Читать книгу Farm Animal Anesthesia - Группа авторов - Страница 40

Benzodiazepine derivatives like diazepam and midazolam are classified as minor tranquilizers. These drugs are used for their anxiolytic, anticonvulsant, and central muscle‐relaxing effects. Benzodiazepines produce little or no analgesic effect, but they can reduce the dose requirement of the concurrently administered general anesthetics [22]. Benzodiazepines produce minimal cardiovascular depression. For this reason these drugs are favorable for use in animals with increased anesthetic risk. Benzodiazepines can be used as alternatives to α₂ agonists to produce tranquilization when adverse effects associated with α₂ agonists (e.g. hypoxemia, pulmonary edema, or increased airway pressure) become undesirable. Diazepam and midazolam are the two most commonly used benzodiazepines in clinical veterinary practice. Diazepam is insoluble in water; its injectable solution contains 40% propylene glycol as solvent. IV propylene glycol administered rapidly sometimes results in hypotension and vascular irritation. Dilution, mixture of the injectable solution of diazepam with water, or a water‐soluble drug solution may cause cloudiness of the mixture which does not affect the potency of the drug. Midazolam is two to three times more potent than diazepam. Its injectable solution is water soluble. Thus, IM administration of midazolam will not cause tissue irritation [129]. In contrast to the general perception that benzodiazepines like diazepam and midazolam do not produce an analgesic effect, Kyle et al. [130] and Lizarraga and Chambers [131] reported that midazolam appeared to provide mediation of antinociception at the level of the spinal cord in sheep. Midazolam was rapidly absorbed with an elimination t½ of midazolam of 0.79 and 0.94 hours following IV and IM administration, respectively. A transient decrease in respiratory rate has been observed during midazolam‐induced tranquilization [132]. Diazepam and midazolam can be used as a preanesthetic for their anxiolytic and muscle‐relaxing effect, or they can be used with ketamine to improve muscle relaxation during anesthesia [133]. Other benzodiazepines, including flurazepam (2 mg/kg IV) [134], lorazepam (0.1 mg/kg IV) [135], and brotizolam (1–10 mg/kg PO) [136], have been used in pigs.