Studies of meclofenamic acid and two metabolites in horses--pharmacokinetics and effects on exercise tolerance

Few Drugs Display Flip-Flop Pharmacokinetics and These Are Primarily Associated with Classes 3 and 4 of the BDDCS

This study was conducted to determine the number of drugs exhibiting flip-flop pharmacokinetics following oral (p.o.) dosing from immediate-release dosage forms and if they exhibit a common characteristic that may be predicted based on BDDCS classification. The literature was searched for drugs displaying flip-flop kinetics (i.e., absorption half-life larger than elimination half-life) in mammals in PubMed, via internet search engines and reviewing drug pharmacokinetic data. Twenty two drugs were identified as displaying flip-flop kinetics in humans (13 drugs), rat (nine drugs), monkey (three drugs), horse (two drugs), and/or rabbit (two drugs). Nineteen of the 22 drugs exhibiting flip-flop kinetics were BDDCS Classes 3 and 4. One of the three exceptions, meclofenamic acid (Class 2), was identified in the horse; however, it would not exhibit flip-flop kinetics in humans where the p.o. dosing terminal half-life is 1.4 h. The second, carvedilol, can be explained based on solubility issues, but the third sapropterin dihydrochloride (nominally Class 1) requires further consideration. The few drugs displaying p.o. flip-flop kinetics in humans are predominantly BDDCS Classes 3 and 4. New molecular entities predicted to be BDDCS Classes 3 and 4 could be liable to exhibit flip-flop kinetics when the elimination half life is short and should be suspected to be substrates for intestinal transporters.

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%.

Effects on plasma endotoxin and eicosanoid concentrations and serum cytokine activities in horses competing in a 48-, 83-, or 159-km endurance ride under similar terrain and weather conditions

OBJECTIVE

To determine plasma endotoxin concentration in horses competing in a 48-, 83-, or 159-km endurance race and its importance with regard to physical, hematologic, or serum and plasma biochemical variables.

ANIMAL

3 horses.

PROCEDURE

Weight and rectal temperature measurements and blood samples were obtained before, during, and after exercise. Blood samples were analyzed for plasma endotoxin concentration; serum antiendotoxin antibody titers; thromboxane B2 (TxB2) and 6-keto-prostaglandin F1alpha (PGF1alpha) concentrations; tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) activities; WBC, plasma protein, lactate, serum electrolyte, and calcium concentrations; PCV; and creatine kinase activity.

RESULTS

Detection of plasma endotoxin increased during exercise for horses competing at all distances but occurred more frequently in the 48- and 83-km groups. Plasma lactate concentration was significantly greater when endotoxin was concurrently detected. Endotoxin in plasma was not significantly associated with success of race completion. Plasma TxB2 and PGF1alpha concentrations and serum IL-6 activity significantly increased with exercise. Horses that had an excellent fitness level (as perceived by their owners) had greater decreases in serum antiendotoxin antibody titers during exercise than did horses perceived as less fit. In horses with better finish times, TxB2 and PGF1alpha concentrations were significantly greater and TNFalpha activity was significantly less than that of slower horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Endotoxemia developed during endurance racing, but was significantly correlated with increased plasma lactate concentration and not with other variables indicative of endotoxemia. Plasma TxB2 and PGF1alpha concentrations and serum TNFalpha activity may be associated with performance success.

Detection of non-steroidal anti-inflammatory drugs in equine plasma and urine by gas chromatography-mass spectrometry

A gas chromatographic-mass spectrometric (GC-MS) procedure for the detection of seventeen non-steroidal anti-inflammatory drugs (NSAIDs) in equine plasma and urine samples is described. The extraction of the compounds from the biological matrix was performed at acidic pH (2-3) with diethyl ether. Ethereal extracts were washed with a saturated solution of sodium hydrogencarbonate (urine) or treated with a solid mixture of sodium carbonate and sodium hydrogencarbonate (plasma). The ethereal extracts were dried and derivatized by incubation at 60 degrees C with methyl iodide in acetone in the presence of solid potassium carbonate. Mono- or bismethyl derivatives of the NSAIDs were obtained. After derivatization kinetic studies, 90 min was the incubation time finally chosen for screening purposes for adequate methylation of all the compounds under study. For individual confirmation analyses, shorter incubation times can be used. The chromatographic analysis of the derivatives was accomplished by GC-MS with a run time of 13 min. In general, extraction recoveries ranged from 23.3 to 100% in plasma and from 37.5 to 83.8% in urine samples. Detection limits from less than 5 to 25 ng/ml were obtained for both plasma and urine samples using selected-ion monitoring. The procedure was applied to the screening and confirmation of NSAIDs in routine doping control of equine samples.

Nonsteroidal anti-inflammatory drugs

NSAIDs' mechanism of action by inhibiting the synthesis of prostanoids accounts for both their therapeutic and toxic effects. They are commonly used in acute and chronic musculoskeletal and soft-tissue conditions. Adverse reactions include gastrointestinal disturbances and hypoproteinemia. Their pharmacologic effect seems to have a longer duration than their plasma concentrations indicate. This gives implications on current regulations for competing horses and the relevance of permitted levels has been questioned. The NSAIDs do not appear to enhance performance, but rather allow the horse to run up to its potential by reducing pain and lameness. There is concern over the possible hazards to the horse by this kind of therapeutic use. In conclusion, NSAIDs have well justifiable therapeutic uses in equine practice. They should, however, be used when there is a clear clinical indication, in safe dose rates and without jeopardizing the welfare of the performance horse.