Remifentanil

Remifentanil is a potent, short-acting synthetic opioid analgesic drug. It is given to patients during surgery to relieve pain and as an adjunct to an anaesthetic. Remifentanil is used for sedation as well as combined with other medications for use in general anesthesia. The use of remifentanil has made possible the use of high-dose opioid and low-dose hypnotic anesthesia, due to synergism between remifentanil and various hypnotic drugs and volatile anesthetics. Remifentanil is a potent, short-acting synthetic opioid analgesic drug. It is given to patients during surgery to relieve pain and as an adjunct to an anaesthetic. Remifentanil is used for sedation as well as combined with other medications for use in general anesthesia. The use of remifentanil has made possible the use of high-dose opioid and low-dose hypnotic anesthesia, due to synergism between remifentanil and various hypnotic drugs and volatile anesthetics. Remifentanil is used as an opioid analgesic that has a rapid onset and rapid recovery time. It has been used effectively during craniotomies, spinal surgery, cardiac surgery, and gastric bypass surgery. While opiates function similarly, with respect to analgesia, the pharmacokinetics of remifentanil allows for quicker post-operative recovery. It is administered in the form remifentanil hydrochloride and in adults is given as an intravenous infusion in doses ranging from 0.1 microgram per kilogram per minute to 0.5 (µg/kg)/min. Children may require higher infusion rates (up to 1.0 (µg/kg)/min). The clinically useful infusion rates are 0.025-0.1 (µg/kg)/min for sedation (rates adjusted to age of patient, severity of their illness and invasiveness of surgical procedure). Small amounts of other sedative medications are usually co-administered with remifentanil to produce sedation. Clinically useful infusion rates in general anesthesia vary but are usually 0.1-1 µg/kg/min. Remifentanil can be administered as part of an anesthesia technique called TIVA (Total Intravenous Anesthesia) using computer controlled infusion pumps in a process called target controlled infusion (TCI). A target plasma concentration is entered as ng/ml into the pump, which calculates its infusion rate according to patient factors like age and weight. Induction levels of 40 ng/ml are commonly used, but it generally varies between 3-8 ng/ml. For certain surgical procedures that produce particularly strong stimuli a level of up to 15 ng/ml might be needed. The relatively short context-sensitive half-life of Remifentanil allows the desired blood plasma level to be achieved quickly and also for the same reason, recovery occurs quickly. Remifentanil's short context-sensitive half-life makes it ideal for intense pain of short duration. As such, it has been used for analgesia in labor successfully; however, it is not as effective as epidural analgesia. In combination with propofol, remifentanil is used for anesthesia of patients undergoing Electroconvulsive therapy. Remifentanil is considered a soft drug, one that is rapidly metabolized to an inactive form. Unlike other synthetic opioids which are hepatically metabolized, remifentanil has an ester linkage which undergoes rapid hydrolysis by non-specific tissue and plasma esterases. This means that accumulation does not occur with remifentanil and its context-sensitive half-life remains at 4 minutes after a 4-hour infusion. Remifentanil is metabolized to a compound (remifentanil acid) which has 1/4600th the potency of the parent compound. Due to its quick metabolism and short effects, remifentanil has opened up new possibilities in anesthesia. When remifentanil is used together with a hypnotic (i.e. one that produces sleep) it can be used in relative high doses. This is because remifentanil will be rapidly eliminated from the blood plasma on termination of the remifentanil infusion, hence the effects of the drug will quickly dissipate even after very long infusions. Owing to synergism between remifentanil and hypnotic drugs (such as propofol) the dose of the hypnotic can be substantially reduced. This leads often to more hemodynamic stability during surgery and a quicker post-operative recovery time.