Материал: 2016_Kaplan_USMLE_Step_1_Lecture_Notes_Pharmacology

Learning Objectives

Describe the site of action, effects, and common complications associated with morphine use

Differentiate between mu-receptor agonists, antagonist, and mixed agonist-antagonist

Describe the appropriate use of these medications in the treatment of pain, opiate withdrawal, and drug abuse

λEndogenous opiate peptides represented by endorphins, enkephalins, and dynorphins

λThree receptor families: µ, κ, and δ

λPresynaptic and postsynaptic inhibition through Gi coupling

λMu pharmacology most important

λMorphine is the prototype µ agonist

λPharmacology of morphine:

−Analgesia: ↑ pain tolerance and ↓ perception and reaction to pain

−Sedation

−Respiratory depression: ↓ response to ↑ pCO2 (do not give O2; give naloxone)

−Cardiovascular: minimal effects on heart, but vasodilation (avoid in head trauma)

−Smooth muscle

ºLongitudinal relaxes

ºCircular constricts

GI: ↓ peristalsis, constipation, cramping

GU: urinary retention, urgency to void

Biliary: ↑ pressure

Pupils: miosis

−Cough suppression: antitussive action, independent of analgesia and respiratory depression

−Nausea and vomiting: stimulation of the chemoreceptor trigger zone (CTZ) in the area postrema

– ↑ histamine release

Clinical Correlate

Contraindications and Cautions for Opioids

λHead injuries (possible increased intracranial pressure)

λPulmonary dysfunction (except pulmonary edema)

λHepatic/renal dysfunction (possible accumulation)

λAdrenal or thyroid deficiencies (exaggerated responses)

λPregnancy (possible neonatal depression or dependence), except meperidine which does not inhibit uterine contractions in delivery and causes less respiratory depression in the newborn