Geriatric Psychopharmacology for PMHNPs: Safe Prescribing for Older Adults

How Aging Changes Drug Metabolism and Response

In the context of PMHNP CME requirements, Aging produces predictable pharmacokinetic changes that affect every psychiatric medication. Reduced hepatic blood flow and decreased CYP450 enzyme activity slow the metabolism of medications processed by the liver, including most psychiatric drugs. The practical result is that standard adult doses produce higher blood levels and longer half-lives in older adults.

Renal function declines with age even in the absence of kidney disease. By age 80, GFR is typically 50-70% of young adult values. This affects lithium clearance (requiring lower doses and more frequent monitoring), gabapentin dosing, and the excretion of active metabolites from medications like venlafaxine and risperidone.

Body composition changes also matter. Increased body fat relative to lean mass in older adults increases the volume of distribution for lipophilic drugs like diazepam and amitriptyline, dramatically extending their half-lives. Decreased plasma albumin in frail older adults increases the free fraction of highly protein-bound drugs like valproate and warfarin, increasing both therapeutic and toxic effects at standard doses.

Applying the Beers Criteria to Psychiatric Prescribing

The American Geriatrics Society Beers Criteria is the definitive guide for identifying potentially inappropriate medications in older adults. Several psychiatric medication classes appear prominently. Benzodiazepines are on the avoid list due to increased fall risk, cognitive impairment, and delirium risk. Tricyclic antidepressants are flagged for their anticholinergic burden, orthostatic hypotension, and cardiac conduction effects.

First-generation antipsychotics are potentially inappropriate due to extrapyramidal effects and fall risk. Even second-generation antipsychotics carry a black box warning for increased mortality in older adults with dementia-related behavioral disturbances. Anticholinergic medications broadly, including diphenhydramine, hydroxyzine at higher doses, and paroxetine, increase delirium and cognitive decline risk.

But the Beers Criteria is not a prohibition list. It is a clinical decision tool. Sometimes the medication on the list is the right clinical choice when alternatives are insufficient or contraindicated. The key is documenting the clinical rationale for prescribing a Beers-listed medication when you choose to do so: tried and failed alternatives, risk-benefit analysis, and enhanced monitoring plans.

Treating Depression and Anxiety in Older Adults

SSRIs remain first-line for geriatric depression and anxiety. Sertraline and escitalopram are preferred due to their relatively clean drug interaction profiles and lower anticholinergic burden. Paroxetine should generally be avoided in older adults due to its anticholinergic effects and short half-life that causes discontinuation symptoms.

Start SSRIs at half the standard adult dose. Sertraline 25mg, escitalopram 5mg, titrating slowly every 2-4 weeks. Response takes longer in older adults, often 8-12 weeks, so patience is essential. If the first SSRI fails, try a second before moving to alternative classes.

For treatment-resistant geriatric depression, venlafaxine XR is a reasonable second-line option with blood pressure monitoring. Mirtazapine 7.5-15mg at bedtime is useful for patients with insomnia and appetite loss, common in geriatric depression. Augmentation with low-dose aripiprazole (2-5mg) or lithium (targeting levels of 0.4-0.6 mEq/L) has evidence in treatment-resistant geriatric depression but requires careful monitoring.

Managing Insomnia and Agitation Without Benzodiazepines

Insomnia in older adults should first be addressed with sleep hygiene optimization and cognitive behavioral therapy for insomnia (CBT-I). When pharmacotherapy is needed, melatonin 0.5-2mg (low dose, not the 5-10mg commonly sold) is first-line. Trazodone 25-50mg at bedtime is a widely used option with a long safety record in older adults, though orthostatic hypotension and priapism are considerations.

Suvorexant (Belsomra) 10mg and lemborexant (Dayvigo) 5mg are orexin receptor antagonists with evidence in geriatric insomnia and lower fall risk than benzodiazepines or Z-drugs. These are appropriate when melatonin and trazodone are insufficient. Avoid zolpidem in older adults due to fall risk, next-day cognitive impairment, and parasomnias.

Agitation in older adults, particularly those with dementia, requires a non-pharmacological-first approach. Environmental modifications, structured activities, and caregiver education should precede medication. When pharmacotherapy is necessary, low-dose risperidone (0.25-0.5mg) or quetiapine (12.5-25mg) can be used short-term with informed consent about the increased mortality risk. Citalopram 10-20mg has emerging evidence for agitation in Alzheimer disease and avoids the antipsychotic black box warning.

The Art of Deprescribing: Reducing Polypharmacy Safely

Polypharmacy, typically defined as 5 or more concurrent medications, is nearly universal in older psychiatric patients. Each additional medication increases the risk of drug interactions, adverse effects, and medication errors. PMHNPs should approach every geriatric visit with a deprescribing lens.

Start by reviewing the complete medication list including over-the-counter drugs, supplements, and medications from other prescribers. Calculate the anticholinergic burden score using a tool like the ACB scale. Identify medications that were started for conditions that may no longer be present or for symptoms that could be caused by other medications in the cascade of prescribing.

Deprescribing should be done one medication at a time with slow tapers. Prioritize removing the medication with the highest risk-to-benefit ratio first. For psychiatric medications specifically, benzodiazepines and anticholinergic medications should be the first targets. Taper benzodiazepines by 10% every 2-4 weeks. Reduce anticholinergic burden by switching to lower-ACB alternatives rather than adding more medications to counter anticholinergic side effects.

Frequently Asked Questions

This article is for educational purposes only and does not constitute medical advice. Geriatric prescribing decisions should be made in collaboration with the patient’s full care team and individualized based on comprehensive geriatric assessment.