Horses excretion

The hypotensive drug, 5-(4-chlorobutyl)plcollnlc acid. Is converted by rats Into four metabolites which each contain the net addition of one Cz unit (, Figure 1). The Isolation of the 8-keto acid and a, 8-unsaturated acid metabolites Implies that alkylsubstituted plcollnlc acids are alternative substrates In the enzymatic chain elongation of natural fatty acids. Similarly, horses excrete benzoic acid In urine as chain-extended metabolites... 

Contrariwise, conservationists have argued that no foreign substances should be discharged into the air and waters. These are natural resources and should be kept pure. The loggers who are using horses in the Bull Run Reservoir area near Portland, Ore., are required to diaper their horses to protect the water quality. What about wild animals such as deer They, like all the other plants and animals, excrete wastes. Often it seems that conservationists consider that it is only man, his domestic animals, factories, and machines that pollute. Purity implies wastes only from natural sources. ... 

Pharmacokinetic studies with horse chestnut focus on the absorption, metabolism, and excretion of the main constituent—p-aescin. 

On the other hand, acidic drugs tend to ionize under conditions of alkaline pH and so are unable to permeate the renal tubular epithelium and are preferentially excreted. Tire converse applies to conditions of acidic urinary pH. This has been demonstrated experimentally for many drugs weak bases are excreted more rapidly in acidic urine, whereas weak acids are excreted more rapidly in alkaline urine. In the horse, phenylbutazone, which is a weak organic acid with a pKa of 4.6, has a more delayed clearance time under conditions of aciduria than under conditions of alkaline urine. 

Results of pharmacokinetic studies of streptomycin are in most cases also applicable to dihydrostreptomycin and vice versa. In animals, the absorption of both streptomycin and dihydrostreptomycin is poor via the oral route but rapid after intramuscular administration. In cattle, peak serum levels were obtained 1 h after intramuscular injection of either streptomycin or dihydrostreptomycin (18), whereas serum concentrations produced in sheep and horses paralleled those obtained in cattle (19). As a result, most of an oral dose is recovered in the feces whereas most of a parenteral dose is recovered in the urine. However, if kidney function is severely impaired, little of an intramuscularly administered dose is excreted in the urine. 

Absorption of cefazolin is poor low concentrations were found in plasma and tissues after intramammary administration. It is bound to plasma proteins in the circulation and crosses tlie placenta. Metabolism of cefazolin is very limited and no major metabolites seem to occur. After parenteral administration to horse, nearly 100% of the dose was excreted unchanged in the urine within 24 h. 

After a single oral administration of 0.4 mg radiolabeled moxidectin/kg bw to horses, a mean peak serum concentration of 0.134 ppm moxidectin equivalents was attained at 6 h postdose (63). Oral availability was estimated at 40%, while the terminal elimination half-life was approximately 80 h. Within 168 h, 77% of the total radioactivity was excreted mostly by Ure fecal route. In feces, the parent drug represented approximately 70% of the fecal radioactivity, whereas a fraction of 0.28-3.45% was due to four minor metabolites resulting from oxidation mainly on Ci4, C24, and/or C28 positions. 

Occasionally, the parent drug is not excreted in urine at a detectable concoitration, and a knowledge of the m bolic pathways in the particuku species is thus essoitial. An example of this is the identification of 5a-estrane-3p,17a-diol in the urine of horses, or of 19-norandrosterone and 19-nor-etiocholanolone in the urine of humans, to prove administration of the anabolic steroid nandrolone. A few drugs are notable for being excreted in urine almost... 

M.S.Moss, The Metabolism and Urinary and Salivary Excretion of Drugs in the Horse and their Relevance to Dope Detection,in Drug Metabolism—from Microbe to Man, D.V. Parke and R.L.Smith (Ed.), London, Taylor and Francis, 1977 M.S.Moss, Role of Referee Samples in European Drug Detection, in 3rd International Symposium on Equine Medication Control, T.Tobm et al (Ed.), Lexmgton, Kentucky, 1979... 

Disposition in the Body. In man, nandrolone is excreted in the urine mainly as the two metabolites, 19-norandrosterone and 19-noretiocholanolone. In the horse, the major metabolites are 5a-estrane-3, 17a-diol, excreted mainly as the glucuronide conjugate, and its 17j5-epimer which is excreted as the sulphate conjugate. 

Pharmacokinetic studies have not been performed in horses however, i.v. doses of 0.7-1.Img/kg three times a day have been suggested as being suitable for use in small animals. Imipenem has to be administered i.v. because it is not absorbed following p.o. administration. Imipenem has been shown to penetrate inflamed meninges. It is metabolized extensively by the renal tubules to a potentially toxic compound. Therefore, it is usually combined with cilastatin, a drug that inhibits the renal tubular enzymes. The combined product produces high urine concentrations of active antibiotic and avoids renal toxicity. In the presence of cilastatin, 70% of a dose of imipenem is excreted unchanged in the urine. The half-life of imipenem in the dog is 30-45 nrin. 

In horses, 75-100% of a gentamicin dose is excreted unchanged in the urine in the first 8-24 h after administration. The half-life is 1-2 h and is longer in neonatal foals than in older foals and adult horses. Any gentamicin that accumulates in the renal cortical tissue is eliminated slowly however, these levels are often below the limits of quantification of the assays used and are, therefore, not demonstrated in pharmacokinetic studies. 

Chloramphenicol and florfenicol undergo hepatic metabolism (glucuronide conjugation) followed by active renal tubular secretion. Only 5-15% of the dose is excreted unchanged (glomerular filtration) in urine. The half-life of chloramphenicol and florfenicol are[Pg.34]

Trimethoprim is metabolized in the liver to oxide and hydroxyl metabolites. It is eliminated by glomerular filtration and active tubular secretion in the kidneys. In horses, a large percentage of trimethoprim is metabolized before excretion in urine (46%) and feces (52%). The clearance of trimethoprim is affected by urine pH, plasma concentrations and the degree of hydration. In horses, the half-life of trimethoprim is 2-3 h and for pyrimethamine it is 12 h. 

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