Doxycycline Residues Research Articles

Investigation of doxycycline residues in bones after oral administration to broiler chickens.

Chicken bones, a by-product of the poultry industry, can directly or indirectly enter the food chain. Bone meal and bone products could be sources of many contaminants. Considering the wide range of uses made of bones in the culinary and food industries, this material needs to be safe and antibiotic residue-free. To determine if such is the case, the concentration of doxycycline in chicken bones was investigated, this antimicrobial being one of the most commonly used in poultry production. Ross 308 broilers were grouped into three experimental and one control group. Doxycycline was administered in drinking water at therapeutic and sub-therapeutic doses, as well as via spray treatment. The concentration of doxycycline in bones was determined post slaughter by ultra-high performance liquid chromatography-tandem mass spectrometry. Doxycycline was quantified at 135 μg/kg 22 days after the last day of antibiotic administration at therapeutic doses; 2,285 μg/kg after sub-therapeutic treatment for 27 days and 9.62 μg/kg 22 days after the end of spray application. High concentrations and long persistence of doxycycline in bones were found in this study. Doxycycline can contaminate all bone-derived products in the food and fertiliser industries.

Rapid discrimination and ratio quantification of mixed antibiotics in aqueous solution through integrative analysis of SERS spectra via CNN combined with NN-EN model

IntroductionAbusing antibiotic residues in the natural environment has become a severe public health and ecological environmental problem. The side effects of its biochemical and physiological consequences are severe. To avoid antibiotic contamination in water, implementing universal and rapid antibiotic residue detection technology is critical to maintaining antibiotic safety in aquatic environments. Surface-enhanced Raman spectroscopy (SERS) provides a powerful tool for identifying small molecular components with high sensitivity and selectivity. However, it remains a challenge to identify pure antibiotics from SERS spectra due to coexisting components in the mixture. ObjectivesIn this study, an intelligent analysis model for the SERS spectrum based on a deep learning algorithm was proposed for rapid identification of the antibiotic components in the mixture and quantitative determination of the ratios of these components. MethodsWe established a water environment system containing three antibiotic residues of ciprofloxacin, doxycycline, and levofloxacin. To facilitate qualitative and quantitative analysis of the SERS spectra antibiotic mixture datasets, we developed a computational framework integrating a convolutional neural network (CNN) and a non-negative elastic network (NN-EN) method. ResultsThe experimental results demonstrate that the CNN model has a recognition accuracy of 98.68%, and the interpretation analysis of Shapley Additive exPlanations (SHAP) shows that our model can specifically focus on the characteristic peak distribution. In contrast, the NN-EN model can accurately quantify each component's ratio in the mixture. ConclusionIntegrating the SERS technique assisted by the CNN combined with the NN-EN model exhibits great potential for rapid identification and high-precision quantification of antibiotic residues in aquatic environments.

Efficient removal of doxycycline by MnNb2O6/sulfite process: Response surface methodology optimization and mechanism analysis

Sulfate radical-based advanced oxidation process could efficiently remove many emerging contaminants from wastewater. Considering the unique properties of MnNb2O6, an efficient MnNb2O6/sulfite system was developed to remove doxycycline residue from the aqueous environment. In this research, MnNb2O6 nanomaterial was successfully synthesized through a one-step hydrothermal route at 260 °C for 24 h. The paramagnetic behavior of MnNb2O6 was observed at 300 K. Scanning electron microscopy and transmission electron microscopy images showed that the size of petal-like MnNb2O6 crystals was 250–700 nm. The specific surface area of MnNb2O6 was 24.84 m2/g. Optimization of MnNb2O6/sulfite process was achieved by Box-Behnken Design based on response surface methodology. Under the predicted optimal conditions (pH of 8.7, MnNb2O6 dosage of 0.29 g/L, doxycycline concentration of 10.8 mg/L, and sodium sulfite concentration of 4.3 mM), the degradation efficiency of doxycycline could reach 85.1%. Mn species was found to be the dominant factor in MnNb2O6/sulfite system. Both SO4•− and •OH were identified as primary active radicals in MnNb2O6/sulfite system. Furthermore, six transformation products of doxycycline were elucidated. This work offers a simple water treatment process for efficiently removing doxycycline residue in the environment.

The occurrence of doxycycline residue in raw dairy milk from Malang and Padang Panjang, Indonesia

Antibiotic residue in milk has a negative impact on human health. The objective of this study was to determine the presence of doxycycline residues in fresh dairy milk and to evaluate its dietary intake to Indonesian population through milk consumption. Ninety milk samples were collected from the District of Malang (East Java Province) and sixty-six milk samples from Padang Panjang City (West Sumatera Province). All samples were analyzed for doxycycline residue using high-performance liquid chromatography (HPLC). The estimated daily intake (EDI) was determined by multiplying the mean concentration of antibiotics and the average daily milk consumption dividing it by the weight of population target. The occurrence of doxycycline residue obtained in raw milk samples was 36.67% for samples from Malang and 12.12% for samples from Padang Panjang. The range and average concentration for doxycycline residue in milk samples were 44.8-557.2 ng/g and 203.0 ng/g for samples from Malang and 14.2-64.5 ng/g and 30.1 ng/g for samples from Padang Panjang, respectively. Samples from Malang shows the highest EDI values of doxycycline both for adult, and children population and demonstrated the toxicological risk of consumption doxycycline together with the present other types or groups of antibiotics residue in milk or other types of foods. The results obtained show that, to prevent the negative effects of antibiotic residues on human health, the presence of antibiotic residues in raw dairy milk still needs to be monitored regularly.

Dispersive liquid-liquid microextraction/HPLC techniques for determination of oxytetracycline and doxycycline residues in beef samples: method developments and statistical analysis

A rapid, cost-effective and environment-friendly sample pre-treatment method involving dispersive liquid-liquid microextraction (DLLME) and high-performance liquid chromatography (HPLC) was developed and applied for the extraction of oxytetracycline and doxycycline residues in beef samples (liver, kidney and muscle). Several influencing factors associated with the extraction and separation of these antibiotics residues, such as sample size, type and volume of disperser and extraction solvents, centrifugation speed and time, were optimized using Plackett-Burman design and central composite design, while insignificant factors were fixed at values determined using univariate analysis. Figures of merit of the analytical methodology including the limit of detection (LOD), the limit of quantification (LOQ), accuracy (in terms of average recoveries), precision and calibration functions were established according to the European Union commission decision 2002/657/EC. Linearity, in the range of 5–500 µg/kg, was obtained with regression coefficients ranging from 0.9983 – 0.9999. Inter-day repeatability, intra-day precision, LODs and LOQs obtained were 3.81 – 14.90%, 3.80 – 8.70%, 4.21 – 4.69 µg/kg and 14.02 – 15.65 µg/kg respectively. Samples with detectable drug residues have oxytetracycline being the most commonly detected. The developed method was successfully established and the concentration levels of drug residues detected were lower than the European Union set maximum residue level (MRL).

A portable test strip fabricated of luminescent lanthanide-functionalized metal-organic frameworks for rapid and visual detection of tetracycline antibiotics.

Tetracycline antibiotics (TCs) are commonly used antibiotics in the treatment of infections, but their overuse has a negative impact on human health and ecosystems. Thus, the development of a facile and on-site visualization method for TC detection is necessary. Here, we propose the potential of using lanthanide-functionalized metal-organic framework (MOF) composites (Ag+/Tb3+@UiO-66-(COOH)2, ATUC) as a probe for the rapid detection of tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC), and doxycycline (DOX) residues, in which UiO-66-(COOH)2 (UC) could be utilized to provide an interaction microenvironment, Tb3+ as recognition units and Ag+ as a fluorescence enhancer. Upon exposure to TCs, significant luminescence quenching of ATUC excited at 255 nm was observed due to the inner filter effect (IFE) and photo-induced electron transfer (PET), and the established strategy has a detection limit (LOD) of 11.0, 20.1, 9.1, and 22.5 nM for TC, CTC, OTC, and DOX, respectively. More importantly, given its portability and conspicuous luminescence color gradation variation, a portable test strip based on ATUC was manufactured and the results could be distinguished immediately by the naked eye and smartphone analysis, allowing for on-site rapid quantitative assay of TCs, not only in the laboratory but also in a point-of-care setting.

A novel nanostructured organic framework sensor for selective and sensitive detection of doxycycline based on fluorescence enhancement

It is critical for human health to develop sensitive and rapid analytical methods for detecting doxycycline (DOX) residues in food. This paper presents a novel metal-organic framework nanomaterial (Zn-MOF) based on dithiodiglycolic acid and its application in DOX detection by fluorescent probe method. Zn-MOF itself does not fluoresce. When DOX is added, the system exhibits strong fluorescence (100-fold) at 530 nm. The fluorescence intensity displayed an excellent linear relationship with DOX concentration with a detection limit of 2.7 nM. The reaction solution's fluorescence displayed a visible color shift from colorless to yellow that was concentration-dependent. A smartphone was used to detect DOX by recognizing the red, green, and blue values of the reaction solution and the corresponding test paper. The use of smartphones can speed up the detection process and streamline operations, offering a sensitive and visible method for the quantitative detection of DOX residues in actual samples. Interestingly, Zn-MOF can discriminate DOX from other tetracyclines with high selectivity. This material has been used successfully as a fluorescent probe to determine DOX in fish samples with an average spiked recovery of 94.6 % ∼ 95.1 %. The DOX levels in the measured perch samples were 1.25 ∼ 157 μg/kg. There are 2 batches of DOX exceeding the standard in 14 batches.

Development of a Highly Specific Fluoroimmunoassay for the Detection of Doxycycline Residues in Water Environmental and Animal Tissue Samples.

Doxycycline (DOX) and its metabolite residues in food and the environment pose a serious threat to human health and the ecological environment. In this work, a novel method, termed competitive fluoroimmunoassays (cFIA), based on monoclonal antibody (mAb) bio-conjugated CdSe/ZnS core-shell quantum dots (QDs), was developed for sensitive and rapid bioanalyses of DOX in natural water and commercial meats. After the optimization of the experimental conditions, 1 μg mL-1 of coating antigen and 0.5 μg mL-1 of QD-labeled mAb were used for the establishment of the cFIA. With this assay, the 50% inhibition concentration was found to be 0.35 ng mL-1 of DOX in phosphate-buffered saline samples, and the limit of detection was 0.039 ng mL-1 with minor cross-reactivity to other tetracycline members. The recoveries from natural water and commercial meats spiked with DOX concentrations of 10-600 ng mL-1 were 81.3-109.8%, and standard deviation were all below 12%. Levels measured with the QD-cFIA for thirty authentic samples were confirmed by high-performance liquid chromatography with good correlations. These results indicate that QD-cFIA is sultable for the rapid and quantitative detection of DOX residue in environmental and food samples.

Synthesis and Performance Testing of a BODIPY Fluorescent Probe for the Detection of Doxycycline Residues in Water Environment

AbstractDoxycycline (DOX) has been used extensively in the control of animal diseases, which leads to its large‐scale accumulation in water and causes serious pollution problems. In this study, a BODIPY‐based fluorescent probe named DOX‐BOD was synthesized by a one‐pot method. The qualitative and quantitative detection of DOX was achieved by the specific response effect of DOX‐BOD on DOX. DOX‐BOD showed excellent performance and its fluorescence intensity decreased with the increase in DOX concentration. Besides, the detection limit was as low as 0.91 μM. The DOX detection method based on BODIPY fluorescent probe has good reproducibility and stability, and can be used for rapid and high‐sensitivity detection of DOX residues in the water environment, which is of great significance for environmental monitoring.

Effect of the Presence of Antibiotic Residues on the Microbiological Quality and Antimicrobial Resistance in Fresh Goat Meat.

A total of 11 fresh goat legs were collected at the retail level. Mesophiles, Pseudomonas spp., Enterobacteriaceae, staphylococci, enterococci, Clostridium perfringens, Campylobacter spp., and Listeria monocytogenes counts were determined. Nine samples were free of antibiotic residues, while in the other two samples the presence of sulfadiazine and doxycycline was detected. The antimicrobial resistance of E. coli, staphylococci, Macrococcus spp., and enterococci isolates was also evaluated. Clostridium perfringens was found in two samples. Methicillin-resistant Staphylococcus aureus was detected in one sample. S. epidermidis isolated from one sample containing doxycycline residues showed resistance to mupirocin. Moreover, multi-resistant S. epidermidis and M. caseolyticus were found. Most of the isolated Enterococcus faecium were multi-resistant. Neither extended-spectrum β-lactamase -producing E. coli nor vancomycin-resistant enterococci were detected in any sample. The presence of doxycycline or sulfadiazine could affect the goat meat microbiota since less microbial diversity was found in these samples compared to those free of antibiotics. The presence of antibiotic residues could increase the antimicrobial resistance of enterococci in fresh goat meat. The presence of multidrug-resistant bacteria in goat meat could be considered a potential threat and should be monitored. Special measures should be taken at the farm level and during slaughter to reduce antimicrobial resistance.

Carbon dots from green sources as efficient sensor and as anticancer agent

This work reports the synthesis of novel fluorescent carbon dots (CD) from green sources via the hydrothermal method for detecting the antibiotic doxycycline. The blue fluorescent carbon dots with an average diameter of 2.64 nm exhibited outstanding stability towards different experimental conditions. The sensing of doxycycline by CDs is due to its fluorescent quenching through the inner filter effect (IFE), which served as the basis for its quantification. In addition, these carbon dots were employed for practical applications like the detection of doxycycline residues in real water samples, and tablets. Moreover, a glassy carbon electrode (GCE) modified with CDs exhibited as a novel electrochemical sensor for doxycycline with a detection limit of 2.86 nM. Also, the anticancer activity of CDs against MCF-7 breast cancer cells is demonstrated. The developed carbon dots have remarkable potential as a dual sensor for the antibiotic doxycycline and anticancer applications.

Tetracycline residues in tilapia and catfish tissue and the effect of different cooking methods on oxytetracycline and doxycycline residues

Fish such as tilapia (Oreochromis niloticus) and catfish (Clarias gariepinus) is an important source of high biological value animal protein. Fish can be exposed to antimicrobials in intensive aquaculture systems or exposed to remnants of the antimicrobials released to various water bodies via drainage systems. This study aimed at screening for antimicrobial residues in two major fish species commonly consumed in Egypt, namely, tilapia, and catfish, either in wild or cultured fish using a microbial inhibition assay. Besides, quantitative estimation of tetracycline (oxytetracycline and doxycycline) residues in the edible fish muscles was carried out using the solid phase extraction (SPE) technique and high-performance liquid chromatography with photodiode-array detection (HPLC-PAD). In addition, the effects of different cooking methods (pan-frying, grilling, and microwaving) on oxytetracycline and doxycycline residues in tilapia and catfish were investigated. The microbiological inhibition assay revealed that 2, 24, 18, and 32% of the examined wild tilapia, cultured tilapia, wild catfish, and cultured catfish, respectively, contained antibiotic residues. Cultured tilapia, wild catfish, and cultured catfish had mean concentrations of oxytetracycline residues of 0.147 ± 0.067, 0.106 ± 0.046, and 0.313 ± 0.044 µg/g. 3 (6%), 4 (8%), and 9 (18%) of the sampled cultured tilapia, wild catfish, and cultured catfish exceeded the established maximum permissible limits (MPL) of tetracycline (0.100 ng/g). The mean concentrations of doxycycline residues were 0.276 ± 0.045, 0.026 ± 0.004, and 0.070 ± 0.010 µg/g in cultured tilapia, wild catfish, and cultured catfish, respectively, with 2 (4%) of the cultured tilapia exceeding the MPL of doxycycline. Consumption of fish with high residual levels of tetracyclines might pose potential health risks to consumers. In an experimental trial, heat treatment of tilapia and catfish could significantly reduce both oxytetracycline and doxycycline residues, particularly grilling had the highest reduction rates.

Microbiological contamination, antimicrobial residues, and antimicrobial resistance in raw bovine milk in Lebanon

A total of 195 raw milk samples were collected over two consecutive years from 48 milk sources in Lebanon. Collected samples were examined for microbiological quality and antibiotic susceptibility. Results revealed non-conformity with local and international standards, in 96% of samples for total aerobic mesophilic bacteria (TAMB), 81% for total coliform (TC), 17% for Staphylococcus aureus (S. aureus), 35% for Salmonella spp., and 65% for Escherichia coli (E. coli). Antimicrobial residues of oxytetracycline, tetracycline, ciprofloxacin, sulfamethazine, and doxycycline were below the maximum residue limits (MRL). On the other hand, E. coli isolates showed resistance to tetracycline (41%), doxycycline (39%), nalidixic acid (20%), and ciprofloxacin (3%), while S. aureus isolates were found resistant to doxycycline (63%), and tetracycline (51%). For Salmonella spp., isolates were found to be resistant to doxycycline (12%), tetracycline (6%), and nalidixic acid (4%). In conclusion, sampled milk shows high levels of pathogenic bacteria and antimicrobial resistance.

The occurrence of antimicrobial residues and antimicrobial resistance genes in urban drinking water and sewage in Southern Brazil.

Antimicrobial resistance (AMR) is currently discussed as an important issue worldwide, and the presence of antimicrobial residues (ARs) and antimicrobial resistance genes (ARGs) in the environment, especially in the water sources, is a challenge for public health. This study was conducted to evaluate the occurrence and diversity of AR and ARG in water sources from an urban center, in Southern Brazil. A total of thirty-two water samples from drinking water treatment plants (24) and sewage systems (8) were collected during two annual samplings, winter and summer. The PCR was performed by 18 ARGs, and the detection of 47 ARs was performed by LC-MS/MS. All sewage samples presented carbapenemases, ESBL, and mcr-1 genes as well as quinolones and sulfamethoxazole residues. In drinking water, we just detected blaTEM and tetB genes and doxycycline residues in samples before treatment. This study provides data about AR and ARG in drinking water and sewage systems showing that these sources are important reservoirs of both. The limited effectiveness of wastewater treatment processes to remove mainly AR demonstrates the need to implement better protocols of disinfection, in order to limit the spread of AMR in the environment.

Risk to Public Health Regarding Doxycycline Residues in Chicken Claws.

Doxycycline residues in claws may pose a potential risk to humans. A study with broiler chickens was performed to find the concentrations of doxycycline in claws after treatment. For the quantification of the antibiotic of interest in claws, an ultrahigh-performance liquid chromatography-tandem mass spectrometry method was developed. Doxycycline was detectable at 3043 μg/kg at sub-therapeutic treatment, 223 μg/kg after therapeutic doses, and 14 μg/kg after spray application on the last day of the experiment (day 22). Almost 70 days is required for the concentration of doxycycline to reach zero. The obtained results show that monitoring of doxycycline in claws should be implemented.

Surface enhanced FRET for sensitive and selective detection of doxycycline using organosilicon nanodots as donors

In order to achieve on-site fluorescent detection of antibiotic doxycycline (DOC) residue, a new kind of fluorescent organosilicon nanodots (OSiNDs) was successfully constructed by a one-pot strategy and used as a novel ratiometric fluorescent probe. This method could enhance the fluorescence of DOC by conformational fixation on the surface of OSiNDs, and subsequently induced fluorescence resonance energy transfer (FRET). Control experimental results showed that phenylamine functional groups on the as-prepared OSiNDs possessed favorable interactions with DOC by hydrogen bond/π–π stacking, leading to both conformational change of DOC molecules and fluorescence resonance energy transfer process from OSiNDs to DOC. This method was then adapted and optimized for visual sensitive and selective detection of DOC based on ratiometric fluorescence signal, displaying a good linear range for DOC in the range of 1–35 μM with an excellent limit detection of ∼80 nM. Other tetracycline derivatives (TCs) and possible interferences have little influence on the determination of DOC using the method. The spike and recovery test of DOC in real water samples demonstrated the feasibility of the OSiNDs for DOC assay in practical samples and a test paper was fabricated with OSiNDs loading, achieving easy and visual detection of DOC by naked eyes.

Enrichment of tetracycline residues from honey samples using carrier-mediated hollow fibre liquid-phase micro-extraction and quantification by LC-Q-TOF/MS.

In this study, development and validation of a simple, miniaturized and, environmentally friendly carrier-mediated three-phase hollow-fibre liquid-phase micro-extraction (HFLPME) technique was investigated for the enrichment of tetracycline residues in honey samples. The extracts were analysed using UV-visible spectrophotometry and liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS). Parameters affecting the extraction efficiency of HFLPME such as pH of the donor and acceptor solutions, salt addition, agitation speed and extraction time were optimized. The calibration curves showed good linearity, in the range of 1-100 μg kg-1 with correlation coefficients ranging between 0.9943 and 0.9992, under the optimized conditions. Recoveries of blank honey samples at three spiking levels (1, 10 and 20 μg kg-1 ) ranged from 81.2% to 107.5%. Relative standard deviations for the precision of the method were less than 15.0%. Limits of detection and limits of quantification were in the range of 0.0861-0.2628 μg kg-1 and 0.2610-0.7964 μg kg-1 , respectively. Finally, the proposed method was successfully applied in the extraction of five tetracyclines from honey samples. Doxycycline residue detected in one of the commercial honey samples was below the limit of quantification. Because of the advantages offered by HFLPME, this method can be employed as an alternative to conventional extraction techniques for the clean-up and pre-concentration of antibiotics in complex matrices, including food samples. © 2021 Society of Chemical Industry.

Photo-assisted removal of doxycycline using H2O2 and simulated sunlight: Operational parameters optimization and ecotoxicity assessment

The presence of antibiotics in different environmental matrices is a problem of great concern. Doxycycline (DOX) is an antibiotic belonging to the family of tetracyclines, whose use has been extensive in the treatment of different diseases. DOX residues have been found in different water bodies, which implies that conventional water treatment technologies are not enough to remove these types of pollutants. This study sought to evaluate the application of simulated sunlight and H2O2 in the removal of DOX at laboratory scale. Effects of different operational parameters including the solution initial pH and the peroxide concentration were studied. The results indicated that DOX elimination was higher at alkaline conditions and that increasing the H2O2 concentration has a positive effect. Pollutant total elimination was achieved in 40 min of reaction under optimized conditions. Additionally, the assessment of the effect of the initial DOX concentration allowed to establish that a pseudo-first order kinetic model fits the experimental data adequately. Data related to the dissolved organic carbon (DOC) and nitrates present in the treated samples were also analyzed. Finally, in terms of the solution ecotoxicity, variation on the bioluminescence of Vibrio fischeri bacteria, showed that evaluated photo-treatment is efficient not only to reduce the DOX presence but also, to inhibit samples toxicity.

A ratiometric fluorescence-scattering sensor for rapid, sensitive and selective detection of doxycycline in animal foodstuffs

The residue problem of tetracycline antibiotics, especially doxycycline (DC), in animal foodstuffs has attracted much attention. This paper reported ZIF-8 and bovine serum albumin (BSA) as a ratiometric fluorescence-scattering sensor for DC. The mechanism relied on the disassembly of ZIF-8 caused by DC, bringing weakened second-order scattering, and the double fluorescence amplification of DC under ZIF-8 with BSA, inducing enhanced fluorescence. The response of the sensor was completed within 1 min, and the detection limit for DC (3.4 nM) was 1–2 orders of magnitude lower than the reported ones. The distinguishment of DC from other tetracycline antibiotics was also achieved by the sensor. The sensor was applied to detecting DC in animal foodstuffs with satisfactory recoveries (80.0–104.0%). Hence, this work develops a rapid, sensitive and selective ratiometric sensor to monitor the DC residue in animal foodstuffs, also opens the window to construct ratiometric DC sensors with the fluorescence-scattering strategy.

DOXYCYCLINE DETERMINATION IN ANIMAL TISSUES AND BLOOD PLASMA SAMPLES USING SCREENING AND CONFIRMATORY METHODS

The article presents the results of validation of sample preparation method for muscle and parenchymal tissues of animals for further determination of doxycycline residual amounts by enzyme-linked immunosorbent assay using Oxytetracycline ELISA test kits from EuroProxima (Netherlands), initially developed for the analysis of other target matrices, viz. honey and shrimp. The results of modification of shrimp sample preparation method for the analysis of muscle and parenchymal tissue samples are showed. In accordance with the European Commission Decision 2002/657/EC, the proposed method was validated taking into account the maximum residue levels (MRLs) of doxycycline in tissues of productive animals: 100 μg/kg for muscle tissue and 300 μg/kg for liver. The suitability of the technique was confirmed on the basis of the established main validation parameters for screening methods (technical threshold and cut-off factor) using control (pure) and spiked with standard doxycycline solution at the level of ½MRL samples of muscle and parenchymal tissues of broiler chickens by means of “added – found” criterion. It was discovered that this approach to sample preparation makes it possible to determine doxycycline residues in poultry tissues at the level of 5-10 μg/kg with the absolute recovery about 54 %. The main advantages of the developed technique are simplicity of performance, rapidity and cost-effectiveness.
 The reliability of the results obtained by the screening method was verified using confirmatory UPLC-MS/MS method, viz. a comparative study of blank and spiked samples of muscle and parenchymal tissues of broiler chickens. The method of sample preparation of the studied specimens, the conditions of analysis carrying out, and the main validation parameters of the confirmatory method are also presented. Based on the obtained results, it was concluded that the developed screening method of enzyme-linked immunosorbent assay is suitable for the determination of doxycycline residual amounts in muscle and parenchymal tissues samples, and it is possible to use it for routine laboratory tests, as well as for the establishment of withdrawal periods of veterinary drugs based on doxycycline from the tissues of productive animals. Also using the same test kit, the sample preparation method for blood plasma samples for doxycycline content assay (at the levels of μg/ml) was suggested to study the bioequivalence of veterinary drugs containing doxycycline as an active pharmaceutical ingredient, which was as well confirmed by UPLC-MS/MS.