Drug-induced torsades de pointes: role of early afterdepolarizations and dispersion of repolarization

Article Abstract:

The action potential is a wave that reflects the change in electrical potential of a nerve or muscle when stimulated. It consists of various phases, which represent different states of membrane polarization, or differences in ion charges between the inside and outside of the membrane. Depolarization is a decrease in the differences in ion charges across the membranes, whereas repolarization is the re-establishment of ion charge differences between the inside and outside of the membrane. These phases of the action potential may contribute to the development of torsades de pointes, which are abnormalities on the electrocardiogram (ECG), a record of the heart's electrical activity. Torsades de pointes indicate the occurrence of ventricular tachyarrhythmias, or abnormally rapid heart rates arising in the heart ventricles. A case is described of a 76-year-old man who developed torsades de pointes after treatment with the antiarrhythmic agent procainamide. The mechanisms leading to the development of torsades de pointes were assessed by examining the electrical activity of the heart ventricles. The findings show that afterdepolarization and repolarization, which are phases of the action potential, may be involved in the development of ventricular tachyarrhythmias, as indicated by torsades de pointes. Knowledge of the mechanisms underlying torsades de pointes may contribute to the development of methods for treating these arrhythmias. (Consumer Summary produced by Reliance Medical Information, Inc.)

Analysis, Electrocardiogram, Electrocardiography, Heart conduction system, Ventricular tachycardia, Anti-arrhythmia drugs, Antiarrhythmia agents, Torsade de pointes

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Pathologic sleepiness induced by caffeine

Article Abstract:

Although caffeine is generally thought to be a stimulant that interferes with normal sleep patterns, six patients were observed in a sleep disorder clinic in whom caffeine consumption induced excessive daytime sleepiness. This condition of sleepiness disappeared after the patients eliminated caffeine from their diets. Although they do not disagree with the view that caffeine is a stimulant, the authors conclude that individuals' reactions to caffeine may vary widely and acknowledge that the patients studied were atypical. One explanation for the atypical response is the long-lasting effects of caffeine (12 to 20 hours). The possibility is raised that the daytime sleepiness observed in the six patients studied may be attributable to caffeine consumed during the previous day, which interfered with sleep the previous night. Another explanation may be that these patients experienced a chronic state of caffeine withdrawal, which produces fatigue and sleepiness. Large morning doses of caffeine, coupled with the long-term effects of caffeine consumption, could produce a cycle of drug withdrawal and tolerance.

Health aspects, Abnormalities, Physiological aspects, Sleep, Sleep disorders, Drug withdrawal symptoms, Substance withdrawal syndrome, Caffeine habit

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Pentamidine-induced severe hyperkalemia

Article Abstract:

Pentamidine isethionate is an antiprotozoal drug used to treat pneumocystis carinii, a common lung complication in patients with acquired immunodeficiency syndrome (AIDS). Some reports indicate that pentamidine can cause an abnormal increase in potassium, or hyperkalemia. In most instances this hyperkalemia is not life-threatening. A 38-year-old black homosexual with a history of intravenous drug abuse, who was presumed to have pneumocystis carinii, was given pentamidine (220 mg per day). Although this treatment improved breathing difficulties, reduced fever and night sweats, the patient's kidney functioning deteriorated and heart problems developed. A increase in his blood potassium level was found with no other possible cause other than the use of pentamidine. The patient's potassium level remained within normal limits after pentamidine was discontinued. Blood tests which measure kidney functioning before, during and after pentamidine treatment are recommended. (Consumer Summary produced by Reliance Medical Information, Inc.)

Drug therapy, Pneumocystis carinii, Hyperkalemia, Pentamidine isethionate, Pentamidine

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