Quinidine enhances digitalis toxicity at therapeutic serum digoxin levels.

OBJECTIVE: To determine the effect of the digoxin-quinidine interaction on rate of in-hospital digitalis toxicity. METHODS: This was a prospective observational study over 9 months, set in two general medical wards. We studied consecutive patients (n = 141) who were receiving digoxin. Measurements included digitalis toxicity, defined by ECG criteria and resolution after stopping digoxin; all additional medications (including antiarrhythmics) continued. The observer was "blinded" to serum digoxin level and to concomitant drugs. RESULTS: Digitalis toxicity rates were as follows: digoxin alone, 4.9% (5 of 101 patients); with amiodarone or verapamil, 5.0% (1 of 20 patients); with quinidine, 50% (10 of 20 patients) (p < 0.01). No toxicity was seen at digoxin levels < 1.0 ng/ml. Toxicity at 1.0 to 2.0 ng/ml was as follows: digoxin alone, 1 of 41 patients; with quinidine, 4 of 15 patients (p = 0.014). Toxicity was similar at levels > 2.0 ng/ml: 4 of 8 patients and 7 of 11 patients, respectively. Independent relative risks and 95% confidence intervals (CI) of digitalis toxicity were as follows: serum digoxin, 9.1 (95% CI, 2.9 to 13.0); concurrent quinidine, 24.3 (95% CI, 3.4 to 124). There was a significant (p < 0.01) interaction between concurrent quinidine, serum digoxin of 1.0 to 2.0 ng/ml, and digitalis toxicity. CONCLUSION: The digoxin-quinidine interaction significantly increases digitalis toxicity, even in the therapeutic range of serum digoxin levels.

[Lead poisoning in two families from a car battery workshop].

Lead poisoning resulting from exposure to lead in a domestic car battery workshop is reported in 10 children in 2 families. 2 girls, aged 2 10/12 and 1 8/12 years, respectively, from 1 of the families were hospitalized for investigation of nausea, vomiting, progressive muscular weakness and peripheral neuropathy. Serum lead levels were 52 and 49 mcg/dl, respectively. Subsequent screening of all members of this family, as well as those of the other family who lived in the same house, revealed abnormally elevated levels of serum lead in all the members of both families. The 2 girls were treated with chelating agents and improved clinically and their serum lead levels decreased to 29 and 34 mcg/dl, respectively. The domestic workshop was closed and the 2 families moved to another neighborhood. These cases illustrate the need to screen all family members and contacts of patients with lead poisoning, as well as the hazards of the uncontrolled use of lead in domestic workshops.