This Phase 1, open-label, single-sequence, non-randomized, multiple-dose, crossover pharmacokinetic study is a single site study in the United States and will be conducted to assess the effect of a CYP1A2 inducer (omeprazole 40 mg once daily [QD]) on the pharmacokinetics of anagrelide (1 mg) when administered concurrently in healthy participants.

Inclusion Criteria:

• Participants who has given, personally signed, and dated informed consent to participate in the study, in accordance with the International Conference on Harmonization Good Clinical Practice Guideline E6 (1996) and applicable regulations, before completing any study-related procedures.
• Age 18-45 years inclusive at the time of consent. The date of signing informed consent is defined as the beginning of the Screening Period. This inclusion criterion will be assessed only at the Screening Visit.
• Male, or non-pregnant, non-lactating female who agrees to comply with any applicable contraceptive requirements of the protocol or females of non-childbearing potential. A female of non-childbearing potential (defined as a female who is post-menopausal [amenorrhea for at least 12 consecutive months], has had a hysterectomy, bilateral tubal ligation, bilateral oophorectomy or bilateral salpingectomy.
• Satisfactory medical assessment with no clinically significant or relevant abnormal findings as determined by medical/surgical history, physical examination, vital signs, 12-lead electrocardiogram, and clinical laboratory evaluation (hematology, biochemistry, thyroid function, and urinalysis) that are likely to interfere with the participant's participation or ability to complete the study as assessed by the investigator.
• An understanding, ability, and willingness to fully comply with study procedures and restrictions.
• Body mass index (BMI) between 18.5 and 30.0 kilograms per square meter (kg/m^2) inclusive; assessed only at the screening visit.
• Able to swallow (multiple capsules or tablets at 1 time or consecutively at 1 time) all investigational product.
• Healthy as determined by the investigator on the basis of screening evaluations.

Exclusion Criteria:

• Current or recurrent disease or conditions (example: cardiovascular, renal, liver, gastrointestinal, malignancy or other conditions) that could affect the absorption, action, or disposition of either omeprazole or anagrelide or its metabolites, or could affect clinical assessments or clinical laboratory evaluations.

• Current or relevant history of physical or psychiatric illness, any medical disorder that may require treatment or make the participant unlikely to fully comply with the requirements of the study or complete the study, or any condition that presents undue risk from the investigational product or study procedures.

• Significant illness, as judged by the investigator, within the 2 weeks of administration of the first dose of investigational product.

• Use of any medication (including prescription, over-the-counter, herbal, multivitamin, oral contraceptives and other hormonal contraceptive treatments, or homeopathic preparations) within the 30 days prior to the first dose of study drug or during the study through Day 9 (occasional use of acetaminophen is allowed).

• Treatment with any known hepatic and/or P450 enzyme-altering agents, including CYP1A2 inducers or inhibitors within 30 days prior to the first dose of investigational product. This includes: Strong inhibitor- ciprofloxacin, enoxacin, fluvoxamine, and zafirlukast; Moderate inhibitor- methoxsalen, mexiletine, and oral contraceptives; Moderate inducer- phenytoin, rifampin, ritonavir, smoking, teriflunomide; Inducer- lansoprazole

• A history of any of the following medical conditions:

  1. History of previous bone marrow suppression.
  2. History of hypersensitivity to the investigational product.
  3. History of adverse hematologic reaction, (such as neutropenia, thrombocytopenia, anemia) to any drug.
  4. History of symptomatic or clinically meaningful orthostatic hypotension or syncope, as assessed by the investigator.
  5. History of controlled or uncontrolled hypertension or a systolic blood pressure greater than or equal to (>=) 140 millimeters of mercury (mmHg) or diastolic blood pressure >= 90 mmHg at the Screening Visit or Day -1.
  6. Participant has any history of seizure disorder.
  7. History or presence of known structural cardiac abnormalities, syncope, cardiac conduction problems (PR interval greater than (>) 220 milliseconds (ms), second or third-degree heart block, bundle branch block [except congenital right bundle branch block], or prolonged QTc interval) or exercise-related cardiac events.
  8. History of alcohol or other substance abuse within the last year.

• A participant's alcohol consumption that fulfils one of the following: (Note: One alcohol unit=1 beer [12 ounce {oz}]=1 wine [5 oz]=1 liquor [1.5 oz])

  1. Has consumed alcohol within 2 days prior to the first dose of investigational product.
  2. Male participants who consume more than 3 units of alcohol per day.
  3. Female participants who consume more than 2 units of alcohol per day.

• Positive screening test results for alcohol, drugs of abuse, or pregnancy (females of childbearing potential only) at the Screening Visit or Day -1.

• A positive human immunodeficiency virus (HIV) antibody screen, hepatitis B surface antigen (HBsAG) or hepatitis C virus antibody (HCV) screen.

• Use of tobacco in any form (smoking or chewing) or other nicotine-containing products in any form (gum, patch) within 30 days prior to the first dose of investigational product and during the in-house stay at the CRC.

• A positive urine cotinine test that is >= 50 Nano grams per milliliter (ng/mL) at either the Screening Visit or on Day -1.

• Routine consumption of more than 2 units of caffeine per day or participants who experience caffeine-withdrawal headaches or have a history of caffeine-withdrawal headaches. (One caffeine unit is contained in the following items: one 6-oz cup of coffee, two 12-oz cans of cola, one 12-oz cup of tea, and three 1-oz chocolate bars. Decaffeinated coffee, tea, or cola are not considered to contain caffeine.)

• Consumption of grapefruit, Seville oranges, and/or products containing these items within 7 days prior to the first dose of investigational product.

• Donation of blood or blood products (egg, plasma, or platelets) within 60 days prior to the first dose of investigational product.

• Known or suspected intolerance or hypersensitivity to the investigational products (anagrelide or omeprazole) or closely related compounds, or any of the stated ingredients.

• Within 30 days prior to the first dose of investigational product:

  1. Have used an investigational product (if elimination half-life is <6 days, otherwise 5 half-lives).
  2. Have been enrolled in a clinical study (including vaccine studies) that, in the Investigator's opinion, may impact this Shire-sponsored study.

• Prior screen failure, participation, or enrollment in this study.

• History of sensitivity to heparin or heparin-induced thrombocytopenia.

Takeda provides access to the de-identified individual participant data (IPD) for eligible studies to aid qualified researchers in addressing legitimate scientific objectives (Takeda's data sharing commitment is available on https://clinicaltrials.takeda.com/takedas-commitment?commitment=5). These IPDs will be provided in a secure research environment following approval of a data sharing request, and under the terms of a data sharing agreement.

IPD from eligible studies will be shared with qualified researchers according to the criteria and process described on https://vivli.org/ourmember/takeda/. For approved requests, the researchers will be provided access to anonymized data (to respect patient privacy in line with applicable laws and regulations) and with information necessary to address the research objectives under the terms of a data sharing agreement.

Safety set included all participants who had taken at least 1 dose of investigational product (anagrelide or omeprazole) and had at least 1 post dose safety assessment.

From start of study drug administration up to follow-up (up to Day 18)