The pharmacokinetics of the effervescent vs.conventional tramadol/paracetamol fixed-dose combination tablet in patients after total gastric resection

Background: Tramadol/paracetamol is a fixed-dose combination prescribed for the relief of moderate to severe pain. The combination acts synergistically and guarantees the rapid onset of paracetamol and the prolonged analgesic effect of tramadol with good tolerability. These drugs are often used in various formulations in the treatment of patients with postoperative pain, e.g.after stomach resection. Gastrectomy leads to pathophysiological changes within the alimentary tract, which may affect the process of drug absorption. The aim of the research was an analysis of the pharmacokinetics of tramadol/paracetamol from effervescent and conventional tablets in patients after total gastrectomy. Methods: The research was carried out on patients after gastrectomy with Roux-en-Y reconstruction. The patients received two tramadol/paracetamol fixed-dose combination tablets in a single orally administered dose of 75/650 mg (2 × 37.5/325 mg). The patients were subjected to one of the two study drug group with: I. effervescent tablet (ET) (n= 14; mean [SD] age, 63.4 [10.1] years; weight, 75.5 [15.3] kg; and BMI, 26.0 [4.6] kg/m²) and II. conventional tablet (CT) (n= 12; mean [SD] age, 66.8 [7.7] years; weight, 79.8 [17.8] kg; and BMI, 27.4 [5.3] kg/m²). Blood samples were collected within 10 h after the drug administration. The plasma concentrations of tramadol and paracetamol were measured with validated HPLC (high-performance liquid chromatography) method with UV detection. Results: The comparison of the paracetamol and tramadol C_maxratio for the ET group with that of the CT group gave ratios of 1.16 [90% confidence interval (CI) 1.06, 1.27] and 0.86 (90% CI 0.72, 1.02), respectively. The comparison of the paracetamol and tramadol AUC_0–tratio for the ET group with that of the CT group showed ratios of 0.99 (90% CI 0.88, 1.10) and 1.00 (90% CI 0.82, 1.22), respectively. The comparison of the difference for the effervescent and conventional formulation gave an estimated decrease in t_maxof 0.5 h for paracetamol and 0.13 h for tramadol. Conclusions: In view of the changes in the pharmacokinetics of paracetamol and tramadol in the patients after gastric resection for both formulations compared the conventional tablet seems to be more appropriate due to the comparable rate of absorption of both substances, higher concentrations of tramadol and comparable exposure to paracetamol.