Patterns of compliance with once versus twice daily antihypertensive drug therapy in primary care: a randomized clinical trial using electronic monitoring.
OBJECTIVE
To evaluate patterns of compliance with once versus twice daily administration of antihypertensive therapy (primary-outcome measure) and relevance of partial compliance for blood pressure control (secondary outcome measure).


METHODS
Multicentre, nonblinded, parallel group randomized design.


METHODS
Nonacademic primary care practices across Canada.


METHODS
Patients with mild essential hypertension (diastolic blood pressure 95 to 110 mmHg) of either sex (40% women), age 18 to 80 years (average 55 years). One hundred and ninety-eight patients were randomized to active treatment; 14 patients discontinued the study because of side effects.


METHODS
After a four-week placebo run-in period, patients were randomized to amlodipine 5 mg once-a-day or diltiazem slow release formulation (SR) 90 mg twice daily. Doses were increased to 10 mg and 180 mg to achieve sitting diastolic blood pressure of 90 mmHg or less.


METHODS
During 20 weeks on active treatment, compliance was assessed by pill counts and medication event monitoring system (MEMS), assessing percentage of prescribed doses taken, percentage days correct doses taken, percentage prescribed doses taken on time and blood pressure control as determined by office blood pressure measurement.


RESULTS
The percentage prescribed doses taken (by either pill count of MEMS) showed a high degree of compliance, similar for the two treatments. However, other parameters of compliance were significantly better with once versus twice daily therapy. Partial compliance (less than 80% by pill count) led to less blood pressure control with the short acting diltiazem, but did not affect blood pressure control for the long acting amlodipine. Side effects profiles did not differ between the two treatments.


CONCLUSIONS
Within the constraints of a clinical trial, hypertensive patients in primary care show a high degree of overall compliance with once or twice daily pill-taking, but patterns of pill-taking are more erratic with twice versus once daily medication, particularly in men. The results suggest that the negative consequences of partial compliance for blood pressure control can be offset by choosing agents with a duration of action well beyond the dosing interval.
Leenen
F H
FH
Hypertension Unit H360, University of Ottawa Heart Institute, Ontario. fleenen@ohi-net.heartinst.on.ca
Wilson
T W
TW
Bolli
P
P
Larochelle
P
P
Myers
M
M
Handa
S P
SP
Boileau
G
G
Tanner
J
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017311:Amlodipine / Q000008:administration & dosage*; D000959:Antihypertensive Agents / Q000627:therapeutic use; D002170:Canada; D004110:Diltiazem / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006973:Hypertension / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D010349:Patient Compliance; D011320:Primary Health Care
D000959:Antihypertensive Agents; D017311:Amlodipine; D004110:Diltiazem