Drug & nutrient interactions Flashcards
What type of drugs may cause weight gain/appetite stimulation?
- psychotropic medicines (anti-psychotic or anti-depressants)
- anti-histamines
- insulin and oral hypoglycemics
- corticosteroids (asthma)
It is thought that anti-psychotic drugs may contribute to an increased risk of diabetes, why?
Potentially due to the associated weight gain (30% weight gain with Olanzapine)
What side effects do some drugs cause that may lead to loss of appetite?
- gastric upset (chemotherapy drugs inducing nausea and vomiting, or opioids)
- dry mouth
- swallowing difficulties
- taste/smell changes
How do amphetamines result in weight loss?
Cause appetite suppression - however potential for addiction and may only have a short term effect due to tolerance
Name an example of a weight loss drug?
Orlistat
How does Orlistat contribute to weight loss?
It inhibits Lipase activity in the small intestine, leading to enhanced dietary triglyceride excretion in the faeces, and consequent reduced fat absorption
(lipase is usually secreted to help breakdown fat for absorption)
What side effects may orlistat cause?
Bloating and oily stools
What drugs act on bile acids to help reduce cholesterol?
Ezetimibe, plant sterols, and bile acid binding resins
How do ezetimibe, plant sterols and bile acid binding resins lower cholesterol?
They bind to bile acids to stop reuptake by the liver, therefore cause the liver to use cholesterol to make more therefore depleting the cholesterol pool
What is the overall role of ezetimibe, plant sterols, and bile acid binding resins?
Lower cholesterol
What is the overall role of statins?
Lower cholesterol
How do statins lower cholesterol?
They inhibit HMG Co-A reductase to inhibit cholesterol production
They also increase LDL receptos on liver to help pull LDL out of the blood, and therefore decrease the cholesterol pool
What are the cons of bile acid binding resins?
- need to be taken with every meal
- powder to mix with drink
- can cause GI upset
- drug-drug interactions
What are 3 therapeutic approaches to managing diabetes?
- direct administration of insulin
- stimulate B cells of pancreas to stimulate release of insulin
- alter glucose absorption, production, utilisation and excretion
Why can’t insulin be given orally?
It is a peptide and too large to be absorbed in GIT and needs to get into the blood
How do rapid acting insulins work?
They are in monomoer form and therefore can rapidly diffuse - reduce BGL at mealtimes
How do longer acting insulins work?
They are aggregated in hexamer form which means they are less quickly absorbed due to limited diffusion - manage the body’s general insulin needs
What are causes of hypoglycemia?
- delay in a meal
- inadequate CHO consumption
- excess insulin dose
What are the symptoms of hypoglycemia?
Adrenaline effects - early: tachycardia, tremor, sweating
neuroglycopenia - mental function/consciousness
What is the role of a SGLT2 inhibitor?
Inhibits SGLT2 and stops reabsorption of glucose in the kidneys, therefore excretes glucose in urine
How can SGLT2 inhibitors cause weight loss?
- decreases calorie usage by excreting glucose
- excess water excretion
What are adverse effects of SGLT2 inhibitors?
- genital and urinary tract infections
- polyuria
What are the two most common diuretic drug classes?
Thiazide and frusemide (loop diuretic)
What is the general effect of diuretics on electrolytes?
Generally increase potassium excretion
What is a side effect of diuretics?
Low potassium due to increased excretion - can cause cardiac arrhythmias
What are angiotensin system inhibitors (ACE inhibitors/angiotensin receptor antagonists) used to treat?
Hypertension/heart failure
What is the general effect of angiotensin system inhibitors & how can this be problematic?
Decrease excretion of potassium
Problematic when - taking potassium supplements or diet high in potassium, can cause cardiac arrhythmias
How do laxatives work?
- act as a bulking agent to stimulate paristalsis
- draw water into soften the stool
What can laxative overuse lead to?
Electrolyte abnormalities
What are the role of proton pump inhibitors?
Decrease gastric acid secretion and increase pH (for peptic ulcers, GORD - reflux)
How can proton pump inhibitors lead to vitamin and mineral deficiencies?
Gastric acid is required for pancreatic proteases to cleave B12 from protein
Acidic stomach environment increases calcium absorption - so without can increase risk of fractures/osteoporosis
What can be used to treat hyperkalaemia?
Insulin + glucose - promotes cellular uptake of potassium
Frusemide + fluid replacement - increases potassium excretion
When are phosphate binders used & what is their mechanism?
In hyperphosphatemia in chronic renal failure
Bind dietary phosphate in GIT to form a poorly absorbed compound
What are drugs that affect GI function?
- laxatives and acid suppressants
- anti-emetics (treat nausea and vomiting)
- prokinetic agents (control acid reflux)
- drugs causing constipation (opioids)
Why should some antibiotics not be taken with alcohol?
Some antibiotics can inhibit the process of breaking down acetaldehyde
What is pharmcokinetics?
Movement of drugs in the body (eg absorption, metabolism, elimination)
What is pharmacodynamics?
The effect of the drug and the mechanism of its action
What does the rate of oral absorption refer to?
How fast or slow it is absorbed
What does the extent of oral absorption refer to?
How much of the drug will be absorbed (e.g. not all 10g of the drug may be absorbed)
What can effect the rate or extent of oral drug absorption?
- rate of gastric emptying
- gastric acid secretion (pH)
- drug dissolution
- drug transporter proteins
Describe chelation and how this can decrease absorption of a drug (nutrient-drug interaction).
Divalent and trivalent cations (calcium, aluminium, magnesium, iron and zinc) bind to the drug and form an insoluble complex and therefore decrease the amount that can be absorbed
Absorption of tetracycline antibiotics is impaired by the concomitant ingestion of ???
- calcium (dairy products)
- aluminium, iron, zinc, magnesium
What is the advice for taking tetracycline antibiotics?
- to take one hour before or two hours after a meal
- not taken with milk (even small amounts in tea or coffee)
What are bisphosphonates used to treat?
Osteoporosis (prevent loss of bone density)
Explain the reaction between bisphosphonates and minerals/calcium?
Minerals/calcium form a complex with bisphosphonates and prevent dissolution (dissolving)
What is the advice for taking bisphosphonates?
- do not take with food
- do not take at same time as calcium supplements
How does a high fat meal increase the absorption of griseofulvin?
Griseofulvin is not very water soluble which effects the rate of dissolution
Absorption is improved when consumed with a high fat meal
What is Cytochrome P450 3A4 (CYP3A4)
A major intestinal drug metabolising enzyme
How does grapefruit/grapefruit juice interfere drugs?
It inhibits intestinal CYP3A4 which increases the bioavailability of some drugs and may cause toxicity by increasing blood concentration
Warfarin has a low therapeutic index - what does this mean?
It has a small window in which its best effective - small changes in concentration can cause big problems
What is the mechanism of action of warfarin?
It is a blood thinner (anti clotting) - clotting factors are vitamin K dependant, warfarin has a similar structure to vitamin K and binds to enzyme vitamin K reductase to inhibit clotting factor production and therefore reduces clotting factor concentration
What effect does Vitamin K have on warfarin?
- increase in Vit K decreases Warfarin therapeutic effect
- decrease in Vit K increases Warfarin therapeutic effect
How can you reduce GI upset from metformin?
Take with food
What is the concern of complementary and alternative medicines (CAMs) with drugs?
They may cause inhibition or induction of
- drug metabolising enzymes
- drug transporters
What is the mechanism of action of St Johns Wart in relation to drug iteractions?
It can induce CYP3A4 which lowers the concentration of many drugs (sub-therapeutic effect)
Who is at biggest risk with taking medicines?
- polypharmacy (those taking multiple medications)
- liver and kidney dysfunction
- elderly (commonly taking multiple medications)
- pregnancy
