What Causes Nausea, Anorexia And Knee Weakness After Taking Antibiotic For Root Canal?

A senior citizen that may be immunosuppressed (possible leukemia) had a root canal. Antibiotics caused nausea and were not taken. Anorexia, headaches on top of the head, weakness in the knees progressed to altered menation and hospitalization. Now on iv saline, and a combination of antibiotics (not sure which ones). CT Mri clear, normal organ function, normal cbc. Still has severely altered mentation. Full cardiovascular work up and spinal tap normal. All blood urine and spinal cultures negative.