Drug stability refers to a drug’s ability to maintain its original properties and characteristics over time, as it was at the time of manufacture. This includes maintaining the chemical, physical, microbiological, therapeutic, and toxicological integrities. Examples of instability include microbial contamination of liquid suspensions, discoloration of tablets, degradation leading to reduced drug efficacy on storage, etc. Conducting stability testing is a regulatory requirement for all drugs.
The physical state of the drug affects the solubility, absorption, potency, etc. Storing drugs in well-closed containers, away from direct light, prevents most physical changes. A few examples of loss of physical stability include the following:
The nature of the drug may change due to chemical reactions, which may decrease its potency or even cause it to form toxic products. Such chemical reactions include oxidation, hydrolysis, dehydration, chelation, polymerization, isomerization, etc. For example, epinephrine oxidizes to a red-colored product, making it ineffective. Commonly used drugs like aspirin, penicillins, and cephalosporins are hydrolyzed when pH changes. Most drugs are stable at neutral pH values. Exposure to light and high temperatures may cause drug oxidation.
Microbial contamination can occur from the presence of water in the drug or contamination of natural polymers used in drug manufacturing. Contamination may originate in raw materials, manufacturing instruments, storage containers, and personnel. Common contaminants include molds, micrococci, Pseudomonas, and E. coli.
Insulin is a commonly used drug that is available in injectable forms. It is recommended that insulin be stored in a refrigerator at approximately 36°F to 46°F. Unopened and stored in this manner, these products maintain potency until the expiration date on the package. Insulin products contained in vials or cartridges supplied by the manufacturers (opened or unopened) may be left unrefrigerated at a temperature between 59°F and 86°F for up to 28 days and continue to work. However, an insulin product that has been altered for the purpose of dilution or by removal from the manufacturer’s original vial should be discarded within two weeks. Frozen insulin should not be used. Insulin should never be exposed to direct sunlight. At pH values below five and above eight, insulin degrades relatively fast.
Suspensions have high moisture content, which increases the risk of microbial contamination, drug degradation, and loss of moisture, which in turn increases drug concentrations. Most suspensions are stable for fourteen days after reconstitution when refrigerated between 36°F and 46°F.
| Name of oral suspension | Expiration date after reconstitution |
| Amoxicillin and Clavulanate Potassium for oral suspension, Augmentin | Suspension must be refrigerated. Discard after 10 days. |
| Amoxil, amoxicillin oral suspension | Store at room temperature or in the refrigerator. Discard after 14 days. |
| Cefdinir oral suspension, Omnicef | Store at room temperature. Discard after 10 days. |
| Cephalexin oral suspension, Keflex | Refrigerate after reconstitution. Discard after 14 days |
| Azithromycin, Zithromax oral suspension | Store constituted suspension between 5-30 degree Celsius and discard when full dosing is completed, maximum up to 10 days |
| Zmax (azithromycin extended release) oral suspension | Store constituted suspension at preferably 25 degree Celsius and discard after 12 hours. Do not refrigerate or freeze. |
| Cleocin Pediatric for oral suspension, Clindamycin | Store at room temperature and discard two weeks after reconstitution. Do not refrigerate the reconstituted solution. |
Proper vaccine storage is essential to maintain vaccine efficacy. A cold chain is a temperature-controlled supply chain that includes all vaccine-related equipment and procedures. The cold chain begins with the cold storage unit at the manufacturing plant, extends to the transport and delivery of the vaccine and correct storage at the provider facility, and ends with administering the vaccine to the patient. Overexposure to heat, cold, or light can decrease vaccine efficacy. The storage temperature depends on the type of vaccine, and manufacturer recommendations must be followed. Vaccines licensed for refrigerator storage should be stored at 2°C-8°C (36°F-46°F). Certain lyophilized (freeze-dried) vaccines like varicella (chicken pox) are stored frozen. Vials and manufacturer-filled syringes should always be stored in their original packaging. Vaccines and diluents with the earliest expiration dates should be kept in front of those with later expiration dates.
BUD is the final date or time beyond which an “altered” vaccine can be used. The BUD is different from the expiry date of the vaccine. The vaccine may be “altered” when it is moved between storage conditions, for example, between the deep freezer and refrigerator, or from either of these to room temperature. Alteration also occurs when a vaccine is mixed with a diluent or after a vaccine vial is punctured. Administering a vaccine after the BUD is a vaccine administration error and may decrease the vaccine’s efficacy.
| Name of vaccine | Storage requirements |
| Pfizer-BioNTech COVID-19 vaccine for ages 6 months to 4 years | Store vaccine between -90 and -60 degrees Celsius (-130 and -76 degrees F). BUD - Store unpunctured vials between 2-8 degrees Celsius (36-46 degrees F) for up to 10 weeks, or between 8-25 degrees Celsius (46-77 degrees F) for up to 12 hours. Discard punctured vials after 12 hours. |
| Pfizer-BioNTech COVID-19 vaccine for ages 5 to 11 years | Store vaccine between -90 and -60 degrees Celsius (-130 and -76 degrees F). BUD - Store unpunctured vials between 2-8 degrees Celsius (36-46 degrees F) for up to 10 weeks, or between 8-25 degrees Celsius (46-77 degrees F) for up to 12 hours. Discard punctured vials after 12 hours. |
| Comirnaty vaccine for ages 12 years and above | Store vaccine between 2-8 degrees Celsius (36-46 degrees F). Do not freeze. BUD - May be stored between 8-25 degrees Celsius (46-77 degrees F) for up to 12 hours. Once activated, use within 4 hours. |
| Novavax COVID-19 vaccine | Store vaccine between 2-8 degrees Celsius (36-46 degrees F). Do not freeze |
| Moderna COVID-19 vaccine for ages 6 months to 11 years | Store vaccine between -50 and -15 degrees Celsius (-58 and 5 degrees F). BUD - Store between 2-8 degrees Celsius (36-46 degrees F) for up to 60 days, or between 8-25 degrees Celsius (46-77 degrees F) for up to 12 hours. |
| Spikevax COVID-19 vaccine for ages 12 years and above | Store vaccine between -50 and -15 degrees Celsius (-58 and 5 degrees F). BUD - Store between 2-8 degrees Celsius (36-46 degrees F) for up to 60 days, or between 8-25 degrees Celsius (46-77 degrees F) for up to 12 hours. |
Always refer to the latest manufacturer product information for best use practices. Recommendations for storage and use may change as new batches are released. Once thawed, vaccines should not be refrozen.
Expiration date: The date by which the manufacturer guarantees the drug’s potency and safety. Ideally, drugs should not be used after the expiration date. Some drugs may still maintain potency for a while after the expiration date, and some degrade to toxic products after the expiration date. The expiration date may contain letters or numbers. The FDA recommends to include a year, date, and month for the expiration date in a YYYY-MM-DD format e.g., 2027-02-01, or a YYYY-MMM-DD format e.g., 2027-FEB-01. In case space is lacking on the package, then a YYYY-MM (2021-01) or YYYY-MMM (2021-JAN) format can be used. The parts should be separated by a hyphen or by a forward slash.
Shelf life: This refers to the quality of a drug. Although they are not toxic, they may not be effective if taken after their shelf life. Shelf life is affected by storage conditions like heat, light, and moisture.
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