ABSTRACT
The administration of alkalinising agents including bicarbonate is of concern to racing authorities because resultant alkalosis may enhance performance and interfere with the detection of drugs in post-race urine. A threshold for total carbon dioxide (TCO2 ) of 36.0 mmol/L in plasma (with action limit of 37.0 mmol/L) has been set. Serial dosing of sodium bicarbonate has gained popularity in human athletes but has not been studied in horses previously. Sodium bicarbonate (200 g per horse) and 60 g of an electrolyte-vitamin complex was administered in 2-L water via nasogastric intubation to five Standardbred horses for three consecutive days (total dose bicarbonate 0.42 ± 0.02 g/kg). Serial blood samples were taken over Days 1-5, with the final day (5) intended to simulate a 'clear day', and TCO2 was analysed. Following the first bicarbonate administration, plasma TCO2 peaked at 6 h (34.8 ± 1.3 mmol/L), returning to baseline by 23 h. On Day 2, four out of the five horses showed a peak greater than 36.0 mmol/L (mean 37.0 ± 2.1 mmol/L). With daily repeated dosing, plasma TCO2 peaked progressively earlier, and by Day 3, the peak occurred at 2 h and concentrations declined more rapidly. On Days 4 and 5, TCO2 levels remained low (<32.1 mmol/L on Day 4 and between 27.0-31.2 mmol/L on Day 5). These studies demonstrate that serial dosing of a 'split dose' of sodium bicarbonate on three consecutive days does not result in the accumulation or carry-over of plasma TCO2 levels beyond the levels observed following a single dose.
