Expired medications are commonplace and inertia notwithstanding, many of us tend to rely on an intuitive sense of their value in continuing to store and use them. Such drugs can be harmful to health in several ways; they can be unpredictable in effectiveness, simply ineffective, or even toxic.
The formal way of classifying a medication as having expired is through it’s labeled expiry date. This date is often set based on a combination of the common properties of the dosage form as well as the stability and expiration studies of the product that have been conducted by the manufacturer. Importantly, this expiry date is contingent on specific storage conditions of the product. Although a medication may pass it’s labeled expiry date, it may not necessarily be any less effective or dangerous to consume depending on the product itself, the storage conditions and the circumstances leading up to expiry.
When most medications pass their expiry date under appropriate storage conditions, they are generally taken to have become so variable in effectiveness as to have become unsuitable for use. This often comes about as a result of the degradation of the active ingredients of the medication with exposure to physical, chemical or microbiological variables like temperature, pressure, humidity, light, bacteria as well as other components of the product known as excipients.
Creams may “crack” once their expiry date is passed, leading to a separation of the components and hence provide a non-uniform delivery of active ingredients. This can lead to the poor control of conditions like eczema or acne. Tablet medications can mechanically “powder” off, change in consistency with exposure to water vapor or even experience the contained drug itself becoming ineffective on prolonged exposure to air as occurs with glyceryl trinitrate, an emergency medicine that can easily become ineffective in relieving acute symptoms of chest pain. With common injections, should the acidity change to fall outside a fairly narrow range, significant pain and tissue damage can result from use. With most eye drops, an expiry date of one month after opening is accepted to minimize the potential for dangerous bacterial contamination.
With any medication, once a specific threshold of remaining active ingredient is passed, the medication can no longer be relied upon to deliver accurate doses. This loss of reliability is often exacerbated by the fact that the active ingredients can degrade into various combinations of active, inactive or toxic breakdown products. The common aspirin is for instance, known to react with moisture to breakdown into salicylic acid, which is active, and acetic acid, which is inactive and can lead to toxicity in excess.
While the expiry date provides a useful gauge of when to stop using a medication, there are also many other factors that can informally accelerate the expiry of a medication and make it dangerous to use, chief among which is how the medication is stored. It is oftentimes not just the medication that is affected by storage conditions but also the storage container. Under inappropriate storage conditions, …