World Health Information Science Consultants, LLC
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Recent Publications
Schneeweiss S, Seeger JD, Landon J, Walker AM. Aprotinin during coronary-artery bypass grafting and risk of death. N Engl J Med 2008;358:771­83

We worked with inpatient data for one-sixth of US hospitalizations (the Premier Perspective Database), to examine the differences in mortality between patients who received aprotinin and aminocaproic acid during coronary artery bypass surgery.  Techniques included mutivariable regression, propensity matching and instrumental variables analysis, which all pointed to the same result.

Schneeweiss S, Walker AM, Seeger JD.  Effect of aprotinin on renal dysfunction. Lancet. 2008 Jul 5;372(9632):26 (letter)

We pointed out an analytic fallacy first articulated by Rothman 30 years ago: drawing false reassurance from nonsignificant p-values.  We synthesized findings across strata using meta-analysis to find and quantify effects that had been previously unnoticed.

Walker AM, Koro C, Landon J. Coronary heart disease outcomes in patients receiving antidiabetic agents in the PharMetrics database. Pharmacoepidemiol Drug Saf. 2008 Aug;17(8):760-8

We conducted a retrospective cohort study of myocardial infarction and coronary revascularization in the PharMetrics database. We performed head-to-head comparisons between rosiglitazone, pioglitazone, metformin and sulfonyl ureas using propensity-score-strati?ed Cox proportional hazards models, examining risks both on-treatment and during total follow-up before regimen switches.

Walker AM, Bennett D. Epidemiology and outcomes in patients with atrial fibrillation in the USA.  Heart Rhythm J 2008 Oct;5(10):1365-1372

Using outpatient laboratory data in conjunction with health insurance claims, we examined treatment and complications in over 100,000 patients with atrial fibrillation or flutter.  INR levels below 2.0 dramatically raised the incidence of stroke and arterial thromboembolism compared with INRs between 2.0 and 3.0.  INR levels above 3.0 doubled the incidence of intracranial hemorrhage.

Patterson MK, Castellsague J, Walker AM. Hospitalization for peptic ulcer and bleeding in users of selective COX-2 inhibitors and nonselective NSAIDs with special reference to celecoxib. Pharmacoepidemiol Drug Saf. 2008 Aug 18;17(10):982-988

Patients receiving COX-2 inhibitors in general and celecoxib in particular have lower rates of hospitalization for peptic ulcer bleeding and perforation than do patients receiving nonselective NSAIDs.  Chart review demonstrated that a hospital discharge diagnosis coded as PUBP had better than 90% predictive value for the confirmed clinical condition.

Velentgas P, Bohn RL, Brown JS, Chan KA, Gladowski P, Holick CN, Kramer JM, Nakasato C, Spettell CM, Walker AM, Zhang F, Platt R.  A distributed research network model for post-marketing safety studies: the Meningococcal Vaccine Study. Pharmacoepidemiol Drug Saf. 2008 Oct 27;17(12):1226-1234

One of the leading models for the FDA Sentinel Initiative is a distributed research network, in which individual data holders maintain control over their resepective databases.   Each data holder agrees to develoop research files in common format, and the operations center circulates analysis programs that operate locally, with return of aggregate results.  This article discusses the architecture, governance and use of distributed data networks.

Loughlin J, Seeger J, Eng PM, Foegh M, Clifford CR, Cutone J, Walker AM. Risk of hyperkalemia in women taking ethinylestradiol/drospirenone and other oral contraceptives.  Contraception 2008 Nov;78(5):377-383

Drospirenone, the progestational component of some newer oral contraceptives, is chemically related to spironolactone, a potassium-sparing diuretic.  Though no disturbance of potassium handling had been during drug development, the analogy raised the theoretical possibly of adverse effects related to potassium levels in drospirenone recipients.  Review of the health experience of 22,000 users of a drospirenone-containing oral contraceptive and a two-fold larger comparison group showed no cause for concern.

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