“Both classical analgesics (nonsteroidal anti-inflammatory drugs, opioid drugs) and … acid can modulate the balance between pro-oxidant and antioxidant processes … indomethacin , meloxicam, tenoxicam, valdecoxib or some metabolites of analgesic drugs formed by the activity of … gastrointestinal ulcers, hepatic failure, agranulocytosis, aplastic anemia, neutropenia, opiate-induced hyperalgesia and tolerance.”