A Phase 1b, Randomized, Double-blind (Sponsor Open), Placebo Controlled Study To Evaluate The Safety, Tolerability, Pharmacokinetics, And Pharmacodynamics Of Pf 04447943, Co-administered With And Without Hydroxyurea, In Subjects With Stable Sickle Cell Disease

Number of Participants With Potentially Clinically Important (PCI) Change From Baseline in Vital Signs

Time Frame: Baseline up to 30 days post last dose on Day 29

Number of participants with changes from baseline in vital signs meeting the following criteria is presented: (1) maximum increase from baseline in supine systolic blood pressure (SBP) \>=30 millimeters of mercury (mmHg); (2) maximum increase from baseline in supine diastolic blood pressure (DBP) \>=20 mmHg; (3) maximum decrease from baseline in supine SBP \>=30 mmHg; and (4) maximum decrease from baseline in supine DBP \>=20 mmHg.

Number of Participants With Potentially Clinically Important (PCI) Change From Baseline in Neurologic Function

Time Frame: Baseline up to Day 29

Clinical assessment of neurologic functions included cranial nerve function, coordination, deep tendon reflexes, muscle strength, and reflexes (left and right ankles). Clinical importance of neurologic function changes was determined by the investigator.

Number of Participants With Potentially Clinically Important (PCI) Change in Physical Examination Findings

Time Frame: Baseline up to 30 days post last dose on Day 29

Physical examination included head, ears, eyes, nose, mouth, skin, heart and lung examinations, lymph nodes, gastrointestinal, musculoskeletal, and neurological systems. Clinical importance of physical examination changes was determined by the investigator.

Number of Participants With Clinically Significant Treatment-Emergent Electrocardiogram (ECG) Findings

Time Frame: Baseline up to 30 days post last dose on Day 29

Maximum absolute values and increases from baseline were summarized for PR interval (time from the beginning of P wave to the start of QRS complex, corresponding to the end of atrial depolarization and onset of ventricular depolarization), QRS complex (time from Q wave to the end of S wave, corresponding to ventricle depolarization), and QTcF interval (time from the beginning of Q wave to the end of T wave corresponding to electrical systole corrected for heart rate using Fridericia's formula). Number of participants with ECG findings meeting the following criteria is presented: (1) PR interval \>=300 msec; (2) QRS complex \>=200 msec; (3) QTcF interval: 450 to \<480 msec; (4) QTcF interval: 480 to \<500 msec; (5) QTcF interval \>=500 msec; (6) PR interval percent increase from baseline \>=25/50 percent; (7) QRS complex percent increase from baseline \>=25/50 percent; (8) QTcF interval increase from baseline: 30 to \<60 msec; (9) QTcF interval increase from baseline \>=60 msec.

Number of Participants With Potentially Clinically Important (PCI) Change From Baseline in Symptoms of Sickle Cell Disease

Time Frame: Baseline up to 30 days post last dose on Day 29

The following symptoms were assessed: anemia; fatigue; chronic pain; acute pain; infections; fever; swelling hands; swelling feet; abdominal swelling; pale skin; pale nail beds; yellow tint to skin; whites of eyes turned yellow; stroke. Number of participants with changes from baseline deemed potentially clinically important by the investigator is presented.

Number of Participants With Treatment-Emergent Adverse Events (TEAEs) and Serious Adverse Events (SAEs)

Time Frame: Day 1 to 30 days post last dose on Day 29

An adverse event (AE) was any untoward medical occurrence in a clinical investigation participant administered a product or medical device, regardless of its causal relationship with study treatment. Serious adverse event (SAE) was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; was life-threatening (immediate risk of death); persistent or significant disability/incapacity; congenital anomaly. Treatment-emergent AEs are events between first dose of study drug and up to follow-up visit (30 days post last dose on Day 29) that were absent before treatment or that worsened after treatment. AEs included both serious and non-serious AEs.

Number of Participants With Laboratory Test Abnormalities

Time Frame: Baseline up to 30 days post last dose on Day 29

The laboratory test included: hematology (hemoglobin, hematocrit, red blood cell count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, platelet count, white blood cell count, absolute total neutrophils, eosinophils, monocytes, basophils, and lymphocytes), chemistry (blood urea nitrogen/urea, serum creatinine, fasting glucose, calcium, sodium, potassium, chloride, total carbon dioxide, aspartate aminotransferase, alanine aminotransferase, total bilirubin, alkaline phosphatase, uric acid, albumin, total protein, and high sensitivity C-reactive protein), urinalysis (pH, qualitative glucose, qualitative protein, qualitative blood, ketones, nitrites, leukocyte esterase, urobilinogen, urine bilirubin, and microscopy), and other tests (follicle stimulating hormone and serum human chorionic gonadotropin, urine drug screening). Abnormality was determined by the investigator.