In what situations should caution be exercised when using antihistamines?

Antihistamines are medications commonly used to relieve allergy symptoms, but certain health conditions require caution due to potential side effects or complications associated with their use. In the case of narrow angle glaucoma, caution is particularly important because antihistamines can cause pupil dilation (mydriasis). This dilation may lead to an increase in intraocular pressure, which can exacerbate the condition and potentially lead to an acute glaucoma attack. Managing a patient's health with existing narrow angle glaucoma necessitates careful selection of medications to avoid adverse effects that could worsen their condition.

In other situations, such as severe headache, pregnancy, or hyperthyroidism, while caution may still be advised, they do not present the specific risk that narrow angle glaucoma does. For instance, antihistamines might be used with careful consideration during pregnancy, but they are not contraindicated in the same way. Therefore, understanding the unique risk presented by narrow angle glaucoma is key to recognizing why this situation requires the utmost caution when considering antihistamine use.