Pharmacokinetics of tramadol after subcutaneous administration in a critically ill population and in a healthy cohort

Subcutaneous versus intravenous tramadol for extremity injury with moderate pain in the emergency department: a randomised controlled noninferiority trial

BACKGROUND AND IMPORTANCE

Musculoskeletal trauma is a common presentation in the emergency department (ED). Tramadol as an analgesic has been recommended by pain management guidelines for musculoskeletal pain. Parenteral tramadol in the ED is commonly administered intravenously. Subcutaneously administered tramadol may have other advantages such as easier and faster preparation, avoids the need for intravenous (i.v.) access, and reduces the incidence of respiratory and gastrointestinal effects. However, studies comparing subcutaneous (s.c.) and i.v. tramadol for the management of acute moderate pain in patients with extremity injury are lacking.

OBJECTIVE

The objective of this study was to compare the clinical efficacy of s.c. tramadol vs. i.v. tramadol in patients with moderate pain due to extremity injury in the ED.

DESIGN, SETTINGS, AND PARTICIPANTS

This non-inferiority randomized controlled trial included adult patients presented to an academic, tertiary hospital ED with moderate pain (pain score of 4-6 on the visual analog scale) due to extremity injury. Intervention patients stratified to pain score were randomized to receive 50 mg of i.v. or s.c. tramadol.

OUTCOMES MEASURE AND ANALYSIS

Primary outcome measure was the difference in the pain score reduction at 30 min after tramadol administration between the two groups. The noninferiority null hypothesis was that the therapeutic difference in terms of pain score reduction of more than 0.8 exists between the two treatment groups at the endpoint.

MAIN RESULTS

In total 232 patients were randomized to i.v. ( n  = 115) or s.c. ( n  = 117). Although 225 were analyzed in the per-protocol population (i.v. = 113; s.c. = 112). The baseline median pain score was 6 (IQR, 5-6). Median pain score reduction at 30 min after administration was 2 (IQR, 1-3) in the IV group vs. 2 (IQR, 1-2) in the s.c. group with a median difference of 0 (IQR, 0-0), which was below the prespecified noninferiority margin of 0.8. Adverse events in the i.v. group were higher compared to the s.c. group (33.6% vs. 8.9%, P  ≤ 0.001).

CONCLUSIONS

The s.c. tramadol is noninferior to i.v. tramadol in the treatment of moderate pain from extremity injuries.

Pharmacokinetic profile of injectable tramadol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

Tramadol is used as an analgesic in humans and some animal species. When tramadol is administered to most species it undergoes metabolism to its main metabolites M1 or O-desmethyltramadol, and M2 or N-desmethyltramadol, and many other metabolites. This study describes the pharmacokinetic profile of tramadol when a single subcutaneous bolus of 2 mg/kg was initially administered to two koalas. Based on the results of these two koalas, subsequently 4 mg/kg as a single subcutaneous injection, was administered to an additional four koalas. M1 is recognised as an active metabolite and has greater analgesic activity than tramadol, while M2 is considered inactive. A liquid chromatography assay to quantify tramadol, M1 and M2 in koala plasma was developed and validated. Liquid chromatography-mass spectrometry confirmed that M1 had been identified. Additionally, the metabolite didesmethyltramadol was identified in chromatograms of two of the male koalas. When 4 mg/kg tramadol was administered, the median half-life of tramadol and M1 were 2.89 h and 24.69 h, respectively. The M1 plasma concentration remained well above the minimally effective M1 plasma concentration in humans (approximately 36 ng/mL) over 12 hours. The M1 plasma concentration, when tramadol was administered at 2 mg/kg, did not exceed 36 ng/mL at any time-point. When tramadol was administered at 2 mg/kg and 4 mg/kg the area under the curve M1: tramadol ratios were 0.33 and 0.50, respectively. Tramadol and M1 binding to plasma protein were determined using thawed, frozen koala plasma and the mean binding was 20% and 75%, respectively. It is concluded that when tramadol is administered at 4 mg/kg as a subcutaneous injection to the koala, it is predicted to have some analgesic activity.

Poloxamer-based binary hydrogels for delivering tramadol hydrochloride: sol-gel transition studies, dissolution-release kinetics, in vitro toxicity, and pharmacological evaluation

In this work, poloxamer (PL)-based binary hydrogels, composed of PL 407 and PL 188, were studied with regard to the physicochemical aspects of sol-gel transition and pharmaceutical formulation issues such as dissolution-release profiles. In particular, we evaluated the cytotoxicity, genotoxicity, and in vivo pharmacological performance of PL 407 and PL 407-PL 188 hydrogels containing tramadol (TR) to analyze its potential treatment of acute pain. Drug-micelle interaction studies showed the formation of PL 407-PL 188 binary systems and the drug partitioning into the micelles. Characterization of the sol-gel transition phase showed an increase on enthalpy variation values that were induced by the presence of TR hydrochloride within the PL 407 or PL 407-PL 188 systems. Hydrogel dissolution occurred rapidly, with approximately 30%-45% of the gel dissolved, reaching ~80%-90% up to 24 hours. For in vitro release assays, formulations followed the diffusion Higuchi model and lower K(rel) values were observed for PL 407 (20%, K(rel) = 112.9 ± 10.6 μg · h(-1/2)) and its binary systems PL 407-PL 188 (25%-5% and 25%-10%, K(rel) =80.8 ± 6.1 and 103.4 ± 8.3 μg · h(-1/2), respectively) in relation to TR solution (K(rel) =417.9 ± 47.5 μg · h(-1/2), P<0.001). In addition, the reduced cytotoxicity (V79 fibroblasts and hepatocytes) and genotoxicity (V79 fibroblasts), as well as the prolonged analgesic effects (>72 hours) pointed to PL-based hydrogels as a potential treatment, by subcutaneous injection, for acute pain.