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What Factors Affect a Sufficient Fentanyl Dose?

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  • Written By: Canaan Downs
  • Edited By: Kaci Lane Hindman
  • Last Modified Date: 30 November 2016
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Fentanyl is a narcotic used as an analgesic, or pain relieving medication, that is roughly 100 times as potent as morphine. It is also used as in anesthesia and as a sedative for children. The appropriate fentanyl dose varies considerably depending on the intended application and method of administration; it is important to use a lower fentanyl dose for patients who are young, elderly, debilitated, or suffer from diminished kidney or liver function. The medication may be administered by injection, lozenge, sublingual tablet, or transdermal patch. Due to opioid cross-tolerance, patients who have been using other narcotic drugs will require a higher initial fentanyl dose.

When used as an adjunct to anesthesia, fentanyl citrate is generally administered by intramuscular injection. As a premedication, dosages between 50 and 100 mcg should be used. If lozenges are used instead of injection, 5 mcg per kilogram of the patient's weight are standard and should not exceed 400 mcg. When using the medication as an adjunct to regional anesthesia, the dose is the same as that of intramuscularly injected anesthesia premedication, although it may also be administered as an intravenous drip over three to five minutes. Post-operative pain management doses may also be injected intramuscularly in doses of 50 to 100 mcg.

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Dosage considerations for the use of fentanyl in general anesthesia are more complex, varying widely according to the severity and duration of the procedure. Minor surgeries require 2 mcg per kilogram of body weight, while the dosage for normal surgeries is 2 to 20 mcg per kilogram and maintenance doses of 25 to 100 mcg, either intramuscularly or through an intravenous drip. Prolonged surgeries may require doses of 20 to 50 mcg per kilogram and maintenance doses of 25 mcg up to half of the initial dose administered.

As a pain management tool, the drug may be administered as a lozenge. The lozenge should be placed between the cheek and gums, allowing the drug to absorb through the mucous membrane of the mouth over 15 minutes. The standard initial dose for fentanyl administered in this way is 200 mcg.

The medication may also be given as a tablet that is allowed to dissolve sublingually, or beneath the tongue, with an initial dose of 100 mcg. When switching a patient from the lozenge to the tablet form of the drug, a transmucosal fentanyl dose of 200 to 400 mcg converts to a starting sublingual dose of 100 mcg. A transmucosal dose of 600 or 800 mcg, however, converts to an initial dose of 200 mcg as a tablet. A dose of 1200 mcg or 1600 mcg used as lozenges is equivalent to an initial sublingual dose of 400 mcg. If during the treatment of episodic pain a single dose is not sufficient, one more doses of the same strength may be administered after 30 minutes elapse from the time of the initial dose.

Transdermal patches are sometimes used to provide extended pain relief. They do not, however, permit the patient to easily adjust the dosage to manage pain levels and side effects. In the absence of an existing tolerance to opioid analgesics, the initial dose for a fentanyl patch should be 25 mcg per hour every 72 hours.

Certain drugs may also interact with fentanyl, potentiating its effects or increasing the incidence of side effects. Nitrous oxide may cause cardiovascular depression when co-administered with fentanyl, while central nervous system (CNS) depressants like tranquilizers, barbiturates, general anesthetics, and other narcotics may decrease the amount of the drug required to be effective. When using these drugs together, lower doses of both should be used.

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