Pharmacokinetics and mechanisms of tracer uptake Flashcards Preview

Medical physics 2: Nuclear Medicine > Pharmacokinetics and mechanisms of tracer uptake > Flashcards

Flashcards in Pharmacokinetics and mechanisms of tracer uptake Deck (17)
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1
Q

Define Pharmacokinetics

A

The process by which a drug is absorbed, distributed, metabolized, and eliminated by the body.

2
Q

Describe initial bio-distribution

A
  • Simple dilution in a compartment, such as plasma,
  • Diffusion process along concentration gradient
  • Substance crosses permeability barrier.
3
Q

Effects of bio-distribution

A

Tissue distribution in the body not necessarily the distribution of the intact radio-pharmaceutical - may result from metabolism of the starting material

4
Q

What is passive diffusion?

A

Moving from higher to lower concentration – down a concentration gradient.

Does not require energy

5
Q

What is a Facilitated diffusion?

A

Proteins in the cell membrane are used to move molecules - grab a molecule passing then shift their position to bring them into the cell.

Still moving into the cell, passive trans through lipid membrane ex. HMPAO in brain

6
Q

What is active transport?

A

Proteins embedded in the cell’s lipid bi-layer move specific molecules and ions in and out of the cell.

Often have to workagainst a concentration gradient by pumping ions from low to higher concentration.

ex. pertechnetate uptake in thyroid, hepatobiliary uptake

7
Q

Describe diffusion

A
  • From a higher to a lower concentration
  • Rate ∝ concentration of the radiotracer.
  • Net movement of molecules continue until concentration is in equilibrium.

Xe admin through inhalation

8
Q

Describe capillary blockade

A

Tracer cannot pass through smallest capillaries, IV solution blocks 0.3% available pulmonary vessels. Filtered out in pulmonary circulation

Microspheres and macroaggregates
- Metabolic degradation and phagocytosis

9
Q

Define phagocytosis

A

Particles of colloid dimensions are engulfed by phagocytic cells

Particulate comes in contact with phagocytic cell: are recognised, attach to the cell surface, and are engulfed.

Kupffer cells of liver, macrophages of spleen and bone marrow up to 10um in size

10
Q

Describe ion exhange / chemisorption

A

Phosphonates accumulate in hydroxyapatite crystal matrix.

Rapid bone uptake proportional to bone turnover:

  • Increased osteoblastic activity
  • Increased regional blood flow
11
Q

Describe facilitated diffusion

A

All cells use glucose to generate metabolic energy.

Tumour cells have increased rates of anaerobic and aerobic glycolysis compared to normal tissue.

18F FDG is metabolically trapped

12
Q

Describe Metabolic incorporation

A

Metabolic pathway same as for natural non-radioactive element

Ex 131I and 123I

13
Q

Examples of active transport

A

201 Thallium potassium analogue:
Thallous ions taken up by active transport system for potassium

Hepatobiliary Studies:
99mTc. IDA transported by the anion transport system of the liver.

14
Q

Describe Autologous products

A

Cells isolated from the body, labelled,
then injected back.

Example RBC labelled in vitro or in vivo 99mTc - eventually filtered by spleen
WBC (infection)
Platelet (thrombus site)

15
Q

Describe receptor binding agents

A

binding analogue of another molecule

ex 123I Ioflupane (FP-CIT) DaTSCAN: Analogue of cocaine

Binds to dopamine active transporter (DaT) sites on presynaptic terminals of the dopaminergic neurones in the corpus striatum.

16
Q

Describe antibodies

A

Proteins in bloodstream recognise and attach to proteins ‘antigens’ on surface of viruses, bacteria, tumour cells

Allows other components of immune system to destroy
and remove the foreign invaders.

A low amount are taken up by tumors

17
Q

What is a monoclonal antibody?

A

Monoclonal antibodies are antibodies which recognise a single target