EVALUATION OF SODIUM PYRIDINETHIONE 13 Further evidence that excretion of the drug took place in preference to tissue concentration was gained when the ratio of urine, serum, liver and kidney levels were determined for the six groups of rabbits (Table IV). Table IV. Ratio of a•S-labelled material in urine, serum, liver, kidney Exposure time (h) Location 4 8 12 16 20 24 Urine 8.7 11.7 16.1 24.4 33.1 44.2 Serum 1.0 1.0 1.0 1.0 1.0 1.0 Liver 1.8 1.3 1.4 1.5 1.5 2.0 Kidney 0.5 0.4 0.3 0.3 0.4 0.6 The only amounts changing significantly with extended exposure were the urine levels. Metabolic rate of sodium pyridinethione In accordance with the method outlined, urine and tissues were sub- jected to a chromatographic and spectrophotometric analysis with the aim of identifying the metabolites following percutaneous absorption. Table V records the Rf values for reference compounds and components of urine and tissues with ass activity. Table V shows that the urine and tissues examined contained pyridine-N- oxide 2 sulphonic acid the urine and liver also had detectable levels of Table V. Rf values for reference compounds and components of urine and tissues with a•S activity Reference compounds and materials examined Solvent systems Isobutanol 1' Propanol 4: Ammonia 2 N-Butanol 5: Acetic acid 1: Water 2 Sodium pyridinethione Pyridine-N-oxide 2 sulphonic acid Urine components Tissue components: Liver Kidney Lung Brain Heart 0.42 0.42 0.43 0.25 0.27 0.26 0.26 0.25 0.24 0.26 0.85 0.86 0.86 0.18 0.16 0.17 0.16 0.16 0.16 0.17

14 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS sodium pyridinethione. Elution of the chromatographic paper spots with Rf value of 0.25 for spectrophotometric analysis, provided uv spectra with absorption peaks at wavelengths 217 and 265 mgm which was in agreement with the reference compound pyridine-N-oxide 2 sulphonic acid. Those spots with an Rf value of 0.42 absorbed at wavelengths 243 mgm, 282 mgm and 332 mgm in the uv spectrum confirming that the parent compound was excreted unchanged. Finally, the urine was assayed radiometrically before and after chloroform extraction to separate sodium pyridinethione from the aqueous soluble acid. Results from this separation indicated pyridine-N- oxide 2 sulphonic acid to be the major excretory product along with sodium pyridinethione in an 8:1 ratio. These findings regarding the metabolic fate of sodium pyridinethione in the rabbit support the conclusions of Min et al. (11) following a derreal study on rats and monkeys. However, there was no evidence to support the findings of Kabacoff and his co-workers (12) whose studies proposed a conjugated mechanism with glucuronic acid as the major metabolic pathway for intravenously-administered sodium pyridinethione to rabbits. SUMMARY Sodium pyridinethione was lethal to rabbits at 1 g kg 4 by i.v. infusion, the prime cause of death being respiratory failure. Respiratory and cardio- vascular effects were evident at 50 mg kg -•, a systemic dose level that was not approached by derma! application of 110 mg kg 4 to intact skin. From the findings on absorption, distribution and excretion there appeared to be no tissue concentration and the major proportion of material was excreted via the urine. The metabolic fate of sodium pyridinethione following per- cutaneous absorption in rabbits appears to be oxidation to pyridine-N- oxide-2-sulphonic acid. ACKNOWLEDGMENTS The authors gratefully acknowledge the advice given by Dr Basil Northover in planning and carrying out these studies thanks are also due to Olin Corporation, New Haven, Connecticut, and to Beecham Products, Brentford, England, for generous financial support. (Received: 6th June 1974)