Tambocor Information
Tambocor ()
Tambocor () Description
Tambocor () ™ (flecainide acetate) is an antiarrhythmic drug available in tablets of 50, 100, or 150 mg for oral administration. Flecainide acetate is benzamide, N-(2-piperidinylmethyl)-2,5-bis (2,2,2-trifluoroethoxy)-monoacetate. The structural formula is given below.
Flecainide acetate is a white crystalline substance with a pKa of 9.3. It has an aqueous solubility of 48.4 mg/mL at 37°C.
Tambocor () tablets also contain: croscarmellose sodium, hydrogenated vegetable oil, magnesium stearate, microcrystalline cellulose and starch.
Tambocor () Clinical Pharmacology
Tambocor () has local anesthetic activity and belongs to the membrane stabilizing (Class 1) group of antiarrhythmic agents; it has electrophysiologic effects characteristic of the IC class of antiarrhythmics.
Electrophysiology.
Sinus node recovery times (corrected) following pacing and spontaneous cycle lengths are somewhat increased. This latter effect may become significant in patients with sinus node dysfunction. (See )
Tambocor () causes a dose-related and plasma-level related decrease in single and multiple PVCs and can suppress recurrence of ventricular tachycardia. In limited studies of patients with a history of ventricular tachycardia, Tambocor () has been successful 30-40% of the time in fully suppressing the inducibility of arrhythmias by programmed electrical stimulation. Based on PVC suppression, it appears that plasma levels of 0.2 to 1.0 μg/mL may be needed to obtain the maximal therapeutic effect. It is more difficult to assess the dose needed to suppress serious arrhythmias, but trough plasma levels in patients successfully treated for recurrent ventricular tachycardia were between 0.2 and 1.0 μg/mL. Plasma levels above 0.7-1.0 μg/mL are associated with a higher rate of cardiac adverse experiences such as conduction defects or bradycardia. The relation of plasma levels to proarrhythmic events is not established, but dose reduction in clinical trials of patients with ventricular tachycardia appears to have led to a reduced frequency and severity of such events.
Hemodynamics.
In animals and isolated myocardium, a negative inotropic effect of flecainide has been demonstrated. Decreases in ejection fraction, consistent with a negative inotropic effect, have been observed after single administration of 200 to 250 mg of the drug in man; both increases and decreases in ejection fraction have been encountered during multidose therapy in patients at usual therapeutic doses. (See )
Metabolism in Humans.
The apparent plasma half-life averages about 20 hours and is quite variable (range, 12 to 27 hours) after multiple oral doses in patients with premature ventricular contractions (PVCs). With multiple dosing, plasma levels increase because of its long half-life with steady-state levels approached in 3 to 5 days; once at steady-state, no additional (or unexpected) accumulation of drug in plasma occurs during chronic therapy. Over the usual therapeutic range, data suggest that plasma levels in an individual are approximately proportional to dose, deviating upwards from linearity only slightly (about 10 to 15% per 100 mg on average).
In healthy subjects, about 30% of a single oral dose (range, 10 to 50%) is excreted in urine as unchanged drug. The two major urinary metabolites are meta-O-dealkylated flecainide (active, but about one-fifth as potent) and the meta-O-dealkylated lactam of flecainide (non-active metabolite). These two metabolites (primarily conjugated) account for most of the remaining portion of the dose. Several minor metabolites (3% of the dose or less) are also found in urine; only 5% of an oral dose is excreted in feces. In patients, free (unconjugated) plasma levels of the two major metabolites are very low (less than 0.05 μg/mL).
In vitro metabolic studies have confirmed that cytochrome P450IID6 is involved in the metabolism of flecainide.
When urinary pH is very alkaline (8 or higher), as may occur in rare conditions (e.g., renal tubular acidosis, strict vegetarian diet), flecainide elimination from plasma is much slower.
The elimination of flecainide from the body depends on renal function (i.e., 10 to 50% appears in urine as unchanged drug). With increasing renal impairment, the extent of unchanged drug excretion in urine is reduced and the plasma half-life of flecainide is prolonged. Since flecainide is also extensively metabolized, there is no simple relationship between creatinine clearance and the rate of flecainide elimination from plasma. (See )
In patients with NYHA class III congestive heart failure (CHF), the rate of flecainide elimination from plasma (mean half-life, 19 hours) is moderately slower than for healthy subjects (mean half-life, 14 hours), but similar to the rate for patients with PVCs without CHF. The extent of excretion of unchanged drug in urine is also similar. (See )
Under one year of age, currently available data are limited but suggest that the half-life at birth may be as long as 29 hours, decreasing to 11-12 hours by three months of age and 6 hours by one year of age. The pharmacokinetics in hydropic infants have not been studied, but case reports suggest prolonged elimination. In children aged 1 year to 12 years the half-life is approximately 8 hours. In adolescents (age 12 to 15) the plasma elimination half-life is approximately 11-12 hours. Since milk may inhibit absorption in infants, a reduction in Tambocor () dosage should be considered when milk is removed from the diet (e.g., gastroenteritis, weaning). Plasma trough flecainide levels should be monitored during major changes in dietary milk intake.
From age 20 to 80, plasma levels are only slightly higher with advancing age; flecainide elimination from plasma is somewhat slower in elderly subjects than in younger subjects. Patients up to age 80+ have been safely treated with usual dosages.
The extent of flecainide binding to human plasma proteins is about 40% and is independent of plasma drug level over the range of 0.015 to about
3.4 μg/mL. Thus, clinically significant drug interactions based on protein binding effects would not be expected.
Hemodialysis removes only about 1% of an oral dose as unchanged flecainide.
Small increases in plasma digoxin levels are seen during coadministration of Tambocor () with digoxin. Small increases in both flecainide and propranolol plasma levels are seen during coadministration of these two drugs. (See )
Tambocor () Clinical Trials
In two randomized, crossover, placebo-controlled clinical trials of 16 weeks double-blind duration, 79% of patients with paroxysmal supraventricular tachycardia (PSVT) receiving flecainide were attack free, whereas 15% of patients receiving placebo remained attack free. The median time-before-recurrence of PSVT in patients receiving placebo was 11 to 12 days, whereas over 85% of patients receiving flecainide had no recurrence at 60 days.
In two randomized, crossover, placebo-controlled clinical trials of 16 weeks double-blind duration, 31% of patients with paroxysmal atrial fibrillation/flutter (PAF) receiving flecainide were attack free, whereas 8% receiving placebo remained attack free. The median time-before-recurrence of PAF in patients receiving placebo was about 2 to 3 days, whereas for those receiving flecainide the median time-before-recurrence was 15 days.
Tambocor () Indications And Usage
In patients without structural heart disease, Tambocor () is indicated for the prevention of
– paroxysmal supraventricular tachycardias (PSVT), including atrioventricular nodal reentrant tachycardia, atrioventricular reentrant tachycardia and other supraventricular tachycardias of unspecified mechanism associated with disabling symptoms
– paroxysmal atrial fibrillation/flutter (PAF) associated with disabling symptoms
Tambocor () is also indicated for the prevention of
– documented ventricular arrhythmias, such as ventricular tachycardia ( VT), that in the judgment of the physician are life-threatening.
Use of Tambocor () for the treatment of VT, like other antiarrhythmics, should be initiated in the hospital. The use of Tambocor () is not recommended in patients with less severe ventricular arrhythmias even if the patients are symptomatic.
Because of the proarrhythmic effects of Tambocor () , its use should be reserved for patients in whom, in the opinion of the physician, the benefits of treatment outweigh the risks.
Tambocor () should not be used in patients with recent myocardial infarction. (See )
Use of Tambocor () in chronic atrial fibrillation has not been adequately studied and is not recommended. (See )
As is the case for other antiarrhythmic agents, there is no evidence from controlled trials that the use of Tambocor () favorably affects survival or the incidence of sudden death.
Tambocor () Contraindications
Tambocor () is contraindicated in patients with pre-existing second- or third-degree AV block, or with right bundle branch block when associated with a left hemiblock (bifascicular block), unless a pacemaker is present to sustain the cardiac rhythm should complete heart block occur. Tambocor () is also contraindicated in the presence of cardiogenic shock or known hypersensitivity to the drug.
Tambocor () Heart Failure
Array
Effects on Cardiac Conduction.
Clinically significant conduction changes have been observed at these rates: sinus node dysfunction such as sinus pause, sinus arrest and symptomatic bradycardia (1.2%), second-degree AV block (0.5%) and third-degree AV block (0.4%). An attempt should be made to manage the patient on the lowest effective dose in an effort to minimize these effects. (See ) If second- or third-degree AV block, or right bundle branch block associated with a left hemiblock occur, Tambocor () therapy should be discontinued unless a temporary or implanted ventricular pacemaker is in place to ensure an adequate ventricular rate.
Sick Sinus Syndrome (Bradycardia-Tachycardia Syndrome).
Effects on Pacemaker Thresholds.
The pacing threshold in patients with pacemakers should be determined prior to instituting therapy with Tambocor () , again after one week of administration and at regular intervals thereafter. Generally threshold changes are within the range of multiprogrammable pacemakers and, when these occur, a doubling of either voltage or pulse width is usually sufficient to regain capture.
Electrolyte Disturbances.
Pediatric Use.
Tambocor () Precautions
In a study involving healthy subjects receiving Tambocor () and concurrently, plasma flecainide levels were increased about 20% and levels were increased about 30% compared to control values. In this formal interaction study, Tambocor () and were each found to have negative inotropic effects; when the drugs were administered together, the effects were additive. The effects of concomitant administration of Tambocor () and on the PR interval were less than additive. In Tambocor () clinical trials, patients who were receiving concurrently did not experience an increased incidence of side effects. Nevertheless, the possibility of additive negative inotropic effects of and flecainide should be recognized.
Flecainide is not extensively bound to plasma proteins. In vitro studies with several drugs which may be administered concomitantly showed that the extent of flecainide binding to human plasma proteins is either unchanged or only slightly less. Consequently, interactions with other drugs which are highly protein bound (e.g., ) would not be expected. Tambocor () has been used in a large number of patients receiving without apparent interaction. Limited data in patients receiving known enzyme inducers () indicate only a 30% increase in the rate of flecainide elimination. In healthy subjects receiving (1 gm daily) for one week, plasma flecainide levels increased by about 30% and half-life increased by about 10%.
When is added to flecainide therapy, plasma flecainide levels may increase two-fold or more in some patients, if flecainide dosage is not reduced. (See )
Drugs that inhibit cytochrome P450IID6, such as , might increase the plasma concentrations of flecainide in patients that are on chronic flecainide therapy; especially if these patients are extensive metabolizers.
There has been little experience with the coadministration of Tambocor () and either or . Because both of these drugs have negative inotropic properties and the effects of coadministration with Tambocor () are unknown, neither nor should be administered concurrently with Tambocor () unless, in the judgment of the physician, the benefits of this combination outweigh the risks. There has been too little experience with the coadministration of Tambocor () with or to recommend concomitant use.
Carcinogenesis, Mutagenesis, Impairment of Fertility.
Pregnancy.
Labor and Delivery.
Nursing Mothers.
Pediatric Use.
CLINICAL PHARMACOLOGY,
WARNINGS,
DOSAGE AND ADMINISTRATION
Hepatic Impairment.
Plasma Level Monitoring
Tambocor () Adverse Reactions
In post-myocardial infarction patients with asymptomatic PVCs and non-sustained ventricular tachycardia, Tambocor () therapy was found to be associated with a 5.1% rate of death and non-fatal cardiac arrest, compared with a 2.3% rate in a matched placebo group. (See )
Adverse effects reported for Tambocor () , described in detail in the Warnings section, were new or worsened arrhythmias which occurred in 1% of 108 patients with PSVT and in 7% of 117 patients with PAF; and new or exacerbated ventricular arrhythmias which occurred in 7% of 1330 patients with PVCs, non-sustained or VT. In patients treated with flecainide for VT, 80% (51/64) of proarrhythmic events occurred within 14 days of the onset of therapy. 198 patients with VT experienced a 13% incidence of new or exacerbated ventricular arrhythmias when dosage was initiated at 200 mg/day with slow upward titration, and did not exceed 300 mg/day in most patients. In some patients, Tambocor () treatment has been associated with episodes of unresuscitatable VT or ventricular fibrillation (cardiac arrest). (See ) New or worsened CHF occurred in 6.3% of 1046 patients with PVCs, non-sustained or VT. Of 297 patients with VT, 9.1% experienced new or worsened CHF. New or worsened CHF was reported in 0.4% of 225 patients with supraventricular arrhythmias. There have also been instances of second- (0.5%) or third-degree (0.4%) AV block. Patients have developed sinus bradycardia, sinus pause, or sinus arrest, about 1.2% altogether (see ). The frequency of most of these serious adverse events probably increases with higher trough plasma levels, especially when these trough levels exceed 1.0 μg/mL.
There have been rare reports of isolated elevations of serum alkaline phosphatase and isolated elevations of serum transaminase levels. These elevations have been asymptomatic and no cause and effect relationship with Tambocor () has been established. In foreign postmarketing surveillance studies, there have been rare reports of hepatic dysfunction including reports of cholestasis and hepatic failure, and extremely rare reports of blood dyscrasias. Although no cause and effect relationship has been established, it is advisable to discontinue Tambocor () in patients who develop unexplained jaundice or signs of hepatic dysfunction or blood dyscrasias in order to eliminate Tambocor () as the possible causative agent.
Incidence figures for other adverse effects in patients with ventricular arrhythmias are based on a multicenter efficacy study, utilizing starting doses of 200 mg/day with gradual upward titration to 400 mg/day. Patients were treated for an average of 4.7 months, with some receiving up to 22 months of therapy. In this trial, 5.4% of patients discontinued due to non-cardiac adverse effects.
The following additional adverse experiences, possibly related to Tambocor () therapy and occurring in 1% to less than 3% of patients, have been reported in acute and chronic studies: – malaise, fever; – tachycardia, sinus pause or arrest; – vomiting, diarrhea, dyspepsia, anorexia; – rash; – diplopia; – hypoesthesia, paresthesia, paresis, ataxia, flushing, increased sweating, vertigo, syncope, somnolence, tinnitus; – anxiety, insomnia, depression.
The following additional adverse experiences, possibly related to Tambocor () , have been reported in less than 1% of patients: – swollen lips, tongue and mouth; arthralgia, bronchospasm, myalgia; – angina pectoris, second-degree and third-degree AV block, bradycardia, hypertension, hypotension; – flatulence; – polyuria, urinary retention; – leukopenia, granulocytopenia, thrombocytopenia; – urticaria, exfoliative dermatitis, pruritis, alopecia; – eye pain or irritation, photophobia, nystagmus; – twitching, weakness, change in taste, dry mouth, convulsions, impotence, speech disorder, stupor, neuropathy; – pneumonitis/pulmonary infiltration possibly due to chronic flecainide treatment; – amnesia, confusion, decreased libido, depersonalization, euphoria, morbid dreams, apathy.
For patients with supraventricular arrhythmias, the most commonly reported noncardiac adverse experiences remain consistent with those known for patients treated with Tambocor () for ventricular arrhythmias. Dizziness is possibly more frequent in PAF patients.
Tambocor () Overdosage
No specific antidote has been identified for the treatment of Tambocor () overdosage. Overdoses ranging up to 8000 mg have been survived, with peak plasma flecainide concentrations as high as 5.3 μg/mL. Untoward effects in these cases included nausea and vomiting, convulsions, hypotension, bradycardia, syncope, extreme widening of the QRS complex, widening of the QT interval, widening of the PR interval, ventricular tachycardia, AV nodal block, asystole, bundle branch block, cardiac failure, and cardiac arrest. The spectrum of events observed in fatal cases was much the same as that seen in the non-fatal cases. Death has resulted following ingestion of as little as 1000 mg; concomitant overdose of other drugs and/or alcohol in many instances undoubtedly contributed to the fatal outcome. Treatment of overdosage should be supportive and may include the following: removal of unabsorbed drug from the gastrointestinal tract, administration of inotropic agents or cardiac stimulants such as dopamine, dobutamine or isoproterenol; mechanically assisted respiration; circulatory assists such as intra-aortic balloon pumping; and transvenous pacing in the event of conduction block. Because of the long plasma half-life of flecainide (12 to 27 hours in patients receiving usual doses), and the possibility of markedly non-linear elimination kinetics at very high doses, these supportive treatments may need to be continued for extended periods of time.
Hemodialysis is not an effective means of removing flecainide from the body. Since flecainide elimination is much slower when urine is very alkaline (pH 8 or higher), theoretically, acidification of urine to promote drug excretion may be beneficial in overdose cases with very alkaline urine. There is no evidence that acidification from normal urinary pH increases excretion.
Tambocor () Dosage And Administration
Flecainide has a long half-life (12 to 27 hours in patients). Steady-state plasma levels, in patients with normal renal and hepatic function, may not be achieved until the patient has received 3 to 5 days of therapy at a given dose. Therefore, , since during the first 2 to 3 days of therapy the optimal effect of a given dose may not be achieved.
For patients with PSVT and patients with PAF the recommended starting dose is 50 mg every 12 hours. Tambocor () doses may be increased in increments of 50 mg bid every four days until efficacy is achieved. For PAF patients, a substantial increase in efficacy without a substantial increase in discontinuations for adverse experiences may be achieved by increasing the Tambocor () dose from 50 to 100 mg bid. The maximum recommended dose for patients with paroxysmal supraventricular arrhythmias is 300 mg/day.
For VT the recommended starting dose is 100 mg every 12 hours. This dose may be increased in increments of 50 mg bid every four days until efficacy is achieved. Most patients with VT do not require more than 150 mg every 12 hours (300 mg/day) and the maximum dose recommended is 400 mg/day.
In patients with VT, use of higher initial doses and more rapid dosage adjustments have resulted in an increased incidence of proarrhythmic events and CHF, particularly during the first few days of dosing (see ). Therefore, a loading dose is not recommended.
Intravenous lidocaine has been used occasionally with Tambocor () while awaiting the therapeutic effect of Tambocor () . No adverse drug interactions were apparent. However, no formal studies have been performed to demonstrate the usefulness of this regimen.
An occasional patient not adequately controlled by (or intolerant to) a dose given at 12-hour intervals may be dosed at eight-hour intervals.
Once adequate control of the arrhythmia has been achieved, it may be possible in some patients to reduce the dose as necessary to minimize side effects or effects on conduction. In such patients, efficacy at the lower dose should be evaluated.
Tambocor () should be used cautiously in patients with a history of CHF or myocardial dysfunction (see ).
Any use of Tambocor () in children should be directly supervised by a cardiologist skilled in the treatment of arrhythmias in children. Because of the evolving nature of information in this area, specialized literature should be consulted. Under six months of age, the initial starting dose of Tambocor () in children is approximately 50 mg/M body surface area daily, divided into two or three equally spaced doses. Over six months of age, the initial starting dose may be increased to 100 mg/M per day. The maximum recommended dose is 200 mg/M per day. This dose should not be exceeded. In some children on higher doses, despite previously low plasma levels, the level has increased rapidly to far above therapeutic values while taking the same dose. Small changes in dose may also lead to disproportionate increases in plasma levels. Plasma trough (less than one hour pre-dose) flecainide levels and electrocardiograms should be obtained at presumed steady state (after at least five doses) either after initiation or change in Tambocor () dose, whether the dose was increased for lack of effectiveness, or increased growth of the patient. For the first year on therapy, whenever the patient is seen for reasons of clinical follow-up, it is suggested that a 12-lead electrocardiogram and plasma trough flecainide level are obtained. The usual therapeutic level of flecainide in children is 200-500 ng/mL. In some cases, levels as high as 800 ng/mL may be required for control.
In patients with severe renal impairment (creatinine clearance of 35 mL/min/1.73 square meters or less), the initial dosage should be 100 mg once daily (or 50 mg bid); when used in such patients, frequent plasma level monitoring is required to guide dosage adjustments (see ). In patients with less severe renal disease, the initial dosage should be 100 mg every 12 hours; plasma level monitoring may also be useful in these patients during dosage adjustment. In both groups of patients, dosage increases should be made very cautiously when plasma levels have plateaued (after more than four days), observing the patient closely for signs of adverse cardiac effects or other toxicity. It should be borne in mind that in these patients it may take longer than four days before a new steady-state plasma level is reached following a dosage change.
Based on theoretical considerations, rather than experimental data, the following suggestion is made: when transferring patients from another antiarrhythmic drug to Tambocor () allow at least two to four plasma half-lives to elapse for the drug being discontinued before starting Tambocor () at the usual dosage. In patients where withdrawal of a previous antiarrhythmic agent is likely to produce life-threatening arrhythmias, the physician should consider hospitalizing the patient.
When flecainide is given in the presence of amiodarone, reduce the usual flecainide dose by 50% and monitor the patient closely for adverse effects.
Plasma level monitoring is strongly recommended to guide dosage with such combination therapy (see below).
Tambocor () How Supplied
All tablets are embossed with 3M on one side and TR 50, TR 100 or TR 150 on the other side.
Tambocor () , 50 mg per white, round tablet, is available in
Bottles of 100 – NDC #0089-0305-10
Tambocor () , 100 mg per white, round, scored tablet, is available in
Bottles of 100 – NDC #0089-0307-10
Tambocor () , 150 mg per white, oval, scored tablet, is available in
Bottles of 100 – NDC #0089-0314-10
Store at controlled room temperature 15°-30°C (59°-86°F) in a tight, light-resistant container.
600900 JUNE 1998
Manufactured by
3M Pharmaceuticals
Northridge, CA 91324
