Design and evaluation of a water-soluble bioadhesive patch formulation for cutaneous delivery of 5-aminolevulinic acid to superficial neoplastic lesions

Photodynamic therapy of superficial neoplastic lesions generally uses high aminolevulinic acid (ALA) loadings (20%, w/w) in emulsion-type systems under occlusion. This approach makes ALA dosing difficult and delivery to demanding areas, such as the vulval, perineal and perianal skin, are seldom possible. This work evaluated a water-soluble bioadhesive patch, loaded with ALA, which can adhere to both intact skin and mucous surfaces. ALA loading in the patch (38 mg cm−2) was chosen using a simple comparative procedure. Tensile measurements showed that large ALA loadings did not adversely affect adhesion to porcine skin, achieving a mean strength of 1.7 N cm−2. Increasing the loading was, however, shown to lower break strength and enhance percentage elongation at break. Water uptake studies showed an initial, rapid weight gain followed by gradual patch dissolution over 60 min. Drug release studies demonstrated that 57% of ALA was released across an aqueous semi-permeable membrane within 6 h, compared to 42% released from a proprietary cream formulation. The patch designed in this work is suited to definable ALA delivery to diverse regions, such as the lower female reproductive tract and lesions on exposed skin. Adhesion is sufficiently tenacious to allow photodynamic therapy (PDT), without the need to immobilise patients for up to 6 h, as was common with the cream-under-occlusion approach.