The following antibiotics should be, theoretically, safe to combine with MDMA (note that these are NOT brand names, but rather the chemical names):
azithromycin
bacitracin
cephalosporin, and forms of (cefepime, cephalexin)
ciprofloxacin
flucloxacillin
flucytosine
griseofulvin
isoniazid (used to treat TB)
minocycline*
moxifloxacin
neomycin
nitrofurantoin (but this may cause oxidative stress and so MDMA would be best avoided)
penicillin
polymyxin
streptomycin
sulfamethoxazole
trimethoprim
The following antibiotics have the potential to be dangerous, because they inhibit one of the enzymes (CYP34A) that breaks down MDMA. Thus, you should be cautious (consider taking a 1/2 dose of MDMA) if you are taking one of these antibiotics. Antibiotics with a (*) indicate that people have rolled on this antibiotic safely -- though it is still recommended that you be careful with these.
amoxicillin *
clarithromycin
doxycycline (common acne med) *
erythromycin
ketoconazole* (but person experienced a very strong, long roll - proceed with caution!)
lansoprazole
primaquine
tetracycline*
troleandomycin