36 - 40 Pharmacology SBAs for the Primary FRCA

• It corrects metabolic alkalosis by increasing the strong ion difference

Acetazolamide decreases the strong ion difference.

The strong ion difference refers to the difference between the measured strong positive and strong negative ions in the blood (similar idea to anion gap).

A 'strong ion' is one that completely dissociates in solution, and those of significance are:

Cations

• Na⁺
• K⁺
• Ca²⁺
• Mg²⁺

Anions

• Cl^-
• SO₄^2-

The strong ion difference is simply the sum of the positives minus the sum of the negatives.

Since there is a huge amount of sodium and chloride in the blood, and not much of the others, we tend to just focus on [Na⁺] - [Cl^-].

A normal SID is around 40 (there are a few ions that we don't measure, which make up this 40 and maintain electroneutrality in the blood).

If you add negative ions (or remove positive ones) and reduce the SID, then the blood becomes negatively charged, and so the body will get rid of bicarbonate (negative) and retain hydrogen ions (positive) to correct it - and you get an acidosis

This is why sodium chloride makes you acidotic - you've added way more chloride (compared to normal plasma concentration) than sodium, and hugely decreased the strong ion difference.

If you add positive ions (or remove negative ones) and increase the SID, then the blood becomes positively charged, and the reverse occurs - and you get an alkalosis

This is why dehydration makes you alkalotic. (Because you usually lose more chloride than sodium)

Acetazolamide encourages bicarbonate and sodium loss, and causes a decrease in the strong ion difference, and therefore lowers the pH.

The other answers are all true.