Generic substitution of antihypertensive drugs: does it affect adherence?
BACKGROUND
Generic substitution is an important opportunity to reduce the costs of pharmaceutical care. However, pharmacists and physicians often find that patients and brand-name manufacturers have doubt about the equivalence of the substituted drug. This may be reflected by decreased adherence to therapy.


OBJECTIVE
To assess the association between generic substitution and nonadherence to antihypertensive drugs.


METHODS
We conducted a matched cohort study between January 1, 1999, and December 31, 2002. Data were obtained from PHARMO, a record linkage system containing drug-dispensing records from community pharmacies and linked hospital discharge records of approximately 950,000 people in The Netherlands. Residents of 30 medium-sized cities who initiated antihypertensive drug therapy were potential subjects. Refill adherence with antihypertensive drugs after substitution was determined; those with refill adherence below 80% were considered nonadherent.


RESULTS
Four hundred sixty-three patients with a substitution in therapy and 565 controls, matched on age, gender, therapy start date, duration of use, and generic product code, were identified. Of the patients who switched from brand-name to generic formulations ("substituted"), 13.6% were nonadherent, and of the non-substituted patients (those who did not switch to generic), 18.7% were nonadherent (OR 0.68; 95% CI 0.48 to 0.96). The association was absent in males. None of the patients discontinued the medication. No differences in hospitalizations for cardiovascular disease in the 6 months after the substitution were observed.


CONCLUSIONS
Generic substitution of antihypertensive drugs does not lead to lower adherence or more discontinuation and cardiovascular disease-related hospitalizations compared with brand-name therapy. When a less-expensive antihypertensive generic equivalent becomes available, generic substitution should be considered to achieve economic benefits.
Van Wijk
Boris L G
BL
Department of Pharmacoepidemiology & Pharmacotherapy, Faculty of Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.
Klungel
Olaf H
OH
Heerdink
Eibert R
ER
de Boer
Anthonius
A
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000959:Antihypertensive Agents / Q000191:economics / Q000627:therapeutic use*; D003627:Data Interpretation, Statistical; D016568:Drugs, Generic / Q000191:economics / Q000627:therapeutic use*; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009426:Netherlands; D010349:Patient Compliance / Q000706:statistics & numerical data; D010358:Patient Participation / Q000706:statistics & numerical data; D010593:Pharmaceutical Services / Q000191:economics / Q000706:statistics & numerical data; D012189:Retrospective Studies; D012737:Sex Factors; D013810:Therapeutic Equivalency; D013997:Time Factors
D000959:Antihypertensive Agents; D016568:Drugs, Generic