Objective—To compare the pharmacokinetics of
penicillin G and procaine in racehorses following IM
administration of penicillin G procaine (PGP) with
pharmacokinetics following IM administration of penicillin
G potassium and procaine hydrochloride (PH).
Animals—6 healthy adult mares.
Procedure—Horses were treated with PGP (22,000
units of penicillin G/kg of body weight, IM) and with
penicillin G potassium (22,000 U/kg, IM) and PH
(1.55 mg/kg, IM). A minimum of 3 weeks was allowed
to elapse between drug treatments. Plasma and urine
penicillin G and procaine concentrations were measured
by use of high-pressure liquid chromatography.
Results—Median elimination phase half-lives of penicillin
G were 24.7 and 12.9 hours, respectively, after
administration of PGP and penicillin G potassium.
Plasma penicillin G concentration 24 hours after administration
of penicillin G potassium and PH was not significantly
different from concentration 24 hours after
administration of PGP. Median elimination phase halflife
of procaine following administration of PGP (15.6
hours) was significantly longer than value obtained
after administration of penicillin G potassium and PH
Conclusions and Clinical Relevance—Results suggest
that IM administration of penicillin G potassium
will result in plasma penicillin G concentrations for 24
hours after drug administration comparable to those
obtained with administration of PGP. Clearance of procaine
from plasma following administration of penicillin
G potassium and PH was rapid, compared with clearance
following administration of PGP. (Am J Vet Res