A Simple Index for Determining the Optimal Dosages of Beta-Methyldigoxin for Patients who Have Variable Degrees of Renal Function when Verapamil is Administered

• Published in: Iryo Yakugaku (Japanese Journal of Pharmaceutical Health Care and Sciences) Vol. 29; no. 2; pp. 184 - 188
• Main Authors: Machida, Seiji, Masuda, Kazuhisa
• Format: Journal Article
• Language: English; Japanese
• Published: Japanese Society of Pharmaceutical Health Care and Sciences 2003
• Subjects: beta-methyldigoxin; creatinine clearance; drug-interaction; verapamil
• ISSN: 1346-342X; 1882-1499
• DOI: 10.5649/jjphcs.29.184

Digoxin is often administered as a medication for congestive heart failure and heart rate control, and its therapeutic range has been reported to be 0.5-2. Ong/mL. However, compared with other medications, the margin between digoxin' s therapeutic range and toxic range is very narrow and it is necessary to monitor this drug therapy very closely. In addition, patients with an impaired renal dysfunction have a predisposition for developing digitalis toxicity. In order to avoid digitalis toxicity in such cases, we previously reported a simple index for the adequate administration dosage of beta-methyldigoxin according to varying degrees of renal function. However, our previous report was a simple index for the optimal dosages of beta-methyldigoxin when verapamil is not administered. In clinical cases, digoxin and verapamil are often co-administered for heart rate control, and we have observed the serum trough level of beta-methyldigoxin to be elevated due to drug-interaction. In order to investigate the influence of verapamil on the serum trough level of beta-methyldigoxin, we compared two groups of hospitalized patients : one group where verapamil was not administered (n=134) and another group where verapamil was administered (n=32). The results showed a correlation between creatinine clearance and clearance of beta-methyldigoxin in the two groups (the group not receiving verapamil : R2=0.51, p< 0.01 ; the group receiving verapamil : R2=0.46, p< 0.01). In addition, using a multiple regression analysis, verapamil was found to influence the clearance of betametyldigoxin. By this correlation, we build upon our previous findings and generated a simple index for the adequate administration dosage of beta-methyldigoxin based on variable degrees of renal function and the serum trough level of beta-methyldigoxin. These results indicate that by using our simple index, we can easily estimate the optimal dosages of betamethyldigoxin for patients who have variable degrees of renal function when verapamil is administered.