Question

Why might a baby born with respiratory depression due to the use of fentanyl by its mother require more than one dose of naloxone?

Answer 1

Ans) Naloxone hydrochloride is essentially a pure opiate antagonist. The precise mechanism of action of the opiate antagonist effects of naloxone is not fully understood.

- Naloxone is thought to act as a competitive antagonist at mc, κ, and σ opiate receptors in the CNS; it is thought that the drug has the highest affinity for the μ receptor. In contrast to levallorphan or nalorphine, naloxone has little or no agonistic activity.

- When administered in usual doses to patients who have not recently received opiates, naloxone exerts little or no pharmacologic effect. Even extremely high doses of the drug (10 times the usual therapeutic dose) produce insignificant analgesia, only slight drowsiness, and no respiratory depression, psychotomimetic effects, circulatory changes, or miosis.

- In patients who have received large doses of morphine or other analgesic drugs with morphine-like effects, naloxone antagonizes most of the effects of the opiate.

- There is an increase in respiratory rate and minute volume, arterial PCO2 decreases toward normal, and blood pressure returns to normal if depressed. Unlike nalorphine or levallorphan, naloxone antagonizes mild respiratory depression caused by small doses of opiates. Because the duration of action of naloxone is generally shorter than that of the opiate, the effects of the opiate may return as the effects of naloxone dissipate. Naloxone antagonizes opiate-induced sedation or sleep. Reports are conflicting on whether or not the drug modifies opiate-induced excitement or seizures.