Choosing the optimal route of paracetamol administration

Paracetamol should preferably be administered orally unless a patient cannot take oral medications or has impaired oral absorption. Immediate-release and modified-release preparations of oral paracetamol have a similar onset of effect (approximately 30 minutes), and either can be used for ‘as required’ or regular dosing. However, do not use modified-release preparations in children younger than 12 years or for longer than 48 hours in children older than 12 years. Liquid formulations or soluble tablets may be preferred in younger children unable to swallow tablets.

Intravenous paracetamol may be used in hospital if an alternative to oral paracetamol is required. Onset of analgesic effect is rapid (occurring within 10 minutes of starting the infusion). The use of rectal paracetamol is limited by slow and variable absorption (peak blood concentrations may not be reached for 90 minutes). See here for dosing of intravenous and rectal paracetamol.