Stability, cost factors in declotting substitute
Providers search for Urokinase replacement
Last month, Home Infusion Therapy Management looked at the use of Alteplase (t-PA) as a possible substitute for Urokinase, which is still unavailable due to the FDA’s stopping Abbot from shipping the product. In the last of a two-part series, the procedure for a second alternative — Streptokinase — is presented.
According to Nadine Nakazawa-Carpol, BS, RN, CRNI, PICC program coordinator and VAD committee chairwoman at the Stanford University (CA) Hospital, says Streptokinase was the right choice as a substitute for Urokinase.
"We knew that Streptokinase and t-PA were available, and from there we went strictly on cost and stability," she explains. "It appears that Streptokinase, once reconstituted, is stable for about 24 hours and is relatively cheap."
A 250,000-unit vial of Streptokinase runs about $83 for Stanford. At 10,000 units/3 mls, Streptokinase proves very affordable. Comparing this to t-PA, which is only available in 50 mg vials, cost became a major issue when stability was factored in.
"You only need 1 to 2 mg of t-PA, but it is only stable for about eight hours once it is reconstituted," explains Nakazawa-Carpol. "When we called Genentech [the manufacturer of t-PA] in January when we first wrote this Streptokinase/t-PA procedure, they would not guarantee t-PA’s potency if frozen. That is why we did not go with the freezing protocol. So unless a patient is allergic to Streptokinase, we do not use t-PA."
Avoiding reactions
Another main concern for many providers is the concern over allergic reactions to Streptokinase. At Stanford, the adverse reaction rate has been much lower than anticipated. In the literature consulted by Nakazawa-Carpol and her colleagues, the adverse reaction rate was listed at 10% (including anaphylactic reactions).
"Based on that preliminary information, we decided to premedicate everyone," she says. "The anaphylactic rate is now about .1%, which is not has high as we thought. It is mostly a pyrogenic reaction, so premedicating with Tylenol should prevent that."
The premed for all patients consists of hydrocortisone 50 mg IV, diphenhydramine 25 mg IV, and Tylenol 650 mg. But in addition to — and prior to — premedicating, the Stanford policy also requires an assessment be done at the outset to not only determine if the catheter is clotted catheter but also if the patient had a recent streptococcal infection or a recent Streptokinase infusion for any other reason. (See pp. 111-112 and above, for part of Stanford’s Streptokinase/t-PA procedure.)
The risk of an adverse reaction to Streptokinase increases with exposure to either the streptococcal bacterium or Streptokinase, or a history of multiple drug allergies. By following the precautionary procedure, Stanford appears to have addressed the issue.
"In those three situations, the nurse does a skin test and waits half an hour," says Nakazawa-Carpol. "If the skin test is negative, then they proceed with the premeds, then the Streptokinase attempt to declot. If the skin test is positive, then we recommend t-PA."
Another reason Nakazawa-Carpol surmises that the reaction rate is minimal is due to the amount being used to declot the catheters.
"You are using a small fraction compared to an infusion of Streptokinase for coronary thrombosis," she says, "so the exposure to Streptokinase is very, very small and may not manifest much of a reaction. But we are still preceding the infusion with heavy premeds."
She adds that she has used higher doses than listed on the policy with positive outcomes.
"We have infused 25,000 units/4 ml — a total of 100,000 units — over an hour by infusing it slowly," she says. "The patient was premedicated, there was no adverse reaction, and we had great blood return afterwards. Anecdotally, this was done with good effect."
Only time will tell
Although there are proponents of both t-PA and Streptokinase, Nakazawa-Carpol notes that it will take some time before anything concrete can be stated about the potential of either drug to declot catheters.
"We don’t have enough experience; it will probably take a year of patients being exposed to Streptokinase to see an actual rate of adverse reactions," she says. "[Urokinase being taken off the market] has forced us to look at other fibrynolitics that are out there. If Streptokinase turns out not to be as dangerous as we thought, it could prove to be a fraction of the cost of Urokinase. Or t-PA may be the answer, the problem is the 50 mg vial. I don’t think we have the answer yet."
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