Detection and pharmacokinetics of salbutamol in thoroughbred racehorses following inhaled administration.

This research studied the detection and behavior of the drug salbutamol in the bodies of thoroughbred racehorses after administering it through inhalation.

Methodology

• The researchers conducted the experiment by administering salbutamol sulphate (also known as Ventolin Evohaler) through inhalation to six horses. Each horse received a dose of 0.5 mg of the drug every four hours during the day for a period of 2 days. This resulted in a total dosage of 4 mg.
• Following the drug administration, samples of urine and blood were collected from the horses up to 92 hours afterwards.
• The hydrolyzed plasma and urine samples were then extracted using a technique termed solid phase extraction (SPE).

Technique Development and Analysis

• The researchers successfully developed a sensitive tandem mass spectrometric method during the study, which enabled them to quantify salbutamol levels in plasma and urine. This method permitted a lower limit of quantification (LLOQ) for the drug at 10 pg/mL in both plasma and urine.
• The parent drug was then identified using a technique known as UPLC-MS/MS.
• Interestingly, they found that most of the determined salbutamol concentrations in the plasma, collected after the last drug administration, were below the LLOQ of the analysis method. This implies these concentrations could not be used for plasma pharmacokinetic (PK) analysis—study of how a drug is absorbed, distributed, metabolized and eliminated by the body.

Urine PK Analysis and Detection Times

• Alternatively, the urine PK analysis showed a half-life time in line with the expected duration of the drug’s pharmacological effect.
• Additionally, the research team managed to estimate an average steady-state urine concentration of salbutamol by averaging measurements taken during the dosing period. This value, calculated to be 9.6 ng/mL, was utilized to estimate an effective urine concentration that could serve as an indicator of effective lung concentration in the horses.
• The researchers also calculated a range of detection times from this estimated urine concentration value using a range of safety factors.

This research on the pharmacokinetics and detection of salbutamol in racehorses provides valuable insight into how much of the drug is absorbed, metabolized, and ultimately, how long it can be detected in the horses’ bodies after administration. This could have practical implications in the field of equine sports medicine and doping control.