Original Scientific Article
Determination of free doxycycline concentrations in the plasma and milk of sheep and in the plasma of rabbits by using the HPLC method
Rositsa Mileva*

Mac Vet Rev 2019; 42 (2): 123 - 130


Received: 15 November 2018

Received in revised form: 11 March 2019

Accepted: 26 March 2019

Available Online First: 09 June 2019

Published on: 15 October 2019

Correspondence: Rositsa Mileva, rossi_bu@abv.bg


A fast and sensitive HPLC method was validated in order to analyze doxycycline in plasma and milk of sheep and in plasma of rabbits. The samples were processed with trifluoroacetic acid (TFA). After the centrifugation step, a supernatant containing extracted doxycycline and internal standard oxytetracycline was injected into the HPLC system with PDA detection. The method showed linearity in the range of 0.125 - 2.5 μg/mL for ovine plasma, 0.125 – 5.0 μg/mL for ovine milk, and 0.125 – 1 μg/mL for rabbit plasma. The inter-assay precision varied between 5.69 – 13.55 %. Values for intraassay precision were between 0.62 – 8.67 %. Accuracy was higher than 90% in all of the tested concentrations in the three types of biological matrices. The mean extraction recovery was higher than 90 % for all matrices. In order to handle only with free drug concentrations, microfiltration of standard solutions with low (0.25mg/mL), medium (0.5mg/mL) and high (1.0mg/mL) concentration was performed. A percentage for correction of the quantified doxycycline was calculated. The most significant adjustments should be made at the low concentrations. The correction for rabbit plasma is 24.63±5.03%, for ovine plasma is 20.10±8.01% and for milk –16.68±0.04 %. This method can be used for routine determination of doxycycline concentrations for pharmacokinetic studies and further dosage adjustment.

Keywords: free doxycycline concentration, HPLC analysis, sheep plasma and milk, rabbit


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© 2019 Mileva R. This is an open-access article publishedunder the terms of the Creative Commons Attribution License whichpermits unrestricted use, distribution, and reproduction in any medium,provided the original author and source are credited.

Conflict of Interest Statement

The authors declared that they have no potential conflict of interest with respect to the authorship and/or publication of this article.

Citation Information

Macedonian Veterinary Review. Volume 42, Issue 2, Pages 123-130, e-ISSN 1857-7415, p-ISSN 1409-7621, DOI: 10.2478/macvetrev-2019-0016, 2019