Although tetracycline (TCN) pleurodesis may be effective in up to 90 percent of patients with recurrent malignant pleural effusions, results as poor as 50 percent have also been reported. Animal studies indicate that commonly prescribed TCN concentrations of 15 mg/kg or less may be ineffective. Complete drainage of the pleural space before and after pleurodesis is also recommended although to our knowledge, no published studies have examined the validity of this statement. In addition, variability in published results may be partially explained by differences in defining and documenting end points of success or failure Reading here.
Tetracycline is probably not the most potent chemical sclerosing agent but it is inexpensive and well tolerated. The withdrawal of injectable TCN from the commercial market has prompted trials with other chemical agents. Insufflation of talc during thoracoscopy has yielded excellent results though the expense and risks are substantial. Bleomycin pleurodesis is also effective though the efficacy is similar to that with TCNs and the expense is substantially higher. Minocycline or doxycycline (DOXY) have benefits and risks similar to those found with TCN.
Several investigators have explored the mechanism of TCN pleurodesis. Initially, the acidity of TCN was believed to be essential, though this hypothesis has been refuted. The role of pleural fluid clotting and fibrinolytic factors in TCN pleurodesis and other clinical instances of pleural injury has been extensively documented; in support of this hypothesis, TCN pleurodesis is inhibited in animal by both heparin and by urokinase. Recently, the capacity of TCNs to inhibit cell and enzyme functions through chelation of divalent cations such as zinc or calcium has been reported. This chelating property of TCNs permits the inhibition of metalloproteinase activity in pleural fluid and may facilitate pleural symphysis.