Pharmacokinetics 2 Flashcards Preview

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Flashcards in Pharmacokinetics 2 Deck (21)
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What is the blood brain barrier

A group of endothelial cells lining the blood vessels in the CNS forming tight junctions impermeable to water soluble molecules - lipid soluble molecules such as caffeine and ethanol can cross easily


What happens to tight junctions during inflammation

They become leaky - in meningitis this allows antiobiotics through the blood brain barrier more readily aiding in treatment


What is the chemoreceptor trigger zone

Found in the medulla oblongata and its stimulation induces the nausea and vomiting reflex - triggered by certain molecules - Dopaminergic antagonist prevent this response


How does albumin effect distribution of a drug

Albumin is a plasma protein that binds many acidic drugs - it carries a charge so prevents the diffusion of the drug across the lipid membrane


How does body fact interact with lipid soluble drugs

Act as a store - anaesthetics are highly lipid soluble - individuals with high body fat require increased concentrations to reach the correct amount in neurons


How do bones and teeth affect tetracycline

Bind with a high affinity for calcium, should not be used in children for this reason


What processes outline the phase 1 reactions in the liver

Catabolic reactions (oxidation, reduction, hydrolysis) often forming a more reactive compound than the initial drug - usually due to the addition of a hydroxyl group - this is necessary as it becomes the target point for the phase two reaction


Give an example drug that has a toxic intermediate compound

Paracetamol - under normal dosage, not very much produced.


What processes outline phase 2 reactions in the ;liver

Anabolic reaction (synthesis) involving conjugation to produce an inactive product - large groups added to prevent their reabsorption


What are pro-drugs

Drugs that become active only after being metabolised - therefore have a slower induction effect - useful for sedative and the controlling of seizures


How is aspirin eliminated from the body

Phase 1 - methyl ester group replaced by a hydroxyl group - Phase 2 - hydroxyl group reacts with a sugar group to form glucuronide. This increases the molecular weight so it is unable to cross the plasma membrane or act on its receptors


How many genes are present for P450 enzymes



What are P450 enzymes

Microsomal enzymes found intracellularly that act upon the uncharged drug once it has crossed the plasma membrane


How are P450 enzymes influenced by other drugs and environmental factors

Expression is influenced - Brussel sprouts induce P450 expression - increasing alcohol metabolism
Grapefruit juice inhibits P450 expression


How is penicillin excreted

Almost completely removed by proximal tubule secretion - and is therefore rapidly eliminated


How is diazepam excreted

Extremely lipophilic so is cleared very slowly from the body


What is first - pass metabolism

Drugs are extracted so effectively from the liver/gut that the amount reaching systemic circulation is considerably less than the amount absorbed.


What is T0.5

How long it takes for half the initial dose to disappear from the body


How are the rate of excretion and drug concentration related

They are independent of each other - Rate is determined by metabolism rather than diminishing concentrations so remains constant


What are saturation kinetics

Some drugs don't reach a plateau between rate of excretion and absorption - linear relationship between amount of drug and concentration in the plasma


What is zero order kinetics

No relationship between amount of drug taken and excretion - Alcohol dehydrogenase - metabolism of alcohol can't keep up with rate of absorption