10.22376/ijpbs.2019.10.1.p1-12 Volume 11 Issue 2 2020 (April-June) Tecovirimat prevents viral egression from the cell by inhibiting protein P37 or its ortholog in orthopox viruses. This results in blocking viral dissemination in hosts. A simple, specific, sensitive LC/MS/MS method for the quantization of Tecovirimat in spiked plasma with Penciclovir as an internal standard by using UPLC-ESI-MS/MS. The chromatographic separation was achieved with 10 mM Ammonium acetate buffer (pH 4.0): Methanol: Acetonitrile (20:40:40% v/v/v) using the CORTECS C18, 90 Å, 2.7 µm, 4.6 mm X 150 mm analytical column. The total analysis time was 4.0 min and flow rate was set to 0.5 ml/min. The mass transitions of Tecovirimat and Penciclovir obtained were m/z 377.1/188.1 and 254.1/152.1. The method was fully validated for its sensitivity, selectivity, accuracy and precision, matrix effect, recovery, and stability. The curve indicates correlation coefficient ( lessThan i greaterThan r lessThan sup greaterThan 2 lessThan /sup greaterThan lessThan /i greaterThan ) was superior than 0.998 with linear range of 0.03-48.0 n.g/m.L. The intra- and inter-day precision and relative error were all within 10 %. Despite achieving high mean recovery ( greaterThan 80 %), no interference peaks or matrix effects were observed. An accurate and reproducible novel bio-analytical method was fabricated for estimation of Tecovirimat in plasma samples by UPLC-ESI-MS/MS lessThan i greaterThan will be used for regular analysis and appropriate for therapeutic drug monitoring. lessThan /i greaterThan The method permits laboratory scientists with access to the appropriate instrumentation to perform rapid Tecovirimat determination. Banothu Bhadru, V.Venkata Rao and Suryadevara Vidyadhara Tecovirimat; Spiked human plasma; UPLC-ESI-MS/MS; Bioanalysis. 24-32