When should I take a second antihistamine?
For years now there are medical protocols to take more than one antihistamine tablet daily for certain allergic-like conditions. I see a lot of people in my office trying to mix and match various over-the-counter medications to get a good effect, when what often will work is simply doubling up on one of the medicines they currently take and already tolerate well. Modern antihistamines cause very little drowsiness or sedation.
The condition were antihistamine updosing is most routinely done is for idiopathic urticaria, or rashes of unexplained cause. There are treatment protocols to take up to 6 tablets of cetirizine daily for instance. While 6 is a whole lot, many patients could improve by taking a twice a day dosing, or perhaps 2 tablets at once (20mg).
The biggest problem with dosing on moderate antihistamines seems to be that it could provoke a cardiac arrhythmia if you are predisposed to long QT syndrome. This is very rare but has been reported. Definitely speak with your doctor before doing this off label treatment, and assess for risk factors of long QT syndrome such as genetic predisposition, other medications that may promote long QT, or a history of electrolyte abnormalities.
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.