Q: Why methanol and ethylene glycol are designated as "primary alcohols" but isopropyl alcohol is not?
Answer: Methanol get oxidized to formic acid. Ethylene glycol get oxidized to glycolic, glyoxylic, and oxalic acids. These acid metabolites cause direct injury and thats why methanol and ethylene glycol are considered primary alcohols.
Isopropyl alcohol metabolized to ketones and cannot be converted to carboxylic acid (formic, glycolic, glyoxylic, and oxalic acids). Ketones does not cause high an-ion gap acidosis and relatively less injurious than other two.