Development and application of a simple and robust liquid chromatography-mass spectrometry method for determination...

To establish a method of measuring diclazuril concentration from kiwi (Apteryx spp.) faeces using liquid chromatography-mass spectrometry (LC-MS), to non-invasively determine drug disposition.

Daily faecal samples were collected from healthy 3- to 4-week-old captive-reared North Island brown kiwi (Apteryx mantelli) chicks (n = 6) following a single dose of 5 mg/kg bodyweight of the anticoccidial drug diclazuril for a period of 5 days. Daily pooled samples from each bird were prepared for LC-MS using dispersive solid phase extraction to isolate the drug for analysis. The LC-MS assay was validated using linear regression, inter-day and intra-day variation, and recovery analysis. Pharmacokinetic parameters were calculated using non-compartmental analysis.

Pharmacokinetic parameters were able to be established for diclazuril from the faeces of five kiwi chicks (three male, two female). Samples from one chick were too low in drug concentration to be analysed. The standard curve for diclazuril was linear from 4 to 20 ng/mg (r² = 0.9997). The limit of quantification for diclazuril was 1 ng/mL. Extraction recoveries were from 76.8% to 96.6%, with intra- and inter-day coefficients of variation of 3-3.9% and 5-8.7%. The mean peak concentration of diclazuril in faeces was 260.46 (SD 335.77) ng/mg, and the highest concentration of diclazuril was detected at 24 hours following administration. Mean faecal concentrations declined to 2.29 (SD 1.13) ng/mg on Day 5 after administration, with a mean elimination half-life of 23.82 (SD 13.69) hours. The elimination constant was 0.0377 (SD 0.02) h^-1, consistent with the previously reported rate in kiwi plasma.

This study establishes that the quantification of diclazuril in kiwi faeces by LC-MS is robust and reliable. Diclazuril exhibits a prolonged elimination half-life in kiwi faeces, supporting its potential for sustained coccidiostatic activity.

The methods developed here have the potential to be modified to analyse other target drugs from faeces of birds and can assist in the evaluation of efficacy of drug treatment regimes, in particular for drugs that target infection in the gastrointestinal tract, such as anticoccidials. This non-invasive approach will be especially valuable in wildlife species where establishing plasma pharmacokinetics for drug treatments is challenging and can have significant animal welfare consequences.