It's a fairly well known, well documented drug interaction. It's also in the stickies, iirc.
And you're right, running an AI with a SERM is a good idea. But not Adex. Aromisin shows no such interaction with Nolva.
GENERALLY AVOID: Coadministration with tamoxifen may decrease the plasma concentrations of anastrozole. The mechanism of interaction has not been described. In one clinical trial, coadministration of tamoxifen (20 mg/day) and anastrozole (1 mg/day) in breast cancer patients resulted in decreased anastrozole plasma concentration by 27% compared to administration of anastrozole alone. In addition, at a median follow-up of 33 months, the combination did not demonstrate any efficacy benefit over tamoxifen therapy alone in all patients as well as in the hormone receptor-positive subpopulation, and this treatment arm was discontinued from the trial. The pharmacokinetics of tamoxifen and its pharmacologically active N-desmethyl metabolite were not affected.
MedicinesComplete: Baxter K (ed). Tamoxifen + Aromatase inhibitors: Stockleys Drug Interactions. RPS Publishing, London, UK,
MedicinesComplete: McEvoy GK (ed). Anastrozole: American Hospital Formulary Service Drug Information. RPS Publishing, London, UK,
Dowsett M, Cuzick J, Howell A et al: Pharmacokinetics of anastrozole and tamoxifen alone, and in combination, during adjuvant endocrine therapy for early breast cancer in postmenopausal women: a sub-protocol of the 'Arimidex and tamoxifen alone or in combination' (ATAC) trial.. Br J Cancer (2001) 85 (3/Aug 3): 317-24