Off-label letrozole for tubal pregnancy monotherapy is not an alternative to methotrexate: a prospective cohort study

Objectives: Inhibition of estradiol production by letrozole may interfere with physiological effects of progesterone necessary to maintain the pregnancy. Treatment of tubal pregnancy (TP) with letrozole would allow to avoid the disadvantages of methotrexate (MTX). The aim was to compare the effectiveness of letrozole with MTX in the management of TP. Material and methods: A prospective open-label cohort study was conducted among women with TP and increasing B-human chorionic gonadotropin (B-hCG) concentrations. MTX was administered in a single dose of 100 mg intravenously, while letrozole in a dose of 5 mg orally for 10 days. Blood parameters (B-hCG, hemoglobin, creatinine, urea, transaminases, bilirubin) were tested on days 0, 4 and 7. Results: Out of 22 eligible women, 14 received MTX and received 8 letrozole. Mean age, lesion diameter, gestation age in the MTX vs letrozole arm were: 31 vs 32 years (p = 0.3), 13.2 vs 16.3 mm (p = 0.1), 7 + 1 vs 7 + 0 weeks (p = 0.6), respectively. In case of 4 women treated with letrozole and in 2 treated with MTX (4/8, 50% vs 2/14, 14.3%, p = 0.07) the treatment was unsuccessful. There were no significant differences in blood parameters on days 0, 4 and 7 between both arms, except for the increasing urea concentration in the letrozole arm (p = 0.01). Conclusions: Even though the results did not reach statistical significance, it is likely that a larger study sample would confirm the trend of letrozole being less effective. The results did not support the use of letrozole in the studied regimen as an alternative to MTX.