This pharmacokinetic study was designed to determine the pharmacokinetics of enrofloxacin at 5 mg/kg when given to sea hares in their hemolymph. Enrofloxacin is a commonly used antimicrobial in veterinary medicine and potentially could be used to treat sea hares exposed to susceptible bacterial species. We individually identified 8 juvenile Aplysia californica and group housed them in an open seawater flow system at 14 to 18 °C; 2 served as untreated controls. The remaining 6 animals were injected into the hemocoel with 0.030 mL of 22.7 mg/mL enrofloxacin (average dose, 5 to 6 mg/kg). At each time point, 300 μL hemolymph was collected from the pedal hemolymph sinus and HPLC-analyzed for enrofloxacin and ciprofloxacin levels. Enrofloxacin was detected in all dosed animals, at an average peak concentration of 3 μg/mL in hemolymph, and remained in the body for 20.3 h with an average clearance of 0.19 μg × h/mL. No ciprofloxacin was detected in any Aplysia in this study. Hemocoel injection appears to be an effective way to administer enrofloxacin to Aplysia and reach clinically relevant concentrations. Enrofloxacin reached therapeutic target concentrations in A. californica when dosed according to the regimen described in the current report.

Organic dairy products are the second largest sector of the organic food market. Organic dairy products come from United States Department of Agriculture (USDA) certified organic dairy cattle that meet USDA organic standards. Organic dairy cattle in the US cannot be treated with antibiotics for mastitis, one of the costliest diseases of dairy cattle, and thus effective alternatives are needed. When any compound (medication or other non-food product) is used in a food producing animal, a withhold time for that compound that meets US Food and Drug Administration (FDA) standards for food safety must be applied to the animal and its products (like milk).However, there are no US FDA products approved for mastitis that maintain USDA certified organic dairy cattle's organic status. Thus, we studied the pharmacokinetics of 3 compounds (garlic, thymol and carvacrol) used on organic both healthy and mastitic organic dairy cattle. We also used this information to estimate a milk withhold time using methods consistent with US FDA requirements. For thymol intra-mammary and carvacrol intra-mammary or topical administration, all compounds were partially absorbed into the body from the milk or skin. Thymol and carvacrol are measurable in plasma (at 0.0183 and 0.0202 mu g/mL, respectively) after intramammary administration with similar elimination half lives of 1.7h. Milk concentrations of thymol and carvacrol are much higher at 2.958 and 4.487 mu g/mL in healthy cattle, respectively. Concentrations are not significantly different in cows with mastitis as compared to those in healthy cows. Despite these compounds being natural products, they should have a withhold time for milk of at least 24h after administration. For garlic, levels remained below the limit of detection in milk and plasma and thus no withdrawal time appears to be needed for milk.

Mastitis is a costly disease for dairy farmers. Some dairy farmers use herbal products, or phytoceuticals, to treat mastitis. Phytoceuticals have not been approved for this use by the United States Food and Drug Administration, and have not been tested to determine how they impact antibiotic residue detection testing. The current study tested the potential for phytoceuticals to cause positive results on two milk antibiotic residue screening tests, the Delvotest P and Charm SL Beta-lactam test, or to interfere with the detection of antibiotics by these tests. The three phytoceuticals tested were labelled for intramammary, topical or intravulvar administration. Testing was performed in vitro using the products diluted in milk obtained from healthy organic dairy cows. Phytoceuticals were tested at concentrations ranging from 1.5 per cent to 100 per cent. Concentration levels were replicated at least twice on each milk antibiotic residue screening test. The Delvotest P is based on detection of bacterial inhibitors and no positive results were obtained for any product at concentrations less than 50 per cent. The Charm SL Beta-lactam test uses a receptor for the detection of beta-lactam antibiotics and no concentration of phytoceuticals caused an interference with these tests. Based on dilution of the products in bovine milk at physiologically achievable levels, phytoceutical products tested at levels expected after treatment do not cause positive test results for the Delvotest P nor do they interfere with the Charm SL Beta-lactam test in detection of various antibiotics.

Mastitis is among the most costly concerns for dairy producers whether cattle are managed conventionally or organically. Unfortunately, there are no USFDA-approved mastitis treatments that allow dairy cows in the United States to maintain organic dairy status. We investigated the plasma pharmacokinetics of three organic mastitis products currently used by organic producers and organic dairy veterinarians. Those products include intramammary, topical and intravaginal preparations, each dosed at two levels. Additionally, tissue data were collected for kidney, liver and fat in order to estimate a withholding time for each of the products. The lower limit of quantification (LOQ) and lower limit of detection (LOD) were 0.001 and 0.0005 µg ml-1, respectively, in plasma and all tissues except fat for both thymol and carvacrol. Fat had an LOQ of 0.01 µg ml-1 and an LOD of 0.005 µg ml-1 for thymol and carvacrol. Diallyl disulfide had an LOQ of 0.005 µg ml-1 and LOD of 0.001 µg ml-1 in all tissues. For diallyl disulfide (garlic), no levels above 0.001 µg ml-1 were measurable in plasma or tissues. For topical and intramammary products, levels were measurable in the plasma, liver, kidney and fat up to 72 h after the last dose. The plasma half-lives were short for thymol (approximately 1.6 h) and carvacrol (approximately 1.5 h), whereas the estimated half-lives for these substances in tissues ranged from 13.9 to 31.5 h for thymol and from 16.9 to 25 h for carvacrol. The predicted amount of time that the molecules would be found in the body based on the slowest depletion time of liver tissue was 13 days for thymol and 10 days for carvacrol. The apparent half-life of topically applied carvacrol was approximately 4.5 h in plasma, with an estimated withhold time of 10 days. These times were calculated using the USFDA's tolerance limit method for meat withdrawal times.

Thymol and carvacrol may be present in several phytoceutical products but there are no well-defined methods to measure these compounds in meat and milk from treated animals. U.S. regulatory authorities deem their presence as an adulteration of food. A rapid and sensitive HS-SPME-GC-MS/MS method was developed for the detection of thymol and carvacrol in bovine milk, plasma, liver, kidney, and fat. Inter- and intraday precision values were all less than 15.7 and 20.2% for thymol and carvacrol, respectively. The accuracy was in ranges of 69.9-111.8% for thymol and 74.0-119.2% for carvacrol. With the exception of fat tissue, stability studies showed that both compounds are stable over a 2 month period. A pilot pharmacokinetic study was conducted to evaluate the developed analytical method and to provide initial estimates of thymol and carvacrol depletion in plasma, milk, and several tissues. Treatment of lactating dairy cattle with phytoceutical products containing these substances resulted in low but measurable residue levels at 96 h for liver and 36 h for milk with very short apparent plasma and milk half-lives (<3.0 h).

The use of water medications is a common practice in the US swine industry to treat and prevent infections in swine herds with minimal labor and without risk of needle breakage. There are concerns that FDA-approved withdrawal times (WDT) may be inadequate for several water medications when exporting pork products to countries where MRLs (maximum residue limits) are lower than US tolerance levels. In this study, withdrawal intervals (WDI) were estimated for pigs when dosed with tetracycline and sulfamethazine in water. The WDI were calculated using the FDA tolerance method (TLM) and a population-based pharmacokinetic method (PopPK). The estimated WDIs (14-16 days using TLM) were similar to the approved WDT of 15 days for sulfamethazine. However, the PopPK method extended WDIs for both sulfamethazine (19-20 days) and tetracycline (12 days) compared to the currently approved WDTs in the U.S. This study also identified potential differences in WDI between weanling and finisher pigs. In conclusion, the TLM may not always provide adequate WDT for foreign export markets especially when MRLs differ from tolerance levels approved for US markets. However, PopPK methods can provide conservative WDIs in situations with considerable variability in medication exposure such as with administration in water.

In the US, organic dairy cattle cannot be treated with antibiotics and maintain their organic status. There are no alternate products approved by US FDA to treat bovine mastitis on organic farms. Therefore, herbal treatments must be investigated for mastitis control. National organic dairy regulations allow the use of herbal products to prevent and manage bacterial mastitis. Phyto-mast is one botanical phytoceutical, composed of five plant extracts in a canola oil base, commonly used on organic dairy farms to manage mastitis and maintain organic status. Unfortunately, there are no data regarding in vitro bacterial activity of Phytomast®; therefore, five different potential mastitis-causing bacteria were tested for their susceptibility to Phyto-mast® in vitro according to the Clinical Laboratory Standards Institute techniques. Based on our results Phyto-mast® appears bacteriostatic to E. coli and S. agalactiae, but is ineffective in decreasing the growth of Staphylococcus species and S. bovis.

Tetracycline is a broad-spectrum antibiotic used to treat infections in swine. The maximum residue levels of tetracycline in pork stomach tissue in Russia, Europe, and the United States are 10, 200, and 2,000 ppb, respectively. This difference in accepted safety levels may be the reason why stomach tissues that the United States exports continue to be residue violators in overseas markets. In this study, 30 pigs at two different stages of production (weanling and finisher) were treated with tetracycline at 22 mg/kg of body weight per day for a total of 5 days via a water medicator. Blood samples were collected at 0, 72, 78, 96, and 102 h after the start of medication. The medication was stopped at 120 h, and blood samples were again collected at 126, 144, 168, 192, and 216 h after exposure. Five animals were slaughtered for stomach tissue 0, 24, 48, 96, and 192 h after the drug was flushed from the water line. All blood and tissue samples were analyzed by high-performance liquid chromatography-UV methods. The tetracycline levels in plasma were below the level of detection after the U.S.-labeled withdrawal time of 4 days. The stomach tissue residues averaged 671.72, 330.31, 297.77, 136.36, and 268.08 ppb on withdrawal days 0, 1, 2, 4, and 8, respectively. Using the U.S. Food and Drug Administration tolerance limit method and a population-based pharmacokinetic model with Monte Carlo simulation, a withdrawal interval was estimated. This study demonstrated that tetracycline residues are still detectable in the stomach tissues after the established United States withdrawal time of 4 days. These residue levels may explain why stomach tissues tested in Russia and Europe show positive residues for tetracycline, even though the meat may pass inspection here in the United States prior to export.

A population-based Population pharmacokinetic (PK) model is composed of a structural PK model and a covariate model. The benefit of this type of modeling is evidenced when data is scarce for individuals and there are differences in PK parameters or measured outcomes across treatments or groups of individuals. If there are no differences in the parameters or groups, then a population model may not be as useful as other PK methods. Population modeling techniques have been applied to veterinary medicine effectively for clinical problems. However, the potential can also be applied to preslaughter withdrawal times. The application of population-based PK models is important for explanations and predictions of therapeutic drug concentrations in veterinary patients. Food and Drug administration (FDA) has advocated the use of population-based PK for human and some animal studies when those studies follow appropriate sampling design and extrapolation guidelines.

OBJECTIVE:To model the plasma tetracycline concentrations in swine (Sus scrofa domestica) treated with medication administered in water and determine the factors that contribute to the most accurate predictions of measured plasma drug concentrations.SAMPLE:Plasma tetracycline concentrations measured in blood samples from 3 populations of swine.PROCEDURES:Data from previous studies provided plasma tetracycline concentrations that were measured in blood samples collected from 1 swine population at 0, 4, 8, 12, 24, 32, 48, 56, 72, 80, 96, and 104 hours and from 2 swine populations at 0, 12, 24, 48, and 72 hours hours during administration of tetracycline hydrochloride dissolved in water. A 1-compartment pharmacostatistical model was used to analyze 5 potential covariate schemes and determine factors most important in predicting the plasma concentrations of tetracycline in swine.RESULTS:2 models most accurately predicted the tetracycline plasma concentrations in the 3 populations of swine. Factors of importance were body weight or age of pig, ambient temperature, concentration of tetracycline in water, and water use per unit of time.CONCLUSIONS AND CLINICAL RELEVANCE:The factors found to be of importance, combined with knowledge of the individual pharmacokinetic and chemical properties of medications currently approved for administration in water, may be useful in more prudent administration of approved medications administered to swine. Factors found to be important in pharmacostatistical models may allow prediction of plasma concentrations of tetracycline or other commonly used medications administered in water. The ability to predict in vivo concentrations of medication in a population of food animals can be combined with bacterial minimum inhibitory concentrations to decrease the risk of developing antimicrobial resistance.

Tetracycline hydrochloride-medicated water samples taken from commercial farms were found to darken to yellow or brown. Tetracycline hydrochloride from collected samples was quantified by high performance liquid chromatography and assessed for its biological activity. Samples were biologically active in the expected range, but safety could not be determined.

There have been numerous reports of melamine-related illnesses following oral exposure to this contaminant. These studies have been in monogastrics, but there are few reports of adverse effects and pharmacokinetics of melamine in ruminants. The purpose of this project was to determine how melamine is systemically cleared from the blood and milk in lactating animals. Five lactating goats were given a single oral dose of 40mg/kg body weight. Milk and blood samples were collected for 144h and analyzed to determine key pharmacokinetic parameters. The apparent plasma half-life (11.12h) was 3 times longer in these ruminants than that reported in monogastrics and the apparent volume of distribution was more than 6 times greater than that reported in monogastrics. The milk had an apparent half-life of 9.44h and less than 0.4% of the melamine dose was eliminated in milk. All milk samples were below the LOQ at 4days (96h) after exposure. In summary, the pharmacokinetics of melamine in ruminants is not predictive from monogastrics and milk from similarly exposed animals should be condemned for at least 4days after the last exposure to avoid violation of proposed MRLs or safe levels for milk.

A physiologically based pharmacokinetic model with partition coefficients estimated from quantum dot (QD) 705 biodistribution was compared with the biodistribution of other QDs in mice and rats to determine the model's predictive ability across QD types, species, and exposure routes. The model predicted the experimentally observed persistence of QDs in tissues but not early time profiles or different QD biodistribution. Therefore, more complex models will be needed to better predict QD biodistribution in vivo.

Sulfamethazine is often used to treat disease in the swine industry. Sulfamethazine is available as water or feed medication and historically (over the past 40 years) has been associated with residue violations in both the United States and Europe. Despite sulfamethazine's approval for use as a water medication, little research on the pharmacokinetics of the water formulation is available. Therefore, a pilot study was performed to determine the plasma levels of an approved sulfamethazine water medication. Plasma levels in pigs treated with an oral bolus (250 mg/kg), which is equivalent to the total drug consumed within a 24-h period, achieved therapeutic concentrations (50 μg/ml). Noncompartmental-based pharmacokinetic model parameters for clearance, half-life, and volume of distribution were consistent with previously published values in swine. However, the above treatment resulted in exposure of pen mates to sulfamethazine at levels currently above tolerance (0.1 ppm). Using a physiologically based pharmacokinetic model, the treatment dose simulation was compared with observed plasma levels of treated pigs. Flexibility of the physiologically based pharmacokinetic model also allowed simulation of control-pig plasma levels to estimate contamination exposure. A simulated exposure to 0.15 mg/kg twice within approximately 8 h resulted in detectable levels of sulfamethazine in the control pigs. After initial exposure, a much lower dose of 0.059 mg/kg maintained the contamination levels above tolerance for at least 3 days. These results are of concern for producers and veterinarians, because in commercial farms, the entire barn is often treated, and environmental contamination could result in residues of an unknown duration.

Melamine-contaminated pet food was recently added as a supplement to livestock feed. There is little or no information concerning the pharmacokinetics of melamine in livestock, and the aim of this study was to obtain pharmacokinetic parameters for this contaminant in pigs. Melamine was administered intravenously to five weanling pigs at a dose of 6.13mg/kg and plasma samples were collected over 24h, extracted for melamine, and then analyzed by HPLC–UV. The data was shown to best fit a one-compartment model with melamine’s half-life of 4.04 (±0.37)h, clearance of 0.11 (±0.01)L/h/kg, and volume of distribution of 0.61 (±0.04)L/kg. These data are comparable to the only mammalian study in rats and suggests that melamine is readily cleared by the kidney and there is unlikely to be significant tissue binding. Further tissue residue studies are required to assess the depletion kinetics of this contaminant in the pig which will determine whether residue levels in the kidney should be of public health concern if pigs were exposed to a similar dose.