Digoxin-specific antibody fragments

⚠️ CONSULT THE POISONS SERVICE. §4.2 opens with this and it is the first thing on the page: 'It is advised to discuss management of patients with digoxin toxicity or cardiac glycoside poisoning with TOXBASE (UK National Poisons Information Service) at the following contact phone number: 0344 892 0111 (in Ireland NPIC (01) 809 2566) and/or refer to the most up to date TOXBASE guidance at https://www.toxbase.org/' || UNIT CONVERSION, verbatim: 'Digoxin concentrations in mmol/L should be converted to ng/mL (same as µg/L) for the estimations above by using the formula: [Digoxin] nmol/L x 0.781 = [Digoxin] ng/mL'. (Reproduced as printed; note the SPC's own sentence says mmol/L while the formula is written in nmol/L.) || ⚠️ ASSAY CEILING (§4.4): 'Digoxin assay kits may not be able to measure accurately digoxin concentrations greater than 5 ng/mL (6.4 mmol/L). Exercise caution when using digoxin concentrations above these figures to calculate the dose of DIGIFAB required.' And: 'Digoxin assays react unpredictably with non-digoxin cardiac glycosides. Digoxin assay kit levels must not be used to dose DIGIFAB in these situations.' || AFTER DOSING, serum digoxin becomes uninterpretable (§4.4): 'DIGIFAB may interfere with digoxin immunoassay measurements. Therefore, standard serum digoxin measurements may be clinically misleading until the Fab fragments are eliminated from the body. This may take several days or more than a week in patients with impaired renal function. The total serum digoxin concentration as measured by immunoassay may rise rapidly following administration of DIGIFAB. Serum digoxin will be almost entirely bound by DIGIFAB and therefore not able to react with receptors in the body.' || SEPARATE REGIMEN FOR NON-DIGOXIN CARDIAC GLYCOSIDES (e.g. yellow oleander) — this page is the DIGOXIN antidote, so these are recorded here rather than in the dose field. Cardiac arrest due to cardiac glycosides other than digoxin: IV bolus, over 40 kg 5 vials (200 mg), 20–40 kg 2 vials (80 mg), 20 kg or less 1 vial (40 mg), further doses if no adequate response after 30 minutes. Severe bradyarrhythmia, life-threatening ventricular arrhythmia OR severe hyperkalaemia resistant to rehydration and conventional treatment: IV bolus, over 40 kg 2 vials (80 mg), 40 kg or less 1 vial (40 mg), repeat doses after 15–30 minutes if the response is inadequate. Note that these are LOWER vial counts than the digoxin arrest bands and must not be interchanged. || NO MAXIMUM DOSE is stated anywhere in the fetched sections — no 'maximum' or 'do not exceed' wording appears — so maxDose is left blank rather than inferred from the largest band. The only stated limit is the caution on repeat dosing (anaphylaxis risk). || The weight bands apply to adults AND children — the SPC's own table header is 'Weight (adult and children)'. See paedDose. || DOSING BASIS (§4.4, truncated at this point): 'Dosage estimates for digoxin toxicity are based on a steady-state volume of distribution of 5 L/kg for digoxin in order to convert serum digitalis...' — the remainder was not retrieved. || TRACEABILITY (§4.4): 'the name and the batch number of the administered product should be clearly recorded.'

⚠️ NOT A PER-KG DOSE — dosePerKg is deliberately null. DigiFab is dosed in WHOLE VIALS by weight band or by a vial-count formula, so no mg/kg figure exists to multiply by weight; the SPC's paediatric figures are the same weight bands as for adults ('Weight (adult and children)'). CARDIAC ARREST due to digoxin toxicity, verbatim bands: over 40 kg, 5 vials (200 mg); 20–40 kg, 2 vials (80 mg); 20 kg or less, 1 vial (40 mg). For severe bradyarrhythmia, life-threatening ventricular arrhythmia or severe hyperkalaemia, the same vial-count formulae as for adults apply and already include the child's weight: number of vials = (serum digoxin concentration in ng/mL × weight in kg) ÷ 200, rounded up; or, when only the ingested dose is known, number of vials = amount of digoxin ingested (mg) × 0.8, rounded up. Each vial is reconstituted with 4 mL of sterile water. FOR NON-DIGOXIN CARDIAC GLYCOSIDES the arrest bands are the same, but the bradyarrhythmia/hyperkalaemia bands are lower: over 40 kg 2 vials (80 mg), 40 kg or less 1 vial (40 mg), repeated after 15–30 minutes if the response is inadequate. §4.2 verbatim on paediatric evidence: 'Data on the safety and efficacy of DIGIFAB in children are limited.' §4.8 adds that no paediatric patients were included in the digoxin-toxicity studies, that eleven adolescents aged 13–17 received DigiFab in the yellow oleander study, and that 'The frequency, type and severity of adverse reactions in children are expected to be the same as in adults.' Discuss every paediatric case with the National Poisons Information Service (0344 892 0111; Ireland NPIC (01) 809 2566) and verify against a children's formulary.