Large electronic databases can often meet the need for a cost-effective and efficient means of conducting surveillance after a new drug is marketed, and to establish baseline data prior to marketing.
Overview of North
American Databases
Large
electronic databases can often meet the need for a cost-effective and efficient
means of conducting surveillance after a new drug is marketed, and to
establish baseline data prior to marketing. Such databases can be used to
assess signals from trials and from spontaneous reports, and, given adequate
power and design, the results of such assessments generally are more credible
than evidence from spon-taneous reports of the same problem (Edwards, Faich and
Tilson, 2005). Large databases are often needed to address acute and serious
regulatory, commercial and public health crises. Post-marketing studies of drug
effects must generally include at least 10 000 exposed persons within a
definable population base.
In
North America, databases able to meet this need are primarily administrative in
origin, generated by the request for payments, or claims, for clinical services
and therapies. Large databases of electronic medical records, like the General
Practice Research Database (GPRD) in the UK (Gelfand, Margolis and Dattani,
2005), do not exist yet in North America. The resulting databases of health
insurance claims are inherently different from medical record databases (Strom,
2005). Health insurance in the United States is typically obtained through
one’s place of employment, and does not always include coverage for
prescrip-tion drugs. The instability of this system is caused by employees’
changing jobs and employers’ chang-ing health plans and coverage for specific
employees and their families. The opportunity for longitudinal analyses is
thereby hindered by the continual enroll-ment and disenrollment of plan
members. However, strategies have been developed for selecting stable
populations within a specific database and for address-ing compliance, such as
examining patterns of refills for chronically used medications. Most of the US
health care programmes described in this chapter are employee-based, but may
offer coverage to Medi-caid and Medicare recipients as well, providing some
representation of the elderly and the economically disadvantaged in its
databases.
Beyond
the employer-based health insurance programmes are the US Medicaid programme,
which provides medical care, including prescription drug coverage, for economically
disadvantaged and disabled persons, and the Medicare programme, which provides
health care to persons aged 65 and older. The latter is now undergoing changes
to include a prescription drug programme. In contrast to the vari-ety of health
care systems for selected eligible subsets of populations in the United States,
Saskatchewan, a province in Canada, provides a publicly funded health system
for all of its residents.
To
meet the needs of drug surveillance and phar-macoepidemiologic studies, claims
data from multiple sources (drug purchases, visits to physicians, hospi-tal
stays, etc.) must be linked on a per patient basis. Depending on the nature of
the study, records from the following sources may need to be included:
inpa-tient and outpatient care, emergency care, mental health care, laboratory
and radiological tests, alter-native therapies and prescribed and
over-the-counter medications. The size of the population covered by the
database must be large enough to permit discov-ery of rare events for the
drug(s) (in surveillance studies); questions such as the stability of the
popu-lation and the completeness of therapies and clini-cal services obtained
solely through the health plan may be considerations in study design. Although
it is generally preferable for the population included in the database to be
representative of the general population from which it is drawn, it may
sometimes be advan-tageous to emphasize the more disadvantaged groups that may
have been absent from pre-marketing test-ing. The drug(s) under investigation
must, of course, be present in the formulary and be prescribed in suffi-cient
quantity to provide adequate power for analyses.
Additional
considerations are that the records are verifiable and are reliable. The
ability to conduct chart review to confirm outcomes is a necessity for most
studies, as diagnoses entered into an electronic database of paid claims may
include interim diagnoses and recurrent or chronic, as opposed to acute,
events. Information on potential confounders, such as smok-ing and alcohol
consumption, and such information as time of menarche and menopause, may only
be available through chart review or, more consistently, through patient
interviews. With appropriate permis-sions and confidentiality safeguards in place,
access to patients is sometimes possible and useful for assessing compliance
with the medication regimen as well as for obtaining information on other
factors that may relate to drug effects. Information on drugs taken
intermit-tently for symptom relief, over-the-counter drugs and drugs not on the
formulary must also be obtained directly from the patient.
The
advantages of a claims database remain, that is, data do not have to be
collected de novo, investigations can
be completed more efficiently and more economically, and data on exposures are
not subject to recall or interviewer bias. Although data on drugs dispensed are
of extremely high quality (West, Strom and Poole, 2005), the quality of disease
data may be less so. With the caveat of the need to confirm outcomes, the
availability of such databases is an important asset for post-marketing
surveillance.
In
the following sections we will discuss the databases associated with four major
US health plans, one Canadian health plan, a unique consortium of health plans
created to meet the needs of the research communities, and a special-purpose
database.
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