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Pharmacology and Therapeutics > Adverse drug reactions and interactions > Flashcards

Adverse drug reactions and interactions Flashcards

1
Q

Adverse drug event

A

Preventable or unpredicted medication event with harm to the patient
-includes medication errors and adverse drug reactions

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2
Q

Epidemiology of adverse drug reactions (ADRs)

A
  • substantial morbidity and mortality
  • estimates of incidence vary with study methods, population and adverse drug reaction definition
  • 4th to 6th leading cause of death among hospitalised patients
  • 6.7% incidence of serious adverse drug reactions
  • 0.3% to 7% of all hospital admissions
  • annual costs in the billions
  • 30% to 60% are preventable
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3
Q

ADR classification basis

A
  • onset
  • severity
  • type
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4
Q

Onset of event

A
  • Acute=within 1 hour
  • Sub-acute=1 to 24 hours
  • Latent=more than 2 days
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5
Q

Severity of reaction

A
  • Mild=no change in therapy required
  • Moderate=change in therapy required, additional treatment and hospitalisation
  • Severe=disabling or life-threatening
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6
Q

Severe ADR

A
  • life-threatening/results in death
  • requires or prolongs hospitalisation
  • causes disability
  • causes congenital anomalies
  • requires intervention to prevent permanent injury
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7
Q

Type A ADR

A

-extension of pharmacologic effect
-usually predictable and dose dependent
-responsible for at least two-thirds of ADRs
Example: atenolol and heart block, NSAIDs and peptic ulcers, anticholinergics and dry mouth

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8
Q

Type B ADR

A
  • idiosyncratic or immunologic reactions
  • includes allergy and ‘pseudoallergy’
  • rare and unpredictable
  • examples include: chloramphenicol and aplastic anaemia, ACE inhibitors and angioedema
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9
Q

Type C ADR

A
  • associated with long-term use
  • involves dose accumulation
  • examples include: methotrexate and liver fibrosis, antimalarials and ocular toxicity
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10
Q

Type D ADR

A
  • delayed effects (sometimes dose independent)
  • carcinogenicity (eg: immunosuppressants)
  • teratogenicity (eg: thalidomide)
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11
Q

Type E ADR

A
  • withdrawal reactions=opiates, benzodiazepines, corticosteroids
  • rebound reactions=clonidine, beta-blockers, corticosteroids
  • ‘adaptive’ reactions=neuroleptics (major tranquilisers)
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12
Q

Classification of allergies

A

-Type 1=immediate, anaphylactic (IgE)
Example: anaphylaxes with penicillin
-Type 2=cytotoxic antibody (IgG, IgM)
Example: methyldopa and haemolytic anaemia
-Type 3=serum sickness (IgG, IgM)=antigen-antibody complex
Example: procainamide-induced lupus
-Type 4=delayed hypersensitivity (T cell)
Example: contact dermatitis

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13
Q

ABCDE classification of ADRs

A 
A=Augmented pharmacological effect
B=Bizarre
C=Chronic
D=Delayed
E=End-of-treatment
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14
Q

Pseudoallergies

A
  • Aspirin/NSAIDs leading to bronchospasm

- ACE inhibitors leading to cough/angioedema

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15
Q

Common causes of ADRs

A

-antineoplastics
-cardiovascular drugs
-NSAIDs/analgesics
-CNS drugs
(account for two-thirds of fatal ADRs)

  • antibiotics
  • anticoagulants
  • hypoglycaemics
  • antihypertensives
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16
Q

ADR detection

A 
SUBJECTIVE REPORT
-patient complaint
OBJECTIVE REPORT
-direct observation of events
-abnormal findings on physical examination, lab tests or diagnostic procedures

-Rare events will probably not be detected before drug is marketed

17
Q

The yellow card scheme

A
  • introduced after 1964 thalidomide incident
  • run by MHRA
  • voluntary
  • can be used by healthcare professionals, patients and members of the public
  • also includes ADRs to blood products, vaccines and contrast media
  • for established drugs, only report serious adverse reactions
  • for newly licensed drugs (<2 years=’black triangle’ drugs), report any suspected adverse reaction
18
Q

ADR frequency by drug use

A

ADR frequency increases with increased individual drug use (increased number of medications)

19
Q

Incidence of drug-drug interactions

A

Incidence is difficult to determine due to:

  • data for drug-related hospital admissions do not differentiate drug interactions and only adverse drug reactions
  • lack of availability of comprehensive databases
  • difficulty in assessing over the counter and herbal drug-therapy use
  • difficulty in determining contribution of drug interaction in complicated patients
  • sometimes principals causes of adverse drug reactions with specific drugs (eg: statins)
20
Q

Pharmacodynamic drug interactions

A

RELATED TO DRUG’S EFFECTS IN THE BODY (receptor site occupancy)

Additive, synergistic or antagonistic effects from co-administration of 2 or more drugs

  • synergistic actions of antibiotics
  • overlapping toxicity (eg: ethanol and benzodiazepines)
  • antagonistic effects (eg: anticholinergic medications)
21
Q

Pharmacokinetic drug interactions

A

RELATED TO THE BODY’S EFFECT ON THE DRUG (absorption, distribution, metabolism and elimination)

  • alteration in absorption
  • protein binding effects
  • changes in drug metabolism
  • alteration in elimination
22
Q

Pharmaceutical drug interactions

A

-DRUGS INTERACTING OUTSIDE THE BODY (eg: in IV infusions)

23
Q

Protein binding interactions=PHARMACOKINETIC INTERACTION

A
  • competition between drugs for protein or tissue binding sites (increase in free/unbound concentration may lead to enhanced pharmacological effects)
  • many interactions previously thought to be protein binding interactions were found to be primarily metabolism interactions
  • protein binding interactions are not usually clinically significant but some are (Eg: Warfarin=99% plasma albumin-bound so increase in free warfarin increases anti-coagulative effects)
24
Q

Phase I metabolism

A

OXIDATION

  • reduction
  • hydrolysis
25
Q

Phase II metabolism

A

CONJUGATION

  • glucuronidation
  • sulphation
  • acetylation
26
Q

Drug metabolism interactions

A
  • drug metabolism can be inhibited or enhanced by co-administration of other drugs
  • CYP450 system most extensively studied
27
Q

CYP 450 substrates

A

Predominantly metabolism by a single isozyme
-few examples of clinically used drugs
-examples of drugs used primarily in research on drug interactions
Metabolism by multiple isozymes
-most drugs metabolised by more than one isozyme
-if co-administered with CYP450 inhibitor, some isozymes may ‘pick up slack’ for inhibited isozyme so metabolic rate unaffected

28
Q

CYP 450 inhibitors

A
  • Cimetidine
  • Erythromycin and related antibiotics
  • Ketoconazole
  • Ciprofloxacin and related antibiotics
  • Ritonavir and other HIV drugs
  • Fluoxetine and other SSRIs
  • Grapefruit juice
29
Q

Drug elimination reactions

A
  • Almost always occur in the renal tubule
  • GOOD=probenecid and penicillin
  • BAD=lithium and thiazides
30
Q

Inhibition and induction

A
  • Inhibition=very rapid

- Induction=takes hours/days

31
Q

Deliberate interactions

A
  • Levodopa and Carbidopa
  • ACE inhibitors and thiazides
  • Penicillins and gentamicin
  • Salbutamol and ipratropium
32
Q

CYP 450 inducers

A
  • Rifampicin
  • Carbamazepine
  • Phenobarbitone
  • Phenytoin
  • St John’s wort (Hypericin)
33
Q

Drug metabolism and elimination=PHARMACOKINETIC INTERACTION

A

/

34
Q

Alterations in absorption=PHARMACOKINETIC INTERACTION

A

CHELATION
-irreversible binding of drugs in GI tract

Example: tetracylines, quinolone antibiotics to ferrous sulfate (Fe2+), antacids (Al3+, Ca2+, Mg2+), dairy products (Ca2+)

Pharmacology and Therapeutics (30 decks)

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