Overview
The expiration date stamped on the bottle of your medication is a curious thing. It doesn't seem likely that medications suddenly go bad one day after the expiration date. Yet, you'll rarely hear anyone say that is is OK to take a medication after it has expired. It should be known that expiration dates are set by the manufacturer of the prescription drug and not the Food and Drug Administration.
How Are Expiration Dates Determined?
The drug manufacturer chooses the time period they desire based on information they have on hand regarding it. Thus, the expiration date of a drug is simply the time period for which the manufacturer can guarantee FDA standards of purity and potency. If a company has data for a drug for a 3 year time period, they may make the expiration date 3 years and no longer since there is no data after that time period.
There is some cynicism with this of course. Many think and feel that the time period chosen by the company is done in an effort to facilitate product sales and that is why many drugs have short expiration dates. If a drug expires, a retailer must re-purchase a newer batch.
Whether that is true or not, the fact of the matter is that there just really is no incentive for a drug company to monitor whether their drug is still "good" after an extended period of time, say 3 years.
Drug Stability
The FDA requires that all drugs pass "stability" tests. These tests determine the ability of the drug to meet the FDA standards of strength, quality, and purity for the duration of a chosen expiration period. For example, if a drug manufacturer chooses the expiration date of a given drug to be three years, then the drug must be tested during this period and at the end of three years to affirm that the drug meets the standards.
These determinations must be made in the packaging that the drug is to be marketed in and under the storage conditions that are appropriate for the product. Usually, maintenance of at least 90% potency is acceptable.
It must be noted that this method only is in reference to medications sealed in their original container! Many states have legislation stating that pharmacists set expiration dates on dispensed drugs no more than a year from dispensing.
This can be significantly shorter than the shelf life of a drug in the original container. It does make sense however that this is the case. How a medication is stored affects its long-term stability. Exposure to light, air, humidity, and temperature extremes can affect the degradation rate of a drug.
The expiration date assigned by the manufacturer or dispensing pharmacist assumes that the medication will be stored properly. Proper store means it is in the closed container it was dispensed in at the appropriate temperature.
In reality, many patients store medications in less than ideal environments: warm, humid areas (bathroom cabinet), window sills (lighted areas), various locations in the interior of automobiles (hot), etc. These storage conditions lend credence to pharmaceutical manufacturers' insistence that "conservative" expiration dating is warranted.
What Do Studies Show?
There have not been many studies based on testing manufacturer expiration dates. One large study was conducted in the military around 30 years ago. The US Air Force began stability testing of stockpiles of prescription medications in 1985.
The testing was begun after officials of the Government Accounting Office (GAO) estimated that the military would have to start spending approximately 100 million dollars per year to replace outdated prescription drugs beginning in the 1990s.
The program is referred to by the Department of Defense (DoD) as the "Shelf Life Extension Program." In the first year of the testing program, the FDA tested 58 different prescription drugs, representing 157 different manufacturing lots. Some of the original drugs tested were penicillin, lidocaine, and lactated Ringer's.
After this initial round of testing was complete, the FDA extended the expiration dates for 80% of the expired lots tested by an average period of 33 months. In 1992, seven years after testing began, the expired lots were retested, and more than 50% met testing standards (i.e., remained useable).
In the year 2000, at least one of those batches remains stable, fifteen years after its original expiration date.
Some specific drugs that have been incorporated into this testing program include:
- Pralidoxime
- Chloroquine
- Diazepam
- Ciprofloxacin
- Atropine
- Sodium chloride for injection
- Cimetidine
The original expiration date of ciprofloxacin tablets that were added to the testing program was 1993, and this expiration date has now been extended to 2001. The Shelf Life Extension testing program is still ongoing.
Consumers who are aware of the results of this study may be able to make more informed decisions about continuing to use certain prescription products beyond their expiration dates.
It is unlikely that pharmacists will begin dispensing out of date medications or recommending that medications be used beyond their expiration dates as a result of this study. There are too many ethical, moral, and legal issues to deal with.
