## 5 From PBTZ169 to Macozinone: First Results of the Clinical Studies
The second part of the study involved the safety, tolerability, and pharmacokinetics of PBTZ169 in 80 mg capsules in healthy volunteers who received 1280 mg daily in fed conditions, for 14 days. In total, 60 healthy volunteers (10 in each cohort) received the investigational drug and completed the study according to the protocol [22]. During these clinical trials, safety and tolerability of PBTZ169 in capsules were studied, including assessment of adverse effects, vital signs (blood pressure, heart rate, body temperature, respiratory rate), laboratory and instrumental parameters (hematology, blood chemistry, coagulation parameters, urinalysis, electrocardiography) and physical examination. In these studies (NCT03036163 and NCT04150224), good tolerability and favorable safety profile were demonstrated for PBTZ169 in the studied dose range. One event of dose-limiting toxicity (increase in the glucose level 2 hours after the drug administration) was documented after a single 80 mg dose of PBTZ169 in 40 mg capsules (NCT03036163). There were no other cases of dose-limiting toxicity in healthy volunteers in these studies. There were no serious adverse effects. There was no increase in the frequency of adverse effects associated with increased dose or with the administration regimen (fasting or in fed conditions), for single or multiple doses. Changes in some mean vital signs, laboratory, instrumental parameters, or physical examination data were not associated with a trend to increase with a growing dose [22]. Efficacy of PBTZ169 based on the early bactericidal activity (EBA), was studied in a Phase 2a clinical trial (PBTZ169-A15-C2A-1, NCT03334734) [27] by Nearmedic Plus LLC in patients with newly diagnosed smear-positive tuberculosis of the respiratory tract, with preserved sensitivity to isoniazid and rifampicin. Although the trial was terminated early because of slow enrollment, relevant  
Figure 3: Pre-clinical and clinical development of macrozinone. information was obtained from 16 patients who participated in the study. The drug was administered in 80 mg capsules, orally as a monotherapy for 14 days, as follows: 160 mg/day dose--4 patients; 320 mg/day dose--4 patients; 640 mg/day dose--7 patients. Isoniazid tablets were used as a control treatment at 600 mg/day dose in one patient. The primary efficacy of the treatment was evaluated by two methods:  
(i) According to quantification of colony forming units in sputum by its inoculation on agar plates, in the group of patients receiving PBTZ169 in the 640 mg dose, EBA 0-14 (mean of the two measurements) and EBA 0-14 (the higher of the two measurements) were 0.071 log10 cells/ml/day [95% confidence interval (CI) 0; 0.143] and 0.080 log10 cells/ml/day [95% CI 0.002; 0.158], respectively. (ii) According to quantitative polymerase chain reaction, in the same group of patients, EBA 0-14 (mean of the two measurements) and EBA 0-14 (the higher of the two measurements) were 0.098 log10 cells/ml/day [95% CI 0.021; 0.175] and 0.100 log10 cells/ml/day[95% CI 0.021; 0.180], respectively. Thus, the analysis of efficacy based on the data obtained in a pilot Phase 2a clinical study revealed statistically significant early bactericidal activity of PBTZ169 14 days after the start of monotherapy (EBA0-14) in the group of PBTZ169 with the 640 mg dose. During this clinical study, there were no cases of death or severe adverse effects related to the PBTZ169. No adverse effects were considered as definitely related to the drug and, at the study completion, all adverse effects were resolved. There was no increase in adverse effects frequency with growing dose [22]. During the clinical studies it was confirmed that PBTZ169 after single, double, or multiple doses was detectable in the blood plasma of all volunteers and patients who had received the drug. However, it should be noted that pharmacokinetic studies in animals and in healthy volunteers (in Phase 1 clinical studies) demonstrated that PBTZ169, being more soluble in an acidic environment, is absorbed primarily in the stomach.