amantadine hydrochloride

Action

Antiviral action unclear; may prevent penetration of influenza A virus into host cell. Antiparkinsonian action unknown; may ease parkinsonian symptoms by increasing dopamine release, preventing dopamine reuptake into presynaptic neurons, stimulating dopamine receptors, or enhancing dopamine sensitivity.

Availability

Capsules (liquid-filled): 100 mg

Syrup: 50 mg/5 ml

Tablets: 100 mg

Indications and dosages

➣ Symptomatic treatment or prophylaxis of influenza type A virus in patients with respiratory conditions

Adults older than age 65 with normal renal function: 100 mg P.O. once daily

Adults to age 64 with normal renal function: 200 mg (tablets) or 4 tsp of syrup P.O. daily in a single dose, or 100 mg tablet or 2 tsp of syrup P.O. b.i.d.

Children ages 9 to 12: 100 mg P.O. q 12 hours

Children ages 1 to 9 or weighing less than 45 kg (99 lb): 4.4 to 8.8 mg/kg/day of syrup P.O. q 12 hours, not to exceed 150 mg daily

➣ Parkinson's disease

Adults: Initially, 100 mg P.O. daily, increased to 100 mg b.i.d. if needed. If patient doesn't respond adequately, give 200 mg b.i.d., up to 400 mg/day.

➣ Drug-induced extrapyramidal reactions

Adults: 100 mg P.O. b.i.d.; may increase dosage to maximum of 300 mg daily in divided doses

Dosage adjustment

• Renal impairment

Contraindications

• Hypersensitivity to drug

Precautions

Use cautiously in:

• cardiac disease, hepatic disease, renal impairment, seizure disorder, psychiatric problems

• untreated closed-angle glaucoma (use not recommended)

• elderly patients

• pregnant or breastfeeding patients.

Administration

• For antiviral use, start therapy within 24 to 48 hours of symptom onset and continue for 24 to 48 hours after symptoms resolve.

• When giving as prophylactic antiviral, start therapy as soon as possible and continue for at least 10 days after exposure to virus.

• When giving with influenza vaccine, continue drug for 2 to 3 weeks while patient develops antibody response to vaccine.

Adverse reactions

CNS: depression, dizziness, drowsiness, insomnia, light-headedness, anxiety, irritability, hallucinations, confusion, ataxia, headache, nervousness, abnormal dreams, agitation, fatigue, delusions, aggressive behavior, manic reaction, psychosis, slurred speech, euphoria, abnormal thinking, amnesia, increased or decreased motor activity, paresthesia, tremor, abnormal gait, delirium, stupor, coma

CV: orthostatic hypotension, tachycardia, peripheral edema, heart failure, cardiac arrest, arrhythmias

EENT: blurred vision, mydriasis, keratitis, photosensitivity, optic nerve palsy, nasal congestion

GI: nausea, vomiting, diarrhea, constipation, dry mouth, dysphagia, anorexia

GU: urine retention, decreased libido Hematologic: leukocytosis

Musculoskeletal: involuntary muscle contractions

Respiratory: tachypnea, acute respiratory failure, pulmonary edema

Skin: purplish skin discoloration, rash, pruritus, diaphoresis

Other: edema, fever, allergic reactions including anaphylaxis

Interactions

Drug-drug. Anticholinergics, antihistamines, phenothiazines, quinidine, tricyclic antidepressants: increased atropine-like adverse effects

CNS stimulants: increased CNS stimulation

Hydrochlorothiazide, triamterene: increased amantadine effects

Drug-diagnostic tests. Alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, bilirubin, blood urea nitrogen, creatine kinase, creatinine, gamma-glutamyltransferase, lactate dehydrogenase: increased levels

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

Drug-behaviors. Alcohol use: increased CNS adverse reactions

Patient monitoring

See Monitor patient for depression and suicidal ideation.

• Watch for mental status changes, especially in elderly patients.

• Stay alert for worsening of psychiatric problems if patient has a history of such problems or substance abuse.

• Monitor for orthostatic hypotension.

• Evaluate for signs and symptoms of fluid overload.

• Monitor kidney and liver function test results.

Patient teaching

See Caution patient that taking more than prescribed dosage may lead to serious adverse reactions or even death.

• Advise patient to establish effective bedtime routine and to take drug several hours before bedtime to minimize insomnia.

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

• Advise patient to minimize GI upset by eating small, frequent servings of foods and drinking plenty of fluids.

• Instruct patient to contact prescriber if he develops signs or symptoms of depression.

• 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.