Pharmacokinetics of orally administered single‐dose ponazuril in cats

Cats and kittens in animal shelters and catteries regularly suffer from severe gastrointestinal coccidiosis, which can be fatal, and there are no drugs labeled for feline coccidiosis in the United States. Ponazuril, a triazine‐class drug, is increasingly used at a dose of 50 mg/kg/d, orally, for three to five days in shelter environments for coccidiosis. A single oral dose of ponazuril paste 15% (Marquis^®; Merial) at 50 mg/kg was administered to six healthy adult cats. Sample analysis was completed via high‐performance liquid chromatography. Plasma concentrations peaked at 7.49 ± 2.06 µg/ml at 14.67 ± 7.45 hr post‐administration. This study shows that ponazuril achieved a plasma concentration that inhibits growth of similar organisms after a single oral dose in cats. Further studies are necessary to optimize dosing for the treatment of clinical coccidiosis in cats.

Pharmacokinetics and pharmacodynamics of repeat dosing of gabapentin in adult horses

Background

The repeated administration of high doses of gabapentin may provide better analgesia in horses than current clinical protocols.

Hypothesis and Objectives

Administration of gabapentin at 40 and 120 mg/kg PO q 12 h for 14 days will not alter serum biochemistry findings or cause adverse effects. Our objectives were to evaluate the effect of gabapentin on serum biochemistry, physical examination, and plasma pharmacokinetics of gabapentin.

Animals

Six healthy adult mares.

Methods

Horses received 40 and 120 mg/kg of gabapentin orally q 12 h for 14 days. Horses were examined and scored for ataxia and sedation daily. Serum biochemistry variables were analyzed before treatment and days 7 and 14 after gabapentin administration. Plasma disposition of gabapentin was evaluated after the first and last drug administration. Pharmacokinetic parameters were estimated using noncompartmental analysis.

Results

No changes occurred in physiologic or biochemical variables. Median (range) maximal plasma gabapentin concentrations (μg/mL) after the last dose (day 15) were 7.6 (6.2‐11) and 22 (14‐33) for 40 mg/kg and 120 mg/kg doses respectively. Maximal concentration of gabapentin was reached within 1 hour after drug administration. Repeated administration of gabapentin resulted in a median (range) area under the curve (AUC_{0‐12 hours}) last/first dose ratio of 1.5 (1.00‐2.63) and 2.92 (1.4‐3.8) for the 40 and 120 mg/kg regimens, respectively.

Conclusion and Clinical Importance

Our results suggest that horses tolerate gabapentin up to 120 mg/kg PO q 12 h for 14 days. The analgesic effect of the dosage regimens evaluated in our study warrants further research.

The influence of storage time on ponazuril concentrations in feline plasma

Background

The pharmacokinetics of ponazuril have been determined in several species; however, there is very little information on the stability of the drug after storage for long periods of time. This study was undertaken to determine the stability of ponazuril in plasma samples stored at -80 °C, which is the temperature most commonly used in the author's laboratory.

Method

Spiked plasma samples (0.3, 7.5, and 15 µg/mL) were stored at -80 °C for three months. Analysis occurred on the first day and then once a week for the following twelve weeks. The drug was extracted using a chloroform extraction and separated by high performance liquid chromatography using ultraviolet detection.

Results

There was no loss of drug for any concentration for the first four weeks of storage. There was an average loss of less than 5% from day 35 through day 70 and an average loss of 6% on day 77 and 84. The data suggest that ponazuril is stable for 4 weeks when stored at -80 °C and undergoes minimal loss in the remaining 8 weeks.

Pharmacokinetics of Orally Administered Prednisolone in Alpacas

This study aimed to determine the pharmacokinetics of prednisolone following intravenous and oral administration in healthy adult alpacas. Healthy adult alpacas were given prednisolone (IV, n = 4), as well as orally (PO, n = 6). Prednisolone was administered IV once (1 mg/kg). Oral administration was once daily for 5 days (2 mg/kg). Each treatment was separated by a minimum 4 month washout period. Samples were collected at 0 (pre-administration), 0.083, 0.167, 0.25, 0.5, 0.75, 1, 2, 4, 8, 12, and 24 h after IV administration, and at 0 (pre-administration), 0.25, 0.5, 0.75, 1, 2, 4, 8, 12, 24 after the first and 5^th PO administration. Samples were also taken for serial complete blood count and biochemistry analysis. Prednisolone concentration was determined by high pressure liquid chromatography. Non-compartmental pharmacokinetic parameters were then determined. After IV administration clearance was 347 mL/kg/hr, elimination half-life was 2.98 h, and area under the curve was 2,940 h^*ng/mL. After initial and fifth oral administration elimination half-life was 5.27 and 5.39 h; maximum concentration was 74 and 68 ng/mL; time to maximum concentration was 2.67 and 2.33 h; and area under the curve was 713 and 660 hr^*ng/mL. Oral bioavailability was determined to be 13.7%. Packed cell volume, hemoglobin, and red blood cell counts were significantly decreased 5 days after the first PO administration, and serum glucose was significantly elevated 5 days after the first PO administration. In conclusion, serum concentrations of prednisolone after IV and PO administration appear to be similar to other veterinary species. Future research will be needed to determine the pharmacodynamics of prednisolone in alpacas.

Pharmacokinetics of Pantoprazole and Pantoprazole Sulfone in Goats After Intravenous Administration: A Preliminary Report

Background: Ruminant species are at risk of developing abomasal ulceration, but there is a lack of pharmacokinetic data for anti-ulcer therapies, such as the proton pump inhibitor pantoprazole, in goats.

Objective: The primary study objective was to estimate the plasma pharmacokinetic parameters for pantoprazole in adult goats after intravenous administration. A secondary objective was to describe the pharmacokinetic parameters for the metabolite, pantoprazole sulfone, in goats.

Methods: Pantoprazole was administered intravenously to six adult goats at a dose of 1 mg/kg. Plasma samples were collected over 36h and analyzed via reverse phase high performance liquid chromatography for determination of pantoprazole and pantoprazole sulfone concentrations. Pharmacokinetic parameters were determined by non-compartmental analysis.

Results: Plasma clearance, elimination half-life, and volume of distribution of pantoprazole were estimated at 0.345 mL/kg/min, 0.7 h, and 0.9 L/kg, respectively following IV administration. The maximum concentration, elimination half-life and area under the curve of pantoprazole sulfone were estimated at 0.1 μg/mL, 0.8 h, and 0.2 hr^*μg/mL, respectively. The global extraction ratio was estimated 0.00795 ± 0.00138. All animals had normal physical examinations after conclusion of the study.

Conclusion: The reported plasma clearance for pantoprazole is lower than reported for foals, calves, and alpacas. The elimination half-life appears to be < that reported for foals and calves. Future pharmacodynamic studies are necessary for determination of the efficacy of pantoprazole on acid suppression in goats.

Bioanalytical RP-HPLC method for the determination of ponazuril in plasma

The goal of this investigation was to establish a reliable technique for the quantitation of ponazuril in limited sample volumes. Samples were extracted with chloroform and separation was achieved with a Symmetry RP₁₈ column. Ultraviolet absorption was measured at 254 nm. A combination of 0.1% formic acid and acetonitrile (50:50) was used as the mobile phase. The calibration curve was linear from 0.1-25 μg/mL, with a lower limit of quantification of 0.1 μg/mL with a 100 μL sample. The precision and accuracy were well within the range set by the Food and Drug Administration and the recovery was over 95%. This technique was used to analyze ponazuril samples and found to be appropriate for pharmacokinetic studies.

Determination of ceftazidime in plasma by RP-HPLC and ultraviolet detection

A simple high-performance liquid chromatography method for the determination of ceftazidime in plasma has been developed. Using an ultrafiltration technique samples were separated by reverse-phase high-performance liquid chromatography on a Symmetry C₁₈ 4.6 × 250 mm column (5.0 μm) and ultraviolet absorbance was measured at 260 nm. The mobile phase was a mixture of 10 mm potassium phosphate monobasic pH 2.5 with phosphoric acid and acetonitrile (90:10). The standard curve ranged from 0.1 to 100 μg/ml. Intra- and inter-assay variability for ceftazidime was <12%, and the average recovery was 89%. The lower limit of quantification was 0.1 μg/ml. This method has been used successfully to analyze frog plasma samples at this institution and it could be applied to other small volume samples in a clinical or research setting.

Evaluation of the pharmacokinetics and efficacy of transdermal flunixin for pain mitigation following castration in goats

The mitigation of pain associated with common management procedures is a rising concern among veterinarians, producers and consumers. Nonsteroidal anti-inflammatory drugs are vital compounds for this purpose due to their cost, convenience, and efficacy. A transdermal formulation of flunixin meglumine (FM) was approved for the treatment of pain in cattle; however, the efficacy has yet to be determined for small ruminants. The current study had two aims: 1) to determine the pharmacokinetics of transdermal flunixin meglumine (TD FM) in bucklings and 2) to evaluate pain mitigation by TD FM following castration. To evaluate pharmacokinetics, 12 male goats (mean age = 6 mo) received 2.2 mg/kg of FM IV (n = 6) or 3.3 mg/kg TD FM (n = 6). Plasma FM concentrations were measured. The mean C_max, T_max, and harmonic mean half-life for TD FM were 1.09 ± 0.65 μg/mL, 5.50 ± 2.95 h, and 7.16 ± 2.06 h, respectively. To evaluate the efficacy of pain mitigation, 18 goats were randomly assigned to three treatment groups: 1) TD FM and castration (FM CAST) (n = 6); 2) transdermal placebo and castration (PL CAST) (n = 6); and 3) TD FM and sham castration (SHAM) (n = 6). Plasma samples were collected at 0, 12, 24, 36, 48, 72, and 96 h to assess cortisol and prostaglandin E₂ (PGE₂)_. Daily dry matter intake (DMI) was recorded and body weight was measured at the beginning and end of the study. Thermography (IRT) images of the scrotum, as well as heart rate (HR), respiratory rate (RR), and rectal temperature, were taken twice daily. Separate mixed analysis of variance models were used to test the effects of treatment, time, and their interaction on mean body temperature, IRT, HR, and RR. Autoregressive covariance structure was utilized to account for repeated measures and individual goat DMI prior to the study was added as a covariate. There were no differences in vital parameters, IRT measurements, cortisol, or PGE₂ in animals receiving either TD FM or placebo following castration (P > 0.05). DMI had a treatment by hour interaction and was significantly higher in FM CAST and SHAM groups than the PL CAST group (P = 0.04). Goats in the SHAM group gained weight throughout the study, whereas goats in all other groups lost weight (P = 0.02). Results indicate that TD FM may mitigate pain as demonstrated by increased DMI; however, a single dose may not be sufficient to reduce physiological indicators of pain associated with castration in goats.

Determination of Thiafentanil in Plasma Using LC-MS

A new method of analysis has been developed and validated for the determination of thiafentanil in plasma. After protein precipitation, samples were separated on an XBridge BEH C18 column and quantified using mass spectrometry. The mobile phase was a mixture of water with 0.1% formic acid and acetonitrile with 0.1% formic acid (90:10). The standard curve ranged from 0.1 to 25 ng/mL. Intra- and Inter-assay variability for thiafentanil was less than 10%, and the average recovery was greater than 95%. The lower limit of quantification was 0.1 ng/mL. This is the first validated method for thiafentanil analysis in plasma.

Determination of grapiprant plasma and urine concentrations in horses

OBJECTIVE

Non-steroidal anti-inflammatory drugs are inhibitors of cyclooxygenase (COX) in tissues and used as therapeutic agents in different species. Grapiprant, a member of the piprant class of compounds, antagonizes prostaglandin receptors. It is a highly selective EP4 prostaglandin E₂ receptor inhibitor, thereby limiting the potential for adverse effects caused by wider COX inhibition. The objectives of this study were to determine if the approved canine dose would result in measurable concentrations in horses, and to validate a chromatographic method of analysis for grapiprant in urine and plasma.

STUDY DESIGN

Experimental study.

ANIMALS

A total of six healthy, adult mixed-breed mares weighing 502 ± 66 (397-600) kg and aged 14.8 ± 5.3 (6-21) years.

METHODS

Mares were administered one dose of 2 mg kg^-1 grapiprant via nasogastric tube. Blood and urine samples were collected prior to and up to 48 hours after drug administration. Drug concentrations were measured using high-performance liquid chromatography.

RESULTS

Grapiprant plasma concentrations ranged from 71 to 149 ng mL^-1 with the mean peak concentration (106 ng mL^-1) occurring at 30 minutes. Concentrations were below the lower limit of quantification (50 ng mL^-1) in four of six horses at 1 hour and in all six horses by 2 hours after drug administration. Grapiprant urine concentrations ranged from 40 to 4077 ng mL^-1 and were still detectable at 48 hours after administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Currently, there are no published studies looking at the pharmacodynamics of grapiprant in horses. The effective concentration needed to control pain in dogs ranges 114-164 ng mL^-1. Oral administration of grapiprant (2 mg kg^-1) in horses did not achieve those concentrations. The dose was well tolerated; therefore, studies with larger doses could be conducted.

Plasma disposition of gabapentin after the intragastric administration of escalating doses to adult horses

Background

In humans, gabapentin an analgesic, undergoes non‐proportional pharmacokinetics which can alter efficacy. No information exists on the pharmacokinetics of dosages >20 mg/kg, escalating dosages or dose proportionality of gabapentin in horses.

Hypothesis and Objectives

Gabapentin exposure in plasma would not increase proportionally relative to the dose in horses receiving dosages ≥20 mg/kg. To assess the plasma pharmacokinetics of gabapentin after nasogastric administration of gabapentin at dosages of 10 to 160 mg/kg in adult horses.

Animals

Nine clinically healthy adult Arabian and Quarter Horses.

Methods

In a randomized blinded trial, gabapentin was administered by nasogastric intubation to horses at 10, 20 mg/kg (n = 3) and 60, 80, 120, 160 mg/kg (n = 6). Plasma was collected before and at regular times over 64 hours after administration of gabapentin. Gabapentin was quantified using a validated chromatographic method. Dose proportionality was estimated using a power model. Pharmacokinetic parameters were estimated using compartmental pharmacokinetic analysis.

Results

Plasma pharmacokinetics parameters of gabapentin were estimated after nasogastric administration at dosages of 10 to 160 mg/kg. Gabapentin plasma concentration increased with dose increments. However, the area under the concentration curve from zero to infinity and maximal plasma concentration did not increase proportionally relative to the dose in horses.

Conclusions and Clinical Importance

Gabapentin exposure in plasma is not proportional relative to the dose in horses receiving nasogastric dosages of 10 to 160 mg/kg.