What is an appropriate pain management regimen for chronic low-back pain in a patient with an estimated glomerular filtration rate of 35 mL/min/1.73 m², a positive urine drug screen for amphetamines, who refuses NSAIDs, acetaminophen, and epidural steroids, and for whom fentanyl is contraindicated?

Pain Management for Chronic Low-Back Pain in a Patient with Renal Impairment and Positive Amphetamine Screen

Given the patient's refusal of first-line therapies and renal impairment (GFR 35 mL/min), I recommend duloxetine 30 mg daily as the primary pharmacologic agent, with consideration for low-dose transdermal buprenorphine if duloxetine provides insufficient relief after 4-6 weeks of adequate trial.

Primary Recommendation: Duloxetine

• Duloxetine is FDA-approved specifically for chronic low back pain and has demonstrated statistically significant pain reduction compared to placebo in multiple trials 1
• The medication is particularly appropriate here because it does not require renal dose adjustment at GFR 35 mL/min and avoids the abuse potential concerns raised by the positive amphetamine screen 1
• Start with 30 mg daily for one week, then increase to 60 mg daily if tolerated, as the 60 mg dose showed efficacy without additional benefit at 120 mg 1
• Duloxetine demonstrated significant improvement in both pain scores and functional outcomes (Oswestry Disability Index) in chronic low back pain trials lasting 12-13 weeks 1

Second-Line Option: Transdermal Buprenorphine

If duloxetine provides inadequate relief after 4-6 weeks:

• Buprenorphine transdermal is one of the safest opioids for patients with renal impairment (GFR 35 mL/min) because it undergoes predominantly hepatic metabolism with no active metabolite accumulation 2, 3
• Start with the lowest available patch strength (5-10 mcg/hour), applied weekly 2
• Buprenorphine has a "ceiling effect" for respiratory depression, making it safer than full mu-agonist opioids, and its partial agonist properties may reduce abuse liability 2
• The positive amphetamine screen warrants caution with any opioid, but buprenorphine's pharmacologic profile makes it the least problematic opioid choice if one becomes necessary 2

Critical Monitoring and Precautions

For Duloxetine:

• Monitor for nausea (most common side effect in first 1-2 weeks), which typically resolves with continued use 1
• Assess liver function at baseline and if symptoms of hepatotoxicity develop 1
• Screen for suicidal ideation, particularly in the first 4 weeks of treatment 1

For Buprenorphine (if needed):

• Institute a bowel regimen with stimulant or osmotic laxatives prophylactically, as constipation occurs in nearly all patients on sustained opioid therapy 2
• Implement a pain management agreement and urine drug screen monitoring given the positive amphetamine screen 2
• Have naloxone available and educate the patient on overdose risk, particularly if combining with other sedating medications 2

Medications to Absolutely Avoid

• Morphine, codeine, tramadol, and meperidine are contraindicated at GFR 35 mL/min due to accumulation of neurotoxic metabolites causing myoclonus, seizures, and respiratory depression 2, 4
• Hydromorphone and oxycodone require significant dose reduction and extended dosing intervals at this level of renal function, with active metabolites that accumulate between doses 2, 3
• Standard NSAIDs would be problematic at GFR 35 mL/min (further nephrotoxicity risk), though the patient has already refused them 5

Alternative Non-Opioid Adjuncts

• Acetaminophen up to 3000 mg/day (not 4000 mg) is safe in renal impairment and should be offered again despite initial refusal, as it has the best safety profile 4
• Topical lidocaine 5% patches or diclofenac gel for localized pain areas provide analgesia without systemic absorption or renal concerns 4
• Gabapentin or pregabalin for neuropathic components require dose adjustment: start gabapentin 100-300 mg daily (not three times daily) at GFR 35 mL/min 4

Common Pitfalls to Avoid

• Do not prescribe short-acting oral opioids (hydrocodone, oxycodone) in this patient—the combination of renal impairment, substance use history, and chronic pain creates high risk for toxicity and misuse 5, 2
• Do not assume the patient understands why you're avoiding opioids—explicitly explain that their kidney function makes most opioids dangerous due to toxic buildup, not just concerns about the positive drug screen 2
• Avoid the temptation to prescribe muscle relaxants (cyclobenzaprine, methocarbamol) as they provide minimal benefit for chronic low back pain and cause significant sedation, particularly problematic with concurrent amphetamine use 5

Evidence Quality Considerations

The recommendation prioritizes duloxetine based on FDA approval for this specific indication with Level I evidence from multiple randomized controlled trials 1. The American College of Physicians guidelines emphasize that opioids should be reserved only for severe, disabling pain uncontrolled by other measures, and even then, guidelines from 2007 onward recommend against routine opioid use for chronic low back pain 5. The 2017 systematic review for ACP found that effects of all medications for chronic low back pain are generally small to moderate, with opioids showing no superiority over non-opioid options while carrying substantially higher risk 5.