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Palliative Care Perspectives : Chapter 4: Pain Management : Parenteral Administration of Opioids

Parenteral administration of opioids should be considered when:

  1. Other routes of administration, especially oral, are not feasible.
  2. Rapid dose titration is desired.
  3. Very high doses are required.
  4. Pain is very unstable, requiring rapid adjustments up and down.

Intravenous Route

The IV route allows the most rapid administration of opioids. This may be useful if rapidly titrating doses is necessary or in treating acute pain. IV administration of opioids offers little, if any, advantage over the SC route. In a prospective cross-over study patients were given IV and SC morphine infusions. There was no significant difference in perceived analgesia between the two routes or in side effects.45 For practical purposes IV and SC doses are equivalent. The IV route does have a slightly faster onset of action by a few minutes. For very rapid dose titration this may be an advantage. The IV route may be used if an IV is otherwise necessary or if long-term IV access is available - via a MediPort or percutaneous intravenous catheter (PIC) line, for example. Rarely should an IV be placed simply for the management of chronic pain. The SC route is safer and better tolerated and provides equivalent analgesia.

Intramuscular Route

opioids may be given via the IM route, although in the majority of cases the SC route is less painful and allows adequate absorption. Of commonly used agents, only meperidine (Demerol) must be given IM, as SC administration is irritating.9 Patients who require large doses of morphine - may also prefer the IM to the SC route, because injection of large volumes may be irritating.

Subcutaneous Route

opioid administration via the SC route is generally preferred to the IM. It is useful when short-acting agents need to be administered infrequently. For example, many patients who die over 24 to 48 hours and cannot tolerate oral opioids may be adequately managed with SC morphine injections alone or in combination with a nonoral basal medication, such as a fentanyl patch. The SC route is also frequently used for long-term parenteral administration of opioids.

I am amazed and appalled by the resistance of the medical community to the use of this route for both injections and infusions of opioids. SC injections of opioids (into fat) hurt much less than those into deeper, more tender muscle. Consider the irony. The whole idea is to relieve pain. Why would clinicians unnecessarily use a more painful route of administration? Demonstrating the power of culture, the environment, and resistance to change, I have noticed some residents I have trained continue to order IM injections when they leave our palliative care ward. When asked about this practice, some have guiltily admitted that they are tired of being hassled when ordering opioids via the SC route by other members of the health care team, attending physicians, nurses, and pharmacists, who question this behavior. While I am sympathetic to the pressure they may experience, courage is encouraged. Almost all of us will be in an emergency room somewhere, someday and require an opioid injection. Personally, I would like a doctor with the courage to do what is right for me (and is less painful), despite what others might say. (This anecdote also highlights the importance of improving education across the spectrum of health care disciplines. It is not enough just to train physicians.)

Continuous SC infusion of opioids (possible with all but meperidine) offers the following advantages:

  1. 1. Ease and comfort of starting infusion: SC infusion needles are quickly and easily inserted into SC fat, either in the abdomen or thigh. Unlike IVs, it is impossible to miss. Insertion is far less painful.
  2. 2. Lower infection rate: Relative to IVs, complications, especially infections, are far less common. SC needles are often changed every three days, but may stay in for up to a week.
  3. 3. Greater freedom of movement: SC pumps are often small and may be worn on a belt. As the arms are not used, patients may use their arms more freely, maximizing their independence of movement.

Problems with subcutaneous infusions

The major problem with SC infusions is that irritation of the subcutaneous tissue is often volume related. As a rule of thumb, if more than 3 cc's per hour are infused, irritation and pain may be experienced.

A problem can arise when high doses of opioids are needed and the SC route is desirable. It may be difficult to administer morphine, for example, if more than 30 to 40 mg per hour are required. Switching to the more potent hydromorphone, which may be delivered in concentrations as high as 10 mg/cc (equivalent of 50 to 70 mg of morphine/cc), will allow most patients to be successfully treated using the subcutaneous route.

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Palliative Care Perspectives

James L. Hallenbeck, M.D.

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Copyright 2003 by Oxford University Press, Inc.

The online version of this book is used with permission of the publisher and author on web sites affiliated with the Inter-Institutional Collaborating Network on End-of-life Care (IICN), sponsored by Growth House, Inc.