Metoprolol

Mechanism

Additive bradycardia and sedation. Fall risk in older patients.

Symptoms

Lower blood pressure, postural dizziness, fatigue. Older patients: fall risk.

Management

In older patients, check pulse and blood pressure 1–2 weeks after starting alprazolam. Alternative anxiolytic: hydroxyzine or a short lorazepam course.

Mechanism

Amitriptyline is a CYP2D6 substrate, as is metoprolol. Enzyme competition raises both drug levels. Plus additive anticholinergic effect on the heart (bradycardia, PR prolongation).

Symptoms

Bradycardia (heart rate below 50/min), dizziness, syncope. ECG: PR prolongation. Older patients: delirium and fall risk.

Management

In older patients, check pulse and ECG 1–2 weeks after starting amitriptyline. Alternative beta-blocker without CYP2D6 dependence: bisoprolol or carvedilol. For neuropathic pain, alternative: gabapentin or pregabalin.

Mechanism

Target combination in angina and hypertension. Amlodipine dilates vessels; metoprolol slows heart rate. The drugs compensate each other's reflex effects.

Symptoms

Lower blood pressure, postural dizziness, fatigue. Older patients: fall risk.

Management

Standard combination in ischaemic heart disease with hypertension. Check pulse and blood pressure 1–2 weeks after start. In patients with ejection fraction below 40%, watch for heart failure decompensation.

Mechanism

Metoprolol is mainly metabolised by CYP2D6; clarithromycin does not clinically significantly inhibit CYP2D6. The effect on metoprolol levels is minimal. Additive bradycardia is possible from clarithromycin's direct effect on the cardiac conduction system.

Symptoms

Bradycardia, dizziness, fatigue. Symptoms appear during clarithromycin courses in older patients and concurrent heart failure.

Management

For short clarithromycin courses (7–14 days) with normal heart rate, no adjustment needed. In older patients and prior first-degree AV block, check ECG at one week. For long-term clarithromycin (e.g. Mycobacterium avium complex), antibiotic alternative: azithromycin (minimal HR effect).

Mechanism

Target combination in heart failure with reduced ejection fraction and in arterial hypertension. Synergistic reduction of blood pressure, preload, and afterload.

Symptoms

On starting, in older or hypovolaemic patients: symptomatic hypotension, dizziness, fatigue. Metoprolol bradycardia is amplified as sympathetic activation drops.

Management

Start both drugs at minimal doses with up-titration every 2 weeks to target. Check standing/sitting BP, heart rate, creatinine and potassium at 2 weeks. In heart failure, the goal is maximum tolerated dose; the RCT evidence base is extensive.

Mechanism

Target combination in heart failure and arterial hypertension. Synergistic blood pressure reduction. The ARB does not mask the adrenergic response to hypoglycaemia.

Symptoms

On starting, in older patients: symptomatic hypotension, dizziness. Metoprolol bradycardia is amplified as sympathetic activation drops.

Management

Start both at minimal doses with up-titration every 2 weeks to target. Check standing/sitting BP, heart rate, creatinine and potassium at 2 weeks. In diabetes, monitor for hypoglycaemia: metoprolol is cardioselective and weakly masks adrenergic symptoms.

Mechanism

Metoprolol is cardioselective but at high doses antagonises theophylline's bronchodilator effect. In bronchial asthma, control may worsen.

Symptoms

Exertional dyspnoea, wheezing, more frequent asthma attacks. In COPD: symptom exacerbation.

Management

In asthma and COPD with atrial fibrillation or hypertension, metoprolol is preferred at cardioselective doses (up to 100 mg/day) under pulmonary function monitoring. In severe asthma, consider alternatives — diltiazem or verapamil for rate control in atrial fibrillation. Theophylline is second-line in COPD; consider switching to long-acting beta-2 agonists (formoterol).