Drug presentation 1
agonist/antagonist
Barry Barkinsky
EMS-I, Paramedic
Receptor sites..
• Drugs either stimulate or inhibit the cells
normal biochemical actions
Receptor sites
• Point of attachment for hormones, viruses,
chemicals
Agonist / antagonist
Lock and key analogy
• Agonist works like
a lock and key
that works
Agonists
• Bind to the receptor
site and initiate the
expected response
• If you put the key in
the lock and turn it
the lock will open
• Side effect
Morphine sulfate
class: opioid agonist
• Prototype drug:
– Causes analgesia, euphoria,
sedation and miosis.
– Decreases preload and
afterload.
– May cause respiratory
depression and hypotension.
Morphine…mechanism
• Opiate agonist
• Cause the desired effect of pain
relief
• Also opens doors to respiratory
depression and hypotension
• Has successfully opened doors to:
– Pain relief / High
– Respiratory depression
– Hypotension via vasodilation
Morphine sulfate
• Indications
– Moderate to severe pain
– Cardiac pain indicative of MI
– Acute pulmonary edema
• Precautions:
– Hypersensitivity, undiagnosed head or
abdomen injury, bronchial asthma, COPD,
severe respiratory depression, pulmonary
edema due to chemical agent
Fentanyl (sublimaze)
•
•
•
•
•
potency many times that of morphine.
Schedule II drug
Also seen as duragesic or actiq
High potential for respiratory depression
Anesthetic and analgesic – dose
dependant
Fentanyl (sublimaze)
synthetic narcotic analgesic
• Indications: Induce sedation for endotracheal
intubation.
• Contraindications: MAO inhibitors within 14
days, myasthenia gravis.
• Precautions: Increased intracranial pressure,
elderly, debilitated, COPD, respiratory problems,
hepatic and
• renal insufficiency.
• Dosage/Route: 25 to 100 mcg slowly IV (2 to 3
min). Ped: 2 mcg/kg slow IV/IM.
Stadol
• Name/Class: BUTORPHANOL (Stadol)/Synthetic
Narcotic Analgesic
• Description: Butorphanol is a centrally acting synthetic
narcotic analgesic about 5 times more potent than
morphine. A schedule IV narcotic.
• Indications: Moderate to severe pain.
• Contraindications: Hypersensitivity, head injury, or
undiagnosed abdominal pain.
• Precautions: May cause withdrawal in narcoticdependent patients
• Dosage/Route: 1 mg IV or 3 to 4 mg IM/3 to 4 hours.
Noncompetitive antagonism
• The antagonism is insurmountable
• Example:
You can’t effectively push CO off of
hemoglobin once its got the site
Competitive antagonism
• Considered surmountable
• Enough of an agonist can overcome the
antagonism
Competitive Antagonists
• Bind to the site but
do not cause the
receptor to initiate
the expected
response
• The key fits in the
lock but will not turn
and cannot open the
lock – however the
lock is now blocked
Opioid antagonists
• Reverse some of the
effects of opioid
drugs
• Typically desired for
respiratory
depression effect
• Shorter half life than
most opioid drugs
Reversal
• Naloxone: opiate antagonist
– Binds to opiate receptor – fits in lock but doesn’t
turn it – blocks it
• Doesn’t elicit the desired response:
– No pain relief / No high– door blocked
– No respiratory depression – door blocked
– Can’t bind to the receptor causing vasodilation
morphine has bound to – so hypotension is not
reversed – door NOT blocked
Morphine----->>>>
Pain relief / High
Respiratory depression
Hypotension
Naloxone (narcan)
• Prototype opioid antagonist drug
• Repeat doses may be needed to combat
shorter half life
• Competitively binds with opioid receptors
without causing the effects of opioid
binding.
• Primary binding is at respiratory centers –
it will not reverse hypotension
narcan
• Indication:
– Natural of synthetic narcotic overdose
– Coma of unknown origin
• Precaution: shorter half life than most of
the drugs it antagonizes
• Dosage/Route: 0.4 to 2.0 mg IV/IM, 2 to
2.5X ET up to 10 mg, 2 mg MAD