Pharmacology: The metabolism of aminolevulinic acid (ALA) is the first
step in the biochemical pathway resulting in heme synthesis. Aminolevulinic
acid is not a photosensitizer, but rather a metabolic precursor of protoporphyrin
IX (PpIX), which is a photosensitizer. The synthesis of ALA is normally tightly
controlled by feedback inhibition of the enzyme, ALA synthetase, presumably
by intracellular heme levels. ALA, when provided to the cell, bypasses this
control point and results in the accumulation of PpIX, which is converted into
heme by ferrochelatase through the addition of iron to the PpIX nucleus.
According to the presumed mechanism of action, photosensitization following
application of LEVULAN KERASTICK Topical Solution occurs through the metabolic
conversion of ALA to PpIX, which accumulates in the skin to which LEVULAN Topical
Solution has been applied. When exposed to light of appropriate wavelength and
energy, the accumulated PpIX produces a photodynamic reaction, a cytotoxic process
dependent upon the simultaneous presence of light and oxygen. The absorption
of light results in an excited state of the porphyrin molecule, and subsequent
spin transfer from PpIX to molecular oxygen generates singlet oxygen, which
can further react to form superoxide and hydroxyl radicals. Photosensitization
of actinic (solar) keratosis lesions using the LEVULAN KERASTICK for Topical
Solution, plus illumination with the BLU-U® Blue Light Photodynamic Therapy
Illuminator (BLU-U), is the basis for LEVULAN photodynamic therapy (PDT).
Pharmacokinetics: In a human pharmacokinetic study (N=6) using a 128
mg dose of sterile intravenous ALA HCl and oral ALA HCl (equivalent to 100 mg
ALA) in which plasma ALA and PpIX were measured, the mean half-life of ALA was
0.70 ± 0.18 h after the oral dose and 0.83 ± 0.05 h after the
intravenous dose. The oral bioavailability of ALA was 50-60% with a mean Cmax
of 4.65 ± 0.94 μg/mL. PpIX concentrations were low and were detectable
only in 42% of the plasma samples. PpIX concentrations in plasma were quite
low relative to ALA plasma concentrations, and were below the level of detection
(10 ng/mL) after 10 to 12 hours.
ALA does not exhibit fluorescence, while PpIX has ahigh fluorescence yield.
Time-dependent changes in surface fluorescence have been used to determine
PpIX accumulation and clearance in actinic keratosis lesions and perilesional
skin after application of LEVULAN KERASTICK Topical Solution in 12 patients.
Peak fluorescence intensity was reached in 11 ± 1 h in actinic keratoses
and 12 ± 1 h in perilesional skin. The mean clearance half-life of fluorescence
for lesions was 30 ± 10 h and 28 ± 6 h for perilesional skin.
The fluorescence in perilesional skin was similar to that in actinic keratoses.
Therefore, LEVULAN KERASTICK Topical Solution should only be applied to the
affected skin.
Clinical Studies: LEVULAN KERASTICK for Topical Solution, 20%, plus
blue light at 6-10.9 J/cm², has been used to treat actinic keratoses in
232 patients in six clinical trials. Phase 3 studies were two, identically designed,
multicenter, two-arm studies using LEVULAN KERASTICK for Topical Solution applicators
plus illumination from the BLU-U for 1000 seconds (16 min 40 sec) for a nominal
exposure of 10 J/cm². Patients were excluded from these studies who had
a history of cutaneous photosensitization, porphyria, hypersensitivity to porphyrins,
photodermatosis, or inherited or acquired coagulation defects. A minimum of
4 and a maximum of 15 clinically typical, discrete, (Grade 1 or 2, see table
2 for definition), target actinic keratosis lesions were identified. Target
lesions on the face or on the scalp, but not in both locations in the same patient,
received treatment. The patients were randomized to receive treatment either
with the LEVULAN KERASTICK Topical Solution plus BLU-U or vehicle plus BLU-U.
Patients were randomized at a 3 to 1 LEVULAN to vehicle ratio. A total of 243
patients were enrolled in two Phase 3 studies (ALA-018, ALA-019). Lesions were
designated as cleared (complete response) if the lesion had completely cleared
and adherent scaling plaques of actinic keratoses were no longer evident on
the surface of the treated skin when palpated. The percentage of patients in
whom 75% or more of treated lesions were cleared, and the percentage of patients
in whom 100% of treated lesions were cleared (Complete Responders), for each
study at 8 weeks after treatment are shown in Table 1.
TABLE 1 - Patient Responses at Week 8
| |
ALA-018 |
ALA-019 |
| LEVULAN |
Vehicle |
LEVULAN |
Vehicle |
| Patients with >75% of AK Lesions Cleared |
| Total No. Patients |
68/87(78%) |
6/29(21%) |
71/93(76%) |
8/32(25%) |
| Patients with Face Lesions |
57/71(80%) |
2/21(10%) |
57/67(85%) |
7/19(37%) |
| Patients with Scalp Lesions |
11/16(69%) |
4/8 (50%) |
14/26(54%) |
1/13 (8%) |
| |
Complete Responders |
| Total No.Patients |
60/87(69%) |
4/29(14%) |
59/93(63%) |
4/32(13%) |
| Patients with Face Lesions |
49/71(69%) |
2/21(10%) |
47/67(70%) |
4/19(21%) |
| Patients with Scalp Lesions |
11/16(69%) |
2/8 (25%) |
12/26(46%) |
0/13 (0%) |
Because clinical studies ALA-018 and ALA-019 had identical protocols, the combined
results from the two trials are shown in the following tables. For actinic keratoses
with a variety of thicknesses (excluding very thick, Grade 3 actinic keratoses
which were not studied in the phase 3 trials), LEVULAN KERASTICK Topical Solution
plus BLU-U is more effective than vehicle plus BLU-U, but as shown in Table
2, the percentage of lesions with complete responses at 8 weeks after treatment
with LEVULAN KERASTICK Topical Solution plus blue light illumination was lower
for those lesions that were thicker at baseline. Efficacy of LEVULAN KERASTICK
Topical Solution plus BLU-U on higher grade lesions was not studied in the Phase
3 clinical efficacy trials.
TABLE 2 - Lesions Complete Responses at Week 8 for Different
Lesion Grades
| |
LEVULAN |
Vehicle |
Lesion Grade 1
(Slightly palpable actinic keratoses: better felt than seen) |
666/756(88%) |
122/302(40%) |
Lesion Grade 2
(Moderately thick actinic keratoses: easily seen and felt) |
495/632(78%) |
52/199 (26%) |
Lesion Grade 3
(Very Thick and/or hyperkeratotic actinic keratoses) |
0 |
0 |
Those patients who were not Complete Responders at week 8 had retreatment of
the persistent target lesions at week 8. Among the patients undergoing retreatment,
efficacy results seen at 12 weeks after the initial treatment, i.e., at 4 weeks
after the second treatment, are shown in Table 3.
TABLE 3 - Complete Responders at Week 12, among Patients
Receiving Two Treatments
| |
LEVULAN |
Vehicle |
| Total No. Patients |
24/56 (43%) |
2/49 (4%) |
| Patients with Face Lesions |
21/40 (53%) |
2/31 (6%) |
| Patients with Scalp Lesions |
3/16 (19%) |
0/18 (0%) |
The efficacy results seen at 12 weeks after treatment, which include the results
at 12 weeks for those patients who received a single treatment as well as the
results at 12 weeks for those patients who received a second treatment at week
8, are shown in Table 4.
TABLE 4 - Patient Responses at Week 12, among Patients who
Received One or Two Treatments
| |
LEVULAN |
Vehicle |
| Patients with >75% of AK Lesions Cleared |
| Total No. Patients |
158/180 (88%) |
12/61 (20%) |
| Patients with Face Lesions |
127/138 (92%) |
8/40 (20%) |
| Patients with Scalp Lesions |
31/42 (74%) |
4/21 (19%) |
| |
Complete Responders |
| Total No. Patients |
129/180 (72%) |
7/61 (11%) |
| Patients with Face Lesions |
108/138 (78%) |
5/40 (13%) |
| Patients with Scalp Lesions |
21/42 (50%) |
2/21 (10%) |
Among Complete Responders at week 8, 93%(in study ALA-018) and 83% (in study
ALA-019) maintained complete response at week 12. Among patients with scalp
lesions, the percentage of patients with 100% of AK lesions having complete
response declined from week 8 (55%) to week 12 (50%), because there were more
patients with scalp lesions with 100% of AK lesions cleared at week 8 who had
a recurrence of a lesion by week 12 than there were patients with scalp lesions
who had retreatment of persistent lesions at week 8 and who then achieved 100%
of AK lesions cleared by week 12. Patients did not receive follow-up past 12
weeks after the initial treatment.
Patient outcomes recorded in the two Phase 3 trials are depicted in the following
flowchart, in which Complete Responders are designated clear. Seven patients
in the active treatment arm and three patients in the vehicle treatment arm
withdrew or were lost to follow-up, and their outcomes are not included in the
flowchart. Three patients in the active treatment arm were treated at baseline
but did not return for evaluation until week 12. One patient in the active treatment
arm and two in the vehicle treatment arm who were not clear at week 8 did not
receive retreatment.
Last updated on RxList: 10/8/2008