Quinidine Sulfate (Page 3 of 4)

Information for patients

Before prescribing quinidine sulfate as prophylaxis against recurrence of atrial fibrillation, the physician should inform the patient of the risks and benefits to be expected (see CLINICAL PHARMACOLOGY ). Discussion should include the facts:

• that the goal of therapy will be a reduction (probably not to zero) in the frequency of episodes of atrial fibrillation; and

• that reduced frequency of fibrillatory episodes may be expected, if achieved, to bring symptomatic benefit; but

• that no data are available to show that reduced frequency of fibrillatory episodes will reduce the risks of irreversible harm through stroke or death; and in fact

• that such data as are available suggest that treatment with quinidine sulfate is likely to increase the patient’s risk of death.

Carcinogenesis, mutagenesis, impairment of fertility

Animal studies to evaluate quinidine’s carcinogenic or mutagenic potential have not been performed. Similarly, there are no animal data as to quinidine’s potential to impair fertility.

Pregnancy

Pregnancy Category C:

Animal reproductive studies have not been conducted with quinidine. There are no adequate and well-controlled studies in pregnant women. Quinidine should be given to a pregnant woman only if clearly needed.

Human placental transport of quinidine has not been systematically studied. In one neonate whose mother had received quinidine throughout her pregnancy, the serum level of quinidine was equal to that of the mother, with no apparent ill effect. The level of quinidine in amniotic fluid was about three times higher than that found in serum. In another case, the levels of quinidine and 3-hydroxyquinidine in cord blood were about 30% of simultaneous maternal levels.

Labor and Delivery

Quinine is said to be oxytocic in humans, but there are no adequate data as to quinidine’s effects (if any) on human labor and delivery.

Nursing Mothers

Quinidine is present in human milk at levels slightly lower than those in maternal serum; a human infant ingesting such milk should (scaling directly by weight) be expected to develop serum quinidine levels at least an order of magnitude lower than those of the mother. On the other hand, the pharmacokinetics and pharmacodynamics of quinidine in human infants have not been adequately studied, and neonates’ reduced protein binding of quinidine may increase their risk of toxicity at low total serum levels. Administration of quinidine should (if possible) be avoided in lactating women who continue to nurse.

Geriatric Use

Safety and efficacy of quinidine in elderly patients has not been systematically studied.

Pediatric Use

In antimalarial trials, quinidine was as safe and effective in pediatric patients as in adults. Notwithstanding the known pharmacokinetic differences between children and adults (see CLINICAL PHARMACOLOGY,Pharmacokinetics a Metabolism), children in these trials received the same doses (on a mg/kg basis) as adults.

Safety and effectiveness of antiarrhythmic use in pediatric patients have not been established.

ADVERSE REACTIONS

Quinidine preparations have been used for many years, but there are only sparse data from which to estimate the incidence of various adverse reactions. The adverse reactions most frequently reported have consistently been gastrointestinal, including diarrhea, nausea, vomiting, and heartburn/esophagitis. In one study of 245 adult outpatients who received quinidine to suppress premature ventricular contractions, the incidences of reported adverse experiences were as shown in the table below. The most serious quinidine-associated adverse reactions are described above under WARNINGS.

Adverse Experiences in a 245-Patient PVC Trial

Incidence (%)

Incidence (%)

diarrhea

85 (35)

“upper gastrointestinal

distress”

55 (22)

lightheadedness

37 (15)

headache

18 (7)

fatigue

17 (7)

palpitations

16 (7)

angina-like pain

14 (6)

weakness

13 (5)

rash

11 (5)

visual problems

8 (3)

change in sleep habits

7 (3)

tremor

6 (2)

nervousness

5 (2)

discoordination

3 (1)

Vomiting and diarrhea can occur as isolated reactions to therapeutic levels of quinidine, but they may also be the first signs of cinchonism, a syndrome that may also include tinnitus, reversible high-frequency hearing loss, deafness, vertigo, blurred vision, diplopia, photophobia, headache, confusion, and delirium.

Cinchonism is most often a sign of chronic quinidine toxicity, but it may appear in sensitive patients after a single moderate dose.

A few cases of hepatotoxicity , including granulomatous hepatitis, have been reported in patients receiving quinidine. All of these have appeared during the first few weeks of therapy, and most (not all) have remitted once quinidine was withdrawn.

Autoimmune and inflammatory syndromes associated with quinidine therapy have included fever, urticaria, flushing, exfoliative rash, bronchospasm, psoriaform rash, pruritus and lymphadenopathy, hemolytic anemia, vasculitis, pneumonitis, thrombocytopenic purpura, uveitis, angioedema, agranulocytosis, the sicca syndrome, arthralgia, myalgia, elevation in serum levels of skeletal-muscle enzymes, and a disorder resembling systemic lupus erythematosus.

Convulsions, apprehension, and ataxia have been reported, but it is not clear that these were not simply the results of hypotension and consequent cerebral hypoperfusion. There are many reports of syncope. Acute psychotic reactions have been reported to follow the first dose of quinidine, but these reactions appear to be extremely rare.

Other adverse reactions occasionally reported include depression, mydriasis, disturbed color perception, night blindness, scotomata, optic neuritis, visual field loss, photosensitivity, and abnormalities of pigmentation.

OVERDOSAGE

Overdoses with various oral formulations of quinidine have been well described. Death has been described after a 5-gram ingestion by a toddler, while an adolescent was reported to survive after ingesting 8 grams of quinidine.

The most important ill effects of acute quinidine overdoses are ventricular arrhythmias and hypotension. Other signs and symptoms of overdose may include vomiting, diarrhea, tinnitus, high-frequency hearing loss, vertigo, blurred vision, diplopia, photophobia, headache, confusion, and delirium.

Arrhythmias

Serum quinidine levels can be conveniently assayed and monitored, but the electrocardiographic QTC interval is a better predictor of quinidine-induced ventricular arrhythmias.

The necessary treatment of hemodynamically unstable polymorphic ventricular tachycardia (including torsades de pointes) is withdrawal of treatment with quinidine and either immediate cardioversion or, if a cardiac pacemaker is in place or immediately available, immediate overdrive pacing. After pacing or cardioversion, further management must be guided by the length of the QTC interval.

Quinidine-associated ventricular tachyarrhythmias with normal underlying QTC intervals have not been adequately studied. Because of the theoretical possibility of QT-prolonging effects that might be additive to those of quinidine, other antiarrhythmics with Class I (disopyramide, procainamide) or Class III activities should (if possible) be avoided.

Similarly, although the use of bretylium in quinidine overdose has not been reported, it is reasonable to expect that the α-blocking properties of bretylium might be additive to those of quinidine, resulting in problematic hypotension.

If the post-cardioversion QTC interval is prolonged, then the pre-cardioversion polymorphic ventricular tachyarrhythmia was (by definition) torsades depointes. In this case, lidocaine and bretylium are unlikely to be of value, and other Class I antiarrhythmics (disopyramide, procainamide) are likely to exacerbate the situation. Factors contributing to QTC prolongation (especially hypokalemia, hypomagnesemia, and hypocalcemia) should be sought out and (if possible) aggressively corrected.

Prevention of recurrent torsades may require sustained overdrive pacing or the cautious administration of isoproterenol (30 to 150 ng/kg/min).

Hypotension

Quinidine-induced hypotension that is not due to an arrhythmia is likely to be a consequence of quinidine-related α-blockade and vasorelaxation. Simple repletion of central volume Trendelenburg positioning, saline infusion) may be sufficient therapy; other interventions reported to have been beneficial in this setting are those that increase peripheral vascular resistance, including α-agonist catecholamines (norepinephrine, metaraminol) and the Military Anti-Shock Trousers.

Treatment

To obtain up-to-date information about the treatment of overdose, a good resource is your certified Regional Poison-Control Center. Telephone numbers of certified poison-control centers are listed in the Physicians’ Desk Reference(PDR). In managing overdose, consider the possibilities of multiple-drug overdoses, drug-drug interactions, and unusual drug kinetics in your patient.

Accelerated removal

Adequate studies of orally-administered activated charcoal in human overdoses of quinidine have not been reported, but there are animal data showing significant enhancement of systemic elimination following this intervention, and there is at least one human case report in which the elimination half-life of quinidine in the serum was apparently shortened by repeated gastric lavage.

Activated charcoal should be avoided if an ileus is present; the conventional dose is 1 gram/kg, administered every 2 to 6 hours as a slurry with 8 mL/kg of tap water.

Although renal elimination of quinidine might theoretically be accelerated by maneuvers to acidify the urine, such maneuvers are potentially hazardous and of no demonstrated benefit.

Quinidine is not usually removed from the circulation by dialysis.

Following quinidine overdose, drugs that delay elimination of quinidine (cimetidine, carbonicanhydrase inhibitors, thiazide diuretics) should be withdrawn unless absolutely required.

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