Bre asked
Can I take Benadryl (diphenhydramine) with metoprolol ER (metoprolol succinate)?
Answer
There is a moderate drug interaction between Benadryl (diphenhydramine) and metoprolol succinate (Toprol XL). Benadryl can inhibit the enzyme (CYP2D6) that breaks down metoprolol. This can cause an increase in exposure to metoprolol which could lead to increased risk of bradycardia (low heart rate) and hypotension (low blood pressure).
Occasional use of Benadryl may not have a significant clinical
impact, however, checking with the prescriber
would be best in order to monitor heart
rate and blood pressure. Since
metoprolol succinate has beta blockade effects over 24 hours, the timing
between the two drugs would not significantly lower the risk of the drug
interaction.
Information About Benadryl
Benadryl is a first-generation antihistamine. Antihistamines are widely used for self-care of allergy symptoms including runny nose, watery eyes, sneezing, and itching of the nose, throat, or eyes. Benadryl may also be used for symptoms of the common cold, allergic reactions, occasional insomnia, and more.
Because Benadryl is a first-generation antihistamine, it is more likely to cause sedation and drowsiness. Other first-generation antihistamines include Dramamine (dimenhydrinate), Chlor-Trimeton (chlorpheniramine), Tavist (clemastine), and Phenergan (promethazine), among others. These medications cross the blood-brain barrier and have CNS effects like drowsiness and dizziness.
First generation antihistamines can also cause urinary retention, GI upset, and blurry vision. The first generation antihistamines are also listed as medications to avoid in elderly adults by the Beers Criteria due to the increased risk of confusion, dry mouth, and drowsiness.
Second generation antihistamines include Claritin (loratadine), Cetirizine (Zyrtec), and Allegra (fexofenadine) and are much less sedating. These antihistamines are generally only used for treatment of allergy symptoms, whereas Benadryl can be used for a variety of reasons including allergies, insect bites, poison ivy, sleep, and motion sickness.
Information About Metoprolol Succinate
Metoprolol Succinate is a beta blocker that is considered to be cardioselective (works primarily in the heart). It works in the cardiac muscle to block the sympathetic effect that increases heart rate. It also has effect in the vascular smooth muscle to block vasoconstriction and therefore lower blood pressure.
It is important to understand that there are two salt forms
of metoprolol—tartrate and succinate. Metoprolol tartrate (Lopressor) is the
immediate release formulation that is generally taken twice daily. Metoprolol
succinate (Toprol XL) is generally taken once daily, but some cardiologists occasionally
prefer twice daily dosing. It is important to understand the dose, frequency,
and formulation of each prescription.
