Effect of milk fraction on concentrations of cephapirin and desacetylcephapirin in bovine milk after intramammary infusion of cephapirin sodium

Clinical mastitis in dairy cows is commonly treated with intramammary (IMM) antimicrobial agents. Pharmacokinetic data are used to design treatment regimens and determine withholding times. In some pharmacokinetic studies, investigators measure antimicrobial concentrations in foremilk, whereas in others, they use bucket milk or do not specify the milk fraction sampled. Our objective was to compare antimicrobial concentrations in foremilk, bucket milk, and strippings after IMM treatment of six healthy Holsteins. One mammary gland/cow was infused with 200 mg of cephapirin (CEPH) after each of the two milkings, using different milking frequencies and treatment intervals in a randomized crossover design. Treated glands were sampled at the first milking following each infusion. Antimicrobial concentrations in milk were measured using HPLC/MS/MS. CEPH concentration was higher in foremilk (geometric mean 44.2 μg/mL) than in bucket milk (15.7 μg/mL) or strippings (18.5 μg/mL), as it was true for desacetylcephapirin (DAC) (59.5, 23.0, and 30.2 μg/mL, respectively). This finding, which was based on milk samples collected at the first milking after IMM infusion, suggests that pharmacokinetic data based on drug concentrations in foremilk may be misleading. Strippings were more representative of bucket milk than foremilk. The relationship between milk fraction and antimicrobial concentration should be investigated for other IMM antimicrobial agents. Meanwhile, it is essential that pharmacokinetic and residue studies report the fraction of milk that was analyzed.     

Modelling the concentration-time relationship in milk from cattle administered an intramammary drug

Whittem, T., Whittem, J. H., Constable, P. D. Modelling the concentration–time relationship in milk from cattle administered an intramammary drug. J. vet. Pharmacol. Therap.  35 , 460–471. Antimicrobial drugs are often infused directly through the streak canal into the bovine udder for the treatment or prevention of mastitis. These infusions have two major problems: drug residues in milk and variable antimicrobial efficacy. Both problems are influenced by the pharmacokinetics of intramammary delivery and elimination of drugs. This pharmacokinetics does not conform to the assumptions of traditional first‐order mamillary pharmacokinetic models. To help understand drug delivery into and elimination from the udder, a new approach to pharmacokinetic modelling of the udder is proposed. This new model was used to predict the movement of drug within the udder and the concentrations of drug achieved within physiological compartments of the udder. These predictions were examined using computer modelling. The model was evaluated using data from in vivo intramammary infusion of cefuroxime. The model predicts that changes in milking efficiency (residual volume), milk productivity and milking frequency can impact both the drug residue persistence and the time that milk drug concentrations exceed the minimum inhibitory concentrations for pathogens. The model provides a new tool for future evaluation of intramammary dosing studies.     

Factors associated with the risk of antibiotic residues and intramammary pathogen presence in milk from heifers administered prepartum intramammary antibiotic therapy

Heifers (n=136) from 5 herds were treated with a commercially available beta-lactam intramammary (IMM) antibiotic preparation containing cephapirin sodium at 10-21 d prior to anticipated parturition to evaluate the risk of antibiotic residues occurring in milk postpartum and to determine factors associated with antibiotic residues and IMM pathogen presence in milk postpartum. Mammary secretions collected from quarters before antibiotic administration and during weeks 1, 2 and 3 postpartum were analyzed for mastitis pathogens. Composite milk was collected at milkings 3, 6 and 10 postpartum and analyzed for beta-lactam residues using a microbial inhibition antibiotic residue screening test. Antibiotic residues were confirmed with beta-lactamase treatment and re-tested for residues. Residues were detected in 28.0, 8.82 and 3.68% of milk samples obtained at the third, sixth, and tenth milking postpartum, respectively. Increases in interval between prepartum antibiotic therapy and parturition and an increase in the postpartum interval to sampling were associated with a decrease in risk of antibiotic residues. The presence of antibiotic residues in milk at the third milking was associated with a reduced risk for IMM pathogen prevalence in the first 21 d postpartum. Lower somatic cell counts, an increase in mean milk yield over 200 days in milk and a reduction in IMM pathogen prevalence were associated with the presence of an antibiotic in milk postpartum. Screening milk for antibiotic residues in milk postpartum following prepartum antibiotic therapy in heifers is recommended to reduce the risk for antibiotic residue contamination of milk.     

Milk production,plasma metabolite profiles and mammary arterial‐venous differences of milk precursors in early lactation cows milked at different frequencies by an automatic milking system

The objective of this study was to clarify the effect of different milking frequencies under an automatic milking system (AMS) on milk yield, plasma metabolite profiles and mammary arterial‐venous (A‐V) differences of milk precursors by mammary tissues in early lactation cows. Twelve Holstein cows were divided into two and four times milking frequency treatments by AMS after calving to 50 days postpartum. Cows were given a partial mixed ration ad libitum and a concentrate diet at every milking. Dry matter intake increased similarly in both treatments with advancing postpartum days. Milk yield was greater (P < 0.001) by 25% with four times milking, but milk composition was not affected by milking frequency. Body weight change was also not affected by milking frequency. Arterial concentrations of glucose and glutamate were lower (P < 0.05) for four times milking frequency. However, arterial concentration of nonesterified fatty acids did not differ between treatments. Although mammary A‐V differences of plasma concentration for most milk precursors did not differ between treatments, estimated plasma flow was higher (P < 0.05) for four times milking frequency. These results indicate that higher milking frequency may increase mammary uptake of milk precursors, whereas may not affect the extent of fat mobilization of early lactating cows from day 20 postpartum onward.     

Residue persistence in sheep milk following antibiotic therapy

Drug residues in milk supplies may have public health implications and can interfere in the manufacture of dairy products, such as cheese. In Spain, most ewe milk production is destined for cheese making, often using raw milk. This study analyses the main factors influencing antibiotic depletion time in lactating dairy sheep. 42, Manchega ewes were distributed into three groups, each receiving a different treatment (cephalexin intramammary infusion, penicillin G intramuscular, and oxytetracycline intravenous injections). During and after the recommended withdrawal period, milk samples were taken at each milking. A microbiological inhibition test (Brilliant Black Reduction, BRT) was used to screen all samples and antibiotic withholding times were established using a logistic regression model. The response to the BRT method in milk from individual ewes treated showed that the effect of the milking order was significant (P<0.001) with the three antibiotics. However the only influence on milk yield was with the intramammary treatment (P<0.005). The BRT method was found to be very sensitive, particularly to the two beta-lactamic antibiotics.     

Diffusion‐limited PBPK model for predicting pulmonary pharmacokinetics of florfenicol in pig

For most bacterial lung infections, the concentration of unbound antimicrobial agent in lung interstitial fluid has been thought to be responsible for antimicrobial efficacy. In this study, a diffusion‐limited physiologically based pharmacokinetic (PBPK) model was developed to predict the pulmonary pharmacokinetics of florfenicol (FF) in pigs. The model included separate compartments corresponding to blood, diffusion‐limited lung, flow‐limited muscle, liver, and kidney and an extra compartment representing the remaining carcass. The absorption rate constant and renal and hepatic clearance of FF were determined in vivo. Other parameters were taken from the literature or optimized based on existing pharmacokinetic data. All mathematical operations during the development of the model were performed using acslXtreme version 3.0.2.1 (Aegis Technologies Group, Inc., Huntsville, AL, USA). The model accurately predicted the concentration–time courses of FF in lung interstitial fluid, serum, and plasma following different dosing schedules, except at the dose of 15 mg/kg. When compared with the tissue residue data, the model generally underestimated the FF concentration at the injection site, whereas it gave good predictions of FF concentrations in lung, liver, and kidney at early time points. The model predictions provide a scientific basis for the dosage regimen design of FF.     

Pharmacokinetic estimation for therapeutic dosage regimens (PETDR) – a software program designed to determine intravenous drug dosage regimens for veterinary applications

Pharmacokinetic estimation for therapeutic dosage regimens (PETDR) is a soft-ware program used to design individualized intravenous dosage regimens, determine concentration-time profiles, predict serum concentrations at a specific time after intravenous dosing and predict the time after the last dose to achieve a specified concentration of drug. The reference pharmacokinetic parameters may be based on an individual animal's pharmacokinetic disposition of drug or on FARAD (Food Animal Residue Avoidance Databank) mean population kinetic parameters. An individual animal's kinetic parameters may be input for predetermined analysis or the program can calculate these values by input of raw serum concentration-time data. The program allows the user to specify certain parameters of the dosage regimen, then calculates the other parameters (given desired maximum and minimum serum concentrations, dose and interval are calculated; given desired maximum serum concentration and interval, dose is calculated, etc.). Given the kinetic parameters, the dose and dosing interval, the program calculates and plots the serum concentration-time profile of the drug for that animal. The time and the number of doses to reach steady state can be calculated as well as the determination of loading dose. The percentage of the time of a dosing interval at steady state that the serum concentration is above a specific minimum inhibitory concentration (MIC) allows evaluation of efficacy of an antimicrobial regimen. Similarly, the time to reach a specific concentration (e.g. residue tolerance) or the MIC of a drug can be calculated. Legal tissue tolerances can be accessed from FARAD to aid in predicting for what period of time illegal residues will remain in the animal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficacy of intramammary infusion of ceftiofur hydrochloride at drying off for treatment and prevention of bovine mastitis during the nonlactating period

This study evaluated the efficacy of intramammary infusion of ceftiofur hydrochloride for the treatment of intramammary infections present at the last milking of lactation and for prevention of new intramammary infections during the nonlactating period. Cows were randomly assigned to five treatments (untreated negative control, 125, 250, and 500 mg of ceftiofur, and a positive control group receiving 300 mg cephapirin benzathine). A dose of 125 mg of ceftiofur per mammary quarter was effective for treatment of existing infections present at the time of milk cessation, but only the 500-mg dose of ceftiofur per mammary quarter was effective for both treatment of existing intramammary infections at the time of milk cessation and for prevention of new intramammary infections during the nonlactating period.     

A rapid analytical method of major milk proteins by reversed‐phase high‐performance liquid chromatography

A reversed‐phase high‐performance liquid chromatography (RP‐HPLC) method with rapid and automated analysis, good separation, high resolution, high accuracy and reproducible results was successfully developed and used to separate and quantify the major cow milk proteins within 30 min analytical time. Standard solutions of single purified cow milk proteins were used to develop calibration equations. The RP‐HPLC method was validated with respect to intra‐day repeatability, inter‐day precision, linearity, accuracy and limit of detection (LOD). The recoveries of the RP‐HPLC analyses of major milk proteins from cows ranged 71.0–114%, the inter‐day precision was expressed as the relative standard deviation, and the ranged from 1.51 to 4.60% and the LOD ranged from 0.08 g/L to 0.28 g/L. Major proteins in cow were quantified according to the chromatographic profiles. Results showed that a rapid RP‐HPLC method for quantifying the major cow milk proteins was developed, which could be used to determine milk protein contents in the dairy industry.     

Effects of Machine‐milking on the Bacterial Flora of Teat Duct and Mammary Gland of Ewes

In total, 308 paired‐samples of teat duct material and milk, were collected before and 50–70 min after machine‐milking, from 30 ewes. Samples were processed bacteriologically. For analysis of results, we compared changes in bacterial isolation following milking, for duct and milk samples; statistical significance was assessed by the Sign Test. Bacteria were isolated from 18 (6%) duct and 19 (6%) milk samples collected before the milking procedure; respective figures after it, were 81 (26%) and 33 (11%). In 77 (25%) cases, bacteriological findings in the two duct samples of each pair were different; in seven cases bacteria were isolated only before, whilst in 70 cases bacteria were isolated only after milking (P < 0.005); respective results for milk samples were 26 (8%): 6 and 20 cases (P = 0.693). The majority of bacterial isolates were staphylococci, accounting for 63% of 99 isolates. The milking procedure predisposes to entrance of bacteria into the teat duct; however, increased bacterial isolation from the teat did not result to increased mammary infections, likely as a consequence of defence mechanisms present in healthy teats.     

Persistence of antibiotics in bovine mammary secretions following intramammary infusion at cessation of milking

A study was conducted to determine the persistence of antibiotic preparations for use in nonlactating cows in bovine mammary secretions following intramammary infusion at cessation of milking. Five commercially available antibiotic formulations were evaluated using 311 cows. All quarters of each cow were sampled once only during the nonlactating period and most cows were sampled at or near parturition. Antibiotic residues were detected qualitatively by the Bacillus stearothermophilus disc assay. Great variation between different antibiotics in persistence in mammary secretion was observed. In general, mammary secretions from most mammary glands infused with cloxacillin or penicillin-dihydrostreptomycin were positive at 28–35 days after infusion and some were positive at 42–49 days after infusion. On the other hand, <13% of mammary secretions at 7 days after infusion of novobiocin and 50% of mammary secretions at 14 days after infusion of penicillin-novobiocin were positive for antibiotics. Cephapirin benzathine persisted for about 21 days after infusion. Some samples that were positive for antibiotics after initial testing were negative following heating of samples, suggesting that component(s) of dry secretion can inhibit growth of B. stearothermophilus and influence the interpretation of results. Colostrum samples from all quarters except one were negative for antibiotics. These data suggest that nonlactating-cow antibiotic formulations persist primarily during the early to mid-nonlactating period. Based upon present methods of formulation, it would appear that antibiotic preparations for use in nonlactating cows most likely provide little protection during the periparturient period, at a time when mammary glands are highly susceptible to new intramammary infections.     

Chronic exposure to the mycotoxin T‐2 promotes oral absorption of chlortetracycline in pigs

The aim of this study was to investigate whether T‐2 toxin, a potent Fusarium mycotoxin, affects the oral absorption of the antibiotic chlortetracycline in pigs. Animals were allocated to blank feed without T‐2 toxin (controls), feed containing 111 μg T‐2/kg feed, T‐2‐contaminated feed supplemented with a yeast‐derived feed additive, or blank feed supplemented solely with the feed additive, respectively. After 21 days, an intragastric bolus of chlortetracycline was given to assess potential alterations in the pharmacokinetics of this commonly used antibiotic. A significantly higher area under the plasma concentration–time curve and maximal plasma concentration of chlortetracycline was observed after intake of T‐2‐contaminated feed compared with control. Thus, exposure to T‐2‐contaminated feed can influence the oral bioavailability of chlortetracycline. This effect could have consequences for the withdrawal time of the drug and the occurrence of undesirable residues in edible tissues.     

Microbiological screening test validation for detection of tylosin excretion in milk of cows with low and high somatic cell counts

Antibiotic residues in milk above tolerance levels interfere with dairy product processing and pose potential health risks to consumers. Residue avoidance programmes include, among other components, the observance of withdrawal times indicated in label instructions. Persistence of antibiotics in milk following treatment is influenced by drug, dosage, route of administration, body weight and mammary gland health status. Compositional changes that take place during intramammary infection (IMI) can affect antibiotic excretion in milk, thus modifying milk withdrawal time. The objectives of this study were to validate sensitivity and specificity of a qualitative microbiological method (Charm AIM-96) to detect tylosin in bovine composite milk and to determine the influence of subclinical IMI in tylosin excretion following intramuscular administration. For test validation, two groups of approximately 120 cows were used; one received a single intramuscular injection of tylosin tartrate at a dose of 20 mg/kg, while the other group remained as untreated control. Test sensitivity and specificity were 100% and 94.1% respectively. To determine the influence of subclinical IMI in tylosin excretion, two groups of seven cows, one with somatic cell counts (SCC) < or =250 000 cells/ml and the other with SCC > or =900 000, were administered a single intramuscular injection of tylosin tartrate at a dose of 20 mg/kg. Milk samples were obtained every 12 h for 10 days following treatment. Milk tylosin excretion averaged between 5 and 9 days for cows with low and high SCC respectively (P < 0.0001). Compositional changes in cows with high SCC most likely affect the pharmacokinetic characteristics of tylosin, extending the presence of the antibiotic in milk, thus influencing milk withdrawal times.     

Impact of lactation on pharmacokinetics of meloxicam in goats

Use of drug in lactating animal should be carefully considered due to its possibility of changes in pharmacokinetics as well as drug penetration in milk. The aim of this study was to assess the effect of lactation on pharmacokinetics of meloxicam after IV and IM administrations in goats. A crossover design (2 × 2) was used for each lactating and nonlactating group of goats with a 3-week washout period. Meloxicam (0.5 mg/kg) was administered into the jugular vein and upper gluteal muscle by IV and IM routes, respectively. The plasma and milk drug concentrations were determined by high-performance liquid chromatography with diode array detector, and the pharmacokinetic analysis was carried out by noncompartmental analysis. The pharmacokinetic parameters of meloxicam in lactating and nonlactating goats were not significantly different. The IM bioavailability of meloxicam was relatively lower in lactating (75.3 ± 18.6%) than nonlactating goats (103.8 ± 34.7%); however, the difference was not statistically significant. Moreover, AUC ratio between milk and plasma, which represent drug milk penetration, for both IV and IM administrations was less than 1 (about 0.3). In conclusion, pharmacokinetic parameters of meloxicam are not significantly altered by lactation for either the IV or IM routes of administration and this drug does not require a different dosage regimen for lactating animals.     

Oral bioavailability of P‐glycoprotein substrate drugs do not differ between ABCB1‐1Δ and ABCB1 wild type dogs

Mealey, K.L., Waiting, D., Raunig, D.L., Schmidt, K.R., Nelson, F.R. Oral bioavailability of P‐glycoprotein substrate drugs do not differ between ABCB1‐1Δ and ABCB1 wild type dogs. J. vet. Pharmacol. Therap. 33 , 453–460. Previous studies have indicated that intestinal P‐glycoprotein (P‐gp) limits the oral bioavailability of substrate drugs and alters systemic pharmacokinetics. In this study, dogs lacking functional P‐gp were used to determine the contribution of P‐gp to the oral bioavailability and systemic pharmacokinetics of several P‐gp substrate drugs. The P‐gp substrates quinidine, loperamide, nelfinavir, cyclosporin and the control (non P‐gp substrate) drug diazepam were individually administered intravenously and per os to ABCB1‐1Δ dogs, which have a P‐gp null phenotype and ABCB1 wildtype dogs. ABCB1‐1Δ dogs have been shown to have greater brain penetration of P‐gp substrates, but limited information is available regarding oral bioavailability of P‐gp substrate drugs in this animal model. Plasma drug concentration vs. time curves were generated and pharmacokinetic parameters were calculated for each drug. There were no differences in oral bioavailability between ABCB1‐1Δ dogs and ABCB1 wildtype dogs for any of the drugs studied, suggesting that intestinal P‐gp does not significantly affect intestinal absorption of these particular substrate drugs in ABCB1‐1Δ dogs. However, small sample sizes and individual variability in CYP enzyme activity may have affected the power of the study to detect the impact of P‐gp on oral bioavailability.     

Oral dosage regimen in the nonlinear pharmacokinetics of sulphadimethoxine in pigs

Summary

An oral high dosage regimen of sulphadimethoxine (SDM) was examined in pigs. The dose (50 mg/kg) in the therapeutic range, showed nonlinear pharmacokinetics, and administered by drench once a day for 4 days. The unbound plasma concentration‐time profile was compared with that of the dosage regimen based on nonlinear pharmacokinetics, where a pharmacokinetic model and parameters were used except for the first order absorption rate constant (ka) and bioavailability (F). F and ka were obtained from oral and intravenous administration of 20 and 10 mg/kg of SDM. The unbound plasma concentration was observed almost within the setting range by the dosage regimen through the experimental period. This result suggested that the dosage regimen, based on the nonlinear pharmacokinetic model, resulted in an appropriate effect in the clinical use.     

Research Progress on Pharmacokinetics and Residue Elimination of Antibacterial Synergist

Antibacterial synergist can enhance the antibacterial activity of the antibiotics, reduce bacterial resistance and improve treatment effect. Pharmacokinetic study is to develop dosage regimen and evaluate efficacy in clinical.Elimination of residual study can understand drug residual target tissue and residual marker to formulate appropriate withdraw time. This review briefly describes the aditoprim, trimethoprim,diaveridine of three kinds of antibacterial synergist pharmacokinetic and residue elimination rule, emphatically when contrast aditoprim to trimethoprim in the pharmacokinetic parameters of different animals. We can conclude aditoprim with longer elimination half-life and larger apparent volume of distribution, and trimethoprim elimination half-life is different in different animals, diaveridine is often used as intestinal antibacterial synergist. Recently researchers always use high performance liquid chromatography (HPLC) method or chromatographic combination method to study antibacterial synergist on pharmacokinetics and residues elimination research, it shows that the method has good specificity and high sensitivity. Currently due to the irrational use even abuse of antibiotics leading to drug failure and bacterial drug resistance problems, the presence of the antibacterial synergist for solving this problem provide a new direction, and three kinds of antibacterial synergist in different animals pharmacokinetic and residues elimination research is helpful to understand various kinds of drugs commonalities and differences in different animals, in order to find problems of this kind of drug in clinical using and continuously perfect applications of antibacterial synergist in clinical.     

抗菌增效剂药动学与残留消除研究进展

抗菌增效剂可以增强抗生素的抗菌活性、减少细菌耐药性的产生、提高治疗效果。药动学研究是临床上制定给药方案,评价药效的重要指标;残留消除研究可以了解药物的残留靶组织、残留标识物,进而制定适宜的休药期。作者简述了艾地普林、甲氧苄啶、二甲氧苄啶3种抗菌增效剂的药动学及残留消除规律,着重对比艾地普林与甲氧苄啶在不同动物体内的药动学参数,显示与甲氧苄啶相比艾地普林具有更长的消除半衰期及更大的表观分布容积,且甲氧苄啶在不同动物体内的消除半衰期差异较大,二甲氧苄啶常作为肠道的抗菌增效剂使用。目前多采用高效液相色谱法及和其他色谱联用的方法,对抗菌增效剂进行药动及残留消除研究,并且也证明了该方法专一性好、灵敏度高。当前由于抗生素的不合理使用甚至滥用导致的药物失效以及细菌耐药性的问题越来越普遍,而抗菌增效剂的出现为解决该类问题提供了新的方向。通过对3种抗菌增效剂在不同动物体内的药动学及残留消除研究,有利于深入了解各种药物在不同动物体内共性和差异性规律,以期发现该类药物在临床使用中存在的问题并且不断地完善抗菌增效剂在临床上的应用。     

Pharmacokinetics and pharmacodynamics of intramammary cefquinome in lactating goats with and without experimentally induced Staphylococcus aureus mastitis

Values for pharmacokinetic variables are usually obtained in healthy animals, whereas drugs are frequently administered to diseased animals. This study investigated cefquinome pharmacokinetics in healthy goats and goats with experimentally induced mastitis. Five adult lactating goats received 75 mg of cefquinome intramammary infusion using a commercially available product into one udder half in healthy goats and goats with clinical mastitis that was induced by intracisternal infusion of 100 cfu of Staphylococcus aureus ATCC 29213 suspended in 5 ml of sterile culture broth. Cefquinome concentrations were determined in plasma and skimmed milk samples using high‐performance liquid chromatography (HPLC). Pharmacodynamics was investigated using the California Mastitis Test and pH of milk. Experimentally induced mastitis significantly increased the California Mastitis Test score and pH, and decreased the maximal cefquinome concentration and shortened the half‐life in milk when compared to healthy goats. In conclusion, mastitis facilitated the absorption of cefquinome from the mammary gland of lactating goats and induced marked changes in milk pH, emphasizing the importance of performing pharmacokinetic studies of antimicrobial agents in infected animals.