PMX-53 is a potent and orally active CD88 (C5aR) antagonist (IC50: 20 nM) and inhibits C5a-induced neutrophil myeloperoxidase release and chemotaxis with IC50 values of 22 nM and 75 nM, respectively. PMX-53 is also an agonist of Mas-related gene 2 (MrgX2).

In HMC-1 cells, PMX-53 (10 nM) inhibits C5a-induced Ca2+ mobilization, but at higher concentrations( ≥30 nM) it causes degranulation in LAD2 mast cells, CD34+ cell-derived mast cells, and RBL-2H3 cells stably expressing MrgX2. Replacement of Trp with Ala and Arg with dArg eliminates the ability of PMX-53 to inhibit C5a-induced Ca2+ mobilization in HMC-1 cells and to cause degranulation in RBL-2H3 cells expressing MrgX2[1].

Local pretreatment of rats with PMX-53 (60-180?μg per paw) inhibits zymosan-, carrageenan-, lipopolysaccharide (LPS)- and antigen-induced hypernociception[2].
Pharmacokinetic analyses demonstrate that PMX-53 appears in the plasma within 5 min of oral administration (3 mg/kg) to rats, with peak blood levels of approximately 0.3 μM being reached within 20 min. The plasma elimination half-life was approximately 70 min in this case[3].