Methohexital

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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Methohexital contains not less than 98.0 percent and not more than 101.0 percent of C₁₄H₁₈N₂O₃, calculated on the anhydrous basis.

1 Packaging and storage

Preserve in well-closed containers.

USP Reference standards 〈11〉—

USP Methohexital RS

Change to read:

Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197S (CN 1-May-2020) —

Solution: 1 in 100.

Medium: chloroform.

Melting range 〈741〉: between 92° and 96°, but the range between beginning and end of melting does not exceed 3°.

Water Determination, Method I 〈921〉: not more than 2.0%.

Chloride 〈221〉—Dissolve 200 mg in a mixture of 75 mL of ether and 25 mL of water, agitate, and allow to separate: the water solution shows no more chloride than corresponds to 0.17 mL of 0.010 N hydrochloric acid (0.03%).

Ordinary impurities 〈466〉—

Test solution: methanol.

Standard solution: methanol.

Eluant: a mixture of chloroform and acetone (7:3).

Visualization—Expose the plate to chlorine gas for 1 minute, and air-dry the plate at room temperature for 2 minutes. Prepare a solution of 0.5g of potassium iodide in 50 mL of water, and prepare a solution of 1.5 g of soluble starch in 50 mL of hot water. Mix 10 mL of each solution with 4 mL of alcohol to obtain the Detection reagent. [Note—The Detection reagent so obtained may be used for up to 3 or 4 days.] Spray the plate with the Detection reagent.

2 Assay

Dissolve about 100 mg of Methohexital, accurately weighed, in chloroform, and dilute quantitatively and stepwise with chloroform to obtain a solution having a concentration of about 10 mg per mL. Dissolve an accurately weighed quantity of USP Methohexital RS in chloroform, and dilute quantitatively and stepwise with chloroform to obtain a Standard solution having a known concentration of about 10 mg per mL. Concomitantly determine the absorbances of both solutions in 0.1-mm cells at the wavelength of maximum absorbance at about 5.93μm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in mg, of C₁₄H₁₈N₂O₃ in the portion of

Methohexital taken by the formula:

10C(A_U/A_S)

in which C is the concentration, in mg per mL, of USP Methohexital RS in the Standard solution; and A_U and A_S are the absorbances of the solution of Methohexital and the Standard solution, respectively.