Purpose: Compare early bioavailability of rectal, effervescent oral, and i.v. paracetamol.

Scope:Five groups of N = 7 patients received 1 or 2 g paracetamol orally or rectally or 1 g i.v. immediately after day surgery. Paracetamol concentrations taken after 20, 40 _{and 80 min. Median plasma paracetamol concentrations for 1 versus 2 g effervescents were 78 (25–114) versus 108 (95–146) μmol L⁻¹ at 80 min and 16 (9–30) versus 17 (10–30) μmol L⁻¹ for 1 versus 2 g suppositories. Paracetamol i.v. gave median 97 (77–135) μmol L⁻¹ after 40 min.}

Conclusion: Only intravenously and 2 g effervescent paracetamol gave therapeutic concentrations during the period studied.