Intermittent Opioid Use Pharmacologic Treatment

analgesic onset within 30–45 min. Subcutaneous, intramuscular and intravenous IV dosing are also equivalent, but the onset of action is faster, typically within 15 min Mercadante 2012 . When switching between oral and IV routes, dos- ing must be adjusted using a standardized equi- analgesia table Table 9.2 . It is important to remind patients changing from IV to oral dosing that while the analgesic effect is expected to be similar between routes, the time to onset of anal- gesia is not. Short-acting doses are given as needed until a clear sense of the total daily opioid dose required to keep the patient comfortable is established. Once stable daily needs are determined and the need for pain medication is expected to persist, long- acting doses should be considered. Unless there are contraindications such as renal failure, morphine is generally used as the fi rst-line opi- oid. Initial doses should be calculated using a dose-per- kilogram basis Table 9.3 . Doses should be increased by 25–30 for uncon- trolled pain. Case 1: Initiating Opioid Therapy A 10-year-old, 30 kg boy presents to your outpa- tient clinic with a 3-month history of progressive right hip and knee pain. CT scan shows a pelvic lesion concerning for Ewing sarcoma, and now you and the family are planning an outpatient work-up of his tumor prior to starting therapy. The mother reports that he has been using fi ve doses a day of acetaminophen for pain relief. Eric says he feels like he’s being “stabbed in the leg” and rates his pain as 8 of 10 with little relief from the acetaminophen. He has no drug allergies. They are asking if he can try something else for pain relief. Plan Looking at the WHO pain ladder, you decide to move up to opioids for moderate pain. Since he will be outpatient, you decide on an oral route, noting the patient prefers tablets to liquid medi- cations. You decide to start with immediate- release morphine at a dose of 0.2–0.3 mgkg every 3 h as needed Table 9.3 . 30 0 2 0 3 6 9 kg mg po morphine kg mg po morphine × − = − . . You note that the smallest tablet preparation of immediate-release morphine is 15 mg, so you instruct him to take 7.5 mg 0.5 tab every 3 h as needed and to call if it is ineffective. Of note, prep- arations including hydrocodone rather than oral morphine would also be reasonable in this case.

9.4.3 Long-Acting Opioids

One should consider the use of long-acting opi- oids when a stable daily dose of opioids is achieved and a persistent use of pain medication is expected. As described above, long-acting agents should not be used for acute pain as they slowly release medication. Long-acting opioids allow for around-the-clock analgesia and are used in combination with short acting opioids that serve to manage acute or breakthrough epi- sodes of pain. The benefi ts of long-acting opioids include less use of breakthrough medication, improved sleep at night, improved comfort upon waking from sleep and less drowsiness. When determining the amount of long-acting opioids, it is important to calculate the previous day’s total opioid requirement oral morphine equivalent or OME. Long-acting opioids should be dosed at 12 to 23 of the total OME. Slow- release morphine is used as fi rst-line treatment and generally prescribed every 8–12 h. Doses should be reevaluated and titrated upwards if optimal pain control is not reached. This often occurs with disease progression or, less often, as a result of opioid tolerance. Table 9.2 Opioid equianalgesia conversions Medication Parenteral mg Oral mg Morphine 10 30 Oxycodone – 20 Hydromorphone 1.5 7.5 Oxymorphone 1 10 Fentanyl 0.1 a – Adapted from Friedrichsdorf and Kang 2007 ; McGhee et al. 2011 a This dosing is not equivalent for transdermal fentanyl patches. Please refer to the specifi c drug information sheet from the manufacturer for fentanyl transdermal patch equivalency. Fentanyl patches and methadone are also effective as long-acting agents but are generally reserved when therapy with morphine or oxyco- done has been unsuccessful or side effects have precluded their use. Equianalgesic conversions of fentanyl and methadone can be complicated and vary based on the total amount of OMEs. Methadone has unique pharmacokinetic proper- ties that must be taken into consideration due to a long half-life requiring initially frequent dosing but later only every 12–24 h dosing. Methadone is potentially benefi cial as it has less pruritus side effect and also may help treat concomitant nau- sea. A fentanyl patch can be a convenient way to provide pain medication delivery in the patient unable to easily take oral medications. Fentanyl and methadone should be prescribed by clinicians experienced in their use. Case 1 Continued Starting Long-Acting Opioids