Methohexital sodium is available in single-use vials containing methohexital sodium 200 mg with anhydrous sodium carbonate 12 mg and multiple-use vials containing methohexital sodium 500 mg with anhydrous sodium carbonate 30 mg or methohexital sodium 2.5 g with anhydrous sodium carbonate 150 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% (10-mg/mL) solution of methohexital sodium for intermittent intravenous injection, reconstitute the 200-mg single-use or the 500-mg multiple-use vials with 20 or 50 mL, respectively, of diluent.2926 For the 2.5-g multiple-use vial, reconstitute with 15 mL of diluent and further dilute by adding the drug to 235 mL of diluent to total 250 mL.2926 The preferred diluent for intermittent intravenous injection is sterile water for injection, but dextrose 5% or sodium chloride 0.9% also may be used.2926
Initial dilution of the 2.5-g vial results in a yellow solution.2926 When further diluted to a final concentration of 1%, the solution must be clear and colorless or it should not be used.2926
To prepare a 0.2% (2-mg/mL) solution of methohexital sodium for continuous intravenous infusion, reconstitute the 500-mg vial with 15 mL of diluent and further dilute by adding the drug to 235 mL of diluent to total 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% (50-mg/mL) solution for intramuscular use, reconstitute the 200- or 500-mg vials with 4 or 10 mL, respectively, of diluent.2926 For the 2.5-g vial, reconstitute with 50 mL of diluent.2926 No further dilution of the reconstituted solution for intramuscular use is required.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 in sterile water for injection 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 is administered intravenously, by intermittent injection at a concentration of 1% or by continuous infusion at a concentration of 0.2%.2926 Intra-arterial injection and extravasation should be avoided.2926
Intramuscular injection of 5% solutions of methohexital sodium has also been described.2926
Intact vials should be stored at controlled room temperature.2926 Reconstituted solutions of methohexital sodium are stable at room temperature for 24 hours.2926
The manufacturer 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
Methohexital sodium is alkaline in solution and is incompatible with acidic solutions and phenol-containing solutions.4
Methohexital sodium exhibits poor solubility in an acidic medium and may precipitate in solutions containing acidic drugs.22
Since solubility is maintained only at relatively high pH, mixing methohexital sodium with acidic solutions is not recommended.4 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 HBr.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 Similarly, atracurium besylate may be inactivated by alkaline solutions, such as barbiturates, and a free acid of the admixed drug may precipitate, depending on the resultant pH of the admixture.4
Methohexital sodium may raise the pH of admixture solutions to the alkaline range and, therefore, should not be mixed with drugs that are alkali labile.4
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
For a list of references cited in the text of this monograph, search the monograph titled References.