Treatment of COVID-19 pneumonia and acute respiratory distress with ramatroban, a thromboxane A2 and prostaglandin D2 receptor antagonist: A 4-Patient Case Series Report

Importance Hypoxemia in COVID-19 pneumonia is dispositive for hospitalization and mechanical ventilation and contributes to mortality. Other than oxygen supplementation, there is no treatment that resolves hypoxemia in COVID-19 pneumonia. Objective COVID-19 pneumonia sustains a massive increase in lipid mediators, especially thromboxane A 2 >> PGE 2 > PGD 2 . Thromboxane A 2 induces pulmonary venoconstriction, increases pulmonary capillary pressure and contributes to pulmonary edema. High thromboxane A 2 metabolite levels are strongly associated with respiratory failure and mortality in hospitalized COVID-19 patients. Ramatroban (Baynas®, Bayer Yakuhin Ltd., Japan) is an inexpensive, orally bioavailable, thromboxane A 2 receptor antagonist. Ramatroban was administered to patients with COVID-19 pneumonia and hypoxemia to explore the effect of thromboxane A 2 antagonism on clinical symptoms and outcomes. Design, A retrospective series comprising 4 immunomodulatory agent, ramatroban addresses the fundamental host response mechanisms underlying respiratory and critical organ failure in COVID-19. Ramatroban merits study in randomized clinical trials that might offer hope for a cost-effective pandemic treatment. Abbreviations: Tx, thromboxane; 11dhTxB 2 , 11-dehydro-thromboxane B 2 ; TPr, thromboxane prostanoid receptor; PG, prostanoid 2; syndrome COVID-19, coronavirus disease syncytial interleukin; monocyte-macrophage derived suppressor cell; interferon; respiratory distress syndrome; blood oxygen saturation by pulse oximetry growth


BACKGROUND
After symptomatic SARS-CoV-2 infection, 10-20% of patients require hospitalization for respiratory distress and hypoxemia. 1 Currently, anti-SARS-CoV-2 monoclonal antibodies are approved for treatment of ambulatory patients with COVID-19, 2 and antiviral treatments have recently been approved, but they are expensive and effective only early after symptom onset. There is an unmet medical need for inexpensive, safe, orally bioavailable drugs that can reduce hypoxemia, provide symptomatic relief, and minimize hospitalization in patients with COVID-19. Identifying the correct therapeutic target is critical to discovering such a drug.
Lungs in COVID-19 patients with acute respiratory distress syndrome (ARDS) produce proinflammatory lipid mediators with predominance of cyclooxygenase metabolites in bronchoalveolar lavage fluid (BALF), notably thromboxane B2 (TxB2) >> prostaglandin E2 (PGE2) > prostaglandin D2 (PGD2). 3 The massive increase in TxA2 metabolites in BALF 3 and systemically in hospitalized COVID-19 patients, 4,5 suggests a critical role for TxA2 / TxA2 prostanoid receptors (TPr) in COVID-19 respiratory distress. We hypothesized that TxA2/TPr induced contraction of pulmonary veins elevates pulmonary capillary pressure and contributes to pulmonary edema and hypoxemia in COVID-19 pneumonia (Fig. 1). TPr signaling leads to selective constriction of intrapulmonary veins and small airways with 10-fold higher potency and greater reduction in luminal area than intrapulmonary arteries. 6 High local concentrations of TxA2 can effectively divert pulmonary blood flow, increase microvascular pressure and permeability, and force fluid and plasma proteins into alveoli. 6 A selective TPr antagonist was previously reported to decrease pulmonary capillary pressure by selectively reducing post-capillary resistance in patients with acute lung injury. 7 TxA2 and isoprostanes stimulate TPr-mediated activation of the TGFβ pathway, 8 and early, untimely TGFβ responses in SARS-CoV-2 infection limit antiviral function of natural killer (NK) cells and promote progression to severe COVID-19 disease. 9 Theken and FitzGerald proposed early administration of a TxA2 antagonist as an antithrombotic agent, and a D-prostanoid receptor 2 (DPr2, formerly referred to as CRTH2) antagonist to boost interferon lambda (IFN-λ) in the upper respiratory tract, thereby limiting SARS-CoV-2 replication and transmission. 10,11 Ramatroban, the only dual TxA2/TPr and PGD2/DPr2 receptor antagonist available for clinical study, has been proposed as an antithrombotic and immunomodulator agent in 13 In their report showing very high levels of TxB2 >> PGD2 in BALF, Archambault and colleagues also suggested ramatroban to block the deleterious effects of TxA2 and PGD2 in COVID-19. 3 Ramatroban has an established safety profile, having been prescribed for over 20 years in Japan for treatment of allergic rhinitis. 14, 15 We report here a small case series of four consecutive COVID-19 patients with worsening respiratory distress and hypoxemia who were treated with ramatroban. Surprisingly, this led to rapid improvement in both respiratory distress and hypoxemia, thereby avoiding hospitalization and promoting recovery from acute disease.
The 1 st case of severe COVID-19 pneumonia treated with ramatroban S.D., an 87-year-old Indian lady, experienced sudden onset of fever, cough, diarrhea, anorexia, profound weakness, and slight shortness of breath, 10 days after a 2-hour flight from New Delhi to Indore, Madhya Pradesh, India. Patient had received the first dose of COVAXIN, a whole virion inactivated vaccine against SARS-CoV-2, 30 days prior to beginning of symptoms. On examination the patient was fully alert, oriented, and able to make intelligent conversation but lay listlessly in bed unable to ambulate. Patient weighed 42 kg and exhibited severe pre-existing muscle wasting and marked kyphosis. Vital signs revealed temperature, 102 o Fahrenheit; heart rate, 100 per minute; blood pressure, 90/60 mm of Hg; and respiratory rate, 22 per minute. Mucosa were moist, and mild pallor was present. There was no jugular venous distention or pedal edema. Chest examination revealed bilateral coarse rales especially prominent at both lung bases but no wheezes. Abdomen, cardiovascular, and neurological examinations were unremarkable. Patient was not taking any medications.
Past medical history included hypertension for over 40 years; thyrotoxicosis for over 30 years treated with radioiodine therapy in 1999; severe osteoporosis with kyphosis; bladder suspension surgery in 1999; coronary artery disease leading to acute myocardial infarction and cardiac arrest in 2015 which required coronary angioplasty and stent placement; chronic kidney disease with estimated glomerular filtration rate of about 20 mL/min ( Table 2).
Investigations: Nasopharyngeal and oropharyngeal swabs were positive for SARS-CoV-2 infection by RNA PCR with cycle threshold (Ct range < 20 cycles). Pulse oximetry revealed oxygen saturation of about 85-88%. Patient was admitted on April 9, 2021 to Medanta Hospital, Indore. CT scan revealed moderate multifocal, patchy ground glass opacities, and consolidation. There was septal thickening in the central and peripheral subpleural aspect of both lung parenchyma. Serial laboratory examinations during the course of the illness are listed in Table 1.
Hospital course: During the hospital stay, the patient was treated with high-flow nasal oxygen, prophylactic low-molecular weight heparin, intravenous remdesivir, antibiotics, and methylprednisolone. Patient continued to have fever, cough, shortness of breath, diarrhea, and profound weakness during the hospital stay. SpO2 on room air ranged between 82-86% (Table 2). After a hospital stay of 5 days, the patient was discharged upon her request on April 14, 2021. Discharge medications included oral oseltamivir, doxycycline, vitamin C, aspirin 75 mg once a day, 5 mg prednisolone, vitamin D3, and nebulization with budesonide and salbutamol twice daily. Continued supportive management with betadine gargles, steam inhalation, and breathing exercises was advised.
Post-discharge course: On April 15, the day after discharge from the hospital, the patient had fever with a temperature of 101 o Fahrenheit. Pulse oximetry revealed an oxygen saturation (SpO2) of 82-84% on room air, and patient was continued on oxygen. Patient was profoundly weak and unable to get out of bed without assistance. At this time all drugs including low-dose aspirin were discontinued, and the patient was started on ramatroban (Baynas®, 75 mg tablet) in a dose of one-half tablet (37.5 mg) orally twice daily. The patient was continued on oxygen using a nasal cannula and SpO2 was not checked on room air. After about 36 hours, having received three one-half doses of ramatroban, there was noticeable improvement in her general condition, and SpO2 increased to 90% on room air. The dose of ramatroban was increased to 37.5 mg in the morning and 75 mg at bedtime. Patient had complete resolution of cough and diarrhea over the next 3 days and started ambulating independently without assistance. Ramatroban was discontinued after 2 weeks due to non-availability, and the patient was switched to 75 mg aspirin daily. Patient had recovered almost completely by April 22, 2021, and gradually recovered fully over the next 3-4 weeks to baseline status. On October 10, 2021, 6 months after the acute COVID-19, a highresolution, non-contrast CT scan demonstrated non-homogenous ground glass pattern with normal lung volumes and absence of lung fibrosis. Patient continues to be asymptomatic.  (Table 2). On the 25 th of April, patient noticed that the sputum was streaked with blood and oral acetylcysteine was started. A chest CT on April 27 th revealed ground glass opacities involving bilateral lung fields with mild interstitial thickening giving the appearance of crazy-paving pattern. There were scattered areas of bronchopneumonic changes and consolidation involving both lungs. A few small fibrotic bands were noted in both lower lobes. The patient had made a near complete recovery by May 5 th , and resumed work on May 10 th . Patient continues to have altered taste and smell 7 months after the acute illness.

Case 3
S.B., a 22-year-old, healthy lady in New Delhi developed fever, cough, loss of smell and taste, and body aches due to COVID-19. S.B. had not received COVID vaccination. S.B. was treated with favipiravir, steroids and multivitamins. Patient experienced progressively worsening shortness of breath and SpO2 dropped to 85% on room air. Patient was prescribed Ramatroban 75 mg twice daily. Within 6-8 hours after taking the first dose of ramatroban, respiratory distress improved and the SpO2 increased to 89%. The next day SpO2 increased to 90-91%. There was progressive improvement with complete resolution of respiratory symptoms over the next 5 days. On day 5, the SpO2 was 94% on room air ( Table 2). Patient has made a complete recovery from COVID-19.

Case 4
B.C., a 70-year-old man living in a rural area of Bihar, India developed high grade fever and cough presumably secondary to SARS-CoV-2 infection. Patient has a history of diabetes mellitus controlled with diet. B.C. was not taking any medications and had only received one dose of COVAXIN vaccine for COVID-19. Patient developed shortness of breath with SpO2 measuring about 80% on room air. Two to three hours after taking 75 mg ramatroban, respiratory distress and cough improved, and the SpO2 increased to 85%. After a total of 10 tablets taken over 5 days, dyspnea had resolved, and SpO2 increased to 96% on room air (Table 2). Patient has made a complete recovery from COVID-19. *SpO2 on room air was not checked at earlier time points ^ For patients 2, 3, and 4, ramatroban could be administered only for a total of 5 days due to limited supplies.

Discussion
We present the first reported cases of COVID-19 treated with ramatroban (Baynas®), a dual antagonist of the TxA2/TPr and PGD2/DPr2 receptors. All four COVID-19 patients were characterized by respiratory distress that was new in onset or had worsened ( Table 2). Despite presenting with severe hypoxemia, gas exchange rapidly improved in all four patients. They were able to avoid hospitalization and recovered without any further need for supplemental oxygen or corticosteroids.

Figure 1. Proposed mechanisms of rapid relief in respiratory distress following ramatroban administration during acute SARS-CoV-2 infection. SARS-CoV-2 induced expression of COX-2
generates PGH2 which is converted into thromboxane A2 >> PGD2. Oxidative stress associated free radicals initiate non-enzymatic peroxidation of arachidonic acid leading to F2-isoprostane generation. PGH2, TxA2 and F2-isoprostanes stimulate thromboxane prostanoid receptors (TPr). TPr stimulation induces pulmonary venoconstriction leading to an increase in transcapillary pressure in pulmonary microvasculature, and transudation of fluid into the alveoli, thereby causing impaired gas exchange and ARDS. TxA2/TPr axis also induces bronchoconstriction and mucus secretion. TxA2 is rapidly converted to 11-dehydro-TxB2 in the lungs. PGD2 and 11-dehydro-TxB2 stimulate the DPr2 receptor on Th2 and ILC2 cells leading to release of type 2 cytokines, IL-4 and IL-13. IL-4 promotes vascular permeability thereby exacerbating fluid transudation while IL-13 induces hyaluronic acid accumulation and mucus hypersecretion. Ramatroban inhibits the DPr2 and TPr receptors thereby promoting pulmonary vasorelaxation, bronchorelaxation and improving capillary barrier function, while attenuating the maladaptive type 2 immune response and mucus secretion, thereby alleviating pulmonary edema and ARDS. Tx, thromboxane; PG, prostaglandin; TPr, thromboxane prostanoid receptor; DPr2; D-prostanoid receptor 2; Th2; T helper 2; ILC2; innate lymphoid class 2 U-46619, a PGH2 analog TPr agonist, at 1 nM reduced guinea-pig pulmonary venous and airways luminal areas by 50% with little or no change in arterial luminal area. 6 Higher concentrations collapsed both pulmonary veins and airways, indicating that sub-nanomolar concentrations of the more potent TxA2 could produce meaningful increases in airway tone and pulmonary venous resistance. 6 This is consistent with the measured effect of ifetroban, a selective TPr antagonist which reduced pulmonary venous resistance and capillary pressure in patients with acute lung injury. 16 Moreover, TPr antagonism prevented hypoxemia in a lethal porcine septic shock model, 17 attenuated airway mucus hyperproduction induced by cigarette smoke 18 and reduced pulmonary edema in mouse models of acute lung injury. 19 In the patient cases presented here, we hypothesize that ramatroban enhanced pulmonary blood flow, reduced pulmonary capillary pressures, improved ventilation-perfusion matching, promoted resolution of edema, reduced bronchoconstriction and airway mucus hyperproduction, improved lung compliance and gas exchange, and thereby mitigated SARS-CoV-2 respiratory distress and hypoxemia ( Fig. 1 and Table 3).
Lung TxA2 generation is sufficiently elevated in symptomatic COVID-19 that TPr activation may affect other critical organ functions. For example, vascular effects might include vasospasm and thrombosis resulting in angina, arrhythmias, myocardial infarction and/or stroke. 20 In the cerebral circulation, TPr activation can increase blood-brain barrier permeability, 21 which may contribute to brain fog in COVID-19. The potential of TPr blockade to affect the lungs and other critical organs during acute illness and during convalescence or long COVID merits focused research.

Table 3. Proposed effect of antagonizing Thromboxane A2/TPr and Prostaglandin D2/DPr2 signaling by ramatroban in patients with COVID-19
PGD2 / DPr2 signaling promotes allergic inflammation by stimulating Th2 and innate lymphocyte class 2 (ILC2) cells as in asthma (Fig. 1). 22,23 The maladaptive immune response in COVID-19 is characterized by a shift from Th1 to Th2 with basophilia, eosinophilia, lymphopenia and an increase in plasma levels of type 2 cytokines produced by Th2 cells, including IL-4 and IL-13. 24-26 IL-4 is known to impair the barrier function of endothelial cells, leading to microvascular leakage and edema formation (Fig. 1). 27 IL-13 increases hyaluronan accumulation in mouse lungs 28 and mucus overproduction in cultured human bronchial epithelial cells. 29 This is correlated with ARDS, need for mechanical ventilation, acute kidney injury (AKI), and mortality in COVID-19. 30 Whether ramatroban inhibits inflammation and hyaluronan accumulation in ARDS remains to be investigated.
The beneficial effects of ramatroban may be additionally attributed to enhanced antiviral activity due to TxA2/TPr and PGD2/DPr2 antagonism. First, TxA2/TPr activation stimulates activation of the TGF-β pathway, 8 and early, untimely TGF-β responses in SARS-CoV-2 infection limit antiviral function of natural killer (NK) cells. 9 Second, TxA2/TPr activation may directly modulate natural cytotoxic effector cell function. 31 Third, PGD2/DPr2 signaling may suppress innate mucosal antiviral responses by inhibiting expression of interferon (IFN)-λ, the first line of defense against viruses at mucosal surfaces.
Notably IFN-λ is markedly suppressed in the upper respiratory tract in COVID-19. 32 Increased expression of phospholipase A2 group IID and PGD2 in the elderly may further suppress IFN-λ expression, 33 thereby impairing antiviral responses and contributing to increased morbidity and mortality observed consistently in the elderly. 11 Expression of nasal and pharyngeal PGD2 and DPr2 in SARS-CoV-2 infection remain to be investigated even though there is significant elevation of PGD2 in bronchoalveolar lavage fluid and human lung epithelial cells, 3,34 and expression of PGD2 synthase and DPr2 in COVID-19 kidneys. 35 Interestingly, 11-dehydro-TxB2 (11dhTxB2), a major stable metabolite of thromboxane A2, serves as a full agonist of DPr2 receptors. 36 Urinary 11dhTxB2 levels are markedly increased in COVID-19 and correlate with length of hospitalization, mechanical ventilation and mortality. 37 In rabbits infused with TxB2, 11dhTxB2 was a major metabolite, and enzymatic conversion of TxB2 to 11dhTxB2 was not detected in blood cells or plasma. 38 The dehydrogenase catalyzing formation of 11dhTxB2 was tissue bound with the highest activity in lung. 38 The above suggests that elevated lung TxA2 is converted to 11dhTxB2 which may exert local or systemic effects via DPr2. In a neonatal mouse model of severe respiratory syncytial virus-induced bronchiolitis, treatment with a DPr2 antagonist decreased viral load and improved morbidity associated with upregulating interferon (IFN)-λ expression. 10,33 Whether ramatroban enhances NK cell and IFN-λ responses and reduces SARS-CoV-2 viral load remains to be investigated.
Currently, there is no treatment for long COVID symptoms following recovery from acute illness. Long COVID is often characterized by neuropsychiatric manifestations including "brain fog," anxiety or depression, fatigue and problems with mobility, dyspnea, in part due to lung fibrosis and lung diffusion impairment, and microvascular thrombosis persisting for > 4 months in about 25% of patients. 39,40 Despite persistence of ground glass opacities 6 months later in patient 1, lung fibrosis was not detected. This is consistent with the antifibrotic effect of ramatroban in an animal model of silicosis that is associated with markedly increased pulmonary thromboxane A2 and PGD2. 41 Moreover, in well-established animal models of depression, elevation in PGD2 mediates depression-like behavior, while ramatroban restores object exploration and social interaction. 42 The above suggests that ramatroban may help prevent and/or treat certain long COVID symptoms (Table 3).
This report has several limitations. Only 4 patients could be treated with ramatroban, and the duration of treatment was brief due to very limited availability of the drug in India. Only the first patient had laboratory studies performed. Patients 2, 3 and 4 were not examined by a physician and the clinical course was reported by patients or their relatives.
During the ongoing pandemic, there is an unmet need for a drug that can provide rapid relief of respiratory symptoms and hypoxemia, halt progression of disease, and minimize hospitalization, which is associated with poor outcomes for the patient and added burden on the healthcare system. Ramatroban (Baynas®, Bayer Yakuhin, Ltd., Japan) has been safely used for the treatment of allergic rhinitis in Japan since 2000. 15 The usual adult oral dose of 75 mg twice daily achieves an average plasma concentration of about 0.1 mg/L or 240 nM which is sufficient to inhibit pulmonary venous constriction, platelet activation, and release of type 2 cytokines (Table 3).