Improved high-performance liquid chromatographic procedure for the determination of tetracyclines in plasma, urine and tissues

Antibiotics threaten wildlife: circulating quinolone residues and disease in Avian scavengers

Antibiotic residues that may be present in carcasses of medicated livestock could pass to and greatly reduce scavenger wildlife populations. We surveyed residues of the quinolones enrofloxacin and its metabolite ciprofloxacin and other antibiotics (amoxicillin and oxytetracycline) in nestling griffon Gyps fulvus, cinereous Aegypius monachus and Egyptian Neophron percnopterus vultures in central Spain. We found high concentrations of antibiotics in the plasma of many nestling cinereous (57%) and Egyptian (40%) vultures. Enrofloxacin and ciprofloxacin were also found in liver samples of all dead cinereous vultures. This is the first report of antibiotic residues in wildlife. We also provide evidence of a direct association between antibiotic residues, primarily quinolones, and severe disease due to bacterial and fungal pathogens. Our results indicate that, by damaging the liver and kidney and through the acquisition and proliferation of pathogens associated with the depletion of lymphoid organs, continuous exposure to antibiotics could increase mortality rates, at least in cinereous vultures. If antibiotics ingested with livestock carrion are clearly implicated in the decline of the vultures in central Spain then it should be considered a primary concern for conservation of their populations.

Chromatographic analysis of tetracycline antibiotics in foods

Tetracycline antibiotics (TCs), such as oxytetracycline, tetracycline, chlortetracycline, and doxycycline, have for decades continued to play an important role in veterinary medicine and feed additives because of the broad spectrum antibiotics and their economical advantages. Many analysis methods of TCs, therefore, have been reported to monitor their residues in foods. We review the recent developments in chromatographic analysis methods for TCs in foods. This review involves the following techniques: thin layer chromatography, capillary electrophoresis, high-performance liquid chromatography, and sample preparation including extraction and clean up procedures.

High-performance liquid chromatographic assay for minocycline in human plasma and parotid saliva

A sensitive and specific high-performance liquid chromatographic (HPLC) method with UV detection was developed for the determination of minocycline in human plasma and parotid saliva samples. Samples were extracted using an Oasis HLB cartridge and were injected into a C8 Nucleosil column. The HPLC eluent contained acetonitrile-methanol-distilled water-0.1% trifluoroacetic acid (25:2:72.9:0.1, v/v). Demeclocycline was used as internal standard. The assay showed linearity in the tested range of 0.1-25 microg/ml. The limit of quantitation was 100 ng/ml. Recovery from plasma or parotid saliva averaged 95%. Precision expressed as %CV was in the range 0.2-17% (limit of quantitation). Accuracy ranged from 93 to 111%. In the two matrices studied at 20 and 4 degrees C, rapid degradation of the drug occurred. Frozen at -30 degrees C, this drug was stable for at least 2 months, the percent recovery averaged 90%. The method's ability to quantify minocycline with precision, accuracy and sensitivity makes it useful in pharmacokinetic studies.

Determination of tetracyclines in bovine kidney by liquid chromatography/tandem mass spectrometry with on-line extraction and clean-up

A novel, sensitive, high performance liquid chromatography/tandem mass spectrometric (i.e. mass spectrometry/mass spectrometry) method with on-line extraction and clean-up for the screening and confirmation of residues of tetracyclines in kidney has been developed. After liquid extraction of homogenised kidney with McIlvain buffer, an aliquot of the extract is directly injected on the LC/MS/MS system with further extraction and clean-up of the sample on-line. Detection of the analytes was achieved by positive electrospray ionization followed by multiple reaction monitoring. For each tetracycline the collisional decomposition of the protonated molecule to a unique, abundant fragment ion was monitored. The method has been validated for tetracycline, oxytetracycline, chlortetracycline and doxycycline. Calibration curves resulting from spiked blank kidney samples at the 100-1200 microgram/kg level showed good linear correlation. At the level of 600 microgram/kg both within- and between-day precision, as measured by relative standard deviation (RSD), were less than 7%. The limits of detection (LODs) for tetracycline, oxytetracycline, chlortetracycline and doxycyline were 18, 23, 24 and 21 microgram/kg, respectively. The limits of quantification (LOQs) for tetracycline, oxytetracycline, chlortetracycline and doxycyline were 36, 46, 47 and 42 microgram/kg, respectively. The recoveries ranged from 71 to 91%. The procedure provides a rapid, reliable and sensitive method for the determination of residues of tetracyclines in bovine kidney. The advantage of this method over existing methods is its decreased sample preparation and analysis time, which makes the method more suitable for routine analysis.

Analysis of tetracyclines in raw urine by column-switching high-performance liquid chromatography and tandem mass spectrometry

The aim of the project was to develop a fast and reliable method for the quantification of the three tetracyclines: tetracycline, oxytetracycline and chlortetracycline in urine. The method is based on column-switching high-performance liquid chromatography with detection by MS-MS. Buffer is added to the sample before it is injected into the chromatographic system, and the first column which is an internal surface reversed-phase column separates the tetracyclines from the bulk of other compounds in urine. The tetracyclines are collected and concentrated on the analytical column before they are separated and eluted into the mass spectrometer in which the tetracycline are detected. The mass spectrometer is a triple quadrupole instrument and is equipped with an electrospray ion source. The MH+ ions are selected in the first quadrupole and collisionally activated in the collision cell. Upon collision, activation all three tetracyclines form fragment ions which could be assigned as: [M+H-H2O-NH3]+ which are selected in the sond mass filter. The detection limits for all three tetracyclines are about 10 ppb, and the calibration curves are linear from 10 to 1000 ppb.

Effects of extraction and spiking procedures on the determination of incurred residues of oxytetracycline in cattle kidney

The effects of different extraction and spiking procedures on the determination of incurred oxytetracycline residues in animal tissues have been investigated. The extraction procedures investigated--direct aqueous or organic solvent extraction, enzymic digestion or sonication--all gave similar results for incurred oxytetracycline concentration in cattle kidney after correction for spike recovery. There was therefore no evidence for binding or conjugation of oxytetracycline in this tissue. Highest recovery from spiked tissue was obtained using ethyl acetate as extractant. The effects of spiking procedure (spike contact time, spike solvent and tissue state) on recovery from spiked cattle kidney were also small, indicating that added oxytetracycline spike does not interact with the tissue.

Development and validation of a sensitive method for tetracycline in gingival crevicular fluid by HPLC using fluorescence detection

Increased interest in the clinical use of antibiotics for periodontal therapy required the development of a sensitive assay for the quantitation of tetracycline in gingival crevicular fluid (GCF). An HPLC method was developed and validated for tetracycline which separates and identifies the degradation component epi-tetracycline. The HPLC assay employs a C18 reversed-phase Hypersil column with a mobile phase composed of methanol and sodium acetate buffer containing CaCl2 and EDTA disodium salt. The chromatographic separation was monitored by a fluorescent detector with an excitation wavelength of 375 nm and an emission wavelength of 512 nm. Tetracycline was extracted from GCF collected on Periopapers by addition of a methanol solution containing the internal standard, doxycycline, and the mobile phase buffer (25:75, v/v). The mean percent recovery for the extraction method was 107.8% with all the % R.S.D. below 7.5%. The mean inter- and intra-batch accuracy was 104.1 and 105.3%, respectively with a coefficient of variation of less than 9.5%. The lower limit of detection was 2.5 ng on the Periopapers. The typical GCF volumes collected were 0.1-1 microliter. The method was validated for the linear concentration range 2.5-1000 ng of tetracycline on the Periopaper. This assay for tetracycline was shown to be an accurate, precise and rugged method.

Validation of a high-performance liquid chromatographic method for the determination of doxycycline in turkey plasma

A high-performance liquid chromatographic method for the analysis of doxycycline in turkey plasma samples using demeclocycline hydrochloride as the internal standard was developed, optimized and validated. A one-step extraction procedure and an isocratic HPLC method with UV detection were used. No interferences with endogenous compounds or with the anticoagulant were observed. Linear calibration curves (r2 > 0.99) were obtained in water and plasma between 0 and 600 micrograms ml-1. Good recoveries for doxycycline (> 66%) and demeclocycline (> 72%) were seen both in water and in plasma. The coefficient of variation was < 9.86% for within-day reproducibility and < 7.53% for the between-day reproducibility. The deviation between the mean value found and the true value was < 14.5% (accuracy). The limit of detection was 0.1 microgram ml-1 in plasma samples. A good stability of doxycycline was observed in water and in plasma samples after storage for six months at -20 degrees C (recovery > 91%).

Determination of oxytetracycline in the live fish feed Artemia using high-performance liquid chromatography with ultraviolet detection

A high-performance liquid chromatographic analytical method was developed for the determination of oxytetracycline in Artemia nauplii. A solid-phase extraction protocol was used to recover oxytetracycline and the internal standard tetracycline, from the Artemia samples. Oxytetracycline was analyzed using a 150 x 4.6 mm I.D. Hypersil-ODS column, a mobile phase of acetonitrile-tetrahydrofuran-0.01 M oxalic acid buffer (pH 3.0) (15:3:82, v/v), and an ultraviolet detection wavelength of 365 nm. The calibration curve of oxytetracycline in Artemia was linear (r2 = 0.9998) from 0.1 to 6.4 micrograms/g of tissue. Using a signal-to-noise ratio of 4:1 the oxytetracycline detection limit was 10 ng/g of tissue. Mean recovery of oxytetracycline amounted to 97%, while intra-assay variability was 1.5%. Quantitative data from an in-vivo feeding study indicated an excellent uptake of oxytetracycline by Artemia, as its levels reached 25.6 micrograms per g of nauplii.

High-performance liquid chromatographic determination of oxytetracycline in channel catfish (Ictalurus punctatus) muscle tissue

A high-performance liquid chromatographic method for the determination of oxytetracycline in channel catfish muscle tissue is presented. Oxytetracycline is extracted three times from muscle tissue with an ethylenediaminetetraacetic acid disodium salt-McIlvaine buffer (pH 4.0) by using an Ultra Turrax. Analysis is carried out by using high-performance liquid chromatography and an acetonitrile-oxalic acid (0.05 mol 1(-1), pH 2.2) mixture (14 + 86, v/v) is used as mobile phase. Oxytetracycline is separated on a Lichrosorb RP-8 125 x 4.0 mm i.d. column and ultraviolet detection at 355 nm is used. The limit of quantification is 10 ng g-1 and the linearity, tested in the spiking range 20-500 ng g-1, is 0.9997. Recovery from muscle spiked at 20, 50, 100, 200 and 500 ng g-1 levels is in the range 70-80%. Precision, expressed as percentage relative standard deviation, is below 7%. The method is applied to muscle tissue from channel catfish fed on a medicated diet.

Rapid determination of tetracycline antibiotics in serum by reversed-phase high-performance liquid chromatography with fluorescence detection

A rapid and accurate determination of tetracycline antibiotics in human serum by reversed-phase high-performance liquid chromatography with fluorescence detection has been developed, based on protein precipitation in serum. Various reagents for precipitation were investigated, and 24% trichloroacetic acid in methanolic solution gave the maximum recovery (at least 94.3%) and interference-free chromatograms of different three tetracyclines. At a concentration of 0.5 micrograms/ml, the precision (relative standard deviation) ranged from 1.12 to 1.94%. In the range 0.04-10.0 micrograms/ml for oxytetracycline and chlorotetracycline and 0.01-10.0 micrograms/ml for tetracycline, linear responses were observed. The detection limits of this method were 10-35 ng/ml for all three antibiotics. The proposed method was applied to the determination of serum concentrations in subjects receiving tetracycline antibiotics.

Liquid chromatographic analysis of antibacterial drug residues in food products of animal origin

This paper reviews recent developments in the liquid chromatographic (LC) methods of analysis for the residues of antibiotics (aminoglycosides, chloramphenicol, sulfonamides, tetracyclines, macrolides, beta-lactams, etc.) in food products of animal origin. The review also covers clean-up procedures, such as, ultrafiltration, liquid-liquid partition, solid-phase extraction, immunoaffinity, and matrix solid-phase dispersion, for use as extraction, deproteination, and concentration steps. The LC methods offer considerable potential for rapid automated analysis, and some may be used as direct screening for residues in meat and milk.

Determination of tetracycline antibiotics by reversed-phase high-performance liquid chromatography with fluorescence detection

A highly sensitive method for the determination of tetracycline antibiotics (TCs) using reversed-phase high-performance liquid chromatography with fluorescence detection is presented. This method was based on the use of disodium ethylenediaminetetraacetate (EDTA) and calcium chloride as fluorescence-increasing reagents in the mobile phase. The concentrations of each reagent in the mobile phase greatly influenced the fluorescence intensity of TCs. When the concentration of EDTA and calcium chloride were 25 and 35 mM, respectively, and the pH of the mobile phase was 6.5, the maximum fluorescence intensity was obtained. The column temperature hardly influenced the fluorescence intensity. At 3.75 ng of TCs injected, the precision (relative standard deviation) ranged from 1.12 to 2.20%. In the range 0.075-37.5 ng for tetracycline and oxytetracycline and 0.225-37.5 ng for chlortetracycline, a linear response was observed. The detection limits of this method were 49-190 pg for three different TCs. The proposed method was applied to the determination of one of the TCs in pharmaceuticals by the internal standard method using other TCs as internal standards and was also applied to determination of TCs added to fish tissue.

On-line dialysis, liquid chromatography and post-column reaction detection of oxytetracycline in salmon muscle extracts

The development of a sensitive automated method for residue control of oxytetracycline (OTC) in salmon muscle is described. Tissue homogenate is dialysed and the dialysate enriched on a small on-line polystyrene column. OTC and the internal standard (tetracycline) are separated by HPLC on a polystyrene column using an ion-pair eluent system. The column effluent is mixed with sodium hydroxide and irradiated at 366 nm and the resulting derivatives monitored by means of a fluorescence detector (excitation: 358 nm, emission: 460 nm). By the method OTC is detected down to 5 ng g-1. The standard curve was linear (r = 0.9999) over the range 50-1000 ng g-1. Within-day and between-day relative standard deviations (n = 6) at 50 and 200 ng g-1 ranged from 1.0 to 1.7%.

Fully automated high-performance liquid chromatographic analysis of whole blood and plasma samples using on-line dialysis as sample preparation. Determination of oxytetracycline in bovine and salmon whole blood and plasma

A fully automated technique for high-performance liquid chromatographic analysis of whole blood and plasma is described. Samples are automatically injected into a dialyser where proteins and blood cells are removed. The dialysates are concentrated on a small column prior to analysis. This technique is used for the determination of oxytetracycline in whole blood and plasma. After dialysis oxytetracycline and the internal standard, tetracycline, are retained on a polystyrene enrichment column and subsequently separated on a polystyrene analytical column by ion-pair chromatography. Using ultraviolet detection 50 ng/ml can be detected. Validation showed good within-day and between-day accuracy and precision. Different oxytetracycline concentrations were found in plasma and whole blood. This difference varied between the species.

Analysis of trace residues of tetracyclines in animal tissues and fluids using metal chelate affinity chromatography/HPLC

A novel method of analysis for the trace residue determination of tetracyclines in animal tissues and fluids has been developed. Clean-up of sample extracts is based upon the specific ability of tetracyclines to chelate with divalent metal ions (metal chelate affinity chromatography, MCAC) and determination made by high-performance liquid chromatography. The method has been tested for the determination of oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) in porcine kidney and muscle, ovine kidney, bovine kidney and milk, and trout muscle. Recoveries at the 0.05 mg/kg level for OTC, TC and CTC respectively were 75%, 63%, 73% in porcine kidney, 77%, 79%, 76% in porcine muscle, 85%, 54%, 53% in bovine kidney, 78%, 63%, 57% in ovine kidney, 75%, 58%, 56% in fish (trout) muscle, and 80%, 59%, 59% in bovine milk. At this level both within- and between-batch precision, as measured by the coefficient of variation (CV), was less than 10%. Determination to the 0.01 mg/kg level was carried out in all cases, although the method becomes less precise. The method has been used for several months and found to be both reliable and sufficiently rapid for use as a routine quantitative screening procedure. When coupled with liquid chromatography-mass spectrometry (LC-MS) it is suitable for use as a confirmatory method. Analysis of animals treated with tetracyclines has been carried out.

An experimental model for pharmacokinetic analysis in renal failure

A renal failure model was developed in the dog to evaluate the effect of varying degrees of renal failure on drug pharmacokinetics. A controlled impairment of renal function was induced by electrocoagulating portions of one kidney and excising the contralateral kidney. The magnitude of renal dysfunction, defined by the percentage of normal glomerular filtration rate (% NGFR), was estimated by 125I-iothalamate total body clearance. The model was evaluated by comparing the pharmacokinetics of oxytetracycline (OTC) before and after the induction of renal failure in two experiments: single intravenous dose (11 dogs); single intravenous and oral doses (8 dogs). Renal failure (RF) was studied in three classes according to % NGFR: less than 25%, severe RF; 25-39%, moderate RF; and greater than or equal to 40%, mild RF. Significant reductions were observed over RF class in OTC pharmacokinetic parameters for elimination and distribution but not for oral absorption.

A rapid fluorimetric screening method for chlortetracycline, oxytetracycline and tetracycline in pig meat and kidney tissues

A rapid fluorimetric screening method for chlortetracycline, oxytetracycline and tetracycline in pig meat and kidney tissues is described. After sonication-aided extraction with ethyl acetate, the extract is cleaned and concentrated by means of solid-phase extraction using an aromatic sulphonic acid cation-exchange column. Subsequent screening is carried out by fluorimetry. The detection level is estimated to be about 0.05 mg kg-1 for oxytetracycline, 0.1 mg kg-1 for chlortetracycline and 0.2 mg kg-1 for tetracycline.

Oxytetracycline residues in rainbow trout analysed by a rapid HPLC method

A rapid and sensitive HPLC method was developed for the determination of oxytetracycline in fish tissues (muscle and liver) based on a clean-up and concentration procedure on Sep-Pak C18. At a coastal fishfarm rainbow trout (Salmo gairdneri) suffering from Vibrio anguillarum were treated with 75 mg oxytetracycline per kg fish and day for ten days. Oxytetracycline residues above the limit of determination (0.005 micrograms/g) were found in fish 82 days after treatment. The recoveries from spiked tissues were about 60% and 70% for muscle and liver, respectively.

Effect of the silica support of bonded reversed-phase columns on chromatography of some antibiotic compounds

Chromatographic behavior of three types of antibiotics was investigated on bonded C18 and polymeric reversed-phase columns. With penicillins with carboxylic acid functions only, retention and separations on the two types of columns were similar. beta-Lactam antibiotics with basic functions did not give as sharp peaks on the C18 column unless a silanol blocking agent, tetramethyl ammonium chloride (TMA) was added. In 0.01 M orthophosphoric acid-acetonitrile, tetracyclines were separated on the polymeric reversed-phase columns, but not on the C18 columns. With addition of TMA, results on C18 and polymeric reversed-phase columns were nearly identical. Addition of an ion pair also improved separations on the C18 columns, but not as much as TMA. Interaction with the silica support of C18 columns was used to separate tylosin from interferences in extracts of biological materials. The results demonstrate the importance of interactions with the silica support in chromatography of basic antibiotics on C18 packings. These interactions can be either beneficial or detrimental to separations, depending on the conditions used.

Determination of tetracycline antibiotics in tissues and blood serum of cattle and swine by high-performance liquid chromatography

Tissue homogenates and blood serum were acidified with hydrochloric acid and deproteinized with acetonitrile. Tetracyclines were partitioned into water and concentrated by solid-phase absorption on the analytical column form 0.01 M phosphoric acid-methanol (80:20). Tetracyclines were eluted with an acetonitrile gradient. An all-organic polymeric column (Polymer Labs. PLRP-S) was used. Similar results were obtained on a bonded reversed-phase column after addition of tetramethyl-ammonium chloride to the mobile phase. Recoveries were near 100% from blood serum, 83-94% from muscle, and 80-100% from liver and kidney with sensitivities of 0.1 ppm or less for muscle and blood serum.

High-performance liquid chromatography of tetracyclines

The possibilities of two non-ionogenic resins (XAD-2 and PRP-1) in the chromatography of tetracyclines and their degradation products are described. It appears that, in contrast to silica-based materials, this type of column material produces linear calibration curves, even in the low nanogram range. Two different methods of sample pretreatment in bioanalysis of tetracyclines and their degradation products are compared with respect to selectivity towards the matrix background and recovery.

Pharmacokinetics of tetracycline in chickens after intravenous administration

Plasma levels of tetracycline in chickens were determined after intravenous (iv) administration of a 65-mg/kg dose. The disposition kinetics of tetracycline in chickens were fitted to a two-compartment open model. Pharmacokinetic parameters were found to be: A (microgram/ml) = 2000 +/- 450, alpha (hr-1) = 4.3 +/- .5, B (microgram/ml) = 82 +/- 6, beta (hr-1) = .252 +/- .009, K12 (hr-1) = 1.515, K21 (hr-1) = .049, and K10 (hr-1) = 2.652. Biliary excretion of tetracycline was also studied in chickens fitted with cannulae inserted into both bile ducts. The maximum values for tetracycline biliary excretion rate (407 and 606 micrograms/hr) were reached at about 1 hr after iv administration of 10- and 15-mg/kg doses. First-order rate constants for the biliary excretion, Kbi (hr-1), were .834 and .665, respectively. The cumulative biliary excretion study showed that about 7% of both administered doses was recovered from the bile within the first 6 hr. In contrast, there was a low recovery of antibiotic in the bile after oral administration of 100 and 200 mg/kg doses.

Rapid, sensitive and specific determination of oxytetracycline residues in bovine milk and meat by CAD MIKEs analysis at the 1 ppb level

A rapid and sensitive method for the selective detection and quantification of oxytetracycline residues at the ppb level in crude extracts of bovine milk and meat is described. The technique employed is a tandem mass spectrometric method: CAD MIKE spectrometry (collisionally activated decomposition mass-analysed ion kinetic energy spectrometry). Quantification is performed by single ion monitoring of CAD species of oxytetracycline and of its internal standard.

Improvement of chemical analysis of antibiotics. VIII. Application of prepacked C18 cartridge for the analysis of tetracycline residues in animal liver

A simple, rapid and precise analytical method for tetracycline (TC) residues in the liver of slaughtered animals has been established. The recoveries of oxytetracycline (OTC), TC, chlortetracycline (CTC) and doxycycline (DC) from beef liver spiked at the level of 1.0 ppm were 87.7, 87.5, 79.6 and 67.5% with coefficients of variations of 1.01-2.87%. Detection limits in beef liver were 0.05 and 0.1 ppm for OTC and TC and for CTC and DC, respectively. It is also possible to apply this method to the analysis of residual TCs in various foods with the same recovery, accuracy and detection limits as in the case of beef liver.

Antibiotic monitoring in body fluids

Analytical procedures recently described for the quantitative determination of antibiotics in body fluids are reviewed. High-performance liquid chromatography (HPLC) and immunoassays appear as an alternative to current microbiological assays. HPLC has been applied to most antibiotics in clinical use and a major part of the review deals with this technique. Attention is given to sample pretreatment, characteristics of chromatography and detection, and limit of sensitivity. Non-isotopic immunoassays have been essentially applied to aminoglycosides and vancomycin and are also reviewed. Advantages and drawbacks of HPLC and immunoassays are presented.

Sample preparation by salts precipitation and quantitation by high-performance liquid chromatography with UV detection of selected drugs in biological fluids

A quantitative clean-up procedure for drugs in plasma and urine in preparation for high-performance liquid chromatographic analysis is discussed. Samples are mixed with zinc sulfate, barium hydroxide, and acetonitrile (or methanol). Resultant solutions are clear and free of visible residue. Injections of over 420 samples of treated urine and 120 samples of treated plasma had no noticeable effect on pressure drop and column performance. An examination of the column head indicated no damage or discoloration to the packing. Baselines of the controls show no interference from endogenous compounds for the drugs studied. Precision study using cyclobenzeprine . HCl in plasma and urine by internal standard and external standard methods has within-run and day-to-day variations of under 5%. Drugs studied in urine and plasma are amiloride . HCl, cyclobenzeprine . HCl, cyproheptadine . HCl, diflunisal, indomethacin, phenylbutazone and sulindac. These drugs are selected for the various functional groups, their binding by proteins and their natural UV absorptivity. Conditions to improve recovery, advantages and limitations are discussed.

Comparative pharmacokinetics of chlortetracycline in milk-fed versus conventionally fed calves

Plasma and tissue concentration and pharmacokinetics of chlortetracycline (CTC) was determined in milk-fed and conventionally fed Holstein calves. A two-compartment open model was used after a single intravenous dose (11 mg CTC/kg body weight). There were no significant differences between dietary treatments. The drug was rapidly distributed from plasma into the peripheral compartment but was slowly eliminated, with detectable concentration of CTC continuing for 72 h after dosing. A single-compartment model was used after a single oral dose (22 mg CTC/kg body weight). All but four of the kinetic parameters were significantly different for the two dietary treatments. Milk-fed calves had a larger area under the plasma level curve, a larger fraction of the dose absorbed, a smaller volume of distribution and a smaller overall body clearance rate. Estimated recovery of CTC in the urine of the milk-fed calves was greater, regardless of route of administration. The concentration of CTC in tissues following an oral dose was greatest in kidney, followed by liver, heart, skeletal muscle, spleen and brain. Tissue depletion of CTC closely paralleled the decline in plasma concentration.

Rapid determination of tetracycline and lumecycline in human plasma and urine using high-performance liquid chromatography

A rapid and accurate method for the determination of tetracycline in human plasma and urine is presented. Determination of tetracycline in plasma is based on precipitation of plasma proteins with trifluoroacetic acid, followed by injection of the centrifuged plasma sample onto a muBondapak C18 column. Acetonitrile in phosphate buffer pH 2.2 is used as mobile phase. Only tetracycline, and no trace of lumecycline can be detected in plasma and urine after administration of lumecycline, indicating that lumecycline is completely degraded to tetracycline, lysine and formaldehyde in the gastrointestinal tract prior to absorption. Determination of tetracycline in urine was performed by injection of urine diluted with phosphoric acid onto a muBondapak Phenyl column. The precision of determination of tetracycline in plasma, expressed as the relative standard deviation, was less than 3% at tetracycline concentrations of 0.05 and 3.7 micrograms/ml. Urine determinations were made with a precision of less than 1.5% at tetracycline concentrations of 0.5 and 6.7 micrograms/ml.

Liquid chromatographic estimation of doxycycline in human tissues

A rapid, sensitive and specific liquid chromatographic method is described for the determination of doxycycline in human tissues. The procedure involves mechanical homogenization of tissue samples in hydrochloric acid followed by extraction of the drug and an internal standard into ethyl acetate. Chromatographic separation is performed on a reversed phase column and allows quantitation of tissue levels as low as 0.68 nmol/g using a 200-400 mg sample. Application of the assay to tissue samples obtained from 36 patients confirmed the excellent penetration of doxycycline in organs. The method supersedes the classical microbiological assays in specificity and speed.