Patent ID: 7888526

Claim:
An acid addition salt of a 5-aminolevulinic acid (5-ALA) ester with an acid which has a pKa of about 5 or less, wherein either said acid is nitric acid, and said 5-ALA ester is a compound of formula X: R 2 2 N—CH 2 COCH 2 —CH 2 CO—OR 1 (X) wherein R 1 represents a straight-chained C 1-6 alkyl group substituted by an aryl group, and R 2 each independently represents a hydrogen atom or an optionally substituted straight-chained, branched or cyclic alkyl group which may optionally be interrupted by one or more —O—, —NR 3 —, —S— or —PR 3 — groups; and R 3 is a hydrogen atom or a C 1-6 alkyl group, or said acid is a sulfonic acid or a sulfonic acid derivative and said 5-ALA ester is a compound of formula XI: R 5 2 N—CH 2 COCH 2 —CH 2 CO—OR 4 (XI) wherein R 4 represents a straight-chained C 1-6 alkyl group optionally substituted by an aryl group, and R 5 each independently represents a hydrogen atom or an optionally substituted straight-chained, branched or cyclic alkyl group which may optionally be interrupted by one or more —O—, —NR 6 —, —S— or —PR 6 — groups; and R 6 is a hydrogen atom or a C 1-6 alkyl group.