Medicine expiry dates: When does it really matter?

20170308060000, Mak Wen Yao 
It is generally unsafe for expired drugs to be consumed as they would have lost their potency. However, in some cases, expired drugs may be used for an intended purpose.
Almost all of us keep medicine in our home for emergency purposes, and a significant portion of these people, including the pharmacists, continue to keep them even after the medicine has passed the expiry date. Common sense dictates that expired medicine must be disposed of appropriately, but many patients may actually wonder: What does the expiry really mean?

Do medicines really expire?

Unlike conventional foodstuffs, common medicines such as painkillers or flu tablets (barring pharmaceutical syrups and reconstituted solutions) are devoid of moisture. Therefore these tablets and capsules do not "turn bad" when they are stored in a proper manner. It is not uncommon to find oral dosages retaining their initial appearance in terms of shape, hardness and colour long after the expiry date is reached.

However, the active ingredients within these capsules and tablets will naturally degrade. The degradation process will be hastened if the medicine is inappropriately exposed to excessive light or heat, as the extra energy will accelerate the chemical degradation reactions. As a result, the potency of these medicines gradually diminish.

Drug expiry dates are not determined arbitrarily. Rather, it is a critical decision that is made based on cumulative scientific evidence gathered through numerous experiments that test how long the drug potency will last. For example, the finished drug product will be intentionally exposed to different environments with varying temperatures, humidity levels and storage periods to examine how drug degradation will respond to these external factors.

As a general rule, drugs are expected to lose approximately 10% of its original potency when they reach their expiry dates.

Is it safe to consume expired medicine?

If expired medicine only loses 10% of their potency, one may wonder if it is still safe to consume them. A tablet that still provides 90% efficacy does not sound like a bad idea after all. While there are no specific reports that evidently link expired drug consumption to toxicity in humans, there are several additional factors that must be taken into consideration.

Firstly, expired drugs that exist in solutions or reconstituted suspensions may not retain their potency as well as those in solid dosage forms. In addition, it is not recommended to use expired injectable drugs as using these compounds inappropriately will place patients at greater risk. For example, epinephrine in the EpiPen autoinjector has been shown to lose its potency after the expired dates; similarly, insulin also displays comparable degradation patterns after expiry.

Secondly, the loss of potency can be a major concern when it comes to drugs with narrow therapeutic index, antibiotics, or those that are indicated to control chronic diseases. Taking antibiotics as the example: sub-potent drugs which do not reach the minimum inhibitory concentration not only will fail to eradicate dangerous infections but may also contribute to the problem of resistance.

Some expired drugs may still be used

Under special circumstances, there were instances where expired drugs are still used for its intended purpose. One of such cases was the U.S. FDA Shelf-Life Extension Program (SLEP) which authorised the use of Tamiflu (Oral Suspension) beyond their labelled expiration dates. Rigorous testings had been conducted to ensure the drugs retained their potency even after expiry prior to granting such authorisation.

Nonetheless, this rare case should be treated as an exception rather than the norm as pharmaceutical products are not intended for use, legally and clinically, after their expiry dates. Caution should be exercised to balance the risks and benefits, and healthcare practitioners are strongly advised to evaluate the need on a case-by-case basis. MIMS

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