**5. Discussion**

This systematic review included 14 articles relating to the e fficacy and safety of LPV/RTV in COVID-19 patients, with a total of 9036 patients included, and only eight articles, that comprised 8438 patients had findings on the e fficacy and safety of LPV/RTV alone or in combination with standard care ± interferons/antiviral treatments compared to other therapies in the treatment of COVID-19, were deemed legible for quantitative synthesis (meta-analysis) [26–29,32–34,36].

In terms of virological cure, three studies reported less time in days for LPV/RTV arm (*n* = 171) compared with no antiviral therapy (conventional) (*n* = 117); however, the overall e ffect was not significant (mean di fference = −0.81 day; 95% CI, −4.44 to 2.81; *p* = 0.66), similarly the virological cure for LPV/RTV alone (*n* = 127) versus the umifenovir arm (*n* = 87) (*p* = 0.37), or LPV/RTV versus umifenovir plus LPV/RTV (*p* = 0.31) [26,27,32–34,36].

Two studies reported no significant e ffect on time to temperature normalization for LPV/RTV arm (*n* = 93) versus umifenovir arm (*n* = 71) (OR = 0.87 day; 95% CI, 0.42 to 1.78; *p* = 0.70, *I* 2 = 0%); or alleviation of cough duration (*p* = 0.69) [27,32]. The total number of cough days was found to be lower in the LPV/RTV arm compared with the umifenovir arm or no antiviral therapy (conventional) arm after 7 days of treatment; however, the overall e ffect was found to be not significant [27,32]. Although a favorable therapeutic e ffect for umifenovir was observed in a small cohort study when the drug was combined with LPV/RTV treatment in (*n* = 16) COVID-19 patients rather than LPV/RTV alone (*n* = 17) [38]; it should be noted that the treatment of LPV/RTV alone groups (*n* = 127) versus umifenovir plus LPV/RTV groups (*n* = 69) did not reveal any significant mean di fference between the two groups in terms of virological cure at day seven [26,32,37]. In another study that involved 81 COVID-19 patients, the umifenovir treatment group had a longer hospital stay than patients in the control group (13 days (IQR 9–17) vs. 11 days (IQR 9–14), *p* = 0.04) [39]. Of note, umifenovir, which is branded as Arbidol ®, has a wide antiviral activity against RNA and DNA viruses, is licensed in Russia and China for the treatment and prophylaxis of influenza and recommended for treatment of MERS-CoV, was investigated in SARS-CoV, and is currently being trialed in COVID-19 patients [40].

In terms of CT evidence for radiological progression of pneumonia/lung damage, fewer patients exhibited radiological progression in the LPV/RTV arm compared with the umifenovir arm or no antiviral therapy (conventional) arm after 7 days of treatment, this e ffect was not significant (*p* = 0.59), and similarly, with LPV/RTV (*n* = 71) versus no antiviral therapy [27,32].

It is worth mentioning that initiating therapy earlier is known to be more e ffective [41], since systemic hyperinflammation rather than viral pathogenicity dominates later stages of SARS-CoV-2 infection. Although patients in five of the studies [15,27,30,31,34] included in our review were administered LPV/RTV early in the infection (median of <7 days); LPV/RTV therapy was not found to be totally e ffective.

In terms of safety, this study found greater adverse events reported in the LPV/RTV arm versus no antiviral treatment (conventional) or umifenovir, respectively. Adverse events associated with LPV/RTV alone or in combination with other medicines were reported in COVID-19 patients, and were typically gastrointestinal (GIT) in nature, including nausea, vomiting, and diarrhea [32]; nevertheless, serious GIT adverse drug reactions such as acute gastritis and GIT bleeding and acute kidney injury (*n* = 3) were also reported [32]. It was reported that most ADRs associated with LPV/RTV in combined groups of medicines are resolved within three days of drug initiation [30].

To address the e fficacy and safety of LPV/RTV combined with other drugs in patients with COVID-9, LPV/RTV plus IFN combination in addition to ribavirin was found to be superior and safer than LPV/RTV alone by shortening the time to negative nasopharyngeal swab compared to the LPV/RTV arm alone [31]. Additionally, a combined treatment regimen of LPV/RTV plus IFN and umifenovir resulted in a shorter time by normalizing body temperature and turning PCRs negative compared to the umifenovir plus IFN arm with reasonable safety profile [37]. However, the use of LPV/RTV plus IFN combination resulted in less therapeutic responses on COVID-19 in terms of viral clearance and chest CT changes compared to the favipiravir plus IFN combination. Favipiravir arm patients had fewer AEs than patients in the LPV/RTV arm [30]. Additionally, there was no significant di fference in average PCR negative conversion times among IFN plus LPV/RTV or IFN plus LPV/RTV plus ribavirin treatment arms [35]. The combination of LPV/RTV, in addition to standard care, or standard care alone revealed no di fference in the time to clinical improvement, duration of hospitalization, initiation of invasive mechanical ventilation and death [15,28,29]. A serious case of elevated alanine aminotransferase (ALT) was reported [28], GI AEs were more common in the LPV/RTV group and treatment was stopped early in 13.8% because of AEs [15].

In a recent systematic review that included 41 studies which considered therapeutics for COVID-19, LPV/RTV was found to be the third therapy associated with positive outcomes (54.9%) with less negative outcomes (12.3%) compared to systemic corticosteroids (21.3%), remdesivir (16.9%), moxifloxacin (13.4%) and oseltamivir (12.5%) [2]; however, further controlled studies were needed to draw a valid conclusion. Antiviral ine ffectiveness of LPV/RTV against SARS-CoV-2 in the studies included in our review was justified by the necessity to give the drug at a daily amount higher than 800 mg/200 mg; as an in vitro analysis identified antiviral activity of LPV/RTV against SARS-CoV-2 with a half-maximal effective concentration (EC50) of 16.4 μg/mL [42]. However, there is a potential to intoxicate the patient, because high doses of LPV/RTV may lead to delayed ventricular repolarisation (QT prolongation) [7]. Thus, it might be logical to argue that there is a need to determine the e ffective and safe dose of LPV/RTV against the SARS-CoV-2 virus for better clinical benefit [13].

It is important to consider drug concentrations at the site of infection, and currently, the lack of robust lung penetration data is an important gap that exists for many agents being considered for repurposing. In the case of LPV/RTV, lung penetration is complex and not well understood; however, typically it is the plasma-free fraction that is available to penetrate into tissues. Therefore, given its potency, lung penetration of LPV/RTV would have to be high to provide concentrations in the therapeutic range [43]. The antiviral activity in vivo is estimated by calculating the ratio of unbound drug concentrations achieved in the lung at the administered dose to the in vitro EC50 (RLTEC) [44]. Even though the majority of the observed total LPV/RTV plasma concentrations in COVID-19 patients were above the published EC50 for SARS-CoV-2 [42], boosted LPV/RTV is unlikely to attain su fficient effective levels in the lung to inhibit the virus. Indeed, the largest trials of RECOVERY [28] and SOLIDARITY [29] found LPV/RTV had little or no e ffect on overall mortality, initiation of ventilation and duration of hospital stay in hospitalized patients.

There is uncertainty about the optimal approach to treat hospitalized COVID-19 patients. Management approaches are based on limited data and evolves rapidly as clinical data emerge. For patients with non-severe disease, care is primarily supportive, with close monitoring for disease progression. Remdesivir is suggested in hospitalized patients with severe disease (i.e., they have hypoxia) but who are not ye<sup>t</sup> on oxygen [45,46]. For patients who are receiving supplemental oxygen (including those who are on high-flow oxygen and noninvasive ventilation), low-dose dexamethasone and, if available, remdesivir is/are suggested [47,48]. However, the optimal role of remdesivir remains uncertain, and some guidelines panels (including the WHO) sugges<sup>t</sup> not using it in hospitalized patients because there is no clear evidence that it improves patient-important outcomes for hospitalized patients (e.g., mortality, need for mechanical ventilation). In general, use of LPV/RTV for treatment of SARS-CoV-2 in hospitalized patients is not suggested as several trials have failed to prove e fficacy [15,28,29]. Evidence as to whether LPV/RTV is beneficial in outpatients with mild or moderate severity COVID-19 infection is lacking; therefore, use of LPV/RTV is suggested in outpatients only in the context of a clinical trial.

Vaccines to prevent COVID-19 infection are considered the most promising approach for controlling the pandemic. COVID-19 vaccine development is occurring at an unprecedented pace. Several di fferent platforms are being utilized to develop COVID-19 vaccines such as: inactivated virus or live-attenuated virus platforms (traditional methods); recombinant proteins and vector vaccines (newer methods); and RNA and DNA vaccines (methods never previously employed in a licensed vaccine) [49]. Several vaccine candidates have demonstrated immunogenicity without major safety concerns in early-phase human trials [50]. Two mRNA vaccine candidates have also been reported to have approximately 95% vaccine e fficacy [51,52]. AstraZeneca's Oxford coronavirus vaccine is 70% e ffective on average, data shows, with no safety concerns [53]. Importantly, the AstraZeneca vaccine can be distributed and administered within existing healthcare systems, as it can be stored, transported and handled in normal refrigerated conditions for at least six months, the company said. The vaccine will also be cheaper than rival coronavirus vaccines from makers Pfizer and Moderna [53].

Since disease resulting from SARS-CoV infection is driven by both virus and host immune response factors, depending on the stage of the disease progression, early initiation of antiviral therapy, and/or holistic combination therapies will likely be needed to diminish virus replication, immunopathology, and/or promote repair and restoration of pulmonary homeostasis [54]. Until su fficient evidence is available, the WHO has warned against physicians and medical associations recommending or administering unproven treatments to patients with SARS-CoV-2 or people self-medicating with them.

The key limitations of this study were the limited number of clinical studies investigating the efficacy and safety of LPV/RTV in combination with a limited number of participants. Another limitation is the inability to perform any type of meta-analysis specifically for the results of e fficacy and safety of using LPV/RTV in combination with other agents versus no antiviral therapy (conventional therapy) or control because of the large methodological di fferences. Despite these limitations, this systematic review provided valuable insight into the e fficacy, safety, and clinical outcomes of LPV/RTV alone or with other antiviral medications.
