Inhalation anesthesia induced by isoflurane alters penicillin disposition in swine tissues.

Twelve healthy swine were dosed with penicillin G intramuscularly. Fluids and tissues samples were collected at the end of two periods of general anesthesia, performed 24 h apart. Tissue samples were collected by minimally invasive laparoscopy under general anesthesia at 8 and 28 h postdose. Four nonanesthetized, penicillin-treated pigs were euthanized at 8 h postdose, and a second set of four similarly treated control pigs were sacrificed 28 h postdose. Liver penicillin tissue concentrations from animals that underwent anesthesia and laparoscopic tissue collection had tissue concentrations that were higher than nonanesthetized pigs at both time points. Urine, plasma, kidney, skeletal, and cardiac muscle showed no differences between the two groups. Laparoscopic tissue collection under general anesthesia in swine induces physiological changes that cause alterations in tissue pharmacokinetics not seen in conscious animals.

A Holstein cow-calf model for the transfer of ciprofloxacin through milk after a long-term intravenous infusion.

This study is part of an ongoing effort to develop animal models that provide milk and sufficient infant (offspring) plasma samples to fully describe a drug's pharmacokinetics to quantitate the risk to the nursing infant. Ciprofloxacin was administered to six healthy Holstein cows as a constant rate intravenous infusion (flow rate was weight adjusted) to achieve a steady-state concentration of approximately 300 ng/mL for 7 days. Plasma and milk samples were collected from the cow at regular intervals over the course of the 7 days. The plasma and milk samples were analyzed for ciprofloxacin by high-performance liquid chromatography. The milk was fed to calves, and calf plasma samples were analyzed to study the lactational transfer of ciprofloxacin from dam to nursing neonate. Remarkably, concentrations of ciprofloxacin in milk were 45 times higher than plasma drug concentrations in the dam. Approximately 6% of the administered dose was transferred to the milk, resulting in an average oral dose of 0.5 mg/kg to the calves with every feeding. The drug did not accumulate in the calves, and plasma concentrations were between one-tenth and one-fifth the plasma concentrations of the dam.

Tissue/fluid correlation study for the depletion of sulfadimethoxine in bovine kidney, liver, plasma, urine, and oral fluid.

Sulfonamides are among the oldest, but still effective, antimicrobial veterinary medicines. In steers and dairy cows, the sulfonamides are effective in the treatment of respiratory disease and general infections. Sulfadimethoxine (SDM) has been approved by US Food and Drug Administration (FDA) for use in steers and dairy cows with a tolerance of 100 ng/g (ppb) in edible tissues and 10 ppb in milk. The detection of SDM residue above tolerance in the animal slaughtered for food process will result in the whole carcass being discarded. This report describes a comprehensive depletion study of SDM (and its main metabolite) in plasma, urine, oral fluid, kidney, and liver. In this study, nine steers were injected intravenously with the approved dose of SDM; the loading dose was 55 mg/kg, followed by 27.5 mg/kg dose at 24 h and again at 48 h. Fluids (blood, urine, and saliva) and tissue (liver and kidney) samples were collected at intervals after the last dose of SMD. The combination of laparoscopic serial sampling technique with the liquid chromatography/mass spectrometry method provided the data to establish the tissue/fluid correlation in the depletion of SMD. A strong correlation and linearity of the log-scale concentration over time in the depletion stage has been confirmed for kidney, liver, and plasma.

Bovine kidney tissue/biological fluid correlation for penicillin.

Penicillin is one of the most commonly misused drugs in steers and dairy cows. In the US, at slaughter the tolerance is 50 ng/g in kidney and other edible tissues. If the tolerance is exceeded, the carcass may not be used for human food. A preslaughter test for penicillin in an easily accessible biological fluid is needed to predict if the concentration of penicillin is below tolerance in the kidney before the bovine is slaughtered. In this study, 12 steers were injected three times with the approved dose (7000 IU) of penicillin at 12-h intervals. Blood and urine samples were collected at intervals after the final dose of penicillin. At each sampling point, one kidney biopsy sample was collected by laparoscopic surgery in the live animal. Another kidney sample was collected at slaughter. Correlations between plasma and kidney concentrations and between urine and kidney concentrations were determined. These correlations predict with 95% confidence that 99% of the animals will have kidney tissue below penicillin tolerance when the plasma concentration of penicillin is below 0.4 ng/mL and/or the urine penicillin concentration is below 140 ng/mL.

Use of tissue-fluid correlations to estimate gentamicin residues in kidney tissue of Holstein steers.

Gentamicin continues to be one of the most effective antibiotics for the treatment of gram-negative infections. Greater than 90% of the drug is rapidly eliminated from the body in <2 days, however, a small residue remains bound to the kidney cortex tissue for many months. In beef steers, the gentamicin residue is unacceptable and its presence is monitored by the FAST (Fast Antimicrobial Screen Test) applied to the kidney at the time of slaughter. The sensitivity of the FAST to gentamicin in the kidney cortex is reported to be 100 ng/g, therefore, this level of gentamicin defines the acceptable limit of gentamicin drug residue in the bovine kidney. In the present study, three doses of 4 mg/kg gentamicin was administered intramuscularly to eight steers. Gentamicin was allowed to deplete from the kidneys for a range of times from 7 to 10 months. At slaughter the level of gentamicin in the kidney cortex varied from 91 to 193 ng/g, but a total of 160 FAST tests performed on the kidneys were negative. Blood and urine samples were collected at varying times following the last dose of gentamicin. Kidney tissue samples were collected by laparoscopic surgery in the live steers as well as the final sample obtained at slaughter. Plasma levels of gentamicin declined rapidly to nondetectable within 3 days, while measurable urine persisted for 75 days before the concentration of gentamicin declined to levels too low to quantitate by the available liquid chromatography tandem mass spectrometry (LC/MS/MS) technique. An estimated correlation between an extrapolation of urine gentamicin concentration to the corresponding kidney tissue sample suggests a urine to kidney tissue relationship of 1:100. A test system sufficiently sensitive to a urine gentamicin concentration of 1 ng/mL will correlate with the estimated 100 ng/g gentamicin limit of the FAST applied to the fresh kidney of the recently slaughtered bovine.

A reproducible nonlethal animal model for studying cyanide poisoning.

Previous studies using bolus intravenous injections of sodium cyanide have been used to model the sudden exposure to high concentrations of cyanide that could occur on the battlefield. This study was designed to develop a model that would simulate the type of exposure to cyanide gas that could happen during actual low-level continuous types of exposure and then compare it with the bolus model. Cardiovascular and respiratory recordings taken from anesthetized dogs have been used previously to characterize the lethal effects of cyanide. The intravenous, bolus injection of 2.5 mg/kg sodium cyanide provides a model in which a greater than lethal concentration is attained. In contrast, our model uses a slow, intravenous infusion of cyanide to titrate each animal to its own inherent end point, which coincides with the amount of cyanide needed to induce death through respiratory arrest. In this model, therapeutic intervention can be used to restore respiration and allow for the complete recovery of the animals. After recovery, the same animal can be given a second infusion of cyanide, followed again by treatment and recovery, providing a reproducible end point. This end point can then be expressed as the total amount of cyanide per body weight (mg/kg) required to kill. In this study, the average dose of sodium cyanide among 12 animals was 1.21 mg/kg, which is approximately half the cyanide used in the bolus model. Thus, titration to respiratory arrest followed by resuscitation provides a repetitive-use animal model that can be used to test the efficacy of various forms of pretreatment and/or therapy without the loss of a single animal.

Antibiotic residues in milk samples obtained from cows after treatment for papillomatous digital dermatitis.

OBJECTIVE: To determine whether there would be detectable antibiotic residues in milk obtained from dairy cattle with papillomatous digital dermatitis (PDD) after topical treatment with oxytetracycline. DESIGN: Randomized controlled clinical trial. ANIMALS: 28 lactating Holstein cows with PDD. PROCEDURE: Cows were assigned to 2 treatment groups. Treatment 1 (n = 16) consisted of spraying of PDD lesions with 15 ml of a solution containing 100 mg of oxytetracycline/ml; lesions were sprayed twice daily for 7 days, using a garden sprayer. Treatment 2 (n = 12) consisted of a one-time application of a bandage that consisted of cotton soaked with 20 ml of a solution containing 100 mg of oxytetracycline/ml. Milk samples were obtained before and after treatment and assayed for tetracycline content by use of high-performance liquid chromatography and a commercially available tetracycline screening test. RESULTS: None of the cows in either treatment group had violative residues of oxytetracycline in milk samples. CONCLUSIONS AND CLINICAL RELEVANCE: Producers treating lactating cows that have PDD, via topical application of oxytetracycline solution at the concentrations reported in this study, have a low risk of causing violative antibiotic residues in milk.

Application of microbial receptor assay to quantitation of residues of spectinomycin in bovine milk and comparison with liquid chromatographic analysis.

Spectinomycin-contaminated bovine milk samples were assayed by liquid chromatographic (LC) and microbial receptor methods. LC involved a newly developed analytical method to quantitate the concentration of spectinomycin in the contaminated milk samples. The receptor assay used reagents and the reaction system used for the Charm II spectinomycin assay. Three standard curves (selected range, full range, and second-order polynomial) were plotted for the receptor assay and used to quantitate spectinomycin in contaminated milk samples. The levels of spectinomycin obtained by the receptor assay, using only the standard curve in the selected range, were comparable to the results obtained by LC analysis.

Effectiveness of intramuscularly administered cyanide antidotes on methemoglobin formation and survival.

Successful first aid therapy for cyanide intoxication is dependent upon immediate administration of antidotes which directly or indirectly interact with the cyanide ion to remove it from circulation. Owing to the severe respiratory, cardiovascular and convulsive episodes following acute cyanide intoxication, the most practical approach is to administer antidotes by intramuscular injection. Exceptionally rapid methemoglobin formers-hydroxylamine hydrochloride (HH) and dimethylaminophenol (DMAP)-are usually able to prevent the lethal effect of cyanide following intramuscular injections in doses sufficient to induce 20% methemoglobin (HH = 20 mg kg-1 and DMAP = 2 mg kg-1). Sodium nitrite, the methemoglobin inducer approved for military use, must be administered by intravenous infusion because it is not an effective cyanide antidote by the intramuscular route. In the normal unintoxicated animal an intramuscular injection of 20 mg kg-1 sodium nitrite will form 20% methemoglobin; however, in acute cyanide intoxication the associated severe bradycardia appears to limit the rate of absorption and thus the rapid formation of methemoglobin. If the bradycardia is prevented or reversed by atropine, the rate of absorption of sodium nitrite and the formation of methemoglobin is able to reverse the otherwise lethal effects of cyanide. Thus, an intramuscularly administered combination of 20 mg kg-1 sodium nitrite and 1 mg kg-1 atropine sulfate, rapidly absorbed from the intramuscular site, appears to achieve the same degree of effectiveness against acute cyanide intoxication as intramuscularly administered HH or DMAP. It would appear from these studies that HH, DMAP and sodium nitrite with atropine are all potentially effective intramuscular antidotes for acute cyanide poisoning.

Effectiveness of oral pyridostigmine pretreatment and cholinolytic-oxime therapy against soman intoxication in nonhuman primates.

Nonhuman primates which were fed Mestinon (pyridostigmine) syrup-impregnated food biscuits (40 mg per animal) exhibited a reproducible inhibition of whole blood cholinestrase activity of 40 to 50% for a period of 1 to 6 hr. Pyridostigmine pretreatment was supplemented by therapy with two doses of an antidotal combination (A,TM,B) consisting of 0.05 mg/kg atropine, 2.24 mg/kg TMB-4, and 0.4 mg/kg benactyzine which assured survival in five of six animals following three separate exposures to 10 LD50 soman. The protective period of this oral dose of pyridostigmine supported by A,TM,B therapy was between 1/2 and 8 hr. Oral pyridostigmine pretreatment in combination with atropine therapy (three doses of 0.07 or 1.00 mg/kg im) also saved monkeys exposed to 10 LD50 soman; however, the period of recovery was prolonged. Oral pyridostigmine pretreatment did not alter the lethality of soman in the absence of A,TM,B or atropine therapy.

Efficacy evaluation of physostigmine and anticholinergic adjuncts as a pretreatment for nerve agent intoxication.

Pretreatment of nonhuman primates with physostigmine (Phy) and scopolamine or physostigmine and trihexyphenidyl 25 min before exposure to 2 LD50 soman im resulted in complete survival without convulsions or loss of consciousness. When identically pretreated animals were challenged with 5 LD50s of soman followed by atropine and 2-PAM therapy 1 min later, all animals experienced a loss of consciousness for approximately 10 min followed by functional recovery within an additional 20 min. These findings indicated that a pretreatment regimen composed of Phy and cholinolytic is capable of protecting primates from an absolute lethal dose of soman with rapid recovery from incapacitation.

The pharmacokinetics of atropine and diazepam in sheep: intramuscular co-administration.

The purpose of this study was to determine whether the co-administration of atropine and diazepam affect the rate and extent of absorption of either drug. A triple crossover pharmacokinetic study using adult sheep was conducted. Each of nine animals received single injections of atropine (2 mg), diazepam (10 mg), and a combination of the two compounds weekly over a 3-week period. The combination of the drugs was injected into a single intramuscular site through a specially designed tandem syringe. Blood samples were obtained from time 0 to 300 min post-injection. Serum samples were analyzed for atropine by radioimmunoassay and for diazepam by gas chromatography/mass spectrometry. Pharmacokinetic parameters were evaluated by non-compartmental analysis. The co-administration of atropine and diazepam intramuscularly in sheep caused a delay in the time to reach maximal concentration of atropine. However, at the time when a single injection of atropine reached its maximum serum concentration, 92 per cent of that concentration was reached by atropine in the presence of diazepam. Additionally, no difference was detected in the rate or extent of diazepam absorption when administered intramuscularly in combination with atropine at the same site.

Pralidoxime chloride stability-indicating assay and analysis of solution samples stored at room temperature for ten years.

A high-performance liquid chromatographic (HPLC) method is described for quantitation of pralidoxime chloride and its decomposition products 2-carboxy-, 2-formyl-, and 2-(aminocarbonyl)-1-methylpyridinium chloride. These decomposition products and 2-cyano- and 2-(hydroxymethyl)-1-methylpyridinium chloride and 1-methyl-2(1H)-pyridinone were separated from pralidoxime chloride on a silica gel column using a mobile phase of acetonitrile:water (86:14) in which the aqueous component was 8.36 mM in tetraethylammonium chloride and 52.5 mM in acetic acid. This method allows quantitation of the relatively low levels of 2-formyl-1-methylpyridinium chloride formed in acidic solution at room temperature. Sensitivity was shown to be at least 5 ng of the pralidoxime chloride and 15 ng of the 2-carboxy-, 2-formyl-, and 2-(aminocarbonyl)-1-methylpyridinium chloride injected on column. The coefficient of variation was 4% or less for all components measured. Autoinjectors containing 300 mg/mL of pralidoxime chloride in water were stored at room temperature for 8-10 years, followed by analysis for hydrogen cyanide using an ion-selective electrode. Less than 15 micrograms of cyanide per autoinjector was detected. The HPLC analysis of the solutions after being stored an additional 3-4 years at approximately 5 degrees C demonstrated that greater than 90% of the total of all measured components consisted of pralidoxime chloride. The remaining percentage was made up of 2-carboxy-, 2-formyl-, and 2-(aminocarbonyl)-1-methylpyridinium chloride.

Intragastric mefloquine is absorbed rapidly in patients with cerebral malaria.

Mefloquine has proved effective in chloroquine- and quinine-resistant falciparum malaria, but it cannot be given parenterally. We have measured the absorption of mefloquine hydrochloride suspension (mean 15.6, range 9.7-28.6 mg/kg) given by nasogastric tube to 19 cerebral malaria patients already receiving intravenous quinine. Absorption was rapid with both dose schedules used; mean absorption half-times were 1.5 and 1.8 hr, and plasma mefloquine concentrations exceeded 200 ng/g within 3 hr of completing administration in all but one exceptionally ill patient who died 40 hr later. Steady state plasma concentrations over 7 days ranged from 300 to 1,050 (mean 561) ng/g. Bioavailability of mefloquine suspension in cerebral malaria therefore appears to be adequate for treatment in all but the most severely ill patients. Although intragastric mefloquine cannot now be recommended as an alternative to intravenous quinine for the treatment of severe chloroquine-resistant falciparum malaria, this situation could change if quinine resistance increases further.

Analysis of the antimalarial, mefloquine, in blood and plasma using high-performance liquid chromatography.

An analytical method is described for the quantitation of mefloquine, a new antimalarial agent, in plasma and blood. A structurally similar quinolinemethanol compound, WR 184,806, is used as the internal standard. The method employs a three-step extraction procedure followed by reversed-phase high-performance liquid chromatography, and octanesulfonate is used as an ion-pairing reagent. Detection is achieved at 222 nm. The entire procedure is relatively simple and requires only 1 ml of sample. Good accuracy and precision are obtained over the wide concentration range tested.

Effect of honeybee (Apis mellifera) venom on the course of adjuvant-induced arthritis and depression of drug metabolism in the rat.

The ability of honeybee venom to suppress Mycobacterium butyricum-induced arthritis was studied in Lewis rats. Bee venom, 2 mg.kg-1.day-1 for 24 days, suppressed but did not abolish the primary and secondary inflammatory responses to the adjuvant as monitored by decreases in the swelling of the left and right hind paws and adjuvant-induced arthritis on heme metabolism were also examined. Bee venom or adjuvant had no effect on hepatic delta-aminolevulinic acid synthase, porphyrin content, or ferrochelatase activity. However, with both treatments cytochrome P-450 and the associated enzymic activities of ethylmorphine N-demethylase and benzo[a]pyrene hydroxylase were depressed markedly. In contrast, both treatments caused several-fold enhancement of hepatic microsomal heme oxygenase activity. Adjuvant-treated rats receiving bee venom showed changes in heme metabolism which were of a magnitude similar to those observed when either agent was administered to the experimental animals. Although the bee venom appears to suppress adjuvant-induced arthritis to a greater extent in female than in male rats, the alterations in heme metabolism were similar in bee venom-treated male and female rats. The observed changes in heme metabolism elicited by the venom or by the adjuvant are strongly suggestive of perturbations of the immune system causing alterations in hepatic microsomal enzymes.