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Nutritional Phamacology (PHARMACOKINETICS (Absorption, Distribution,…
Nutritional Phamacology
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categories
General Sale List (GSL) medication
– Able to be sold anywhere
– Limits on pack size and strength that can be sold
Pharmacy Only Medication (P)
– Only able to be sold in pharmacy
– Sale must be supervised by a pharmacist who will check for any medical conditions/
other medicines to make sure it is safe to take the drug
Prescription Only Medication (POM)
– Only able to be sold on prescription
– There are some exceptions to this law e.g. Midwives may be able to obtain POM,
prescribing nurses and pharmacists
Some prescription only medicines are further classified as Controlled drugs, such as
morphine, pethidine and methadone
Misuse of Drugs Act 1971
Prohibits certain activities in relation to controlled drugs e.g. their
manufacture, supply and possession
Class A: e.g. Morphine
• Class B: e.g. Codeine, Dexamphetamine
• Class C: e.g. Anabolic steroids, Diazepam
Drug Naming
Proprietary, brand or trade
name
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Adverse Effects
Predictable:
– Exaggerated physiological effect
– Side Effect
– Toxicity
– Cumulative toxicity
– Iatrogenic – Induced by physician e.g. wrongly prescribed medication or dose
Unpredictable:
– Allergy – Hypersensitivity reaction to a particular drug
– Idiosyncratic reaction – Specific to the sufferer Commonly, this is caused by a
disturbance in enzyme function, congenital or acquired, so that the triggering
substance cannot be processed properly
Example: Patients with a genetic deficiency of the glucose-6-phosphate
dehydrogenase enzyme cannot take oxidant drugs such as aspirin because
this would result in haemolysis
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Barriers to Distribution
Blood brain barrier
• Protective mechanism that stops harmful substances from reaching the brain.
• The endothelium cells of the capillaries in the brain are much closer together than in normal tissue
• Astrocytes in the CNS help to maintain tight junctions that create a barrier between the capillaries
and the brain tissue
• This means only very lipophilic substances or those which are actively transported can enter the
CNS
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Drug Metabolism
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Some drugs can interfere with certain liver enzymes interfering with their own
metabolism and that of other drugs. This is an important consideration for drug
interaction
Smokers can also show increased metabolism of certain drugs due to induction
of cytochrome P448 by a component of tobacco smoke
P450 Enzyme System
The activity of the P450 enzyme system can be
markedly increased by exposure to certain drugs
or dietary factors
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Renal Excretion
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Active tubular secretion – Larger drugs and metabolites are actively transported into the
kidney tubules. Drugs may have to compete for transport proteins – this can change
their excretion rate
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Hepatic Excretion
Bile is the major excretion route for some
drugs e.g. Cromoglycate and rather more
drug metabolites e.g. morphine
glucuronide
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Half Life
The time it takes for a drug’s concentration in the body to fall by half
• Very dependant on rate of elimination