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Case Study – Certified Pain Management Pharmacist (CPMP)
CPMP Interactive Case Studies
Certified Pain Management Pharmacist (CPMP)
The Scenario: Opioid Rotation in a Cancer Patient
A 65-year-old male with metastatic pancreatic cancer is admitted for uncontrolled pain and adverse effects from his high-dose opioid regimen. The palliative care team has consulted you, the CPMP, to recommend and dose an opioid rotation to methadone to improve analgesia and reduce side effects. This is a high-risk conversion that requires careful calculation and planning.
Patient Data & Clinical Guidelines
Patient Profile
- Current Regimen: Morphine ER 100 mg PO q8h.
- Breakthrough Use: Morphine IR 30 mg PO q3h PRN, averaging 4 doses per day.
- Reported Issues: Pain score 7/10; constant drowsiness.
- Renal Function: eGFR 45 mL/min (Stage 3b CKD).
Methadone Conversion Guideline
- Methadone conversion is complex and variable. For patients on 300-600 mg of oral morphine equivalents (OME) per day, a conservative conversion ratio of 20:1 (Morphine:Methadone) is recommended.
- Due to incomplete cross-tolerance, the initial calculated daily dose of methadone must be reduced by 25% to 50% for safety.
- The long half-life of methadone requires frequent initial dosing (e.g., q8h) and slow titration.
Your Task
Task 1: Calculate the patient's total daily Oral Morphine Equivalent (OME) dose.
Answer:
The patient's total daily OME is 420 mg.
Methodology:
- Scheduled Dose: $$100 \text{ mg/dose} \times 3 \text{ doses/day} = 300 \text{ mg}$$
- Breakthrough Dose: $$30 \text{ mg/dose} \times 4 \text{ doses/day} = 120 \text{ mg}$$
- Total OME: $$300 \text{ mg} + 120 \text{ mg} = 420 \text{ mg/day}$$
Task 2: Using the 20:1 ratio and applying a conservative 50% reduction for cross-tolerance, calculate the final starting total daily dose of methadone.
Answer:
The final starting total daily dose is 10 mg of methadone.
Methodology:
- Initial Conversion: $$\frac{420 \text{ mg OME}}{20} = 21 \text{ mg methadone}$$
- Safety Reduction: $$21 \text{ mg} \times 0.50 = 10.5 \text{ mg}$$
- Final Dose: Round down to the nearest practical dose, which is 10 mg total per day.
Task 3: How should this 10 mg total daily dose be prescribed, and what is the pharmacokinetic rationale?
Answer:
The safest way to prescribe this is Methadone 2.5 mg PO every 6 hours or **Methadone 5 mg PO every 12 hours** (if only 5mg tablets are available). A q8h interval is also acceptable.
Rationale:
Methadone has a very long and unpredictable half-life (15-60 hours). When therapy is initiated, giving smaller, more frequent doses prevents high peak concentrations and allows the drug to accumulate to a safe steady state over several days. A once-daily dose at initiation would be dangerous as it would not provide consistent analgesia and could lead to toxicity as it accumulates.
Task 4: Why is methadone a good choice in this patient beyond just his high OME dose?
Answer:
Methadone is an excellent choice due to his **renal impairment (CKD)**. Morphine has active metabolites (M6G, M3G) that are cleared by the kidneys and accumulate in patients with renal dysfunction, which is the likely cause of his severe drowsiness and neurotoxicity. Methadone is primarily metabolized by the liver and has inactive metabolites, making it a much safer opioid choice for patients with renal failure.
The Scenario: Refractory Painful Diabetic Neuropathy
A 58-year-old female with poorly controlled type 2 diabetes presents with a 6-month history of burning, tingling pain in her feet. She was trialed on gabapentin by her PCP but had to discontinue it due to intolerable sedation. The patient is frustrated and her pain remains uncontrolled. As the CPMP, you must recommend a new evidence-based strategy and provide comprehensive counseling.
Patient Data & Clinical Guidelines
Patient Profile
- Diagnosis: Painful Diabetic Neuropathy
- Current Meds: Metformin, Lisinopril
- Failed Meds: Gabapentin (intolerable sedation at 600 mg/day)
- Labs: A1c 9.2%, eGFR > 60 mL/min
Neuropathic Pain Guideline (ADA)
- First-line agents include gabapentinoids (gabapentin, pregabalin) and SNRIs (duloxetine, venlafaxine).
- If a first-line agent is not effective or tolerated, a trial of an agent from the other first-line class is recommended.
- Intensive glycemic control is essential to prevent the progression of neuropathy.
Your Task
Task 1: The patient failed a gabapentinoid. What is the most appropriate next-line agent to recommend from a different first-line class?
Answer:
The most appropriate recommendation is to start an SNRI, specifically duloxetine (Cymbalta). As an SNRI, it belongs to a different first-line class than gabapentin (a gabapentinoid). Duloxetine is FDA-approved for painful diabetic neuropathy and is a strongly recommended agent in clinical practice guidelines.
Task 2: What is the appropriate starting dose for duloxetine, and what is the single most important counseling point regarding patient expectations?
Answer:
The appropriate starting dose is duloxetine 30 mg once daily. The single most important counseling point is that the pain relief is not immediate and builds slowly over time. You must counsel the patient that it may take 2-4 weeks to begin noticing a benefit and up to 8-12 weeks to feel the full effect. This manages expectations and prevents the patient from prematurely stopping the medication because it "didn't work" after a few days.
Task 3: Beyond treating the pain symptoms, what is the most critical underlying factor that must be addressed to prevent the neuropathy from worsening?
Answer:
The most critical factor is her severely uncontrolled diabetes. Her HbA1c of 9.2% is the root cause of the progressive nerve damage. While analgesic medications can help manage the pain symptoms, the only way to slow or prevent the progression of the neuropathy is to achieve intensive glycemic control. This requires intensifying her diabetes regimen (e.g., adding a second agent to metformin) and referring her for diabetes self-management education.
Task 4: The patient asks if she can use a topical agent as well. What is an appropriate over-the-counter recommendation?
Answer:
An excellent OTC recommendation is capsaicin 0.075% cream. It is an evidence-based option for localized neuropathic pain. You must provide crucial counseling on its use: it needs to be applied regularly (3-4 times a day) for several weeks to be effective, and it will cause a significant burning sensation initially that typically lessens with continued use. The patient should wear gloves during application and wash her hands thoroughly afterward.
The Scenario: Designing an Opioid-Sparing ERAS Protocol
A 45-year-old female is scheduled for a total abdominal hysterectomy. She is opioid-naïve and has a history of post-operative nausea and vomiting (PONV) with a previous surgery where she received codeine. She is very anxious about pain and side effects. As the CPMP, you have been tasked with designing a comprehensive, opioid-sparing multimodal analgesic plan based on Enhanced Recovery After Surgery (ERAS) principles.
Patient Profile and Formulary Options
Patient Profile
- Procedure: Total Abdominal Hysterectomy
- Opioid Status: Opioid-naïve
- Allergies: Codeine (severe nausea/vomiting)
- Renal Function: Normal
Available Formulary Analgesics
- IV & PO Acetaminophen
- IV Ketorolac, PO Ibuprofen
- Gabapentin
- IV Lidocaine Infusion
- Hydromorphone IV PCA
- Oxycodone PO
Your Task
Task 1: What is the core principle of multimodal analgesia, and why is it central to an ERAS protocol?
Answer:
The core principle is to target multiple pain pathways simultaneously by using a combination of analgesic agents with different mechanisms of action. This creates a synergistic or additive effect, providing superior pain relief while allowing for lower doses of each drug. It is central to ERAS because its primary goal is to **reduce opioid consumption**, which in turn decreases opioid-related side effects (like PONV, sedation, and ileus), leading to faster recovery and shorter hospital stays.
Task 2: Design a three-component, scheduled, around-the-clock non-opioid regimen for this patient, starting pre-operatively.
Answer:
- Pre-operative Dose: Give a one-time oral dose of Gabapentin 600 mg and PO Ibuprofen 600 mg 1-2 hours before surgery. This is pre-emptive analgesia to blunt the central sensitization caused by the surgical incision.
- Intra-operative/PACU: Administer IV Acetaminophen 1000 mg near the end of the case.
- Post-operative Scheduled Regimen: Continue IV Acetaminophen 1000 mg every 6 hours AND IV Ketorolac 15 mg every 6 hours (for a maximum of 48 hours).
Task 3: What is the most appropriate option for managing this patient's breakthrough pain in the first 24 hours post-op? Specify the drug, route, and delivery method.
Answer:
The most appropriate option is an IV Hydromorphone Patient-Controlled Analgesia (PCA) with no continuous infusion.
- Drug: Hydromorphone is an excellent choice as the patient has a documented severe intolerance to codeine (and by extension, likely other morphine-like opioids).
- Route: IV is appropriate for the acute, severe pain expected after this surgery.
- Delivery Method: A PCA is the safest method. For an opioid-naïve patient, it should be set up with a small demand dose (e.g., 0.2 mg), a lockout interval (e.g., 10 minutes), and crucially, no basal (continuous) infusion, as this significantly increases the risk of respiratory depression.
Task 4: How does your proposed multimodal plan specifically help mitigate her high risk for Post-Operative Nausea and Vomiting (PONV)?
Answer:
The plan mitigates PONV in two main ways:
- Opioid-Sparing Effect: The entire foundation of the plan (Acetaminophen, Ketorolac, Gabapentin) is designed to minimize the total amount of opioid needed. Since nausea and vomiting are primary, dose-dependent side effects of opioids, reducing the total opioid dose is the single most effective strategy to prevent PONV.
- Direct Anti-emetic Properties: Specific agents in the plan have known benefits for PONV. Both Gabapentin and NSAIDs (Ketorolac) have been shown in studies to independently reduce the incidence of PONV, separate from their opioid-sparing effects.
