A 67-year-old man comes to the hospital due to an acute worsening of chronic back pain associated with new-onset bilateral leg weakness and numbness. He has a history of colorectal cancer with vertebral metastases for which he has received colectomy, chemotherapy, and radiation treatment. The patient takes oral morphine sulfate for his back pain. Examination shows focal vertebral tenderness, along with reduced muscular strength, decreased sensitivity to light touch, and spasticity in both legs. Imaging studies reveal a vertebral compression fracture with cord compression. Surgical decompression is planned. Which of the following drugs may precipitate opioid withdrawal symptoms if used in this patient?

Question

A 67-year-old man comes to the hospital due to an acute worsening of chronic back pain associated with new-onset bilateral leg weakness and numbness.  He has a history of colorectal cancer with vertebral metastases for which he has received colectomy, chemotherapy, and radiation treatment.  The patient takes oral morphine sulfate for his back pain.  Examination shows focal vertebral tenderness, along with reduced muscular strength, decreased sensitivity to light touch, and spasticity in both legs.  Imaging studies reveal a vertebral compression fracture with cord compression.  Surgical decompression is planned.  Which of the following drugs may precipitate opioid withdrawal symptoms if used in this patient?

Quizplus · Accepted Answer

Opioids work by selectively binding to G protein-coupled opioid receptors, mimicking the actions of endogenous opioid peptides. However, long-term activation of mu-opioid receptors on nociception-transmitting neurons is associated with increased pain sensitivity (central sensitization) due to: Increased turnover of inhibitory opioid receptors (receptor downregulation) and decoupling of receptors from their second messenger system (receptor decoupling) Upregulation of excitatory N-methyl-D-aspartate (NMDA) receptors This manifests as an increasing dose requirement to provide the same level of pain relief (tolerance) and pain sensations triggered by benign stimuli (opioid-induced hyperalgesia). Opioid withdrawal can occur within 24-48 hours of acute cessation in opioid-tolerant patients and is characterized by nausea/vomiting, myalgias, dilated pupils, diaphoresis, and tachycardia. Buprenorphine is a partial opioid agonist that has low intrinsic activity (efficacy) for opioid mu-receptors. However, it binds with high affinity (potency) and can prevent binding of other opioid medications. Therefore, buprenorphine acts as an opioid receptor antagonist in the presence of full opioid agonists and can precipitate withdrawal in opioid-tolerant patients with chronic pain. (Choices B, C, D, E, F, and G) These other agents are full agonists of the opioid mu-receptor. Although they vary in potency, none have significant opioid receptor antagonist properties. Use of these drugs in equianalgesic doses should not cause withdrawal. Educational objective: Buprenorphine is a partial opioid receptor agonist that binds with high affinity but has low intrinsic activity. In patients on long-term opioid therapy, buprenorphine can displace other opioids and precipitate withdrawal. __________ References: Buprenorphine is a weak partial agonist that inhibits opioid receptor desensitization. (http://www.ncbi.nlm.nih.gov/pubmed/19494155)

A 67-Year-Old Man Comes to the Hospital Due to an Acute