HEXAMINOLEVULINATE HYDROCHLORIDE, AN OPTICAL IMAGING DRUG THAT IN SOLUTION FORM IS INSTILLED INTRAVESICALLY FOR USE WITH PHOTODYNAMIC BLUE LIGHT CYSTOSCOPY AS AN ADJUNCT TO WHITE LIGHT CYSTOSCOPY.
HEXAMINOLEVULINATE HYDROCHLORIDE INTRAVESICAL SOLUTION IS AN ESTER OF THE HEME PRECURSOR, AMINOLEVULINIC ACID. AFTER BLADDER INSTILLATION, IT ENTERS THE BLADDER MUCOSA AND IS PROPOSED TO ENTER THE INTRACELLULAR SPACE OF MUCOSAL CELLS WHERE IT IS USED AS A PRECURSOR IN THE FORMATION OF THE PHOTOACTIVE INTERMEDIATE PROTOPORPHYRIN IX (PPIX) AND OTHER PHOTOACTIVE PORPHYRINS (PAPS). PPIX AND PAPS ARE REPORTED TO ACCUMULATE PREFERENTIALLY IN NEOPLASTIC CELLS AS COMPARED TO NORMAL UROTHELIUM, PARTLY DUE TO ALTERED ENZYMATIC ACTIVITY IN THE NEOPLASTIC CELLS. AFTER EXCITATION WITH LIGHT AT WAVELENGTHS BETWEEN 360 AND 450 NM, PPIX AND OTHER PAPS RETURN TO A LOWER ENERGY LEVEL BY FLUORESCING, WHICH CAN BE DETECTED AND USED FOR CYSTOSCOPIC DETECTION OF LESIONS. THE FLUORESCENCE FROM TUMOR TISSUE APPEARS BRIGHT RED AND DEMARCATED, WHEREAS THE BACKGROUND NORMAL TISSUE APPEARS DARK BLUE. SIMILAR PROCESSES MAY OCCUR IN INFLAMED CELLS.