A preliminary assessment of oral monepantel's tolerability and pharmacokinetics in individuals with treatment-refractory solid tumors

PURPOSE

Monepantel is an approved veterinary anthelmintic with a strong safety profile. Preclinical evidence suggests novel mTOR pathway-associated anticancer activity. An open-label Phase I trial assessed tolerability, pharmacokinetics, pharmacodynamics and PET-CT imaging following oral Zolvix^® monepantel administration to adults with treatment refractory, progressing and unresectable solid tumors.

METHODS

Subjects were scheduled to daily home-based monepantel administration for 28 days in a 3 + 3 dose escalation study (5.0, 25.0 and 62.5 mg/kg bw).

RESULTS

Of 41 reported drug-related AEs, 68% were Grade 1 and 24% were Grade 2; 35 AEs related to gastrointestinal effects including very poor palatability. DLT and MTD could not be determined due to early termination. Myelosuppression was not observed at the lowest level tested. Three of four Cohort 1 subjects had reduced mTOR pathway marker p-RPS6KB1 levels in PBMCs and achieved RECISTv1.1 SD by CT; one had progressive bony metastases by FDG-PET. One subject recorded PD on day 28, correlating with no detectable plasma monepantel from day 7. Monepantel sulfone dominated monepantel in pharmacokinetics. Both Cohort 2 subjects withdrew early due to AEs and the trial was terminated.

CONCLUSIONS

Short-term 5 mg/kg bw monepantel administration provides a combined steady-state trough plasma monepantel and monepantel sulfone concentration of 0.5 μM. Gastrointestinal AEs including very poor palatability are concerning and suggested to be resolved by future drug product reformulation. RECISTv1.1, p-RPS6KB1 and plasma tumor marker outcomes provide preliminary evidence of anticancer activity.

The Influence of Ionic Liquids on the Effectiveness of Analytical Methods Used in the Monitoring of Human and Veterinary Pharmaceuticals in Biological and Environmental Samples-Trends and Perspectives

Recent years have seen the increased utilization of ionic liquids (ILs) in the development and optimization of analytical methods. Their unique and eco-friendly properties and the ability to modify their structure allows them to be useful both at the sample preparation stage and at the separation stage of the analytes. The use of ILs for the analysis of pharmaceuticals seems particularly interesting because of their systematic delivery to the environment. Nowadays, they are commonly detected in many countries at very low concentration levels. However, due to their specific physiological activity, pharmaceuticals are responsible for bioaccumulation and toxic effects in aquatic and terrestrial ecosystems as well as possibly upsetting the body's equilibrium, leading to the dangerous phenomenon of drug resistance. This review will provide a comprehensive summary of the use of ILs in various sample preparation procedures and separation methods for the determination of pharmaceuticals in environmental and biological matrices based on liquid-based chromatography (LC, SFC, TLC), gas chromatography (GC) and electromigration techniques (e.g., capillary electrophoresis (CE)). Moreover, the advantages and disadvantages of ILs, which can appear during extraction and separation, will be presented and attention will be given to the criteria to be followed during the selection of ILs for specific applications.

Residue Distribution and Depletion of Ractopamine in Goat Tissues After Exposure to Growth-Promoting Dose

The objectives of the present study was to investigated the ractopamine (RAC) distribution and depletion process in various tissues of goat including liver, kidney, spleen, lung, heart, fat, bile, brain and the eyes. The experiment was carried out on 21 goats (18 treated and 3 controls). Treated goats were orally administered RAC in a dose of 1 mg/kg body mass per day for last 28 days and randomly sacrificed on withdrawal days of 0.25, 1, 3, 7, 14 and 21. RAC in all matrices were determined by ultra-high performance liquid chromatography-quadrupole orbitrap high resolution mass spectrometry. After 21 days treatment discontinuation, the levels of RAC in bile reached at 13.48 ± 3.36 mg/L, which was significantly higher than that in the other tissues. The concentrations of RAC were followed by kidney, the excretory organ and liver, the major metabolic organ (4.49 ± 0.16 mg/kg for kidney and 1.81 ± 0.11 mg/kg for liver, respectively). The residual concentration of the drug in the eyes of goat was less than that in bile, kidney, liver, lung and spleen on withdrawal days 0.25. RAC residues was higher than the limits of detection = 0.15 μg/mL in liver on Day 21. These findings demonstrated that liver can serve as an alimentary matrix and as a matrix for the control of RAC abuse hypothetically except for urine.

Therapeutic Contraindications in Exotic Pets

The selection and dosing of medications for exotic pets are often challenging because most drugs are used in an extralabel manner without pharmacokinetic and pharmacodynamic studies. Doses are often extrapolated from common domestic animals and safety data are often lacking in exotic species. Just as the bioavailability and therapeutic levels are different for each species, what may be a safe and commonly used medication in one species can be deadly in another. Various drugs with documented contraindications in certain exotic pet species are outlined in this review and the pathophysiology, clinical signs, and treatment options are described when applicable.

The use of toxicokinetics and exposure studies to show that carprofen in cattle tissue could lead to secondary toxicity and death in wild vultures

Veterinary medicines can be extremely damaging to the environment, as seen with the catastrophic declines in Gyps vulture in South Asia due to their secondary exposure to diclofenac in their primary food source. Not surprisingly, concern has been raised over other similar drugs. In this study, we evaluate the toxicity of carprofen to the Gyps vulture clade through plasma pharmacokinetics evaluations in Bos taurus cattle (their food source) and Gyps africanus (a validated model species); tissue residues in cattle; and the effect of carprofen as a secondary toxicant as both tissue-bound residue or pure drug at levels expected in cattle tissues. Carprofen residues were highest in cattle kidney (7.72 ± 2.38 mg/kg) and injection site muscle (289.05 ± 98.96 mg/kg of dimension of 5 × 5 × 5 cm). Vultures exposed to carprofen as residues in the kidney tissue or pure drug equivalents showed no toxic signs. When exposed to average injection site concentrations (64 mg/kg) one of two birds died with evidence of severe renal and liver damage. Toxicokinetic analysis revealed a prolonged drug half-life of 37.75 h in the dead bird as opposed to 13.99 ± 5.61 h from healthy birds dosed intravenously at 5 mg/kg. While carprofen may generally be harmless to Gyps vultures, its high levels at the injection site in treated cattle can result in lethal exposure in foraging vultures, due to relative small area of tissue it is found therein. We thus suggest that carprofen not be used in domesticated ungulates in areas where carcasses are accessible or provided to vultures at supplementary feeding sites.

Feline Transdermal Formulation Considerations

Transdermal delivery of drugs is comparatively new in feline patients. However, transdermal formulations can be a desirable option for treating feline patients that are not willing participants to medication administration. However, achieving drug penetration across the skin is not always easy, and there are a wide variety of variables that can further affect penetration. This, coupled with a lack of studies, make transdermal administration an unknown with regards to efficacy and safety for many drugs. This article focuses on drugs that are administered transdermally with the intent of producing systemic effects.

Distribution of Flunixin Residues in Muscles of Dairy Cattle Dosed with Lipopolysaccharide or Saline and Treated with Flunixin by Intravenous or Intramuscular Injection

Twenty dairy cows received flunixin meglumine at 2.2 mg/kg bw, administered once daily by either the intravenous (IV) or intramuscular (IM) route for three consecutive days with either intravenous normal saline (NS) or lipopolysaccharide (LPS) providing a balanced design with five animals per group. Cows were sacrificed after a 4 day withdrawal period, and 13 muscle types were collected and assayed for flunixin by LC-MS/MS. After elimination of sample outliers, the main effects of route of administration (IV or IM), treatment (NS or LPS), and tissue type significantly (P < 0.05) affected flunixin residues, with no interaction (P > 0.05). Intramuscular (nonlabel) flunixin administration produced greater (P < 0.05) flunixin residues in muscle than the IV (label) administration, whereas LPS resulted in lower flunixin levels. Differences among the tissue levels indicate it is necessary to specify the tissue to be used for any monitoring of drug levels for consumer protection.

Human Food Safety Implications of Variation in Food Animal Drug Metabolism

Violative drug residues in animal-derived foods are a global food safety concern. The use of a fixed main metabolite to parent drug (M/D) ratio determined in healthy animals to establish drug tolerances and withdrawal times in diseased animals results in frequent residue violations in food-producing animals. We created a general physiologically based pharmacokinetic model for representative drugs (ceftiofur, enrofloxacin, flunixin, and sulfamethazine) in cattle and swine based on extensive published literature. Simulation results showed that the M/D ratio was not a fixed value, but a time-dependent range. Disease changed M/D ratios substantially and extended withdrawal times; these effects exhibited drug- and species-specificity. These results challenge the interpretation of violative residues based on the use of the M/D ratio to establish tolerances for metabolized drugs.

A combined liquid chromatography-triple-quadrupole mass spectrometry method for the residual detection of veterinary drugs in porcine muscle, milk, and eggs

A liquid chromatography-electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed for monitoring and detection of four different drugs, namely acetanilide, pentylenetetrazole, phenacetin, and tetramethrin in porcine muscle, pasteurized milk, and table egg samples. For acetanilide and pentylenetetrazole, the samples were extracted with 0.1 % formic acid in acetonitrile, followed by defatting with n-hexane, partitioning at -20 °C for 1 h, centrifugation, and filtration, whereas the quick, easy, cheap, effective, rugged, and safe "QuEChERS" method was used for phenacetin and tetramethrin. The final extracts were combined and analyzed in a single chromatographic run using an XBridge(TM) analytical column and 0.1 % formic acid and 10 mM ammonium formate in ultrapure water (A) and 0.1 % formic acid and 10 mM ammonium formate in methanol (B) as the mobile phase. Owing to the unavailability of internal standards, matrix-matched calibrations were used for analyte quantification with coefficients of determination (R (2)) ≥ 0.9865. The intra- and inter-day accuracies ranged from 60.75 to 90.90 % and from 63.75 to 89.30 %, respectively, while the respective analytical precisions were 1.48-17.44 % (23.3 % for porcine sample spiked with phenacetin) and 1.97-15.78 %. The limits of quantification (LOQ) were between 0.5 and 2.5 ng/g in the matrices tested. Food samples purchased from local markets in Seoul were analyzed using the developed method and none of the tested drugs was detected.

Comparison of Active Drug Concentrations in the Pulmonary Epithelial Lining Fluid and Interstitial Fluid of Calves Injected with Enrofloxacin, Florfenicol, Ceftiofur, or Tulathromycin

Bacterial pneumonia is the most common reason for parenteral antimicrobial administration to beef cattle in the United States. Yet there is little information describing the antimicrobial concentrations at the site of action. The objective of this study was to compare the active drug concentrations in the pulmonary epithelial lining fluid and interstitial fluid of four antimicrobials commonly used in cattle. After injection, plasma, interstitial fluid, and pulmonary epithelial lining fluid concentrations and protein binding were measured to determine the plasma pharmacokinetics of each drug. A cross-over design with six calves per drug was used. Following sample collection and drug analysis, pharmacokinetic calculations were performed. For enrofloxacin and metabolite ciprofloxacin, the interstitial fluid concentration was 52% and 78% of the plasma concentration, while pulmonary fluid concentrations was 24% and 40% of the plasma concentration, respectively. The pulmonary concentrations (enrofloxacin + ciprofloxacin combined) exceeded the MIC₉₀ of 0.06 μg/mL at 48 hours after administration. For florfenicol, the interstitial fluid concentration was almost 98% of the plasma concentration, and the pulmonary concentrations were over 200% of the plasma concentrations, exceeding the breakpoint (≤ 2 μg/mL), and the MIC₉₀ for Mannheimia haemolytica (1.0 μg/mL) for the duration of the study. For ceftiofur, penetration to the interstitial fluid was only 5% of the plasma concentration. Pulmonary epithelial lining fluid concentration represented 40% of the plasma concentration. Airway concentrations exceeded the MIC breakpoint for susceptible respiratory pathogens (≤ 2 μg/mL) for a short time at 48 hours after administration. The plasma and interstitial fluid concentrations of tulathromcyin were lower than the concentrations in pulmonary fluid throughout the study. The bronchial concentrations were higher than the plasma or interstitial concentrations, with over 900% penetration to the airways. Despite high diffusion into the bronchi, the tulathromycin concentrations achieved were lower than the MIC of susceptible bacteria at most time points.

Excretory, Secretory, and Tissue Residues after Label and Extra-label Administration of Flunixin Meglumine to Saline- or Lipopolysaccharide-Exposed Dairy Cows

Twenty lactating dairy cattle were intravenously infused with either lipopolysaccharide (LPS) (n = 10) or sterile saline (n = 10). Five cattle in each group received three doses of flunixin meglumine administered by either intravenous infusion or intramuscular injection at 24 h intervals. Milk, urine, and tissues were collected. Thirty-six hours after the last flunixin administration, milk from six cows contained 5-hydroxyflunixin (5OHF) levels greater than the milk tolerance of 2 ng/mL; by 48 h, milk from two cows, a saline and a LPS-treated animal, had violative milk concentrations of 5OHF. A single animal treated with LPS and intramuscular flunixin contained violative flunixin residues in liver. The ratio of urinary flunixin/5OHF was correlated (P < 0.01; R(2) = 0.946) with liver flunixin residues in LPS-treated animals, but not (P = 0.96; R(2) = 0.003) in cows treated with saline in lieu of LPS. Violative residues of flunixin in dairy cattle may be related to LPS inhibition of flunixin metabolism.

Simultaneous Determination of Residual Veterinary Drugs in Bovine, Porcine, and Chicken Muscle Using Liquid Chromatography Coupled with Electrospray Ionization Tandem Mass Spectrometry

A simple and rapid method using liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC/MS/MS) for the simultaneous determination of 130 veterinary drugs and their metabolites in bovine, porcine, and chicken muscle was developed. The drugs (1 to 10 ng/g, in muscle) were extracted from bovine, porcine, or chicken muscles with acetonitrile-methanol (95:5, v/v), and the extracts were delipidated with n-hexane saturated with acetonitrile. The extracts were evaporated, dissolved with methanol, analyzed by liquid chromatography with gradient elution on a C18 column, and determined by electrospray ionization tandem mass spectrometry. The detection limits ranged from 0.03 to 3 ng/g. The quantitation limits ranged from 0.1 to 10 ng/g. One hundred eleven, 122, and 123 drugs from bovine, porcine, and chicken muscle respectively showed recoveries between 70 and 110%.

Biodegradation of veterinary ionophore antibiotics in broiler litter and soil microcosms

Ionophore antibiotics (IPAs) are polyether compounds used in broiler feed to promote growth and control coccidiosis. Most of the ingested IPAs are excreted into broiler litter (BL), a mixture of excreta and bedding material. BL is considered a major source of IPAs released into the environment as BL is commonly used to fertilize agricultural fields. This study investigated IPA biodegradation in BL and soil microcosms, as a process affecting the fate of IPAs in the environment. The study focused on the most widely used IPAs, monensin (MON), salinomycin (SAL), and narasin (NAR). MON was stable in BL microcosms at 24-72% water content (water/wet litter, w/w) and 35-60 °C, whereas SAL and NAR degraded under certain conditions. Factor analysis was conducted to delineate the interaction of water and temperature on SAL and NAR degradation in the BL. A major transformation product of SAL and NAR was identified. Abiotic reaction(s) were primarily responsible for the degradation of MON and SAL in nonfertilized soil microcosms, whereas biodegradation contributed significantly in BL-fertilized soil microcosms. SAL biotransformation in soil microcosms yielded the same product as in the BL microcosms. A new primary biotransformation product of MON was identified in soil microcosms. A field study showed that MON and SAL were stable during BL stacking, whereas MON degraded after BL was applied to grassland. The biotransformation product of MON was also detected in the top soil layer where BL was applied.

Probabilistic risk assessment of veterinary medicines applied to four major aquaculture species produced in Asia

Aquaculture production constitutes one of the main sources of pollution with veterinary medicines into the environment. About 90% of the global aquaculture production is produced in Asia and the potential environmental risks associated with the use of veterinary medicines in Asian aquaculture have not yet been properly evaluated. In this study we performed a probabilistic risk assessment for eight different aquaculture production scenarios in Asia by combining up-to-date information on the use of veterinary medicines and aquaculture production characteristics. The ERA-AQUA model was used to perform mass balances of veterinary medicinal treatments applied to aquaculture ponds and to characterize risks for primary producers, invertebrates, and fish potentially exposed to chemical residues through aquaculture effluents. The mass balance calculations showed that, on average, about 25% of the applied drug mass to aquaculture ponds is released into the environment, although this percentage varies with the chemical's properties, the mode of application, the cultured species density, and the water exchange rates in the aquaculture pond scenario. In general, the highest potential environmental risks were calculated for parasitic treatments, followed by disinfection and antibiotic treatments. Pangasius catfish production in Vietnam, followed by shrimp production in China, constitute possible hot-spots for environmental pollution due to the intensity of the aquaculture production and considerable discharge of toxic chemical residues into surrounding aquatic ecosystems. A risk-based ranking of compounds is provided for each of the evaluated scenarios, which offers crucial information for conducting further chemical and biological field and laboratory monitoring research. In addition, we discuss general knowledge gaps and research priorities for performing refined risk assessments of aquaculture medicines in the near future.

Residue depletion of nifuroxazide in broiler chicken

BACKGROUND

Several nitrofuran drugs have been prohibited for use in food producing animals due to their carcinogenic and mutagenic effects. However, one of the nitrofurans, nifuroxazide, is still used as a veterinary drug in some countries. This study was conducted to investigate the residue depletion of nifuroxazide in broiler chicken. Chickens were fed with dietary feeds containing 50 mg kg⁻¹ of nifuroxazide for seven consecutive days. Liver, kidney, muscle and plasma samples were collected at different withdrawal periods, and the residues of parent nifuroxazide and its acid-hydrolysable side chain, 4-hydroxybenzhydrazide (HBH), in these samples were determined.

RESULTS

Nifuroxazide was metabolised in vivo and its metabolite HBH was formed. Parent nifuroxazide was not detectable in these samples after 14 days of cessation. HBH was detectable in these samples even after 28 days of cessation and the total HBH residues were higher than 1.0 ng g⁻¹. Furthermore, the residue level of tissue bound HBH was much higher than that of free HBH.

CONCLUSION

The tissue-bound HBH could be used as a marker to monitor the residue of nifuroxazide in chicken and the best target tissue should be liver. This is the first paper reporting the residue depletion of nifuroxazide in chicken.

Environmental Risk Assessment of antimicrobials applied in veterinary medicine-A field study and laboratory approach

The fate and environmental risk of antimicrobial compounds of different groups of veterinary medicine pharmaceuticals (VMP's) have been compared. The aim was to demonstrate a correlation between the physical and chemical properties of active compounds and their metabolism in target animals, as well as their fate in the environment. In addition, the importance of techniques for manure management and agricultural practice and their influence on the fate of active compounds is discussed. The selected active compounds are shown to be susceptible to at least one environmental factor (sun, water, bacterial or fungal degradation) to which they are exposed during their life cycle, which contributes to its degradation. Degradation under a number of environmental factors has also to be considered as authentic information additional to that observed in the limited conditions in laboratory studies and in Environmental Risk Assessment calculations.

[Pharmacology of licensed antibiotics for use in cattle]

There is an ongoing public debate about the use of antibiotics in farm animals. In this context it is reasonable to provide an update of the pharmacodynamics and pharmacokinetics of antibiotics currently licensed for cattle. The key pharmacologic data of β-lactam-antibiotics, sulfonamide/trimethoprim combinations, tetracyclines, aminoglycosides, fluoroquinolones, macrolide antibiotics, phenicoles, lincosamides and polypeptide antibiotics are presented with particular focus on their use in cattle.

Qualitative structure residue relationship analysis in the determination of the maximum residue limit of veterinary drugs

Aim of the present study was an attempt to find a correlation between physicochemical structure of veterinary drugs and the maximum residue limit (MRL) for muscle tissue of food producing animals. Direct correlation and analysis in quintile groups for 52 physicochemical parameters were performed. An internal validation using leave-one-out cross-validation was performed. In the quintile groups, there were 11 arithmetic expressions created for the limited group of individual parameters (13 from 52 analyzed), which showed a significant linear or quadratic correlation between the number of quintile group and the mean value of MRL within the quintile. The results obtained suggest that there is no direct correlation between individual physicochemical parameters and MRL value in muscle tissue; however, such correlation can be determined for arithmetic expressions created on the basis of several physicochemical parameters, using quintile group analysis.

Tissue depletion and concentration correlations between edible tissues and biological fluids of 3-amino-2-oxazolidinone in pigs fed with a furazolidone-medicated feed

Furazolidone has been prohibited for use in food animal production worldwide for its carcinogenicity and mutagenicity, but it is still illegally used in some farms because of its effectiveness and cheap price. Because of the food safety and economical concerns, it is necessary to find an efficient and low-cost way to monitor the misuse of furazolidone in food-producing animals. For this regard, the tissue depletion and tissue-biological fluid concentration correlations of 3-amino-2-oxazolidinone (AOZ), which is the marker residue of furazolidone, were studied in pigs. Pigs were dosed with 400 mg/kg of furazolidone in feed for 7 days and were sacrificed at the withdrawal time of 0.5, 7, 21, 35, 56, and 63 days. Muscle, liver, kidney, urine, and plasma were collected to detect the AOZ by a simplified indirect competitive enzyme-linked immunosorbent assay (ic-ELISA). Results showed that AOZ was widely distributed in pigs and eliminated slowly after the digestion of furazolidone. The half-lives of AOZ in the plasma, urine, liver, kidney, and muscle were 13.7, 14.7, 13.6, 13.6, and 15.0 days, respectively. Good correlations of the AOZ concentration were found between plasma and muscle, plasma and liver, urine and liver, and urine and kidney in the depletion period of 7-63 or 21-63 days, with correlation coefficients of more than 0.97 and p values less than 0.05. These correlations can provide a basis for a simple and economical way using plasma/urine to monitor the illegal use of furazolidone in pigs without slaughter.

[Oral medication via feed and water -- pharmacological aspects]

By treatment of single animals or a live stock a treatment regimen has to be chosen, which guarantees a sufficient concentration of the administered drug in the target tissue. On the other hand, particular care has to be taken to avoid that single animals get a too high, intolerable dose of the administered drug. These elementary requirements must be met by the attending veterinarian.The treatment schedule must be in line with the current phamaceutical law. Some of the most outstanding problems associated with application via feed and water are discussed. Crucial factors apart from practicability are the bioavailability depending on pharmaceutical form and the avoidance of displacements of drugs. Future efforts should focus on the optimization of oral medication.

Distribution of trenbolone residues in liver and various muscle groups of heifers that received multiple implants at the recommended site of application

Twenty heifers which were each administered 3 or 4 implants containing trenbolone acetate were slaughtered at 30 days post-implantation. Liquid chromatographic analyses were conducted on muscle collected from the rump, loin, shoulder, and neck, and on the liver of each animal. Residues present in liver were primarily 17alpha-trenbolone, and the residues found in the various muscle samples were primarily 17beta-trenbolone. The mean concentration of 17alpha-trenbolone in liver was 4.3 +/- 2.3 ng/g; the mean concentration of 17beta-trenbolone in muscle tissues was < 0.4 ng/g. There was a small but statistically significant effect of the number of implants used on the mean concentration of residues in loin muscles; animals with 3 trenbolone implants had higher mean residue concentrations than animals with 4 trenbolone implants. This suggests that, though the impact of implant numbers on the mean concentration of residues in muscle tissues is negligible relative to currently generally accepted maximum residue levels, mechanisms may exist for selective distribution and retention of residues within different muscle groups.

Application of allometric principles for the prediction of pharmacokinetics in human and veterinary drug development

The concept of correlating pharmacokinetic parameters with body weight (termed as pharmacokinetic interspecies scaling) from different animal species has become a useful tool in drug development. Interspecies scaling is based on the power function, where the body weight of the species is plotted against the pharmacokinetic parameter of interest. Clearance, volume of distribution, and elimination half-life are the three most frequently extrapolated pharmacokinetic parameters. The predicted pharmacokinetic parameter clearance can be used for estimating a first-in-human dose. Over the years, many approaches have been suggested to improve the prediction of aforementioned pharmacokinetic parameters in humans from animal data. A literature review indicates that there are different degrees of success with different methods for different drugs. Interspecies scaling is also a very useful tool in veterinary medicine. The knowledge of pharmacokinetics in veterinary medicine is important for dosage selection, particularly in the treatment of large animals such as horses, camels, elephants, or other large zoo animals. Despite the potential for extrapolation error, the reality is that interspecies scaling is needed across many veterinary practice situations, and therefore will be used. For this reason, it is important to consider mechanisms for reducing the risk of extrapolation errors that can seriously affect animal safety and therapeutic response. Overall, although interspecies scaling requires continuous refinement and better understanding, the rationale approach of interspecies scaling has a lot of potential during the drug development process.

Pharmacogenetics

Pharmacogenetics, the study of genetic determinants of response to drug therapy, is likely the ultimate way to establish the right drug and dose for each patient, thereby optimizing efficacy and minimizing toxicity. Despite the fact that this branch of pharmacology is still in its infancy as a science, a number of important discoveries have already contributed to improved pharmacotherapy in human and veterinary patients.

Use of probabilistic modeling within a physiologically based pharmacokinetic model to predict sulfamethazine residue withdrawal times in edible tissues in swine

The presence of antimicrobial agents in edible tissues of food-producing animals remains a major public health concern. Probabilistic modeling techniques incorporated into a physiologically based pharmacokinetic (PBPK) model were used to predict the amounts of sulfamethazine residues in edible tissues in swine. A PBPK model for sulfamethazine in swine was adapted to include an oral dosing route. The distributions for sensitive parameters were determined and were used in a Monte Carlo analysis to predict tissue residue times. Validation of the distributions was done by comparison of the results of a Monte Carlo analysis to those obtained with an external data set from the literature and an in vivo pilot study. The model was used to predict the upper limit of the 95% confidence interval of the 99th percentile of the population, as recommended by the U.S. Food and Drug Administration (FDA). The external data set was used to calculate the withdrawal time by using the tolerance limit algorithm designed by FDA. The withdrawal times obtained by both methods were compared to the labeled withdrawal time for the same dose. The Monte Carlo method predicted a withdrawal time of 21 days, based on the amounts of residues in the kidneys. The tolerance limit method applied to the time-limited data set predicted a withdrawal time of 12 days. The existing FDA label withdrawal time is 15 days. PBPK models can incorporate probabilistic modeling techniques that make them useful for prediction of tissue residue times. These models can be used to calculate the parameters required by FDA and explore those conditions where the established withdrawal time may not be sufficient.

Verification of compliance with organic meat production standards by detection of permitted and nonpermitted uses of veterinary medicines (tetracycline antibiotics)

In the production of "organic" meat, one of the controlled processes is the use of veterinary drugs. Strict standards are in place as to when and how such drugs may be used. Therefore, the aim of this project was to determine whether it was possible to distinguish between a single therapeutic dose of a tetracycline (permitted under the standards) and both multiple therapeutic dosing and prophylactic dosing (not permitted). This comprised an evaluation of (i) pigs that were treated with oxytetracycline and (ii) chickens dosed with two different tetracycline antibiotics (oxytetracycline and chlortetracycline). The methodology described, using bone sectioning and examination under ultraviolet illumination (either direct observation or fluorescent microscopy), allows samples from animals that have been treated with different dosing regimes (a single therapeutic dose, two successive therapeutic doses, and long-term, low-level "prophylactic" dosing) to be assessed for compliance with organic farming regulations. Validation of the methodology by blind checks of unknown samples by a second operator has been successfully performed, and validation results are presented. The developed methodology has been shown to be applicable to a variety of species and a selection of tetracycline drugs.

High-throughput screening for multi-class veterinary drug residues in animal muscle using liquid chromatography/tandem mass spectrometry with on-line solid-phase extraction

A rapid qualitative method using on-line column-switching liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated for screening 13 target veterinary drugs: four macrolides - erythromycin A, josamycin (leucomycin A3), kitasamycin (leucomycin A5), and tylosin A; six (fluoro)quinolones - ciprofloxacin, danofloxacin, enrofloxacin, flumequine, oxolinic acid, and sarafloxacin; and lincomycin, virginiamycin M1, and trimethoprim in different animal muscles. Clindamycin, norfloxacin, nalidixic acid, oleandomycin, ormetoprim, and roxithromycin were used as the internal standards. After simple deproteination and analyte extraction of muscle samples using acetonitrile, the supernatant was subjected to on-line cleanup and direct analysis by LC/MS/MS. On-line cleanup with an extraction cartridge packed with hydrophilic-hydrophobic polymer sorbent followed by fast LC using a short C18 column resulted in a total analysis cycle of 6 min for 19 drugs. This screening method considerably reduced the time and the cost for the quantitative and confirmatory analyses. The application of a control point approach was also introduced and explained.

Oral Controlled-Release Formulation in Veterinary Medicine

The development of controlled-release dosage forms (CRDFs) is highly desirable both from a convenience and compliance perspective. Furthermore, these formulations release drugs at a prescribed rate, leading to relatively constant blood drug concentrations or to pulse dosing. Another benefit is the ability to administer medications in infrequent regimens. For example, antimicrobial agents generally require very frequent administration regimens. In recent years, the pharmaceutical industry has realized the potential of this treatment modality and efforts have been made to develop a variety of CRDFs exclusively for veterinary use. While there are a number of controlled-release products available for veterinary applications, only a limited number of therapeutic niches (such as the application of antiparasitic drugs in cattle) are associated with products that have been developed as oral controlled-release products. In addition to reviewing potential new therapeutic areas where oral controlled-release products can be applied in veterinary medicine, this article reviews differences in the gastrointestinal tracts of various species and the significance of the dissimilarity in the development of CRDFs. Technological aspects involved in veterinary CRDFs are also assessed.

Fish drug analysis--Phish-Pharm: a searchable database of pharmacokinetics data in fish

Information about drug residues and pharmacokinetic parameters in aquatic species is relatively sparse. In addition, it is difficult to rapidly compare data between studies due to differences in experimental conditions, such as water temperatures and salinity. To facilitate the study of aquatic species drug metabolism, we constructed a Fish Drug/Chemical Analysis Phish-Pharm (FDA-PP) database. This database consists of more than 400 articles that include data from 90 species (64 genera) of fish. Data fields include genus, species, water temperatures, the average animal weight, sample types analyzed, drug (or chemical) name, dosage, route of administration, metabolites identified, method of analysis, protein binding, clearance, volume of distribution in a central compartment (Vc) or volume of distribution at steady-state (Vd), and drug half-lives (t((1/2))). Additional fields list the citation, authors, title, and Internet links. The document will be periodically updated, and users are invited to submit additional data. Updates will be announced in future issues of The AAPS Journal. This database will be a valuable resource to investigators of drug metabolism in aquatic species as well as government and private organizations involved in the drug approval process for aquatic species.

Challenges with the development and approval of pharmaceuticals for fish

With an increase in consumer recognition of the health benefits associated with seafood consumption, the volume of fisheries and aquaculture products consumed by the average American is expected to rise. With a concomitant expectation for high-quality products, aquaculture is likely to become a greater source of consumed fish. As the United States aquaculture industry grows, so does the need to provide veterinary services. As with any intensive farming system, appropriate medications are needed to maintain animal health and to manage fish populations. This article introduces some of the challenges associated with drug approvals for aquatic species and describes how the process of development and regulation of drugs for use in aquatic animals differs from that associated with uses in terrestrial species.

Geriatric pharmacology

When faced with the geriatric dog or cat, the practitioner should consider the following: 1. Avoid using any drugs at all unless there are definite therapeutic indications. If the patient has some degree of renal insufficiency, try to select drugs that are hepatically metabolized and excreted in bile rather than eliminated by the kidneys (eg, doxycycline, tolfenamic acid). If hepatic insufficiency is present, select drugs that do not undergo metabolism before renal excretion (eg, penicillins, cephalosporins). 2. If therapeutic drug monitoring is available, tailor the drug dosage regimen to that specific patient (eg, phenobarbital, digoxin, amino-glycosides). 3. If therapeutic drug monitoring is unavailable, determine if there are clinically proven adjusted dosage regimens for specific drugs. The package insert on human pharmaceutics often gives guidelines for adjusting dosages in geriatric patients. 4. If the drug has not been sufficiently studied to have dosage adjustment recommendations, determine if there is sufficient information about its kinetics to estimate the proper drug dose in a geriatric patient. Some general guidelines for commonly used drugs in geriatric veterinary patients are provided in Table 1. In general, if the Vd changes in your patient, change the dose. If the elimination half-life changes, change the dosing interval. 5. Carefully monitor treated patients for signs of efficacy and toxicity.

Senior and Geriatric Care Programs for Veterinarians

Earlier detection allows earlier intervention, and thus improved treatment success. Senior profiling improves anesthetic safety by identifying hidden existing diseases and permitting the postponement of anesthesia or altering the anesthetic plan. Furthermore, pharmaceutic safety is increased through the detection of underlying diseases that may preclude the use of certain drugs or suggest new alternative treatments. Many dietary recommendations are based on disease diagnosis, making senior profiling an important dietary database. Finally, earlier disease management by means of improved anesthetic, pharmaceutic, and dietary recommendations offers our patients and clients the best medical management possible.

A SAS/IML program for simulating pharmacokinetic data

Data simulation can be an invaluable tool for optimizing the design of bioequivalence trials. It can be particularly useful when exploring alternative approaches for assessing product comparability especially in the context of encountering various complex experimental situations that can occur in veterinary medicine. With this in mind, we designed a novel SAS/IML program to generate pharmacokinetic datasets that reflect the various kinetic, population, and study design characteristics that complicate the bioequivalence evaluation of animal health products. Developing this simulation program within SAS provides an opportunity to utilize the statistical capabilities of this software platform.

Direct determination of five fluoroquinolones in chicken whole blood and in veterinary drugs by HPLC

A direct, accurate, and sensitive chromatographic analytical method for the quantitative determination of five fluoroquinolones (enoxacin, ofloxacin, norfloxacin, ciprofloxacin, and enrofloxacin) in chicken whole blood is proposed in the present study. For quantitative determination lamotrigine was used as internal standard at a concentration of 20 ng/microL. The developed method was successfully applied to the determination of enrofloxacin, as the main component of commercially available veterinary drugs. Fluoroquinolone antibiotics were separated on an Inertsil (250 x 4 mm) C8, 5 microm, analytical column, at ambient temperature. The mobile phase consisted of a mixture of citric acid (0.4 mol L(-1))-CH3OH-CH3CN (87:9:4% v/v) leading to retention times less than 14 min, at a flow rate 1.4 mL min(-1). UV detection at 275 nm provided limits of detection of 2 ng/mL per 20 microL injected volume for enoxacin, norfloxacin, and ciprofloxacin, 0.4 ng/mL for ofloxacin, and 4 ng/mL for enrofloxacin. Preparation of chicken blood samples is based on the deproteinization with acetonitrile while the pharmaceutical drug was simply diluted with water. Peaks of examined analytes in real samples were identified by means of a photodiode array detector. The method was validated in terms of within-day (n=6) precision and accuracy after chicken whole blood sample deproteinization by CH3CN. Using 50 microL of chicken blood sample, recovery rates at fortification levels of 40, 60, and 80 ng ranged from 86.7% to 103.7%. The applicability of the method was evaluated using real samples from chicken under fluoroquinolone treatment.

Pharmacokinetic/pharmacodynamic relationships of antimicrobial drugs used in veterinary medicine

The rise in incidence of antimicrobial resistance, consumer demands and improved understanding of antimicrobial action has encouraged international agencies to review the use of antimicrobial drugs. More detailed understanding of relationships between the pharmacokinetics (PK) of antimicrobial drugs in target animal species and their action on target pathogens [pharmacodynamics (PD)] has led to greater sophistication in design of dosage schedules which improve the activity and reduce the selection pressure for resistance in antimicrobial therapy. This, in turn, may be informative in the pharmaceutical development of antimicrobial drugs and in their selection and clinical utility. PK/PD relationships between area under the concentration time curve from zero to 24 h (AUC(0-24)) and minimum inhibitory concentration (MIC), maximum plasma concentration (C(max)) and MIC and time during which plasma concentrations exceed the MIC have been particularly useful in optimizing efficacy and minimizing resistance. Antimicrobial drugs have been classified as concentration-dependent where increasing concentrations at the locus of infection improve bacterial kill, or time-dependent where exceeding the MIC for a prolonged percentage of the inter-dosing interval correlates with improved efficacy. For the latter group increasing the absolute concentration obtained above a threshold does not improve efficacy. The PK/PD relationship for each group of antimicrobial drugs is 'bug and drug' specific, although ratios of 125 for AUC(0-24):MIC and 10 for C(max):MIC have been recommended to achieve high efficacy for concentration-dependent antimicrobial drugs, and exceeding MIC by 1-5 multiples for between 40 and 100% of the inter-dosing interval is appropriate for most time-dependent agents. Fluoroquinolones, aminoglycosides and metronidazole are concentration-dependent and beta-lactams, macrolides, lincosamides and glycopeptides are time-dependent. For drugs of other classes there is limited and conflicting information on their classification. Resistance selection may be reduced for concentration-dependent antimicrobials by achieving an AUC(0-24):MIC ratio of greater than 100 or a C(max):MIC ratio of greater than 8. The relationships between time greater than MIC and resistance selection for time-dependent antimicrobials have not been well characterized.

Integration and modelling of pharmacokinetic and pharmacodynamic data to optimize dosage regimens in veterinary medicine

In veterinary drug development procedures, pharmacokinetic (PK) and pharmacodynamic (PD) data have generally been established in separate, parallel studies to assist in the design of dosage schedules for subsequent evaluation in clinical trials. This review introduces the concept of PK/PD modelling, an approach in which PK and PD data are generated in the same study, and used to derive numerical values for PD parameters based on drug plasma concentrations. The PD parameters define the efficacy, potency and slope (sensitivity) of the concentration-effect relationship. It is proposed that the parameters derived from PK/PD modelling may be used as an alternative and preferred approach to dose titration studies for selecting rational dosage regimens (both dose and dosing interval) for further evaluation in clinical trials. In PK/PD modelling, the explicative variable for effect is the plasma concentration profile. The PK/PD approach provides several advantages over dose-titration studies, including determination of a projected dosage regimen by investigation of a single dose, in contrast to dose-ranging studies which by definition require testing of multiple dosage. Implementation of PK/PD modelling in the veterinary drug development process is currently constrained by the limited number of veterinary studies performed to date, and the consequently limited understanding of PK/PD concepts and their absence from regulatory authority guidelines. Nevertheless, PK/PD modelling has major potential for rational dosage regimen determination, as it considers and quantifies the two main sources of interspecies variability (PK and PD). It is therefore applicable to interspecies extrapolation and to multiple species drug development. As well as the currently limited appreciation of PK/PD principles in the veterinary scientific community, a further constraint in implementing PK/PD modelling is the need to validate PK/PD approaches and thereby gain confidence in its value by pharmaceutical companies and regulatory authorities.

Pharmacodynamics and pharmacokinetics of nonsteroidal anti-inflammatory drugs in species of veterinary interest

This review summarises selected aspects of the pharmacokinetics (PK) and pharmacodynamics (PD) of nonsteroidal anti-inflammatory drugs (NSAIDs). It is not intended to be comprehensive, in that it covers neither minor species nor several important aspects of NSAID PD. The limited objective of the review is to summarise those aspects of NSAID PK and PD, which are important to an understanding of PK-PD integration and PK-PD modelling (the subject of the next review in this issue). The general features of NSAID PK are: usually good bioavailability from oral, intramuscular and subcutaneous administration routes (but with delayed absorption in horses and ruminants after oral dosing), a high degree of binding to plasma protein, low volumes of distribution, limited excretion of administered dose as parent drug in urine, marked inter-species differences in clearance and elimination half-life and ready penetration into and slow clearance from acute inflammatory exudate. The therapeutic effects of NSAIDs are exerted both locally (at peripheral inflammatory sites) and centrally. There is widespread acceptance that the principal mechanism of action (both PD and toxicodynamics) of NSAIDs at the molecular level comprises inhibition of cyclooxygenase (COX), an enzyme in the arachidonic acid cascade, which generates inflammatory mediators of the prostaglandin group. However, NSAIDs possess also many other actions at the molecular level. Two isoforms of COX have been identified. Inhibition of COX-1 is likely to account for most of the side-effects of NSAIDs (gastrointestinal irritation, renotoxicity and inhibition of blood clotting) but a minor contribution also to some of the therapeutic effects (analgesic and anti-inflammatory actions) cannot be excluded. Inhibition of COX-2 accounts for most and possibly all of the therapeutic effects of NSAIDs. Consequently, there has been an intensive search to identify and develop drugs with selectivity for inhibition of COX-2. Whole blood in vitro assays are used to investigate quantitatively the three key PD parameters (efficacy, potency and sensitivity) for NSAID inhibition of COX isoforms, providing data on COX-1:COX-2 inhibition ratios. Limited published data point to species differences in NSAID-induced COX inhibition, for both potency and potency ratios. Members of the 2-arylpropionate sub-groups of NSAIDs exist in two enantiomeric forms [R-(-) and S-(+)] and are licensed as racemic mixtures. For these drugs there are marked enantiomeric differences in PK and PD properties of individual drugs in a given species, as well as important species differences in both PK and PD properties.

Plasma terminal half-life

Terminal plasma half-life is the time required to divide the plasma concentration by two after reaching pseudo-equilibrium, and not the time required to eliminate half the administered dose. When the process of absorption is not a limiting factor, half-life is a hybrid parameter controlled by plasma clearance and extent of distribution. In contrast, when the process of absorption is a limiting factor, the terminal half-life reflects rate and extent of absorption and not the elimination process (flip-flop pharmacokinetics). The terminal half-life is especially relevant to multiple dosing regimens, because it controls the degree of drug accumulation, concentration fluctuations and the time taken to reach equilibrium.

Principles of pharmacodynamics and their applications in veterinary pharmacology

Pharmacodynamics (PDs) is the science of drug action on the body or on microorganisms and other parasites within or on the body. It may be studied at many organizational levels--sub-molecular, molecular, cellular, tissue/organ and whole body--using in vivo, ex vivo and in vitro methods and utilizing a wide range of techniques. A few drugs owe their PD properties to some physico-chemical property or action and, in such cases, detailed molecular drug structure plays little or no role in the response elicited. For the great majority of drugs, however, action on the body is crucially dependent on chemical structure, so that a very small change, e.g. substitution of a proton by a methyl group, can markedly alter the potency of the drug, even to the point of loss of activity. In the late 19th century and first half of the 20th century recognition of these facts by Langley, Ehrlich, Dale, Clarke and others provided the foundation for the receptor site hypothesis of drug action. According to these early ideas the drug, in order to elicit its effect, had to first combine with a specific 'target molecule' on either the cell surface or an intracellular organelle. It was soon realized that the 'right' chemical structure was required for drug-target site interaction (and the subsequent pharmacological response). In addition, from this requirement, for specificity of chemical structure requirement, developed not only the modern science of pharmacology but also that of toxicology. In relation to drug actions on microbes and parasites, for example, the early work of Ehrlich led to the introduction of molecules selectively toxic for them and relatively safe for the animal host. In the whole animal drugs may act on many target molecules in many tissues. These actions may lead to primary responses which, in turn, may induce secondary responses, that may either enhance or diminish the primary response. Therefore, it is common to investigate drug pharmacodynamics (PDs) in the first instance at molecular, cellular and tissue levels in vitro, so that the primary effects can be better understood without interference from the complexities involved in whole animal studies. When a drug, hormone or neurotransmitter combines with a target molecule, it is described as a ligand. Ligands are classified into two groups, agonists (which initiate a chain of reactions leading, usually via the release or formation of secondary messengers, to the response) and antagonists (which fail to initiate the transduction pathways but nevertheless compete with agonists for occupancy of receptor sites and thereby inhibit their actions). The parameters which characterize drug receptor interaction are affinity, efficacy, potency and sensitivity, each of which can be elucidated quantitatively for a particular drug acting on a particular receptor in a particular tissue. The most fundamental objective of PDs is to use the derived numerical values for these parameters to classify and sub-classify receptors and to compare and classify drugs on the basis of their affinity, efficacy, potency and sensitivity. This review introduces and summarizes the principles of PDs and illustrates them with examples drawn from both basic and veterinary pharmacology. Drugs acting on adrenoceptors and cardiovascular, non-steroidal anti-inflammatory and antimicrobial drugs are considered briefly to provide a foundation for subsequent reviews in this issue which deal with pharmacokinetic (PK)-PD modelling and integration of these drug classes. Drug action on receptors has many features in common with enzyme kinetics and gas adsorption onto surfaces, as defined by Michaelis-Menten and Langmuir absorption equations, respectively. These and other derived equations are outlined in this review. There is, however, no single theory which adequately explains all aspects of drug-receptor interaction. The early 'occupation' and 'rate' theories each explain some, but not all, experimental observations. From these basic theories the operational model and the two-state theory have been developed. For a discussion of more advanced theories see Kenakin (1997).