But sometimes physicians can't find suitable vessels, and transplants from tissue donors or even from animals have not proven safe or effective.
The distributors say the vapor contains virtually none of the cancer-causing chemicals of traditional cigarettes, but the F.D.A. says it has not been proved safe.
Mr. Blumenthal said he would use evidence supplied by two former Connecticut Air National Guard pilots suggesting that the vaccine has not been proved safe or effective.
Any woman who became pregnant was removed from the study, because Truvada has not been proved safe for pregnant women; for unknown reasons, more women taking the medication became pregnant, which may also have skewed the early results.
The hurry-up mechanism allows approval of a drug that has not yet been proved safe and effective in thorough clinical trials but has shown promise that it might benefit patients with life-threatening diseases.
They want them to be considered dietary supplements, which do not need the F.D.A.'s premarket approval and are not required to be proved safe or effective.
But the bonds had not proved as safe as advertised.
Unlike drugs, supplements do not have to be proved safe and effective before they are marketed, and no outside agency even checks to make sure that the products actually contain the ingredients on the label.
"Avastin is not manufactured or approved and to date has not been proven safe for use in the eye," a spokesman for the company said Tuesday.
