Reptiles elimination

As with the situation in mammals, wide variations exist among avian species in the half-life of drugs that are primarily eliminated by hepatic biotransformation.The half-life of antimicrobial agents is prolonged in poikilothermic species (fish and reptiles), which is consistent with their much lower metabolic turnover rate, and is influenced by ambient (in the case of fish, water) temperature (Table 12). The rate of drug elimination increases (i.e., half-life decreases) with increase in ambient temperature and varies among fish species. 

Because of the slow elimination (long half-life) of antimicrobial agents in reptiles, dosage intervals are substantially longer in reptilian compared with mammalian species (Jacobson, 1993) (Table 6.14). To avoid significantly decreased systemic availability of drugs that are eliminated by renal excretion (e.g. (3-lactam and aminoglycoside antibiotics), the site of intramuscular injection should be the anterior half of the body most reptilian species have a well-developed renal portal system. 

Researchers have not found it easy to design experiments that clearly indicate chemoreception to be the primary orientation system in amphibians and reptiles. In many cases (e.g., newts such as Taricha or chelonlans such Clemmys or Chelonia) chemoreception has been singled out as important for homing more by a process of elimination of the other senses than by sound laboratory and field research. 

The ammonia resulting from amino acid deamination is eliminated in one of three ways depending on the organism. Fish and other aquatic animals simply excrete the ammonia to their aqueous surroundings, but terrestrial organisms must first convert the ammonia into a nontoxic substance—either nrea for mammals or uric acid for birds and reptiles. 

Adenine is converted into hypoxanthine, and guanine is converted into xanthine. Subsequently, by the action of xanthine oxidase both hypoxanthine and xanthine are converted into uric acid. Here the transformation stops in man, the higher apes, the Dalmatian dog, and the birds and reptiles in consequence, uric acid is the characteristic end-product of purine metabolism. Most of the higher animals, however, are able to oxidise uric acid, and by opening part of the purine ring convert it into the more much soluble compound, allantoin, which is readily eliminated as a urinary solute. 

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