Citalopram
Severe
Database
Drug interaction classified as: metabolism.
Source: DDInter
Drug reference
Letrozole
Aromatase inhibitor (non-steroidal, third-generation) / anti-estrogen · Antineoplastic
Also known as Femara
START
2.5 mg OD (fixed dose); confirm postmenopausal status (FSH >40 IU/L); check baseline bone density (DEXA), lipid panel, liver function; ensure adequate calcium (1000-1200 mg) and vitamin D (800-1000 IU)
TYPICAL MAX
2.5 mg/day (no dose escalation)
STOP IF
Disease progression (advanced), completion of 5-year adjuvant course (may extend to 10 years in high risk), severe osteoporosis, intolerable side effects
WATCH
Bone density (DEXA at baseline, 1-2 years, then every 2 years), lipid panel annually, liver function if symptoms, fracture risk assessment, musculoskeletal symptoms
CDSCO approvedSchedule HJan AushadhiATC L02BG04
KDIGO 2024 + manufacturer label
- ONSET
- 15min · absorption onset
- PEAK
- 1h · Peak plasma concentration
- t½
- 1.9d · 40-50 hours
- DURATION
- 1d · 24-hour estradiol suppression
EXCRETION
Renal (metabolites)
route + CYP
INTERACTIONS
2 major
incl. contraindicated
PREGNANCY
Contraindicated in pregnancy; may cause fetal harm; teratogenic
FDA category + note
Top interactionssee all 5 →
- CitalopramSevereDatabaseDDInter
- ThalidomideSevereDatabaseDDInter
Available in India
167 branded formulations. Look up specific brands in the Drugs workspace.
Jan Aushadhi — generic available at GoI pharmacies
Mechanism
Potent, selective, reversible competitive inhibitor of aromatase (CYP19), the enzyme that converts androgens (androstenedione, testosterone) to estrogens (estrone, estradiol) in peripheral tissues. Reduces circulating estradiol by >95% in postmenopausal women. Does not affect adrenal corticosteroid or aldosterone synthesis.
Indications
Hormone receptor-positive early breast cancer (adjuvant therapy in postmenopausal women)Hormone receptor-positive advanced breast cancer (first-line in postmenopausal women)Ovulation induction (off-label, in PCOS and infertility)Endometriosis (off-label)Gynecomastia in men (off-label)
Dosing
- Adult
- 2.5 mg once daily (fixed dose, no titration needed); continue for 5 years (adjuvant) or until disease progression (advanced)
- Pediatric
- Not recommended in children
- Renal adjustment
- No adjustment needed; minimal renal excretion
- Hepatic adjustment
- Mild–moderate: no adjustment. Cirrhosis / severe hepatic impairment: reduce dose by 50% (FDA §2.5) — not 'not recommended'.
- Geriatric
- Standard dosing (2.5 mg OD); no adjustment needed based on age
- Max dose
- 2.5 mg/day
Pharmacokinetics
Onset
Days (estradiol suppression begins within hours)
Peak effect
1 hour (Tmax); estradiol suppression >95% within 2-3 days
Duration
24 hours
Half-life
2 days (40-50 hours)
Bioavailability
99.9%
Protein binding
60% (weakly bound to albumin)
Metabolism
Hepatic CYP2A6 (major) and CYP3A4; glucuronidation to inactive metabolite
Excretion
Renal (majority, as metabolites); fecal (minor)
Contraindications
- Hypersensitivity to letrozole
- Premenopausal women (unless ovarian function suppressed with GnRH agonist)
- Pregnancy and breastfeeding
- Severe hepatic impairment
Side effects
Common
Hot flashesArthralgia / myalgiaFatigueHeadacheNauseaOsteoporosis / bone lossIncreased cholesterolSweatingInsomnia
Serious
- Osteoporosis and fractures
- Cardiovascular events (increased risk in some studies)
- Hypercholesterolemia
- Hepatotoxicity (rare)
- Severe allergic reactions (rare)
- Endometrial thickening (rare, less than tamoxifen)
Pregnancy & lactation
Pregnancy
Contraindicated in pregnancy; may cause fetal harm; teratogenic
Lactation
Contraindicated during breastfeeding
Drug interactions
Thalidomide
Severe
Database
Clinical effect not specified
Source: DDInter
Estrogens
Moderate
Database
Pharmacologic antagonism; estrogens counteract letrozole effect
Avoid concurrent use
Source: Kimi deep-research + Cla
Phenobarbital
Moderate
Database
Decreased plasma concentrations and reduced efficacy of letrozole due to increased metabolism.
Avoid concomitant use if possible. If co-administration is necessary, monitor for reduced efficacy of letrozole and consider alternative antiepileptic drugs. Dose adjustment of letrozole is not typically recommended based on current data, but close monitoring for disease progression is crucial.
Source: DDInter
Tamoxifen
Moderate
Database
Letrozole and tamoxifen should not be used together; sequential therapy (letrozole after tamoxifen) is standard
Do not combine; if switching, allow washout period
Source: Kimi deep-research + Cla
7 additional unreviewed or low-confidence interactions hidden because their provenance or source detail is insufficient.
Related guidelines
Ask House about Letrozole
Continue into a citation-backed clinical answer with the drug context already attached.
Textbook-sourced·Sources: KD Tripathi 7e, Goodman & Gilman 14e, Harrison 22e, Katzung·Updated: 2026-05-19·Cockpit curated: 2026-05-19