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MICROBIOLOGY PART 1 303 > Drug metabolism and interaction - Pharmacology > Flashcards

Drug metabolism and interaction - Pharmacology Flashcards

1
Q

What percentage of hospitalisations involve adverse drug events?

A

2.9-3.7%
4th leading cause of death
Drug poisoning = 1 in 7 deaths in UK in people in their 20s

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2
Q

What are type A and type B adverse drug effects?

A 
A = pharmacological or toxic effect
B = idiosyncrasy and drug allergy
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3
Q

What are the typical pharmacopeia in dental practice?

A

Sedative
LA
Analgesic
Antibiotics

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4
Q

What drugs have a low therapeutic index?

A

Anticoagulant - warfarin
Aminoglycoside antibiotics - gentamicin
Anticonvulsants - phenytoin

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5
Q

Give the therapeutic index of remifentanyl (opioid analgesic) and diazepam

A

Remifentanyl - 33000:1

Diazepam - 100:1

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6
Q

What are the types of adverse drug effects?

A

Circumstances;

  • Accidental/deliberate overdose
  • Normal therapy - side effects

Site of action;

  • Localised aspirin (mouth ulcers, GI irritation)
  • Systemic - majority of rxns

Time course;

  • Acute toxicity - single intake/rapid onset - Narcotics (resp depression)
  • Sub-acute toxicity-repeated exposure - Tetracycline
  • Chronic toxicity - repeated exposure - chemical carcinogenesis
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7
Q

What are the mechanisms of adverse drug effects?

A

Type A (for augmented)

  • Exaggerated therapeutic responses
  • 2ndry unwanted actions
  • More predictable or anticipated effects

Type B (for Bizarre)

  • Pharmacologically unexpected, unpredictable or idiosyncratic adverse rxns
  • Immunological (allergic/anaphylactic)
  • Idiosyncratic (qualitatively abnormal adverse rxn - mechanism not yet understood)
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8
Q

What are the major and minor concerns of type A reactions?

A

Major

  • Resp depression
  • Cardiac toxicity (LA)

Minor

  • Diarrhoea
  • Dry mouth
  • Drowsiness
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9
Q

What does a higher dose of the drug cause?

A

Higher possibility of side effects

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10
Q

Give examples of drug risk situations in patients? (high risk of adverse drug effects)

A 
Childhood
Elderly
Pregnancy
Lactation
Renal failure
Haemodialysis
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11
Q

Pharmacokinetics

A

Absorption
Distribution
Metabolism
Excretion

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12
Q

How is absorption reduced? (tetracycline)

A

By chelation of drugs/food/vitamins/divalent cations

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13
Q

What is distribution? (tetracycline)

A

Sequestration of tetracycline in bone (tissue
binding) leading to depression of bone growth in children and
irreversible staining of tooth enamel

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14
Q

Who should tetracycline not be prescribed to?

A

Pregnant women and children under 12

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15
Q

How are drugs involved in metabolism?

A

Effect drug metabolising enzymes = inhibition/induction of enzyme
Diseases may alter drug metabolism (renal/hepatic dysfunction)

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16
Q

What can cause abnormal drug metabolism?

A

Inherited factors of either phase I oxidation or phase II conjugation

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17
Q

What is renal excretion of drugs controlled by?

A

Glomerular filtration, tubular secretion and tubular reabsorption

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18
Q

What factors affect renal excretion of drugs?

A

Kidney function
Protein binding
Urine pH
Urine flow

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19
Q

What may impaired renal function result in?

A

Accumulation of drugs eliminated by the kidneys

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20
Q

Features of type B reactions?

A 
No dose relationship
Unexpected
Mechanism uncertain
Not reproducible
Serious
Low background frequency
Pseudoallergic
Metabolic intolerance
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21
Q

Give examples of type B reactions

A

Anaphylaxis, hepatitis, blood dycrasias

22
Q

How do type A and B reactions differ?

A

A = pharmacologically predictable, B is not
A is dose dependent, B is not
A has high incidence and morbidity, B is low
A has low mortality, B has high mortality
A = treatment = decrease dose, B = stop

23
Q

What is valproic acid?

A

Antiepileptic used to control certain types of seizures

24
Q

Characteristics of drug allergy?

A 
Delay after initial exposure
Precipitated with small doses of drug
Does not resemble normal pharmacology
Classical symptoms of allergic response
Due to drug related factors or host related factors
25
Q

Causes of drug allergy;

Features of drug related factors?

A

Nature of drug
Degree of exposure (dose, duration, freq, repeated administration)
Route of administration
Cross sensitisation (reactivity to drugs with close structural chem relationship)

26
Q

Causes of drug allergy:

Host related factors?

A 
Age (20-49 = higher risk of allergic rxns)
Sex (women more common)
Genetic factors
Diseases
Previous exposure
27
Q

Features of anaphylaxis?

A

Acute response
Potentially fatal
Drug related = 3 per 100000, deathers 1-2 per 100000
Mechanism; Release of inflam mediators from mast cells due to tissue oedema/damage

28
Q

Signs and symptoms of anaphylaxis?

A
  • Runny nose
  • Light headed, loss of consciousness, confusion, headache, anxiety
  • Shortness of breath, wheezes, pain with swallowing, cough
  • Diarrhoea, vomitting
  • Hives, itchiness, flushing
  • Fast/slow HR, low BP
  • Swelling of lips, tongue or throat
29
Q

What causes anaphylaxis in dentistry?

A

Penicillin (75% of anaphylactic deaths)
Aspirin
LA - procaine, lidocaine

30
Q

How to treat anaphylaxis?

A

Adrenaline
Antihistamine (clorphenamine)
Steroids
Bronchodilator

31
Q

Medications for Stephen/Johnson syndrome?

A

Anti-gout medications
Pain relievers - acetaminophen, ibuprofen
Naproxen sodium
Antibiotic - penicillin
Medications to treat seizures or mental illness = anticonvulsants
Radiation therapy

32
Q

Name the drug-drug interaction mechanisms?

A

Pharmaceutical
Pharmacodynamic
Pharmacokinetic - absorption, distribution, metabolism, excretion

33
Q

What does adrenaline in LA do?

A

Enhances therapeutic effect of lidocaine by slowing absorption from site of action into systemic circulation = prolonged intensity of anaesthesia, reduced bleeding and systemic toxicity

34
Q

Pharmodynamics - what does warfarin do?

A

Increased risk of anticoagulation

Antagonises recycling of vitamin K by depleting active vitamin K in the liver

35
Q

Pharmacokinetic: metabolism

A

Not for water soluble drugs (penicillins)
Drugs metabolised in the liver - substrates of the cytochrome P450 enzymes
Enzyme inhibitors - increase blood levels
Enzyme inducers - reduce blood levels

36
Q

What does grapefruit juice do?

A

Doubles the conc of midazolam = risk of oversedation, airway obstruction

37
Q

List the inducers of cytochrome CYP3A

A 
Carbamazepine
Phenytoin
Rifampicin
Glucocorticoids
St. John's Wort
38
Q

List the substrates of cytochrome CYP3A

A 
Midazolam/other benzodiazepines
Cyclosporine
Methadone
Statins
HIV protease 
Inhibitors
39
Q

List the inhibitors of cytochrome CYP3A

A

Erythromycin
Ketaconazole
Grapefruit juice
Omeprazole

40
Q

What does erythromycin increase the effects of? How?

A

Warfarin
Carbamazepine
Theophylline
Cyclosporin

By inhibition of CYP450

41
Q

How does midazolam increase the plasma concentration? How?

A 
Erythromycin
Ketoconazole (or other antifungal)
Omeprazole
Grapefruit juice
By CYP3A inhibition
42
Q

CYP3A induction?

A

Induction of enzyme activity particularly cytochrome P450

Requires synthesis of new enzymes

43
Q

What does St. John’s Wort do?

A

Enhances metabolism of drugs, reducing their plasma levels by inducing CYP3A
Oral contraceptive - risk unwanted pregnancies
Immunosuppressant - risk organ rejection
Can interact with midazolam, methadone

44
Q

What causes acetaldehyde dehydrogenase?

A

Metronidazole and alcohol
= Nausea, vomiting, tachycardia, shortness of breath, headache
No alcohol consumption

45
Q

What can antibiotic/antifungal agents in dental practice cause?

A

More prolonged duration than other treatments = increased risk of interactions - liver enzyme inhibitors

46
Q

How are lidocaine and the liver connected?

A

CYP3A4 substrate;
Clearance limited by hepatic blood flow rather than metabolism (45 min half life)
Hepatic blood flow reduced by propanolol
Hepatic enzyme metabolism inhibited by cimetidine (used to treat ulcers and GERD)

47
Q

What does LA do?

A

Inhibit neuronal activity in brain and heart
Initially CNS stimulation by depressing inhibitory pathways = tremor/convulsion
Followed by CNS depression: resp depression and unconsciousness

48
Q

In LA - which LA reaches the maximum safe dose more rapidly?

A

More rapid with mepivacaine 3% than 2% lignocaine with adrenaline

49
Q

How does adrenaline work?

A

α1 vasoconstriction – skin and mucous membrane
• β2 vasodilation – skeletal muscle properties add to safety
Compromised pts - reduce the dose and test the dose

50
Q

Adrenaline - potentiation?

A
  • Non selective β blockers
  • Tetracyclin antidepressants – inhibit
    uptake
  • Cocaine – inhibit uptake
  • Ritalin – ADHA (release endogenous
    norepinephrine)
  • Parkinson’s disease (COMT
    inhibitors reduce breakdown)
  • Felypressin – alternative
    vasoconstriction
51
Q

Benzodiazepines

A 
Anxiolytic without sedation or ataxia
• Temazepam/diazepam
• Large margin safety – wide therapeutic index
Liver CYP3A4
• Inhibition (increased plasma levels)
• Calcium channel blockers /macrolide / azole antifungal/
protease inhibitors
• Induction (decreased plasma levels)
• Anti-TB, anti epileptic

MICROBIOLOGY PART 1 303 (12 decks)

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