Stability indicating RP-HPLC method development and validation for the determination of pyrimethamine in an oral paediatric suspension

The aim of this study is to validate a high-performance liquid chromatography (HPLC) – UV assay method for a stability assay of an oral suspension of PYR developed for newborns. Analyses were performed by HPLC with a Kinetex Coreshell C18 column, thermostated at 40°C, coupled to a diode array (λ=230 nm, 280 nm, scan from 190 to 400 nm) with an acetonitrile/methanol/KH₂PO₄ buffer gradient (pH 3, 10 mM). A forced degradation study was performed to validate the stability-indicating character. PYR was subjected to acidic (pH 2) and basic (pH 12) hydrolysis stress, thermal hydrolysis stress at native pH (60°C and 4°C), H₂O₂ oxidation stress (3 % and 15 %) and photolysis stress (UV and natural light) at day 0, 3 and 16. Linearity, specificity, precision, and accuracy of this assay method have been tested. Forced degradation tests demonstrated the stability indicator character of the method and showed that PYR was very sensitive to oxidation, sensitive to light (UV) and insensitive to hydrolysis (thermal and pH). The method of quantification was linear, specific, precise, and accurate according to ICH recommendations. A stability study on the formulation under development will be carried out with this HPLC – UV method.