Analysis of responses to vancomycin in carotid blood flow in the male rat.

Vancomycin is known to cause vasodilation, and hypotension secondary to histamine release. We studied the actions of two forms of vancomycin, a clinically available preparation, clinical vancomycin, and a research grade preparation, laboratory vancomycin, in the presence of an H1 receptor blockade and during H2 receptor blockade with Doppler flow probe analysis of carotid artery flow rate. Clinical vancomycin, laboratory vancomycin, and histamine, increased the mean carotid artery blood flow from baseline in a dose-dependent manner. Diphenhydramine, H1 receptor antagonist, attenuated the increase in mean carotid artery blood flow for the highest dose of clinical vancomycin and for each dose of histamine. Famotidine, H2 receptor antagonist, significantly attenuated the increase in mean carotid artery blood flow for the highest dose of clinical vancomycin, the two higher doses of laboratory vancomycin, and with each dose of histamine. Both diphenhydramine and famotidine attenuated the increase of mean carotid artery blood flow with clinical vancomycin, laboratory vancomycin, and histamine. These data suggest that the change in carotid flow produced by vancomycin, is dependent, in part, on either H1 or H2 receptor activation.