<p style="text-align:justify"><span style="font-size:12pt"><span style="color:black"><strong><span style="font-size:10.0pt">Background:</span></strong><span style="font-size:10.0pt"> In order to measure the plasma levels of Losartan and Bosentan, a sensitive Reverse Phase-High Performance Liquid Chromatography (RP-HPLC) technique was developed.</span></span></span></p> <p style="text-align:justify"><span style="font-size:12pt"><span style="color:black"><strong><span style="font-size:10.0pt">Methods:</span></strong><span style="font-size:10.0pt"> To compare bioavailability, the Area Under the Curve (AUC), peak plasma concentration (Cmax), and time to Cmax (Tmax) were employed. The standard curve (150-2400 <em>ng/ml</em>) was linear (R²=0.999), relative errors were between 2.4 to 10.05% and the coefficient of variation (CV%) ranged from 1.52 to 10.88. A single dosage (test and reference) was used for the <em>in vivo</em> investigation, which involved 16 healthy individuals.</span></span></span></p> <p style="text-align:justify"><span style="font-size:12pt"><span style="color:black"><strong><span style="font-size:10.0pt">Results:</span></strong><span style="font-size:10.0pt"> The AUC0-48, AUC0-, Cmax, and Tmax of the test and reference had no statistically significant differences. The C_max and 95% confidence intervals of the ratio of C_max of the two formulations were 0.93-0.96 and 97.6-135%, respectively. </span></span></span></p> <p style="text-align:justify"><span style="font-size:12pt"><span style="color:black"><strong><span style="font-size:10.0pt">Conclusion:</span></strong> <span style="font-size:10.0pt">Therefore, it was established that </span><span style="font-size:10.0pt">generic Bosentan was equivalent to Bosentan from Actelion and that both medications could be regarded as equally effective in clinical settings. The blood level of Bosentan could be measured using this straightforward procedure in all hospital laboratories.</span></span></span></p>