The cellular basis for opioid-induced immunosuppression

An update on the role of opioids in the management of chronic pain of nonmalignant origin

PURPOSE OF REVIEW

To summarize and reflect over primarily recent epidemiological and randomized controlled trials in opioid-treated chronic nonmalignant pain patients, focusing on effects, side effects, risks and long-term consequences of the treatment.

RECENT FINDINGS

In the western world opioids are increasingly being used for long-term treatment of chronic nonmalignant pain. While the long-term benefits of opioids regarding pain relief, functional capacity and health-related quality of life still remain to be proven, studies are emerging that describe serious long-term consequences such as addiction, opioid-induced hyperalgesia, cognitive disorders, and suppression of the immune and reproductive systems.

SUMMARY

Much more research is needed concerning long-time effects and consequences of opioid therapy in chronic nonmalignant pain patients; however, some clear warning signals have been sent out within recent years.

The contribution of opiate analgesics to the development of infectious complications in burn patients

BACKGROUND

Immune and infectious complications are associated with burn injury. Opiate analgesics also can induce similar complications, however, their impact on postburn infectious complications is unknown.

METHODS

A retrospective survey of records from 1997 to 2002 from an academic burn center was conducted. Information on all opiate analgesic use was obtained and expressed as opiate equivalents (OEs). Total OEs were summed for each patient and then compared between cases and controls.

RESULTS

Patients who developed infections were more likely to be in the high OE group. This association was modified by burn severity. Patients with small burns and infection were more likely to be in the high OE group, whereas patients with moderate to large burns and infections were not associated significantly with opiate use.

CONCLUSIONS

The results of this preliminary study suggest that opiate analgesics can contribute to the development of postburn infectious complications when the burn injury is of a less severe nature.

Opiate Analgesics Contribute to the Development of Post-Injury Immunosuppression1

BACKGROUND

Immune dysfunction and post-injury infections are complications associated with thermal injury. Opiates, the analgesic of choice for the treatment of post-burn pain, can also induce similar immune complications. However, the impact of therapeutic opiates on post-burn immune dysfunction is unknown.

MATERIALS AND METHODS

C57BL/6 mice were subjected to a small 6.25% total body surface area (TBSA) burn or sham procedure. The mice were left untreated or treated with morphine sulfate by subcutaneous implantation of an Alzet pump that administered morphine sulfate at a rate of 2 mg/kg body weight/day. Plasma, splenocytes and splenic macrophages were isolated for in vitro analysis 1, 4, or 7 days later.

RESULTS

Neither burn injury nor morphine treatment alone significantly altered splenic T-cell proliferation at 1, 4, or 7 days post-injury/treatment. In contrast, morphine treatment of injured mice suppressed splenic T-cell proliferation at 4 and 7 days post-injury/treatment. The suppressed proliferation of T-cells correlated with increased levels of the nitric oxide and an immunosuppressive Th-2 type phenotype. In contrast morphine treatment did not accentuate the suppressed T-cell proliferative responses associated with larger injuries covering 12.5% and 25% TBSA. Splenic macrophage function was unaffected with the exception that LPS-induced nitric oxide production was elevated in the injured mice treated with morphine.

CONCLUSIONS

These findings demonstrate that those mice treated with a clinically relevant dose of morphine sulfate after an "immunologically insignificant" burn displayed immunosuppression and a Th-2 cytokine profile. Thus, the therapeutic administration of exogenous opiates appears to contribute to the development of post-burn immune dysfunction.