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Therapeutics > ADRs and Interactions > Flashcards

ADRs and Interactions Flashcards

1
Q

Examples of side effects, beneficical and adverse:

A
  • Beneficial:
    • sedation with antihistamines when used an OTC sleep medicine (e.g. promethazine)
  • Adverse:
    • Sedation with antihistamines for allergy.
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2
Q

Side-effect frequency descriptors

A
  • >1 in 10 people = Very common
  • 1:10 to 1:100 = Common
  • 1:100 to 1:1,000 = Uncommon
  • 1:1,000 to 1:10,000= Rare
  • < 1 in 10,000 = Very rare
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3
Q

ADR statistics

A
  • 5% of hospital admissions are ADR-related
  • 10-20% of hospital patients suffer ADR
  • 0.1% of medical patient mortality
  • Many patients receiving polypharmacy, increases chances of interactions/ADRs
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4
Q

Most common ADRs on hospital admission

A
  • NSAIDs 29.6%
    • GI bleeding, renal impairment, wheezing
  • Diuretics 27.3%
    • Hypotension, electrolyte disturbances
  • Warfarin: 10.5%

Ohers: ACEI/ATRAs, ADs and lithium, B-blockers, opioids, digoxin, prednisolone, clopidogrel

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5
Q

Define type A ADR

A
  • The normal pharmacological response is undesirable
  • Dose-related
  • Predictable
  • Usually managed by dose adjustment
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6
Q

Some adverse side effects of B-blockers

A
  • Cold extremities
  • Bradycardia
  • Asthma interactions
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7
Q

Some adverse side effects of NSAIDS

A
  • Asthma interactions
  • Gastric damage
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8
Q

ADR with Cimetidine/sprionolactone

A

reduce testosterone synthesis or oestrogenic

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9
Q

ADR in opioids/antimuscarinics

A

Constipation

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10
Q

ADR associated with antibiotics

A

Diarrhoea

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11
Q

ADR associated with digoxin

A

Nausea, vomiting, visual disturbances

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12
Q

ADR associated with cytotoxics

A

Myelosurpression

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13
Q

Pharmacokinetic mechanisms of ADRs

A
  • Absorption
  • Elimination
    • ​Renal+Hepatic

I.E can be adjusted by concentration (Type A)

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14
Q

Digoxin in the renally impaired

A

Cuased reased plasma concentrations as 2/3rds of digoxin is renally cleared

  • Nausea
  • Visual distrubances
  • Heart block
  • Arrythmias

Adjust concentration (type A)

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15
Q

ADRs as a consequence of metabolism

A
  • Metabolism: reduced metabolism may lead to increased plasma conc.
    • T1/2 diazepam increase by 1hr for each year of age
  • Neonates conjugate at a slow rate. Microsomal enzyme activity decreases variably with age
  • Genetic differences: 10% of population have defective isoenzyme of cytochrome P450
  • Hepatic failure: LFTs poorly predict ability to metabolise.
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16
Q

Define type B ADR

A

Bizarre or idiosyncratic

  • Unrelated to pharmacology
  • Unpredictable
  • Rare
  • Often Severe
  • Often related to genetics or immunology
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17
Q

Example of immunological ADRs

A

(Type B)

Penicillins:

  • penicillins couple to proteins, forming immunogens
    • hypersensitivity reaction

Cephalosporins?

  • Recent evidence suggests that cross reactivity is less (0.5-6.5%) than originally thought, some may be used if no alternative is available (see BNF)
18
Q

Examples of of heamatological ADRs

A

Agranulocytosis: absence of neutrophils – mouth ulcers, severe sore throat; infections.

  • Clozapine
  • Carbimazole
  • Carbamazepine

Thrombocytopenia: bruising/bleeding

19
Q

Ulcerogneic NSAID effect

A

(Also for oral steroids)

  • Oral NSAIDs (commonly) and corticosteroids (less commonly but especially when co-prescribed with NSAIDs) associated with peptic damage/ulceration.

Very important ADR

  • Annually 10,000 hospital admissions and 2,000 deaths.
  • (MRSA kills 1,500 pa)
  • Risk = 1 in 2,000 for long term users

Use Paracetamol for analgesia instead? Prophylax with PPI

20
Q

NSAIDs and Cardivascular disease interactions

A
  • NSAIDs may cause fluid retention
  • NSAIDs may exacerbate hypertension / CHF
  • Low dose aspirin – ‘less of a problem’
  • Increased CV risk with diclofenac
21
Q

NSAIDs and Renal Damage

A
  • By inhibiting renal PGs
  • Reduced renal blood flow
  • Reduced GFR
  • Especially in CHF pts
  • May lead to acute renal failure (7% of all cases)
22
Q

Beta-blockers and asthma

A

These are contraindicated in asthma as they block bronchial b2 adrenoceptors and may cause bronchospasm

  • Caution in COPD

This even applies to ‘selective’ b1-antagonists

  • Poor selectivity
23
Q

Statins and myopathy

A
  • Myopathy may rarely progress to rhabdomyolysis – may result in renal damage.
  • Often due to drug interactions
24
Q

Cause of green blood

A
  • This was an ADR to sumatriptan
  • Sumatriptan rarely leads to sulphahaemoglobinaemia: a sulphur atom incorporated in the haem group
  • Reversed on stopping to sumatriptan
25
Q

NSAIDS in elderly, consider. Even low dose aspirin isnot without risk

A
26
Q

Drug interactions with pharmacokinetic mechanisms

A
  • Absorption: 2 drugs may interact to alter rate of uptake e.g. tretracycline + Fe2+ salts or Ca2+ (milk)
  • pH: passive absorption of drugs best in uncharged form, governed by pKa value.
    • Rises in pH (antacids, H2 antagonists, PPIs) may influence absorption of other drugs.
    • Separate by several hours.
27
Q

Inducers of metabolism for ADRs

A
  • Rifampicin
  • Phenytoin
  • Ethanol
  • Carbamazepine-autoinduction
  • St John Wort
  • Reduce plasma conc of range of drugs E.g. barbiturates, carbamazepine, rifampicin increase metabolism of OCs
  • May take a week or 2 for effect
  • Effect may persist on stopping inducer
28
Q

Enzyme inhibitor Interactions

A

Cy P450 inhibition

  • erythromycin / clarithromycin
  • ciclosporin
  • Psoralen (from grape fruit juice)

Rapid onset : 1-2 days

Often reverse quickly on stopping

29
Q

Simvastatin drug interactions

A

Contraindicated with macorlides

Interaction with amlodipine, verapamil, diltiazem

For amlodipine plus statin:

  • Pravastatin does not interact
  • Use 20mg simvastatin as maximum dose.
30
Q

Renal elimination drug interactions

A
  • Competition for weak acid or base transports:
  • Aspirin and Methotrexate compete for elimination and NSAIDs in general may reduce renal perfusion– severe interaction
    • Counsel pts taking methotrexate NOT to take OTC ibuprofen or aspirin
  • NSAIDs prescribed with care in RA
31
Q

Drug interactions affecting Fluid and Electrolyte interactions

A

Diuretics: lead to volume depletion, when adding an ACEi increased risk of severe first dose hypotension

–Stop diuretic?

–Separate in time?

–Take ACEi on retiring to bed?

Diuretics: loops and thiazide cause hypokalaemia – so increase toxicity of digoxin

32
Q

K-sparing diuretics Drug interactions

A

e.g. Sprinolactone, amiloride

  • Increase K
  • This may be a problem if the pt takes K supplements or ACEIs (which also increase K)
    • Risk of hyperkalaemia
33
Q

Salbutamol and B-blocker

A
34
Q

Beta-blockers and rate-limiting Ca-Channel blockers

A

Beta blockers and verapamil: risk of bradycardia/asystole

  • Potentially fatal

Beta-blockers and diltiazem may interact

  • Avoid/extreme caution

Much less of a problem with dihydropyridines

35
Q

Warfarin

A

Used to prevent thrombosis in:

  • Atrial fibrillation
  • Artificial heart valves
  • PE
  • DVT

Several days to act¨

  • Narrow therapeutic window, Many interactions
  • Enzyme inducers lead tofailure of therapy
  • Enzyme inhibitors lead to increased bleeding

Increased bleeding with aspirin

36
Q

Monitoring Warfarin

A
  • INR (Prothrombin time)
37
Q

Action of DOACS

A

eg Rivaroxaban

  • Direct Oral Anticoagulants
  • Factor X inhibitor
  • Fewer interactions
  • No requirement to monitor
38
Q

St Johns Wort drug interactions

A

Enzyme indiucer

AVOID with

  • OC
  • Antiepileptics
  • HIV drugs, some
  • Ciclosporin
  • Warfarin
  • Simvastatin

Serotonergic syndrome: Avoid with MAOIs and SSRIs

39
Q

Food drug interaction

A
  • Cranberry juice thought to potentiate warfarin leading to fatalities
  • Grapefuit juice interacts with simvastatin and some Ca-antagonists
40
Q

Alcohol Interactions

A

Labels 2 & 4 (avoid if affected or avoid)

  • Mostly CNS depressant / sedating actions enhanced
    • E.g. TCAs, sedating antihistamines, benzodiazepines
  • Few antibiotics actually interact
    • Metronidazole leads to disulfiram-like effect
  • Gastric effects
    • Avoid aspirin containing products for hangover

Therapeutics (17 decks)

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