks, and some are very short. 1 min
Opened vials and mixed vaccines have their own clocks, and some are very short.
- Multiple-dose vials: CDC says to date an opened vial and discard it within 28 days, unless the manufacturer states another date.
- Epoetin alfa (Epogen) multiple-dose vial: discard 21 days after first entry, because the label's date replaces the 28-day default.
- Single-dose vials: one patient only; never kept for later doses.
- Varicella vaccine (Varivax): discard if not used within 30 minutes of reconstitution.
5 How do you count a discard date?Add the allowed period to the mixing or first-use date, using the real length of each month. 1 min
Add the allowed period to the mixing or first-use date, using the real length of each month. Work it in three steps.
- Find the start date: the day the product was mixed, punctured or first used.
- Find the period on the label (minutes, days or months).
- Add it. Tresiba first used June 1: June 1 + 29 days = June 30, and 27 more days = July 27.
If the printed expiration date comes first, the earlier date wins.
6 What the technician doesThe technician applies the label's stability rules every time a product is mixed or opened. 1 min
The technician applies the label's stability rules every time a product is mixed or opened.
- Reconstitute with the amount of water the label specifies, then write the discard date on the bottle.
- Add the right auxiliary label, such as "Shake well," "Refrigerate" or "Do not refrigerate."
- Refer any question about using a product past its date to the pharmacist.
Common mistakes
The traps students fall into most. Read these before you practice.
Watch out: Amoxicillin-clavulanate suspension lasts 10 days, not the 14 days of plain amoxicillin.
Watch out: Clarithromycin suspension is labeled "Do not refrigerate," not "Refrigerate."
Watch out: Tresiba lasts 56 days in use, not the 28 days of most insulins.
Watch out: The 28-day multiple-dose vial rule is a default, not a rule that overrides a shorter manufacturer date such as Epogen's 21 days.
Watch out: For a Humulin N pen, the 14-day room-temperature clock starts when it leaves the refrigerator, not at the first injection.
How to remember it
Say "mix it, date it" every time you reconstitute a bottle or open a vial. Memory hook: "Amox-clav ten, amoxicillin fourteen; Lantus 28, Tresiba double."
Self-check:
- Name the discard period for reconstituted amoxicillin-clavulanate and for cefdinir.
- Which suspension in this lesson is labeled "Do not refrigerate"?
- A Lantus vial is first used on March 5. Which discard date goes on it?
Show answers
- 10 days for both.
- Amoxicillin-clavulanate: refrigerate, discard after 10 days.
- Cefdinir: keep at 68°F to 77°F, use within 10 days.
- Clarithromycin.
- Its label says to store it at 59°F to 86°F and not to refrigerate it.
- April 2.
- Lantus lasts 28 days in use.
- March 5 + 26 days = March 31.
- 2 more days = April 2.
- If the printed expiration date comes first, use that date instead.