Bioavailability of ascorbic acid in horses

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Abstract
Snow, D.H. & Frigg, M. Bioavailability of ascorbic acid in horses. J. vet. Pharmacol. Therap. 13, 393–403.The bioavailability of ascorbic acid administered to thoroughbreds by intramuscular injection was investigated. For intramuscular injection two preparations were studied, and the percentage bioavailability up to 24h of 10g of ascorbic acid was 95%±22 in four horses and 60% in two horses with preparations A and B, respectively. Bioavailability at 24h in three horses injected subcutaneously with 10g of preparation B was 82%. Intramuscular injection of both preparations was apparently well tolerated while subcutaneous injection of preparation B (pH 6.0) was associated with marked irritancy. In a cross‐over trial in seven thoroughbreds the effect of 13 or 15 days of oral administration of crystalline ascorbic acid (20g) or ascorbyl palmitate (47g) on plasma ascorbic‐acid concentrations was investigated. Marked differences occurred between individuals. There was a greater increase in plasma ascorbic‐acid concentration with ascorbyl palmitate compared to ascorbic acid at 6 and 24h following administration. In two horses there was no increase in plasma ascorbic acid at 6h following either oral preparation. The finding of lowered plasma ascorbic‐acid concentrations following a period of supplementation warrants further investigation to assess its significance. D. H. Snow, 18 Rowe Street, Roseville Chase, 2069 NSW, Australia.