Tramadol does not impair the phagocytic capacity of human peripheral blood cells

The inhibitory effect of opioids on phagocytic cell capacity is well established. However, the effect of synthetic analgesics on this aspect of cell function is controversial. It was the aim of the study to compare the in vitro effect of tramadol with that of morphine on the engulfing ability of peripheral blood phagocytic cells from healthy volunteers.

Peripheral blood polymorphonuclear cells and monocytes from healthy volunteers were incubated with 5, 10 and 20 microg.mL(-1) tramadol, or with 20, 40 and 80 etag.mL(-1) morphine. To each tube, 0.05 mL of 5% suspension of latex beads 0.8 microm in diameter was added. After incubation for 60 min the percentage of cells engulfing latex particles and the phagocytic index (number of particles phagocytized by each individual cell) were detected.

Tramadol affected neither the percentage of cells phagocyting latex particles, nor the phagocytic index of both polymorphonuclear cells and monocytes. On the other hand, incubation with 20, 40 and 80 etag.mL(-1) morphine caused 11%, 14% and 24% decrease in phagocytosis (P < 0.01 - P < 0.001). The percentage of monocytes phagocyting latex particles was lower by 16%, 19% and 12% at the three doses tested (P < 0.01 - P < 0.001). The three doses of morphine caused a dose dependent decrease in the monocyte phagocyting index by 20%, 29% and 35.5% respectively (P < 0.05). The polymorphonuclear phagocyting index was not significantly lower following incubation with the drug (P = 0.053).

The lack of noxious effect of tramadol on the engulfing capacity of phagocytic cells suggests additional benefit to the relatively safe profile of the drug.