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Updated: Jan 31, 2026

Continuous Manual Exchange Transfusion for Patients with Sickle Cell Disease: An Efficient Method to Avoid Iron Overload
Published on: March 14, 2017
PF-04447943, a Phosphodiesterase 9A Inhibitor, in Stable Sickle Cell Disease Patients: A Phase Ib Randomized,
Robert J Charnigo1, David Beidler2, Denis Rybin2
1Pfizer, Inc., Collegeville, Pennsylvania, USA.
Abstract:
This phase Ib study randomized patients with stable sickle cell disease (SCD) aged 18-65 years to twice-daily PF-04447943 (a phosphodiesterase 9A inhibitor; 5 or 25 mg) or placebo, with/without hydroxyurea coadministration, for up to 29 days. Blood samples were collected at baseline and various posttreatment time points for assessments of PF-04447943 pharmacokinetics (PKs)/pharmacodynamics (PDs). Change from baseline in potential SCD-related biomarkers was evaluated. Of 30 patients, 15 received hydroxyurea and 28 completed the study. PF-04447943, with/without hydroxyurea, was generally well tolerated, with no treatment-related serious adverse events. Plasma PF-04447943 exposure was dose proportional. Twice-daily PF-04447943 25 mg significantly reduced the number and size of circulating monocyte-platelet and neutrophil-platelet aggregates and levels of circulating soluble E-selectin at day 29 vs. baseline (adjusted P < 0.15). PF-04447943 demonstrated PK/PD effects suggestive of inhibiting pathways that may contribute to vaso-occlusion. This study also provides guidance regarding biomarkers for future SCD studies.
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