PRALIDOXIME CHLORIDE
(pra-li-dox'eem)
2-PAM, Protopam Chloride
Classifications: antidote
Pregnancy Category: C

Availability

600 mg, 1 g injection

Actions

Reactivates cholinesterase inhibited by phosphate esters by displacing the enzyme from its receptor sites; the free enzyme then can resume its function of degrading accumulated acetylcholine, thereby restoring normal neuromuscular transmission.

Therapeutic Effects

Less effective against carbamate anticholinesterases (ambenonium, neostigmine, pyridostigmine). More active against effects of anticholinesterases at skeletal neuromuscular junction than at autonomic effector sites or in CNS respiratory center; therefore, atropine must be given concomitantly to block effects of acetylcholine and its accumulation in these sites.

Uses

As antidote in treatment of poisoning by organophosphate insecticides and pesticides with anticholinesterase activity (e.g., parathion, TEPP, sarin) and to control overdosage by anticholinesterase drugs used in treatment of myasthenia gravis (cholinergic crisis).

Unlabeled Uses

To reverse toxicity of echothiophate ophthalmic solution.

Contraindications

Use in poisoning by carbamate insecticide Sevin, inorganic phosphates, or organophosphates having no anticholinesterase activity; asthma, peptic ulcer, severe cardiac disease, patients receiving aminophylline, theophylline, morphine, succinylcholine, reserpine, or phenothiazines; pregnancy (category C).

Cautious Use

Myasthenia gravis; renal insufficiency; concomitant use of barbiturates in organophosphorous poisoning; lactation, children.

Route & Dosage

Organophosphate Poisoning
Adult: IV 1–2 g in 100 mL NS infused over 15–30 min; or 1–2 g as 5% solution in sterile water over not less than 5 min, may repeat after 1 h if muscle weakness not relieved IM/SC 1–2 g if IV route is not feasible
Child: IV 20–40 mg/kg. May repeat in 1–2 h if needed.

Anticholinesterase Overdose in Myasthenia Gravis
Adult: IV 1–2 g in 100 mL NS infused over 15–30 min, followed by increments of 250 mg q5min prn

Administration

Subcutaneous/Intramuscular

Give only if unable to give IV; NOT preferred routes.
Reconstitute as for direct IV injection (see below).

Intravenous

PREPARE: Direct: Reconstitute 1-g vial by adding 20 mL NS to yield 50 mg/mL (a 5% solution). If pulmonary edema is present, give without further dilution. IV Infusion: Preferred method is to further dilute in 100 mL NS.

ADMINISTER: Direct: In pulmonary edema, 1 g or fraction thereof over 5 min; do not exceed 200 mg/min. IV Infusion: Give over 15–30 min (preferred).

Stop infusion and reduce rate if hypertension occurs.

Adverse Effects (1%)

CNS: Dizziness, headache, drowsiness. GI: Nausea. Special Senses: Blurred vision, diplopia, impaired accommodation. CV: Tachycardia, hypertension (dose-related). Body as a Whole: Hyperventilation, muscular weakness, laryngospasm, muscle rigidity.

Interactions

Drug: May potentiate the effects of barbiturates.

Pharmacokinetics

Peak: 5–15 min IV; 10–20 min IM. Distribution: Distributed throughout extracellular fluids; crosses blood–brain barrier slowly if at all. Metabolism: Probably metabolized in liver. Elimination: Rapidly excreted in urine. Half-Life: 0.8–2.7 h.

Nursing Implications

Assessment & Drug Effects

Monitor BP, vital signs, and I&O. Report oliguria or changes in I&O ratio.
Monitor closely. It is difficult to differentiate toxic effects of organophosphates or atropine from toxic effects of pralidoxime.
Be alert for and report immediately: Reduction in muscle strength, onset of muscle twitching, changes in respiratory pattern, altered level of consciousness, increases or changes in heart rate and rhythm.
Observe necessary safety precautions with unconscious patient because excitement and manic behavior reportedly may occur following recovery of consciousness.
Keep patient under close observation for 48–72 h, particularly when poison was ingested, because of likelihood of continued absorption of organophosphate from lower bowel.
In patients with myasthenia gravis, overdosage with pralidoxime may convert cholinergic crisis into myasthenic crisis.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug