Nitrendipine/digoxin interaction.

The effect of nitrendipine in two different dosages on digoxin plasma levels, urinary recovery, and systolic time intervals was investigated in eight healthy volunteers. Following an adequate loading dose of the glycoside, 0.25 mg digoxin twice daily was given alone for 2 weeks orally. After that, 0.25 mg digoxin twice daily was administered for two 1-week periods combined with nitrendipine, 10 mg or 20 mg once daily. The study was completed with a second digoxin monotherapy phase lasting seven days. Nitrendipine, 20 mg daily, led to a significant increase of the digoxin plasma concentration and of its area under the plasma concentration-time curve (AUC0-12) compared with digoxin monotherapy. Thus, AUC0-12 was 9.7 +/- 0.75 ng ml-1 h (X +/- SEM) when digoxin was given alone and was 11.2 +/- 0.92 ng ml-1 h under coadministration of the calcium antagonist (p less than 0.05). Nitrendipine in the dosage of 10 mg once daily caused a small, insignificant tendency to elevate digoxin plasma levels. In conclusion, nitrendipine, 20 mg daily, causes a significant increase of digoxin plasma concentration and of its AUC, which in certain patients might be of clinical relevance.