The Impact of Patent Expiration on Overall Utilization of Azithromycin Open Access

Hong, Dongzhe (2017)

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Antibiotics have been widely used to treat patients with bacterial infections. Overuse of antibiotics is one of the most pressing public health problems worldwide because of its association with the increase in antibiotic resistance. Azithromycin is a widely used antibiotic and commonly prescribed for Upper Respiratory Tract Infections (URIs) and Urinary Tract Infections (UTIs). In 2005, azithromycin went off patent. The average price of both branded and generic azithromycin decreased, and the copayment of generic azithromycin was much lower than branded azithromycin. This study examined the impact of patent expiration on overall utilization of both branded and generic azithromycin.


The National Ambulatory Medical Care Survey (NAMCS) and National Hospital Ambulatory Medical Care Survey (NHAMCS) from 2002 - 2009 were used as the data source. The sample included patient visits with URIs and/or UTIs. Five multivariate logistic regression models determined the association between patent expiration and the probability that azithromycin was prescribed in a particular visit among all patients with URIs and/or UTIs, including privately insured patients and patients covered by Medicaid.


The likelihood of receiving azithromycin for URIs and/or UTIs increased from 10.8% to 14.0% after patent expiration. The increase in the likelihood of patients receiving azithromycin was larger among privately-insured patients than patients covered by Medicaid, 6.3% and 2.9%, respectively. There was a statistically significant 0.03 percentage point increase, or a 27.8% increase, in azithromycin utilization after patent expiration.


There was an increase in azithromycin utilization for patients with URIs and/or UTIs after patent expiration. The larger increase among privately insured patients is expected since private insurance programs try harder than Medicaid to reduce pharmaceutical use. This study also shows that generic entry leads to increased drug use. Consumers bear negative consumption externalities since generic entry may increase antibiotic resistance and harm the whole society. One approach for reducing antibiotic resistance is to grant longer patents to antibiotics, thereby delaying generic entry and increased use. Other price-based interventions, including changes in demand side cost sharing by patients, and the use of physician bonuses for antibiotic rational use, may also reduce antibiotic use in outpatient settings.

Table of Contents

Azithromycin 3
Azithromycin Utilization and Resistance 4
Drug Prices 5
Demand for Antibiotics 6
Antibiotic Regulations 7
Patent Expiration and Utilization 8
Conceptual Model 9
Study Sample Identification 10
Focal Relationship & Mediator 13
Covariates 15
Variables 16
Research Question 21
Testable Hypothesis 21
Research Design 21
Analytic strategy 21
Descriptive Statistics 24
Regression Results 29
Conclusion 34
Limitations 35
Recommendations for Future Studies 36
Policy Implications 37

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