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| __NOTOC__
| | #REDIRECT [[Digoxin immune fab#Adult Indications and Dosage]] |
| {{Digoxin immune fab}}
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| {{CMG}}; {{AE}} {{AK}}
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| '''''For patient information about Digoxin immune fab, click [[Digoxin immune fab (patient information)|here]].'''''
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| ==DOSAGE AND ADMINISTRATION ==
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| ===General Guidelines: ===
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| The dosage of DigiFab will vary according to the amount of digoxin or digitoxin to be neutralized.
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| Dosage for Acute Ingestion of Unknown Amounts of Digoxin or Digitoxin:
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| If a patient presents with life-threatening digitalis toxicity caused by an acute ingestion and neither a serum digitalis concentration nor an estimated ingestion amount is available, 20 vials of DigiFab may be administered. This amount should be adequate to treat most life-threatening overdoses in adults and children. However, in small children it is important to monitor for volume overload. In general, a larger dose of DigiFab has a faster onset of effect but may enhance the possibility of a febrile reaction. In such cases, 10 vials may be administered first with careful monitoring of the patient's response followed at the physician's discretion by 10 additional vials and continued monitoring. Failure of the patient to respond to DigiFab should alert the physician to the possibility that the clinical problem may not be caused by digitalis toxicity.
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| ===Dosage for Toxicity During Chronic Therapy:===
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| For adult patients who are in acute distress or for whom a serum digoxin concentration is not available, 6 vials (240 mg) should be adequate to reverse most cases of toxicity. For infants and small children (≤ 20 kg) on chronic therapy with digoxin and showing signs of toxicity, a single vial should be sufficient.
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| ===DOSAGE CALCULATION ===
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| Methods for calculating a neutralizing dose of DigiFab, based on a known or estimated amount of digoxin or digitoxin in the body, are provided below. When using the dose calculation methods provided, the following guidelines should be considered:
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| *Inaccurate estimates of the amount of digitalis ingested or absorbed may occur due to non-steady state serum concentrations or due to digitalis assay limitations. Most serum digoxin assay kits are designed to measure concentrations less than 5 ng/mL, therefore sample dilution is required to accurately measure serum concentrations > 5 ng/mL. <br>
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| *Dosage calculations are based on a steady state volume of distribution of approximately 5 L/kg for digoxin, which is used to convert serum digoxin concentrations to total body burden of digoxin in milligrams. The volume of distribution is a population average and may vary among individuals. Many patients may require higher doses for complete neutralization and doses should usually be rounded up to the nearest whole vial. <br>
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| *If toxicity has not adequately reversed after several hours, or appears to recur, re-administration of DigiFab, at a dose guided by clinical judgment, may be necessary. If a patient is in need of re-administration of DigiFab due to recurrent toxicity, or to a new toxic episode that occurs soon after the first episode, measurement of free (unbound) serum digitalis concentrations should be considered since Fab may still be present in the body. <br>
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| *Failure of a patient to respond to DigiFab treatment may indicate that the clinical problem is not caused by digitalis intoxication. If there is no response to an adequate dose of DigiFab, the diagnosis of digitalis toxicity should be questioned.
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| ===For Ingestion of Known Amount:===
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| Each vial of DigiFab contains 40 mg of purified digoxin-specific Fab, which will bind approximately 0.5 mg of digoxin. The total number of vials required can be calculated by dividing the total body load of digoxin in milligrams (mg) by 0.5 mg per vial (see Formula 1). Following an acute ingestion, total body load will be approximately equal to the amount ingested in milligrams for either digoxin capsules or digitoxin. If digoxin tablets were ingested, the total body load will be approximately equal to the amount ingested (in mg) multiplied by the bioavailability of the tablet preparation, which is 0.8.
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| Table 1 gives dosage estimates in number of vials for adults and children who have ingested a single large dose of digoxin and for whom the approximate number of tablets or capsules is known. The dose of DigiFab (in number of vials) represented in Table 1 can be approximated using the following formula:
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| [[image:digifab1.png]]
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| If, after several hours, toxicity is not adequately reversed, or appears to recur, additional administration of DigiFab at a dose guided by clinical judgment may be required.
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| Calculations Based on Steady-State Serum Digoxin Concentrations:
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| Table 2 gives dosage estimates in number of vials for adult patients for whom a steady-state serum digoxin concentration is known. The dose of DigiFab (in number of vials) represented in Table 2 can be approximated using the following formula:
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| Formula 2 (see Table 2)
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| [[image:digifab2.pg]]
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| Table 3 gives dosage estimates in milligrams for infants and small children based on the steady-state serum digoxin concentration. The dose of DigiFab represented in Table 3 can be estimated by multiplying the dose (in number of vials) calculated from Formula 2 by the amount of DigiFab contained in a vial (40 mg/vial) (see Formula 3). Since infants and small children can have much smaller dosage requirements, it is recommended that the 40 mg vial be reconstituted as directed and administered with a tuberculin syringe. For very small doses, a reconstituted vial can be diluted with 36 mL of sterile isotonic saline to achieve a concentration of 1 mg/mL.
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| Formula 3 (see Table 3)
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| [[image:digifab3.png]]
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| Calculation Based on Steady-State Digitoxin Concentrations:
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| The dose of DigiFab for digitoxin toxicity can be approximated by using the following formula (which differs from Formula 2 in the denominator due to a 10-fold decrease in the volume of distribution of digitoxin as compared to digoxin).
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| Formula 4
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| [[image:digifab4.png]]
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| If in any case, the dose estimated based on ingested amount (Formula 1) differs substantially from that calculated based on the serum digoxin or digitoxin concentration (Formulas 2 and 4), it may be preferable to use the higher dose estimate.
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| [[image:digifab5.png]]
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| ==Administration: ==
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| Each vial of DigiFab should be reconstituted with 4 mL of Sterile Water for Injection USP and gently mixed to provide a solution containing approximately 10 mg/mL of digoxin immune Fab protein. The reconsituted product should be used promptly. If not used immediately, it may be stored under refrigeration at 2° to 8°C (36° to 46°F} for up to 4 hours. The reconstituted product may be added to an appropriate volume of 0.9% sodium chloride for injection.
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| DigiFab should be administered slowly as an intravenous infusion over at least 30 minutes. If infusion rate-related reactions occur, the infusion should be stopped and re-started at a slower rate. If cardiac arrest is imminent, DigiFab can be given by bolus injection. With bolus injection, an increased incidence of infusion-related reactions may be expected.
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| For infants and small children who may require very small doses, it is recommended that the 40 mg vial be reconstituted as directed and administered undiluted using a tuberculin syringe. For very small doses, a reconstituted vial can be diluted with an additional 36 mL of isotonic saline to achieve a concentration of 1 mg/mL.
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| ==References==
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| {{Reflist|2}}
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| http://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=6832767f-db6b-4eea-b88b-bdfc905749e1
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| [[Category:Cardiovascular Drugs]]
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| [[Category:Drugs]]
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