Possible mechanism involved in the anticonvulsant action of butorphanol in mice

The study was designed to examine the effect of butorphanol, a classical opioid on convulsive behaviour using maximal electroshock (MES) test. An attempt was also made to investigate the role of possible receptor mechanisms involved. MES seizures were induced in mice via transauricular electrodes (60 mA, 0.2 s). Seizure severity was assessed by the duration of tonic hindlimb extensor phase and mortality due to convulsions. Intraperitoneal administration of butorphanol produced a dose-dependent (0.25-2 mg/kg) protection against hindlimb extensor phase. The anticonvulsant effect of butorphanol was antagonized by all the three opioid receptor antagonists (i.e., naloxone [mu], MR2266 [kappa], and naltrindole [delta], respectively). Coadministration of gamma-aminobutyric acid (GABA)-ergic drugs (diazepam, GABA, muscimol, and baclofen) and N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine (MK801), with butorphanol augmented the anticonvulsant action of the latter drug. In contrast, flumazenil, a central benzodiazepine (BZD) receptor antagonist, reversed the facilitatory effect of diazepam on the anti-MES effect of butorphanol. Similarly, delta-aminovaleric acid (DAVA), a GABA(B) receptor antagonist, antagonized the facilitatory effect of baclofen, a GABA(B) agonist on anti-MES action of butorphanol. These BZD-GABAergic antagonists, flumazenil or DAVA, per se also counteracted the anti-MES effect of butorphanol given alone. These data exemplify the benefits of using the MES test, which is sensitive to opioidergic compounds and distinguished convulsive behavioural changes associated with GABAergic and NMDAergic effects. Taken together, the results implicate a role for multitude of neurotransmitter systems, i.e., opioid (mu, kappa, delta), NMDA channel, BZD-GABA(A) chloride channel complex, and GABA(B) receptors in the anti-MES action of butorphanol.

Cardiorespiratory effects of medetomidine-butorphanol, medetomidine-butorphanol-diazepam, and medetomidine-butorphanol-ketamine in captive red wolves (Canis rufus)

Safe, effective, and reversible immobilization protocols are essential for the management of free-ranging red wolves (Canis rufus). Combinations using an alpha2-adrenoceptor agonist and ketamine have been shown to be effective for immobilization but are not reversible and can produce severe hypertension and prolonged or rough recoveries. To minimize hypertension and provide reversibility, 24 red wolves were immobilized using three medetomidine-butorphanol (MB) combinations without the use of ketamine in the initial injection. All wolves were administered medetomidine (0.04 mg/kg i.m.) and butorphanol (0.4 mg/kg i.m.). Seven wolves received no other immobilization agents (MB wolves), nine received diazepam (0.2 mg/kg i.v.) at the time they were instrumented (MBD wolves), and eight received ketamine (1 mg/kg i.v.) 30 min after instrumentation (MBK30 wolves). Physiologic parameters were monitored during immobilization. The heart rate was similar among the three groups for the first 30 min, and marked bradycardia was noted in one wolf from each group. Hypertension was observed initially in all three groups but was resolved within 10-30 min. The MBK30 wolves had significant elevations in heart rate and transient hypertension after intravenous ketamine administration. Most wolves had mild to moderate metabolic acidemia. Immobilizing drugs were antagonized in all wolves with atipamezole (0.2 mg/kg i.m.) and naloxone (0.02 mg/kg i.m.). The medetomidine-butorphanol-diazepam wolves were also given flumazenil (0.04 mg/kg i.v.). All wolves were standing within 12 min and were fully recovered within 17 min. Medetomamine-butorphanol and MBD combinations provided effective and reversible immobilization of red wolves without the sustained hypertension associated with the use of alpha2-adrenoceptor agonist-ketamine combinations. Delaying the administration of ketamine reduced its hypertensive effects.

Intranasal butorphanol-induced apraxia reversed by naloxone

Intranasal butorphanol is an opioid agonist-antagonist that is effective for the treatment of acute pain. Common adverse effects associated with the agent are somnolence, dizziness, nausea, and vomiting; they are readily reversed with naloxone. A patient developed signs and symptoms consistent with apraxia after a single dose of intranasal butorphanol. She was mentally alert, but she was unable to move or speak despite normal muscle tone and reflex movements. When she attempted to speak she had no voluntary control. At the emergency room she was administered naloxone 2 mg intramuscularly, which resulted in complete reversal of the symptoms in a short time. No other published cases describe these findings with butorphanol. Health care professionals should be aware that patients who are prescribed intranasal butorphanol, even in typical doses, may be at risk for such a reaction. This is important because, unlike the injectable formulation, the intranasal product is primarily used in the outpatient setting.

The effect of selective opioid antagonists on butorphanol-induced feeding

Butorphanol tartrate (BT) potently stimulates food intake in satiated rats. The opioid receptor profile of BT is complex and is dependent upon the assay and animal species studied. In the present study we utilized three selective opioid antagonists; namely beta-funaltrexamine (beta-FNA), naltrindole (NTI) and norbinaltorphimine (nor-BNI), to probe the opioid receptor profile of BT as an orexigenic agent. Intracerebroventricular administration of nor-BNI (kappa) antagonized the feeding effects of BT (8 mg/kg, s.c.) at doses of 1, 10 and 100 nmol at the 1-2 h time point and decreased feeding at all time points for the 10 nmol dose. After 1 h, the 100 nmol dose of nor-BNI decreased BT-induced feeding by about 72%. In contrast, intraventricular injection of only the highest dose of the selective mu opioid antagonist, beta-FNA (50 nmol), decreased BT-induced feeding. Intraventricular administration of the delta opioid agonist, NTI, failed to alter BT-induced feeding at doses as high as 50 nmol. These data suggest that BT is dependent upon the kappa and perhaps the mu opioid receptors to increase food intake in satiated rats.

Medetomidine-butorphanol-midazolam for anaesthesia in dogs and its reversal by atipamezole

The clinical efficacy of a combination of medetomidine, butorphanol and midazolam for anaesthesia in dogs, and its reversal by atipamezole, was evaluated in two experimental groups of four adult beagle dogs and compared with a control group of four dogs receiving only midazolam and butorphanol. The anaesthetic procedure was used for surgical procedures in another group of 14 dogs. After the injection of medetomidine, a rapid loss of coordination followed by mild sedation was observed. Anaesthesia was attained 2 +/- 1 minutes after the administration of butorphanol and midazolam and lasted 82 +/- 5 minutes, the dogs recovered 51 +/- 6 minutes later and there were no side effects. Analgesia and skeletal muscle relaxation were optimal throughout the period of anaesthesia. Statistically significant bradycardia and hypothermia were observed but there were no significant effects on respiratory function. After atipamezole the dogs recovered their normal posture, heart rate and body temperature in less than 20 minutes. In the control group, the short-lived light sedation was accompanied by inadequate analgesia and poor muscle relaxation. In the surgical group, no differences, except in drug requirements, were recorded in comparison with the experimental groups. Good analgesia and muscle relaxation, total absence of side effects and stability in vital body functions were observed. The injection of atipamezole was always effective, devoid of side effects and induced recovery in less than 20 minutes.

Yohimbine/flumazenil antagonism of hemodynamic alterations induced by a combination of midazolam, xylazine, and butorphanol in dogs

Reversal of hemodynamic alterations induced by midazolam maleate (1.0 mg/kg of body weight), xylazine hydrochloride (0.44 mg/kg), and butorphanol tartrate (0.1 mg/kg) with yohimbine (0.1 mg/kg) and flumazenil (0.25 mg/kg) was evaluated in 5 dogs. The dogs were anesthetized with isoflurane for instrumentation. With return to consciousness, baseline values were recorded, and the midazolam/xylazine/butorphanol mixture with glycopyrrolate was administered IV. Hemodynamic data were recorded for 60 minutes, and then a reversal mixture of yohimbine and flumazenil was administered IV. All variables were measured 1 minute from beginning of the reversal injection. Mean arterial pressure, pulmonary arterial pressure, systemic vascular resistance, and right ventricular stroke work index increased significantly (P < 0.05) above baseline at 60 minutes. Cardiac index and central venous pressure significantly decreased below baseline at 60 minutes. After reversal, mean arterial pressure and central venous pressure significantly decreased from baseline, whereas cardiac index, pulmonary arterial pressure, and right ventricular stroke work index increased significantly above baseline. Heart rate, cardiac index, and right ventricular stroke work index increased significantly above the 60-minute value after reversal. Mean arterial pressure and systemic vascular resistance decreased significantly (P < 0.05) below the 60-minute value after reversal. The hemodynamic alterations accompanying midazolam/xylazine/butorphanol sedation-anesthesia may be rapidly reversed with a combination of yohimbine and flumazenil.

A balanced anesthesia with a combination of xylazine, ketamine and butorphanol and its antagonism by yohimbine in pigs

The effects of intramuscular injections of xylazine (2 mg/kg)-ketamine (15 mg/kg) [X-K15], and xylazine (2 mg/kg)-ketamine (5 mg/kg)-butorphanol (0.22 mg/kg) [X-K5-B] were compared in atropinized (0.05 mg/kg) miniature pigs (pigs). Both combinations induced the anesthesia for more than 1 hr, however X-K5-B induced the more potent and well balanced anesthesia as compared with X-K15, although the amount of ketamine was reduced to one third. The duration of loss of pedal reflex, an indicator of surgical anesthesia, in X-K5-B (62 +/- 13 min) was significantly (P less than 0.05) longer than in X-K15 (28 +/- 19 min). In addition, X-K5-B was accompanied by loss of laryngeal reflex in all pigs. Recovery from anesthesia in X-K5-B was much smoother than in X-K15, and the administration of yohimbine (0.05 mg/kg) could rapidly and smoothly reverse the anesthesia induced by X-K5-B, although it was accompanied by a transient fall in blood pressure and tachycardia. The combination of xylazine, ketamine and butorphanol appears to be a relatively safe and widely available anesthesia for the period of one hour in pigs.

[Influence of four opioids on pulmonary oxygenation and naloxone's effects in mechanically ventilated dogs]

In order to examine effects of opioids on pulmonary oxygenation during constant ventilation, we investigated changes in PaO2 following four different opioids and after reversal with naloxone in mechanically ventilated, lightly anesthetized dogs. The systemic administration of morphine 1.0mg.kg-1, buprenorphine 0.03mg.kg-1, butorphanol 0.1mg.kg-1, and cyclazocine 0.05mg.kg-1, did not affect PaO2, although these opioids decreased mean arterial pressure and heart rate significantly. Naloxone 0.04mg.kg-1 after four opioids affected the hemodynamics, significantly, but it did not cause any detrimental effects on pulmonary oxygenation. Although naloxone alone did not affect mean arterial pressure and heart rate at all, subsequent morphine decreased mean arterial pressure and heart rate significantly. Neither naloxone nor subsequent morphine produced any change in PaO2. The results suggest that reversal with naloxone may not cause any significant influences on pulmonary oxygenation in mechanically ventilated and anesthetized patients.

Physiological response of gray wolves to butorphanol-xylazine immobilization and antagonism by naloxone and yohimbine

Captive gray wolves (Canis lupus) were immobilized (loss of consciousness) with 2.0 mg/kg xylazine hydrochloride (XYL) and 0.4 mg/kg butorphanol tartrate (BUT) administered intramuscularly. Induction time was 11.8 +/- 0.8 min (mean +/- SE). Immobilization resulted in bradycardia, respiratory depression, and normotension. Fifteen min after induction, six wolves were given either 0.05 mg/kg naloxone hydrochloride (NAL) and 0.125 or 0.250 mg/kg yohimbine hydrochloride (YOH), or an equal volume of saline (control) intravenously. Antagonism resulted in shortened recovery times compared to control animals (P less than 0.03); there was no difference in recovery times between the YOH doses (P greater than 0.05). Antagonism caused increases in heart rate (HR) and respiratory rate (RR), but no changes in MABP. Eight other wolves were similarly immobilized, but given only NAL. This resulted in partial antagonism with the animals appearing to be sedated with XYL only. Three wolves given only 0.4 mg/kg BUT assumed a state described as "apathetic sedation." Three other wolves sedated with only 2.0 mg/kg XYL showed a profound sedation characterized by recumbency, bradycardia and shallow, but regular, respiration. This study demonstrated that (1) BUT and XYL together, but not separately, can completely immobilize wolves, (2) this combination can be rapidly antagonized by NAL and YOH, and (3) there appeared to be no adverse cardiopulmonary reactions to any of the drugs used.

Antiemetic activity of butorphanol against cisplatin-induced emesis in ferrets and dogs

The analgesic agent butorphanol was evaluated for its ability to block cisplatin-induced emesis in ferrets and dogs. In ferrets, butorphanol (0.15, 0.3, or 0.45 mg/kg; expressed in terms of the tartrate salt) administered sc 30 minutes prior to cisplatin (8 mg/kg iv) reduced the number of emetic episodes but did not eliminate them. When these doses of butorphanol were administered 30 minutes before and 30 and 90 minutes after cisplatin, they caused a dose-related reduction in the number of emetic episodes; there was complete protection at a dose of 0.45 mg/kg/injection. In dogs, butorphanol (0.185 or 0.37 mg/kg/injection, expressed in terms of the tartrate salt) was administered sc on the same multiple-dose schedule used in the ferrets; this caused a nearly complete elimination of the emetic response to cisplatin (3 mg/kg iv). Butorphanol caused some sedation in both species at effective antiemetic doses but had no effect on the antitumor activity of cisplatin against murine L1210 leukemia. Naloxone blocked the antiemetic effect of butorphanol in ferrets, indicating the involvement of opiate receptors. The results of these studies suggest that butorphanol may be useful clinically in mitigating the emetic effects of cisplatin.