Personalised therapy during preconception and gestation in SLE: usefulness of 6-mercaptopurine metabolite levelswith azathioprine

Given that approximately 20% of SLE pregnancies experience placenta-mediated complications, it is unclear if the non-detectable 6-TG levels contributed to pre-eclampsia in this patient.Table 1 Characteristics of patients with SLE on AZA who were pregnant or trying to conceive at the time of 6-mercaptopurine metabolite level monitoring Case Conception status Prior lupus nephritis AZA dose (mg/kg/day) Metabolite levels (pmol/8×108 RBC) Disease activity at time of metabolite measurement Pregnancy outcome Metabolite levels interpretation Action based on therapeutic drug monitoring 6-TG 6-MMP 1 Preconception Yes 2.6 141 (low) 5899 (elevated) LLDAS Not applicable ‘Shunter’* Switched to tacrolimus 2.6 129 (low) 5888 (elevated) LLDAS 2 Preconception Yes 1.9 Not detectable Not detectable LLDAS Not applicable Non-adherence† Adherence discussion 3 Pregnant No 1.2 109 (low) 384 No LLDAS Pre-eclampsia and preterm birth Subtherapeutic dosing‡ Dose increased 1.8 207 (low) 3361 LLDAS 2.1 Not detectable Not detectable LLDAS Non-adherence Adherence discussion 4 Preconception Yes 2.3 330 (normal) 3019 LLDAS Not applicable Therapeutic dosing Continued same dose 5 Pregnant Yes 2.5 44 (low) 269 LLDAS Uncomplicated term pregnancy Non-adherence versus subtherapeutic dosing Adherence discussion 6 Pregnant Yes 1.5 155 (low) 3392 LLDAS Uncomplicated term pregnancy Subtherapeutic dosing Discussion about dose increase (patient refused) *Shunter: 6-MMP to 6-TG ratio ≥20 with high 6-MMP. †Non-adherence: not detectable or barely detectable metabolite levels (ie, up to twice the minimal detectable 6-TG levels which is 30 pmol/8×108 RBC) despite adequate AZA dosing. ‡Subtherapeutic dosing: 6-TG levels