The pH of commercially available thiopental is which value?

The pH of commercially available thiopental is which value?

• A. 4.5
• B. 5.5
• C. 7.4
• D. 10.5

Answer: (D)

Thiopental is formulated as a highly alkaline intravenous solution so that it stays in the nonionized, lipid-soluble form. This increases its ability to cross the blood-brain barrier quickly, giving a rapid onset of anesthesia. The commercially prepared solution has a pH around 10.5, which is purposefully high to maximize CNS penetration. If the solution were more acidic or closer to neutral, thiopental would be more ionized and less lipid-soluble, resulting in slower or less reliable onset. The marked alkalinity explains why 10.5 is the correct value for the pH of the preparation.

Thiopental is formulated as a highly alkaline intravenous solution so that it stays in the nonionized, lipid-soluble form. This increases its ability to cross the blood-brain barrier quickly, giving a rapid onset of anesthesia. The commercially prepared solution has a pH around 10.5, which is purposefully high to maximize CNS penetration. If the solution were more acidic or closer to neutral, thiopental would be more ionized and less lipid-soluble, resulting in slower or less reliable onset. The marked alkalinity explains why 10.5 is the correct value for the pH of the preparation.