Gentamicin is an aminoglycoside antibiotic effective against aerobic gram-negative bacteria and is also used in veterinary medicine, particularly in the swine and bovine industries. However, no gentamicin product is currently approved for treating equine diseases in Korea. The present study aims to examine the time-dependent residue of gentamicin in horses after intravenous injection (IV) via jugular vein. The test product was injected at 6.6 mg/kg BW via jugular vein in nine horses. Blood was collected from the horse's jugular vein at 15 minutes, 30 minutes, 1, 4, 8, 12, 24 and 48 hours after injection. To purify the gentamicin in serum, 100μL of 20 mM HFBA in DW, 100 μL of 30% trichloroacetic acid and 300 μL of 20 mM heptafluorobutyric acid (HFBA) in acetonitrile (ACN) were added to 500 μL of serum and supernatant was applied to LC-MS/MS after centrifugation. LC-MS/MS-8050 analyzed the level of gentamicin in serum with Electrospray ionization (ESI) and multiple reaction monitoring (MRM) positive mode. Gentamicin C1 was 478 m/z and product ions were 322, 157 m/z. Precursor ion of Gentamicin C1a was 450 m/z and product ions were 322, 160 m/z. Precursor ion of Gentamicin C2 and C2a was 464 m/z and product ions were 322, 160 m/z. The LC column was a C18 and mobile phase composed of 20 mM HFBA in 5% ACN and 20 mM HFBA in 50% ACN. The amount of gentamicin was calculated by adding four components of gentamicin (C1, C1a, C2 and C2a). The pharmacokinetic parameters of gentamicin were calculated by the WinNonlin program. The Cmax of gentamicin in horse serum was 93 ± 17 μg/kg and the Tmax was 0.25 ± 0 hours. The T1/2 was 6.41 ± 2.32 hours and the CLt was 0.05 ± 0.01L/hr/kg. The Vd was shown as 0.44 ± 0.13 L/kg and the MRT was 1.98 ± 0.55 hours. In conclusion, our data provides useful pharmacokinetic parameters for gentamicin in horses following IV injection.

In Korea, twenty-nine types of microbial pesticides and thirty-two types of naturally occurring materials and chemicals are exempt from MRL (maximum residue level), and fifty types of active ingredients of pesticides are exempt from establishing the acceptable daily intake (ADI) during the pesticide registration process. Out of these materials, twenty-nine types of microbial pesticides and thirty-two types of naturally occurring materials and chemicals are exempt from MRL. Twenty-seven microorganisms and fifteen chemicals are exempt from both ADI and MRL. The European Union exempts the MRL for 148 active pesticide ingredients, and CODEX suggested sixty-three substances as exempt substances from setting the MRL. In Japan, sixty-five types of pesticide components were exempted from MRL. MRL-exempted substances differed depending on the referenced agency, which is presumed to be due to differences in the types of pesticides approved and the approved usage methods in each country. In most countries, MRL exemptions for pesticides are based on toxicity and exposure assessments, and these substances are composed of substances that have a very low risk to the human body or remain in food and are not exposed to the human body and MRLs are exempted based on GAP (good agricultural practice) approved during the licensing process. By referring to the CODEX and the European Union's MRL exemption guidelines, a guideline for evaluating pesticide safety was prepared to determine it as an MRL-exempt substance when setting standards for pesticide residue in Korea. Conclusively, most regulatory agencies decide whether to exempt pesticides from MRL by considering GAP and indications for use during the registration process, and criteria for evaluating exemptions include risk factors, possibility of human exposure and management options.