Contrast medium formulation and related preparation method

A liquid pharmaceutical composition comprising a complex of formula (I):

• in which R1, R2 and R3 represent —COOH,
• X1, X2 and X3 represent, independently of one another, L-Y in which L represents a C1-C3 alkylene group, preferably (CH2)n with n=1 to 3, and Y represents —CONH2, —CO—NR7R8 or —NR7—CO—R8, in which R7 represents H or a C1-C6 alkyl group or a C1-C6 hydroxyalkyl group, which is in particular C2-C4, advantageously —CH2—CH2OH, —CHOH—CH2OH, —CH—(CH2OH)2, —(CH2)m—(CHOH)p—CH2OH with m=1 to 3, p=1 to 4 and m+p=2 to 5 or —C—(CH2OH)3 and R8 represents a C1-C6 alkyl or C1-C6 hydroxyalkyl group, which is in particular C2-C4, advantageously —CH2—CH2OH, —CHOH—CH2OH, —CH—(CH2OH)2, —(CH2)m—(CHOH)p—CH2OH with m=1 to 3, p=1 to 4 and m+p=2 to 5 or —C—(CH2OH)3, provided that at least R7 or R8 represents a C1-C6 hydroxyalkyl group;
• D represents CH or N;
• E represents CH or N;
• F1 represents CH or N;
• K1 to K12 each independently represent H, —(CH2)j—CH3 or —(CH2)i—OH in which j=0 to 3 and i=1 to 3, advantageously H, or K3 or K4 with K5 or K6, and/or K7 or K8 with K9 or K10 forming a ring having 3 to 6 carbon atoms;
• and
• M represents an ion of a paramagnetic metal;
• or an enantiomer or a diastereoisomer (preferentially chosen from the RRS, RSR and RSS diastereoisomers) thereof or mixtures thereof,
• said composition also comprising a calcium complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, and having a concentration of free paramagnetic metal of less than 1 ppm (m/v), preferentially less than 0.5 ppm (m/v).