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.