Palnat 100 — Palbociclib 100 mg

Palnat is supplied as capsules for oral administration. The packaging contains 1 plastic vial with a child-resistant closure. The composition includes:

• Active Ingredient (per capsule): Palbociclib — 100 mg.
• Inactive Excipients: Microcrystalline cellulose, lactose monohydrate, sodium starch glycolate, colloidal silicon dioxide, magnesium stearate.
• Appearance: Hard gelatin capsules containing white to off-white powder. Supplied as 21 capsules per bottle, enclosed in an original cardboard box with manufacturer labeling and the official package insert.

Pharmacodynamics: Palbociclib reduces the phosphorylation of retinoblastoma protein (pRb), resulting in cell cycle arrest in the G1 phase. This halts the proliferation of CDK4/6-dependent breast cancer cell lines, including hormone receptor-positive (HR+) cohorts.

Pharmacokinetics: Following oral intake, maximum plasma concentrations (Cmax) are achieved within 6–12 hours. The absolute bioavailability of the drug is approximately 46%. Food intake, particularly a high-fat meal, increases absorption and ensures steady systemic exposure. Palbociclib is approximately 85% bound to human plasma proteins. The drug is extensively metabolized in the liver, primarily via the CYP3A4 enzyme and sulfotransferase pathways. The mean elimination half-life (T1/2) is approximately 29 hours, supporting a once-daily dosing routine. Excretion occurs predominantly as metabolites via feces (around 74%) and urine (around 17%).

Palnat 100 mg is indicated for the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer:

• 🔹 First-Line Therapy: In combination with an aromatase inhibitor (such as letrozole or anastrozole) as initial endocrine-based therapy in postmenopausal women or in men.
• 🔹 Subsequent Treatment Lines: In combination with fulvestrant in patients whose disease has progressed following prior endocrine therapy.

Dosage parameters and schedules are established exclusively by a clinical oncologist. Capsules must be swallowed whole with food, preferably at the same time each day:

• Standard Schedule (28-Day Cycle): The standard recommended starting dose is 125 mg once daily (for the 100 mg strength, the dosage is individually calibrated or managed by the physician). The capsules are taken consecutively for 21 days, followed by a 7-day treatment-free interval (two weeks on, one week off). A full treatment cycle comprises 28 days.
• Administration Rules: Do not chew, crush, open, or dissolve the capsule. If a patient vomits or misses a dose, an additional capsule should not be taken that day; the next scheduled dose should be taken as planned.
• Dose Modifications: In cases of hematological toxicity (e.g., severe neutropenia) or other adverse reactions, the daily dose is reduced in a stepwise fashion (from 125 mg to 100 mg, and if necessary down to 75 mg once daily).

The administration of Palnat 100 capsules is contraindicated in the presence of the following conditions:

• ⛔ Hypersensitivity: Documented hypersensitivity to palbociclib or any inactive component of the capsule formulation.
• ⛔ Special Patient Populations: Pediatric patients under 18 years of age (safety and efficacy have not been evaluated in children), pregnancy, and breastfeeding periods.
• ⛔ Dietary Restrictions: Concurrent consumption of grapefruit, grapefruit juice, or starfruit is contraindicated (as they drastically increase drug plasma exposure).
• ⚠️ With Caution: Exercise caution in patients with severe hepatic impairment (Child-Pugh class C), severe renal dysfunction requiring hemodialysis, active systemic infections, or severe lactose intolerance.

Palbociclib participates in clinically significant interactions with medications that modulate hepatic metabolic pathways:

• ❌ Strong CYP3A4 Inhibitors: Concomitant use with agents like ketoconazole, itraconazole, ritonavir, or clarithromycin significantly escalates palbociclib plasma exposure, increasing the incidence of severe toxicities. Avoid concurrent use.
• ❌ Strong CYP3A4 Inducers: Co-administration with rifampin, phenytoin, carbamazepine, phenobarbital, or St. John's wort accelerates palbociclib clearance, critically reducing its therapeutic efficacy.
• ❌ CYP3A4 Substrates with Narrow Therapeutic Index: Palbociclib can elevate the plasma concentrations of co-administered midazolam, alfentanil, cyclosporine, dihydroergotamine, or tacrolimus, requiring careful dose adjustments of those agents.

Based on its cytotoxic mechanism of action affecting cell division, Palnat poses a severe developmental risk to the unborn fetus:

• Fetal Risk Factors: Palbociclib can cause fetal harm, congenital structural abnormalities, or embryo-fetal death when administered to pregnant women. Use during pregnancy is strictly prohibited.
• Contraception for Females: Females of reproductive potential must utilize highly effective contraceptive methods during treatment and for at least 3 weeks (21 days) after the final dose of Palnat.
• Contraception for Males: Male patients with female partners of reproductive potential must use effective contraception during treatment and for at least 14 weeks after the last dose of the drug.
• Lactation: Breastfeeding should be discontinued during Palnat therapy and for at least 3 weeks following the final dose due to the risk of severe adverse reactions in the nursing infant.
• Fertility Implications: The drug can impair male fertility, suppress spermatogenesis, and lead to temporary or permanent infertility. Preservation of sperm samples may be considered prior to starting treatment.

CDK4/6 inhibitor therapy is frequently associated with hematological and constitutional adverse events that require routine clinical monitoring:

• 🟢 Hematological Toxicity (Very Common): Neutropenia (reduction in neutrophil counts, requiring complete blood count monitoring prior to each cycle), leukopenia, anemia, and thrombocytopenia.
• 💡 Infections: Heightened susceptibility to bacterial or viral infections (nasopharyngitis, influenza, urinary tract infections) due to decreased immune function.
• 🟡 Gastrointestinal and Skin Reactions: Nausea, diarrhea, stomatitis (inflammation of oral mucosa), vomiting, fatigue, alopecia (hair thinning or loss), rash, dry skin, and hand-foot syndrome.
• 🟠 Interstitial Lung Disease (ILD): A rare but serious adverse event (pneumonitis) presenting as pulmonary inflammation.
• ⚠️ Urgent Clinical Signals: If a patient develops a fever (above 38 degrees Celsius), severe chills, sore throat, new or worsening cough, or shortness of breath, they must seek immediate emergency medical care (risk of febrile neutropenia).

Clinical data concerning acute systemic overdose with palbociclib are scarce, but excessive doses amplify expected toxicities:

• Expected Symptoms: Overdosage is anticipated to induce severe bone marrow suppression (profound neutropenia, thrombocytopenia with bleeding risks) and aggravated gastrointestinal toxicities (severe nausea, unremitting diarrhea).
• Management Protocol: There is no known specific antidote. Treatment should consist of standard supportive and symptomatic measures under medical supervision. Regular complete blood counts are mandatory. Hemodialysis or peritoneal dialysis is completely ineffective due to palbociclib's high plasma protein binding properties.

To preserve the chemical integrity of Palnat capsules, standard environmental storage parameters must be observed:

• 🌡️ Temperature Controls: Store in the original bottle at a temperature not exceeding 30 °C. Protect from excessive heat and direct sunlight.
• 📦 Moisture Mitigation: Keep the bottle tightly sealed. Do not remove the desiccant canister from the original bottle or transfer capsules to unapproved containers.
• 👶 Safety Precautions: Keep out of the reach of children, adolescents, and domestic pets. As a cytotoxic compound, any unused capsules must be disposed of in accordance with hazardous medical waste regulations.
• ⏳ Shelf Life: The shelf life is 24 months from the date of manufacture. Do not ingest the medication past the expiration date displayed on the outer box and bottle label.