Antibiotic Suspension


As a pharmacist, one of the most common questions we get is what to do if you accidentally leave a medication, that is supposed to be stored in the refrigerator, out at room temperature.

The answer depends on the drug in question and unfortunately, there often isn't enough available published information to determine whether the medication has been adversely affected by improper storage.

When it comes to antibiotic suspensions like Keflex (cephalexin), we fortunately have a variety of stability studies available to us.

One study, published in the American Journal of Hospital Pharmacy, showed that reconstituted cephalexin suspension was stable for at least 24 hours (one day) when left at room temperature.

Per you question, having your daughter's cephalexin out of the refrigerator for 2-4 hours, it should not have any appreciable loss in potency and should still be safe to continue to use. Just be sure to store it in the refrigerator going forward.

Antibiotic Suspensions And Refrigeration

Storage requirements for antibiotic suspensions vary by drug.

Some can safely be stored at room temperature for up to ten days. These include:

Some are recommended to not be stored in the refrigerator at all. These include:

Antibiotics that are required to be stored in the refrigerator to retain potency can often be left at room temperature for up to 24 hours without a loss in potency. These include:

It is important to read and follow the storage instructions on your medication. If you ever have questions about proper storage, be sure to ask your pharmacist.

Keflex Suspension Storage Requirements

Per the prescribing information for Keflex (cephalexin):

After mixing, store in refrigerator. May be kept for 14 days without significant loss of potency.

While the reconstituted Keflex (cephalexin) suspension should be stored in the refrigerator, as stated in the 'overview' section of this article, studies show that if you accidentally leave it at room temperature, it will be stable for at least 24 hours (one day).

In fact, the study referenced earlier reported the following:

"At temperatures of -20, 4, and 25 degrees C [77 degrees F], cephalexin monohydrate exhibited no appreciable degradation during the 90-day study period. Cephalexin monohydrate suspension reconstituted from powder as a suspension and repackaged in clear polypropylene oral syringes was stable for 90 days when stored under ambient, refrigerated, and frozen conditions."

Other studies have reported similar results, that Keflex (cephalexin) suspension is stable at room temperature for at least 24 hours, and likely longer.


  • Based on all the available published information, the Keflex (cephalexin) suspension that was accidentally left out of the refrigerator for 2 to 4 hours will still be safe to use.

  • References
    1. Stability of cephalexin monohydrate suspension in polypropylene oral syringes. PubMed
    2. Dissolution Stability of Cephalexin Extemporaneous Suspensions During an Accelerated Stability Study. Dissolution Tech
    3. Keflex Prescribing Information. AccessFDA