Laboratory Monitoring for Korlym (Mifepristone)
For patients starting Korlym, you must order serum potassium 1-2 weeks after initiation or dose increase and periodically thereafter, as hypokalemia occurs in 44% of patients and can develop at any time during treatment. 111
Essential Laboratory Tests
Potassium Monitoring (Critical)
- Timing: 1-2 weeks after starting or increasing dose, then periodically throughout treatment
- Rationale: Hypokalemia was observed in 44% of patients in clinical trials
- Action: Correct hypokalemia before starting Korlym; treat with IV or oral supplementation if it develops; consider mineralocorticoid antagonists if persistent despite supplementation 11
Thyroid Function Tests
- Monitoring: Close monitoring required with adjustment of thyroid hormone replacement as needed
- Rationale: Mifepristone affects thyroid function, and replacement doses may need adjustment 2
Lipid Panel
- Monitoring: Periodic HDL-cholesterol levels
- Rationale: Reductions in HDL-C have been observed during treatment (levels return to baseline after discontinuation) 1
Clinical Monitoring (Not Laboratory-Based)
Signs of Adrenal Insufficiency
Critical caveat: Serum cortisol levels remain elevated during Korlym treatment and cannot be used to assess for adrenal insufficiency 11. You must rely entirely on clinical signs:
- Weakness
- Nausea
- Increased fatigue
- Hypotension
- Hypoglycemia
If adrenal insufficiency is suspected, discontinue Korlym immediately and administer high-dose glucocorticoids (preferably dexamethasone) without delay. The long half-life of mifepristone (85 hours) requires prolonged glucocorticoid coverage 221.
For Female Patients
- Gynecologic evaluation: Refer any patient with vaginal bleeding for gynecologic assessment due to risk of endometrial hyperplasia (occurred in 38% of patients) 1
Additional Considerations
Baseline Assessment
- Correct hypokalemia before initiating therapy 1
- Review all concomitant medications for drug-drug interactions (mifepristone is a strong CYP3A inducer and inhibitor) 2
- Obtain baseline ECG if concerned about QTc prolongation risk 1
Common Pitfalls to Avoid
- Do not use cortisol levels to monitor treatment response or adrenal insufficiency - this is the most critical error. Cortisol remains elevated or increases during treatment 22
- Do not delay potassium monitoring - hypokalemia can occur at any time, not just early in treatment
- Do not assume normal baseline potassium means no monitoring needed - 44% develop hypokalemia during treatment
The FDA label emphasizes that mifepristone should only be used by clinicians with extensive experience in Cushing's disease, specifically because reliable biochemical markers for monitoring are not available 2.