Fentanyl is an opioid analgesic. Fentanyl interacts predominately with the opioid mu-receptor but also binds to kappa and delta-type opioid receptors. These mu-binding sites are discretely distributed in the human brain, spinal cord, and other tissues. In clinical settings, Fentanyl exerts its principal pharmacologic effects on the central nervous system. Its primary actions of therapeutic value are analgesia and sedation. Fentanyl may increase the patient's tolerance for pain and decrease the perception of suffering, although the presence of the pain itself may still be recognized. In addition to analgesia, alterations in mood, euphoria and dysphoria, and drowsiness commonly occur. Fentanyl depresses the respiratory centers, depresses the cough reflex, and constricts the pupils.

Fentanyl is indicated for the management of breakthrough pain in patients with cancer who are already receiving and who are tolerant to opioid therapy for their underlying persistent cancer pain. Patients considered opioid tolerant are those who are taking at least 60 mg of oral morphine/day, at least 25 mcg of transdermal Fentanyl/hour, at least 30 mg of oxycodone daily, at least 8 mg of oral hydromorphone daily or an equianalgesic dose of another opioid for a week or longer.

Oral-

• Starting Dose: The initial dose of Fentanyl should be 100 mcg.
• Re-dosing patients within a single episode: Dosing may be repeated once during a single episode of breakthrough pain if pain is not adequately relieved by one Fentanyl dose. Re-dosing may occur 30 minutes after the start of administration of Fentanyl and the same dosage strength should be used.
• Increasing the dose: Titration should be initiated using multiples of the 100 mcg Fentanyl tablet. Patients require to titrate above 100 mcg can be instructed to use two 100 mcg tablets (one on each side of the mouth in the buccal cavity). If this dose is not successful in controlling the breakthrough pain episode, the patient may be instructed to place two 100 mcg tablets on each side of the mouth in the buccal cavity (total of four 100 mcg tablets). Titrate above 400 mcg by 200 mcg increments bearing in mind using more than 4 tablets simultaneously has not been studied and it is important to minimize the number of strengths available to patients at any time to prevent confusion and possible overdose. To reduce the risk of overdose during titration, patients should have only one strength of Fentanyl tablet available at any one time.
• Dosage Adjustment: Generally, the dose of Fentanyl should be increased when patients require more than one dose per breakthrough pain episode for several consecutive episodes.

Injection-

• Fentanyl injection can be administered intravenously either as a bolus or by infusion & by intramuscular route also. The dose of fentanyl should be individualized according to age, body weight, physical status, underlying pathological condition, use of other drugs and type of surgery and anesthesia.
• Doses in excess of 200mcg are for use in anesthesia only. As a premedicant, 1-2 ml fentanyl may be given intramuscularly 45 minutes before induction of anesthesia. After IV administration in unpremedicated adult patients, 2ml fentanyl may be expected to provide sufficient analgesia for 10-20 minutes in surgical procedures involving low pain intensity. 10 ml fentanyl injected as a bolus gives analgesia lasting about one hour. The analgesia produced is sufficient for surgery involving moderately painful procedures. Giving a dose of 50mcglkg fentanyl will provide intense analgesia for some four to six hours, for intensely stimulating surgery.
• Fentanyl may also be given as an infusion. In ventilated patients, a loading dose of fentanyl may be given as a fast infusion of approximately 1 mcg/kg/min for the first 10 minutes followed by an infusion of approximately 0.1 mcg/kg/min. Alternatively the loading dose of fentanyl may be given as a bolus. Infusion rates should be titrated to individual patient response; lower infusion rates may be adequate. Unless it is planned to ventilate post operatively, the infusion should be terminated at about 40 minutes before the end of surgery.
• Lower infusion rates, e.g. 0.05-0.08 mcg/kg/min. are necessary if spontaneous ventilation .is to be maintained. Higher infusion rates (up to 3 mcg/kg/min) have been used in cardiac surgery. Fentanyl is chemically incompatible with the induction agents thiopentone & methohexitone because of wide differences in pH
• Use in elderly and debilitated patients: It is wise to reduce the dosage in the elderly and debilitated patients. The effect of the initial dose should be taken into account in determining supplemental doses.

Transdermal-

Intractable chronic pain:

• Adult: Patches deliver fentanyl in doses that range from: 12-100 mcg/hr. Doses should be individually titrated based on previous use of opioids. Opioid-naive patients: Initially, ≤25 mcg/hr; it is recommended to initially titrate w/ low doses of short-acting opioids before starting fentanyl patches. Patients receiving a strong opioid analgesic: Initial dose should be based on the previous 24-hr opioid requirements. During transfer to fentanyl patches, previous opioid treatment should be phased out gradually. If patient requires doses >100 mcg/hr, >1 patch may be used; consider alternative or additional therapy if doses >300 mcg/hr are required. Replace patch every 72 hr and apply the new patch to a different site; avoid using the same area of skin for a few days.
• Elderly: Dose reduction may be needed.

Administration

Tablet Administration: Patients should remove the tablet from the blister strip and immediately place the entire tablet in the buccal cavity (above a rear molar, between the upper cheek and gum). Patients should not attempt to split the tablet. The tablet should not be chewed or swallowed, as this will result in lower plasma concentrations than when taken as directed. The tablet should be left between the cheek and gum until it has disintegrated, which usually takes approximately 14-25 minutes. After 30 minutes, if remnants from the tablet remain, they may be swallowed with a glass of water.

Fentanyl is contraindicated in the management of acute or postoperative pain. This product must not be used in opioid non-tolerant patients. Fentanyl is contraindicated in patients with known intolerance or hypersensitivity to any of its components or the drug Fentanyl.

As with other narcotic analgesics, the most common serious adverse reactions reported to occur with Fentanyl are respiratory depression, apnoea, muscular rigidity, myoclonic movements, and bradycardia. Respiratory depression is more likely to occur with intravenous administration if a dose is given too rapidly and it rarely occurs with intramuscular administration.

Overdose Effects

In insufficient overdosage, Fentanyl would produce narcosis, marked skeletal muscle rigidity. Cardio-respiratory depression and cyanosis may also occur. In the presence of hypoventilation or apnoea, oxygen should be administered and respiration should be assisted. A specific narcotic antagonist, such as naloxane, should be available for use as indicated to manage respiratory depression.

Opioid analgesics impair the mental and/or physical ability required for the performance of potentially dangerous tasks (e.g. driving a car or operating machinery). Patients taking Fentanyl should be warned of these dangers and should be counseled accordingly. The use of concomitant CNS active drugs requires special patient care and observation.

Chronic pulmonary disease: Fentanyl should be titrated with caution in patients with chronic obstructive pulmonary disease or pre-existing medical conditions predisposing them to respiratory depression. 

Head injuries and increased intracranial pressure: Opioids may obscure the clinical course of a patient with a head injury and should be used only if clinically warranted.

Cardiac disease: Intravenous Fentanyl may produce bradycardia. Therefore, Fentanyl should be used with caution in patients with bradyarrhythmias.

Hepatic or renal disease: Fentanyl should be used with caution because of the hepatic metabolism and renal excretion of Fentanyl.

Pregnancy & Lactation

Pregnancy category C. There are no adequate and well-controlled studies in pregnant women. Fentanyl should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Fentanyl is excreted in human milk; therefore Fentanyl should not be used in nursing women because of the possibility of sedation and/or respiratory depression in their infants.