What medications should not be mixed with alcohol?

Pretty much all of them, though to greatly varying degrees.

There are many medications that can be dangerous and even fatal when taken with alcohol, far too many to enumerate here in detail, but the CNS depressants make up the biggest category. These would include benzodiazepines (like Valium and xanax) to barbiturates (like phenobarbitol), ketamine, ambien, imovane, quaalude, noctec, and so on.

With many other drugs, alcohol can simply interfere with their ability to work. For example, mixing alcohol with antibiotics can inhibit the antibiotics making them less likely to work and increasing the risk of an even worse re-infection.

When in doubt, ask your doctor.