CLINICAL PHARMACOLOGY
Endogenous lung surfactant is essential for effective
ventilation because it modifies alveolar surface tension thereby stabilizing
thealveoli. Lung surfactant deficiency is the cause of Respiratory Distress
Syndrome (RDS) in premature infants. Infasurf restores surfaceactivity to the
lungs of these infants.
Activity
Infasurf adsorbs rapidly to the surface of the air:liquid
interface and modifies surface tension similarly to natural lung surfactant. A
minimum surface tension of ≤3 mN/m is produced in vitro by Infasurf as
measured on a pulsating bubble surfactometer. Ex vivo, Infasurf restores the
pressure volume mechanics and compliance of surfactant-deficient rat lungs. In
vivo, Infasurf improves lung compliance, respiratory gas exchange, and survival
in preterm lambs with profound surfactant deficiency.
Animal Metabolism
Infasurf is administered directly to the lung lumen
surface, its site of action. No human studies of absorption, biotransformation,
or excretion of Infasurf have been performed. The administration of Infasurf
with radiolabeled phospholipids into the lungs of adult rabbits results in the
persistence of 50% of radioactivity in the lung alveolar lining and 25% of
radioactivity in the lung tissue 24 hours later. Less than 5% of the
radioactivity is found in other organs. In premature lambs with lethal
surfactant deficiency, less than 30% of instilled Infasurf is present in the
lung lining after 24 hours.
Clinical Studies
The efficacy of Infasurf was demonstrated in two
multiple-dose controlled clinical trials involving approximately 2,000 infants
treated with Infasurf (approximately 100 mg phospholipid/kg) or Exosurf
Neonatal®. In addition, two controlled trials of Infasurf versus Survanta®, and
four uncontrolled trials were conducted that involved approximately 15,500
patients treated with Infasurf.
Infasurf versus Exosurf Neonatal®
Treatment Trial
A total of 1,126 infants ≤72 hours of age with RDS
who required endotracheal intubation and had an a/A PO2 <0.22 were enrolled
into a multiple-dose, randomized, double-blind treatment trial comparing
Infasurf (3 mL/kg) and Exosurf Neonatal® (5 mL/kg). Patients were given an
initial dose and one repeat dose 12 hours later if intubation was still
required. The dose was instilled in two aliquots through a side port adapter
into the proximal end of the endotracheal tube. Each aliquot was given in small
bursts over 20-30 inspiratory cycles. After each aliquot was instilled, the
infant was positioned with either the right or the left side dependent. Results
for efficacy parameters evaluated at 28 days or to discharge for all treated
patients from this treatment trial are shown in Table 1.
Table 1: Infasurf vs Exosurf Neonatal® Treatment
Trial
Efficacy Parameter |
Infasurf
(N=570)% |
Exosurf Neonatal®
(N=556)% |
p-Value |
Incidence of air leaks a |
11 |
22 |
<0.001 |
Death due to RDS |
4 |
4 |
0.95 |
Any death to 28 days |
8 |
10 |
0.21 |
Any death before discharge |
9 |
12 |
0.07 |
BPD b |
5 |
6 |
0.41 |
Crossover to other surfactant c |
4 |
4 |
1 |
a Pneumothorax and/or pulmonary interstitial
emphysema.
b BPD is bronchopulmonary dysplasia, diagnosed by positive X-ray and
oxygen dependence at 28 days.
c Protocol permitted use of comparator surfactant in patients who
failed to respond to therapy with the initial randomized surfactant if the
infant was < 96 hours of age, had received a full course of the randomized surfactant,
and had an a/A PO2 ratio < 0.10 |
Prophylaxis Trial
A total of 853 infants <29 weeks gestation were
enrolled into a multiple-dose, randomized, double-blind prophylaxis trial
comparing Infasurf (3 mL/kg) and Exosurf Neonatal® (5 mL/kg). The initial dose
was administered within 30 minutes of birth. Repeat doses were administered at
12 and 24 hours if the patient remained intubated. Each dose was administered
divided in 2 equal aliquots, and giventhrough a side port adapter into the
proximal end of the endotracheal tube. Each aliquot was given in small bursts
over 20-30 inspiratory cycles. After each aliquot was instilled, the infant was
positioned with either the right or the left side dependent. Results for efficacy
parameters evaluated to day 28 or to discharge for all treated patients from
this prophylaxis trial are shown in Table 2.
Table 2: Infasurf vs Exosurf Neonatal® Prophylaxis
Trial
Efficacy Parameter |
Infasurf
(N=431)% |
Exosurf Neonatal®
(N=422)% |
p-Value |
Incidence of RDS |
15 |
47 |
<0.001 |
Incidence of air leaks a |
10 |
15 |
0.01 |
Death due to RDS |
2 |
5 |
<0.01 |
Any death to 28 days |
12 |
16 |
0.10 |
Any death before discharge |
18 |
19 |
0.56 |
BPD b |
16 |
17 |
0.60 |
Crossover to other surfactant c |
0.2 |
3 |
<0.001 |
a Pneumothorax and/or pulmonary interstitial
emphysema.
b BPD is bronchopulmonary dysplasia, diagnosed by positive X-ray and
oxygen dependence at 28 days.
c Protocol permitted use of comparator surfactant in patients who
failed to respond to therapy with the initial randomized surfactant if the
infant was < 72 hours of age, had received a full course of the randomized surfactant,
and had an a/A PO2 ratio < 0.10 |
Infasurf versus Survanta®
Treatment Trial
A total of 662 infants with RDS who required endotracheal
intubation and had an a/A PO2 <0.22 were enrolled into a multiple-dose, randomized,
double-blind treatment trial comparing Infasurf (4 mL/kg of a formulation that
contained 25 mg of phospholipids/mL rather than the 35 mg/mL in the marketed
formulation) and Survanta® (4 mL/kg). Repeat doses were allowed ≥6 hours
following the previous treatment (for up to three doses before 96 hours of age)
if the patient required ≥30% oxygen. The surfactant was given through a 5
French feeding catheter inserted into the endotracheal tube. The total dose was
instilled in four equal aliquots with the catheter removed between each of the
instillations and mechanical ventilation resumed for 0.5 to 2 minutes. Each of
the aliquots was administered with the patient in one of four different
positions (prone, supine, right, and left lateral) to facilitate even
distribution of the surfactant. Results for the major efficacy parameters
evaluated at 28 days or to discharge (incidence of air leaks, death due to respiratory
causes or to any cause, BPD, or treatment failure) for all treated patients
from this treatment trial were not significantly different between Infasurf and
Survanta®.
Prophylaxis Trial
A total of 457 infants ≤30 weeks gestation and
<1251 grams birth weight were enrolled into a multiple-dose, randomized,
double-blind trial comparing Infasurf (4 mL/kg of a formulation that contained
25 mg of phospholipids/mL rather than the 35 mg/mL in the marketed formulation)
and Survanta® (4 mL/kg). The initial dose was administered within15 minutes of
birth and repeat doses were allowed ≥6 hours following the previous
treatment (for up to three doses before 96 hours of age) if the patient
required ≥30% oxygen. The surfactant was given through a 5 French feeding
catheter inserted into the endotracheal tube. The total dose was instilled in
four equal aliquots with the catheter removed between each of the instillations
and mechanical ventilation resumed for 0.5 to 2 minutes. Each of the aliquots
was administered with the patient in one of four different positions (prone,
supine, right, and left lateral). Results for efficacy endpoints evaluated at
28 days or to discharge for all treated patients from this prophylaxis trial
showed an increase in mortality from any cause at 28 days (p=0.03) and in death
due to respiratory causes (p=0.005) in Infasurf-treated infants. For evaluable
patients (patients who met the protocol-defined entry criteria), mortality from
any cause and mortality due to respiratory causes were also higher in the
Infasurf group (p = 0.07 and 0.03, respectively). However, these observations
have not been replicated in other adequate and well-controlled trials and their
relevance to the intended population is unknown. All other efficacy outcomes
(incidence of RDS, air leaks, BPD, and treatment failure) were not
significantly different between Infasurf and Survanta® when analyzed for all
treated patients and for evaluable patients.
Acute Clinical Effects
As with other surfactants, marked improvements in
oxygenation and lung compliance may occur shortly after the administration of
Infasurf. All controlled clinical trials with Infasurf demonstrated significant
improvements in fraction of inspired oxygen (FiO2) and mean airway pressure
(MAP) during the first 24 to 48 hours following initiation of Infasurf therapy.