Morphine and Urinary Retention
Yes, morphine can cause urinary retention, particularly in older adults and those with pre-existing urinary tract issues, with approximately 25% of postoperative patients affected, and elderly patients face substantially higher risk due to benign prostatic hyperplasia and polypharmacy. 1
Mechanism and Risk Profile
Morphine causes urinary retention through opioid receptor activation in the bladder and sphincter, resulting in failure of bladder contraction and increased sphincter tone. 1 This effect occurs regardless of administration route—systemic, epidural, or intrathecal morphine all inhibit bladder function through opioid receptors in both supraspinal and spinal micturition centers. 2, 3
Elderly patients are at substantially elevated risk due to: 1, 4
- Pre-existing benign prostatic hyperplasia in men
- Polypharmacy with multiple anticholinergic medications
- Compromised autonomic function
- Neurogenic bladder from diabetic autonomic insufficiency 5
The FDA drug label explicitly warns that concomitant use of morphine with anticholinergic drugs increases the risk of urinary retention, requiring monitoring for signs of urinary retention when these medications are combined. 6
Clinical Presentation and Timing
Urinary retention is more common during the early course of opioid treatment. 1 After epidural morphine administration, marked detrusor relaxation occurs shortly after injection with corresponding increases in maximal bladder capacity, lasting an average of 14-16 hours. 2 With intrathecal morphine pumps, urinary retention can develop even at low doses (2 mg/24 hr). 7
Critical Differential Diagnosis
Before attributing urinary retention solely to morphine in cancer patients, spinal cord compression must be excluded, as this is a life-threatening condition that can be missed. 1 Additionally, evaluate for other reversible causes common in elderly patients: 5, 8
- Fecal impaction (frequently overlooked)
- Urinary tract infection
- Restricted mobility
- Polyuria from uncontrolled diabetes
- In women: atrophic vaginitis, vaginal candidiasis, cystocele
Review all medications to identify drug-drug interactions, particularly other anticholinergics. 1, 4
Management Algorithm
Acute Management
Catheterization provides immediate relief for acute urinary retention. 1 In neonates and patients where catheterization is unsuccessful, methylnaltrexone (0.15 mg/kg IV) can reverse urinary retention within 20 minutes without affecting central analgesia. 9
Pharmacologic Interventions
Peripheral opioid antagonists are the preferred pharmacologic approach as they reverse urinary retention by blocking peripheral opioid receptors in the bladder without compromising pain control: 1
- Methylnaltrexone or naldemedine
- Low-dose naloxone infusion (0.25 mcg/kg/h) may be considered
Naloxone (0.8 mg IV) promptly reverses the bladder effects of epidural morphine, and prophylactic naloxone infusion started before epidural morphine can prevent urinary retention entirely. 2
Tamsulosin (alpha-blocker) has been reported beneficial, particularly in postoperative opioid use. 1
Opioid Rotation Strategy
Consider rotating to synthetic opioids like fentanyl, which have lower rates of urinary retention compared to morphine. 1 A meta-analysis of randomized controlled trials demonstrated that transdermal fentanyl has lower rates of urinary retention compared to oral morphine regimens. 5
Prevention in High-Risk Patients
For elderly patients initiating morphine therapy: 4
- Avoid combining multiple anticholinergic agents
- Document baseline urinary symptoms and post-void residual if available
- Monitor for decreased urinary output, suprapubic discomfort, or changes in voiding pattern during the first 1-2 weeks
- Address reversible causes including fecal impaction, restricted mobility, and urinary tract infections
Common pitfall: Failing to recognize that urinary retention from intrathecal or epidural morphine can be reversed by decreasing the dose—one case report showed complete reversal within 4 days after reducing intrathecal morphine from 2 mg/24 hr to 0.5 mg/24 hr. 7