A pharmaceutical composition comprising: (i) a trypsin inhibitor; and (ii) a compound of general formula: X-C -NR 1 -(C(R 2)(R 3)) n -NH-C -CH(R 4)-NH(R 5) or a pharmaceutically acceptable salt thereof, in which: X represents a residue of a phenolic opioid, wherein the hydrogen atom of the phenolic hydroxyl group is replaced by a covalent bond to -C -NR 1 -(C(R 2)(R 3)) n -NH-C -CH(R 4)-NH(R 5); R 1 is selected from alkyl, substituted alkyl, arylalkyl, substituted arylalkyl, aryl and substituted aryl; each R 2 is independently selected from hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, acyl, and aminoacyl; each R 3 is independently selected from hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, acyl, and aminoacyl; or R 2 and R 3 together with the carbon to which they are attached form a cycloalkyl or substituted cycloalkyl group, or two R 2 or R 3 groups on adjacent carbon atoms, together with the carbon atoms to which they are attached, form a cycloalkyl or substituted cycloalkyl group; n represents an integer from 2 to 4; R 4 represents -CH 2 CH 2 CH 2 NH(C=NH)NH 2 or -CH 2 CH 2 CH 2 CH 2 NH 2, the configuration of the carbon atom to which R 4 is attached corresponding with that in an L-amino acid; and R 5 represents a hydrogen atom, an N-acyl group, a residue of an amino acid, a dipeptide, or an N-acyl derivative of an amino acid or dipeptide. (i) a trypsin inhibitor; and (ii) a compound of general formula: X-C -NR 1 -(C(R 2)(R 3)) n -NH-C -CH(R 4)-NH(R 5) or a pharmaceutically acceptable salt thereof, in which: X represents a residue of a phenolic opioid, wherein the hydrogen atom of the phenolic hydroxyl group is replaced by a covalent bond to -C -NR 1 -(C(R 2)(R 3)) n -NH-C -CH(R 4)-NH(R 5); R 1 is selected from alkyl, substituted alkyl, arylalkyl, substituted arylalkyl, aryl and substituted aryl; each R 2 is independently selected from hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, acyl, and aminoacyl; each R 3 is independently selected from hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, acyl, and aminoacyl; or R 2 and R 3 together with the carbon to which they are attached form a cycloalkyl or substituted cycloalkyl group, or two R 2 or R 3 groups on adjacent carbon atoms, together with the carbon atoms to which they are attached, form a cycloalkyl or substituted cycloalkyl group; n represents an integer from 2 to 4; R 4 represents -CH 2 CH 2 CH 2 NH(C=NH)NH 2 or -CH 2 CH 2 CH 2 CH 2 NH 2, the configuration of the carbon atom to which R 4 is attached corresponding with that in an L-amino acid; and R 5 represents a hydrogen atom, an N-acyl group, a residue of an amino acid, a dipeptide, or an N-acyl derivative of an amino acid or dipeptide. X represents a residue of a phenolic opioid, wherein the hydrogen atom of the phenolic hydroxyl group is replaced by a covalent bond to -C -NR 1 -(C(R 2)(R 3)) n -NH-C -CH(R 4)-NH(R 5); R 1 is selected from alkyl, substituted alkyl, arylalkyl, substituted arylalkyl, aryl and substituted aryl; each R 2 is independently selected from hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, acyl, and aminoacyl; each R 3 is independently selected from hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, acyl, and aminoacyl; or R 2 and R 3 together with the carbon to which they are attached form a cycloalkyl or substituted cycloalkyl group, or two R 2 or R 3 groups on adjacent carbon atoms, together with the carbon atoms to which they are attached, form a cycloalkyl or substituted cycloalkyl group; n represents an integer from 2 to 4; R 4 represents -CH 2 CH 2 CH 2 NH(C=NH)NH 2 or -CH 2 CH 2 CH 2 CH 2 NH 2, the configuration of the carbon atom to which R 4 is attached corresponding with that in an L-amino acid; and R 5 represents a hydrogen atom, an N-acyl group, a residue of an amino acid, a dipeptide, or an N-acyl derivative of an amino acid or dipeptide.