Landmark midline
catheters (Menlo Care, Inc., Palo Alto, CA) provide peripheral venous access for the infusion of medications or fluids. They are constructed of an inner layer of
polyurethane and an outer layer of the
biomaterial Aquavene, a blend of
polyurethane and
polyethylene oxide to which butylated hyroxyanisole (
BHA),
butylated hydroxytoluene (
BHT), and triallyl-s-
triazine trione (TTT) are added. Once inside the vein, the
Aquavene material becomes hydrated and the
catheter swells resulting in minimal
trauma to the vein. It is well recognized that some patients experience reactions to catheterization. Recent reports of
hypersensitivity-like reactions in some patients catheterized with Landmark
catheters have prompted the manufacturer to reexamine biocompatibility data and clinical data to assess whether
Aquavene was the source of the patient responses. None of the biocompatibility studies provided by Menlo Care in support of U.S. registration and marketing of
Aquavene-based
catheters demonstrated any tendency for
Aquavene or material extracted from
Aquavene to invoke an immunological or toxicological response. Examination of potential
catheter residuals revealed that significant amounts of
BHA and
BHT were unlikely to be released from the
catheters during expected use. The amounts of
polyethylene oxide and TTT expected to be released during the first few minutes after
catheter insertion (when most of the patient reactions were reported) are almost 92,500 and 270,000 times lower, respectively, than nontoxic animal exposures. These analyses do not support chemically mediated toxicity as an explanation for the adverse events experienced by some patients. A review of the postmarket surveillance data on
Aquavene-based
catheters revealed that the reported events were not consistent with a
hypersensitivity (immunogenic) response to the
biomaterial. The rare reported adverse events tend to occur quickly, most often after
flushing of the
catheter, and resolve quickly, even when the
catheter remains in place. Determining the frequency and severity of adverse events reported in association with the use of Landmark
catheters will ultimately require a controlled prospective study, preferably one with a concurrent control group using alternative products.