Letrozole / Ribociclib
Letrozole and ribociclib is a combination used to treat hormone receptor-positive, HER2-negative breast cancer — both early-stage high-risk disease and advanced or metastatic breast cancer in adults.
🧬 Where this information comes from Click to expand
The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 1 clinical label set within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →
📖 Letrozole / Ribociclib: Patient Information Guide
A plain-language walkthrough of Letrozole / Ribociclib — what it treats, how it works, how it’s taken, side effects, warnings and interactions. Tap any section to expand it.
🎯What it's used for▾
Letrozole and ribociclib, co-packaged as KISQALI FEMARA CO-PACK, is approved to treat two types of HR-positive, HER2-negative breast cancer in adults:
- KISQALI FEMARA CO-PACK is used as adjuvant therapy (post-treatment to prevent recurrence) for Stage II or Stage III early breast cancer that carries a high risk of coming back.
- KISQALI FEMARA CO-PACK is used as initial hormone-based therapy for advanced or metastatic breast cancer (cancer that has spread to other parts of the body).
⚙️How it works▾
Ribociclib (KISQALI) blocks enzymes called CDK4 and CDK6, which cancer cells depend on to progress through their growth cycle. By blocking these enzymes, ribociclib prevents cancer cells from replicating. Letrozole (FEMARA) stops the aromatase enzyme from converting other hormones into estrogen throughout the body — including inside tumor tissue itself. Because this type of breast cancer is driven by estrogen, cutting off the estrogen supply slows tumor growth. Studies show that combining these two mechanisms produces greater tumor suppression than either drug achieves alone.
💊How it's taken▾
KISQALI FEMARA CO-PACK is taken by mouth and can be taken with or without food. Both medicines should be taken once daily at approximately the same time each day, preferably in the morning. Ribociclib follows an on-off schedule — 21 days on, then 7 days off — within each 28-day cycle; the duration of the ribociclib treatment course differs depending on whether the cancer is early-stage or advanced. Letrozole is taken every day throughout the full 28-day cycle without a break.
- Swallow tablets whole — do not chew, crush, split, or take any tablet that is broken or cracked.
- If you miss a dose or vomit after taking it, skip that dose and resume your next dose at the usual time — never double up.
- Your doctor may adjust your ribociclib dose based on side effects; follow all dosing instructions from your prescriber and pharmacist.
🤒Side effects — in detail▾
The most frequently reported side effects include:
- Low white blood cell count (neutropenia/leukopenia) and low lymphocyte count
- Low red blood cell count (anemia)
- Nausea and vomiting
- Fatigue
- Headache
- Hair loss (alopecia)
- Diarrhea and constipation
- Infections (urinary tract, respiratory)
- Elevated liver enzymes on blood tests
Contact your doctor right away if you develop signs of a serious infection (fever, chills), new breathing problems, chest pain, a rapid or irregular heartbeat, yellowing of the skin or eyes, or a severe skin reaction with blistering or peeling — these require prompt medical attention.
⚠️Warnings & precautions▾
- Heart rhythm changes (QT prolongation): Ribociclib can alter the heart's electrical activity in a way that raises the risk of a dangerous irregular rhythm. Avoid other medicines that also prolong QT. ECGs and electrolyte levels are monitored before and throughout treatment.
- Serious lung inflammation (ILD/pneumonitis): Severe, life-threatening, and fatal cases have occurred. Report any new cough, shortness of breath, or low oxygen to your doctor immediately.
- Severe skin reactions (SCARs): Rare but life-threatening skin conditions including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) have been reported. Seek urgent care for blistering, widespread rash, or skin peeling.
- Liver toxicity: Significant rises in liver enzymes and drug-induced liver injury have occurred. Liver function is tested before treatment begins and monitored regularly.
- Neutropenia (low white blood cells): This is common and can be severe, increasing infection risk. Blood counts are checked before and throughout treatment.
- Embryo-fetal toxicity: Both medicines can cause serious harm to an unborn baby. Effective contraception is required during treatment and for at least 3 weeks after the last dose.
🔀What it interacts with▾
Several drug interactions are important to know about with KISQALI FEMARA CO-PACK:
- Strong CYP3A inhibitors (e.g., certain antifungals, some HIV antivirals, some antibiotics): These raise ribociclib blood levels significantly, increasing the risk of side effects including QT prolongation. Avoid if possible; a dose reduction of ribociclib may be needed if unavoidable.
- Strong CYP3A inducers (e.g., rifampin, certain seizure medicines): These lower ribociclib levels and may reduce how well the drug works. Avoid if possible.
- QT-prolonging drugs (e.g., antiarrhythmic heart medications): Combining these with ribociclib further increases the risk of a dangerous heart rhythm abnormality. Avoid this combination.
- CYP3A substrates with a narrow therapeutic index: Ribociclib can increase the levels of these medicines in your blood, raising the chance of their side effects. Your doctor may need to reduce the dose of those medicines.
This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.
📋Before taking it▾
- Tell your doctor if you have a known allergy to letrozole or any ingredient in FEMARA — this is a contraindication.
- Tell your doctor about any heart conditions, including history of abnormal heart rhythm, QT prolongation, heart failure, recent heart attack, unstable angina, or uncontrolled high blood pressure — ribociclib affects heart electrical activity.
- Tell your doctor if you have liver problems; moderate or severe liver impairment increases ribociclib exposure.
- Tell your doctor about every medicine, supplement, or herbal product you take — particularly those that affect the CYP3A liver enzyme pathway or heart rhythm.
- A pregnancy test is required before starting if you are a woman of childbearing potential. Use highly effective contraception throughout treatment and for at least 3 weeks after the last dose.
- Do not breastfeed during treatment or for at least 3 weeks after the last dose — the medicines may pass into breast milk and harm a nursing infant.
- Both men and women: this combination may affect fertility. Discuss this with your doctor before starting.
- Safety and effectiveness have not been established in children and adolescents.
📡Pharmacodynamics — effects in the body▾
Ribociclib lowers levels of a key cell-cycle protein (phosphorylated retinoblastoma protein, or pRb), which stalls cancer cells in a resting phase so they cannot divide. Letrozole suppresses estrogen levels by up to 75–95% in postmenopausal patients, with maximal suppression reached within 2–3 days of starting treatment. Letrozole does not interfere with the body's production of cortisol, aldosterone, or other adrenal hormones, and does not affect thyroid function or sex hormone precursor levels — so no supplemental steroids are needed.
🔬Pharmacokinetics — how your body processes it▾
Ribociclib reaches peak blood levels within 1–4 hours after an oral dose and has an average half-life of about 32 hours; steady-state levels are typically achieved after about 8 days. Food does not meaningfully change how much ribociclib is absorbed. Ribociclib is broken down mainly by the liver enzyme CYP3A4 and eliminated primarily in the feces. Letrozole is rapidly and completely absorbed from the gut — food does not affect its absorption — and has a terminal half-life of about 2 days, with steady-state plasma levels reached within 2–6 weeks of daily dosing. Letrozole is broken down to an inactive metabolite that is cleared mainly through the urine.
📦How to store it▾
Store at room temperature at 20°C to 25°C (68°F to 77°F), excursions permitted between 15°C and 30°C (59°F and 86°F). Store in the original blister package in order to protect from moisture.
📄 Written from Letrozole / Ribociclib’s FDA-approved label information, summarized in plain language with AI, and reviewed by our pharmacy team before publication. Every point is grounded in that labeling — nothing is invented. How we use AI →
🩺 Pharmacist Counseling Corner
Quick, plain-English answers to the questions patients ask most about Letrozole / Ribociclib — the kind of thing our pharmacy team would talk through with you at the counter.
What exactly is KISQALI FEMARA CO-PACK and why did my doctor prescribe both medicines together? ▾
How do I take these medicines — do I take both pills every day? ▾
What side effects should I expect, and which ones mean I should call my doctor right away? ▾
I heard this medicine can affect my heart. What does that mean and what do I need to do? ▾
Can I get pregnant while taking this medicine? ▾
Are there medicines, supplements, or foods I should avoid while taking this combination? ▾
Is Letrozole / Ribociclib available over the counter? ▾
When was Letrozole / Ribociclib first available? ▾
💬 Answers drafted from Letrozole / Ribociclib’s FDA-approved label information, summarized in plain language with AI, and reviewed by our pharmacy team before publication. Grounded in that labeling — nothing is made up. How we use AI →
🧰 Keep exploring
📊 Letrozole / Ribociclib across the U.S. market
How Letrozole / Ribociclib appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.
Also listed with the FDA, not a patient dose form: Kit (12) — bulk drug substance sold to compounders/manufacturers and multi-item kits. These aren’t counted in the dose-form total above.
🔍 Compare Letrozole / Ribociclib products
A representative set of FDA-listed product records for Letrozole / Ribociclib — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)
| Manufacturer / Labeler | Category ⓘ | Details |
|---|---|---|
| 💊Kits | ||
| Novartis Pharmaceuticals Corporation × 12 listings | NDA | View NDC → |
Showing 12 of 12 products — FDA National Drug Code Directory. See every product, package size and price: browse all 12 Letrozole / Ribociclib NDCs →
📈 What people report — real-world data (FDA FAERS)
After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Letrozole / Ribociclib — a signal of what to watch for, not proof the drug caused it.
Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Letrozole / Ribociclib in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.
🏛️ The road to your pharmacy
How Letrozole / Ribociclib went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Source: Drugs@FDA.
🚨 Recall history
A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.
Source: openFDA drug enforcement (recall) reports.
📦 Supply & shortage status
Whether Letrozole / Ribociclib is in short supply in the U.S. right now, plus any shortage history the FDA has on record. A shortage usually reflects a manufacturing or demand issue — not a safety problem with the drug.
Source: openFDA, from the FDA Drug Shortages database.
🏷️ Sold under these brand names
🏭 Manufacturers & labelers
🔬 Where this comes from
Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.
How we combine label and product data
HelloPharmacist combines public FDA and NLM records; we don’t author the underlying clinical facts. We identified 1 FDA-filed SPL label set within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. The representative label is the starting point for the displayed reference monograph; the 12 largest stored in-scope SPL records, which may include that representative, are compared section by section, and the longest available version of each section is retained. Forms, routes, brands, labelers, product-listed strengths, and product-record counts are aggregated separately from ingredient-matched FDA NDC Directory records; package records listed above are associated with the linked SPL; and the normalized concept hierarchy comes from NLM RxNorm.
For canonical ingredient pages, bounded product-attributed indication and administration excerpts may be added to the AI evidence, and the generator is instructed to preserve available product, brand, route, and form qualifiers instead of treating one label as universal. Where a section is identified as AI-written, its plain-language text is generated from bounded label evidence. New draft drug pages remain in the admin review queue before first publication. Novartis Pharmaceuticals Corporation is the representative DailyMed label linked for verification and dates; it is not the sole source used for the page.
This is general education, not medical advice — always consult your doctor or pharmacist about your medications and any medical condition. For the exact wording of the linked representative label, view that label on DailyMed; some displayed composite sections may come from other in-scope SPL labels. Learn how we use AI and our data sources & update cadence.