Fentanyl is an opioid analgesic. Fentanyl interacts predominantly with the opioid m-receptor. These m-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 patients 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 and the cough reflex, and constricts the pupils. Analgesic blood concentrations of fentanyl may cause nausea and vomiting by directly stimulating the chemoreceptor trigger zone, but nausea and vomiting are significantly more common in ambulatory than in recumbent patients, as is postural syncope. Opioids increase the tone and decrease the propulsive contractions of the smooth muscle of the gastrointestinal tract. The resultant prolongation in gastrointestinal transit time may be responsible for the constipating effect of opioids. Because opioids may increase biliary tract pressure, some patients with biliary colic may experience worsening rather than relief of pain.

While opioids generally increase the tone of urinary tract smooth muscle, the net effect tends to be variable, in some cases producing urinary urgency, in others, difficulty in urination.

At therapeutic dosages, fentanyl usually does not exert major effects on the cardiovascular system. However, some patients may exhibit orthostatic hypotension and fainting. Histamine assays and skin wheal testing in humans indicate that clinically significant histamine release rarely occurs with fentanyl administration. Assays in humans show no clinically significant histamine release in dosages up to 50 mcg /kg.

When patients titrated themselves to analgesic effect with IONSYSÃ? 40 mcg, serum concentrations were in the range of 0.4 to 1.5 ng/mL over the 24-hour dosing period.

Hypoventilation can occur throughout the therapeutic range of fentanyl serum concentrations and may occur at any time during therapy, especially for patients who have an underlying pulmonary condition or who receive doses of opioids or other CNS drugs associated with hypoventilation in addition to IONSYSÃ?. The respiratory effects of IONSYSÃ? should be monitored by clinical evaluation, including oxygen saturation, respiratory rate, and degree of sedation. After delivery of the maximum number of doses in the shortest possible time period (80 consecutive doses delivered over approximately 13 hours), the fentanyl serum concentration was in the range of 1.51 to 2.37 ng/mL, which is in the range that could result in respiratory depression.

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