4.12 Beta-1 Antagonists

Metoprolol is a selective Beta-1 antagonist.

Mechanism of Action: Metoprolol primarily blocks Beta-1 receptors in the heart, causing decreased heart rate and decreased blood pressure. However, higher doses can also block Beta-2 receptors in the lungs, causing bronchoconstriction.

Indications: Metoprolol is commonly used to treat high blood pressure, chest pain due to poor blood flow to the heart, as an early intervention during a myocardial infarction (MI), and in several heart conditions involving an abnormally fast heart rate.

Nursing Considerations: Don’t crush extended-release (ER) formulations. Assess the client’s apical pulse rate and blood pressure before administering the drug. Withhold the drug and call the provider immediately if the heart rate is slower than 60 beats/minute, unless other parameters are provided. In diabetic clients, monitor glucose level closely because the drug masks common signs and symptoms of hypoglycemia.

Side Effects/Adverse Effects: Beta-1 antagonists may result in decreased blood pressure or heart rate. Significant adverse effects include hypotension, bradycardia, and worsening heart failure. Other potential side effects include fatigue, dizziness, depression, insomnia, nightmares, GI upset, erectile dysfunction, dyspnea, and wheezing.

Boxed Warning: When stopping therapy, the dosage should be tapered over 1 to 2 weeks because abrupt discontinuation may cause chest pain or myocardial infarction (MI).

Health Teaching & Health Promotion: Clients should be instructed to take the medication as prescribed. They should be advised that abrupt cessation of medication therapy may result in life-threatening cardiac arrhythmias. Clients should also be taught how to self-check pulse and blood pressure to assess the effectiveness of medication therapy. Additionally, they should be cautioned against sudden changes in position due to orthostatic blood pressure changes. Clients may experience increased sensitivity to cold and should be cautioned to avoid caffeinated substances.^[1]

Now let’s take a closer look at the medication grid on metoprolol in Table 4.12.^[2]

Table 4.12 Metoprolol Medication Grid