Paracetamol:

  • It is also known as acetaminophen
  • It is para-aminophenol derivatives that possesses analgesic and antipyretic effects but is not anti-inflammatory agent.
  • It is popular in use for human medicine due to less toxic effect than salicylates but limited application in veterinary medicine due to toxic effect, especially in cats.

MOA:

  • Recent findings suggest that it selectively inhibits COX-2 than COX-1.
  • It mediates its analgesic-antipyretic effects by inhibition of COX enzyme in brain.

Pharmacological Effect:

  • It has good analgesic and antipyretic effect but has weak peripheral anti-inflammatory activity.
  • It donot produce gastric irritation, erosion or bleeding that occur after administration of salicylates.
  • It has no effect on platelets, bleeding time or excretion of uric acid.

Pharmacokinetics:

  • Data on domestic animals is limited.
  • In humans, it is well-absorbed orally and uniformly distributed in body
  • It is bound to about 35% to plasma protein in blood
  • It is metabolized in liver by conjugation with glucuronic acid (~60%), sulphate (~35%) and cysteine 30%.
  • Small portion of paracetamol undergoes cytochrome P-450 mediated N-hydroxylation to form N-acetyl-p-benzoquinone.
  • It is excreted as mercapturic acid in urine after reaction with glutathione.

Side effects/Adverse effects:

  • In dogs, it causes renal, hepatic, GI and hematological effects
  • In high dose, it causes damage to liver and kidney
  • It can cause frank hemolysis by reducing lifespan of erythrocytes.

Drug Interactions:

  • It should not be used in post-operative phase in animal that receive halothane.
  • It potentiates the effect of oral anti-coagulant
  • Additive action of analgesic with aspirin.

Contraindications and precautions:

  • It is contraindicated in cat at any dosage.
  • In dogs, it is not recommended to use in hepatic toxicity, live toxicity and hematological abnormalities
  • It should be avoided in intermediate post-operative phase in dogs due to increased risk of hepatotoxicity.

Indications:

  • It is occasionally used as oral analgesic in dog.
  • In human, it is one of the best drugs to be used as antipyretic and most commonly used “over the counter (OTC)” analgesic.

Dose:

  • Dogs: 10-15 mg/kg, PO, BID