indication

Carfentanil is similar (but more potent) to the opioid analgesic fentanyl. It is used as a tranquilizer for large animals.

pharmacology

Carfentanil acts primarily on the mu (some kappa and delta) opioid receptors as an agonist. It will induce similar effects of analgesia as other opioids, however, due to its potency, it will also induce strong side effects such as sedation. Consequently, that is why it is used as a tranquilizer for large animals. Carfentanil interacts predominately with the opioid mu-receptor. These mu-binding sites are discretely distributed in the brain, spinal cord, and other tissues. It exerts its principal pharmacologic effects on the central nervous system. Its primary actions of therapeutic value are analgesia and sedation. Carfentanil also depresses the respiratory centers, depresses the cough reflex, and constricts the pupils.

mechanism of action

Carfentanil binds very strongly to mu opioid receptors and acts as a competitive agonist. Opiate receptors are coupled with G-protein receptors and function as both positive and negative regulators of synaptic transmission via G-proteins that activate effector proteins. Binding of the opiate stimulates the exchange of GTP for GDP on the G-protein complex. As the effector system is adenylate cyclase and cAMP located at the inner surface of the plasma membrane, opioids decrease intracellular cAMP by inhibiting adenylate cyclase. Subsequently, the release of nociceptive neurotransmitters such as substance P, GABA, dopamine, acetylcholine and noradrenaline is inhibited. Opioids also inhibit the release of vasopressin, somatostatin, insulin and glucagon. Opioids close N-type voltage-operated calcium channels (OP2-receptor agonist) and open calcium-dependent inwardly rectifying potassium channels (OP3 and OP1 receptor agonist). This results in hyperpolarization and reduced neuronal excitability.