PENETRATION OF BRODIMOPRIM INTO HUMAN NEUTROPHILS AND INTRACELLULAR ACTIVITY

The entry of an antibiotic into phagocytes is a prerequisite for its i ntracellular bioactivity against susceptible facultative or obligatory intracellular microorganisms, Brodimoprim is a dimethoxybenzylpyrimid ine that has recently entered into clinical use, and its uptake into a nd elimination from human polymorphonuclear neutrophils (PMNs), togeth er with its effects on normal phagocytic and antimicrobial mechanisms, have been investigated, Brodimoprim uptake by PMNs was determined by a velocity-gradient centrifugation technique under various experimenta l conditions and was expressed as the ratio of the intracellular to th e extracellular drug concentration (CIE) in comparison with the CIE of trimethoprim, which was used as a control drug, After incubation with 7.5 mu g of brodimoprim per mi, PMNs accumulated brodimoprim (CIE, 74 .43 +/- 12.35 at 30 min) more avidly than trimethoprim (C/E, 20.97 +/- 6.61 at 30 min), The cellular uptake of brodimoprim was not affected by temperature, 2,4-dinitrophenol, or potassium fluoride and was incre ased with an increase in the pH of the medium, It was reduced in forma ldehyde-killed PMNs, The efflux of brodimoprim was very rapid (46% aft er 5 min), The liposolubility of brodimoprim was about three times tha t of trimethoprim, as was the uptake, Therefore, a possible passive tr ansmembrane diffusion mechanism might be proposed, Brodimoprim did not decrease either phagocytosis or phagocyte-mediated bactericidal activ ity, nor did it affect oxidative burst activity, as investigated by lu minol-amplified chemiluminescence. On the basis of the pharmacokinetic data for brodimoprim, the concentration of 7.5 mu g/ml was chosen as the highest concentration attainable in serum by oral therapy, and at this concentration of brodimoprim, the amount of drug that penetrated into PMNs was able to maintain its antimicrobial activity without inte rfering with the functions of the PMNs.