Aspirin

Question 1

Drug class?

Answer 1

Anti-platelet agent

Question 2

How does it work?

Answer 2

Aspirin is analgesic, anti-inflammatory, antipyretic and an inhibitor of platelet aggregation. It prolongs the bleeding time. It inhibits fatty acid cyclo-oxygenase by acetylation of the active site of the enzyme, and most of its pharmacological effects are due to inhibition of the formation of cyclo-oxygenase products including thromboxanes, prostaglandins and prostacyclin.

Question 3

Indications?

Answer 3

Ssecondary prophylaxis following myocardial infarction, and in patients with unstable angina and cerebral transient ischaemic attacks.

Question 4

Contra-indications?

Answer 4

• Known hypersensitivity to aspirin, other ingredients in the product, other salicylates or non-steroidal anti-inflammatory drugs (a patient may have developed anaphylaxis, angioedema, asthma, rhinitis or urticaria induced by aspirin or other NSAIDs).
• Nasal polyps associated with asthma (high risk of severe sensitivity reactions).
• Active peptic ulceration or a past history of ulceration or dyspepsia.
• Haemophilia or other haemorrhagic disorder (including thrombocytopenia) as there is an increased risk of bleeding.
• Concurrent anticoagulant therapy should be avoided.
• Severe hepatic impairment
• Severe renal impairment
• Severe cardiac failure
• third trimester of pregnancy
• Methotrexate used at doses >15mg/week (see section 4.5).
• children under 16 years old, unless specifically indicated (e.g. Kawasaki’s disease).

Question 5

Side effects?

Answer 5

Increased bleeding tendency, dyspepsia.

Question 6

Possible interactions?

Answer 6

The following drug interactions should be considered when prescribing aspirin:
• Analgesics - avoid concomitant administration of other salicylates or other NSAIDs (including topical formulations) as increased risk of side effects.
• Alkalizers of urine (eg antacids, citrates) - increased excretion of aspirin.
• Metoclopramide and domperidone - increased rate of absorption of aspirin.
• Mifepristone - avoid aspirin until 8-12 days after mifepristone.
• Ototoxic medicine (eg vancomycin) - potential for ototoxicity increased. Hearing loss may occur and may progress to deafness even after discontinuation of the medication. Effects may be reversible but are usually permanent.
• Laboratory investigations - aspirin may interfere with some laboratory tests such as urine 5-hydroxyindoleacetic acid determinations and copper sulphate urine sugar tests.
• Calcium-channel blockers – reduced hypotensive effects, increased antiplatelet effect which rarely results in pro-longed bleeding time.
• Varicella vaccine - Vaccine recipients should avoid use of salicylates for 6 weeks after vaccination with varicella vaccine as Reye’s syndrome has been reported following use of salicylates during wild-type varicella infection.
• Ginkgo Biloba – possible increase in risk of bleeding.
CONTRAINDICATED with Methotrexate.