1. Intractable nausea and vomiting
2. Bowel obstruction
3. Impaired swallowing
4. Impaired mental state with compromised ability to swallow medication; note that pain can still occur when patient obtunded and may account for restlessness and agitation
5. Unpleasant side-effects related to very high oral dose of narcotic, e.g. confusion, drowsiness, myoclonus; switching to alternate strong narcotic analgesic by oral route may suffice
   * Remember that oral route is preferred and is usually possible
   * Tolerance to narcotic appears to develop more rapidly when parenteral routes are used.

Methods of Administering Parenteral Narcotic Analgesics

Subcutaneous Infusion

Pumps for chemotherapy can be used to infuse narcotic analgesic over a 24-hour period, for days, weeks, or months (e.g. Pharmacia, MVP, Travenol Infusor, etc.).

Choose a drug with high solubility so that low volume yet high concentration can be given; Morphine 5, 20 or 50 mg/ml or hydromorphone (Dilaudid) either 2 mg/ml or 10 mg/ml preparation.

Use #25 butterfly needle and standard tubing; pump can be held in small sling or bag for mobile patient or can be worn on belt.

Advantages of this method are relative ease of giving high dose narcotic analgesic, usually with fewer side-effects than with oral route, allowing patient mobility (can be used at home and does not require patient to be in hospital).

Most pumps use 50 cc volume bag for solution; filling of bag with medication, setting of pump, insertion of needle, etc. must all be supervised by competent RN or MD; patient and/or relative, etc. must never be left solely responsible for maintenance of pump, filling of bag, etc.

Consider the example of a patient requiring very high dose narcotic analgesic, with poor pain control and marked drowsiness and confusion on 100 mg hydromorphone (Dilaudid), or one requiring over 500 mg morphine solution, in each case po q4h; this is a good indication for use of a parenteral method such as subcutaneous infusion, as follows:

Because pain control is poor, calculate dose of drug for subcutaneous infusion at slightly higher dose.

e.g. hydromorphone 120 mg po q4h
or morphine solution 600 mg po q4h.

This example will be for use of hydromorphone:

Hydromorphone 120 mg po q4h = 720 mg po per 24 hours
For hydromorphone, oral:parenteral ratio=2:1
(see chart of equianalgesic doses, Section 7.2);
therefore parenteral dose = 360 mg per 24 hours
= 15 mg per hour

If using hydromorphone 10 mg/ml solution
= 1.5 ml/hour
= 36 ml hydromorphone (10 mg/ml)
plus 14 ml sterile water (to fill 50 cc bag) per 24 hours
= 50 cc volume to run over 24 hours

* Most pumps also allow for s/c bolus dose narcotic for controlling breakthrough pain. Dose is approximately 10-20% of regular hourly dose, and can be given every hour if necessary.

Note: While adjusting dose, constantly assess pain level; use extra hydromorphone if required, either 2-4 mg po q3-4h or extra intravenous, intramuscular or subcutaneous if more appropriate; can still use small dose oral narcotic for breakthrough pain if required, e.g. 2-4 mg hydromorphone q3-4h.

Intermittent subcutaneous or intramuscular injections

Rarely required if pain is well controlled by oral or subcutaneous infusion route; if pain control poor by these methods and intermittent injections are required, this is indication to increase oral or infusion dose

For sudden, severe breakthrough pain or pain occurring in relation to change of position (e.g. turning in bed, transfer to stretcher, or brief procedure), a rapidly acting narcotic analgesic may be desirable to supplement the regular narcotic; diamorphine (heroin) is a good narcotic for this purpose, in dose of 5-10 mg subcutaneously or intramuscularly; but hydromorphone (Dilaudid) is equally good, 2-4 mg im or sc. (Hydromorphone is more readily available and less expensive.)

Note: Diamorphine (heroin) is available only in parenteral form in Canada; many hospital pharmacies are unwilling to dispense it.

Intravenous infusions

Rarely required for pain control alone but useful if intravenous required for other reasons. Use either morphine or hydromorphone (Dilaudid) in dose appropriate for pain control, e.g. 5-10 mg morphine per hour in mild to moderate pain, 40 or more mg per hour morphine for severe pain; when intravenous route is used, volume and solubility of drug are less important than for s/c infusion.

Method of intravenous infusion

1. Convert oral dose per twenty-four hours to parenteral equivalent per twenty-four hours (refer to table

e.g. morphine - oral:parenteral = 3:1
hydromorphone (Dilaudid) - oral:parenteral = 2:1

If narcotic chosen for intravenous infusion is different from narcotic presently being used, convert to appropriate equivalent dose (using table, Section 7.2) and use half this amount over next 24 hours (because exact equianalgesic doses are not adequately worked out and because of incomplete cross tolerance between different narcotics).

2. Give loading bolus at start of infusion as follows:
   • 5 mg morphine iv (or equivalent of other narcotic) if infusion rate is 15 mg/hr morphine or less
     • Number of mg equal to infusion rate for 15 to 30 mg morphine iv/hr
     • 30 mg morphine iv (or equivalent) for doses of 30 mg or more per hour morphine iv
     • Bolus doses should be given as slow iv injection
3. Take vital signs q1/2h x 4 hours after bolus injection
4. If pain control still poor, increase maintenance infusion by ten to twenty percent every few hours and monitor closely or give "rescue doses" equal to loading bolus q3h iv and alter maintenance dose as needed

Morphine oral:parenteral = 3:1

Hydromorphone (Dilaudid) oral:parenteral = 2:1

Transdermal Fentanyl (Duragesic Patch)

See Fentanyl (Duragesic). Much easier to use than subcutaneous infusion.

Epidural Narcotic

This method requires placement of a catheter into the lumbar or thoracic epidural space for delivery of drug either by intermittent injection or infusion.

An anaesthetist skilled in the technique is required and must also supervise this method of drug delivery over days, weeks, etc.

When carried out and supervised by a properly qualified MD this is a useful method of pain control when high oral dose of strong narcotic is not feasible or when it causes prolonged, unpleasant side effects.

Best for severe pain below mid-thoracic region (including lower limbs). Not advisable when spinal cord compression due to epidural tumour is present, because of variable absorption of narcotic.

Infection in epidural space is a potential complication but is rare in qualified hands.

Narcotic Equivalent Doses

All drugs compared to standard dose morphine 10mg im or 20-30 mg po.

*MS Contin suppository now available in 30, 60, 100, or 200 mg strengths for q12h dosing.

Watch for extrapyramidal side-effects and stop if they occur.