bisoprolol and diltiazem

Additive pharmacodynamic effects. Bisoprolol blocks beta-1 adrenergic receptors, reducing heart rate, conduction velocity, and contractility. Diltiazem blocks L-type calcium channels in the myocardium and smooth muscle, similarly slowing SA node depolarisation and AV node conduction. Combined, these effects synergistically depress the SA and AV nodes and reduce myocardial contractility.

Clinically significant bradycardia, AV block, hypotension, and worsening heart failure can occur. Both drugs reduce cardiac output and can precipitate symptomatic bradycardia, particularly in patients with conduction disease or impaired ventricular function. Severe sinus bradycardia and high-grade AV block are possible, as is decompensation of pre-existing heart failure. The risk is increased with higher doses and in elderly patients.

If possible, avoid the combination, especially in patients with heart failure, bradycardia, AV conduction disease, or hypotension. If co-prescription is necessary, start with low doses, monitor heart rate, blood pressure, and ECG regularly, and adjust doses cautiously. Consider alternatives such as a dihydropyridine calcium channel blocker or an alpha/beta blocker if appropriate. Patients should be advised to report symptoms of bradycardia, dizziness, or syncope.

The interaction is well established from pharmacodynamic principles and clinical studies. It is widely cited in drug interaction compendia and guidelines. No specific citations are provided here.