5-Aminolevulinic Acid

Exogenous aminolevulinic acid (ALA) is metabolized to PpIX, but the fraction of administered ALA that is metabolized to PpIX is unknown. The average plasma AUC of PpIX is less than 6% of that of ALA.

Following topical administration, synthesis into protoporphyrin IX takes place in situ in the skin. Half Life: Mean half-life is 0.70 ± 0.18 h after the oral dose and 0.83 ± 0.05 h after the intravenous dose.

88755TAZ87

AMINOLEVULINIC ACID

Established Pharmacologic Class [EPC] - Porphyrin Precursor

Chemical Structure [CS] - Porphyrinogens

Established Pharmacologic Class [EPC] - Optical Imaging Agent

Mechanisms of Action [MoA] - Fluorescence Contrast Activity

Drugs that are pharmacologically inactive but when exposed to ultraviolet radiation or sunlight are converted to their active metabolite to produce a beneficial reaction affecting the diseased tissue. These compounds can be administered topically or systemically and have been used therapeutically to treat psoriasis and various types of neoplasms.

Oral bioavailability is 50-60%. ### **Topical gel** Pharmacokinetics (PK) of aminolevulinic acid (ALA) and PpIX was evaluated in a trial of 12 adult subjects with mild to moderate AK with at least 10 AK lesions on the face or forehead. A single dose of one entire tube of ALA (2 grams) was applied under occlusion for 3 hours followed by photodynamic therapy (PDT) to a total area of 20 cm2. The mean ± SD baseline plasma ALA and PpIX concentrations were 20.16 ± 16.53 ng/mL and 3.27 ± 2.40 ng/mL, respectively. In most subjects, an up to 2.5-fold increase of ALA plasma concentrations was observed during the first 3 hours after ALA application. The mean ± SD area under the concentration time curve (AUC0-t) and maximum concentration (Cmax) for baseline corrected ALA (n=12) were 142.83 ± 75.50 ng.h/mL and 27.19 ± 20.02 ng/mL, respectively. The median Tmax (time at which Cmax occurred) was 3 hours. ### **Topical solution** Two human pharmacokinetic (PK) studies were conducted in subjects with minimally to moderately thick actinic keratoses on the upper extremities, having at least 6 lesions on one upper extremity and at least 12 lesions on the other upper extremity. A single dose comprising of two topical applications of ALA topical solution (each containing 354 mg ALA HCl) were directly applied to the lesions and occluded for 3 hours prior to light treatment. The first PK study was conducted in 29 subjects and PK parameters of ALA were assessed. The baseline corrected mean ± SD of the maximum concentration (Cmax) of ALA was 249.9 ± 694.5 ng/mL and the median Tmax was 2 hours post dose. The mean ± SD exposure to ALA, as expressed by area under the concentration time curve (AUCt) was 669.9 ± 1610 ng·hr/mL. The mean ± SD elimination half-life (t1/2) of ALA was 5.7 ± 3.9 hours. A second PK study was conducted in 14 subjects and PK parameters of ALA and PpIX were measured. The baseline corrected PpIX concentrations were negative in at least 50% of samples in 50% (7/14) subjects and AUC could not be estimated reliably. The baseline-corrected mean ± SD of Cmax for ALA and PpIX was 95.6 ± 120.6 ng/mL and 0.95 ± 0.71 ng/mL, respectively. The median Tmax of ALA and PpIX was 2 hours post dose and 12 hours post dose, respectively. The mean AUCt of ALA was 261.1 ± 229.3 ng·hr/mL. The mean ± SD t1/2 of ALA was 8.5 ± 6.7 hours. ### **Oral solution** In 12 healthy subjects, the absolute bioavailability of ALA following the recommended dose of ALA solution was 100.0% + 1.1 with a range of 78.5% to 131.2%. Maximum ALA plasma concentrations were reached with a median of 0.8 hour (range 0.5 – 1.0 hour).

In 12 healthy subjects, excretion of parent aminolevulinic acid (ALA) in urine in the 12 hours following administration of the recommended dose of ALA solution was 34 + 8% (mean + std dev) with a range of 27% to 57%.

In healthy volunteers, the administration of aminolevulinic acid resulted in a volume of distribution of 9.3 ± 2.8 L intravenously and 14.5 ± 2.5 orally.[11961050]