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Flashcards in Pharmacokinetics 1 Deck (18)
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What is pharmacokinetics

How drugs are absorbed into the body, how they are distributed and how they are eliminated


What are the four areas to consider in pharmacokinetics

Absorption, distribution, metabolism, excretion


Where does the bulk flow of transfer take place

Through the bloodstream


How do lipid soluble drugs cross the membrane of cells

Passivley diffuse down their concentration gradient


What will result from a rapid absorption of a drug through the gut

Rapid increase in concentration in the blood and brain - may also mean its rapidly metabolised however


What is the partition coefficient

Determines lipid solubility - how quickly the drug will dissolve in oil rather than water


How do non-polar molecules interact with cells

Diffuse freely in lipids and penetrate the cell freely


What is the best mechanism to achieve fast absorption of drugs

Intravenous injection - preferential in emergency circumstances


What effects the rate of absorption in intrauscular injections

Depends on the perfusion of that muscle - greater blood supply = greater rate of absorption


What are inrathecal injections

Drugs of the CNS - administered into the cerebrospinal fluid - used in pain relief


What is a characteristic needed for oral medication

Has to be resistent to being broken down in the gut - some will be metabolised in the liver and kidneys but not a huge amount


How does particle size effect a drugs metabolism

Large particle sized drugs are more easily metabolised/ less is absorbed into the blood stream


When would rectally administered drugs be used

For small infants that can't swallow tablets and for seriously ill patients that can't stop vomiting.


Why is a low pH beneficial to the absorption of weak acids (Many drugs are weak acids or bases)

Shifts the dissociation equation of a weak acid to the associated side - so no longer carries a charge and is able to diffuse across the membrane


Give the eqn to show aspirin is in its active form at a pH of 3 in the stomach

pKa= pH + log10 [HA]/[A-]
pKa = 3.5


Once aspirin gets into the bloodstream what changes occur

The pH becomes more neutral - so the drug dissociates more - this means it stays in the blood longer as it can't move across the lipid membrane


How does the pH of the kidney effect absorption

pH or 8 so the drug dissociates more readily - This is good as this is where the associated is metabolised


How are overdose drug situations combated

Administration of NaHCO3 to neutralise the compartments so drug is in a more dissociated form in the blood so doesn't act on CNS etc - metabolised at the kidney