Phenoxybenzamine treatment can lead to loss of endothelial cell viability

Phenoxybenzamine, an irreversible alpha-adrenoceptor antagonist, is used as a topical treatment against catecholamine-induced contraction in radial artery bypass grafts. Published data suggest that a wide range of phenoxybenzamine doses may be equally effective. This study aimed to investigate whether lower doses of phenoxybenzamine would benefit grafts by better preserving endothelium. To this end human vascular endothelial cells were isolated from sections of radial artery or saphenous vein, and treated with phenoxybenzamine for 30 min. Cells were then washed free of drug and viability assayed using a resazurin-based toxicology assay or returned to culture for assay at 24 h. Phenoxybenzamine treatment showed a dose-dependent effect on cell viability over several clinically employed concentrations. Concentrations above 0.1 mM led to a loss of viability, which became more pronounced with time. The loss of viability was shown to be independent of the carrier used, as results were identical when phenoxybenzamine was dissolved in dimethylsulphoxide, which alone did not affect viability. Changes in pH alone were also not sufficient to affect viability. In conclusion, phenoxybenzamine treatment is likely to cause damage to graft endothelium if employed at concentrations above 0.1 mM (0.03 mg/ml). Phenoxybenzamine may be safely used at lower doses with no potential loss of endothelial cell viability.