Is it safe to use enzalutamide (Xtandi) in a patient with Parkinson's disease who is taking Parkinson medications?

Enzalutamide Use in Parkinson's Disease Patients: Proceed with Extreme Caution

Enzalutamide can be used in Parkinson's disease patients on PD medications, but requires heightened vigilance for neurological adverse events, particularly seizures, falls, and mental impairment disorders, which may be exacerbated by underlying PD pathology.

Critical Safety Considerations

Seizure Risk - The Primary Concern

The FDA label for enzalutamide (Xtandi) documents a baseline seizure risk of 0.9% in general populations 1. However, this risk increases substantially in patients with predisposing factors. In a dedicated trial of 366 patients with seizure risk factors, 2.2% experienced seizures, with three patients experiencing recurrent seizures despite continuation 1.

Key predisposing factors relevant to PD patients include:

• Use of medications that lower seizure threshold (~54% of at-risk patients) 1
• History of cerebrovascular events or TIA (~24%) 1
• History of traumatic brain injury (~28%) 1

Many Parkinson's medications—particularly dopamine agonists and amantadine—can lower seizure threshold 2. This creates an additive risk when combined with enzalutamide.

Falls and Fractures - Amplified Risk in PD

Enzalutamide increases fall risk from 6% (placebo) to 12% in clinical trials 1. For PD patients who already have compromised balance, gait instability, and postural hypotension, this represents a compounded hazard. Falls in the enzalutamide trials were not associated with loss of consciousness or seizure, suggesting a direct effect on motor function or balance 1.

Fracture rates also increase:

• 13% with enzalutamide vs 6% with placebo 1
• Grade 3-4 fractures: 3.4% vs 1.9% 1
• Median time to fracture: 420 days (range 1-2348 days) 1

Mental Impairment Disorders

The PROSPER trial documented mental impairment disorders in 5% of enzalutamide patients versus 2% on placebo 3, 4. This includes memory impairment and cognitive changes 5. Given that PD patients frequently develop cognitive impairment and dementia as the disease progresses, enzalutamide may accelerate or worsen these symptoms.

Drug Interaction Considerations

CYP-Mediated Interactions

Enzalutamide is a strong CYP3A4 inducer and moderate CYP2C9 and CYP2C19 inducer 6. This creates potential interactions with PD medications:

Specific concerns:

• Enzalutamide reduced midazolam (CYP3A4 substrate) exposure by 86% 6
• Reduced omeprazole (CYP2C19 substrate) by 70% 6
• Reduced S-warfarin (CYP2C9 substrate) by 56% 6

While most PD medications are not primarily metabolized through these pathways, selegiline (MAO-B inhibitor) undergoes extensive hepatic metabolism 7. Enzalutamide could theoretically reduce selegiline efficacy, though this specific interaction has not been studied.

Dosage adjustments required:

• If strong CYP2C8 inhibitors cannot be avoided: reduce enzalutamide to 80 mg daily 1
• If strong CYP3A4 inducers cannot be avoided: increase enzalutamide to 240 mg daily 1

Avoid Narrow Therapeutic Index Drugs

The FDA label explicitly recommends avoiding concomitant use with narrow therapeutic index drugs metabolized by CYP2C9, CYP2C19, or CYP3A4 6. While most PD medications don't fall into this category, careful review of the complete medication list is essential.

Cardiovascular Risks in PD Population

Enzalutamide increases ischemic heart disease risk (3.5% vs 2% placebo), with Grade 3-4 events in 1.8% vs 1.1% 1. PD patients often have:

• Autonomic dysfunction affecting cardiovascular regulation
• Orthostatic hypotension (worsened by dopaminergic medications)
• Higher baseline cardiovascular risk due to age

Management approach:

• Optimize cardiovascular risk factors (hypertension, diabetes, dyslipidemia) before starting 1
• Monitor for ischemic symptoms throughout treatment
• Discontinue for Grade 3-4 ischemic events 1

Practical Management Algorithm

Pre-Treatment Assessment

1. Seizure risk stratification:

   • Document history of seizures, head trauma, CVA/TIA
   • Review all medications for seizure threshold-lowering effects
   • Consider EEG if borderline risk factors present

2. Fall risk evaluation:

   • Assess baseline gait, balance, and postural stability
   • Document bone density (DEXA scan)
   • Initiate bone-protective therapy if osteopenic/osteoporotic 1

3. Cognitive baseline:

   • Formal cognitive testing (MoCA or similar)
   • Document baseline mental status

4. Cardiovascular optimization:

   • Control hypertension, diabetes, dyslipidemia
   • Baseline ECG
   • Assess for symptomatic orthostatic hypotension

Monitoring During Treatment

Monthly for first 3 months, then quarterly:

• Fall diary and fracture assessment
• Cognitive screening
• Blood pressure monitoring
• Cardiovascular symptom review

Immediate discontinuation if:

• Any seizure occurs 1
• Grade 3-4 ischemic heart disease 1
• Posterior reversible encephalopathy syndrome (PRES) develops 1
• Severe hypersensitivity reactions 1

PD Medication Management

No specific contraindications exist between enzalutamide and standard PD medications based on available evidence. However:

• Monitor for worsening PD symptoms (may indicate inadequate PD medication levels due to enzyme induction)
• Be vigilant for cumulative CNS effects (sedation, confusion, hallucinations)
• Avoid adding medications that further lower seizure threshold if possible

Special Considerations

Dysphagia Risk

Enzalutamide carries a warning for severe dysphagia or choking due to product size 1. PD patients frequently develop dysphagia as the disease progresses. Consider using the smaller 40 mg tablet formulation rather than 80 mg tablets or capsules to reduce choking risk 1. Ensure adequate water intake with each dose.

Posterior Reversible Encephalopathy Syndrome (PRES)

PRES has been reported with enzalutamide, presenting with seizure, headache, confusion, visual disturbances, with or without hypertension 1. This requires MRI confirmation and immediate discontinuation 1. PD patients may have difficulty articulating subtle neurological changes, necessitating careful questioning of caregivers.

Clinical Trial Evidence Context

The major enzalutamide trials (AFFIRM, PREVAIL, PROSPER, ARCHES, ENZAMET) generally excluded patients with predisposing factors for seizure 3, 4. No specific data exist on PD patients in these trials. The safety profile in PD populations must be extrapolated from general populations and patients with seizure risk factors.

The NCCN guidelines (2023-2025) establish enzalutamide as a Category 1 preferred option for metastatic castration-resistant prostate cancer 3, 4, but provide no specific guidance for PD patients.

Bottom Line Recommendation

Enzalutamide is not contraindicated in PD patients, but the risk-benefit calculation shifts unfavorably due to overlapping toxicities (falls, cognitive impairment, seizures). If the oncologic indication is strong (metastatic castration-resistant prostate cancer with limited alternatives), proceed with:

1. Comprehensive pre-treatment risk assessment
2. Aggressive fall prevention strategies (physical therapy, home safety evaluation, bone protection)
3. Closer monitoring intervals than standard patients
4. Lower threshold for dose reduction (120 mg or 80 mg daily) if any concerning neurological symptoms emerge 1
5. Caregiver education on warning signs requiring immediate medical attention
6. Consider alternative androgen receptor pathway inhibitors (apalutamide, darolutamide) if they have more favorable neurological profiles for this specific patient

The absence of PD as an exclusion criterion in the FDA label suggests use is permissible, but the cumulative neurological risks demand heightened clinical vigilance and shared decision-making with patients and caregivers about the amplified safety concerns.