What are the oral medication options for pruritus in an elderly post-operative hip replacement patient?

Oral Medications for Post-Operative Pruritus in Elderly Hip Replacement Patients

For an elderly post-operative hip replacement patient with pruritus, start with gabapentin as the first-line oral agent, while strictly avoiding sedating antihistamines due to fall risk and cognitive impairment. 1

Context-Specific Considerations

If Opioid-Induced Pruritus (Most Likely in Post-Op Setting)

The pruritus is most likely opioid-related given the post-operative context, as opioid-induced pruritus affects 10-50% of patients receiving intravenous opioids. 2

First-line oral treatment:

• Diphenhydramine 25-50 mg orally is recommended as initial treatment for opioid-induced pruritus, despite general cautions about sedating antihistamines in the elderly. 2 This represents a specific exception where the benefit outweighs risk in the acute post-operative setting.
• Alternative: Promethazine can be used if diphenhydramine is ineffective. 2

Second-line options if antihistamines fail:

• Naloxone or naltrexone (μ-opioid receptor antagonists) with careful dose titration to avoid reversing analgesia. 2
• Nalbuphine (mixed agonist/antagonist) can treat pruritus without completely reversing pain control. 2
• Methylnaltrexone (peripheral opioid antagonist) may be considered as it has reduced ability to cross the blood-brain barrier. 2

Preventive agents shown effective in surgical settings:

• Mirtazapine 30 mg daily has been shown in RCTs to prevent morphine-induced pruritus in surgical patients. 3
• Gabapentin 1200 mg daily in divided doses has also demonstrated efficacy in preventing morphine-induced pruritus perioperatively. 3

Ondansetron is NOT recommended: Despite its use for opioid-induced nausea, ondansetron does not reduce the incidence or time to onset of opioid-induced pruritus compared to placebo, and more recent studies refute even its modest effect on severity. 3, 2

If Non-Opioid Related Pruritus (Less Likely but Consider)

First-line oral treatment:

• Gabapentin is the preferred oral agent specifically for elderly pruritus with a Strength D recommendation. 1
• Start at low doses and titrate up to 900-3600 mg daily as tolerated. 3

Second-line oral options:

• Fexofenadine 180 mg or loratadine 10 mg daily as non-sedating antihistamines. 1
• Cetirizine 10 mg (mildly sedating) may be used if non-sedating options fail. 1
• Consider combining H1 and H2 antagonists (e.g., fexofenadine with cimetidine) for enhanced effect. 1

Alternative systemic agents for refractory cases:

• Paroxetine or fluvoxamine (SSRIs) - paroxetine has been shown effective at doses as low as 5 mg in the evening. 1, 4
• Pregabalin 25-150 mg daily as an alternative to gabapentin. 3
• Aprepitant (NK-1 receptor antagonist) for refractory pruritus. 3, 1

Critical Safety Warnings for Elderly Patients

Absolutely contraindicated:

• Sedating antihistamines (hydroxyzine, diphenhydramine for non-opioid pruritus) are explicitly contraindicated in elderly patients due to fall risk, cognitive impairment, and anticholinergic burden (Strength of recommendation C). 1 This contraindication does NOT apply to acute opioid-induced pruritus where diphenhydramine remains first-line. 2

Use with extreme caution:

• NSAIDs should be used with extreme caution and are contraindicated in those with renal dysfunction. 3
• Codeine should not be administered as it is constipating, emetic, and associated with perioperative cognitive dysfunction. 3
• Opioids and tramadol require dose reduction (e.g., halved) in patients with renal dysfunction. 3

Important Clinical Pitfalls

• Do not start oral medications without adequate topical therapy trial (minimum 2 weeks with emollients and topical steroids) to exclude asteatotic eczema, the most common cause of elderly pruritus. 1
• Do not use ondansetron for opioid-induced pruritus despite its efficacy for opioid-induced nausea. 2
• Assess for medication-induced pruritus: Calcium channel blockers and hydrochlorothiazide are important causes of pruritic skin eruptions in older patients. 5
• Consider neuropathic pruritus which may cause localized or generalized truncal pruritus, especially in diabetic patients. 5
• When using opioid antagonists, careful dose titration is essential to avoid reversing analgesia and inducing significant pain. 2

When to Refer

Referral to secondary care is recommended if diagnostic uncertainty exists or primary care management fails to relieve symptoms. 1