This review provides an overview of the immunological effects of commonly used
analgesic opioid drugs, focusing mainly on two aspects: the mechanisms involved and the potential clinical relevance. The immunomodulatory effects of
morphine have been characterized in animal and human studies.
Morphine decreases the effectiveness of both natural and acquired immunity, interfering with intracellular pathways involved in immune regulation, both directly and indirectly via the activation of central receptors. The mechanisms and the targets at the basis of
opioid-induced
immunomodulation have started to be elucidated, demonstrating an interaction between
opioid receptors and several molecules involved in the complex and well orchestrated immune response, such as
transcription factors and receptors of both myeloid and lymphoid cells. Due to their widespread and expanding use, the immunological effects of
opioid are receiving considerable attention because of concerns that
opioid-induced changes in the immune system may affect the outcome of surgery or of variety of disease processes, including bacterial and
viral infections and
cancer. It is also emerging that not all
opioids induce the same immunosuppressive effects and evaluating each
opioid profile is important for appropriate
analgesic selection. The impact of the
opioid-mediated immune effects could be particularly dangerous in selective vulnerable populations, such as the elderly or immunocompromised patients. Indeed, it is evident that the possibility of reaching adequate and equivalent
pain control by choosing either immunosuppressive drugs or drugs without an effect on immune responses may be an important consideration in
opioid therapy.