Novel Inhalation Formulations of Repurposed Drugs for Potential Treatment of COVID-19

Abstract

The spread of COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in massive numbers of infections and deaths. Despite the current containment attempts, the complete prevention of COVID-19 infection is not certain even with the use of vaccines that have proven to be quite effective. Hence, the need for pharmacological therapies still exists to treat the disease and protect lives. Many drugs have been repurposed and tested as a potential COVID-19 treatment. A large proportion of these drugs showed promising efficacy results against SARS-CoV-2 when tested in vitro or in animals. However, the findings of the clinical studies have not supported the benefits of some of these drugs after they showed inconclusive or even adverse outcomes. Noticeably, the focus of the current approved or authorised pharmacological therapy is based on systemic administration although COVID-19 is mainly a respiratory disease. The pathogenesis of COVID-19 is initiated when the virus finds its way to the upper respiratory tract of the patient, and it may worsen to acute respiratory distress syndrome (ARDS) if it reached the lower respiratory tract. Therefore, inhaled administration of the potential drugs may be more relevant and effective for COVID-19 treatment. The objective of this thesis was to develop inhalation formulations of repurposed drugs for potential COVID-19 treatment. Hydroxychloroquine and ivermectin have been repurposed after they showed antiviral activity against COVID-19 in vitro. However, the pharmaceutical and pharmacokinetic issues associated with their systemic administration have limited their bioavailability. Therefore, they were formulated as inhalable dry powders so that the formulations will be in place as a potential COVID-19 treatment for future clinical trials. Characterisation studies of both drugs were conducted to assess physical stability, in vitro dispersion performance, in vivo pharmacokinetics and safety in animal model was further tested for ivermectin. In chapter 1, the background of COVID-19 was briefly introduced, from identifying the aetiology (SARS-CoV-2) through developing accurate diagnostic methods to managing the disease by preventive vaccines and authorised repurposed treatment. The inhalation therapy of COVID-19 was also introduced and the current status of drug formulations, preclinical and clinical data were reviewed. In chapter 2, inhalable HCQ powders were prepared and characterised for potential COVID-19 therapy. Hydroxychloroquine sulfate (HCQ-sul) was jet-milled followed by conditioning by storage at different relative humidities (43, 53, 58, and 75% RH) for seven days. The solid-state properties including particle morphology and size distribution, crystallinity and moisture sorption profiles of HCQ-sul samples were characterised by scanning electron microscopy, laser diffraction, X-ray powder diffraction, differential scanning calorimetry, thermogravimetric analysis and dynamic vapour sorption. The dispersion performance of the HCQ-sul powders was assessed using a medium-high resistance Osmohaler coupling to a next-generation impactor (NGI) at a flow rate of 60 L/min. The jet-milled powder showed a volume median diameter of 1.7 µm (span 1.5) and retained the same crystalline form as the raw HCQ-sul. A small amount of amorphous materials was present in the jet-milled HCQ-sul which was convertible to the stable, crystalline state after conditioning at 53, 58, and 75% RH. The recovered fine particle fraction (FPFrecovered) and emitted fine particle fraction (FPFemitted) of the HCQ-sul sample immediately after jet-milling and the samples after conditioning at 43, 53, and 58% RH were similar at c.a. 43% and 61%, respectively. In contrast, the sample having conditioned at 75% RH showed lower corresponding values at 33% and 26 %, respectively, due to the formation of solid bridges caused by excessive moisture. Thus, inhalable crystalline powders of HCQ-sul were successfully prepared which can be used for preclinical study and clinical testing as a potential inhaled COVID-19 treatment. In chapter 3, inhalable dry powders of ivermectin with lactose crystals were prepared and characterised for the potential treatment of COVID-19. Ivermectin was co-spray dried with lactose monohydrate crystals and conditioned by storage at two different relative humidity points (43 and 58% RH) for a week. The in vitro dispersion performance of the stored powders was examined using a medium-high resistance Osmohaler connecting to a NGI at 60 L/min flow rate. The solid-state characteristics including particle size distribution and morphology, crystallinity, and moisture sorption profiles of raw and spray-dried ivermectin samples were assessed by laser diffraction, scanning electron microscopy, Raman spectroscopy, X-ray powder diffraction, thermogravimetric analysis, differential scanning calorimetry and dynamic vapour sorption. All the freshly spray-dried formulation (T0) and the conditioned samples could achieve the anticipated therapeutic dose with fine particle dose (FPD) of 300 µg, FPFrecovered of 70%, and FPFemitted of 83%. In addition, the formulations showed a similar volume median diameter of 4.3 µm and span of 1.9. The spray-dried formulations were stable even after conditioning and exposing to different relative humidity points as ivermectin remained amorphous with the predominantly crystalline lactose. Thus, an inhalable and stable dry powder of ivermectin with lactose crystals was successfully formulated. In chapter 4, the pharmacokinetic profile (PK) and local safety of inhaled dry powders of ivermectin with lactose were investigated in healthy mice. Female BALB/c mice received the spray-dried formulation of ivermectin by intratracheal administration at high (3.15 mg/kg) or low doses (2.04 mg/kg). Plasma, bronchoalveolar lavage fluid (BALF), lung, kidney, liver, and spleen were collected at predetermined time points up to 48 hr and analysed for PK. Histological evaluation of lungs was used to examine the safety of the formulation. Inhalation delivery of the dry powder formulation of ivermectin showed improved pharmacokinetic performance as it avoided protein binding issue encountered in systemic delivery and maintained a high exposure above the in vitro antiviral concentration in the respiratory tract for at least 24 hours after administration. The local toxicity was mild with less than 20% of the lung showing histological damage at 24 hr, which resolved to 10% by 48 hr. The major findings and conclusions from the previous chapters were summarised in chapter 5. In addition, future directions are discussed.