Can you provide comprehensive teaching points for ripretinib, including dosing, administration, monitoring, adverse effect management, dose adjustments, drug interactions, and contraception counseling?

Ripretinib Teaching Points

Ripretinib is administered at 150 mg orally once daily continuously for advanced gastrointestinal stromal tumors (GIST) after progression on at least three prior tyrosine kinase inhibitors (imatinib, sunitinib, and regorafenib), and should be continued indefinitely until disease progression or unacceptable toxicity 1, 2.

Clinical Indication and Line of Therapy

Ripretinib is the standard fourth-line treatment for metastatic GIST after failure of imatinib, sunitinib, and regorafenib 1. The pivotal INVICTUS trial demonstrated significant progression-free survival benefit (6.3 months vs 1.0 month with placebo, HR 0.15, p<0.0001) 3, 4. However, note that a recent trial comparing ripretinib with sunitinib as second-line therapy failed to show PFS improvement, though it had better tolerability 5.

Dosing and Administration

Standard Dosing

• 150 mg orally once daily continuously (no breaks) 2, 3
• Take with or without food
• Swallow tablets whole; do not crush or chew
• Continue treatment indefinitely until progression or intolerance

Dose Modifications for Adverse Reactions

Hold ripretinib for:

• Grade 3 or 4 adverse reactions
• Intolerable Grade 2 adverse reactions

Resume at reduced dose when toxicity resolves to Grade ≤1 or baseline:

• First dose reduction: 100 mg once daily
• Second dose reduction: 50 mg once daily
• Discontinue if unable to tolerate 50 mg daily 2

Drug Interaction Adjustments

Avoid strong CYP3A inducers (rifampin, phenytoin, carbamazepine, St. John's wort) - they decrease ripretinib exposure by 61% 6. If unavoidable, refer to approved labeling for specific dose adjustments 2, 6.

No dose adjustment needed with:

• Strong CYP3A inhibitors (itraconazole increases exposure by 99%, but monitor more frequently for adverse reactions) 6
• Gastric acid reducers (proton pump inhibitors, H2 blockers) - no effect on pharmacokinetics 6

No dose adjustment required for hepatic impairment, including severe impairment 7.

Monitoring Requirements

Baseline Assessment

• Complete blood count with differential
• Comprehensive metabolic panel including lipase
• Blood pressure
• Electrocardiogram if cardiac risk factors present
• Pregnancy test for females of reproductive potential
• Skin examination (document baseline lesions)

Ongoing Monitoring

• Blood pressure: Check at each visit, especially first 2 months
• Lipase: Monitor periodically (lipase elevation occurred in 5% as Grade 3-4) 3
• Liver function tests: Periodic monitoring
• Electrolytes: Monitor for hypophosphataemia, hyperkalaemia 3
• Skin examination: Regular assessment for new cutaneous malignancies 2, 4
• Cardiac function: Monitor for signs/symptoms of heart failure or decreased ejection fraction 2, 4

Timing of Adverse Events

Critical pitfall: 39.80% of adverse reactions occur within the first month of treatment, requiring intensive early monitoring 8. However, some reactions can emerge after one year of therapy 8.

Adverse Effect Management

Most Common Adverse Events (≥20%)

In order of frequency: alopecia, fatigue, nausea, abdominal pain, constipation, myalgia, diarrhea, decreased appetite, palmar-plantar erythrodysesthesia (hand-foot syndrome), vomiting 4.

Specific Management Strategies

Palmar-Plantar Erythrodysesthesia (Hand-Foot Syndrome)

• Most common dose-limiting toxicity 2
• Management: Topical emollients, urea-based creams, pain control
• Hold drug for Grade 3; resume at reduced dose when improved to Grade ≤1
• Preventive measures: avoid tight-fitting shoes/gloves, minimize friction, use thick cotton socks

New Primary Cutaneous Malignancies

• Critical warning: Skin squamous cell carcinoma and keratoacanthoma reported 2, 4, 8
• Perform dermatologic evaluation before treatment and every 2 months during therapy
• Manage with excision; ripretinib can continue without dose modification
• Counsel patients on sun protection and self-skin examination

Hypertension

• Occurred in 4% as Grade 3-4 3
• Management: Standard antihypertensive therapy
• Hold ripretinib for Grade 3 hypertension uncontrolled with medical management
• Resume at reduced dose when controlled to Grade ≤1

Cardiac Dysfunction

• Monitor for heart failure symptoms, decreased ejection fraction 2, 4
• Hold for Grade 3-4 cardiac dysfunction
• Consider cardiology consultation for symptomatic patients

Photosensitivity

• Advise sun protection: SPF 50+ sunscreen, protective clothing, avoid prolonged sun exposure
• Limit sun exposure during peak hours (10 AM - 2 PM)

Wound Healing Complications

Critical pitfall: Hold ripretinib at least 1 week before elective surgery 2. Do not administer for at least 2 weeks after major surgery and until adequate wound healing. For minor procedures, hold based on clinical judgment of wound healing risk.

Contraception Counseling

Females of Reproductive Potential

• Verify pregnancy status before initiating therapy 2
• Use effective contraception during treatment and for 1 week after the final dose 2
• Ripretinib can cause fetal harm based on mechanism of action and animal data 2

Males with Female Partners

• Use effective contraception during treatment and for 1 week after the final dose 2

Lactation

• Advise not to breastfeed during treatment and for 1 week after the final dose 2
• Unknown if ripretinib or metabolites are present in human milk

Special Populations

Hepatic Impairment: No dose adjustment needed for any degree of hepatic impairment, including severe 7. This is notable as ripretinib exposure increases by 99% in moderate and 163% in severe hepatic impairment, but combined ripretinib + active metabolite exposure increases are modest (51% and 37% respectively) and not clinically significant 7.

Geriatric Patients: No specific dose adjustment required 2.

Pediatric Use: Safety and efficacy not established 2.

Emerging Safety Signals

Real-world FAERS data identified new potential signals not prominent in clinical trials 8:

• Liver abscess (rare but significant signal strength)
• Prostatomegaly (rare but significant signal strength)
• Reinforced skin cancer risk (8 cases of squamous cell carcinoma reported)

These require clinical vigilance despite low frequency.

Patient Education Essentials

• Take at the same time each day for consistency
• Do not skip doses; if a dose is missed and it's been >8 hours until the next scheduled dose, skip the missed dose
• Report immediately: new skin lesions, chest pain, shortness of breath, severe hand/foot pain, severe abdominal pain
• Avoid grapefruit and grapefruit juice (moderate CYP3A inhibitor)
• Use sun protection rigorously
• Report all medications including over-the-counter and herbal supplements
• Do not stop treatment without discussing with oncologist, even if feeling well