Inclusion Criteria:
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Healthy Volunteers Only (Stage I and II (Phase 1a and 1b)):
1. Male or female 18 to 55 years of age at the time of signing the informed consent.
2. In good health as determined by the Investigator, based on medical history and screening evaluations.
3. Body weight of ≥ 50 kg and BMI within the range 18-30 kg/m2 (inclusive)
Patients with Epilepsy Only (Stage II (Phase 1b)):
4. Male or female 18 to 70 years of age at the time of signing the informed consent.
5. A clinical diagnosis of focal or generalized epilepsy. Subjects must have motor seizures, with or without impaired awareness.
6. Has a minimum of 4 seizures per 4-week period while taking 1 to 3 anti-seizure medications
7. All medications and epilepsy interventions must be stable for 8 weeks before screening and are expected to remain stable during the study
All Subjects:
8. Negative serum pregnancy test at screening and urine pregnancy test on Day -1 before starting study treatment in all pre-menopausal women and women \< 12 months after the onset of menopause.
9. Female participants of child-bearing potential and male participants must agree to use adequate contraception for the duration of the protocol.
10. Able to sign informed consent and comply with the protocol.
Exclusion Criteria:
* Healthy Volunteers (Stage I and II (Phase 1a and 1b)):
1. Subjects with any unresolved history of clinically significant disease, in the opinion of the investigator.
2. Past or intended use of over-the-counter (OTC) or prescription medication (other than ≤ 2 g/day paracetamol \[acetaminophen\] or ≤ 800-mg/day ibuprofen), vitamins, and dietary or herbal supplements within 7 days or 5 half-lives of the respective drug, if known (whichever is longer), prior to dosing.
Patients with Epilepsy (Stage II (Phase 1b)):
3. Acute precipitant of seizure within the past 3 months prior to screening such as major trauma, hypoglycemia, hyperglycemia, cardiac arrest, or post-anoxia
All Subjects:
4. Any uncontrolled medical or psychiatric condition (e.g., hypertension, diabetes, chronic obstructive pulmonary disorder, asthma, depression) as judged by the investigator.
5. Any clinically significant findings in medical examination, including physical examination, 12-lead ECG, vital signs, clinical laboratory tests. Specifically:
1. alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≥ 3 × upper limit of normal (ULN), Total bilirubin ≥ 2 × ULN
2. QT interval corrected by Fridericia's formula (QTcF) \> 450 msec (male) or \> 470 msec (female)
6. Undergone major surgery ≤ 2 months prior to Day -1.
7. Received any investigational drug within 30 days or 5 half-lives (whichever is longer, if known) before screening.
8. Received any vaccine within 6 weeks before planned SIF001 administration.
9. Loss of more than 100 mL blood (e.g., a blood donation) within 2 months before Day -1, or has received any blood, plasma, or platelet transfusions within 3 months before admission.
10. Active liver disease or severe renal impairment, including serum creatinine ≥ 1.5 × ULN or estimated glomerular filtration rate of \< 60 mL/min/1.73m2.
11. Known history of substance use disorder.
12. History of active human immunodeficiency virus (HIV), active hepatitis C virus (HCV), or active hepatitis B virus (HBV)
13. Recent (2 weeks) history of a positive COVID-19 test result or disease symptoms of COVID-19 disease such as shortness of breath, cough, rhinorrhea, sore throat etc.
14. Known history of hypersensitivity or anaphylactic reaction to intravenous medications, biologicals, or fluids.
15. History of any clinically significant disease or disorder which, in the opinion of the investigators, may either put the subject at risk because of participation in the study, or influence the results or the subject's ability to participate in the study.
16. History of status epilepticus within 2 years of screening
17. Known history of suicidality within 2 years of screening, or answering "yes" to questions 4 and 5 of the Columbia Suicide Severity Rating Scale (C-SSRS)
18. Unable to complete this study for other reasons or the investigator believes that the subject should be excluded.
