Dronedarone

Mechanism

Amiodarone and dronedarone are class III antiarrhythmics with overlapping mechanism and additive QT prolongation. Dronedarone was developed as a less toxic replacement for amiodarone, so combining them is not meaningful.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk rises with hypokalaemia and hypomagnesaemia.

Management

The combination is not prescribed. Choose one: amiodarone for high-risk atrial fibrillation with reduced ejection fraction, dronedarone for preserved ejection fraction without heart failure.

Mechanism

Amitriptyline (tricyclic antidepressant) prolongs QT. Dronedarone also prolongs QT. Additive effect raises ventricular arrhythmia risk. FDA Multaq Section 4.3 specifically lists QT-prolonging antidepressants as contraindications.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk rises with hypokalaemia and hypomagnesaemia.

Management

The combination is not prescribed. Replace the TCA with sertraline (minimal QT effect, up to 100 mg/day) or agomelatine. If a TCA is required, choose a non-QT antiarrhythmic (beta-blocker).

Mechanism

Dronedarone is cleared mainly by CYP3A4. The FDA classes cyclosporine as a strong CYP3A inhibitor and names it in section 4 (Contraindications) of the dronedarone label. The labels give no figure for cyclosporine itself; ketoconazole raised dronedarone levels 17-fold. The effect also runs the other way: dronedarone may raise cyclosporine levels, so the EU SmPC of dronedarone asks for monitoring of the immunosuppressant.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk rises with hypokalaemia and hypomagnesaemia.

Management

The combination is not prescribed. For post-transplant atrial fibrillation, use amiodarone or rhythm control via catheter ablation. Alternative immunosuppression: tacrolimus, with attention to its own QT risk.

Mechanism

Dronedarone is a class III antiarrhythmic. Its SmPC describes a QTc increase of about 10 ms as its own effect and separately contraindicates torsade-inducing drugs alongside it. The citalopram SmPC lists ongoing treatment with any drug capable of prolonging the QT interval among its contraindications, with no exceptions.

Symptoms

QTc prolongation on ECG, palpitations, dizziness, syncope. The end point is polymorphic ventricular tachycardia of the torsade type progressing to ventricular fibrillation. The risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, decompensated heart failure and in women.

Management

The pair sits in the citalopram SmPC contraindications, so the question is which drug stays, not how far to cut the dose. The ban runs both ways: the dronedarone label contraindicates torsade-inducing drugs, the SSRI label contraindicates QT-prolonging ones. Before either drug starts, potassium, magnesium and QTc are checked.

Mechanism

Clarithromycin is a strong CYP3A4 inhibitor and prolongs QT itself. Dronedarone is cleared via CYP3A4 and also prolongs QT. Double mechanism: dronedarone levels rise 4-fold plus additive QT prolongation. FDA Multaq Section 4.3 specifically lists strong CYP3A4 inhibitors.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk rises with hypokalaemia and hypomagnesaemia.

Management

The combination is not prescribed. Alternative antibiotics: azithromycin (minimal CYP3A4 effect and weaker QT effect) or doxycycline by susceptibility.

Mechanism

Dronedarone is a moderate CYP3A4 inhibitor and a potent P-glycoprotein inhibitor (dronedarone SmPC). Colchicine is cleared through both pathways and has a narrow therapeutic margin (colchicine SmPC), so its blood levels rise, and with them the risk of myopathy, neuropathy and bone marrow suppression.

Symptoms

Profuse diarrhoea, vomiting, abdominal pain. With prolonged combination: muscle weakness, peripheral neuropathy, falling leukocytes and platelets.

Management

The combination is contraindicated: the Spanish colchicine SmPC forbids colchicine during use of CYP3A4 or P-glycoprotein inhibitors and for 14 days afterwards (colchicine SmPC), and dronedarone inhibits both pathways (dronedarone SmPC). The US label of colchicine 0.5 mg for cardiovascular prevention, approved by the US Food and Drug Administration (FDA), also contraindicates it with P-glycoprotein inhibitors (colchicine label, FDA). Other colchicine manufacturers require a lower maximum colchicine dose and close monitoring with a P-glycoprotein inhibitor, and avoid the combination whenever possible in renal or hepatic impairment (colchicine SmPC). At the first sign of nausea, vomiting, abdominal pain or diarrhoea, colchicine is stopped and the patient needs urgent care (colchicine SmPC).

Mechanism

Dronedarone strongly inhibits intestinal P-glycoprotein, the clearance route of dabigatran. Dabigatran plasma levels rise 2-fold or more. FDA Multaq Section 4.3 specifically lists dabigatran etexilate as an absolute contraindication.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage, gross haematuria with renal colic, spontaneous retroperitoneal haematomas. Symptoms may appear within days of co-prescription.

Management

The combination is not prescribed. For atrial fibrillation patients on dronedarone, anticoagulate with warfarin, apixaban, or rivaroxaban (the latter two use P-glycoprotein less and are acceptable without dose change).

Mechanism

Both drugs prolong the QT interval. The dronedarone label lists erythromycin among drugs that can induce torsade de pointes and contraindicates the combination because of the risk of proarrhythmia. Erythromycin also moderately inhibits the enzyme CYP3A4 and the transporter P-glycoprotein (erythromycin label). The liver breaks down dronedarone mainly through this enzyme. Erythromycin 500 mg three times a day for 10 days raised steady-state dronedarone levels 3.8-fold (dronedarone label, European Medicines Agency, EMA). The QT interval gets longer as dronedarone concentration rises (dronedarone label, US Food and Drug Administration, FDA). Dronedarone is a class III antiarrhythmic. The label of intravenous erythromycin contraindicates erythromycin with class Ia and III antiarrhythmics, which also prolong the QT interval.

Symptoms

The main risk is ventricular arrhythmia from a prolonged QT interval, up to torsade de pointes: palpitations, skipped beats, dizziness, fainting. Deaths from these arrhythmias have been reported during erythromycin treatment, and older people are more sensitive to its effect on the QT interval. A fast intravenous infusion of erythromycin can by itself prolong the QT interval and cause arrhythmia or low blood pressure. A slow pulse is common with dronedarone. As its concentration rises, the QT and PR intervals on the electrocardiogram (ECG) get longer.

Management

The combination is contraindicated (dronedarone labels, European Medicines Agency, EMA, and US Food and Drug Administration, FDA). Both labels name erythromycin. The contraindication also applies to intravenous erythromycin. The FDA dronedarone label does not limit it to any route of administration. The label of intravenous erythromycin contraindicates its use with class III antiarrhythmics (Spanish Agency of Medicines and Medical Devices, AEMPS), and dronedarone belongs to this class (dronedarone label, EMA). If erythromycin has been started during dronedarone treatment, stop dronedarone: the label requires stopping it whenever any contraindicated condition develops (dronedarone label, EMA). After stopping 400 mg twice daily, dronedarone and its metabolite are fully cleared from plasma within 2 weeks (dronedarone label, EMA). The documents set no specific interval before starting erythromycin. Correct potassium and magnesium before starting dronedarone and keep them in the normal range during treatment (dronedarone labels, EMA and FDA). Do not give erythromycin to patients with low potassium or magnesium (erythromycin label, AEMPS). Monitor the electrocardiogram (ECG) during dronedarone treatment and stop dronedarone if the QTc interval (QT corrected for heart rate) reaches 500 milliseconds or more (dronedarone label, EMA). Infuse intravenous erythromycin over 60 minutes, and over a longer time in patients with risk factors or a history of arrhythmia (intravenous erythromycin label, AEMPS).

Mechanism

Dronedarone is a class III antiarrhythmic. Its SmPC describes a QTc increase of about 10 ms as its own effect and separately contraindicates torsade-inducing drugs alongside it. The escitalopram SmPC contraindicates any QT-prolonging drug alongside it: the ban is written broadly, and the classes in brackets are examples.

Symptoms

QTc prolongation on ECG, palpitations, dizziness, syncope. The end point is polymorphic ventricular tachycardia of the torsade type progressing to ventricular fibrillation. The risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, decompensated heart failure and in women.

Management

The pair sits in the escitalopram SmPC contraindications, so the question is which drug stays, not how far to cut the dose. The ban runs both ways: the dronedarone label contraindicates torsade-inducing drugs, the SSRI label contraindicates QT-prolonging ones. Before either drug starts, potassium, magnesium and QTc are checked.

Mechanism

Both drugs prolong the QT interval on the electrocardiogram. Dronedarone prolongs the corrected QT interval (QTc) by about 10 ms and can itself cause arrhythmias when used with other drugs that favour arrhythmias (dronedarone SmPC). The haloperidol SmPC reports QT prolongation, ventricular arrhythmias and sudden death; the risk is higher with high doses, high plasma levels and parenteral use, especially intravenous. There is a second mechanism: dronedarone is a moderate CYP3A4 inhibitor and a weak CYP2D6 inhibitor (dronedarone SmPC), and haloperidol is partly cleared by both enzymes; with such inhibitors its levels may rise by 20–40%, in some cases by up to 100% (haloperidol SmPC).

Symptoms

QT prolongation on the electrocardiogram (ECG) causes no symptoms by itself. Palpitations, dizziness or fainting may occur. The dangerous complication is torsades de pointes, a ventricular tachycardia. The risk is higher with low potassium or magnesium (dronedarone and haloperidol SmPCs), bradycardia or heart disease (haloperidol SmPC). Haloperidol can also cause a fast heart rate and a drop in blood pressure on standing (haloperidol SmPC).

Management

The combination is contraindicated: the Spanish haloperidol SmPC contraindicates haloperidol with drugs that prolong the QT interval and names dronedarone (haloperidol SmPC). The dronedarone SmPC approved by the European Medicines Agency (EMA) contraindicates it with drugs that can induce torsades de pointes and gives phenothiazines, tricyclic antidepressants, some macrolides and class I and III antiarrhythmics as examples; haloperidol is not on that list (dronedarone SmPC). Potassium and magnesium deficits are corrected before the start and checked during treatment (dronedarone and haloperidol SmPCs). Before haloperidol is started, an electrocardiogram (ECG) is recorded; if the corrected QT interval (QTc) lengthens, the haloperidol dose is reduced, and haloperidol is stopped if QTc exceeds 500 ms (haloperidol SmPC). On dronedarone the ECG is monitored, and dronedarone is stopped if QTc reaches 500 ms or more (dronedarone SmPC). Haloperidol solution for injection is given intramuscularly only; if it is given intravenously, the ECG is monitored continuously (haloperidol injection SmPC).

Mechanism

The liver breaks down dronedarone mainly through the enzyme CYP3A4, and itraconazole strongly inhibits this enzyme (labels of both drugs). No study has looked at this pair directly. According to the itraconazole label, itraconazole is likely to raise dronedarone levels. The dronedarone label reports a 17-fold rise in dronedarone levels with ketoconazole 200 mg a day, another strong inhibitor of the enzyme. The QT interval gets longer as dronedarone concentration rises. The itraconazole labels explain the contraindication for such drugs by the risk of ventricular tachyarrhythmias, including life-threatening torsade de pointes. Beyond the kinetics, both drugs carry a risk for the heart muscle. Itraconazole has a negative inotropic effect and has been linked to congestive heart failure. Dronedarone reduces myocardial contractility and is contraindicated in current or past heart failure (labels of both drugs).

Symptoms

The main risk is ventricular arrhythmia from a prolonged QT interval, up to life-threatening torsade de pointes: palpitations, skipped beats, dizziness, fainting. Both drugs list a slow heart rate (bradycardia) among their adverse effects. Both can cause new heart failure or make it worse. Signs include increasing shortness of breath, rapid weight gain and swelling of the legs.

Management

The combination is contraindicated in the labels of both drugs: dronedarone (European Medicines Agency, EMA, and US Food and Drug Administration, FDA) and itraconazole (Spanish Agency of Medicines and Medical Devices, AEMPS, and FDA). Do not give dronedarone during itraconazole treatment or for 2 weeks after itraconazole is stopped (itraconazole labels, AEMPS and FDA). After itraconazole is stopped, its plasma levels take 7–14 days to become almost undetectable, and even longer in liver cirrhosis or with other inhibitors of the enzyme CYP3A4 (itraconazole label, AEMPS). If itraconazole has been started during dronedarone treatment, stop dronedarone: the label requires stopping it whenever any contraindicated condition develops (dronedarone label, EMA). Correct potassium and magnesium before starting dronedarone and keep them in the normal range during treatment (dronedarone labels, EMA and FDA). Monitor the electrocardiogram (ECG) during dronedarone treatment and stop dronedarone if the QTc interval (QT corrected for heart rate) reaches 500 milliseconds or more (dronedarone label, EMA). If signs of heart failure appear, stop itraconazole (itraconazole labels, AEMPS and FDA) and dronedarone (dronedarone label, EMA).

Mechanism

Ketoconazole is a strong CYP3A4 inhibitor, the main dronedarone clearance route. Dronedarone plasma levels rise 17-fold. FDA Multaq Section 4.3 specifically lists strong CYP3A4 inhibitors.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk rises with hypokalaemia and hypomagnesaemia.

Management

The combination is not prescribed. Alternative antifungals: echinocandins (micafungin, caspofungin) or fluconazole for candidiasis (weaker CYP3A4 effect). Alternative antiarrhythmic: amiodarone or catheter ablation.

Mechanism

Ritonavir is the most potent CYP3A4 inhibitor available. Dronedarone plasma levels may rise 25-fold or more, plus both drugs prolong QT. FDA Multaq Section 4.3 specifically lists ritonavir.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk rises with hypokalaemia and hypomagnesaemia.

Management

The combination is not prescribed. For HIV-positive patients with atrial fibrillation, use a beta-blocker (rate control) or catheter ablation (rhythm control). Ritonavir-free antiretroviral regimens are discussed with the infectious diseases team.

Mechanism

The liver breaks down dronedarone mainly through the enzyme CYP3A4, and voriconazole strongly inhibits this enzyme (labels of both drugs). The labels give no study of this exact pair. The dronedarone label reports a 17-fold rise in dronedarone levels with ketoconazole 200 mg a day, another strong inhibitor of the enzyme. For this reason, it contraindicates voriconazole and other strong inhibitors. The QT interval gets longer as dronedarone concentration rises, and voriconazole prolongs the QT interval on its own. Dronedarone itself moderately inhibits CYP3A4, and the liver clears voriconazole partly through this enzyme. The documents give no figures for the rise in voriconazole levels.

Symptoms

The main risk of the pair is arrhythmia from a prolonged QT interval, up to torsade de pointes: palpitations, skipped beats, dizziness, fainting. As dronedarone levels rise, the QT and PR intervals on the electrocardiogram (ECG) get longer. A slow pulse is common with dronedarone even without other drugs. With voriconazole, rare cases of torsade de pointes have occurred in people with risk factors such as cardiomyopathy, low potassium, past cardiotoxic chemotherapy or other drugs taken at the same time.

Management

The combination is contraindicated (dronedarone labels, European Medicines Agency, EMA, and US Food and Drug Administration, FDA). Both labels name voriconazole among the strong inhibitors of the enzyme CYP3A4. Stop a strong CYP3A4 inhibitor before starting dronedarone (dronedarone label, FDA). If voriconazole has been started during dronedarone treatment, stop dronedarone: the label requires stopping it whenever any contraindicated condition develops (dronedarone label, EMA). After stopping 400 mg twice daily, dronedarone and its metabolite are fully cleared from plasma within 2 weeks (dronedarone label, EMA). The documents set no specific interval before starting voriconazole. Correct potassium and magnesium before starting dronedarone and keep them in the normal range during treatment (dronedarone labels, EMA and FDA). Correct low potassium, magnesium and calcium before and during voriconazole treatment (voriconazole labels, EMA and FDA). Monitor the electrocardiogram (ECG) during dronedarone treatment and stop dronedarone if the QTc interval (QT corrected for heart rate) reaches 500 milliseconds or more (dronedarone label, EMA). In dronedarone overdose, monitor heart rhythm and blood pressure and give supportive treatment. There is no specific antidote (dronedarone labels, EMA and FDA).

Mechanism

Dronedarone is a strong CYP3A4 inhibitor, the main alprazolam metabolic route. Alprazolam plasma levels may rise 2- to 4-fold. Deep sedation, fall risk in older patients.

Symptoms

Deep sedation, drowsiness, ataxia. Older patients: fall and fracture risk. Symptoms appear within 1–2 days.

Management

During dronedarone therapy, halve alprazolam or use lorazepam/oxazepam (glucuronidated, no CYP3A4 dependence).

Mechanism

Dronedarone is a strong CYP3A4 inhibitor, the main amlodipine metabolic route. Amlodipine plasma levels may double.

Symptoms

Blood pressure drop: postural dizziness, syncope. Ankle oedema (typical of amlodipine), facial flushing, reflex tachycardia are possible.

Management

Cap amlodipine at 5 mg/day when combined. Alternative calcium channel blocker: diltiazem (with caution combined with an antiarrhythmic), or replace amlodipine with an ACE-I/ARB.

Mechanism

Both drugs prolong the QT interval. Dronedarone prolongs the corrected QT interval (QTc) by about 10 ms (dronedarone SmPC). The azithromycin SmPC reports QT prolongation and torsades de pointes with macrolides, azithromycin included. The effects add up, and the dronedarone SmPC warns that proarrhythmic effects may occur when it is combined with drugs that favour arrhythmias or with potassium and magnesium disorders.

Symptoms

QT prolongation on the electrocardiogram (ECG) causes no symptoms by itself. Palpitations, dizziness or fainting may occur. The dangerous complication is torsades de pointes, a ventricular tachycardia that can end in cardiac arrest (azithromycin SmPC). The risk is higher in women and older people, with low potassium or magnesium, marked bradycardia or severe heart failure (azithromycin SmPC).

Management

The dronedarone SmPC contraindicates it with drugs that can induce torsades de pointes and lists some oral macrolides, such as erythromycin; azithromycin is not named on that list (dronedarone SmPC). The azithromycin SmPC asks for caution in patients on class III antiarrhythmics, dronedarone among them, and in anyone taking QT-prolonging drugs (azithromycin SmPC). The azithromycin label approved by the US Food and Drug Administration (FDA) advises weighing the risk of fatal QT prolongation in these patients (azithromycin FDA label). If azithromycin is still given with dronedarone, potassium and magnesium deficits are corrected before and during treatment, the electrocardiogram (ECG) is checked during treatment, and dronedarone is stopped if the corrected QT interval (QTc) reaches 500 ms or more (dronedarone SmPC).

Mechanism

Dronedarone has properties of all four Vaughan-Williams antiarrhythmic classes, including antiadrenergic activity (dronedarone SmPC). In healthy volunteers it lengthened the PR interval, meaning slower conduction from the atria to the ventricles, by about 12 ms at 400 mg twice daily (dronedarone label of the US Food and Drug Administration, FDA). Bisoprolol, as a beta-blocker, also slows the heart rate and conduction. In clinical studies bradycardia was seen more often when dronedarone was combined with beta-blockers (dronedarone SmPC).

Symptoms

Slow pulse, weakness, dizziness, fainting. On the electrocardiogram (ECG): bradycardia, PR prolongation, atrioventricular block.

Management

The dronedarone SmPC says beta-blockers should be used with caution with dronedarone: start at a low dose and increase it only after an electrocardiogram (ECG) check. In patients already on a beta-blocker, record an ECG when dronedarone is started and adjust the beta-blocker dose if needed (dronedarone SmPC). The US Food and Drug Administration (FDA) gives the same rule: a low starting dose of the beta-blocker, increased only after the ECG confirms good tolerability (dronedarone FDA label). Dronedarone is contraindicated with a heart rate below 50 beats per minute and with second- or third-degree atrioventricular block without a pacemaker (dronedarone SmPC); bisoprolol is contraindicated with second- or third-degree atrioventricular block without a pacemaker and with symptomatic bradycardia (bisoprolol SmPC). During dronedarone treatment, record an ECG regularly, at least every 6 months (dronedarone SmPC).

Mechanism

Carbamazepine is a strong CYP3A4 inducer, and dronedarone is cleared through this enzyme. The labels give no data for this pair; with another strong inducer, rifampicin, dronedarone levels fell by 80% and the antiarrhythmic effect weakens. The EU SmPC of dronedarone does not recommend strong CYP3A4 inducers and names carbamazepine; the FDA label says to avoid them. No label lists the pair as a contraindication.

Symptoms

First, recurrence of atrial fibrillation symptoms: palpitations, irregular pulse, fatigue, dyspnoea. Possible rhythm breakthroughs requiring admission.

Management

Avoid the combination. If long-term anticonvulsant therapy is needed, consider a drug without CYP3A4 induction, such as levetiracetam or lamotrigine, or another rhythm control strategy, including catheter ablation. While the pair continues, watch for recurrence of atrial fibrillation: pulse, ECG, palpitations and irregular heartbeat.

Mechanism

Additive QT prolongation. Dronedarone is on the FDA list of drugs that contraindicate strong QT-prolonging antibiotics. Ciprofloxacin prolongs QT dose-dependently.

Symptoms

QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.

Management

Avoid the combination. Alternative antibiotics: a cephalosporin (no QT effect) or nitrofurantoin for urinary tract infection.

Mechanism

Dronedarone blocks intestinal P-glycoprotein – the main route of digoxin absorption and elimination. Digoxin plasma levels rise 1.7- to 2.5-fold. Dronedarone also enhances contractile and bradycardic effects.

Symptoms

Nausea, anorexia, visual disturbances (yellow-green halos around lights), arrhythmias ranging from premature beats to ventricular tachycardia. Older adults: confusion, dizziness. Symptoms appear within 1–2 weeks of co-administration.

Management

When dronedarone starts, halve the digoxin dose; check level at 1 week. If sinus node or AV conduction symptoms appear, hold digoxin temporarily.

Mechanism

Dual mechanism. Fluconazole blocks CYP3A4 (the main dronedarone clearance route) and prolongs QT itself. Dronedarone plasma levels rise; QT effects add up.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

Avoid the combination. Alternative antifungals: echinocandins (micafungin, caspofungin) for systemic mycoses or terbinafine for dermatophytosis. If fluconazole is needed: ECG before start and every 3 days during therapy.

Mechanism

Fluoxetine blocks CYP2D6 (strongly) and CYP3A4 (moderately). Dronedarone plasma levels may rise. Additive QT risk.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

Avoid the combination. Alternative antidepressants without CYP3A4/CYP2D6 inhibition: sertraline or escitalopram. Alternative antiarrhythmic: a beta-blocker for rate control.

Mechanism

Furosemide (loop diuretic) increases urinary potassium loss. Low potassium amplifies dronedarone's QT effect, which itself carries an FDA boxed warning for this risk.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

The combination is common (atrial fibrillation + heart failure). Check potassium and magnesium every 1–3 months; if potassium drops below 4.0 mmol/L, add a potassium-sparing diuretic or potassium supplement.

Mechanism

Hydrochlorothiazide (thiazide diuretic) increases urinary potassium loss. Low potassium amplifies dronedarone's QT effect.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

The combination is common (hypertension + atrial fibrillation). Check potassium and magnesium every 3 months; if potassium drops below 4.0 mmol/L, add a potassium-sparing diuretic or potassium supplement.

Mechanism

Indapamide (thiazide-like diuretic) increases urinary potassium loss. Low potassium amplifies dronedarone's QT effect.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

The combination is common (hypertension + atrial fibrillation). Check potassium and magnesium every 3 months; if potassium drops below 4.0 mmol/L, add a potassium-sparing diuretic or potassium supplement.

Mechanism

Mirtazapine prolongs QT dose-dependently (especially above 30 mg/day). Combined with dronedarone, torsades de pointes risk rises.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

The combination is acceptable at low mirtazapine doses (≤30 mg/day) and normal potassium. ECG before start and at 2 weeks. Alternative antidepressants with minimal QT effect: agomelatine or sertraline (up to 100 mg).

Mechanism

Both drugs prolong the QT interval. Dronedarone prolongs the corrected QT interval (QTc) by about 10 ms (dronedarone SmPC). After quetiapine reached the market, QT prolongation was reported at therapeutic doses and in overdose (quetiapine SmPC). Together they raise the risk of torsades de pointes. Dronedarone is also a moderate CYP3A4 inhibitor (dronedarone SmPC), and quetiapine is cleared mainly by this enzyme (quetiapine SmPC), so quetiapine levels may rise.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

The combination is avoided: the quetiapine label approved by the US Food and Drug Administration (FDA) advises against using it with class III antiarrhythmics, and dronedarone is one of them. The dronedarone SmPC contraindicates it with drugs that can induce torsades de pointes and lists them: phenothiazines, tricyclic antidepressants, some oral macrolides, class I and III antiarrhythmics; quetiapine is not on that list (dronedarone SmPC). If the combination is still needed, potassium and magnesium deficits are corrected before and during dronedarone treatment, the electrocardiogram (ECG) is checked regularly, and dronedarone is stopped if the corrected QT interval (QTc) reaches 500 ms or more (dronedarone SmPC). Quetiapine needs particular caution in older patients and in congenital long QT syndrome, heart failure, cardiac hypertrophy, low potassium or low magnesium (quetiapine SmPC).

Mechanism

Rifampicin is a strong CYP3A4 inducer. At 600 mg daily it lowered dronedarone levels by 80% without major change in the active metabolite, and the antiarrhythmic effect weakens. The EU SmPC of dronedarone does not recommend the combination, and the FDA label says to avoid it. Neither the dronedarone nor the rifampicin labels list the pair as a contraindication.

Symptoms

Recurrence of atrial fibrillation symptoms: palpitations, irregular pulse, fatigue, dyspnoea. Possible rhythm breakthroughs requiring admission.

Management

Avoid the combination. In a patient with atrial fibrillation who needs tuberculosis treatment, plan rhythm control with a cardiologist for the rifampicin course, including catheter ablation. Rifampicin is hard to replace because it is part of the standard first-line regimen. Other antiarrhythmics lose exposure too: the rifampicin SmPC reports falls of 80% for quinidine and 87% for propafenone. If the pair continues, watch for recurrent atrial fibrillation on ECG and by symptoms.

Mechanism

Sertraline at high doses (above 150 mg/day) moderately prolongs QT. Combined with dronedarone, risk of torsades de pointes rises, especially in older patients.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

Avoid the combination with sertraline above 100 mg. At low doses (50–100 mg) with normal potassium and magnesium, the combination is acceptable with ECG monitoring at 2 weeks. Alternative antidepressants: mirtazapine or agomelatine.

Mechanism

Dronedarone inhibits CYP3A4 – the main simvastatin metabolic route. Simvastatin plasma levels rise 4-fold. FDA Zocor 2012 caps simvastatin at 10 mg/day with dronedarone.

Symptoms

Pain and weakness in large muscle groups (thighs, shoulders, calves), dark urine, elevated creatine kinase. Severe cases progress to rhabdomyolysis with acute kidney injury. Symptoms appear within 1–4 weeks of co-administration.

Management

Cap simvastatin at 10 mg/day when combined. If LDL targets are missed, switch to pravastatin or rosuvastatin (no CYP3A4 dependence).

Mechanism

Dronedarone is a moderate CYP3A4 inhibitor and a potent P-glycoprotein inhibitor (dronedarone label). Tacrolimus is metabolized mainly by CYP3A4 in the liver and gut wall, so its blood levels can rise with dronedarone (tacrolimus and dronedarone labels). The second mechanism is electrical: dronedarone moderately prolongs the QT interval, and tacrolimus can itself prolong QT and cause torsades de pointes (labels of both drugs).

Symptoms

Signs of tacrolimus excess: worsening kidney function with rising creatinine, tremor, headache, and raised blood pressure, blood glucose and potassium (tacrolimus label). The combination prolongs the QT interval on the ECG; marked prolongation can lead to torsades de pointes with palpitations, dizziness and fainting (tacrolimus and dronedarone labels).

Management

Give CYP3A4 inhibitors with tacrolimus only after consulting a transplant specialist (tacrolimus label). Measure tacrolimus blood levels often from the first days of co-administration and adjust the dose (tacrolimus and dronedarone labels). For CYP3A4 inhibitors that also prolong the QT interval, the FDA tacrolimus label recommends a lower tacrolimus dose, frequent level checks and QT monitoring. Monitor kidney function and the ECG closely during the combination (tacrolimus label). Correct low potassium and magnesium before and during dronedarone treatment, and stop dronedarone if QTc reaches 500 ms or more (dronedarone label).

Mechanism

Additive QT risk. Tramadol weakly prolongs QT and blocks serotonin/norepinephrine reuptake. Dronedarone is a potent QT prolonger. Tramadol also lowers seizure threshold.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

Avoid the combination. For analgesia on dronedarone, use paracetamol, an NSAID, or morphine/oxycodone (no QT effect).

Mechanism

Additive QT prolongation. Venlafaxine prolongs QT at high doses; dronedarone carries an FDA boxed warning for this effect.

Symptoms

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

Management

Avoid the combination. Alternative antidepressants with minimal QT effect: mirtazapine or agomelatine. Alternative antiarrhythmic: a beta-blocker for rate control.

Mechanism

Dronedarone is a moderate inhibitor of the CYP3A4 enzyme and a strong inhibitor of the P-glycoprotein transporter, and apixaban is cleared through both routes. Dronedarone can therefore raise apixaban blood levels and the bleeding risk. The dronedarone SmPC does not class it as a strong inhibitor of both routes together, and the labels give no figures for the rise in apixaban levels (dronedarone SmPC of the European Medicines Agency, EMA).

Symptoms

Gum bleeding, epistaxis, bruising without trauma, black stools, blood in urine. Severe cases include gastrointestinal or intracranial haemorrhage.

Management

The combination is allowed with caution. Do not change the apixaban dose because of dronedarone: the dronedarone SmPC of the European Medicines Agency (EMA) says so directly, and the apixaban SmPC requires no dose adjustment with inhibitors that are not strong (dronedarone and apixaban SmPCs, EMA). The dronedarone SmPC requires monitoring of co-administered anticoagulants (dronedarone SmPC, EMA). In atrial fibrillation, reduce apixaban to 2.5 mg twice daily if two of three criteria are present: age 80 years or older, body weight 60 kg or less, serum creatinine 133 µmol/L or higher (apixaban SmPC, EMA). Dronedarone itself raises serum creatinine, on average by 10 µmol/L, usually within the first week. Measure creatinine before starting dronedarone and after 7 days, take the stable value as the new baseline, and then check kidney function regularly (dronedarone SmPC, EMA). Dronedarone is contraindicated with creatinine clearance below 30 mL/min (dronedarone SmPC, EMA). The European Heart Rhythm Association (EHRA) advises caution, especially with polypharmacy. If at least one more risk factor is present (age 75 years or older, body weight 60 kg or less, chronic kidney disease, antiplatelet drugs, non-steroidal anti-inflammatory drugs, systemic steroids, previous bleeding, anaemia or low platelets, frailty or falls), EHRA suggests considering an anticoagulant with fewer interactions or replacing the other drug (EHRA 2021).

Mechanism

Dronedarone blocks CYP3A4 – a partial atorvastatin metabolic route. Atorvastatin plasma levels rise 2-fold, raising myalgia risk.

Symptoms

Pain and weakness in large muscle groups (thighs, shoulders, calves), dark urine, elevated creatine kinase. Symptoms usually appear 2–6 weeks after starting the combination.

Management

Cap atorvastatin at 20 mg/day when combined. If LDL targets are missed, switch to pravastatin or rosuvastatin (no CYP3A4 dependence).