What are suitable PRN (pro re nata) medications for nausea and constipation in a 92-year-old female resident in assisted living?

PRN Medications for Nausea and Constipation in a 92-Year-Old Lady in Assisted Living

For a 92-year-old female resident in assisted living, the most appropriate PRN medications are ondansetron 4-8 mg PO every 6 hours as needed for nausea and polyethylene glycol (PEG) 17g mixed in 4-8 ounces of fluid daily as needed for constipation.

Management of Nausea

First-line PRN options:

• Ondansetron 4-8 mg PO every 6 hours PRN is recommended for elderly patients due to its favorable side effect profile and effectiveness 1, 2
• Metoclopramide 10 mg PO every 6 hours PRN is an alternative option but carries risk of extrapyramidal side effects in elderly patients 1, 3

Second-line options (if first-line ineffective):

• Prochlorperazine 10 mg PO every 6 hours PRN may be considered, but has higher risk of sedation and falls in elderly 1
• Haloperidol 0.5-1 mg PO every 6-8 hours PRN can be effective but should be used with caution due to potential for QT prolongation 1

Considerations for elderly patients:

• Start with lower doses (e.g., ondansetron 4 mg rather than 8 mg) to minimize side effects 1
• Avoid medications with strong anticholinergic effects as they can cause confusion in elderly patients 4
• Monitor for drug interactions, especially with other CNS depressants 1

Management of Constipation

First-line PRN options:

• Polyethylene glycol (PEG) 17g mixed in 4-8 ounces of fluid daily PRN is the preferred first-line agent due to efficacy and safety profile 5, 6
• Bisacodyl 10 mg PO or suppository PRN can be used as an alternative stimulant laxative 1

Second-line options (if first-line ineffective):

• Lactulose 30-60 mL daily PRN is effective but may cause bloating and flatulence 1
• Magnesium hydroxide 30-60 mL daily PRN, but use with caution in renal impairment 1, 7

Preventive measures:

• Maintain adequate fluid intake if medically appropriate 1, 5
• Encourage physical activity as tolerated 5
• Consider prophylactic laxative if starting opioid therapy 5

Algorithm for Constipation Management

1. Initial assessment:

   • Rule out impaction and obstruction through physical exam 1, 5
   • Assess for other causes: medications, metabolic disorders, immobility 5

2. First intervention:

   • PEG 17g in 4-8 oz of fluid daily PRN 5, 6
   • Goal: one non-forced bowel movement every 1-2 days 1

3. If inadequate response after 2-3 days:

   • Add bisacodyl 10 mg PO or suppository 1
   • Consider glycerin suppository if impaction suspected 1, 8

4. For persistent constipation:

   • Reassess for cause and severity 1
   • Consider adding another agent (lactulose or magnesium hydroxide) 1
   • Consider tap water enema if severe 1

Algorithm for Nausea Management

1. Initial assessment:

   • Evaluate for causes: constipation, medications, metabolic disorders 1

2. First intervention:

   • Ondansetron 4 mg PO every 6 hours PRN 1, 2

3. If inadequate response after 24 hours:

   • Increase to ondansetron 8 mg PO every 6 hours PRN 1, 2
   • Or switch to metoclopramide 10 mg PO every 6 hours PRN 1, 3

4. For persistent nausea:

   • Consider combination therapy with different mechanisms of action 1
   • Reassess underlying causes 1

Important Considerations and Pitfalls

• Avoid long-term use of magnesium-based laxatives in elderly due to risk of toxicity, especially with renal impairment 7
• Avoid bulk-forming laxatives like psyllium (Metamucil) as they are unlikely to be effective and may worsen constipation if fluid intake is inadequate 1, 5
• Monitor for anticholinergic burden when prescribing multiple medications, as this increases risk of confusion and falls 4
• Be aware that benzodiazepines and certain antidepressants may worsen constipation in elderly patients 4
• Consider medication review to discontinue or reduce doses of constipating medications 9
• Remember that elderly patients in assisted living facilities have high rates of laxative use (>11%) and may already be taking other medications that affect bowel function 10, 11