Drug Classification: Acute pulmonary oedema

Morphine

Mechanism of action:

Morphine is an opioid, a mu (µ) opioid receptor agonist, which results in analgesia and a reduction in peristalsis (constipation), together with various other effects.

Indications:

  • Pain
  • Historically, but less relevant now, as a treatment for diarrhoea.

Opioids are agonists at mu (mu = µ, Greek m, m is for morphine), delta and kappa opioid receptors (ORs). The highest affinity of morphine is for the mu receptor. There is some evidence for subtypes (1 and 2) of mu ORs, although the functional significance of this remains to be confirmed. Opioid receptors are found on neurons in somatosensory cortex, thalamus, various other brain centres involved in the pain pathway – the spinal cord and also on nociceptive terminals in the periphery, to relieve pain by reducing the “pain” signal.

Naloxone is an opioid antagonist (high affinity for mu Rs) which is used to classify ORs as GPCR [Gi/Go] 7TM metabotropic receptors that are antagonized by naloxone. ACTION of opioid agonists on peripheral nociceptors and in the spinal cord & brain (CNS): increased K+ conductance, decreased Ca++ results in hyperpolarization and decreased neurotransmission at pre- and post-synaptic sites on neurons in the pain pathway. Overall effect is a reduction in pain sensation.

Lecture and CAL materials:

Oxygen

UNDER REVIEW (September 2016)

Mechanism of Action:

Oxygen is a naturally occurring gas that is vital for life in all aerobic cells. Its tetravalent reduction to water in the mitochondrial electron transport chain provides the energy for all cellular activities. It is normally found at a partial pressure of 13KPa in arterial blood which is equivalent to 99% saturation of haemoglobin. In several cardiac and respiratory disease states gas exchange in the lung is impaired leading to arterial hypoxaemia. This reduction in oxygen carriage and delivery to cells can be partially reversed by increasing the inspired oxygen concentration above the 20% found in room air with supplementary oxygen. Oxygen should be regarded as a drug.

Lecture and CAL materials:

Furosemide

Indications

  • Heart failure and other states of intravascular volume overload.
  • Emergency treatment of acute pulmonary oedema.
  • Oedema associated with generalised extravascular volume expansion (nephrotic syndrome and other low-albumin or other salt-retaining states).

Mechanism of Action

Loop diuretic: the most powerful and rapidly effective class of diuretics. In kidney inhibits Na+/K+/2Cl- cotransporter in (thick) ascending loop of Henle where the drug is concentrated. As NaCl is not absorbed, it passes on through the tubule with an osmotic equivalent of water. Also get loss of K+ and H+.

Further resources