Method for producing antibody-drug conjugate

A method for producing an antibody-drug conjugate (ADC) comprising an antibody and a drug linked to each other via a linker, or a pharmaceutical comprising the ADC, the method comprising:

• (a) mixing, using a microreactor, a solution comprising an IgG antibody with a solution comprising tricarboxyethyl phosphine (TCEP) to generate a partially reduced antibody;
• (b) mixing, using a microreactor, a solution comprising tricarboxyethyl phosphine (TCEP) and the partially reduced IgG antibody under reduction reaction with TCEP with a solution comprising a stoichiometrically excessive amount of an inhibitor of TCEP based on TCEP;
• and
• (c) reacting the partially reduced antibody with a linker having a functional group reactive with an SH group of the antibody to generate the antibody linked to the linker.