Physician Prescribing Behavior and Its Impact on Patient-Level Outcomes

Physicians prescribe more broadly than commonly perceived. Although most physicians have a favorite drug, they are not reluctant to try new therapies.
Published Online: December 20, 2011
Geoffrey F. Joyce, PhD; Mariana P. Carrera, PhD, MA; Dana P. Goldman, PhD; and Neeraj Sood, PhD

Objectives: Concerns over rising drug costs, pharmaceutical advertising, and potential conflicts of interest have focused attention on physician prescribing behavior. We examine how broadly physicians prescribe within the 10 most prevalent therapeutic classes, the factors affecting their choices, and the impact of their prescribing behavior on patient-level outcomes.
 

Study Design: Retrospective study from 2005 to 2007 examining prescribers with at least 5 initial prescriptions within a class from 2005 to 2007. Medical and pharmacy claims are linked to prescriber information from 146 different health plans, reflecting 1975 to 8923 unique providers per drug class.

 

Methods: Primary outcomes are the number of distinct drugs in a class initially prescribed by a physician over 1- and 3-year periods, medication possession ratio, and out-of-pocket costs.

 

Results: In 8 of 10 therapeutic classes, the median physician prescribes at least 3 different drugs and fewer than 1 in 6 physicians prescribe only brand drugs. Physicians prescribing only 1 or 2 drugs in a class are more likely to prescribe the most advertised drug. Physicians who prescribe fewer drugs are less likely to see patients with other comorbid conditions and varied formulary designs. Prescribing fewer drugs is associated with lower rates of medication adherence and higher out-ofpocket costs for drugs, but the effects are small and inconsistent across classes.

 

Conclusions: Physicians prescribe more broadly than commonly perceived. Though narrow prescribers are more likely to prescribe highly advertised drugs, few physicians prescribe these drugs exclusively. Narrow prescribing has modest effects on medication adherence and out-of-pocket costs in some classes.

 

(Am J Manag Care. 2011;17(12):e462-e471)

Physicians prescribe more broadly than commonly perceived. Although most physicians have a “favorite” drug, they are not reluctant to try new therapies. Physicians who prescribe broadly see more patients with varied comorbidities and formulary designs. Prescribing fewer drugs is associated with lower rates of medication adherence and higher out-of-pocket costs, but the effects are small and inconsistent across classes. Broad prescribing may be due to:

 

  •  The increasing number of drugs in a class.

 

  •  Pharmaceutical marketing, particularly direct-to-physician promotions.

 

  •  The role of pharmacy benefit managers and third-party payers.
In 2004, pharmaceutical firms spent more than $57 billion on marketing in the United States, roughly twice their expenditure on research and development.1 Most of this spending targeted physicians through sales representatives (detailing), sampling (provision of drugs at no cost), physician meetings, and advertisements in medical journals.2 For example, industry-sponsored promotional events increased from 120,000 in 1998 to 371,000 events in 2004.3 There has also been a significant increase in the frequency and size of federal and state penalties for illegal promotion of drugs and pricing irregularities.1

These trends have raised the concern that pharmaceutical companies might have undue influence on the prescribing behavior of physicians. In particular, there is concern that a significant percentage of physicians might be prescribing a narrow range of heavily promoted drugs, or might be exclusively prescribing branded drugs to the detriment of patient welfare. However, empirical evidence on the prescribing behavior of physicians and its consequences for patients is limited. Some studies suggest that physicians exhibit narrow prescribing behavior, particularly general practitioners, but much of this evidence is decades old.4-8 More recent work finds that the prescribing patterns of physicians are substantially more concentrated than the aggregate market in each class, and that physicians differ in their preferred drug within a class.9,10

While theory suggests that habitual prescribing can be both clinically suboptimal and economically wasteful, the appropriateness of broad versus narrow prescribing is likely to depend on the composition of the drug class. Narrow prescribing patterns may be optimal when 1 drug is clearly superior to the others, or if all the drugs in the class act in a similar way. For example, prescribing only a generic or low-cost brand in a largely homogeneous class may be beneficial given that lower patient cost-sharing is associated with improved adherence.11-13 In addition, most generics are inherently safer than newer drugs because of their longer track record in clinical practice and known side effects.14,15 Alternatively, some drug classes are characterized by heterogeneous effects, where a specific drug provides therapeutic benefit to some patients and little to others, or has known side effects that are problematic for a subset of patients. If the heterogeneous benefits and side effects of these drugs are known ex-ante, a better informed physician will engage in broader prescribing behavior, taking into account the specific medical characteristics of each patient. Levine-Taub and colleagues9 found that psychiatrists have broader prescribing patterns than general practitioners within the atypical antipsychotic class, but they cannot determine how much of the difference is explained by variation in the case mix of patients seen by psychiatrists versus nonspecialists.9

Beyond the challenge of predicting a drug’s therapeutic value for a new patient, an unrelated factor further complicates the prescribing decision; plan formularies. Most modern drug classes include an array of similar products that compete for essentially the same population of patients, and health plans typically choose a small subset of these products to offer at low cost-sharing rates. In addition, direct-to-consumer advertising has emboldened patients to request specific treatments. 16-18 How these factors have affected physicians’ choice of drug therapies is uncertain.

In this paper, we examined the prescribing patterns of physicians in 10 large drug classes with several similar-acting agents. We measured the number and type (generic or brand) of different drugs prescribed as initial prescriptions by each physician and the factors that affected their choices. We then examined whether broad or narrow prescribing is associated with patient-level outcomes, such as rates of medication adherence, therapeutic switching, and out-of-pocket drug spending. We know of no other study that examines the relationship between how broadly physicians prescribe and patient-level outcomes (eg, adherence, medical care use) that can proxy for clinical measures.

METHODS

Data

We used unique data, matching prescriptions to prescribing physicians. The data included medical and pharmaceutical claims from 29 large employers in the United States from 2003 to 2007. The drug claims included information on the type of drug, drug name, National Drug Code, dosage, days supplied, and place of purchase (retail or mail order). Starting in 2005, all pharmacy claims identify the prescriber by masked Drug Enforcement Administration number; thus, from 2005 to 2007, we could observe prescriptions made by the same physician to different patients in different insurance plans. We did not have any additional information about the prescribers. To be eligible for the sample, a patient had to be at least 18 years of age, and continuously enrolled for at least 1 year before initiating therapy and for at least 6 months afterward.

We used the IMS Advertising Database to measure the degree of drug promotion for each product. The advertising data were reported quarterly and contained expenditures on direct-to-consumer and direct-to-physician advertising for each drug, including medical journal advertisements, promotional visits to physicians, and drug samples.

Measurement

We use a common classification scheme—the 2007 Red Book published by Thomson—to associate each drug with a therapeutic class. Table 1 shows the 10 most common therapeutic classes (in terms of dollars spent) in our sample for 2005. These are cholesterol-reducing drugs, antidepressants, non–histamine-2 receptor antagonist (H2A) stomach drugs, antihistamines, nonsteroidal anti-inflammatory drugs (NSAIDs), opiates, beta-blockers, calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, and antidiabetic drugs, excluding insulin. To further narrow the classes, we focused on statins within the cholesterol-reducing drugs (dropping ezetimibe, fibrates, and others), on selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs) within the antidepressants (keeping bupropion formulations and dropping tricyclic antidepressants), and on proton pump inhibitors (PPIs) within the non-H2A stomach drugs. In the antihistamine class, we dropped promethazine, which is prescribed primarily as an acute treatment and often used as a sedative or antiemetic rather than for allergy treatment. We defined an initial prescription as the absence of any pharmacy claim in the same therapeutic class for at least 12 months.

As most plans assign lower copayments to generic drugs, and often charge the same copayment for all generics, narrow prescribing patterns are most likely to impact average costs in classes where brand drugs are dominant. For this reason, some analyses focused on the 5 drug classes in which more than 50% of initial prescriptions are for brand drugs: statins, SSRIs/SNRIs, PPIs, antihistamines, and calcium channel blockers. We called these the “brand-dominated” classes.

In 3 of these classes, 1 major drug became available as a generic during the study period: simvastatin (statin, starting June 2006), sertraline (SSRI, June 2006), and fexofenadine (antihistamine, September 2005). In the calcium channel blocker class, 2 generics entered the market toward the end of our study period (2007); amlodipine in March and amlodipine/ benazepril in May. In measuring the number of drugs prescribed, we treated brand and generic formulations of a multisource product as different drugs; however, the results are not sensitive to this choice.

We restricted the sample to physicians with at least 5 initial prescriptions within a class from 2005 to 2007. We focused on initial prescriptions because refills may reflect the prescribing decisions of other providers. This yielded a sample of 74,163 initial statin prescriptions, prescribed by 8923 unique providers. The corresponding prescription/provider counts for the other brand-dominant classes were PPIs (52,978/6621), SSRI/SNRI (46,040/5866), antihistamines (39,644/4788), and calcium channel blockers (13,633/1975). We categorized providers within each class by the number of distinct drugs prescribed as initial prescriptions over the sample period (2005-2007). For example, a doctor with 2 initial prescriptions of escitalopram, 3 initial prescriptions of sertraline, and 1 initial prescription of duloxetine is categorized as prescribing 3 drugs in the SSRI/SNRI class.

Given that new drugs may have entered the market and additional clinical evidence may have emerged over the 3-year study period, we also categorized physicians based on the number of distinct drugs prescribed each year. This reduced our sample substantially, as two-thirds to three-fourths of physicians (depending on the class) in the 3-year sample did not have 5 initial prescriptions within a calendar year. To facilitate comparison with other studies of prescribing concentration, we also calculated the share of prescriptions for each physician’s “favorite” drug.

Statistical Analyses

We examined the use of the top-selling and most heavily promoted drugs in the class, as well as rates of generic drugs, by prescriber type. We also calculated the share of a physician’s observed prescriptions that are in the relevant therapeutic category (eg, cardiovascular drugs for statin prescriptions) as a proxy for their degree of specialization.

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