Oestrogens
Severe
Database
Pharmacologic antagonism — negates anastrozole effect
Avoid all oestrogens (including HRT/vaginal)
Source: Kimi deep-research + Cla
Drug reference
Anastrozole
Non-steroidal aromatase inhibitor (third generation) · Antineoplastic
Also known as Arimidex, Anzol, Armotraz, Anazone, Femistra
START
1 mg PO once daily (postmenopausal HR+ breast cancer)
TYPICAL MAX
1 mg/day (fixed)
STOP IF
Severe hepatic dysfunction, disabling musculoskeletal symptoms unresponsive, significant fragility fracture risk progression
WATCH
Bone density (baseline DXA + periodic) with calcium/vitamin D, lipids, hepatic enzymes, bone health
CDSCO approvedSchedule HATC L02BG03
KDIGO 2024 + manufacturer label
- ONSET
- 30min · absorption onset
- PEAK
- 2h · Cmax
- t½
- 2.1d · plasma t½
- DURATION
- 1d · once-daily
EXCRETION
Hepatic metabolism; <10% renal unchanged
route + CYP
INTERACTIONS
3 major
SEVERE in our sources
PREGNANCY
Contraindicated — may cause fetal harm; not for premenopausal/pregnant women
FDA category + note
Top interactionssee all 6 →
- OestrogensSevereDatabaseKimi deep-research + Cla
- TamoxifenSevereDatabaseKimi deep-research + Cla
- ThalidomideSevereDatabaseDDInter
Available in India
43 branded formulations. Look up specific brands in the Drugs workspace.
Mechanism
Selective, reversible inhibition of the aromatase enzyme, blocking peripheral conversion of androgens to oestrogens — markedly lowers circulating oestradiol in postmenopausal women, depriving hormone-receptor-positive breast tumours of oestrogen.
Indications
Adjuvant treatment of hormone-receptor-positive early breast cancer (postmenopausal)Advanced/metastatic HR-positive breast cancerOvulation induction (off-label)
Dosing
- Adult
- 1 mg PO once daily.
- Pediatric
- Not indicated.
- Renal adjustment
- No adjustment (even severe).
- Hepatic adjustment
- Mild–moderate: no adjustment. Severe: not studied — use with caution.
- Geriatric
- No specific adjustment.
- Max dose
- 1 mg/day (fixed)
Pharmacokinetics
Onset
Oestradiol suppression within ~24 h; ~85% by day 14
Peak effect
~2 h (Cmax)
Duration
~24 h (once daily)
Half-life
~50 h
Bioavailability
Well absorbed (not affected clinically by food)
Protein binding
~40%
Metabolism
Extensive hepatic (N-dealkylation, hydroxylation, glucuronidation)
Excretion
<10% renal unchanged; metabolites renal/biliary
Contraindications
- Premenopausal women / pregnancy / breastfeeding
- Hypersensitivity to anastrozole
Side effects
Common
Hot flushesArthralgia/myalgia, joint stiffnessFatigueMood disturbanceVaginal dryness
Serious
- Decreased bone mineral density / fractures
- Ischaemic cardiovascular events / hypercholesterolaemia
- Hepatic enzyme elevation/hepatitis (rare)
- Severe skin reactions (rare, incl. SJS); angioedema
Pregnancy & lactation
Pregnancy
Contraindicated — may cause fetal harm; not for premenopausal/pregnant women
Lactation
Contraindicated — do not breastfeed
Drug interactions
Tamoxifen
Severe
Database
Tamoxifen lowers anastrozole concentration ~27% — antagonistic; do not co-administer
Do not combine; sequence per protocol
Source: Kimi deep-research + Cla
Thalidomide
Severe
Database
Drug interaction classified as: synergy.
Source: DDInter
Cimetidine
Moderate
Textbook
Decreases anastrozole levels by 27%.
Monitor for reduced efficacy of anastrozole. Consider alternative agents or dose adjustment.
Source: G&G 14e · p1443
Bisphosphonates
Moderate
Database
Beneficial — counteract AI bone loss (managed combination)
Use for bone protection per fracture risk
Source: Kimi deep-research + Cla
Tibolone
Moderate
Database
Oestrogenic activity may antagonise AI
Avoid
Source: Kimi deep-research + Cla
6 additional low-confidence interactions hidden — those rows lack a documented mechanism or management plan in our sources.
Related guidelines
Ask House about Anastrozole
Continue into a citation-backed clinical answer with the drug context already attached.
Sources: KD Tripathi 7e, Goodman & Gilman 14e, Harrison 22e, Katzung·Verified: 2026-05-19 · House clinical team·Cockpit curated: 2026-05-19