thiopental sodium
Pentothal

Available forms
Available by prescription only
Injection: 250-mg (2.5%), 400-mg (2%), 500-mg (2.5%) syringes; 500-mg (2.5%), 1-g (2.5%), 2.5-g (2.5%), 5-g (2.5%), 1-g (2%), 2.5-g (2%), 5-g (2%) kits

Indications and dosages
 General anesthetic for short-term procedures. Adults and children: 2 to 4 ml 2.5% solution (50 to 100 mg) administered I.V. for induction and repeated as a maintenance dosage; dose is individualized.
 Convulsive states following anesthesia. Adults: 50 to 125 mg (2 to 5 ml 2.5% solution) I.V.
 Neurosurgical patients with increased ICP. Adults: 1.5 to 3.5 mg/kg I.V. bolus. May give intermittently as long as patient is adequately ventilated.

Pharmacodynamics
Anesthetic action: Thiopental produces anesthesia by direct depression of the polysynaptic midbrain reticular activating system. Thiopental decreases presynaptic (by way of decreased neurotransmitter release) and postsynaptic excitation. These effects may be subsequent to increased gamma-aminobutyric acid (GABA) levels, enhancement of GABA effects, or a direct effect on GABA receptor sites.

Pharmacokinetics
Absorption: Administered I.V.
Distribution: Distributed throughout the body; highest initial level occurs in vascular areas of the brain, primarily gray matter; drug is 80% protein-bound. Redistribution of drug is primarily responsible for its short duration of action.
Metabolism: Metabolized extensively but slowly in the liver.
Excretion: Unchanged thiopental isn’t excreted in significant amounts; duration of action depends on tissue redistribution.

Contraindications and precautions
Contraindicated in patients with acute intermittent or variegate porphyria (not in other porphyrias); in patients hypersensitive to drug; and in patients for whom general anesthesia is contraindicated.
  Use with extreme caution in patients with respiratory, cardiac, circulatory, renal, or hepatic dysfunction; severe anemia; shock; myxedema; and status asthmaticus because drug may worsen these conditions. Also use cautiously in breast-feeding women and in patients with hypotension, Addison’s disease, myasthenia gravis, or increased intracranial pressure.

Interactions
Drug-drug. Antihistamines, benzodiazepines, hypnotics, narcotics, phenothiazines, sedatives: Increases CNS effect. Monitor patient closely.
Drug-lifestyle. Alcohol use: Increases CNS depressant effects. Discourage alcohol use.

Adverse reactions
CNS: anxiety, restlessness, retrograde amnesia, prolonged somnolence, dose-dependent alteration in EEG patterns, pain.
CV: thrombophlebitis, hypotension, tachycardia, peripheral vascular collapse, myocardial depression, arrhythmias.
GI: nausea and vomiting, abdominal pain, diarrhea, cramping.
Respiratory: cough, sneezing, hiccups, respiratory depression, apnea, laryngospasm, bronchospasm.
Skin: swelling, ulceration, necrosis on extravasation (unlikely at levels less than 2.5%).
Other: gangrene after intra-arterial injection, allergic reactions, shivering, local irritation.

Effects on lab test results
None reported.

Overdose and treatment
Effects of overdose include respiratory depression, respiratory arrest, hypotension, and shock.
 Treat supportively, using mechanical ventilation if needed; give I.V. fluids or vasopressors (dopamine, phenylephrine) for hypotension. Monitor vital signs closely.

Special considerations
• Solutions of succinylcholine, tubocurarine, or atropine shouldn’t be mixed with thiopental but can be given to the patient at the same time.
• A small test dose of 25 to 75 mg may be administered to assess tolerance or unusual sensitivity.
 ALERT Discontinue drug if peripheral vascular collapse, respiratory arrest, or hypersensitivity occurs.
• Depth of anesthesia may increase for up to 40 seconds. Consciousness returns in 20 to 30 minutes.
• Monitor cardiac and respiratory status.
Pediatric patients
• Use cautiously in children.
Geriatric patients
• These patients may need lower dosages.

Patient education
• Reassure patient and family that patient will be monitored continuously throughout anesthesia.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use