What labs and monitoring parameters should be considered when prescribing Rexulti (brexpiprazole) to an elderly patient?

Laboratory and Monitoring Requirements for Rexulti (Brexpiprazole) in Elderly Patients

When prescribing Rexulti to elderly patients, initiate treatment at lower doses (0.5-1 mg) with gradual titration, and monitor for metabolic parameters, orthostatic hypotension, extrapyramidal symptoms, and cognitive changes, while being particularly vigilant about QTc prolongation and drug interactions given the altered pharmacokinetics and pharmacodynamics in this population.

Baseline Laboratory Assessment

Metabolic Monitoring

• Obtain baseline metabolic parameters including fasting glucose, lipid panel, and weight, as brexpiprazole can cause metabolic abnormalities and moderate weight gain, though the incidence is relatively low compared to other atypical antipsychotics 1, 2.
• Measure baseline blood pressure in both supine and standing positions to assess for orthostatic dysregulation, which is particularly problematic in elderly patients due to blunted baroreceptor sensitivity 3.

Cardiac Assessment

• Obtain baseline ECG to assess QTc interval, as brexpiprazole produces small changes in QT interval that require monitoring 1.
• Evaluate for conduction abnormalities, particularly in patients with pre-existing cardiac disease, as elderly patients have increased susceptibility to bradycardia and AV block due to degeneration of sinoatrial and atrioventricular nodal function 3.

Renal Function

• Calculate creatinine clearance using CKD-EPI Cr-cystatin C equation if available, as this is more accurate than creatinine-based equations alone in elderly patients who may have reduced muscle mass 3.
• Adjust dosing based on renal function, as elderly patients exhibit delayed elimination of many psychotropic medications 3, 4.

Additional Baseline Labs

• Check serum sodium if the patient has risk factors for SIADH, including advanced age (>80 years), concurrent diuretic use, history of hyponatremia, or volume depletion 5.
• Assess liver function tests, as hepatic metabolism may be impaired in elderly patients 3, 6.

Ongoing Monitoring Parameters

Early Treatment Phase (First 2-4 Weeks)

• Recheck sodium at 2-4 weeks if risk factors for SIADH are present, as this typically manifests early in treatment 5.
• Monitor blood pressure (supine and standing) to detect orthostatic hypotension, which increases fall risk in elderly patients 3.
• Assess for extrapyramidal symptoms (EPS), though brexpiprazole has a lower propensity for EPS than other antipsychotics due to lower intrinsic activity at D2 receptors 1, 2.
• Evaluate for akathisia, insomnia, and agitation, though these occur at relatively low incidences with brexpiprazole compared to aripiprazole 2.

Maintenance Monitoring

• Repeat metabolic parameters (glucose, lipids, weight) at 3 months, then annually or more frequently if abnormalities develop 1.
• Monitor for cognitive changes, as some cardiovascular and psychotropic drugs can increase neurocognitive impairment in elderly patients 3.
• Assess for tardive dyskinesia at each visit, though brexpiprazole has low potential for this adverse effect 2.
• Evaluate functional status and fall risk, as elderly patients are more susceptible to adverse effects including sedation and orthostatic hypotension 3.

Special Considerations for Elderly Patients

Dosing Adjustments

• Start at 0.5-1 mg daily rather than standard adult doses, as elderly patients require lower initial doses and more gradual titration due to altered pharmacokinetics and pharmacodynamics 3.
• Titrate slowly over prolonged periods, as elderly patients have reduced drug clearance and increased sensitivity to psychotropic medications 3, 4.
• Reduce doses further in patients with renal or hepatic impairment, as these conditions are common in elderly populations 3.

Drug Interaction Monitoring

• Review all medications including over-the-counter drugs, vitamins, and herbal supplements, as polypharmacy is extremely common in elderly patients and increases risk of adverse drug reactions 3, 7.
• Monitor for CYP2D6 and CYP3A4 interactions, as brexpiprazole is metabolized through these pathways 3.
• Be cautious with concurrent use of other QTc-prolonging medications, as elderly patients have decreased repolarization reserve 3.

Comorbidity Considerations

• Avoid use in patients with Parkinson's disease or dementia with Lewy bodies due to risk of extrapyramidal symptoms, similar to other antipsychotics 3.
• Exercise caution in patients with severe pulmonary insufficiency or myasthenia gravis, particularly if combining with benzodiazepines 3.
• Monitor more closely in patients with multiple comorbidities, as these affect both pharmacokinetics and pharmacodynamics of antipsychotic medications 3, 4.

Key Clinical Pitfalls to Avoid

• Do not assume normal renal function based on serum creatinine alone, as elderly patients may have reduced muscle mass masking renal impairment 3.
• Do not overlook orthostatic vital signs, as standing blood pressure should always be measured to detect postural hypotension 3.
• Do not prescribe standard adult doses initially, as this substantially increases risk of adverse reactions in elderly patients 3, 6.
• Do not fail to document all medications including non-prescription drugs, as unreported OTC medications and supplements can cause serious interactions 3.