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Butyrophenone derivatives like droperidol and azaperone have pharmacological effects very similar to acepromazine (phenothiazine derivatives). Droperidol alone has been administered to pigs at 0.3 mg/kg IM to produce sedation for 2 hours [18]. However, droperidol is seldom administered alone to animals; it is manufactured as a proprietary combination of droperidol (20 mg/ml) and fentanyl (0.4 mg/ml) and marketed as Innovar‐Vet for veterinary use. Innovar‐Vet is a neuroleptanalgesic combination which consists of a tranquilizer (droperidol) and an analgesic (fentanyl). The combination of two drugs not only potentiates the central nervous system (CNS)‐depressing effect and the analgesic effect of each drug but also reduces the dose requirement for each drug, which decreases the side effects of each drug. Innovar‐Vet is often used to calm intractable or vicious animals but is rarely used in ruminants. When given at 0.19, 0.25, or 0.3 ml/kg to sheep, Innovar‐Vet was reported to produce adequate analgesia and smooth induction and recovery [19]. Innovar‐Vet had been shown to produce satisfactory calming effect in pigs (1 ml/12–25 kg [26.4–55 lb] IM). However, pigs often sneezed and became more excited if stimulated while under the influence of Innovar‐Vet [20]. Variable responses ranging from light sedation to pronounced relaxation and analgesia have been reported when 1 ml/10 kg (22 lb) of Innovar‐Vet was administered to young pigs [21]. Better and more reliable sedation was observed when xylazine was administered with Innovar‐Vet [14]. When administered to miniature pigs, Innovar‐Vet induced CNS stimulation rather than sedation [22]. Contrary to the previous report, Piermattei and Swan [23] showed that 1 ml/14 kg (30.8 lb) of Innovar‐Vet IM produced good sedation prior to halothane anesthesia.

Azaperone, another butyrophenone derivative, has pharmacologic effects similar to acepromazine and droperidol. Hughes et al. [24] compared the effects of azaperone and acepromazine in free‐ranging sheep. At 1 mg/kg, azaperone produced a calming effect and reduced the stress response as evidenced by calmer behavior and a greater comfort level of the animals studied. In this study, azaperone appeared to be more effective in reducing the stress response than acepromazine [24]. Madsen et al. [25] observed greater disorientation for a longer duration with azaperone. Interestingly, sheep tended to disperse with acepromazine but they tended to congregate with azaperone.

In pigs, azaperone has been shown to be the most effective tranquilizer. Azaperone has been used for the prevention of aggressiveness and savaging of newborn pigs by sows, for the treatment of stress, and for the completion of minor surgical procedures. At 2.2 mg/kg IM, azaperone was effective in reducing fighting following intermingling [26]. Approximately 20 minutes of deep sedation sufficient for minor surgeries was produced by 4–8 mg/kg of azaperone IM. Excessive salivation during deep sedation has been observed [26–31]. Practitioners should keep in mind that tranquilizers like acepromazine, droperidol, azaperone, diazepam, and midazolam do not possess analgesic effect. Therefore, a tranquilizer may render the animal unresponsive to painful manipulations, but the physiological stress response resulting from painful stimulations still exists. Similar to acepromazine, azaperone is effective in preventing malignant hyperthermia episodes due to halothane in susceptible pigs. Doses of 0.5–2.0 mg/kg IM azaperone offered 100% protection against malignant hyperthermia in susceptible Pietrain pigs [32].