acids, are highly bound to serum proteins, and are biotransformed extensively by hepatic mixed-function oxidases. Differences in rates of drug biotransformation might underlie much of the variation among species in the elimination kinetics of NSAIDs (Mazue et al., 1982)—for example, variation in the plasma half-life of aspirin (horse, 1 hour; dog, 8 hours; cat, 38 hours) and phenylbutazone (horse, 3–6 hours; cattle, 35–72 hours) (Jenkins, 1987). Such differences should be taken into account in the establishment of dose schedules to provide effective drug concentrations in the body during therapy and to prevent drug toxicity.

Dose Recommendations (Table 5-9)

Before NSAIDs are used, references should be consulted for more information on length of treatment and reactions specific to the animals in question. For example, acetaminophen should not be used in cats, because of deficiencies in detoxifying mechanisms and an inherent sensitivity of feline red blood cells to oxidative damage.

NSAIDS constitute a potentially valuable group of drugs for producing analgesia in laboratory animals. Dose recommendations are available for treating individual animals of a given species, but information on administration in drinking water (e.g., dose, stability, and palatability) is lacking and would be especially valuable for treating large numbers of animals, such as rodents, simultaneously with a minimum of handling.

SPECIAL ANESTHETIC CONSIDERATIONS

α-Chloralose

α-Chloralose (40–80 mg/kg intravenously) is useful for providing prolonged anesthesia for nonsurvival experiments (6–10 hours) with minimal cardiovascular and respiratory depression (Van Citters et al., 1964). However, the depth of analgesia is usually inadequate for surgical procedures (Flecknell, 1987; Holzgrefe et al., 1987), and its use for this purpose requires clear justification. When combined with adjunctive drugs in nonsurvival procedures, chloralose can be used for preparative surgery and later for maintenance (Holzgrefe et al., 1987). Its onset of action is slow (15 minutes after intravenous administration), so a short-acting barbiturate usually is given first to induce anesthesia. But chloralose can be administered to animals already deeply sedated with opioids, tranquilizers, or cyclohexamines.

Urethane

Urethane, like chloralose, produces prolonged anesthesia with minimal cardiovascular and respiratory depression. Unlike chloralose, it produces analgesia



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