Pharmacokinetics and pharmacodynamics of tolfenamic acid in calves

Pharmacokinetics of tolfenamic acid in ducks (Anas platyrhynchos domestica) after different administration routes

1. The objective of this research was to compare the pharmacokinetics and bioavailability of tolfenamic acid, analgesic, antipyretic and anti-inflammatory compound, after administration through different routes to Pekin ducks. The investigation was carried out over four time periods using a randomised cross-pharmacokinetic design.2. Tolfenamic acid was administered to ducks intravenously, intramuscularly, subcutaneously and orally at a dose of 2 mg/kg. Tolfenamic acid analysis was performed using HPLC-UV and pharmacokinetic data were conducted by non-compartmental analysis.3. The total clearance, volume of distribution at steady state and terminal elimination half-life after intravenous administration were 0.14 l/h/kg, 0.29 l/kg and 1.80 h, respectively. The peak plasma concentration and bioavailability for intramuscular, subcutaneous and oral administration were 4.59, 3.55 and 2.23 μg/ml and 93.62, 74.30 and 43.43%, respectively.4. Tolfenamic acid was absorbed rapidly, eliminated quickly and exhibited a small distribution volume in Pekin ducks. Pharmacokinetic parameters, including maximum concentration, area under the plasma concentration - time curve and bioavailability, were found to be different in ducks from other bird species.

Pharmacokinetics, bioavailability and plasma protein binding of tolfenamic acid in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Although research on the mechanism and control of pain and inflammation in fish has increased in recent years, the use of analgesic drugs is limited due to the lack of pharmacological information about analgesic drugs. Tolfenamic acid is a non-steroidal anti-inflammatory drug and can be used in fish due to its low side effect profile and superior pharmacokinetic properties.

OBJECTIVES

The pharmacokinetics, bioavailability and plasma protein binding of tolfenamic acid were investigated following single intravascular (IV), intramuscular (IM) and oral administration of 2 mg/kg in rainbow trout at 13 ± 0.5°C.

METHODS

The experiment was carried out on a total of 234 rainbow trout (Oncorhynchus mykiss). Tolfenamic acid was administered to fish via IV, IM and oral route at a dose of 2 mg/kg. Blood samples were taken at 13 different sampling times until the 72 h after drug administration. The plasma concentrations of tolfenamic acid were quantified using high pressure liquid chromatography-ultraviolet (UV) and pharmacokinetic parameters were assessed using non-compartmental analysis.

RESULTS

The elimination half-life (t1/2ʎz) of tolfenamic acid for IV, IM and oral routes was 3.47, 6.75 and 9.19 h, respectively. For the IV route, the volume of distribution at a steady state and total body clearance of tolfenamic acid were 0.09 L/kg and 0.03 L/h/kg, respectively. The peak plasma concentration and bioavailability for IM and oral administration were 8.82 and 1.24 µg/mL, and 78.45% and 21.48%, respectively. The mean plasma protein binding ratio of tolfenamic acid in rainbow trout was 99.48% and was not concentration dependent.

CONCLUSIONS

While IM route, which exhibits both the high plasma concentration and bioavailability, can be used in rainbow trout, oral route is not recommended due to low plasma concentration and bioavailability. However, there is a need to demonstrate the pharmacodynamic activity of tolfenamic acid in rainbow trout.

Analysis of Tolfenamic Acid using a Simple, Rapid, and Stability-indicating Validated HPLC Method

BACKGROUND

Tolfenamic acid (TA) belongs to the fenamates class of nonsteroidal anti-inflammatory drugs. Insufficient information is available regarding the availability of a reliable and validated stability-indicating method for the assay of TA.

OBJECTIVE

A relatively simple, rapid, accurate, precise, economical, robust, and stabilityindicating RP-HPLC method has been developed to determine TA in pure and tablet dosage forms.

METHODS

The method was validated according to the ICH guideline, and parameters like linearity, range, selectivity, accuracy, precision, robustness, specificity, and solution stability were determined. TLC and FTIR spectrometry were used to ascertain the purity of TA. The specificity was determined with known impurities and after performing forced degradation, while the robustness was established by Plackett-Burman's experimental design. The mobile phase used for the analysis was acetonitrile and water (90:10, v/v) at pH 2.5. The detection of the active drug was made at 280 nm using a C18 column (tR = 4.3 min.). The method's applicability was also checked for the yellow polymorphic form of TA.

RESULTS

The results indicated that the method is highly accurate (99.39-100.80%), precise (<1.5% RSD), robust (<2% RSD), and statistically comparable to the British Pharmacopoeia method with better sensitivity and specificity.

CONCLUSION

It was observed that the stress degradation studies do not affect the method's accuracy and specificity. Hence the proposed method can be used to assay TA and its tablet dosage form.

The Surface Area to Volume Ratio Changes the Pharmacokinetic and Pharmacodynamic Parameters in the Subcutaneous Tissue Cage Model: As Illustrated by Carprofen in Sheep

Introduction

Pharmacokinetic and pharmacodynamic models can be powerful tools for predicting outcomes. Many models are based on repetitive sampling of the vascular space, due to the simplicity of obtaining samples. As many drugs do not exert their effect in the vasculature, models have been developed to sample tissues outside the bloodstream. Tissue cages are hollow devices implanted subcutaneously, or elsewhere, that are filled with fluid allowing repetitive sampling to occur. The physical dimensions of the cage, namely, the diffusible surface area to volume ratio, would be expected to change the rate of drug movement into and out of tissue cages.

Methods

Seven sheep were implanted with five pairs of tissue cages, subcutaneously. Each pair of cages had a different length but a fixed diffusible surface area, so the surface area to volume ratio differed. Carrageenan was injected into half of the cages in each animal during one sampling period in a cross-over design. Samples from each cage and the bloodstream were obtained at 14-time points during two sampling periods. The concentration of carprofen was measured using LC–MS/MS and the results were modeled using nonlinear mixed-effects techniques. Prostaglandin metabolites were also measured and the change over time was analyzed using linear mixed effect modeling.

Results

The presence of carrageenan within an animal changed the systemic pharmacokinetics of carprofen. The rate of drug movement into and out of the tissue cages varied with the surface area to volume ratio. The concentration time curve for prostaglandin metabolites changed with cage size.

Conclusion

The surface area volume ratio of tissue cages will influence the calculated pharmacokinetic parameters and may affect calculated pharmacodynamics, thus, it is an important factor to consider when using tissue cage data for dosing regimes.

Pharmacokinetics of intravenous meloxicam, ketoprofen and tolfenamic acid in chukar partridge (Alectoris chukar)

1. The aim of this study was to determine the pharmacokinetics of meloxicam (MLX, 1 mg/kg body weight (BW)), ketoprofen (KETO, 2 mg/kg BW), and tolfenamic acid (TA, 2 mg/kg BW) in chukar partridge (Alectoris chukar) following intravenous (IV) administration.2. Twenty-four healthy chukar partridges were randomly divided into three equal groups (n = 8) as MLX, KETO and TA. Plasma concentrations of MLX, KETO and TA were measured using high-performance liquid chromatography-ultraviolet detection and analysed using non-compartmental analysis.3. No adverse effects were determined in chukar partridges after IV administration of MLX, KETO and TA. MLX, KETO and TA were detected in plasma up to 10, 12 and 12 h, respectively. The terminal elimination half-life of MLX, KETO and TA was 1.22, 1.77 and 1.95 h, respectively. MLX, KETO and TA exhibited volumes of distribution at a steady-state of 0.03, 0.23 and 0.41 l/kg BW, respectively. The total plasma clearance of MLX, KETO and TA was 0.02, 0.11 and 0.15 l/h/kg, respectively. The extraction ratios for MLX, KETO and TA were calculated as 0.002, 0.011 and 0.016, respectively.4. MLX, KETO and TA offer treatment in chukar partridges for various conditions with an absence of adverse reactions and properties such as short elimination half-life and low volume of distribution. However, there is a need to establish the safety and adverse effects of repeated administration, pharmacokinetics of other administration routes and pharmacological efficacy of MLX, KETO and TA in chukar partridges.

Co-formulation of ketoprofen with tulathromycin alters pharmacokinetic and pharmacodynamic profile of ketoprofen in cattle

The current studies aimed to evaluate the pharmacokinetic (PK) and pharmacodynamic (PD) profile and to establish a PK-PD model for ketoprofen in a new fixed combination product containing tulathromycin (2.5 mg/kg) and ketoprofen (3 mg/kg) to treat bovine respiratory disease associated with pyrexia in cattle. Firstly, the effect of different ketoprofen doses as mono-substance (1, 3, and 6 mg/kg subcutaneous) on lipopolysaccharide-induced fever was evaluated which indicated that rectal temperature reduction lasted longer in the calves receiving 3 and 6 mg/kg ketoprofen. Secondly, the PK profile of the combination product was compared with mono-substance products (3 mg/kg subcutaneous and intramuscular). The PK profile of ketoprofen in the combination product was characterized by longer t_1/2 , lower C_max and increased AUC in comparison with mono-substance products. Due to prolonged ketoprofen exposure in the combination product, the pyrexia reducing effect of the combination product lasted longer in a second lipopolysaccharide challenge study in comparison with mono-substance products. Finally, a PK-PD model for the anti-pyretic effect of ketoprofen was developed based on the data from the different studies. The PK-PD model eliminated the need for additional animal experiments and indicated that a 3 mg/kg ketoprofen dose in the combination product provided optimal efficacy.

Pharmacokinetics of meloxicam, carprofen, and tolfenamic acid after intramuscular and oral administration in Japanese quails (Coturnix coturnix japonica)

The aim of this study was to determine the pharmacokinetics of meloxicam (MLX), carprofen (CRP), and tolfenamic acid (TA) in Japanese quails (Coturnix coturnix japonica) following intramuscular (IM) and oral administration at doses of 1, 10, and 2 mg/kg, respectively. A total of 72 quails were randomly divided into 3 equal groups as MLX, CRP, and TA. Each group was separated into two sub-groups that received IM and oral administration of each drug. Plasma concentrations of MLX, CRP, and TA were determined using HPLC-UV and analyzed by non-compartmental method. The t_1/2ʎz and MRT of MLX, CRP, and TA after oral administration were similar to those after IM administration. The V_darea /F of MLX, CRP, and TA after IM administration was 0.28, 2.05, and 0.20 L/kg. The Cl/F of MLX, CRP, and TA after IM administration was 0.12, 0.19, and 0.09 L/h/kg. MLX, CRP, and TA after oral administration showed significantly lower C_max and longer T_max compared with IM administration. The relative bioavailability of MLX, CRP, and TA following oral administration in quails was 76.13%, 61.46%, and 57.32%, respectively. The IM and oral route of MLX, CRP, and TA can be used for the treatment of various conditions in quails. However, further research is necessary to determine the pharmacodynamics and safety of MLX, CRP, and TA before use in quails.

Pharmacokinetics of tolfenamic acid after different administration routes in geese (Anser cygnoides)

The pharmacokinetics and bioavailability of tolfenamic acid were determined in geese (Anser cygnoides) following intravenous (IV), intramuscular (IM), subcutaneous (SC), and oral administrations at 2 mg/kg dose. In this study, eight healthy geese (3.5 ± 0.5 kg) were used. The study was performed in four periods according to a crossover design with a 15-day washout period between two administrations. The plasma concentrations of tolfenamic acid were analyzed using HPLC-UV, and pharmacokinetic parameters were calculated by noncompartmental analysis. The elimination half-life was 1.73, 2.51, 2.34, and 2.31 hr for IV, IM, SC, and oral routes, respectively. The volume of distribution at steady state and total clearance after IV administration were 0.25 L/kg and 0.16 L hr^-1  kg^-1 , respectively. The peak plasma concentrations of tolfenamic acid after IM, SC, and oral administrations were 4.89, 2.94, and 2.92 μg/ml at 0.25, 0.75, and 1 hr, respectively. The bioavailability was 87.91, 77.87, and 76.03% for the IM, SC, and oral routes, respectively. Tolfenamic acid, which exhibits the good bioavailability and plasma concentration following IM, SC, and oral administrations at 2 mg/kg dose, may be useful in the treatment of inflammatory disease conditions in geese.

Pharmacokinetics of tolfenamic acid in goats after different administration routes

The aim of this study was to determine the pharmacokinetics and bioavailability of tolfenamic acid in goats after intravenous (IV), intramuscular (IM), subcutaneous (SC), and oral (PO) administrations at 2 mg/kg dose. In this study, eight clinically healthy goats were used. The study comprised four periods, according to a crossover design with at least a 15-day washout period between treatments. Plasma concentrations of tolfenamic acid were determined by HPLC-UV, and the pharmacokinetic parameters were estimated using a non-compartmental method. Following IV administration, terminal elimination half-life, volume of distribution at steady state, and total clearance were 1.60 h, 0.37 L/kg, and 0.27 L/h/kg, respectively. The mean peak plasma concentration following IM, SC, and PO administrations was 1.77, 1.22, and 0.30 μg/ml, respectively. The mean bioavailability following IM, SC, and PO administrations was 64.46, 55.43, and 19.46%, respectively. The PO route, which exhibits both the low plasma concentration and bioavailability, is not recommended in goats. The IV, IM, and SC routes, which show comparable pharmacokinetic profiles, may be proposed for use in goats. However, the multi-dose and pharmacodynamic studies are necessary to establish more accurately its safety and efficacy in the goat.

Effect of dose on the intravenous pharmacokinetics of tolfenamic acid in goats

The objective of this study was to determine the pharmacokinetics of tolfenamic acid (TA) following intravenous (IV) administration at doses of 2 and 4 mg/kg in goats. In this study, six healthy goats were used. TA was administered intravenously to each goat at 2 and 4 mg/kg doses in a cross-over pharmacokinetic design with a 15-day washout period. Plasma concentrations of TA were analyzed using the high performance liquid chromatography with ultraviolet detector, and pharmacokinetic parameters were assigned by noncompartmental analysis. Following IV administration at dose of 2 mg/kg, area under the concentration-time curve (AUC_0-∞ ), elimination half-life (t_1/2ʎz ), total clearance (Cl_T ) and volume of distribution at steady state (V_dss ) were 6.64 ± 0.81 hr^* µg/ml, 1.57 ± 0.14 hr, 0.30 ± 0.04 L h^-1  kg^-1 and 0.40 ± 0.05 L/kg, respectively. After the administration of TA at a dose of 4 mg/kg showed prolonged t_1/2ʎz , increased dose-normalized AUC_0-∞ , and decreased Cl_T . In goats, TA at 4 mg/kg dose can be administered wider dose intervals compared to the 2 mg/kg dose. However, further studies are needed to determine the effect of different doses on the clinical efficacy of TA in goats.

Pharmacokinetics of tolfenamic acid in Hawksbill turtles (Eretmochelys imbricata) after single intravenous and intramuscular administration

To the best of our knowledge, limited pharmacokinetic information to establish suitable therapeutic plans is available for Hawksbill turtles. Therefore, the present study aimed to assess the pharmacokinetic features of tolfenamic acid (TA) in Hawksbill turtles, Eretmochelys imbricata, after single intravenous (i.v.) and intramuscular (i.m.) administration at dosage 4 mg/kg body weight (b.w.). The study (parallel design) used 10 Hawksbill turtles randomly divided into equal groups. Blood samples were collected at assigned times up to 144 hr. The concentrations of TA in plasma were quantified by a validated liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS). The concentration of TA in the experimental turtles with respect to time was pharmacokinetically analyzed using a noncompartment model. The C_max values of TA were 89.33 ± 6.99 µg/ml following i.m. administration. The elimination half-life values were 38.92 ± 6.31 hr and 41.09 ± 9.32 hr after i.v. and i.m. administration, respectively. The absolute i.m. bioavailability was 94.46%, and the average binding percentage of TA to plasma protein was 31.39%. TA demonstrated a long half-life and high bioavailability following i.m. administration. Therefore, the i.m. administration is recommended for use in clinical practice because it is both easier to perform and provides similar plasma concentrations to the i.v. administration. However, further studies are needed to determine the clinical efficacy of TA for treatment of inflammatory disease after single and multiple dosages.

Use of validated objective methods of locomotion characteristics and weight distribution for evaluating the efficacy of ketoprofen for alleviating pain in cows with limb pathologies

In veterinary practice pain alleviation plays a part in managing lameness. The aim of this randomized and placebo-controlled clinical study was to evaluate the effect of a single administration of ketoprofen on locomotion characteristics and weight distribution in cattle with foot (located up to and including the fetlock; n = 31) and (proximal to the fetlock; n = 10) pathologies. Cattle were randomly allocated to either the ketoprofen (group K; intravenous 3 mg/kg of body weight; n = 21) or an equivalent volume of isotonic sterile saline solution (group P; n = 20). Two accelerometers (400 Hz; kinematic outcome = stance phase duration; kinetic outcome = foot load and toe-off), a 4-scale weighing platform (weight distribution and SD of the weight) and a subjective locomotion score were measured before (baseline) and after 1 h and 18 h of treatment. All variables were expressed as differences across contralateral limbs, and the measurements at 1 h and 18 h were compared to the baseline. A repeated measures ANOVA was used to determine the differences between groups K and P. A logistic regression model with a binary outcome (0 = no improvement and 1 = improvement of the differences across the contralateral limbs over time) was calculated. Mean (± SD) of locomotion scores at baseline were not significantly different (P = 0.102) in group K (3.10 ± 0.80) as compared to group P (3.48 ± 0.64). Cattle of group K showed significantly lower differences across contralateral limbs at 1 h as compared to group P for the relative stance phase and the weight distribution. Only the treatment (P versus K) remained a significant factor in the model for relative stance phase (odds ratio (OR) = 6.5; 95% CI = 1.38–30.68) and weight distribution (OR = 6.36; 95% CI = 1.30–31.07). The effects of ketoprofen were evident in improving the differences across contralateral limbs—both for stance phase during walking and weight bearing during standing—after 1 h but not after 18 h of administration.

Pharmacokinetics of tolfenamic acid in red-eared slider turtles (Trachemys scripta elegans)

OBJECTIVE

To determine the pharmacokinetics of tolfenamic acid (TA) after different routes of administration [intravenous (IV) and intramuscular (IM), 2 mg kg^-1] and doses (IV, 2 and 4 mg kg^-1) in red-eared slider turtles (Trachemys scripta elegans).

STUDY DESIGN

Randomized experimental trial.

ANIMALS

Sixteen healthy red-eared slider turtles.

METHODS

Turtles were randomly assigned to two groups (n = 8 each). Group 1 received TA at a dose of 2 mg kg^-1 IV and then IM, after a washout period of 30 days. Group 2 received 4 mg kg^-1 TA IV. A noncompartmental analysis was used to calculate pharmacokinetic variables.

RESULTS

No local and/or systemic adverse drug effects were observed in any turtle. Elimination half-life and mean residence time following IM administration at 2 mg kg^-1 were significantly longer than those following IV administration. The bioavailability following IM administration was complete. The area under the plasma concentration-time curve, elimination half-life, mean residence time and total clearance were significantly different between the dose groups.

CONCLUSIONS AND CLINICAL RELEVANCE

The absence of adverse reactions in the turtles of the study of TA along with the favourable pharmacokinetic properties (the long half-life and the complete bioavailability) of TA administered at the single doses of 2 and 4 mg kg^-1 suggest the possibility of its effective use in turtles. However, further studies are required to establish a multiple dosage regimen of TA and to evaluate the clinical efficacy of administering TA.

Pharmacokinetics and bioavailability of tolfenamic acid in sheep

The pharmacokinetics, bioavailability, and tolerability of tolfenamic acid (TA) were determined after treating sheep with TA via different routes and doses. This crossover study was carried out with a washout period of 15 days. In the study, 16 clinically healthy sheep were randomly assigned to two equal groups. In the first group (n = 8), animals received TA by intravenous (IV), intramuscular (IM), subcutaneous (SC), or oral (OR) routes at 2 mg/kg. In the second group (n = 8), TA was administered intravenously to each sheep at 2, 4, 8, and 16 mg/kg. Plasma samples were analyzed with a high-performance liquid chromatography assay. Noncompartmental pharmacokinetic analyses were used to evaluate the data. The area under the concentration-time curves (AUC_0-∞ ), elimination half-life (t_1/2ʎz ), and the mean residence time (MRT) significantly differed among the administration routes at 2 mg/kg of TA. Following IM, SC, and OR administrations, TA demonstrated different peak concentrations (C_max ) and time to reach C_max (T_max ), with a bioavailability of 163%, 127%, and 107%, respectively. The dose-normalized AUC_0-∞ revealed a significant difference among the dose groups; however, the relationship between dose and AUC_0-∞ was linear. Both t_1/2ʎz and MRT increased depending on the dose. Although the total clearance (Cl_T ) decreased depending on dose, the volume of distribution at steady-state (V_ss ) increased. Tolfenamic acid indicated a long half-life and high bioavailability following IM, SC, and OR administrations at 2 mg/kg. TA exhibited linear kinetics and was well tolerated by the animals, except at 16 mg/kg. Thus, TA may be used in different routes and doses (≤8 mg/kg) in sheep; however, further studies are needed to determine the clinical efficacy of TA during the inflammatory and painful conditions and the pharmacokinetics and safety of repeated administration in sheep.

Tolfenamic Acid

Tolfenamic acid (TA) is a nonsteroidal antiinflammatory drug and belongs to the group of fenamates. It is used as a potent pain reliever in the treatment of acute migraine attacks, and disorders like dysmenorrhea, rheumatoid, and osteoarthritis. TA has shown excellent in vitro antibacterial activity against certain ATCC strains of bacteria when complexed with bismuth(III). It has also been reported to block pathological processes associated with Alzheimer's disease. In the recent past, TA has also been used as a novel anticancer agent for the treatment of various cancers. In view of the clinical importance of TA, a comprehensive review of the physical and pharmaceutical properties and details of the various analytical methods used for the assay of the drug in pharmaceutical and biological systems has been made. The methods reviewed include identification tests and titrimetric, spectrophotometric, chromatographic, electrochemical, thermal, microscopic, enzymatic, and solid-state techniques. Along with the analytical profile, the stability and degradation of TA, its pharmacology and pharmacokinetics, dosage forms and dose, adverse effects and toxicity, and interactions have been discussed.

Using non-steroidal anti-inflammatory drugs around calving: maximizing comfort, productivity and fertility

Non-steroidal anti-inflammatory drugs (NSAIDs) have analgesic, anti-inflammatory, anti-endotoxic and anti-pyretic effects in cattle. As such, they could be expected to have significant effects in cows and calves in the post-calving period. This review evaluates the published data on the use of NSAIDs in the dam and its calf after dystocia, the impact of NSAIDs on uterine involution, the restoration of ovarian function and prevention and treatment of the metritis complex, and the benefits of using NSAIDs in the recumbent cow. Overall, the published data are very limited, despite frequent use of NSAIDs by veterinarians in the post-calving cow, and the small number of published studies focus on blanket treatment of calving cows rather than targeted treatment after dystocia. Blanket treatment had no economic benefit; indeed, some studies reported adverse effects, such as pyrexia and increased risk of metritis. There is even less information on the value of treating calves with NSAIDs after dystocia, despite significant tissue damage which may benefit from NSAID use. Appreciably more studies have evaluated the influence of NSAIDs on uterine and ovarian function, but clinical relevance is limited. In cows with a normal puerperium, prolonged treatment with NSAIDs may slow the restoration of normal function, but most reported studies are small and use NSAIDs more frequently and for longer periods than is common in general practice. The evidence of a clinical benefit in cows with puerperal disease is limited and equivocal, and the evidence base for the use of NSAIDs in the treatment of recumbent cows is also small, even though an expert panel concluded that NSAIDs were a key aspect of veterinary treatment of downer cows. The lack of evidence identified by this review supports the contention that NSAIDs are likely to be under-used and sub-optimally prescribed in the post calving period. Further research on the use of NSAIDs in the post-calving cow and calf is required.

Thermodynamic and structural study of tolfenamic acid polymorphs

The article deals with the study of two polymorphic modifications in the space groups P2(1)/c (white form) and P2(1)/n (yellow form) of the tolfenamic acid. It also describes how the white form vapor pressure temperature dependence was determined by using the transpiration method and how thermodynamic parameters of the sublimation process were calculated. We have estimated the difference between the crystal lattice energies of the two polymorphic forms by solution calorimetry and found that the crystal lattice energy of the yellow form is 6.7+/-1.2 kJ mol(-1) higher than that of the white form, whereas Gibbs free energies of the forms obtained from the vapor pressure temperature dependence are practically the same. The modifications under consideration are monotropically related. From the practical point of view, the white form is more preferable due to its lower crystal lattice energy and better performing procedure. We have also studied the solubility, solvation and transfer processes of the tolfenamic acid white form in buffers (with various values of pH and ionic strengths), n-hexane and n-octanol. The thermodynamic parameters of the investigated processes have been discussed and compared with those determined for others fenamates. In the study we estimated specific and non-specific contributions of the solvation enthalpic term of the fenamate molecules with the solvents as well. The driving forces of the transfer processes from the buffers with pH 7.4 and different ionic strengths to n-octanol were analyzed. It was found that the relationship between the enthalpic and entropic terms depends essentially on the ionic strength. For the considered fenamates the transfer processes of the neutral molecules and the ionic forms are enthalpy-determined, whereas for the niflumic acid this process is entropy-determined.

Pharmacokinetic and pharmacodynamic interactions of tolfenamic acid and marbofloxacin in goats

Pharmacokinetic and pharmacodynamic properties in goats of the non-steroidal anti-inflammatory drug tolfenamic acid (TA), administered both alone and in combination with the fluoroquinolone marbofloxacin (MB), were established in a tissue cage model of acute inflammation. Both drugs were injected intramuscularly at a dose rate of 2 mg kg(-1). After administration of TA alone and TA+MB pharmacokinetic parameters of TA (mean values) were Cmax=1.635 and 1.125 microg ml(-1), AUC=6.451 and 3.967 microgh ml(-1), t1/2K10=2.618 and 2.291 h, Vdarea/F=1.390 and 1.725Lkg(-1), and ClB/F=0.386 and 0.552 L kg(-1) h(-1), respectively. These differences were not statistically significant. Tolfenamic acid inhibited prostaglandin (PG)E2 synthesis in vivo in inflammatory exudate by 53-86% for up to 48 h after both TA treatments. Inhibition of synthesis of serum thromboxane (Tx)B2 ex vivo ranged from 16% to 66% up to 12h after both TA and TA+MB, with no significant differences between the two treatments. From the pharmacokinetic and eicosanoid inhibition data for TA, pharmacodynamic parameters after dosing with TA alone for serum TxB2 and exudate PGE2 expressing efficacy (Emax=69.4 and 89.7%), potency (IC50=0.717 and 0.073 microg ml(-1)), sensitivity (N=3.413 and 1.180) and equilibration time (t1/2Ke0=0.702 and 16.52 h), respectively, were determined by PK-PD modeling using an effect compartment model. In this model TA was a preferential inhibitor of COX-2 (COX-1:COX-2 IC50 ratio=12:1). Tolfenamic acid, both alone and co-administered with MB, did not affect leucocyte numbers in exudate, transudate or blood. Compared to placebo significant attenuation of skin temperature rise over inflamed tissue cages was obtained after administration of TA and TA+MB with no significant differences between the two treatments. Marbofloxacin alone did not significantly affect serum TxB2 and exudate PGE2 concentrations or rise in skin temperature over exudate tissue cages. These data provide a basis for the rational use of TA in combination with MB in goat medicine.

Influence of marbofloxacin on the pharmacokinetics and pharmacodynamics of tolfenamic acid in calves

Pharmacokinetic and pharmacodynamic properties of tolfenamic acid (TA) in calves were determined in serum and fluids of inflamed (carrageenan administered) and non-inflamed subcutaneously implanted tissue cages after intramuscular administration both alone and in combination with marbofloxacin (MB). MB significantly altered the pharmacokinetics of TA: mean values were Cmax = 2.14 and 1.64 microg/mL, AUC = 27.38 and 16.80 microg.h/mL, Vd(area)/F = 0.87 and 1.17 L/kg, and ClB/F = 0.074 and 0.128 L/kg/h, respectively, after administration of TA alone and TA + MB. T(1/2)K10 and MRT were not significantly different for the two treatments. The pharmacodynamic properties of TA were not influenced by MB co-administration, in spite of the alterations in some TA pharmacokinetic parameters. TA inhibited prostaglandin E2 (PGE2) synthesis in vivo in inflammatory exudate by 50-88% for up to 48 h after both TA treatments. Inhibition of synthesis of serum thromboxane B2 (TxB2) ex vivo ranged from 40 to 85% up to 24 h after both TA and TA + MB. From the derived pharmacokinetic and eicosanoid inhibition data for TA, pharmacodynamic parameters for serum TxB2 and exudate PGE2 inhibition expressing efficacy (Emax = 78.1 and 97.5%), potency (IC50 = 0.256 and 0.265 microg/mL), sensitivity (N = 1.96 and 2.29) and the pharmacokinetic parameter equilibration time (t(1/2)K(e0) = 0.695 and 24.0 h), respectively, were determined. In this model TA was a nonselective inhibitor of cyclo-oxygenase (COX) (COX-1:COX-2 IC50 ratio = 1.37). TA, both alone and co-administered with MB, did not affect leucocyte numbers in exudate, transudate or blood. Partial attenuation of skin temperature rise over inflamed tissue cages and reduction of zymosan-induced skin swelling were recorded after administration of TA and TA + MB with no significant differences between the two treatments. These data provide a basis for the rational use of TA in combination with MB in calf medicine.

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.

PK-PD integration and PK-PD modelling of nonsteroidal anti-inflammatory drugs: principles and applications in veterinary pharmacology

Much useful information relevant to elucidation of mechanism of action of nonsteroidal anti-inflammatory drugs (NSAIDs) at the molecular level can be obtained from integrating pharmacokinetic (PK) and pharmacodynamic (PD) data, such data being obtained usually, although not necessarily, in separate studies. Integrating PK and PD data can also provide a basis for selecting clinically relevant dosing schedules for subsequent evaluation in disease models and clinical trials. The principles underlying and uses of PK-PD integration are illustrated in this review for phenylbutazone in the horse and cow, carprofen and meloxicam in the horse, carprofen and meloxicam in the cat and nimesulide in the dog. In the PK-PD modelling approach for NSAIDs, the PK and PD data are generated (usually though not necessarily) in vivo in the same investigation and then modelled in silico, usually using the integrated effect compartment or indirect response models. Drug effect is classically modelled with the sigmoidal E(max) (Hill) equation to derive PD parameters which define efficacy, potency and sensitivity. The PK-PD modelling approach for NSAIDs can be undertaken at the molecular level using surrogates of inhibition of cyclooxygenase (COX) isoforms (or indeed other enzymes e.g. 5-lipoxygenase). Examples are provided of the generation of PD parameters for several NSAIDs (carprofen, ketoprofen, vedaprofen, flunixin and tolfenamic acid) in species of veterinary interest (horse, calf, sheep and goat), which indicate that all drugs investigated except vedaprofen were non-selective for COX-1 and COX-2 in the four species investigated under the experimental conditions used, vedaprofen being a COX-1 selective NSAID. In these studies, plasma concentration was linked to COX inhibitory action in the biophase using an effect compartment model. Data for S-(+)-ketoprofen have been additionally subjected to inter-species modelling and allometric scaling of both PK and PD parameters. For several species values of four PK parameters were highly correlated with body weight, whilst values for PD parameters based on COX inhibition lacked allometric relationship with body weight. PK-PD modelling of NSAIDs has also been undertaken using clinical end-points and surrogates for clinical end-points in disease models. By measurement of clinically relevant indices in clinically relevant models, data generated for PD parameters have been used to set dosages and dose intervals for evaluation and confirmation in clinical trials. PK-PD modelling of NSAIDs is likely to prove superior to conventional dose titration studies for dosage schedule determination, as it sweeps the whole of the concentration-effect relationship for all animals and therefore permits determination of genuine PD parameters. It also introduces time as a second independent variable thus allowing prediction of dosage interval. Using indirect response models and clinically relevant indices, PD data have been determined for flunixin, phenylbutazone and meloxicam in the horse, nimesulide in the dog and meloxicam in the cat.

Pharmacokinetics of sodium meclofenamate in pre-ruminant cattle

The pharmacokinetic profile of sodium meclofenamate, a non-steroidal antiinflammatory drug, was determined in six pre-ruminant calves after intravenous and intramuscular administration at a dose of 2.2mg/kg of body weight. Meclofenamate concentrations were measured using a high performance liquid chromatography assay. The pharmacokinetics of sodium meclofenamate after intravenous and intramuscular administration to calves were characterised by a rapid distribution phase (t½alpha ), 15.45± 4.85min and 23.14± 7.24min for the intravenous and intramuscular administration, respectively, followed by a longer elimination phase (t½beta ) after intramuscular treatment (17.55± 6.52h.). The apparent volume of distribution (Vd) of the drug after intravenous administration was moderate (0.72± 0.12l/kg), and high (3.51± 1.05l/kg) after intramuscular administration. This can be explained by the flip-flop effect or by enterohepatic shunting. The bioavailability achieved after intramuscular administration was 61%.

Pharmacology of drugs used to treat osteoarthritis in veterinary practice

As in humans, pain in animals may be associated with a wide range of conditions and circumstances, ranging from acute trauma to joint diseases. Joint diseases are common in companion animal medicine (horse, dog, cat) and at least 80% of cases are classified as osteoarthritis (OA). Several drug classes are available for OA therapy, including corticosteroids, non-steroidal antiinflammatory drugs (NSAIDs), agents with potential disease modifying properties and nutraceuticals. For long-term maintenance OA treatment, particularly in the horse and dog, NSAIDs are routinely and extensively used. This review outlines the pharmacokinetics (PK) and pharmacodynamics (PD) of NSAIDs in companion and farm animal species. NSAID PK and PD have been studied in models of acute inflammation, which enable use of PK-PD modeling to facilitate (a) studies of mechanism of action at the molecular level and (b) prediction of dosages for clinical use. The PK-PD approach is a powerful but underutilized tool which also facilitates inter-species comparisons.

Tissue chamber model of acute inflammation in farm animal species

A tissue chamber model of acute inflammation for use in comparative studies in calves, sheep, goats and pigs has been established and validated. Tissue chambers were prepared from silicon rubber tubing, of inner diameter 12.7 mm, length 115 mm and volume 15 ml, with 10 holes, each of 6mm diameter, at each end. In each animal two or four chambers were inserted at subcutaneous sites. Six weeks after implantation an acute inflammatory reaction in a single cage was generated by the intracaveal injection of 0.5 ml of 1% carrageenan solution. Serial samples of exudate (injected chamber), transudate (non-injected chamber) and blood were collected for measurement of exudate and transudate leucocyte count, prostaglandin (PG)E(2) concentration in exudate and serum thromboxane (Tx)B(2) concentration. In addition, skin temperature changes over exudate and transudate chambers were recorded. In all four species, carrageenan induced an acute inflammatory response, indicated by increases to peak values followed by return towards baseline in skin temperature, leucocyte count and PGE(2) concentration. For each of these variables in calves, sheep and goats the increases were significantly greater for exudate than for transudate. The degree of intra-species variation in each variable was acceptable. Marked inter-species differences were recorded: skin temperature rise was greatest in calves and least in sheep and goats; exudate PGE(2) concentration was increased in the order sheep>goat>pig>calf; serum TxB(2) concentration was increased in the order calf>goat>sheep>pig and exudate leucocyte count was increased to a greater extent in the pig than in the three ruminant species. The model has advantages over some previously described tissue chamber models of inflammation and will be suitable for use in comparative studies of inflammatory mechanisms and the pharmacokinetics and pharmacodynamics of anti-inflammatory drugs.

Pharmacodynamics and pharmacokinetics of phenylbutazone in calves

Phenylbutazone (PBZ) was administered to six calves intravenously (i.v.) and orally at a dose rate of 4.4 mg/kg in a three-period cross-over study incorporating a placebo treatment to establish its pharmacokinetic and pharmacodynamic properties. Extravascular distribution was determined by measuring penetration into tissue chamber fluid in the absence of stimulation (transudate) and after stimulation of chamber tissue with the mild irritant carrageenan (exudate). PBZ pharmacokinetics after i.v. dosage was characterized by slow clearance (1.29 mL/kg/h), long-terminal half-life (53.4 h), low distribution volume (0.09 L/kg) and low concentrations in plasma of the metabolite oxyphenbutazone (OPBZ), confirming previously published data for adult cattle. After oral dosage bioavailability (F) was 66%. Passage into exudate was slow and limited, and penetration into transudate was even slower and more limited; area under curve values for plasma, exudate and transudate after i.v. dosage were 3604, 1117 and 766 microg h/mL and corresponding values after oral dosage were 2435, 647 and 486 microg h/mL. These concentrations were approximately 15-20 (plasma) and nine (exudate) times greater than those previously reported in horses (receiving the same dose rate of PBZ). In the horse, the lower concentrations had produced marked inhibition of eicosanoid synthesis and suppressed the inflammatory response. The higher concentrations in calves were insufficient to inhibit significantly exudate prostaglandin E2 (PGE2), leukotriene B4 (LTB4) and beta-glucuronidase concentrations and exudate leucocyte numbers, serum thromboxane B2 (TxB2), and bradykinin-induced skin swelling. These differences from the horse might be the result of: (a) the presence in equine biological fluids of higher concentrations than in calves of the active PBZ metabolite, OPBZ; (b) a greater degree of binding of PBZ to plasma protein in calves; (c) species differences in the sensitivity to PBZ of the cyclo-oxygenase (COX) isoenzymes, COX-1 and COX-2 or; (d) a combination of these factors. To achieve clinical efficacy with single doses of PBZ in calves, higher dosages than 4.4 mg/kg will be probably required.

Pharmacokinetic/pharmacodynamic integration in drug development and dosage-regimen optimization for veterinary medicine

Pharmacokinetic (PK)/pharmacodynamic (PD) modeling is a scientific tool to help developers select a rational dosage regimen for confirmatory clinical testing. This article describes some of the limitations associated with traditional dose-titration designs (parallel and crossover designs) for determining an appropriate dosage regimen. It also explains how a PK/PD model integrates the PK model (describing the relationship between dose, systemic drug concentrations, and time) with the PD model (describing the relationship between systemic drug concentration and the effect vs time profile) and a statistical model (particularly, the intra- and interindividual variability of PK and/or PD origin). Of equal importance is the utility of these models for promoting rational drug selection on the basis of effectiveness and selectivity. PK/PD modeling can be executed using various approaches, such as direct versus indirect response models and parametric versus nonparametric models. PK/PD concepts can be applied to individual dose optimization. Examples of the application of PK/PD approaches in veterinary drug development are provided, with particular emphasis given to nonsteroidal anti-inflammatory drugs. The limits of PK/PD approaches include the development of appropriate models, the validity of surrogate endpoints, and the acceptance of these models in a regulatory environment.

A pharmacokinetic/pharmacodynamic approach vs. a dose titration for the determination of a dosage regimen: the case of nimesulide, a Cox-2 selective nonsteroidal anti-inflammatory drug in the dog

The present experiment was designed to determine a dosage regimen (dose, interval of administration) in the dog for nimesulide, a nonsteroidal anti-inflammatory drug with in vitro selectivity for the inhibition of cyclo-oxygenase 2 (Cox-2), using a pharmacokinetic/pharmacodynamic (PK/PD) approach. The PK/PD results were compared with those obtained using a classical dose titration study. In the PK/PD experiment, 11 dogs were subjected to Freund's adjuvant arthritis characterized by permanent hyperthermia. Nimesulide (5 mg/kg, oral route) was tested during the secondary phase of the inflammatory response. In the dose titration study, nimesulide (0, 3, 6 and 9 mg/kg, oral route) was tested in eight other dogs using a reversible urate crystal arthritis in a 4-period crossover design. Different PD endpoints (including lameness assessed by force plate and hyperthermia) were regularly measured during the PK/PD experiment, and plasma samples were obtained to determine the plasma nimesulide concentration. The data were modeled using an indirect effect model. The IC50 of nimesulide for lameness was 6.26 +/- 3.01 microg/mL, which was significantly higher than the EC50 value obtained for antipyretic effect (2.72 +/- 1.29 microg/mL). The ED50 estimated from the classical dose titration study were 1.34 mg/kg (lameness) and 3.0 mg/kg (skin temperature). The PK/PD parameters were used to simulate different dosage regimens (dose, interval of administration). The antipyretic and anti-inflammatory effects were calculated from the model for the recommended dosage regimen (5 mg/kg/24 h). It was apparent from this approach, that this dosage regimen enabled 76% of the theoretical maximal drug efficacy to be obtained for pyresis and 43% for lameness. It was concluded from the comparison of in vivo and in vitro IC50, that nimesulide is a potent NSAID for which some Cox-1 inhibition is required to obtain clinically relevant efficacy.

Enantiospecific pharmacokinetics and pharmacodynamics of ketoprofen in sheep

Pharmacokinetic and pharmacodynamic parameters were established for the enantiomers of the 2-arylpropionic acid (APA) nonsteroidal anti-inflammatory drug (NSAID), ketoprofen (KTP). Each enantiomer was administered separately (1.5 mg/kg) and in a racemic mixture (3 mg/kg) intravenously (i.v.) to a group of eight sheep in a four-way, four-period cross-over study using a tissue cage model of inflammation. Plasma disposition of each KTP enantiomer was similar following separate administration of the pure compounds compared to administration of the racemic mixture. S(+)KTP volume of distribution (Vd(area)) was higher and clearance (ClB) faster than those of R(-)KTP. S(+) and R(-)KTP achieved relatively low concentrations in exudate and transudate. Unidirectional limited chiral inversion of R(-) to S(+)KTP was demonstrated. After R(-)KTP administration S(+)KTP was detected in plasma, but not in either exudate or transudate. Pharmacokinetic/pharmacodynamic (PK/PD) modelling of the data could not be undertaken following R(-)KTP administration because of chiral inversion to S(+)KTP, but the pharmacodynamic parameters, calculated maximum effect (Emax), concentration producing 50% effect (EC50), Hill's coefficient (N), rate constant of elimination of drug effect from the compartment (KeO) and mean equilibration half-life (t1/2KeO) were determined for S(+)KTP after administration of the racemic mixture as well as the pure compound.

A pharmacodynamic and pharmacokinetic study with vedaprofen in an equine model of acute nonimmune inflammation

The pharmacodynamics and enantioselective pharmacokinetics of vedaprofen were studied in six ponies in a two period cross-over study, in which a mild acute inflammatory reaction was induced by carrageenan soaked sponges implanted subcutaneously in the neck. Vedaprofen, administered intravenously at a dosage of 1 mg/kg, produced significant and prolonged inhibition of ex vivo serum thromboxane B2 (TXB2) synthesis and short-lived inhibition of exudate prostaglandin E2 (PGE2) and TXB2 synthesis. Vedaprofen also partially inhibited oedematous swelling and leucocyte infiltration into exudate. Vedaprofen displayed enantioselective pharmacokinetics, plasma concentrations of the R(-) enantiomer exceeding those of S(+) vedaprofen. The plasma concentration ratio, R:S, increased from 69:31 at 5 min to 96:4 at 3 h and plasma mean AUC values were 7524 and 1639 ng x h/mL, respectively. Volume of distribution was greater for S(+) vedaprofen, whilst elimination half-life (t(1/2beta)) and mean residence time were greater for R(-) vedaprofen. The penetration of vedaprofen into inflammatory exudate was also enantioselective. For R(-) and S(+) vedaprofen maximum concentration (Cmax) values were 2950 and 1534 ng/mL, respectively, and corresponding AUC values were 9755 and 4400 ng x h/mL. Vedaprofen was highly protein bound (greater than 99%) in both plasma and exudate. The significance of these data for the therapeutic use of vedaprofen is discussed.

Pharmacodynamics and pharmacokinetics of tolfenamic acid in ruminating calves: evaluation in models of acute inflammation

Injections of mild irritants intradermally (carrageenan, zymosan and dextran) and intracaveally (carrageenan) in a tissue cage model of inflammation were used in studies of the pharmacodynamics and pharmacokinetics of tolfenamic acid administered intramuscularly in calves. Inhibition of serum thromboxane (TX)B2 and inflammatory exudate prostaglandin (PG)E2 were used as indicators of the magnitude and time course of blockade of cyclo-oxygenase isoforms COX-1 and COX-2, respectively. Single doses of 2, 4 and 8 mgkg-1 tolfenamic acid partially inhibited irritant-induced rises in skin temperature (non-dose dependently) and skin oedema (dose-dependently). These doses also markedly inhibited serum TXB2 synthesis and the duration of inhibition was dose-related. A dose of 2 mgkg-1 tolfenamic acid also attenuated skin temperature rise over carrageenan-injected tissue cages, and markedly inhibited exudate PGE2 synthesis, even though drug penetration into both exudate and tissue cage transudate was limited. Tolfenamic acid pharmacokinetics were characterized by a relatively short tmax (0.94-2.04 h), a high estimated Vdarea (1.79-3.20 Lkg-1), an estimated t1/2 beta of 8.01-13.50 h and Cl beta of 0.142-0.175 Lkg-1h-1. The actions of tolfenamic acid in inhibiting PGE2 synthesis and in attenuating two of the cardinal signs of inflammation (heat and swelling) suggest that a dosage of 2 mgkg-1 administered intramuscularly should be effective clinically as an anti-inflammatory agent.