My internist has told me to avoid drugs such as phenergan because it is related to anti-psychotic drugs that can cause an MH-like reaction. Is this true? If so, which drugs should I avoid that may be present during delivery?

Your internist is advising you well, but very conservatively. Some anti-psychotic agents cause a condition called neuroleptic malignant syndrome (NMS), which looks something like MH but has a different underlying cause.

Nonetheless, the conservative approach is to avoid this class of drugs in MH-affected patients. Phenergan is used for nausea in the hospital; it is unlikely you would need it, but it would be reasonable to avoid this class.

The drugs used for labor analgesia are safe.