Nalbuphine

Nalbuphine is a semi-synthetic opioid used commercially as an analgesic under a variety of trade names, including Nubain. It is noteworthy in part for the fact that at low dosages, it is found much more effective by women than by men, and may even increase pain in men, leading to its discontinuation in the UK in 2003.

History and control status
In the search for narcotic analgesics with less abuse potential, a number of semi-synthetic opiates were developed. These substances are referred to as mixed agonist-antagonists analgesics. Nalbuphine (Nubain®) belongs to this group of substances. It was approved for marketing in the United States in 1979 and remains as the only narcotic analgesic of this type (marketed in the U.S.) not controlled under the Controlled Substances Act (CSA). When the Controlled Substances Act (CSA) was enacted in 1971, nalbuphine was placed in schedule II. Endo Laboratories, Inc. subsequently petitioned the DEA to exclude nalbuphine from all schedules of the CSA in 1973. After receiving a medical and scientific review and a scheduling recommendation from the Department of Health, Education and Welfare, forerunner to the Department of Health and Human Services, nalbuphine was removed from schedule II of the CSA in 1976. Presently, nalbuphine is not a controlled substance under the CSA. Kentucky has controlled nalbuphine in schedule IV of state law.

Clinical pharmacology
Nalbuphine is a semi-synthetic narcotic agonist-antagonist analgesic of the phenanthrene series. It is chemically related to both the widely used narcotic antagonist, naloxone, and the potent narcotic analgesic, oxymorphone. It is available in two concentrations, 10 mg and 20 mg of nalbuphine hydrochloride per mL. Both strengths contain 0.94% sodium citrate hydrous, 1.26% citric acid anhydrous, 0.1% sodium metabisulfite, and 0.2% of a 9:1 mixture of methylparaben and propylparaben as preservatives; pH is adjusted, if necessary, with hydrochloric acid. The 10 mg/mL strength contains 0.1% sodium chloride.

Nalbuphine is also available in a sulfite and paraben-free formulation in two concentrations, 10 mg and 20 mg of nalbuphine hydrochloride per mL. One mL of each strength contains 0.94% sodium citrate hydrous, 1.26% citric acid anhydrous; pH is adjusted, if necessary, with hydrochloric acid. The 10 mg/mL strength contains 0.2% sodium chloride.

Nalbuphine is a potent analgesic. Its analgesic potency is essentially equivalent to that of morphine on a milligram basis. Its onset of action occurs within 2 to 3 minutes after intravenous administration, and in less than 15 minutes following subcutaneous or intramuscular injection. The plasma half-life of nalbuphine is 5 hours and in clinical studies the duration of analgesic activity has been reported to range from 3 to 6 hours.

The narcotic antagonist activity of Nalbuphine is one-fourth as potent as nalorphine and 10 times that of pentazocine.

Indication
Nalbuphine is indicated for the relief of moderate to severe pain. It can also be used as a supplement to balanced anesthesia, for preoperative and postoperative analgesia, and for obstetrical analgesia during labor and delivery.

Although Nalbuphine possesses narcotic antagonist activity, there is evidence that in nondependent patients it will not antagonize a narcotic analgesic administered just before, concurrently, or just after an injection. Therefore, patients receiving a narcotic analgesic, general anesthetics, phenothiazines, or other tranquilizers, sedatives, hypnotics, or other CNS depressants (including alcohol) concomitantly with Nalbuphine may exhibit an additive effect. When such combined therapy is contemplated, the dose of one or both agents should be reduced.

Dosing
The usual recommended adult dose is 10 mg for a 70 kg individual, administered subcutaneously, intramuscularly or intravenously; this dose may be repeated every 3 to 6 hours as necessary. Dosage should be adjusted according to the severity of the pain, physical status of the patient, and other medications which the patient may be receiving. In non-tolerant individuals, the recommended single maximum dose is 20 mg, with a maximum total daily dose of 160 mg.

The use of NUBAIN as a supplement to balanced anesthesia requires larger doses than those recommended for analgesia. Induction doses of NUBAIN range from 0.3 mg/kg to 3.0 mg/kg intravenously to be administered over a 10 to 15 minute period with maintenance doses of 0.25 to 0.50 mg/kg in single intravenous administrations as required.

In case of overdose or adverse reaction, the immediate intravenous administration of naloxone (Narcan) is a specific antidote. Oxygen, intravenous fluids, vasopressors and other supportive measures should be used as indicated.

Side effects
The most frequent side effect in 1066 patients treated with nalbuphine was sedation in 381 (36%).

Other, less frequent reactions are: feeling sweaty/clammy 99 (9%), nausea/vomiting 68 (6%), dizziness/vertigo 58 (5%), dry mouth 44 (4%), and headache 27 (3%). Other adverse reactions which may occur (reported incidence of 1% or less) are: Other possible, but rare side effects include speech difficulty, urinary urgency, blurred vision, flushing and warmth.
 * CNS effects: Nervousness, depression, restlessness, crying, euphoria, floating, hostility, unusual dreams, confusion, faintness, hallucinations, dysphoria, feeling of heaviness, numbness, tingling, unreality. The incidence of psychotomimetic effects, such as unreality, depersonalization, delusions, dysphoria and hallucinations has been shown to be less than that which occurs with pentazocine.
 * Cardiovascular: Hypertension, hypotension, bradycardia, tachycardia, pulmonary edema.
 * Gastrointestinal: Cramps, dyspepsia, bitter taste.
 * Respiration: Depression, dyspnea, asthma.
 * Dermatological: Itching, burning, urticaria.
 * Obstetric: Pseudo-sinusoidal fetal heart rhythm.