Tambocor (flecainide acetate)

Dosage of flecainide acetate should be carefully adjusted according to individual patient response and tolerance. Clinical and ECG monitoring of cardiac function is recommended during therapy with the drug. When feasible, plasma trough flecainide concentrations should be monitored; monitoring is required in patients with severe renal or hepatic impairment, and is recommended in other patients in whom elimination of the drug may be impaired (e.g., those with moderate renal impairment or congestive heart failure, or those receiving concomitant amiodarone therapy). Dosage should be adjusted to maintain trough plasma flecainide concentrations at less than 0.7-1 mcg/mL since concentrations above this range have been associated with a higher rate of adverse cardiac effects, especially when the trough concentration exceeds 1 mcg/mL. Since steady-state plasma concentrations of flecainide and the optimum therapeutic effect may not be attained for 3-5 days (or longer in some patients) at a given dosage in patients with normal renal and hepatic function, increases in flecainide dosage should be made at intervals of not less than 4 days. Once adequate control of arrhythmias has been attained, dosage reduction to minimize adverse effects or effects on cardiac conduction may be possible in some patients; however, efficacy of the drug at the lower dosage should be evaluated. If congestive heart failure, myocardial dysfunction, or renal or hepatic failure develops in patients receiving flecainide, dosage reduction may be necessary. Many clinicians recommend the use of low initial dosages in geriatric patients.

Any use of flecainide in children should be supervised directly by a cardiologist experienced in the treatment of arrhythmias in this age group. (See Cautions: Pediatric Precautions.) In pediatric patients, flecainide should be initiated in a hospital setting with facilities available for cardiac rhythm monitoring. Because of the evolving nature of flecainide use in children, specialized references should be consulted for the most recent information. The manufacturer states that the initial flecainide acetate dosage in infants younger than 6 months of age is approximately 50 mg/m2 daily, divided into 2 or 3 equally spaced doses. For older children, an initial dosage of 100 mg/m2 daily may be given. The maximum dosage recommended by the manufacturer for pediatric patients is 200 mg/m2 daily, which should not be exceeded. Plasma trough flecainide concentrations (less than 1 hour before dosing) and ECGs should be obtained at presumed steady state (after at least 5 doses) after initiation of therapy or after any change in dosing, whether the dosage was increased for lack of effectiveness or for increased growth of the child. In some children receiving higher dosages, plasma drug concentrations are labile; while receiving the same dosage, plasma flecainide concentrations have increased rapidly to far above therapeutic concentrations, despite previously low plasma concentrations. Small changes in dosage also may lead to disproportionate increases in plasma drug concentrations. For the first year of flecainide treatment whenever the pediatric patient is seen for clinical follow-up, a 12-lead ECG and plasma trough flecainide concentrations are suggested. The usual therapeutic concentration of flecainide in children is 200-500 ng/mL, although concentrations up to 800 ng/mL may be required for adequate control in some children.

Since initial flecainide acetate dosages higher than those recommended and dosage adjustments at shorter intervals than recommended have resulted in an increased risk of arrhythmogenicity and congestive heart failure in patients with sustained ventricular tachycardia, especially during the first few days of flecainide therapy, a loading dose of the drug is not recommended; however, single oral loading doses (e.g., 200-300 mg) have been used for conversion of recent-onset atrial fibrillation to normal sinus rhythm+ in selected patients (''pill-in-the-pocket'' approach). IV lidocaine has occasionally been used concomitantly and without any apparent adverse interaction until the therapeutic effect of oral flecainide therapy was attained; however, studies have not been performed to determine the value of this regimen.

Based on theoretical considerations, it is recommended that, when transferring patients from therapy with another antiarrhythmic agent to flecainide, at least 2-4 plasma half-lives of the agent being discontinued be allowed to elapse before therapy with flecainide is initiated at the usual dosage. When withdrawal of another antiarrhythmic agent is likely to result in life-threatening arrhythmias, initiation of flecainide therapy in a hospital setting should be considered.

In patients with renal impairment, dosage of flecainide acetate must be carefully adjusted based on the degree of renal impairment. The recommended initial oral dosage of flecainide acetate in patients with severe renal impairment (creatinine clearance of 35 mL/minute per 1.73 m2 or less) is 100 mg once daily (or 50 mg twice daily). In patients with less severe renal impairment, an initial dosage of 100 mg every 12 hours is recommended. Since the elimination half-life of the drug may be prolonged in patients with renal impairment, steady-state plasma concentrations with a given dosage may not be attained for longer than 4 days. Consequently, increases in dosage should be made with caution and at intervals of longer than 4 days, with the patient closely monitored for signs of adverse cardiac effects or other toxicity. Plasma trough flecainide concentrations should be monitored in patients with severe renal impairment and also may be useful in patients with moderate renal impairment.

Since flecainide is extensively metabolized, probably in the liver, elimination may be markedly prolonged in patients with substantial hepatic impairment, and therefore the drug should not be used in such patients unless the potential benefits are considered to clearly outweigh the risks. If flecainide is used in patients with hepatic impairment, plasma flecainide concentrations should be monitored closely to guide dosage, and dosage should be increased cautiously at intervals of longer than 4 days.

Flecainide acetate is administered orally. Flecainide also has been administered IV+, but a parenteral dosage form of the drug is currently not commercially available in the US.

Flecainide acetate is administered orally, usually in 2 equally divided doses daily at 12-hour intervals; however, in patients in whom arrhythmias are not adequately controlled or the drug is not well tolerated with twice-daily dosing, the drug may be given in 3 divided doses daily at 8-hour intervals. The elimination half-life of flecainide suggests that once-daily oral dosing may be possible in some patients, but once-daily dosing regimens of the drug have not been evaluated to date.

Absorption of flecainide is not affected by food or antacids; however, milk may inhibit absorption in infants. Dosage reduction of flecainide acetate may be necessary when milk is removed from the diet in infants.

Because of the risk of proarrhythmia, initiation of therapy in a hospital setting is recommended in patients with sustained ventricular tachycardia, regardless of their cardiac status. Some clinicians recommend that withdrawal of therapy should also occur in a hospital setting under continuous ECG monitoring.

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There is no enhanced messaging for this drug.

There are no contraindication interactions for this drug.

There are no severe interactions for this drug.

There are no moderate interactions for this drug.

There is no enhanced messaging for this drug.

There are no contraindication contraindications for this drug.

There are no severe contraindications for this drug.

There are no moderate contraindications for this drug.

There is no enhanced messaging for this drug.

There are no severe adverse reactions for this drug.

There are no less severe adverse reactions for this drug.

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No enhanced messaging available.

Reproduction studies in rats and mice using oral flecainide acetate dosages up to 50 and 80 mg/kg daily, respectively, have not revealed evidence of fetal malformation; however, delayed sternebral and vertebral ossification were observed in rats receiving the highest dosages. Club paws, sternebral and vertebral abnormalities, pale hearts with contracted ventricular septum, and increased fetal resorptions were observed in one breed of rabbits (New Zealand white rabbits) receiving dosages of 30 and 35 mg/kg daily; reproduction studies in Dutch Belted rabbits using similar dosages did not reveal evidence of teratogenicity or embryotoxicity. There are no adequate and controlled studies to date using oral flecainide acetate in pregnant women, and the drug should be used during pregnancy only when the potential benefits justify the possible risks to the fetus. It is not known whether use of the drug during labor or delivery could have any immediate or delayed adverse effects on the mother or fetus, affect the duration of labor, or increase the likelihood of forceps delivery or other obstetrical intervention.

Limited data suggest that flecainide is distributed into milk in humans. In one study in postpartum women receiving multiple doses of flecainide, milk flecainide concentration averaged 2.5 times (sometimes as high as 4 times) that of maternal plasma concentrations. It is estimated that less than 3 mg of the drug would be ingested by a nursing infant (receiving about 700 mL of milk) over a 24-hour period assuming a maternal plasma flecainide concentration of 1 mcg/mL, which is considered at the top of the therapeutic range.

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