Effect of Antihypertensive Drugs Retention Using Multilevel Cox Model

  The Cox model is one of the methods used in survival data; however, the use of hierarchical data, such as the data of this study, violates the assumption of independence, the the Cox model cannot be used assuming independence of observations. One of the important methods for analyzing survival hierarchy data is the use of the multilevel Cox model. In this method, in addition to modeling the response variable, regression coefficients are also modeled and the measurement error resulting from the lack of data independence is reduced. The present study used a multilevel Cox model to investigate the effect of the retention of antihypertensive drugs in people with hypertension.

This longitudinal survival study was conducted in 346 workers with hypertension in Mobarakeh Steel Company in Isfahan. During the years 1390-1394, when the staff attended the health center in the factory, they were treated with six drugs, including captopril, losartan, atenolol, propranolol, amlodipine, and hydrochlorothiazide. In order to examine the relationship of the retention of drugs with job experience, body mass index, and drug history, a two-level Cox model was used as h_ij (t)=h_0 (t)exp⁡(α_g+x_ij β_j), where i and j is the first and second level units, respectively.

During five years, the findings of model fitting showed the effect of body mass index (P = 0.019), atenolol (P=0.046), and amlodipine (P=0.021) in a single form, and the effect of losartan-amlodipine (P=0.042) and atenolol-hydrochlorothiazide (P = 0.003) in a combination form were significant.

Based on the study results, the most effective drugs for hypertension control are amlodipine monotherapy, amlodipine-losartan combination therapy, and atenolol monotherapy, respectively.