Dynamic detection of non-protein-bound strychnine and brucine in rabbit muscle and synovial fluid after topical application of total Strychnos alkaloid patches.

Semen Strychni, a known toxic drug in Chinese pharmacopoeia, is notable for its therapeutic effects on local muscle and joint pain. However, oral administration can be risky. Topically administered drugs accumulate in the topical muscles and knee joints without any major increase in plasma levels; only non-protein-bound drugs in the biological fluids of target tissues are effective for therapeutic effects. A sensitive and rapid ultra performance liquid chromatography - mass spectrometry (UPLC-MS) method coupled with a microdialysis technique was developed to determine the non-protein-bound strychnine (Str) and brucine (Bru) in rabbit muscle and synovial fluid microdialysate. The UPLC separation was carried out using a 1.7μm BEH C18 column (50 mm × 2.1 mm) with a mobile phase consisting of methanol: water (29.5:70.5, v/v) with 0.1% formic acid and 20 mM ammonium acetate in water. The method was validated at concentrations ranging from 0.58 ng/ml to 467.20 ng/ml for Str and from 0.42 ng/ml to 422.40 ng/ml for Bru. Intra-day and inter-day accuracy ranged from 99.1% to 103.2% for Str and from 95.8% to 108.8% for Bru with intra-day and inter-day precision within 9.7%. The proposed method was successfully applied to determine non-protein-bound Str and Bru, and the analysates concentration remained stable in rabbit muscle and synovial fluid after topical application of total Strychnos alkaloid patches, which indicated that total Strychnos alkaloid patches could substitute for the traditional oral administration of Semen Strychni.