Excipients and patients

Last updated: Thursday, October 06, 2016

Excipients can occasionally be the cause of a medicine's side effects. Many healthcare professionals are unlikely to know much about this subject or to consider it clinically, so adverse reactions to excipients can be overlooked. As a pharmacist you need to be able to offer advice about it.

Reactions to excipients 

Courtesy of Simon Wills
It can be difficult to find out about adverse reactions to excipients and how frequently they occur, although note that one of the reasons for a substance being selected as an excipient is that it should not commonly cause side effects. In addition, the amounts of excipients in medicines are usually small.

However, occasionally, excipients can cause dose-related adverse reactions. Persistent administration of sugar-containing medicines might cause tooth decay, for example, and the popular sweetener sorbitol used in some liquid medicines can cause diarrhoea because it acts as an osmotic laxative. Another example is the sodium content of medicines. Sometimes this is high enough for a medicine not to be recommended for patients on a restricted salt diet (e.g. those with hypertension). A number of antacids contain quite high amounts of sodium. Injections containing preservatives are not used intrathecally or epidurally because they might cause neurotoxicity, and this would also be expected to be dose-related.

In practice, the commonest side effects of excipients tend to be due to intolerance, which is often dose-related, and allergy, which is not dose-related. In these situations it is important to help patients to avoid further exposure.

Factors influencing risk

Some excipients are not absorbed from the gut, and so are particularly unlikely to cause systemic reactions after oral administration (e.g. talc). Certain other common excipients are natural to the human body and in the amounts used in pharmaceuticals are unlikely to cause side effects (e.g. citric acid). Many excipients also occur naturally in food (e.g. starches). However, note that certain excipients may present special problems in children.

As already noted, the commonest reason you may be asked about excipients is that a patient has a known allergy or intolerance to it. In this situation you need to find out the history and nature of the reaction in order to best help the patient. We examine this aspect in more detail on the next page.