Spinal fluid concentrations of mepivacaine in horses and procaine in cows after thoracolumbar subarachnoid analgesia.

The research article discusses a study on the effects of mepivacaine in horses and procaine in cows when administered by thoracolumbar subarachnoid injection, focusing mainly on the concentrations of these drugs in the cerebrospinal fluid (CSF) and the level of analgesia produced.

Study Participants and Administration of Drugs

• The study involved a total of 20 animals: 10 Standardbred horses and 10 Holstein cows.
• Mepivacaine hydrochloride was administered to the horses at an average dosage of 30 mg.
• Procaine hydrochloride was given to the cows with the dosage ranging between 75 mg and 100 mg.
• The drugs were not given orally or intravenously, but were introduced by thoracolumbar subarachnoid injection, directly into the spinal fluid.

Analgesic Effects and Duration

• In both species, analgesia (absence of pain sensation) was produced within 10 minutes of the drug administration.
• In horses, the analgesia extended between spinal cord segments T13 and L3, while in cows, the coverage was from T11 to L4.
• The analgesic effect lasted, on average, for approximately 47 minutes for both species.

Concentration of Local Anesthetics in CSF

• The researchers also determined the “analgesic threshold” – the minimum concentration of the drugs in CSF required to eliminate response to pinprick stimulation.
• For mepivacaine in horses, this threshold was 204.4 +/- 90.3 micrograms/ml in the CSF.
• For procaine in cows, the threshold was slightly lower, at 197.0 +/- 86.1 micrograms/ml in the CSF.

In Vitro Experiments on Drug Hydrolysis

• The researchers conducted in vitro experiments to find out the rates of hydrolysis (chemical breakdown due to reaction with water) of mepivacaine and procaine in the CSF.
• After a duration of 120 minutes at 37°C, the CSF concentrations of both drugs did not change significantly, implying that these drugs are not rapidly broken down in the CSF.

The results suggest a similar analgesic threshold between mepivacaine in horses and procaine in cows, effectively providing a comparative guideline for the administration and expected effects of these two drugs in large animal veterinary medicine.