title: In vitro demonstration of transport and delivery of antibiotics by polymorphonuclear leukocytes.
abstract: Several antibiotics are concentrated inside polymorphonuclear leukocytes (PMN). To investigate whether PMN could act as vehicles for delivery of antibiotics, we combined an assay measuring PMN chemotaxis under agarose with a bioassay measuring levels of antibiotic in agar. Double-layer plates were made by pouring a layer of chemotaxis agarose into tissue culture plates and then adding a thin layer of Trypticase soy agar. Neutrophils were incubated with antibiotic for 1 h and then were washed and placed in wells made in the plates. After allowing PMN to migrate under the agar toward a chemoattractant well containing formyl-methionine-leucine-phenylalanine for 3 h, Streptococcus pyogenes was streaked on top of the agar and grown overnight. PMN migration and zones of inhibition of bacterial growth were measured. Neutrophils migrated 2.51 +/- 0.16 mm toward the chemoattractant well and 1.48 +/- 0.12 mm toward the medium well; migration was not significantly affected by any of the antibiotics used. Plates with PMN incubated without antibiotic showed insignificant inhibition of bacterial growth toward chemoattractant and medium wells (0.38 +/- 0.18 and 0.14 +/- 0.12 mm, respectively; for both, P > 0.05 for difference from 0). PMN incubated with oxacillin (3 micrograms/ml), a drug not concentrated in PMN, caused a similar lack of inhibition (0.28 +/- 0.09 mm toward chemoattractant; 0.14 +/- 0.03 mm toward medium). Incubation with 30 microns of ciprofloxacin per ml resulted in inhibition that was similar in both directions (1.40 +/- 0.16 versus 1.18 +/- 0.13 mm). However, for PMN incubated with azithromycin (3 micrograms/ml), an agent highly concentrated inside phagocytes, there was a large degree of inhibition which was significantly greater in the direction of chemoattractant than in the direction of medium (3.47 +/- 0.30 versus 1.89 +/- 0.25 mm; P < 0.001), indicating that release of bioactive azithromycin by neutrophils occurred after migration. Likewise, after incubation with rifampin (10 micrograms/ml), which is also concentrated by PMN, inhibition was significantly greater in the direction of chemoattractant than in the direction of medium (1.54 +/- 0.24 versus 0.81 +/- 0.28 mm; P = 0.001). We conclude that for certain antibiotics, PMN may act as vehicles for transport and delivery of active drug to sites of infection.
authors.affiliation: Division of Infectious Disease, University of Virginia School of Medicine, Charlottesville 22908.
authors.forename: M O
authors.initials: MO
authors.lastname: Frank
authors.forename: G W
authors.initials: GW
authors.lastname: Sullivan
authors.forename: H T
authors.initials: HT
authors.lastname: Carper
authors.forename: G L
authors.initials: GL
authors.lastname: Mandell
mesh_terms: D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics* / Q000494:pharmacology; D017963:Azithromycin; D002634:Chemotaxis, Leukocyte / Q000187:drug effects*; D002939:Ciprofloxacin / Q000493:pharmacokinetics; D016503:Drug Delivery Systems / Q000379:methods; D004917:Erythromycin / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D008826:Microbial Sensitivity Tests; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism*; D012293:Rifampin / Q000493:pharmacokinetics; D013297:Streptococcus pyogenes / Q000187:drug effects / Q000254:growth & development
chemical_list: D000900:Anti-Bacterial Agents; D006131:Growth Inhibitors; D002939:Ciprofloxacin; D004917:Erythromycin; D017963:Azithromycin; D012293:Rifampin