Remifentanil, marketed under the brand name Ultiva is a potent, short-acting synthetic opioid analgesic drug.

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.

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.

Unlike other synthetic opioids which are hepatically metabolized, remifentanil has an ester linkage which undergoes rapid hydrolysis by non-specific tissue and plasma esterases.

The most common side effects reported by patients receiving this medication are a sense of extreme "dizziness" (often short lived, a common side effect of other fast-acting synthetic phenylpiperidine narcotics such as fentanyl and alfentanil) and intense itching (pruritus), often around the face.

Because pruritus is partially due to excessive serum histamine levels, antihistamines such as diphenhydramine (Benadryl) are often co-administered.

Nausea can occur as a side effect of remifentanil, however, it is usually transient in nature due to the drug's short half-life which rapidly removes it from the patient's circulation once the infusion is terminated.

[21][22] Prior to the development of remifentanil, most short-acting hypnotics and amnestics faced issues with prolonged use, where accumulation would result in unfavorable lingering effects during post-operative recovery.

Remifentanil was designed to serve as a strong anesthetic with an ultra-short and predictable duration that would not have accumulation issues.

Possession of the substance for consumption without license from the Department of Health is illegal with a HK$1,000,000 (US$155,000) fine and/or 7 years of jail time.

Remifentanil is a Schedule II narcotic controlled substance in the United States with a DEA ACSCN of 9739 and a 2013 annual aggregate manufacturing quota of 3,750 grams, unchanged from the prior year.