Pharmacokinetics, Tolerability and Safety of Favipiravir Compared to Ribavirin for the Treatment of Lassa Fever

The currently used antiviral for the treatment of LF, which is also recommended by the World Health Organization (WHO) and the Nigeria Center for Disease Control, is ribavirin. However, evidence for ribavirin efficacy in LF patients adds up to the results of a single study with serious limitations. A promising new treatment candidate that showed efficacy against LF in preclinical studies is Favipiravir. It has further been evaluated for the treatment of Ebola Virus disease during the West-African Ebola outbreak and is approved for treatment of pandemic influenza virus infections in Japan.

The study will be conducted at two study sites in Nigeria: the Irrua Specialist Teaching Hospital (ISTH) and the Federal Medical Center of Owo (FMCO). Lassa fever patients of 18 years and older with LF confirmed by reverse-transcription polymerase chain reaction (RT-PCR) hospitalized at either ISTH or FMCO will be asked to participate in this study. A total of 40 evaluable participants will be randomized to two treatment arms (20 participants per arm): intravenous ribavirin standard of care treatment (Irrua regimen), oral favipiravir. Patients will be included in the study after giving written informed consent and if all inclusion criteria and no exclusion criteria are met. Multiple blood draws with the purpose of virologic, serologic and immunological analyses, hematological and biochemical analyses as well as pharmacokinetic analyses will be performed throughout the study duration of ten days. Adverse events (AEs), serious adverse events (SAEs) and pregnancy will be captured, monitored and followed-up. A medical monitor will be available for study investigators to assist with any clinical and safety related questions. An external data safety monitoring board (DSMB) will conduct periodic safety reviews.

Data will be captured on source documents and electronic case report forms (eCRFs). Informed consent forms will be stored in a lockable cabinet. Participants data will only be linked to the unique identifier to ensure pseudonymity.

Statistical analysis of study endpoints and pharmacokinetic parameters will be performed descriptively. Missing data will be treated as such, no imputation will be applied.

The study will be conducted in compliance with the protocol, the Declaration of Helsinki, the International Conference on Harmonisation-Good Clinical Practice (ICH-GCP) guideline and the Nigerian National Code for Health Research Ethics, in particular concerning the submission to the ethics committees and the protection of personal data as well as other national and regulatory requirements.

Inclusion criteria

• Age ≥ 18 years
• LF confirmed by RT-PCR (reverse-transcription polymerase chain reaction)
• Written informed consent

Exclusion criteria

• Inability to give consent (e.g. unconscious patients/ cognitively impaired patients)
• Pregnancy/lactation (evidenced by negative urine pregnancy test in women of child-bearing potential)
• Women who plan to get pregnant within the upcoming 6 months
• Severe malnutrition (BMI<16)
• Known intolerance to ribavirin or favipiravir
• History of hemoglobinopathies (i.e., sickle-cell anaemia or thalassemia major) and/or haemophilia
• Organ failure as evidenced by:

• Creatinine ≥ 3x upper limit of normal (ULN)
• Aspartate aminotransferase (AST/GOT) > 150 IU/l
• Alert, confusion, voice, pain, unresponsive (ACVPU) score = V or P or U (corresponds to Glasgow Coma Scale (GCS) ≤ 12)
• Severe central nervous system features (e.g. seizures, restlessness, confusion and coma)
• O2 Saturation < 90%
• Hematocrit <30 %
• Severe anaemia requiring blood transfusion
• Inability to take oral drug (e.g. encephalopathy, severe vomiting)
• Patients who already received ribavirin or favipiravir within the preceding 7 days