This was achieved by enhancing the solubility of the lipophilic MPTS with the application of FDA approved co-solvents, surfactants and their combinations. The aim of the animal studies was therefore dual as the test not only gave answer
to the in vivo efficacy of the drug candidate drug discovery but would also answer the question of whether the drug shows a fast enough absorption from an intramuscular injection for combating cyanide intoxication. Materials for the conversion test were potassium cyanide (KCN), formaldehyde, ferric nitrate reagent, monobasic sodium phosphate monohydrate and dibasic sodium phosphate anhydrous (VWR International, Suwanee, GA, USA). Methyl propyl trisulfide (50% purity; water solubility = 0.15 ± 0.003 mg/ml) was purchased from Sigma–Aldrich (St. Louis, Missouri, USA), TS were learn more purchased from VWR International (Suwanee, GA, USA). Ethanol, PEG 200, PEG 300, PEG 400, PG (VWR International, Suwanee, GA, USA), Cremophor EL, Cremophor RH40, sodium cholate, sodium deoxycholate, polysorbate 80 (Sigma Aldrich, St. Louis, MO, USA) were used as solubilizers. Cyclohexanone (Sigma–Aldrich, St. Louis, MO, USA) was used as solvent for the GC–MS measurements. KCN solutions (1.0 mg/ml and 3.5 mg/ml) were used throughout the animal studies. 250, 100 and 50 μl Hamilton
Luer-lock syringes (VWR International, Suwanee, GA, USA) were used in the animal studies with 27G 1/2 needles for intramuscular and mafosfamide 25G 1½ needles (VWR International, Suwanee, GA, USA) for subcutaneous injection. In vitro efficacy of MPTS was determined based on
its ability to convert CN to SCN. The method applied was a spectrophotometric measurement of the formed SCN based on the method of Westley (1981) with minor modifications ( Petrikovics et al., 1995). Briefly, 200 μl of various concentrations of SDs, 200 μl of 10 mM phosphate buffered saline, 200 μl of 250 mM KCN and 400 μl of deionized water were mixed. The reaction was incubated for 5 min and was quenched with 500 μl of 15% (v/v) formaldehyde. 1.5 ml of ferric nitrate reagent was added to form a reddish brown complex (Fe(SCN)3) that was quantitatively determined at 464 nm using a spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA). Tests were performed with MPTS and TS at concentrations ranging from 25 mM to 0.156 mM with two fold serial dilutions in between. The solubility of MPTS was determined in co-solvents, surfactants and their combinations. Aqueous solutions of co-solvents and surfactants were prepared at 10%, 25%, 50%, 75%, 90% and 1%, 5%, 10%, 15%, 20% respectively. Based on the solubility enhancing efficacy of the co-solvent/water and surfactant/water systems the most effective excipients were combined into one system forming a co-solvent/surfactant/water system.