Early inflammatory response of minocycline and tetracycline on the rabbit pleura.

The histopathologic findings were compared from 20 mg/kg intrapleural tetracycline hydrochloride (TCN) and three doses of intrapleural minocycline hydrochloride (5, 10, and 20 mg/kg) (MCN) in New Zealand white rabbits. Both TCN and MCN produced an early neutrophilic predominant pleural effusion that became mononuclear over 48 h. There was no difference in pleural fluid accumulation, number of adhesions, or histologically measured visceral and parietal pleural thickness between TCN and MCN (all p = ns). The TCN, 20 mg/kg, produced more visceral pleural plaque than MCN, 5 mg/kg (p < 0.05). Increasing MCN doses resulted in greater pleural fluid neutrophil accumulation. With higher dose MCN, greater mesothelial cell desquamation and fibroblast proliferation was evident compared to the 5 mg/kg dose. The MCN and TCN produce similar histopathologic condition in the rabbit pleura which suggests that MCN should cause a similar clinical response in humans.