A pharmaceutical composition comprising a compound of formula (I) wherein X is an electron withdrawing group, Y.sup.1 is hydrogen, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, --SO.sub.2R.sup.4, --CO.sub.2R.sup.4, --CONHR.sup.4 or --COR.sup.4, and each of R.sup.1, R.sup.2 and R.sup.4, which may be the same or different, is hydrogen, alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl or heterocyclyl, or a compound of formula (II) wherein each of Y.sup.2 and Y.sup.3, which may be the same or different, is hydrogen, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, --SO.sub.2R.sup.9, --CO.sub.2R.sup.9, --CONHR.sup.9 or --COR.sup.9, Z is hydrogen, alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heterocyclyl, --CH.dbd.C(NHR.sup.10)CH((CH.sub.2)m CO.sub.2R.sup.11)(C.dbd.O)CH.sub.3 or --CH.sub.2(C.dbd.O)CH((CH.sub.2).sub.mCO.sub.2R.sup.11)(C.dbd.O)CH.sub.3, R.sup.8 is --(CH.sub.2).sub.nCO.sub.2R.sup.12, each of R.sup.5 to R.sup.7 and R.sup.9 to R.sup.12, which may be the same or different, is hydrogen, alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl or heterocyclyl, and each of m and n, which may be the same or different, is 1 to 6 or a compound of formula (III) wherein each of Y.sup.4 to Y.sup.6, which may be the same or different, is hydrogen, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, --SO.sub.2R.sup.19, --CO.sub.2R.sup.19, --CONHR.sup.19 or --COR.sup.19, each of R.sup.16 and R.sup.17, which may be the same or different, is --(CH.sub.2)p CO.sub.2R.sup.20, each of R.sup.13 to R.sup.15 and R.sup.18 to R.sup.20, which may be the same or different, is hydrogen, alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl or heterocyclyl, and p is 1 to 6, or other photolabile degradation product of bilirubin or biliverdin or derivative of a photolabile degradation fragment of bilirubin or biliverdin, or a pharmaceutically acceptable salt thereof, together with a pharmaceutically acceptable carrier or diluent.