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Action/Kinetics:
Similar to lidocaine. Decreases the excitability of cells in the myocardium by decreasing sodium and potassium conductance. Increases pulmonary and aortic arterial pressure and slightly increases peripheral resistance. Effective in both digitalized and nondigitalized clients.
Peak plasma levels: 0.5-2 hr.
t
1/2: 11-15 hr.
Therapeutic serum levels: 4-10 mcg/mL.
Duration: 8 hr. Approximately 10% is bound to plasma protein. From 28% to 55% is excreted unchanged in the urine. Alkalinization decreases the excretion of the drug although acidification does not produce any changes in excretion.
Uses:
Life-threatening ventricular arrhythmias, including ventricular tachycardia. Has not been shown to improve survival in clients with ventricular arrhythmias.
Investigational: Myotonic dystrophy, trigeminal neuralgia.
Contraindications:
Allergy to amide-type local anesthetics, second- or third-degree AV block in the absence of artificial ventricular pacemaker. Lactation.
Special Concerns:
Increased risk of death when used in those with non-life-threatening cardiac arrhythmias. Safety and efficacy have not been established in children. Use with caution in clients with impaired renal or hepatic function (dose may have to be decreased). Geriatric clients may have an increased risk of dizziness and hypotension; the dose may have to be reduced in these clients due to age-related impaired renal function.
Side Effects:
CV:
Increased arrhythmias increased ventricular rate (when given for atrial flutter or fibrillation), CHF, tachycardia, hypotension,
conduction disturbances bradycardia, chest pain, LV failure, palpitations.
CNS: Dizziness, vertigo, headache, tremors, confusion, disorientation, hallucinations, ataxia, paresthesias, numbness, nervousness, altered mood, anxiety, incoordination, walking disturbances.
GI: N&V;, anorexia, diarrhea.
Respiratory:
Pulmonary fibrosis, fibrosing alveolitis interstitial pneumonitis,
pulmonary edema pneumonia.
Hematologic: Leukopenia,
agranulocytosis hypoplastic anemia,
aplastic anemia bone marrow depression, neutropenia,
thrombocytopenia and sequelae as septicemia and septic shock.
Musculoskeletal: Arthritis, arthralgia, myalgia.
Dermatologic: Rash, skin lesion, diaphoresis.
Other: Blurred vision, visual disturbances, nystagmus, tinnitus, hearing loss, lupus-like syndrome.
Laboratory Test Alterations:
Abnormal LFTs (esp. in early therapy).
ANA.
Overdose Management:
Symptoms: Initially are CNS symptoms including tremor (see above). GI symptoms may follow (see above).
Treatment: Gastric lavage and activated charcoal may be useful. In the event of respiratory depression or arrest or seizures, maintain airway and provide artificial ventilation. An IV anticonvulsant (e.g., diazepam, thiopental, thiamylal, pentobarbital, secobarbital) may be required if seizures are persistent.
Drug Interactions:
-
Cimetidine /
Tocainide bioavailability
-
Metoprolol / Additive effects on wedge pressure and cardiac index
-
Rifampin /
Tocainide bioavailability
How Supplied:
Tablet: 400 mg, 600 mg
Dosage
?Tablets
Antiarrhythmic.
Adults, individualized, initial: 400 mg q 8 hr, up to a maximum of 2,400 mg/day;
maintenance: 1,200-1,800 mg/day in divided doses. Total daily dose of 1,200 mg may be adequate in clients with liver or kidney disease.
Myotonic dystrophy.
800-1,200 mg/day.
Trigeminal neuralgia.
20 mg/kg/day in three divided doses.
