Over-the-counter medication: the drug interactions we overlook.

The effective use of medication involves awareness of both the interpersonal interaction between provider and patient and potential drug--drug interactions. Elderly patients are especially vulnerable to drug--drug interactions because many in this population are very likely to be undergoing treatment for two or more concurrent diseases, probably while self-medicating with over-the-counter (OTC) preparations. Both patient and provider behaviors generate poor patient--provider interactions. The elderly patient is unwilling to ask for help or admit weaknesses that may become restrictive; providers often lack training in the psychosocial and economic aspects of geriatric care. The cost of OTC preparations for people over 65 is about half of what they spend on prescription drugs. The effects of salicylate use (as internal analgesics) and antacid use illustrate potential OTC--prescription drug interactions. Aspirin, used with other drugs, can contribute to accidental hypothermia; idiosyncratic reactions are particularly dangerous in the asthmatic patient. In addition, many OTC products contain aspirin but are not clearly labelled as such. Antacid overuse can be detrimental in itself, and antacids can also affect the absorption and excretion of prescribed drugs when they alter gastric or urinary pH. It is suggested that providers pay more attention to dosage form, as this can influence drug effectiveness, particularly in the elderly. The OTC drugs are therapeutically valuable, but providers must be aware of the potential difficulties when patients use them.