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Opiod analgesics
UVa med pharmacology block 2
| Question | Answer |
|---|---|
| Morphine | Opiod agonist - selective mu agonist tx moderate/severe pain - opiod fx = pharmacodynamic tolerance, phys dependence, w/drawal sx's, GI stim, constipation T1/2 4hrs |
| Codeine | Morphine prodrug - demethylated into morphine tx low/moderate pain, cough same Fx as morphine |
| Heroin | Morphin prodrug - demethy'd into morphine, highly abused, fast action rapid penetration of BBB |
| Hydromorphone/oxymorphone | opiod agonist - phys affect approx to morphine tx moderate/severe pain t1/2 1-2hrs |
| Oxycodone/hydrocodone | opioid agonist phys fx approx to morphine better absorbed orally than morphine tx cough, low/moderate pain, fever T1/2 2-4hrs |
| Levorphanol | opioid agonist more favorable or/paranteral ratio than morphine |
| Meperidine | opioid agonist approx fx to morphine but decr spasmogenic, constipation, urine retention, no anti-tussive fx - tx pref'd for obstetrical alagesia T1/2 short fx: decr resp depression in newborns, does not alter induced labor |
| Diphenoxylate | opioid agonist tx diarrhea give w/atropine |
| Fentanyl/Sufentanyl | opioid 80X potency of morphine - tx anesthesia, cancer analgesic |
| Methadone | opioid approx fx of morphine but incr absorption, incr T1/2, decr w/drawal T1/2 15hrs |
| 1-acetylmethadol | opioid - promethadone tx opiate addiction - very long lasting depot |
| Propoxyphene | opioid sim to methadone decr efficacy than codeine (prescribed over codeine decr abuse potential) T1/2 6-12hrs |
| Pentazocin | mixed action opioid weak mu, powerful kappa agonist, decr potency to morphine, decr resp depression, incr dysphoria - tx moderate/severe pain CNS fx at high doses also incr BP, HR, NE/Epi release (bad for CAD) |
| Buprenorphine | mixed action opioid partial mu agonist tx moderate/severe pain, opiate addiction |
| Naloxone | opioid antagonist - antags all effects of opioids, no fx in untreated px's - tx opiate overdose/addiction in early phase of detox t1/2 short prod's w/drawal in tolerant px's |
| Naltrexone | opioid antagonist - antags all effects of opioids, no fx in untreated px's - tx opiate overdose/addiction in early phase of detox t1/2 much longer than naloxone |
| Dextromethorphan | Antitussive methoxylated form of dextrophan (isomer of levorphanol) - better absorbed than dextrophan - does not produce sidefx of morphine |
| Amitryptiline | TCA for neuropathic pain - first gen NE/5-HT reuptake blocker |
| Carbamazepine | anticonvulsant for neurpathic pain decr repetitive firing in axons |
| Gabapentin | anticonvulsant for neuropathic pain potent's effect of GABA in CNS |
| NSAIDs + acetominophen | COX inhibitors - analgesic effects additive w/opiates |
| What is the major biologically active product of POMC cleavage? | Endorphin |
| What is the major biologically active product of Proenkephalin cleavage? | Metenkaphalin and Leu-Enkephalin |
| What is the major biologically active product of Prodynorphin cleavage? | Dynorphin A and Dynorphin B |
| Most of the therapeutic and side effects of Morphine are from activation of what receptor? | The mu (looks like a u with a vertical line on the left) opioid receptor. Morphine is a full and selective agonist of this receptor. |
| Why are some opioids more efficacious than morphine? | They are more lipid soluble, and have a higher affinity for mu receptors (Morphine is only slightly lipid soluble, and has a moderate affinity for mu receptors). |
| Which compounds are Pro-drugs of morphine? | Codeine and Heroin. |
| Of the morphine pro-drugs, which is the quickest to convert and most powerful? | Heroine is the quickest and most powerful. Codeine is much slower to convert to morphine. Heroine is also very lipid soluble and penetrates the CNS quickly. |
| How do opioids theoretically decrease pain responses? | The Dorsal horn of the spinal cord contains opioid interneurons that "gate" pain nociceptors by pre and post-synaptic inhibition. |
| What are some ways to take advantage of the opioid analgesic effect, and the location of the receptors? | Because the opioid receptors are located in the spinal cord, an Epidural or Spinal analgesia give excellent results. |
| What drugs are sometimes mixed with Opiates to potentiate their response in powerful analgesic mixtures? What is this mixture indicated for? | TCA's and SSRI's potentiate opiate analgesia. They are combined with opiates to help ease pain associated with Cancer. |
| How do TCA's and SSRI's potentiate opiate analgesia? | Serotonin can stimulate opioid receptors. |
| What type of pain is best relieved by Morphine? | Continuous dull pain is better relieved than sharp intermittent pain. |
| How does morphine affect sensory modalities? | They are only altered in a minor fashion. |
| How does morphine affect consciousness? | It does not cause loss of consciousness. |
| What is the most dangerous side-effect of Morphine? | Respiratory depression. Rate and tidal volume are decreased, but the main effect is repiratory rate. This can be life-threatening. |
| How does Morphine depress respiration? | It depresses the primary respiratory pattern generator in the pons. |
| How is the respiratory drive maintained in a Morphinized patient? | Increased PCO2, and Hypoxic stimulation of Carotid chemoreceptors. *The hypoxic stimulation becomes essential to maintain respiration during an overdose. DO NOT give patient too much oxygen! |
| How does morphine affect coughing? | Morphine depresses the cough reflex. |
| Which morphine side effects are more commonly seen in ambulatory patients, as opposed to recumbent patients? | Nausea (40%) and Vomiting (15%) and postural hypotension. *The cardiovascular effects of vasodilation from morphine do not tend to affect BP in a recumbent patient. |
| What is the usefulness of the miosis effect of Morphine? | It is a minor effect, usually only when high amounts of drug are taken. Thus, it is an easy way to detect toxicity. "Pin-point" pupils. |
| How can Morphine be used to treat diarrhea? | It stops propulsion in the GI tract, but the spasmogenic contractions are a problem. This is remedied by combining Morphine with Atropine. Morphine + Atropine treats diarrhea. |
| How effective is Morphine orally as compared to an IM injection? | Only 1/5 to 1/6 the effectiveness (due to conjugation in the liver). |
| A patient presents with pinpoint pupils, a respiratory rate of 4/min. and is hypotensive. How would you treat this patient? | Ventilate the patient, and give repeated, small dose injections of Naloxone - Naloxone has a short duration, so repeated injections are necessary. |
| How common is morphine dependence? How does with withdrawal compare to ethanol or barbituates? | Physical dependence is very common, but withdrawal symptoms are less severe than from ethanol or barbituates. |
| How does Hydromorphone and Oxymorphone compare to Morphine in their effects? | Almost identical, but more potent. |
| How do Oxycodone and Hydrocodone compare to the effects of Morphine? | They are equipotent to morphine, but better absorbed orally. "Oxycontin" is a slow-release form of Oxycodone and is widely abused. |
| Why are Diphenoxylate and Loperamide not used intravenously or parenterally? | They are not soluble in water. |
| How does Fentanyl compare to Morphine? | It is 80 times more potent than morphine. |
| How is Fentanyl used clinically? | As an anesthetic with Droperidol (neuroleptic), and for pain relief (cancer) via skin patch. |
| What is Methadone used for clinically? | - Relief of moderate to severe pain - Replacement therapy of opiate addiction. *It is superior to morphine in a lot of ways (Oral absorption, longer half life, lesser withdrawal symptoms.) |
| What is unique about 1-Acetylmethadol? | It is a very long-lasting opiate that only needs to be administered every 2 or 3 days (it is active after 1st pass as Methadone). |
| What is 1-acetylmethadol used for clinically? | Used in the treatment of opiate addiction. |
| What is special about Pentazocin? What makes it different than morphine? | It is a "Mixed action" opioid. It has a weak antagonist for mu receptors and is a powerful kappa agonist. It is 1/2 to 1/5 as potent as morphine. |
| What are the two main Opioid Antagonists? | Naloxone and Naltrexone |
| What types of effects do Naloxone and Naltrexone have in the absences of an opiate agonist? | No effects, suggesting that opioids are not normally released in healthy unstressed individuals. |
| What is the difference between Naloxone and Naltrexone? | Nalonxone is given IV, and has a short half life. Naltrexone is given orally, and has a much longer half life. |
| What is Dextromethorphan? What is it used for clinically? | It is a methoxylated form of Destrorphan, and is absorbed better. It has no analgesic potency, and is used as an antitussive. |
| What is the most common opiate combination for intense pain? | NSAIDS + Morphine, or Oxymorphone (iv, or sc). |
| What type of dose of opiates is necessary for diarrhea treatment? | Much lower than those needed for analgesia. |
| What are some advantages to Replacement therapy for an opiate abuser? | Replacement therapy (Methadone, acetyl-methadol) - Does not dread withdrawal with legal access to drug / does not have to steal, buy illegal drugs, etc. - Instead of the patient shooting an IV, they take a pill every day or two with a long half life |
| How is Buprenorphine possibly helpful in treating opiate abuse? | It is a partial agonist of the mu receptor. Thus, it gives some benefits of naloxone, and some benefits of methadone. |
| Opioids are produced by proteolytic cleavage of what three main proteins? | POMC Proenkephalin Prodynorphin |
| What are the major effects of mu receptor activation? | Opening of K+ channels (inhibits discharge rate --> postsynaptic inhibition) Reduce opening of Ca++ channels (reduce amount of transmitter released) Inhibit Adenylate Cyclase (reduce amount of transmitter released) |
| Some opioid DRUGS (not endogenous) bind to Sigma and "Phencyclidine" receptors. What effects do these receptors have? | Psychotomimetic effects. They open a Ca++ channel by a glutamate receptor, which is involved in synaptic plasticity and memory encoding. |
| What would be the effect of using NSAIDs with Opioids? | The effects are additive, since Opioids affect central nerves, and NSAIDs affect peripheral nerves. |
| How does Morphine affect the GI tract? | - Decreased propulsive peristatltic contractions (can cause constipation) - Increased non-propulsive "spasmogenic" contractions (can cause epigastric pain) - Increases tone of urethral sphincter, and depresses mictuition reflex (difficult to urinate). |
| How does Levorphanol compare to Morphine? | Almost exactly the same, except it is more potent orally/parenterally than morphine. |
| Why is Meperidine preferred over Morphine in obstetrical analgesia? | It is the preferred opiate for obstetrical analgesia, because it produces less respiratory depression in newborns, and does not alter spontaneous oxytocin-induced labor (morphine can prolong labor) |
| What is Diphenoxylate used for? Why? | They are used for diarrhea, because in the therapeutic range they produce no perceptible CNS effects. |
| How does Methadone compare to Morphine? | It is absorbed better orally/parenterally, and has a longer half life (15hrs). |
| What is Propoxyphene used for clinically? | Mild to moderate pain. It's abuse liability is slightly lower than codeine, and is often prescribed in lieu of codeine. |
| What is the most often used opiate combination for low to moderate pain? | Oral Codeine, Oxycodone, or Hydrocodone + Aspirin. |
| What is the most preferred opiate for cough control? | Dextromethorphan, because it is not a controlled drug and is very safe. |
| How is Clonidine used in opiate abuse treatment? | Reduces aversive quality of physical withdrawal by attenuating intensity of autonomic components, and producing sedation. It also helps reduce craving. |
| Which opioids have anti-tussive effects? | Codeine and Dextromethorphan |
| How does Meperidine compare to morphine in effects? | It is equianalgesic, but is less spasmogenic, and produces less constipation, less urine retention, and does not inhibit cough. |
| What types of physiological effects does Pentazocin have? | Analgesia, respiratory depression (but lower than morphine). At high doses: Anxiety, disturbing thoughts, nightmares, hallucinations, increased BP and HR, elevate NE and Epi in blood. |
Created by:
sam.mrosenfeld
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