Methohexital sodium is available as a lyophilized powder in preservative-free multiple-dose vials containing methohexital sodium 500 mg with anhydrous sodium carbonate 30 mg.2926 Recommended diluents are based on the intended route of administration.2926 Diluents containing bacteriostatic agents should not be used.2926
To prepare a 1% solution (10 mg/mL) for intermittent intravenous injection or rectal administration, reconstitute the 500-mg vial with 50 mL of diluent.2926 The preferred diluent for intermittent intravenous injection or rectal administration is sterile water for injection, but dextrose 5% or sodium chloride 0.9% also may be used.2926
To prepare a 0.2% solution (2 mg/mL) for continuous intravenous infusion, reconstitute the 500-mg vial with 15 mL of diluent and further dilute the reconstituted solution in 235 mL of diluent to a total volume of 250 mL.2926 For continuous intravenous infusion, use only dextrose 5% or sodium chloride 0.9% as a diluent.2926 Do not use sterile water for injection to prepare this concentration for continuous intravenous infusion to avoid extreme hypotonicity.2926
To prepare a 5% solution (50 mg/mL) for intramuscular use, reconstitute the 500-mg vial with 10 mL of diluent.2926 The preferred diluent for intramuscular use is sterile water for injection, but sodium chloride 0.9% also may be used.2926
pH
A 0.2% solution in dextrose 5% has a pH of 9.5 to 10.5; a 1% solution has a pH of 10 to 11.2926
Sodium Content
Methohexital sodium contains 4.652 mEq of sodium per gram of drug; the sodium carbonate provides 1.132 mEq while the balance comes from the drug itself.869
Trade Name(s)
Brevital Sodium
Methohexital sodium may be administered by direct intravenous injection as a 1% solution or by continuous intravenous infusion as a 0.2% solution in adults.2926 In children, methohexital sodium may be administered by intramuscular injection as a 5% solution or rectally as a 1% solution.2926 Intra-arterial injection and extravasation should be avoided; intra-arterial injection can result in platelet aggregation and thrombosis which can result in necrosis and gangrene.2926
Intact vials should be stored at controlled room temperature.2926 Reconstituted solutions of methohexital sodium are stated to be stable at room temperature for 24 hours.2926
Product labeling states that Ringer’s injection, lactated is incompatible as a diluent; the potential for incompatibility exists between the sodium carbonate in the drug formulation and the calcium ions of the infusion solution.282; 2926
pH Effects
Solubility of sodium salts of barbiturates, including methohexital sodium, requires a relatively high pH.2926 Solutions are alkaline and are stated to be incompatible with acidic solutions.2926 Methohexital sodium exhibits poor solubility in an acidic medium and may precipitate in solutions containing acidic drugs.22 Mixed with methohexital sodium, a haze or precipitate forms in 15 minutes with atropine sulfate, in 30 minutes with succinylcholine chloride, and in 60 minutes with scopolamine hydrobromide.2926
When barbiturates are mixed with succinylcholine chloride, either free barbiturate precipitates or the succinylcholine chloride is hydrolyzed, depending on the final pH of the admixture.4; 21
Sorption
Methohexital sodium (Lilly) 32 mg/L displayed 7.9% sorption to a PVC plastic test strip in 24 hours.12 However, another test did not confirm this finding. No significant loss in PVC containers and no difference between glass and PVC containers were found.282
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