CLINICAL PHARMACOLOGY
Alteplase is an enzyme (serine protease) that has the
property of fibrin-enhanced conversion of plasminogen to plasmin. It produces
limited conversion of plasminogen in the absence of fibrin. Alteplase binds to
fibrin in a thrombus and converts the entrapped plasminogen to plasmin, thereby
initiating local fibrinolysis1.
In patients with acute myocardial infarction administered
100 mg of Activase as an accelerated intravenous infusion over 90 minutes,
plasma clearance occurred with an initial halflife
of less than 5 minutes and a terminal halflife
of 72 minutes. Clearance is mediated primarily by the liver2.
When Cathflo Activase is administered for restoration of
function to central venous access devices according to the instructions in
DOSAGE AND ADMINISTRATION, circulating plasma levels of Alteplase are not expected
to reach pharmacologic concentrations. If a 2 mg dose of Alteplase were administered
by bolus injection directly into the systemic circulation (rather than
instilled into the catheter), the concentration of circulating Alteplase would
be expected to return to endogenous circulating levels of 5–10 ng/mL within 30
minutes1.
Clinical Studies
Three clinical studies were performed in patients with
improperly functioning central venous access devices (CVADs).
A placebocontrolled,
doubleblind,
randomized trial (Trial 1) and a larger openlabel
trial (Trial 2) investigated the use of Alteplase in predominately adult
patients who had an indwelling CVAD for administration of chemotherapy, total
parenteral nutrition, or longterm
administration of antibiotics or other medications. Both studies enrolled
patients whose catheters were not functioning (defined as the inability to
withdraw at least 3 mL of blood from the device) but had the ability to instill
the necessary volume of study drug. Patients with hemodialysis catheters or a
known mechanical occlusion were excluded from both studies. Also excluded were
patients considered at high risk for bleeding or embolization (see PRECAUTIONS,
Bleeding), as well as patients who were younger than 2 years old or
weighed less than 10 kg. Restoration of function was assessed by successful
withdrawal of 3 mL of blood and infusion of 5 mL of saline through the
catheter.
Trial 1 tested the efficacy of a 2 mg/2 mL Alteplase dose
in restoring function to occluded catheters in 150 patients with catheter
occlusion up to 24 hours in duration. Patients were randomized to receive either
Alteplase or placebo instilled into the lumen of the catheter, and catheter
function was assessed at 120 minutes. Restoration of function was assessed by
successful withdrawal of 3 mL of blood and infusion of 5 mL of saline through
the catheter. All patients whose catheters did not meet these criteria were
then administered Alteplase, until function was restored or each patient had
received up to two active doses. After the initial dose of study agent, 51
(67%) of 76 patients randomized to Alteplase and 12 (16%) of 74 patients
randomized to placebo had catheter function restored. This resulted in a treatmentassociated difference
of 51% (95% CI is 37% to 64%). A total of 112 (88%) of 127 Alteplasetreated patients had
restored function after up to two doses.
Trial 2 was an openlabel,
single arm trial in 995 patients with catheter dysfunction and included
patients with occlusions present for any duration. Patients were treated with
Alteplase with up to two doses of 2 mg/2 mL (less for children who weighed less
than 30 kg, see DOSAGE AND ADMINISTRATION) instilled into the lumen of
the catheter. Assessment for restoration of function was made at 30 minutes after
each instillation. If function was not restored, catheter function was reassessed at 120
minutes. Thirty minutes after instillation of the first dose, 516 (52%) of 995
patients had restored catheter function. One hundred twenty minutes after the
instillation of the first dose, 747 (75%) of 995 patients had restored catheter
function. If function was not restored after the first dose, a second dose was administered.
Two hundred nine patients received a second dose. Thirty minutes after
instillation of the second dose, 70 (33%) of 209 patients had restored catheter
function. One hundred twenty minutes after the instillation of the second dose,
97 (46%) of 209 patients had restored catheter function. A total of 844 (85%)
of 995 patients had function restored after up to 2 doses.
Across Trials 1 and 2, 796 (68%) of 1043 patients with
occlusions present for less than 14 days had restored function after one dose,
and 902 (88%) had function restored after up to two doses. Of 53 patients with occlusions
present for longer than 14 days, 30 (57%) patients had function restored after
a single dose, and a total of 38 patients (72%) had restored function after up
to two doses.
Three hundred forty-six patients who had successful
treatment outcome were evaluated at 30 days after treatment. The incidence of
recurrent catheter dysfunction within this period was 26%.
Trial 3 was an openlabel,
singlearm trial
in 310 patients between the ages of 2 weeks and 17 years. All patients had
catheter dysfunction defined as the inability to withdraw blood (at least 3 mL
for patients ≥ 10 kg or at least 1 mL for patients < 10 kg). Catheter
dysfunction could be present for any duration. The indwelling CVADs (single-,
double-, and triplelumen,
and implanted ports) were used for administration of chemotherapy, blood
products or fluid replacement, total parenteral nutrition, antibiotics, or
other medications. Patients with hemodialysis catheters or known mechanical
occlusions were excluded from the study, as were patients considered at high
risk for bleeding or embolization. Patients were treated with up to two doses
of Cathflo Activase instilled into the catheter lumen. For patients weighing
≥ 30 kg, the dose was 2 mg in 2 mL. For patients weighing < 30 kg, the
dose was 110% of the estimated internal lumen volume, not to exceed 2 mg in 2
mL. Restoration of function was assessed at 30 and 120 minutes (if required)
after administration of each dose. Restoration of function was defined as the
ability to withdraw fluid (3 mL in patients ≥ 10 kg; 1 mL in patients
< 10 kg) and infuse saline (5 mL in patients ≥ 10 kg; 3 mL in patients
< 10 kg).
The overall rate of catheter function restoration of 83%
(257 of 310) was similar to that observed in Trial 2, as were the rates of function
restoration at the intermediate assessments.
The three trials had similar rates of catheter function
restoration among the catheter types studied (single-, double-, and triplelumen, and implanted
ports). No gender differences were observed in the rate of catheter function
restoration. Results were similar across all age subgroups.
REFERENCES
1. Collen D, Lijnen HR. Fibrinolysis and the control of
hemostasis. In: Stamatoyannopoulos G, Nienhui AW, Majerus PW, Varmus H,
editors. The molecular basis of blood diseases, 2nd edition. Philadelphia:
Saunders, 1994:662–88.
2. Tanswell P, Tebbe U, Neuhaus K-L, Glasle-Schwarz L,
Wojick J, Seifried E. Pharmacokinetics and fibrin specificity of alteplase
during accelerated infusions in acute myocardial infarction. J Am Coll Cardiol
1992;19:1071–5.