Evaluation of gemtuzumab ozogamycin associated sinusoidal obstructive syndrome: Findings from an academic pharmacovigilance program review and a pharmaceutical sponsored registry.

Background: In 2000, the Food and Drug Administration (FDA) approved gemtuzumab ozogamycin for monotherapy for older patients with relapsed AML. A 0.9% rate of hepatic sinusoidal obstructive syndrome (SOS) was noted in licensing trials. In 2001, FDA received reports of 14 GO-associated SOS cases from MD Anderson Cancer Center. A State of South Carolina/National Cancer Institute funded pharmacovigilance program and a manufacturer sponsored registry independently evaluated this concern.
Methods: The manufacturer's registry and the academic program focused on risk factors and incidence of GO-associated SOS in routine clinical practice and clinical trial settings, respectively. Comparisons were made of findings and dissemination efforts from the two studies.
Results: Retrospective analysis of clinical trials by the academic initiative identified 99 cases of SOS among 221 GO-treated stem cell patients and 649 patients who did not undergo HSCTs. SOS rates were 3% when GO was administered at doses ≤6 mg/m(2) as monotherapy or with non-hepatotoxic agents; 28% when administered with 6-thioguanine, a hepatotoxic agent; 15% when administered as monotherapy at doses at a dose of 9 mg/m(2), and between 15% and 40% if a stem cell transplant (SCT) was performed within 3 months of GO administration. Death from SOS occurred in 33% of the cases. The manufacturer's registry prospectively evaluated 482 GO-treated patients who received a mean dose of 7.8 mg/m(2). Overall, 41% received concomitant chemotherapy, 18% had undergone prior SCT, 9.1% developed SOS, and death from SOS occurred in 60% of the SOS cases. Findings from each initiative were disseminated at national conferences and in peer-reviewed manuscripts beginning in 2003.
Conclusion: Retrospective review of clinical trials, case series, and FDA reports and prospective registries can provide important information on safety signals initially identified in licensing trials.
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