Drug stability is the property of a drug to maintain the same properties and characteristics as at the time that the drug was manufactured. It involves chemical, physical, microbiological, therapeutic, and toxicological stability. Examples of loss of drug stability include - microbial contamination of liquid suspensions, change in color of tablets, loss of drug activity on storage, etc. Stability testing is a legal 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.
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. Most vaccines become inefficient when frozen. 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.
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.
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.
Sign up for free to take 7 quiz questions on this topic