HISTOLOGIC-CHANGES OF DOXYCYCLINE PLEURODESIS IN RABBITS - EFFECT OF CONCENTRATION AND PH

The effects of doxycycline hyclate (DOXY) pleurodesis were compared wi th those of tetracycline hydrochloride (TCN) in 25 healthy New Zealand White rabbits. One group of rabbits received TCN (pH 2.0) in the left pleural space at a concentration of 35 mg/kg in 3.0 ml of saline solu tion. Four other groups of rabbits received DOXY in two concentrations (35 mg/kg or 10 mg/kg) and at two pHs (an acid of 2.0 and a NaOH neut ralized pH of 7.6). No attempt was made to drain the pleural space aft er pleurodesis. At autopsy 2 weeks later, bloody fluid filled the pleu ral cavity and extensive intrapleural adhesions compressed the underly ing lung. Microscopically, fibrin and collagen were diffusely deposite d in the pleural connective tissue and in the intrapleural adhesions. The visceral pleural thickness increased from its normal value of 0.01 mm to values of 0.5 to 0.9 mm in the TCN and DOXY groups. Fibroblasts were the predominant inflammatory cell in the pleural connective tiss ue with few neutrophils or lymphocytes. No significant differences of histologic characteristics were observed between the TCN and DOXY grou ps. Alterations in pH or concentration in the DOXY groups produced sim ilar changes in the gross and microscopic appearance of the pleural sp ace. We conclude that DOXY is as effective as TCN in producing chemica l pleurodesis. Doxycycline concentrations of 10 mg/kg were sufficient to substantially sclerose the pleural space in these healthy rabbits. Doxycycline pleurodesis was effective at neutral pH suggesting a mecha nism of action independent of acid injury to the mesothelium.