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Mechanism of Action Opioid
- Located on CNS and possible in peripheral nerve tissue
- ----CNS: responsible for transmitting nociceptive input to higher levels (pain transmission and interpretation)
- 1. Inhibit synaptic pain transmission (bc substance P)
- 2. Decrease neurotransmitter from the presynaptic terminal decreasing excitability of postsynaptic neuron
- 3. G proteins
- ---- activate G protein which inhibits opening of Ca channels on neuron, decreasing NT release for excitation
- ---- increase release of K which causes hyperpolarization, decreasing likelihood of restimulation
- ----Decreases synthesis cAMP (2nd messenger), decreases transmission of pain
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Peripheral Effects of Opioids
- Decrease excitability of sensory neurons
- ----Endogenous opioids (endorphins, Enkephalins) produced by leukocytes in peripheral tissues during painful inflammation and act locally on peripheral sensory terminals
- Opioids that work at the peripheral level have decreased CNS mediated side effects
- ----Bc don’t cross BBB
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Clinical Applications of Opioids
- Pain management (post surgery/injury) by altering the perception
- ----Moderate-to-severe
- ----Acute pain
- ----Surgery
- ----Trauma
- ----MI
- ----Alter the perception of pain rather than eliminating sensation
- ----Route of administration is important
- --------Parenteral more effective in chronic/severe pain
- Dosing schedules
- ----Oral
- --------More effective when given at regularly scheduled intervals
- Parenteral
- ----Continuous infusions into epidural or Intrathecal space provides optimal pain relief but causes GI side effects
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Adverse Effects Opioids
- Sedation
- Mental slowness
- Drowsiness
- Respiratory depression
- Orthostatic hypotension
- GI distress
- ----Nausea, constipation
- Tolerance
- Physical dependence
- Withdrawal syndrome
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Withdrawal syndrome
- 6-10 hrs after last dose, peak 2-3 days after drug stopped, last 5 days
- Body aches
- Diarrhea
- Fever
- Goose flesh
- Insomnia
- Irritability
- Loss of appetite
- Nausea/vomiting
- Runny nose
- Shivering
- Sneezing
- Stomach cramps
- Sweating
- Tachycardia
- Uncontrollable yawning
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Other Opioid Uses
- Anesthesia premedication
- Cough suppression
- Decrease GI motility
- Pulmonary edema
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Tolerance
Greater dose needed for effect due to enzyme induction
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Dependence
- Dependent on physiologic and psychologic need
- Exhibit withdrawal symptoms
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Methadone
Reduce addition from heroine
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Therapist concerns
- Education pts about GI motility and constipation
- ----Usually take laxative and GI stimulant
- Pt can use physical agents (heat, electrotherapy) and manual techniques (massage, relaxation techniques) to aid in opioid withdrawal
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