A Study of S-033188 Compared With Placebo or Oseltamivir in Otherwise Healthy Patients With Influenza

Inclusion Criteria:

1. Patients who are able to understand the study and comply with all study procedures,
and willing to provide written informed consent/assent prior to the predose
examinations appropriately. As for adolescent patients, informed consent/assent of
voluntary participation should be obtained in accordance with local requirements

2. Male or female patients aged ≥ 12 to ≤ 64 years at the time of signing the informed
consent/assent form.

3. Patients with a diagnosis of influenza virus infection confirmed by all of the
following:

1. Fever ≥ 38ºC (axillary) in the predose examinations or > 4 hours after dosing of
antipyretics if they were taken

2. At least one of the following general systemic symptoms associated with
influenza are present with a severity of moderate or greater

- Headache

- Feverishness or chills

- Muscle or joint pain

- Fatigue

3. At least one of the following respiratory symptoms associated with influenza are
present with a severity of moderate or greater

- Cough

- Sore throat

- Nasal congestion

4. The time interval between the onset of symptoms and the predose examinations is 48
hours or less. The onset of symptoms is defined as either:

1. Time of the first increase in body temperature (an increase of at least 1ºC from
normal body temperature)

2. Time when the patient experiences at least one general or respiratory symptom

5. Women of childbearing potential who agree to use a highly effective method of
contraception for 3 months after the first dose of study drug

Exclusion Criteria:

1. Patients with severe influenza virus infection requiring inpatient treatment.

2. Patients aged ≥ 20 years with known allergy to oseltamivir (Tamiflu®).

3. Patients with any of the following risk factors

1. Women who are pregnant or within 2 weeks post-partum

2. Residents of long-term care facilities (eg, welfare facilities for the elderly,
nursing homes)

3. Chronic respiratory diseases including bronchial asthma

4. Neurological and neurodevelopmental disorders including disorders of the brain,
spinal cord, peripheral nerve, and muscle (eg, cerebral palsy, epilepsy [seizure
disorders], stroke, intellectual disability, moderate to severe developmental
delay, muscular dystrophy, or spinal cord injury)

5. Heart disease (such as congenital heart disease, congestive heart failure, or
coronary artery disease), excluding hypertension without any other heart-related
symptoms)

6. American Indians and Alaskan natives

7. Blood disorders (such as sickle cell disease)

8. Endocrine disorders (including diabetes mellitus)

9. Kidney disorders

10. Liver disorders

11. Metabolic disorders

12. Compromised immune system (including patients receiving immunosuppressant
therapy, or those with cancer or human immunodeficiency virus [HIV] infection)

13. Morbid obesity (body mass index [BMI] ≥ 40)

4. Patients unable to swallow tablets or capsules.

5. Patients who have previously received S-033188.

6. Patients weighing < 40 kg

7. Patients who have been exposed to an investigational drug within 30 days prior to the
predose examinations.

8. Women who are breastfeeding or have a positive pregnancy test in the predose
examinations. The following female patients who have documentation of either a or b
below do not need to undergo a pregnancy test in the predose examinations:

1. Postmenopausal (defined as cessation of regular menstrual periods for 2 years or
more and confirmed by a follicle-stimulating hormone test) women

2. Women who are surgically sterile by hysterectomy, bilateral oophorectomy, or
tubal ligation

9. Patients with concurrent infections requiring systemic antimicrobial and/or antiviral
therapy at the predose examinations.

10. Patients who have received peramivir, laninamivir, oseltamivir, zanamivir,
rimantadine, umifenovir, or amantadine within 30 days prior to the predose
examinations.

11. Patients who have received an investigational monoclonal antibody for a viral disease
in the last year.

12. Patients with severe underlying diseases.

13. Patients with known creatinine clearance ≤ 60 mL/min.

14. Patients who, in the opinion of the investigator, would be unlikely to comply with
required study visits, self-assessments, and interventions