Inapsine

Action

Produces marked sedation by directly blocking subcortical receptors. Produces antiemetic effect by blocking CNS receptors in chemoreceptor trigger zone.

Availability

Injection: 2.5 mg/ml in 1-ml, 2-ml, and 5-ml ampules and in 2-ml, 5-ml, and 10-ml vials

Indications and dosages

➣ Perioperative nausea and vomiting

Adults: Initially, 2.5 mg I.M. or I.V. Additional doses of 1.25 mg may be given. Dosages are highly individualized according to patient's age, weight, physical status, and underlying pathologic condition.

Children ages 2 to 12: Initially, 0.1 mg/kg I.M. or I.V. Additional doses up to a total of 2.5 mg may be given. Dosages are highly individualized according to patient's age, weight, physical status, and underlying clinical condition.

Dosage adjustment

• Elderly or debilitated patients

• High-risk patients (such as patients over age 65 and those with heart failure, alcohol abuse, or other factors that predispose to prolonged QT interval)

• Patients who have received other CNS depressants (such as analgesics or anesthetics)

Contraindications

• Hypersensitivity to drug

• Known or suspected QT-interval prolongation (more than 440 millisec in males or 450 millisec in females)

Precautions

Use cautiously in:

• severe cardiac or renal disease, diabetes mellitus, respiratory insufficiency, prostatic hypertrophy, angle-closure glaucoma, CNS depression, CNS tumors, intestinal obstruction, bone marrow depression

• elderly patients

• pregnant or breastfeeding patients

• children younger than age 2.

Administration

• Know that drug is indicated to ease perioperative nausea and vomiting only in patients who don't respond adequately to other treatment.

• Be aware that drug doesn't need to be diluted for I.V. or I.M. use.

• Give by slow I.V. injection, or inject I.M. into large muscle.

Adverse reactions

CNS: weakness, dysarthria, dysphonia, dizziness, extrapyramidal reactions, headache, postoperative hallucinatory episodes with transient depression, tremor, irritability, paresthesia, aggression, vertigo, ataxia, loss of consciousness, seizures, neuroleptic malignant syndrome

CV: chest pain, hypertension, hypotension, vasodilation, arrhythmias, atrial fibrillation

EENT: cataracts, blurred vision, eye irritation, sore throat

GI: nausea, vomiting, diarrhea, abdominal cramps, bloating, epigastric pain, fecal incontinence, increased salivation, dysphagia

GU: urinary frequency, increased libido

Hepatic: cholestatic jaundice

Metabolic: dehydration

Musculoskeletal: muscle cramps, arthritis, bone fractures

Respiratory: bronchitis, dyspnea

Skin: bruising, rash, urticaria, facial sweating, diaphoresis, pruritus, flushing

Other: toothache, weight loss, hot flashes, influenza, chills

Interactions

Drug-drug. Antihypertensives, nitrates: additive hypertension

CNS depressants (including antidepressants, antihistamines, opioids): additive CNS depression

Drugs that induce hypokalemia or hypomagnesemia (such as diuretics and laxatives and supraphysiologic use of steroid hormones with mineralocorticoid activity): possible precipitation, QT interval prolongation

Drugs that prolong QTc interval (such as antidepressants, class I or III antiarrhythmics, antimalarials, calcium channel blockers, some antihistamines, some neuroleptics): increased risk of conduction abnormalities

Drug-herbs. Chamomile, hops, kava, skullcap, valerian: increased CNS depression

Drug-behaviors. Alcohol use: additive CNS depression

Patient monitoring

☞ Monitor QT interval; report prolongation. Also watch for torsades de pointes.

☞ Know that drug may cause sudden death at high doses (above 25 mg) in patients at risk for arrhythmias.

☞ Monitor for signs and symptoms of neuroleptic malignant syndrome, such as hyperthermia, severe extrapyramidal symptoms, altered mental status, stupor, coma, hypertension, tachycardia, pallor, or diaphoresis. (However, this syndrome is rare.)

• Assess vital signs frequently. Stay alert for orthostatic hypotension and tachycardia. Keep I.V. fluids and vasopressors on hand to treat pronounced hypotension.

☞ Don't place hypotensive patient in Trendelenburg position because this may deepen anesthesia, precipitating respiratory arrest.

• Avoid abrupt position changes.

• Observe for signs and symptoms of respiratory compromise if drug is used concurrently with narcotics.

Patient teaching

• Advise patient not to drink alcohol or take CNS depressants for 24 hours after receiving drug.

• Tell patient drug may cause extreme drowsiness for several days after administration.

• Caution patient not to drive or perform other activities requiring mental alertness.

• Instruct patient to change positions slowly.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, herbs, and behaviors mentioned above.