When should I take a second antihistamine?
For years, medical protocols have allowed taking more than one antihistamine tablet daily for certain allergy-like conditions. I often see people in my office trying to mix and match various over-the-counter medications to achieve better results. However, what often works just as well, if not better, is simply doubling the dosage of a medicine they already take and tolerate well. Modern antihistamines cause minimal drowsiness or sedation.
The condition where antihistamine up-dosing is most commonly done is idiopathic urticaria, or unexplained rashes. There are treatment protocols that recommend taking up to six tablets of cetirizine daily. While six is a significant amount, many patients could see improvement by taking the medicine twice daily or perhaps two tablets at once (20 mg).
One major concern with increasing the dosage of moderate antihistamines is the potential risk of provoking a cardiac arrhythmia, especially in those predisposed to long QT syndrome. A cardiac arrythmia is a serious heart condition that can be disabling or deadly. Although this is rare, it has been reported. Another risk includes potential interactions with other medications that prolong the QT interval or a history of electrolyte abnormalities. It’s crucial to consult your doctor before trying this off-label treatment and to assess any risk factors for long QT syndrome.
On bad allergy weeks, it is reasonable for many patients to double-up on some of their meds to improve symptoms without the need for adding more medication types to their mix (“polypharmacy”). Talk to your doctor first, and make sure she is aware of any current medications you are taking already. If allergy symptoms are moderate to severe for more than one season a year, consider allergy evaluation with your ENT or allergist.