Treatment: antiarrhythmics (flecainide, propafenone, sotalol, digoxin, dronedarone)

Before starting

• Serum electrolytes (potassium)
• Serum magnesium
• Serum creatinine (calculate Cockcroft–Gault clearance)
• ASTif neededPatient started on propafenone: contraindicated in cirrhosis, reduced starting dose in moderate hepatic impairment, stop if liver enzymes exceed 3 times normal (SmPC) ^[3].
• ALT (propafenone)if neededPatient started on propafenone: contraindicated in cirrhosis, reduced starting dose in moderate hepatic impairment, stop if liver enzymes exceed 3 times normal (SmPC) ^[3].

At least once a year (atrial fibrillation)

• Serum electrolytes (potassium)
• Serum creatinine (calculate Cockcroft–Gault clearance)
• Flecainide (blood level) (renal impairment or older patient)if neededIn renal failure and in older people, slowed elimination exposes to accumulation: the SmPC (RCP) recommends “treatment monitoring” ^[4]. Can be measured under the code for antiarrhythmics not specifically listed ^[5].

Before starting, and before each dose change

• Serum electrolytes (potassium)
• Serum magnesium
• Serum creatinine (calculate Cockcroft–Gault clearance)

At least once a year, and without waiting if a potassium-lowering drug is added (diuretic, stimulant laxative, corticosteroid)

• Serum electrolytes (potassium)
• Serum creatinine (calculate Cockcroft–Gault clearance)

Before starting

• Serum electrolytes (potassium)
• Serum creatinine (calculate Cockcroft–Gault clearance)
• TSH (if known or suspected thyroid dysfunction)if needednon-French guidelineThe NHS pharmacy service (SPS) measures thyroid function before digoxin, as the dose is adjusted in case of thyroid dysfunction ^[12]; the Dutch formulary also asks for this adjustment ^[10]. The French SmPC (RCP) lists hypothyroidism among the situations of increased sensitivity ^[13]; HAS provides for TSH at diagnosis of atrial fibrillation, not in the tests specific to digoxin ^[7].
• Serum magnesium (if long-term PPI or diuretic)if needednon-French guidelineThe NHS pharmacy service (SPS) measures magnesium before digoxin and then every year, more often with long-term PPI or another drug exposing to hypomagnesaemia, as it favours toxicity ^[12]; diuretics are among these ^[11], and the Dutch formulary flags the same risk ^[10]. The French digoxin SmPC (RCP) does not mention magnesium ^[13] and HAS retains serum potassium and creatinine ^[7].
• Serum calcium (if calcium or vitamin D co-prescribed, or known hypercalcaemia)if neededHypercalcaemia increases sensitivity to digoxin ^[12,13]. The French SmPC (RCP) asks, where appropriate, for a calcium check with oral calcium supplements, in particular combined with vitamin D ^[13]; the NHS pharmacy service (SPS) measures calcium before treatment and then every year in everyone ^[12]; HAS does not list it ^[7].

End of the first week, at least 8 hours after the last dose (older patient or renal impairment)

• Serum digoxinif neededNecessary in older people and in renal failure to adjust the dose, at steady state (end of the first week) ^[7,13].
• Serum electrolytes (potassium)

Then periodically (at least once a year; more often in older patients, renal impairment or on a diuretic)

• Serum electrolytes (potassium)
• Serum creatinine (calculate Cockcroft–Gault clearance)
• Serum digoxin (signs of overdose, interaction, renal deterioration)if neededAnorexia, nausea, vomiting, diarrhoea or ECG abnormality ^[13]; visual or psychiatric disturbances in older people ^[13]; addition of a drug that raises serum digoxin (amiodarone, verapamil, quinidine or hydroquinidine, clarithromycin, erythromycin, telithromycin, itraconazole, ritonavir ^[13], propafenone ^[3], dronedarone ^[14]) or lowers it (St John's wort, sulfasalazine, carbamazepine) ^[13]; functional renal failure in heart failure ^[13]; pregnancy near term ^[13].
• Serum magnesium (if long-term PPI or diuretic)if needednon-French guidelineThe NHS pharmacy service (SPS) measures magnesium every year on digoxin, more often with long-term PPI or another drug exposing to hypomagnesaemia, as it favours toxicity ^[12]; diuretics are among these ^[11], and the Dutch formulary flags the same risk ^[10]. The French digoxin SmPC (RCP) does not mention magnesium ^[13] and HAS retains serum potassium and creatinine ^[7].
• Serum calcium (if calcium or vitamin D co-prescribed, or known hypercalcaemia)if neededHypercalcaemia increases sensitivity to digoxin ^[12,13]. The French SmPC (RCP) asks, where appropriate, for a calcium check with oral calcium supplements, in particular combined with vitamin D ^[13]; the NHS pharmacy service (SPS) measures calcium every year in everyone ^[12]; HAS does not list it ^[7].

Before starting

• AST
• ALT
• Serum creatinine (calculate Cockcroft–Gault clearance)
• Serum electrolytes (potassium)
• Serum magnesium
• Serum β-hCG (woman of childbearing potential)if neededWoman of childbearing potential: the SmPC (RCP) asks to make sure she is not pregnant before starting dronedarone, and then effective contraception ^[14].

On D7

• ALT
• Serum creatinine

At 1 month, then every month up to 6 months, then at 9 and 12 months, then regularly

• ALT
• Serum creatinine (renal function regularly)
• Serum electrolytes (potassium)if neededPotassium-lowering diuretic, vomiting, diarrhoea: any potassium or magnesium deficit must be corrected during treatment (SmPC) ^[14].
• Serum magnesium (during treatment, if risk of deficiency)if neededPotassium-lowering diuretic, vomiting, diarrhoea: any potassium or magnesium deficit must be corrected during treatment (SmPC) ^[14].

• See the "Treatment: amiodarone" page (TSH, liver function tests, electrolytes).