Determination of acyclovir in horse plasma and body fluids by high-performance liquid chromatography combined with fluorescence detection and heated electrospray ionization tandem mass spectrometry.

The research presents two analytical methods for determining the amounts of the drug acyclovir in horse plasma and body fluids, utilizing high-performance liquid chromatography, fluorescence detection, and tandem mass spectrometry.

Objectives and Methods

• The aim of this research was to introduce two effective methods to measure the concentration of acyclovir in horse plasma and body fluids. Acyclovir is an antiviral drug, and understanding its concentration in the horse’s system can help in optimizing its therapeutic use.
• The first method involved a liquid-liquid extraction on plasma and used high-performance liquid chromatography (HPLC) combined with fluorescence detection to determine the total plasma concentration of the drug.
• The second method introduced a more sensitive method utilizing similar high-performance liquid chromatography, but this time combined with heated electrospray ionization tandem mass spectrometry (LC-HESI-MS/MS) for analyzing both plasma and body fluids.
• The researchers also used a Microcon filter to deproteinize the plasma, which aided in figuring out the unbound concentration of acyclovir.
• Ganciclovir, another antiviral drug, was utilized as an internal standard for comparison during the analysis.

Instruments and Columns Used

• A chromatographic column called Inertsil 5 ODS-3 was used for the HPLC-fluorescence method to separate the components in the plasma.
• For the LC-HESI-MS/MS method, a PLRP-S column was utilized.

Limits of Quantification

• The limits of quantification (LOQs) were specified for both methods. For the total concentration, the LOQ was 50 ng mL(-1) with the HPLC-fluorescence method and 2 ng mL(-1) for the LC-HESI-MS/MS method.
• The LOQ for the unbound concentration was set at 5 ng mL(-1), and more specifically at 2 ng mL(-1) for body fluids.

Findings and Application

• Both these methods, with their established LOQs, were successfully used to conduct pharmacokinetic and clinical studies in horses following intravenous and oral dosage of acyclovir and its prodrug valacyclovir.
• This use and validation suggest these methods might be valuable tools for veterinary medicine, especially in optimizing dosage and treatment plans involving acyclovir and related drugs.