Table 1.

Sampling considerations and selected pharmacokinetic parameters for analgesics monitoring.1

AnalgesicsChiralitySampleHalf-lifeExcreted in urineTime to peakTherapeutic doseTherapeutic concentrationsTime of sampling
Salicylate (Acetylsalicylic acid)NA2Serum, plasma (heparin or EDTA), urine, saliva, synovial fluids3–20 h (∼ dose) (saturation kinetics) (10–30 min, ASA)5% (SA)1–2 h30.5–1 g4 5–6 g620–100 mg/L4 5 100–250 mg/L6After acute OD: on presentation, then every 2 h until peak, and every 4–6 h thereafter
DiflunisalNASerum or plasma5–12 h<10%2–3 h250–500 mg50–200 mg/LNA
AcetaminophenNASerum/plasma (EDTA),7 urine, CSF1–3 h 3.2 h<5%0.5–1.0 h>4 h for OD8 4 h0.5–1 g10–20 mg/L >Plasma4 h after a single acute ingestion; 4–8 h following ER OD; 2 levels needed, if co-ingested, to assure complete absorption
(S)-(+)-IbuprofenEutomerSerum, plasma,1–3 h<10%1–2 h200–800 mg15–30 mg/LNA
(S)-(+)-NaproxenEutomerSerum, plasma,9–22 h10%1–4 h275–1500 mg50–100 mg/LNA
(+/−)-Tramadol?Serum, plasma,6.3 h30%2–3 h50–400 mgNE (300 μg/L, CmaxNA
urinefor 100-mg dose)
(+/−)-M1-tramadol?7.4 h<60%NE (55μg/L, Cmax
metabolite9for 100-mg dose)