SOMI

Action

Interferes with histamine effects at histamine₁-receptor sites; prevents but doesn't reverse histamine-mediated response. Also possesses CNS depressant and anticholinergic properties.

Availability

Capsules: 25 mg, 50 mg

Elixir: 12.5 mg/5 ml

Injection: 10 mg/ml, 50 mg/ml

Strips (orally disintegrating): 12.5 mg, 25 mg

Syrup: 12.5 mg/5 ml

Tablets: 25 mg, 50 mg

Tablets (chewable): 12.5 mg, 25 mg

Tablets (orally disintegrating): 12.5 mg

Indications and dosages

➣ Allergy symptoms caused by histamine release (including anaphylaxis, seasonal and perennial allergic rhinitis, and allergic dermatoses); nausea; vertigo

Adults and children over age 12: 25 to 50 mg P.O. q 4 to 6 hours, or 10 to 50 mg I.V. or I.M. q 2 to 3 hours p.r.n. (Some patients may need up to 100 mg.) Don't exceed 400 mg/day.

Children ages 6 to 12: 12.5 to 25 mg P.O. q 4 to 6 hours, or 1.25 mg/kg (37.5 mg/m²) I.M. or I.V. q.i.d. Don't exceed 150 mg/day.

Children ages 2 to 5: 6.25 mg P.O. q 4 to 6 hours. Don't exceed 37.5 mg/day.

➣ Cough

Adults: 25 mg P.O. q 4 hours p.r.n. Don't exceed 150 mg/day.

Children ages 6 to 12: 12.5 mg P.O. q 4 hours. Don't exceed 75 mg/day.

Children ages 2 to 5: 6.25 mg P.O. q 4 hours. Don't exceed 37.5 mg/24 hours.

➣ Dyskinesia; Parkinson's disease

Adults: Initially, 25 mg P.O. t.i.d.; may be increased to a maximum of 50 mg q.i.d.

➣ Mild nighttime sedation

Adults: 50 mg P.O. 20 to 30 minutes before bedtime

Dosage adjustment

• Elderly patients

Off-label uses

• Drug-induced extrapyramidal reactions

Contraindications

• Hypersensitivity to drug

• Alcohol intolerance

• Acute asthma attacks

• MAO inhibitor use within past 14 days

• Breastfeeding

• Neonates, premature infants

Precautions

Use cautiously in:

• severe hepatic disease, angle-closure glaucoma, seizure disorders, prostatic hypertrophy, cardiovascular disease, hyperthyroidism

• elderly patients

• pregnant patients (safety not established)

• children younger than age 2 (safety not established).

Administration

• For motion sickness, administer 30 minutes before activity.

• For I.V. use, check compatibility before mixing with other drugs.

• Inject I.M. dose deep into large muscle mass; rotate sites.

• Discontinue drug 4 days before allergy skin testing to avoid misleading results.

☞ Don't give within 14 days of MAO inhibitors.

Adverse reactions

CNS: drowsiness, dizziness, headache, paradoxical stimulation (especially in children)

CV: hypotension, palpitations, tachycardia

EENT: blurred vision, tinnitus

GI: diarrhea, constipation, dry mouth

GU: dysuria, urinary frequency or retention

Skin: photosensitivity

Other: decreased appetite, pain at I.M. injection site

Interactions

Drug-drug. Antihistamines, opioids, sedative-hypnotics: additive CNS depression

Disopyramide, quinidine, tricyclic antidepressants: increased anticholinergic effects

MAO inhibitors: intensified and prolonged anticholinergic effects

Drug-diagnostic tests. Skin allergy tests: false-negative results

Hemoglobin, platelets: decreased values

Drug-herbs. Angel's trumpet, jimson weed, scopolia: increased anticholinergic effects

Chamomile, hops, kava, skullcap, valerian: increased CNS depression

Drug-behaviors. Alcohol use: increased CNS depression

Patient monitoring

• Monitor cardiovascular status, especially in patients with cardiovascular disease.

• Supervise patient during ambulation. Use side rails as necessary.

Patient teaching

• Advise patient to avoid alcohol and other depressants such as sedatives while taking drug.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

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

Action

Blocks effects but not release of histamine and exerts strong alphaadrenergic effect. Also inhibits chemoreceptor trigger zone in medulla and alters dopamine effects by indirectly reducing reticular stimulation in CNS.

Availability

Injection: 25 mg/ml and 50 mg/ml in 1-ml ampules and 1- and 10-ml vials

Suppositories: 12.5 mg, 25 mg, 50 mg

Syrup: 6.25 mg/5 ml

Tablets: 12.5 mg, 25 mg, 50 mg

Indications and dosages

➣ Type 1 hypersensitivity reaction

Adults: 25 mg P.O. or P.R. at bedtime or 12.5 mg P.O. before meals and at bedtime. Or 25 mg I.M. or I.V.; may repeat in 2 hours.

Children older than age 2: 25 mg P.O. or P.R. at bedtime or 6.25 to 12.5 mg P.O. t.i.d.

➣ Motion sickness

Adults: Initially, 25 mg P.O. or P.R. 30 to 60 minutes before traveling; may repeat 8 to 12 hours later if needed. On successive travel days, 25 mg P.O. or P.R. b.i.d. (on arising and before evening meal).

Children older than age 2: 12.5 to 25 mg P.O. or P.R. b.i.d.

➣ Sedation

Adults: 25 to 50 mg P.O., I.M., I.V., or P.R. at bedtime

Children older than age 2: 12.5 to 25 mg P.O. or P.R. at bedtime

➣ Adjunct to preoperative or postoperative analgesia

Adults: 25 to 50 mg P.O., P.R., I.M., or I.V. given with appropriately reduced dosage of narcotic or barbiturate and required dosage of belladonna alkaloid

Children older than age 2: 0.5 mg/lb P.O., P.R., I.M., or I.V., given with appropriately reduced dosage of narcotic or barbiturate and required dosage of belladonna alkaloid

➣ Nausea

Adults: 25 mg P.O. or P.R.; may repeat doses of 12.5 to 25 mg P.O. or P.R. q 4 to 6 hours p.r.n. Or 12.5 to 25 mg I.M. or I.V.; may repeat q 4 hours p.r.n.

Children older than age 2: 25 mg or 0.5 mg/lb P.O. or P.R.; may repeat doses of 12.5 to 25 mg P.O. or P.R. q 4 to 6 hours p.r.n. May give I.M. or I.V. as no more than half of adult dosage. Know that drug should not be given if cause of vomiting is unknown.

Contraindications

• Hypersensitivity to drug

• Previous idiosyncratic reaction to phenothiazines

• Coma

• Intra-arterial and subcutaneous injection

• Children younger than age 2

Precautions

Use cautiously in:

• cardiovascular or hepatic disease, seizures, bone marrow depression, narrow-angle glaucoma, prostatic hypertrophy, stenosing peptic ulcer, pyloroduodenal or bladder neck obstruction

• CNS depression caused by narcotics, barbiturates, general anesthesia, tranquilizers, or alcohol

• pregnant or breastfeeding patients.

Administration

• Don't give I.V. at concentrations greater than 25 mg/ml or faster than 25 mg/minute.

• Use light-resistant covering for I.V. drug.

☞ Inject I.M. deep into large muscle. Don't give by subcutaneous route.

Adverse reactions

CNS: confusion, disorientation, fatigue, marked drowsiness, sedation, dizziness, extrapyramidal reactions, insomnia, nervousness, neuroleptic malignant syndrome

CV: hypertension, hypotension, bradycardia, tachycardia

EENT: blurred vision, diplopia, tinnitus

GI: constipation, dry mouth

Hematologic: blood dyscrasias

Hepatic: cholestatic jaundice

Respiratory: respiratory depression

Skin: photosensitivity, rash

Other: hypersensitivity reaction

Interactions

Drug-drug. Anticholinergics: additive anticholinergic effects

CNS depressants: additive CNS depression

Epinephrine: reversal of epinephrine's vasopressor effects

MAO inhibitors: increased extrapyramidal effects

Drug-diagnostic tests. Glucose: increased level

Granulocytes, platelets, white blood cells: decreased counts

Pregnancy test: false-positive or false-negative result

Skin tests using allergen extracts: false-negative results

Drug-herbs. Betel nut: increased risk of extrapyramidal reactions

Evening primrose oil: increased risk of seizures

Kava: increased risk of adverse drug effects

Drug-behaviors. Alcohol use: additive CNS depression

Sun exposure: increased risk of photosensitivity

Patient monitoring

☞ Monitor neurologic status. Stay alert for signs and symptoms of neuroleptic malignant syndrome (high fever, sweating, unstable blood pressure, stupor, muscle rigidity, and autonomic dysfunction).

• In long-term therapy, assess for other adverse CNS effects, including extrapyramidal reactions.

• Monitor CBC and liver function tests.

Patient teaching

☞ Teach patient to recognize and immediately report signs and symptoms of hypersensitivity reaction or neuroleptic malignant syndrome.

• Tell patient about drug's other significant neurologic effects. Instruct him to contact prescriber if these occur.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration, vision, alertness, and motor skills.

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