Abstract
Tamoxifen is a selective oestrogen receptor modulator indicated for the treatment of breast cancer in adults. The recommended dose is 20 mg orally once daily. We report an accidental tamoxifen ingestion in a 2-year-old female who accessed the tamoxifen from a pill bottle stored in a bag while unsupervised. Activated charcoal and sodium sulphate were administered approximately 2.5 h after ingestion. Plasma concentrations of both tamoxifen and active metabolite endoxifen were determined. The maximum plasma concentration of tamoxifen was 53.8 ng/mL, occurring two hours after ingestion. In contrast, the plasma concentration of endoxifen measured at 22 h after ingestion was 0.771 ng/L, which is considered subtherapeutic in adults. However, given the prolonged half-life of endoxifen, the plasma levels may still be rising at this point. The ingested dose was estimated to be around 31-37 mg, based on the plasma levels of tamoxifen and endoxifen. The actual ingested amount may have been higher due to early oral administration of activated charcoal. No direct serious events occurred during a hospital admission of 31 h. Given the anti-oestrogen properties of tamoxifen and the critical role of oestrogen in pubertal development long-term follow-up is recommended to monitor potential delayed effects.