Opioid Flashcards
Opioids - MoA
Activation of opioid receptors leads to inhibition of adenylyl cyclase, and a decrease in the concentration of cyclic adenosine monophosphate, an increase in K+ conductance and a decrease in Ca2+ conductance.
The activated Gai subunit of the G protein directly inhibits the adenylate cyclase enzyme, and the Gbetagamma subunits are thought to mediate the changes at the Ca and K channels. These actions cause both presynaptic inhibition of neurotransmitter release from the central terminations of small diameter primary afferent fibers and postsynaptic inhibition of membrane depolarization of dorsal horn nociceptive neurons.
Opioid agonists - Effects
CNS: Analgesia, sedation, euphoria or dysphoria, miosis, respiratory depression and inhibition of coughing reflex, nausea and vomiting
Analgesia: produced by activation of opioid receptor in the spinal cord and at several supraspinal levels.
Sedation and euphoria due to effects on midbrain dopaminergic, serotonergic and noradrenergic nuclei.
Miosis (constricted pupils): produced by the direct stimulation of the Edinger Westphal nucleus of the oculomotor nerve parasymp stimulation of iris sphincter muscle.
Cardiovascular: Vasodilation (caused by histamine release from mast cells in peripheral tissues), Orthostatic hypotension (peripheral resistance and reduction in baroreceptor reflex activity). Pt w CAD the peripheral resistance reduction of cardiac work and myocardial oxygen demand.
GI, Biliary and Genitourinary system: Constipation ( intestinal smooth muscle tone), biliary sphincter tone and pressure exacerbation of pain in patients with biliary dysfunction or gallbladder attack.
Genitourinary: bladder sphincter tone, prolongation of labor, urinary retention
Neuroendocrine: inh of LH release. Stimulation of release of ADH and prolactin.
Immune system: Suppress the activity of some lymphocytes, incl natural killer cells high rate of infectious diseases in heroin addicts.
Dermal: flushing, pruritus, urticaria
Opioids - Adverse effects
Respiratory depression
Decreased Hypercapnic drive (stimulation of resp centers by increased CO2 levels) + little effect of hypoxic drive
Decreased Respiratory tidal volume and rate –> rate falls to 3-4 pr min after overdose
Increased intracranial pressure due to increased cerebral blood flow
Nausea and vomiting by stimulating the chemoreceptor trigger zone in medulla
Itching/pruritus, flushing reaction (histamine release by mast cells)
Allergic reactions
Tolerance: decrease in initial pharm effect observes after chronic or long-term adm. Results from down-regulation of opioid receptors. Not developed to miosis and constipation. Considerable tolerance to resp depp. Accompanied by physical dependence
Cross tolerance
Opioids - Contraindication and antidote
Closed-head injury
Naloxone
Strong opioid agonists
Morphine Fentanyl Sufentanil Alfentanil Remifentanil Meperidine Methadone Oxycodone
Which strong opioid agonists have some effect on Kabba receptor?
Morphine and Sufentanil
Morphine - Clinical use
Severe pain associated with trauma, MI and cancer.
MI: relieves pain and anxiety + dilating coronary arteries and decrease myocardial oxygen demand.
Which drugs is the diacetic acid ester of morphine?
Heroin
Metabolites of Morphine
Principle metabolite: 3-glucuronide (inactive)
6-glucuronide is more active than morphine + longer half-life. It contributes to analgesic effectiveness of morphine.
Most potent opioid agonists
Fentanyl
Sufentanil
Alfentanil
Remifentanil
Sufentanil - MoA
Strong mu receptor agonist. Some effect on kabba and delta receptors.
Fentanyl - Clinical use
Long-acting transdermal skin patch: Continuous pain relief for pt with severe or chronic pain
Mucosal, buccal and nasal spray: Breakthrough pain
Parenteral: preop and postop + adjunct to general anesthesia
Fentanyl - Adverse effects
Produces less nausea and vomiting.
Truncal rigidity when used as an adjunct to parenteral anesthesia.
Alfentanil - Clinical use
Part of anesthesia procedures
Remifentanil - Clinical use
Short term procedures and outpatient surgery
Meperidine - Clinical use
DOC for pain ass w labor and pt w biliary dysfunction or gallbladder attack because it has less pronounced action of smooth muscle.
Analgesia for obstetric or postsurgical analgesic.
Oral: moderate to severe pain in outpatient setting
Short-term: acute pain syndromes.
Meperidine - Adverse effects
Less constipation (Less pronounced effect on GI, biliary and uterine smooth muscle --> less likely to cause constipation or increased biliary pressure) High doses --> converted to toxic metabolite normeperide -->CNS excitation, convulsions and tremors.
Methadone - Clinical use
Ambulatory patients to treat opioid dependence (methadone maintenance program) or chronic pain.
Opioid-dependent pt: prevent craving for heroin or other opioids
Moderate opioid agonist
Codeine
Hydrocodone
Propoxyphene
Moderate opioid agonists - MoA
Are less potent than the strong opioid agonists. Because they do not produce maximal analgesia at doses that are well tolerated by patient, they are used in submaximal doses, and almost always combined with an NSAID analgesic.