POTENTIALLY SERIOUS DRUG-INTERACTIONS SECONDARY TO HIGH-DOSE DILTIAZEM USED IN THE TREATMENT OF PULMONARY-HYPERTENSION

Two patients had potentially serious drug interactions (phenytoin, dig oxin) that were probably attributable to changes in pharmacokinetics a nd pharmacodynamics caused by high-dose calcium channel blocker therap y (diltiazem) in the treatment of pulmonary hypertension. Even in the approved normal dosages for the treatment of angina and hypertension, calcium channel blockers are known to cause significant changes in the metabolism of other drugs. Currently, no data exist on the effects of the very high dosages of these drugs, administered to patients with p ulmonary hypertension, on the metabolism and clearance of other agents , although, based on our experience and literature reports, recommenda tions for monitoring therapy can be made.