Remifentanil in the horse: identification and detection of its major urinary metabolite

Behavioral and Cardiopulmonary Effects of a Constant Rate Infusion of Remifentanil-Xylazine for Sedation in Horses

Xylazine and remifentanil in constant rate infusion (CRI) could be used for sedation in horses without adverse effects. The objective was to evaluate behavioral and cardiopulmonary effects of an intravenous (IV) infusion of xylazine and remifentanil for sedation in horses. Xylazine (0.8 mg/kg IV) followed after 3 minutes by a CRI of xylazine and remifentanil (0.65 mg/kg/h and 6 μg/kg/h, respectively) was administered in 10 healthy horses for 60 minutes. Sedation, ataxia, and cardiopulmonary, hematological, and blood gases variables were evaluated. Heart rate decreased significantly during the first 25 minutes after CRI of xylazine and remifentanil, whereas the respiratory rate showed a significant decrease at 20 minutes and remained significantly low until the endpoint. There were no statistically significant fluctuations in blood arterial pressure, blood pH, partial pressure of arterial carbon dioxide, lactate, creatinine, calcium, chlorine, and sodium, compared with baseline values. Blood partial pressure of arterial oxygen and bicarbonate values were significantly higher compared with baseline values, whereas potassium decreased. Sedation and ataxia developed immediately after the administration of xylazine in all horses. All horses recovered successfully within 10 minutes after interruption of the CRI of xylazine and remifentanil, with no ataxia. No adverse effects were observed. The use of a combination of xylazine and remifentanil as sedation protocol has no adverse effects at the described dosage.

Suicide with remifentanil and midazolam : a case report

Background : Remifentanil (Ultiva®) is a recently introduced esterase-metabolized potent opioid (EMO) μ-receptor agonist with a rapid onset and offset of action for use as part of general anaesthesia in association with isoflurane or propofol or with midazolam (Dormicum®) and in combination with mivacurium. Case Report : A nurse from the anaesthesiology department of a hospital was found dead at home with a syringe and empty vials of Ultiva® (2 mg) and of Dormicum ® (1 mg/mL). At autopsy several injection sites were found on her body. Usual toxicology screening operated in our laboratory revealed only the presence of benzodiazepines in blood. Regarding the case history, we decided to adapt a method specially designed for remifentanil and its inactive metabolite testing. The analytes were isolated by SPE on a Clean-Screen column. After silylation with BSTFA with 1% TMCS, the analytes were detected by GC/MS-EI operating in the SIM mode. No Remifentanil could be detected, whereas the metabolite of remifentanil GR90291 was determined in femoral blood, liver, kidney and lung. Furthermore, midazolam could be detected in femoral and cardiac blood. Hair analysis of a segment of 5 cm revealed the presence of diazepam and midazolam, whereas neither remifentanil nor its metabolite could be detected.

Managing chronic whiplash associated pain with a combination of low-dose opioid (remifentanil) and NMDA-antagonist (ketamine)

The aim was to investigate the efficacy of a combination of low-dose remifentanil (REMI) and ketamine (KET) compared to the single drugs and placebo (P) on whiplash associated pain (WAD) in a double-blind, randomized, placebo-controlled, cross-over study. Twenty patients with chronic (>1 year) WAD were included. Four different drug combinations were tested in four sessions: placebo/placebo (P/P), placebo/remifentanil (P/REMI), ketamine/placebo (KET/P) and ketamine/remifentanil (KET/REMI). Target concentrations were 1 and 2ng/ml (stepwise) for remifentanil and 100ng/ml for ketamine. Habitual pain intensity was assessed on a visual analogue scale (VAS). Experimental pain was assessed with electrical stimulation (single and repeated) of tibialis anterior (TA) muscle, pressure pain algometry applied over infraspinatus (IS) and TA muscles and VAS scores after intramuscular hypertonic saline infusion in TA. KET/REMI significantly reduced habitual pain. KET/REMI infused at low REMI target concentration (1ng/ml) significantly elevated electrical intramuscular pain thresholds (single and repeated). Pain thresholds to electrical stimulation were similarly increased by both P/REMI and KET/REMI at 2ng/ml target concentration. Pressure pain thresholds were increased by both KET/REMI and P/REMI. VAS-scores after intramuscular saline were also similarly decreased by both REMI combinations. Seven out of 20 subjects were non-responders (<50% pain relief). No correlation was found between effects on spontaneous pain and experimental pain. KET/REMI showed an analgesic effect on habitual pain. Experimental pain was attenuated by both combinations containing the opioid, however, KET seemed to enhance the effect of REMI on electrical pain thresholds when a low REMI target concentration was used.