Methadone: Essential Hospice Analgesic or Too Risky for Prime Time?

Transcription

1 Methadone Background Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? Developed originally as an antispasmodic and later used as an analgesic, starting in late 1940 s Used extensively as a treatment for opioid addiction starting in the 1960 s Increased use for treatment of chronic pain starting in 2000 Jim Joyner, Pharm.D, C.G.P. Director of Clinical Operations Outcome Resources Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 1

2 Methadone Pharmacology Potent mu- opioid receptor agonist (similar to morphine, greater efficacy) Has non-opioid analgesic mechanisms of action: N-methyl-D-aspartate (NMDA) antagonism (1) Inhibits reuptake of serotonin (1) Extremely lipid soluble (good bioavailability & offers a variety of administration routes) (2) Metabolized in liver to inactive metabolites (2) Renal impairment has no significant influence on clearance (3) Advantages of Methadone Extended dosing interval (8-12hrs) (2) The only long-acting oral opioid in liquid form The only long-acting oral opioid tablet that can be crushed Very well absorbed by sublingual route (4) Roxanol is NOT absorbed well by sublingual route (4, 5) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 2

3 more Advantages of Methadone Great for opioid rotation when: Tolerance develops to other opioids Intolerable side effects occur Opioid of choice in renal impairment (no toxic metabolites to accumulate, as w/ Morphine/Hydromorphone) Opioid of choice for neuropathic pain Available in variety of dosage forms Very inexpensive Neurotoxicity Risk of Morphine & Hydromorphone in Renal Impairment Morphine - 3 glucuronide (a) Myoclonus Hyperalgesia Allodynia Hydromorphone -3 glucuronide (b, c) Agitation Myoclonus Seizures a) Anderson, et al. (2003) J. Pain & Symptom Management) b) Lee. Palliat. Med 2001;15:26-34 c) Thwaites. Program and abstracts of the American Academy of Hospice and Palliative Medicine/Hospice and Palliative Nurses Association Annual Assembly; January 19-23, 2005 Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 3

4 Morphine pseudo-allergy Symptoms: itching, flushing, sweating, bronchoconstriction related to histamine release (mast cells in skin) (6) not mediated by IgE or T-cell (7) Methadone is a good alternative (no histamine release) a synthetic opioid from a different structural class than morphine does not trigger or exacerbate asthmatic attacks like morphine can (2) Advantage in neuropathic pain Neuropathic pain occurs in 40% of cancer patients a) More effective for neuropathic pain than other opioids. Additional non-opioid analgesic activity: Inhibition of the NMDA receptor Inhibition of serotonin re-uptake (SSRI) a) Grond, et al. Pain 1999:79 (1):15-20 Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 4

5 Cost Comparison for Long Acting Opioids Approximate cost of a 15 day supply of equivalent doses (based upon AWP) Drug Name Dose Price Oxycodone ER (OxyContin) 80mg BID $ Oxymorphone ER (Opana ER) 30mg BID $ Fentanyl Patch 100mcg Q72h $ Morphine ER 100mg BID $ Methadone 10mg BID $12.00 Long-Acting Opioids in Opioid Naïve Patients? Avoid starting any LA opioid in an opioid naïve patient Initial opioid responses may be unpredictable and vary from patient to patient Risk of toxicity may be magnified and extended if using a LA opioid to initiate therapy Patient may be considered as no longer opioid naïve after 5 days of opioid therapy with 60mg/day of morphine or equivalent opioid. Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 5

6 Methadone Dosage Forms Methadone: Negative Aspects Oral Tablets: 5mg, 10mg (may be crushed) 40mg dispersible tablet (restricted usage methadone maintenance detox clinics, hospitals only) Oral solution: 5mg/5ml, 10mg/5ml, 10mg/ml Sterile solution for injection 10mg/ml (IV, SC) Suppository (compounded) Unfamiliar to some clinicians (bi phasic analgesic duration) Negative connotation (opioid detox. use, drug addicts ) Respiratory depression may persist longer than analgesic effects (during initial dosage period) Drug interactions? Cardiac effects w/ high doses? No high strength tablets available Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 6

7 Methadone Kinetics by the Numbers 14 Time until detected in plasma after oral dose: 30 min. Time to reach maximum plasma conc. (T max): hr Plasma protein binding: 60 90% (alpha-1 acid glycoprotein rises in cancer methadone binds to this) Lipid solubility: 98% of drug that reaches central compartment is rapidly transferred to tissues 2% remains in blood compartment Plasma half-life (T 1/2) is bi-phasic: Initial or alpha phase: 2 4hr (distribution phase about 5 days ) Maintenance or beta phase: hrs (big differences b/w individuals) Kinetics of Methadone Distribution & Bi-phasic Analgesic Duration Extensive tissue distribution High degree of drug-tissue binding (only unbound drug is active) Reservoir of drug is created during distribution phase Steady-state reached in 5 days on average (distribution phase complete) Duration of analgesic effect is bi-phasic correlates w/ above 4-6 hours when therapy initiated 8-12 hours after repeated routine dosing (average of 5 days to reach steady-state level) Above have important implications for Methadone dosing Next Slide Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 7

8 Implications for Methadone Dosing Duration of analgesic effect: Before distribution phase complete: 4-6hrs After distribution phase complete: 8 12hrs Recognize increased risk of methadone accumulation during initial distribution phase ( first 5 days) avoid frequent dosage intervals if possible Prefer fixed routine Methadone dose: Q8h or Q12h interval Avoid methadone dose increases more frequently than q- 5 days Anticipate need for PRN analgesic for BTP during initial 5 days Use short-acting opioid (morphine, oxycodone, or hydromorphone) PRN for BTP Methadone for PRN BTP?? What Does a Typical Methadone Regimen Look Like? Methadone 10mg PO Q12h routine Morphine (solution or IR tab) PO 20 or 30mg Q2 4h prn BTP Reassess PRN usage after 5 days & increase Methadone dose if indicated Base Methadone dose increase on PRN morphine required during 24h period on day 5 of distribution phase Monitor daily during initial week of therapy Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 8

9 Several Published Methadone Conversion Methods MD Anderson Med Cntr Guidelines (Ayonrinde & Bridge) United Kingdom Model (Morely & Makin) Edmonton Model aka Canadian Model ( Bruera) Italian Method (Ripamonti) German Model (author?) All except MD Anderson guidelines use Q4h dosing initially, then gradually lengthen dosage interval - high risk for accumulation/toxicity Most methods are based on oral morphine equivalents for conversiondose calculation some do not account for differences in cross tolerance among opioids at higher doses Converting to Methadone Outcome Resources Conversion Guide (11,12) Total Daily Oral Morphine Dose Morphine to Methadone Ratio <100mg 5: mg 10: mg 12:1 >1500mg 15:1 Adapted from MD Anderson Cancer Center guidelines, Ayonrinde and Bridge (Med J Aust 2000), and Ripamonti (Cancer Pain & Palliative Care 1999) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 9

10 Rationale for Sliding Scale Conversion Chart: Morphine to Methadone Tolerance to analgesic effects develops to all opioids over time with continuous treatment The higher the current dose, the higher likelihood of greater tolerance to the current opioid Cross-tolerance from one opioid to another is incomplete The sliding-scale chart is an attempt to account for incomplete cross-tolerance b/w Morphine & Methadone Opioid Equivalent Dosage Chart Drug Oral Dose Parenteral Dose Morphine 30mg 10mg Hydromorphone 7.5mg 1.5mg Oxycodone 20mg Methadone See methadone guidelines Hydrocodone 30mg Codeine 200mg Propoxyphene 180mg Meperdine 300mg 75mg Fentanyl Patch 0.3mg/24h topical (12.5mcg/hr) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 10

11 Morphine Conversion Factor Chart Drug Multiply current dose by this factor to equal oral Morphine dose Hydromorphone oral 4 Hydromorphone IV 20 Oxycodone 1.5 Morphine IV, SC 3 Methadone See methadone guidelines Hydrocodone 1 Codeine 0.15 Fentanyl patch 25mcg/hr patch roughly = 50mg Oral morphine/day (ratio of 1:100) Key Points of Outcome Resources Methadone Conversion Guideline Based on MD Anderson Cancer Center guidelines Employs fixed dose at long routine interval (8-12h) from day 1 Does NOT rely on PRN methadone usage Emphasizes use of a short-acting opioid for BTP (i.e. morphine) Sliding scale equivalency ratios account for incomplete crosstolerance at higher doses Works well for patients on low or high dose opioid therapy Less risk of methadone accumulation/toxicity than other methods Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 11

12 Conversion Case Study #1 Ima Payne: 71 year old female with lung cancer, mets to the bone, and painful diabetic neuropathy. Current pain meds: Fentanyl patch 250mcg Q72h & PRN Vicodin ES 10/750 (7 tabs daily) Has persistent c/o severe burning, shooting pains in her legs, despite current pain meds What s can we do to improve pain control? Decision to convert A decision is made to convert from Fentanyl to methadone to try and achieve a better response to her pain. Rationale: Neuropathic pain is not responding to current meds She can swallow tablets Fentanyl is expensive She is receiving 5250mg Acetaminophen/day May not be a candidate for TCA therapy due to age Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 12

13 Determine Total Daily Oral Morphine Equivalent From the morphine conversion factor chart: Fentanyl 250mcg/hr = Oral morphine? mg/day Hydrocodone/Apap 10/750; 7 tabs = Oral morphine? mg/day Total daily oral morphine equivalent =? Morphine Conversion Factor Chart Drug Multiply current dose by this factor to equal oral Morphine dose Hydromorphone oral 4 Hydromorphone IV 20 Oxycodone 1.5 Morphine IV, SC 3 Methadone See methadone guidelines Hydrocodone 1 Codeine 0.15 Fentanyl patch 25mcg/hr patch roughly = 50mg Oral morphine/day (ratio of 1:100) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 13

14 Oral morphine equivalent From the morphine conversion factor chart: Fentanyl 250mcg/hr = 250mcg/25mcg = x 50mg Oral morphine/day = 500mg Oral morphine/day Hydrocodone/Apap 10/750; 7 tabs = 70mg hydrocodone x 1 = 70mg Oral morphine/day Total daily oral morphine equivalent = 570mg Methadone conversion Using the oral morphine equivalent, determine the appropriate conversion ratio from the table: Total Daily Oral Morphine Dose Morphine to Methadone Ratio <100mg 5: mg 10: mg 12:1 >1500mg 15:1 Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 14

15 Case Study Continued Convert oral morphine equivalent to methadone: From the morphine to methadone conversion chart: Ratio is 10:1 for this patient s current dose of 570mg/day Case Study Continued Convert oral morphine equivalent to methadone: From the morphine to methadone conversion chart: Ratio is 10:1 for this patient s current dose of 570mg/day 570mg/10 = 57mg total daily methadone dose Divide total daily dose by 2 = 28.5mg Q12h Round off to nearest 5mg increment = methadone 30mg Q12h Initiate methadone 12 hours after fentanyl patch removed (8) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 15

16 Converting back from methadone Conversion we have described here is ONLY for conversion of other opioids TO methadone Conversion FROM methadone to another opioid must take into account the extensive half-life of methadone (related to tissue binding and wide distribution) Methadone Side Effects Common to All Opioids Constipation Sedation Nausea/vomiting Confusion, delirium (reported to be less with Methadone) Hypotension Respiratory depression (more prolonged with Methadone) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 16

17 Opioid Respiratory Depression General risk factors: opioid naïve patient introduction of fentanyl patch in opioid naïve pt. rapid escalation of the opioid dosage (especially long-acting opioids) presence of sleep apnea frail elderly and severely debilitated patients combination with other drugs that contribute to respiratory depression (benzodiazepines, phenobarbital, sedative-hypnotic drugs) Little difference in risk among opioids w/ equi-analgesic doses (2) Less common with oral opioid therapy, than injection or transdermal forms (2) Tolerance to respiratory depression develops rapidly (14) Potential Methadone Cardiac Side Effects EKG changes: possible prolonged QT interval Potential for serious arrhythmia (torsades de pointes). Rare. Not usually associated with low dose methadone (<200mg/day) -Reddy, Fisch, Bruera; J Pain Symptom Manage 2004;28(4): No clinical confirmation of this effect with oral methadone; only IV (retrospective study) -Reddy, Willey, Burkett, Fisch, Bruera; Program/Proceedings: 39 th Annual Mtg. of Amer. Soc. Clin. Oncologists 2003 Patient Risk Factors for proglonged QT interval: Cardiac hypertrophy or conduction disorder Methadone doses > 200mg/day (Warning methadone package insert labeling) Low potassium & or magnesium levels (use caution with diuretic therapy) Combination with other drugs that prolong QT interval (some 35 other drugs have FDA approved warnings for this ) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 17

18 Methadone Drug Interactions Primary means of metabolism: demethylation by CYP-3A4 (Lesser metabolism: CYP-2D6) CYP-3A4 activity varies considerably among patients Variation in 3A4 metabolic activity is responsible for large differences methadone bioavailability and difficulty of predicting interactions Methadone interactions are generally of a delayed onset, and of moderate severity Short-term changes in methadone blood levels not often associated with clinically significant changes (due to large vol. of distribution) Management recommendation: careful observation & adjustment of methadone dosage, if indicated on the basis of clinical response. Some drugs that may increase activity of Methadone (by decreasing the metabolism of Methadone) SSRI s Prozac(fluoxetine), Paxil (paroxetine), Luvox (fluvoxamine). Newer SSRI s not as significant (Citalopram, Escitalopram) Elavil (amitriptyline) Antifungals Fluconazole, ketoconzole Antibiotics: Ciprofloxacin, erythromycin, Clarithromycin Chronic alcohol consumption Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 18

19 Some drugs that Decrease activity of Methadone (by increasing the metabolism of Methadone) Other Methadone Drug Interactions Rifampin Carbamazepine (Tegretol) Phenytoin (Dilantin) Phenobarbital Risperidone (Risperdal) Protease Inhibitors Acute high dose alcohol use Additive effects upon respiratory depression w/ other meds: -anxiolytics, sedative-hypnotics, alcohol, muscle relaxants, & other opioids Additive chance of QT interval prolongation w/ other meds that have that effect tricyclic antidepressants, anti-arrhythmics, antipsychotics, macrolide antibiotics Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 19

20 Case study #2 Adam Able: a 68 year old man with severe cancer pain. Dx: Pancreatic CA, CHF, Renal insufficiency Currently on MS-Contin 130mg Q8hr, since his last morphine dose increase has experienced myoclonic tremors & mental status changes (hallucinations, confusion) pain fairly well managed on this dose Roxanol 30mg PRN (using 1-2 doses per day) Patient and family are concerned about recent changes in his mental status and the tremors??? Conversion process Opioid rotation to methadone is considered so that he can avoid possible morphine neurotoxicity. First determine the total daily oral morphine equivalent for MS Contin 130mg Q8hr Determine the equivalent ratio of oral morphine equivalent to methadone from the Methadone Conversion Chart (5:1, 10:1, 12:1, or 15:1) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 20

21 Conversion process continued Determine total daily Methadone conversion dose by dividing OME by the appropriate ratio number Divide total daily methadone dose by 2 (round off ): mg Q12h Conversion dose OME for Mr. Able: MS Contin 130mg Q8h OME = 390mg/day Appropriate ratio: from Methadone Conversion Chart = 10:1 Methadone total daily dose: 390mg/10 = 39mg total daily methadone dose Divide total daily methadone dose by 2: 19.5mg Round off for ease of measurement: 20mg Q12h Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 21

22 Case study #3 Bert B: a 54 year old male with pancreatic cancer Meds: Fentanyl 250mcg q72hr Oxycontin 80mg Q12h Oxyfast 20mg Q2h prn BTP Pain was controlled initially, but Pain control has been steadily deteriorating over the past 2 weeks. He is taking 6 doses per day of the PRN med and rates his pain at 8 of 10. What s next for pain control? The next step for Mr B. A decision is made to rotate to Methadone since this patient is likely exhibiting tolerance to current therapy. First determine the total daily oral morphine equivalent Fentanyl 250mcg patch = mg oral morphine Oxycontin 160mg = mg oral morphine Oxyfast 120mg = mg oral morphine Total daily OME: mg Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 22

23 OME: Methadone conversion dose for Mr B. Fentanyl 250mcg patch = 500mg oral morphine Oxycontin 160mg = 240mg oral morphine Oxyfast 120mg = 180mg Total daily OME: = 920mg Appropriate ratio: from Methadone Conversion Chart = 12:1 Methadone total daily dose: 920mg/12 = 76.7mg total daily methadone dose Divide total methadone dose by 2 & round off : 40mg Q12h When is methadone the right choice? Severe neuropathic pain Poor pain relief/tolerance to other opioids (> 600mg oral morphine/day) Unacceptable side effects that could be signs of opioid neurotoxicity or pseudo-allergy (hyperalgesia, myoclonus, allodynia) Liver disease (no active metabolites) Chronic Renal Failure---may be the opioid of choice (no toxic metabolites as there is with MS, hydromorphone) When a low cost, long-acting opioid is indicated. Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 23

24 Methadone Bottom Line Methadone is an analgesic of indisputable value that continues to gain acceptance for chronic severe pain management. Methadone has no active metabolites Methadone is an inexpensive long-acting opioid with a rapid onset of action available in various dosage forms. Methadone is an excellent alternative from both a clinical and economic perspective. References 1. J. Palliative Medicine (1): Goodman & Gilman s The Pharmacological Basis of Therapeutics, 11 th edition (McGraw-Hill) 3. Clinical Pharmacology & Therap (3): Clinical Pharmacology & Therap (44): Clinical Pharmacology & Therap (47): Immunol Allergy Clin North Amer. 1991;111: Anesthesiology 1989; 71: Cancer 2004; 101(12): J. Pain and Symptom Management (5): Cancer 1996; 78(4): Program/Proceedings of 39 th Annual Meeting of American Society of Clinical Oncologists May 31-June 3, 2003; Chicago Ill. Abstract Med J Aust 2000; 173: Cancer Pain and Palliative Care,IASP, J Pain and Symptom Management 2004;28 (4): Pharmacological Research 50 (2004) Methadone: Essential Hospice Analgesic or Too Risky for Prime Time? 24