Results
Sixty-six adult patients with history of confirmed COVID-19 and olfactory dysfunction persisted more than 90 days after SARS-CoV-2 negative testing were enrolled in this prospective study. The age of the patients ranged from 18 to 55 years. There were 38 females and 28 males. The complete characteristics of the patients were described in Table 1. Fisher’s exact probability test was used to assess the sample size. Non-significant difference in the frequency of smoking between the sodium chloride group and the DTPA group (5/28 vs. 4/29; p = 1.00). Differences in the frequency of comorbidities were also assessed and the results were not significant between the sodium chloride group and the DTPA group, as shown in Table 1.
Intra-nasal administration of DTPA had the ability to form a calcium-DTPA complex and decreased the concentrations of calcium cations in the mucus of the participants. DTPA had the selective ability to sequester calcium cations at an optimized pH of 8 and form stable complex products. The schematic reaction pathway for the reaction of DTPA with calcium cations was shown in Figure 2.
Olfactory performance was evaluated using the Sniffin’ Sticks test before and after treatment with topical sodium chloride or DTPA. T, D, I and TDI were measured in each participant before treatment and 1 month later. Mean T, D, I and TDI values before and after topical sodium chloride and DTPA treatment for patients were shown in Table 2. The TDI values were compared with the reported reference values. The mean values of the TDI scores were calculated and presented in Table 2. Regarding to the olfactory assessed score of DTPA group, 27 patients (84.38%) showed an improved olfactory function and 5 patients (15.63%) did not show improvement. This may be due to topical nasal sprays generally have quite variable compliance and delivery efficiency, especially to the olfactory cleft, so one would expect some subjects with little to no response even to a highly efficacious drug. The results showed that the mean ± SD of the TDI value before and receiving sodium chloride was 10.87±1.24 and 10.93±1.09, respectively, Table 2. While, the mean ± SD of the TDI value before and after receiving DTPA was 11.75±1.22 and 20.39±3.25, respectively, Table 2. The results indicated non-significant improvement in patients receiving sodium chloride. On the other hand, there was a significant improvement in patients receiving DTPA with clinical change from functional anosmia to hyposmia.
The concentration of calcium cations was quantitatively determined in the nasal mucus of all patients. A selective electrode made of carbon paste was developed for the electrochemical determination of calcium cations. First, the values of electromotive force were measured in a calcium concentration range of 100 to 0.001 mM to obtain a calibration diagram relating the values of electromotive force to the negative logarithmic value of calcium cation concentration. The designed sensor exhibited a near Nernstian slope of 28.25 mV/decade with a detection limit of 0.0001 mM in a linear range of 100 to 0.001 mM calcium cation concentration. The concentrations of calcium cations in nasal secretions were successfully determined using the developed electrode. The mean ± SD of calcium cation concentration (mM) before and after receiving sodium chloride was 38.39±3.04 and 37.06±2.64, respectively, Table 2. Also, the mean ± SD of calcium concentration (mM) before and after receiving DTPA was 37.54±2.06 and 24.39±4.52, respectively, Table 2. The results showed a significant decrease in calcium concentration in the patients received DTPA.
Statistical analysis, paired t test, was used to compare the means and standard deviations of the TDI values for the sodium chloride or DTPA groups before and after treatment. Comparison of the results for the DTPA group revealed a significant difference with a relevant clinical improvement in olfactory performance, t (32) = 16.60,p < 0 .00001. Similarly, comparison of the results for the sodium chloride group revealed non-significant difference without clinical improvement in olfactory performance, t (32) = 0.42,p =0.338. Also, an unpaired t test was used to compare mean TDI values after receiving DTPA with TDI values after receiving sodium chloride. The significant difference was indicated, t (39) = 15.76, p < 0 .00001.