Propacetamol is a prodrug

Prodrug

A prodrug is a pharmacological substance administered in an inactive form. Once administered, the prodrug is metabolised in vivo into an active metabolite, a process termed bioactivation. The rationale behind the use of a prodrug is generally for absorption, distribution, metabolism, and...

 form of paracetamol

Paracetamol

Paracetamol INN , or acetaminophen USAN , is a widely used over-the-counter analgesic and antipyretic . It is commonly used for the relief of headaches and other minor aches and pains and is a major ingredient in numerous cold and flu remedies...

 which is formed from esterification of paracetamol, and the carboxylic acid Diethylglycin. This has the advantage of making it more water soluble. It is used in post-operative care and is delivered by I.V.

Intravenous therapy

Intravenous therapy or IV therapy is the infusion of liquid substances directly into a vein. The word intravenous simply means "within a vein". Therapies administered intravenously are often called specialty pharmaceuticals...

. It is given if the patient is unable to take oral or rectally delivered paracetamol and non-steroidal anti-inflammatory drugs are contraindicated. The onset of analgaesia from propacetamol is more rapid than paracetamol given orally.
2g of propacetamol are equivalent to 1g of paracetamol.