Beta-blockers are safe cardioactive agents if the warnings and contraindications are followed. They are not advisable in patients with severe class IV heart failure. They are indi¬cated, however, in class I–III heart failure. Class IV patients who have been stabilized and are no longer decompensated can be started on very small doses of carvedilol (3.5 mg).
Beta-blockers are contraindicated in patients with bronchial asthma and in patients with severe chronic obstructive pulmonary disease including emphysema. Patients with mild chronic bronchitis may be given a cardioselective beta-1 agent and may require supplemental salbutamol. Other contraindications include:
1. Complete heart block and varying grades of heart block
2. Severe bradycardia less than 48 beats per minute
3. Allergic rhinitis
4. Insulin-dependent diabetics who are prone to hypogly-cemia
5. Raynaud’s phenomenon
Adverse side effects of beta-blockers include tiredness and fatigue in about 10% of patients, erectile dysfunction in about 10%, precipitation of heart failure in patients with poor left ventricular function, slowing of the heart rate causing bradycardia less than 50 beats per minute, depression in less than 5%, very cold extremities in less than 10%, and vivid dreams. Switching to a hydrophilic drug excreted by the kidney may decrease vivid dreams.