The appearance of
adverse drug reactions may depend on the category of used drugs as well as on the coexistence of a pathological stage. Clinically important are: interactions of digitalis
glycoside drugs leading to the occurrence or intensification of toxic symptoms characteristic for those drugs; interactions of
antiarrhythmic drugs which may cause proarrhythmic effects and
hypotension, and also interactions of
nitrates resulting in lowering of the blood pressure.
Quinidine, verapamil,
nitrendipine, amiodaron,
propafenone,
captopril,
spironolactone decrease renal clearance of
digoxin, and amilorid/triamteren lower the extrarenal clearance of this drug. Thus the outcome of those concommitant
therapies is the increase of
digoxin serum concentration and appearance of toxic symptoms. Clinically dangerous, in the course of the antiarrhythmic
therapy, is the increased risk of the
arrhythmia appearance when two or more
antiarrhythmic drugs are applied concomitantly.
Antiarrhythmic drugs class IA (
quinidine,
disopyramide), class III (
sotalol,
amiodarone), class IV (
calcium channel blockers) used at the same time with
potassium depleters
diuretics or beta-blocking agents result in the inhibition of repolarization and the increased duration of activation potential with the risk of developing
arrhythmia of the
torsade de pointes types.
Nitrates interactions are mainly of the pharmacodynamic character. Most common
adverse drug reaction, observed during the concomitant
nitrates and another circulatory
drug therapy, is excessive lowering of the blood pressure. These may lead to the decrease in the therapeutic efficacy of these combinations. Interactions of circulatory drugs are numerous, sometimes difficult to predict and they may lead to the intensification of the
adverse drug reaction and lowering of their therapeutic efficacy.