Rationale and Aims: Infection by dengue virus (DENV) causes major morbidity and mortality throughout the world. In 2012, an estimated 3.6 billion people live in areas at risk for DENV infection, including Singapore. The key pathology of DENV infection is vascular leakage, which can occur in mild cases and can become life-threatening in severe cases when patients may develop dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). Mast cells (MCs) are strongly activated by DENV with preliminary studies showing that activation levels are correlated to disease severity in human patients. Thus, the investigators propose to use the MC stabilizing drug, ketotifen, to limit the immune pathology that is characteristic of dengue infection and treat dengue-induced vascular leakage. Methods: The ability of Ketotifen to reduce vascular leakage in DENV patients will be determined by assessing the pooling of fluid in the pleural cavity (measured by MRI and CXR) after 5 days of drug administration, evaluated as a percent change compared to baseline fluid levels. Additional measures of vascular leakage and immune pathology will be compared as secondary objectives. The trial will be conducted as a randomized, double-blind study comparing the responses of dengue patients given either ketotifen or placebo (n=55 per arm). Importance of proposed research: Currently, no targeted treatments exist to limit vascular leakage during DENV infection. If Ketotifen is identified as effective for preventing pleural effusion and/or plasma leakage in DENV patients, this would constitute an advance for the clinical management of DENV fever. This finding would also support a large-scale trial to determine whether Ketotifen can be used to prevent severe vascular leakage as occurs during DHF/DSS. Benefits/Risks: Ketotifen has a record of safety and tolerability in humans, regulatory approval, and widespread use. Side effects are generally mild. The potential exists that, if effective, many of the painful and life-threatening symptoms of DENV infection that result from plasma leakage would be improved.

Approximately 230 million individuals are infected each year by dengue virus (DENV) a Flavivirus spread by mosquito vectors that causes substantial worldwide morbidity and mortality. Infection by DENV results in dengue fever (DF), which is usually a self-limiting illness. However, many individuals can experience much more severe forms of disease, such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), which are characterized by widespread vascular pathology, the most prominent manifestation of which is plasma leakage that can lead to shock and, potentially, death. Currently, treatment for DHF/DSS is supportive care with analgesics, fluid replacement and bed rest. Management of severe DENV infections typically requires prolonged hospitalization accompanied by careful fluid management . At this time, there are no targeted treatments for DF, DHF or DSS, making improvements in care for DENV patients an urgent clinical need. In particular, there is a need for therapeutic intervention to prevent the vascular leakage.

Animal studies suggested that drugs in the class of mast cell (MC) "stabilizers" can effectively limit vascular leakage in mouse models of DENV infection. Drugs targeting MCs have been in use in humans for decades, particularly for the treatment of allergy and asthma. One "MC stabilizer", ketotifen, acts by preventing degranulation of MCs. Ketotifen is an oral drug currently used to prevent asthma. It is most commonly supplied in the form of a salt with fumaric acid, as ketotifen fumarate. Ketotifen has a clinical track record of greater than 30 years as a safe drug and it is currently approved for use in Singapore. In other formulations it is also used to treat irritation and reduce vascular leakage, such as in the eye. It is a MC stabilizing agent that prevents degranulation of MCs, as well as the production of additional mediators that are not contained within MC granules, including leukotrienes and platelet activating factor. Ketotifen also functions as an antihistamine with direct H1-receptor blocking function. The bioavailability of an oral dose of ketotifen in humans is approximately 80-90% . Drug levels peak in the serum between 2-4 hours after ingestion. Patients with asthma sometimes require treatment with ketotifen for weeks prior to observing improved asthmatic responses, but this is thought to represent the time required for chronic inflammation to subside and not the time required for MC stabilization, which occurs immediately in animal models. The mean elimination half-life of ketotifen is 12 hours. Side effects include drowsiness, dry mouth, slight dizziness, central nervous system (CNS) stimulation and weight gain. Patients are commonly prescribed 1-2mg tablets, twice a day. Treatment of DENV-infected mice with MC stabilizers, cromolyn or ketotifen, resulted reduced vascular leakage compared to untreated controls in two separate mouse models of DENV infection. These findings were apparent using two separate measures of vascular leakage as the endpoint readout: evans blue perfusion, which is a key experimental technique to show plasma leakage into tissues, and hematocrit analysis, which is the clinical parameter that is most commonly used to diagnose DHF in human patients.

This is a randomized, double blind, placebo-controlled, clinical study of ketotifen in adults with dengue infection. The study will be conducted as an outpatient study at National University Hospital (NUH) and Singapore General Hospital (SGH), daily with the MRIs and chest X-rays conducted at the Clinical Imaging Research Centre (CIRC) of the National University of Singapore (NUS). A final visit at convalescence (Day 21) can be at the site of enrolment. One hundred and ten (110) patients will be randomized 1:1 to ketotifen or placebo. A baseline MRI of the pleural cavity, liver, spleen and kidney will be taken. Tablets of placebo or ketotifen will be self-administered for 5 days. Patients will be given daily clinical exams, Day 1 to Day 5, and blood samples will be collected for plasma chymase levels, viral load, hematology, clinical chemistry, inflammatory product profiling and additional laboratory tests. After the administration of the final dose of drug, blood will be drawn and a follow up MRI will be performed at the CIRC in NUS to assess fluid accumulation within the pleural cavity as a primary clinical endpoint, with assessment of the liver, spleen and kidney as experimental endpoints.

Inclusion Criteria:

1. Male or female, age 21-60 years
2. Fever of ≥ 37.5°C (directly measured or patient reported) of ≤ 72 hr duration.
3. Positive Nonstructural protein 1 (NS1) strip assay or dengue polymerase chain reaction (PCR)
4. Able and willing to give written or oral informed consent
5. Willing to be an outpatient from Study Day 1 to 5, to undergo an MRI and chest X-ray day 1 at the hospital, to return to the hospital on day 5 for an MRI and chest X-ray, and return on Study Days 7 and 21.
6. Willing to keep a diary of pain medication usage and side effects

Exclusion Criteria:

1. Clinical signs and symptoms for severe dengue, such as: a. Persistent vomiting b. Altered mental state c. Liver enlargement > 2 cm
2. A person with any of the following laboratory values: a. aspartate aminotransferase (AST) or alanine aminotransferase (ALT) ≥ 1000 U/L
3. Current usage of any anticoagulant drugs including, but not limited to, aspirin, warfarin, or clopidogrel.
4. Current usage of any drugs that are known to block the functions of ketotifen, such as propranolol.
5. Current usage of oral anti-diabetic agents.
6. Any other clinically significant acute illness within 7 days prior to first study drug administration.
7. Patients with renal impairment.
8. Exposure to any new investigational agent within 30 days prior to the study drug administration.
9. Clinically significant abnormal physical examination unrelated to dengue infection.
10. Females of childbearing potential who are pregnant, breast feeding, or unwilling to avoid pregnancy by the use of appropriate contraception, including oral and subcutaneous implantable hormonal contraceptives, condoms, diaphragm, or intrauterine device (IUD), during the period that the experimental drug is administered. Prospective female participants of childbearing potential must have a negative pregnancy test (point of care).
11. Current significant medical condition or illness including cardiac arrhythmias, cardiomyopathy or other cardiac disease, immunocompromised state including known HIV infection, or any other illness that the Investigator considers should exclude the patient, especially those that require continuation of other medications likely to have an interaction with the study drug. Patients with a history of allergy will not be excluded unless the allergy may be directed to the Study Drug or other tablet ingredient.
12. Any condition that would render the informed consent invalid, or limit the ability of the patient to comply with the study requirements.
13. Any condition that, in the opinion of the investigator, would complicate or compromise the study or well being of the patient.