Ketamine effects on bupivacaine local anaesthetic activity and pharmacokinetics of bupivacaine in mice

Effects of Ketamine and Tramadol As Adjuvants to Bupivacaine in Spinal Anesthesia for Unilateral Open Ovarian Cystectomy: A Randomized Controlled Trial

BACKGROUND

Spinal anesthesia offers numerous advantages and desirable features. However, it is associated with various side effects related to local anesthetic agents used. Reducing the dose of local anesthetic in spinal anesthesia can help minimize side effects but may lead to a diminished analgesic effect or failure of anesthesia. Therefore, adding an adjuvant may enhance the benefits while mitigating side effects.

OBJECTIVE

This study aimed to evaluate the effects of ketamine and tramadol as adjuvants to bupivacaine on the duration of spinal analgesia. The objectives were to compare the three groups and prove their analgesic effects, safety, and superiority. The primary outcomes were the duration of spinal analgesia, as well as the onset and duration of both sensory and motor blocks. Secondary outcomes included the heart rate, mean arterial pressure, and the incidence of undesired effects such as nausea, vomiting, sedation, shivering, and postoperative headache.

METHODS

In this double-blind randomized controlled trial, 120 female patients undergoing elective open unilateral ovarian cystectomy under spinal anesthesia were studied. The inclusion criteria included patients aged 16-45 years with a physical status classified as American Society of Anesthesiologists (ASA) class I and II. Patients were randomly allocated into three groups: group B (n=40) received only bupivacaine, group BK (n=40) received bupivacaine mixed with preservative-free ketamine, and group BT (n=40) received bupivacaine mixed with preservative-free tramadol.

RESULTS

The mean duration of spinal analgesia, measured in minutes, showed significant differences (P < 0.001) between group BK (165 ± 4) and group B (170 ± 5). There was also a significant difference between group BT (313 ± 8) and group B (170 ± 5) (P < 0.001). Additionally, significant differences were observed between group BK (165 ± 4) and group BT (313 ± 8) (P < 0.001).

CONCLUSION

The administration of 25 mg of ketamine and 25 mg of tramadol as adjuvants to bupivacaine in spinal anesthesia significantly affected the postoperative duration of analgesia. Tramadol prolonged the duration of spinal anesthesia, while ketamine shortened it. The use of both adjuvants did not result in undesired effects.

Anaesthetic benefits of a ternary drug delivery system (Ropivacaine-in-Cyclodextrin-in-Liposomes): in-vitro and in-vivo evaluation

OBJECTIVES

To evaluate whether a ternary system composed of hydroxypropyl-β-cyclodextrin (HP-βCD) further encapsulated into egg phosphatidylcholine liposomes (LUV) could prolong the action and reduce the toxicity of ropivacaine (RVC).

METHODS

Dynamic light scattering and NMR were used to characterize the inclusion complex (RVC : HP-βCD), liposomal (RVC : LUV) and ternary (LUV : RVC : HP-βCD) systems containing 0.25% RVC. Their encapsulation efficiency, release kinetics, in-vitro cytotoxicity and in-vivo anaesthetic effect (paw-withdraw tests in mice) were also evaluated.

KEY FINDINGS

1 : 1 RVC : HP-βCD inclusion complex was encapsulated in liposomes (220.2 ± 20.3 nm size, polydispersity <0.25, zeta potentials = -31.7 ± 1.4 mV). NMR (diffusion-ordered spectroscopy (DOSY)) revealed stronger anaesthetic binding to LUV : RVC : HP-βCD (K_a  = 342 m^-1 ) than to RVC : HP-βCD (K_a  = 128 m^-1 ) or liposomal formulation (K_a  = 22 m^-1 ). The formulations promoted in-vitro sustained drug release and partially reverted the cytotoxicity of RVC against 3T3 fibroblasts in the profile: LUV : RVC : HP-βCD ≥ RVC : HP-βCD > RVC : LUV. Accordingly, in-vivo sensory block of free RVC (180 min) was prolonged ca. 1.7 times with the ternary system and RVC : HP-βCD (300 min) and 1.3 times with RVC : LUV (240 min).

CONCLUSIONS

These results confirm the suitability of this double-carrier system in clinical practice, to decrease the toxicity and prolong the anaesthesia time evoked by RVC.

Liposomal-based lidocaine formulation for the improvement of infiltrative buccal anaesthesia

This study describes the encapsulation of the local anaesthetic lidocaine (LDC) in large unilamellar liposomes (LUV) prepared in a scalable procedure, with hydrogenated soybean phosphatidylcholine, cholesterol and mannitol. Structural properties of the liposomes were assessed by dynamic light scattering, nanoparticle tracking analysis and transmission electron microscopy. A modified, two-compartment Franz-cell system was used to evaluate the release kinetics of LDC from the liposomes. The in vivo anaesthetic effect of liposomal LDC 2% (LUV_LDC) was compared to LDC 2% solution without (LDC_PLAIN) or with the vasoconstrictor epinephrine (1:100 000) (LDC_VASO), in rat infraorbital nerve blockade model. The structural characterization revealed liposomes with spherical shape, average size distribution of 250 nm and low polydispersity even after LDC incorporation. Zeta potential laid around -30 mV and the number of suspended liposomal particles was in the range of 10¹² vesicles/mL. Also the addition of cryoprotectant (mannitol) did not provoke structural changes in liposomes properties. In vitro release profile of LDC from LUV fits well with a biexponential model, in which the LDC encapsulated (EE% = 24%) was responsible for an increase of 67% in the release time in relation to LDC_PLAIN (p < 0.05). Also, the liposomal formulation prolonged the sensorial nervous blockade duration (∼70 min), in comparison with LDC_PLAIN (45 min), but less than LDC_VASO (130 min). In this context, this study showed that the liposomal formulations prepared by scalable procedure were suitable to promote longer and safer buccal anaesthesia, avoiding side effects of the use of vasoconstrictors.

Adjuvants to local anesthetics: Current understanding and future trends

Although beneficial in acute and chronic pain management, the use of local anaesthetics is limited by its duration of action and the dose dependent adverse effects on the cardiac and central nervous system. Adjuvants or additives are often used with local anaesthetics for its synergistic effect by prolonging the duration of sensory-motor block and limiting the cumulative dose requirement of local anaesthetics. The armamentarium of local anesthetic adjuvants have evolved over time from classical opioids to a wide array of drugs spanning several groups and varying mechanisms of action. A large array of opioids ranging from morphine, fentanyl and sufentanyl to hydromorphone, buprenorphine and tramadol has been used with varying success. However, their use has been limited by their adverse effect like respiratory depression, nausea, vomiting and pruritus, especially with its neuraxial use. Epinephrine potentiates the local anesthetics by its antinociceptive properties mediated by alpha-2 adrenoreceptor activation along with its vasoconstrictive properties limiting the systemic absorption of local anesthetics. Alpha 2 adrenoreceptor antagonists like clonidine and dexmedetomidine are one of the most widely used class of local anesthetic adjuvants. Other drugs like steroids (dexamethasone), anti-inflammatory agents (parecoxib and lornoxicam), midazolam, ketamine, magnesium sulfate and neostigmine have also been used with mixed success. The concern regarding the safety profile of these adjuvants is due to its potential neurotoxicity and neurological complications which necessitate further research in this direction. Current research is directed towards a search for agents and techniques which would prolong local anaesthetic action without its deleterious effects. This includes novel approaches like use of charged molecules to produce local anaesthetic action (tonicaine and n butyl tetracaine), new age delivery mechanisms for prolonged bioavailability (liposomal, microspheres and cyclodextrin systems) and further studies with other drugs (adenosine, neuromuscular blockers, dextrans).

Metabolism and metabolomics of ketamine: a toxicological approach

Ketamine is a phencyclidine derivative and a non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptor for which glutamate is the full agonist. It produces a functional dissociation between the thalamocortical and limbic systems, a state that has been termed as dissociative anaesthesia. Considerable variability in the pharmacokinetics and pharmacodynamics between individuals that can affect dose-response and toxicological profile has been reported. This review aims to discuss pharmacokinetics of ketamine, namely focusing on all major and minor, active and inactive metabolites. Both ketamine optical isomers undergo hepatic biotransformation through the cytochrome P450, specially involving the isoenzymes 3A4 and 2B6. It is first N-demethylated to active metabolite norketamine. Different minor pathways have been described, namely hydroxylation of the cyclohexanone ring of ketamine and norketamine, and further conjugation with glucuronic acid to increase renal excretion. More recently, metabolomics data evidenced the alteration of several biological pathways after ketamine administration such as glycolysis, tricarboxylic acid cycle, amino acids metabolism and mitochondrial β-oxidation of fatty acids. It is expected that knowing the metabolism and metabolomics of ketamine may provide further insights aiming to better characterize ketamine from a clinical and forensic perspective.

Pharmacological and local toxicity studies of a liposomal formulation for the novel local anaesthetic ropivacaine

This study reports an investigation of the pharmacological activity, cytotoxicity and local effects of a liposomal formulation of the novel local anaesthetic ropivacaine (RVC) compared with its plain solution. RVC was encapsulated into large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine, cholesterol and α-tocopherol (4:3:0.07, mole%). Particle size, partition coefficient determination and in-vitro release studies were used to characterize the encapsulation process. Cytotoxicity was evaluated by the tetrazolium reduction test using sciatic nerve Schwann cells in culture. Local anaesthetic activity was assessed by mouse sciatic and rat infraorbital nerve blockades. Histological analysis was performed to verify the myotoxic effects evoked by RVC formulations. Plain (RVCPLAIN) and liposomal RVC (RVCLUV) samples were tested at 0.125%, 0.25% and 0.5% concentrations. Vesicle size distribution showed liposomal populations of 370 and 130 nm (85 and 15%, respectively), without changes after RVC encapsulation. The partition coefficient value was 132 ± 26 and in-vitro release assays revealed a decrease in RVC release rate (1.5 fold, P &lt; 0.001) from liposomes. RVCLUV presented reduced cytotoxicity (P &lt; 0.001) when compared with RVCPLAIN. Treatment with RVCLUV increased the duration (P &lt; 0.001) and intensity of the analgesic effects either on sciatic nerve blockade (1.4–1.6 fold) and infraorbital nerve blockade tests (1.5 fold), in relation to RVCPLAIN. Regarding histological analysis, no morphological tissue changes were detected in the area of injection and sparse inflammatory cells were observed in only one of the animals treated with RVCPLAIN or RVCluv at 0.5%. Despite the differences between these preclinical studies and clinical conditions, we suggest RVCLUV as a potential new formulation, since RVC is a new and safe local anaesthetic agent.

A double-blind comparison of intrathecal S(+) ketamine and fentanyl combined with bupivacaine 0.5% for Caesarean delivery

BACKGROUND

In this prospective, randomized, double-blind, controlled study, we investigated the sensory, motor and analgesic block characteristics of S(+) ketamine, fentanyl and saline given intrathecally (IT) in addition to 0.5% plain bupivacaine (10 mg) for spinal analgesia.

METHODS

Ninety ASA I or II adult patients undergoing Caesarean section were randomly allocated to receive 1.0 mL of 0.9% saline in Group S (n = 30), 0.05 mg kg-1 of S(+) ketamine (1.0 mL) in Group K (n =30) or 25 microg (1.0 mL) of fentanyl in Group F (n =30) following 10 mg of plain bupivacaine 0.5% IT. We recorded onset and duration of sensory and motor block, time to reach the maximal dermatomal level of sensory block and duration of spinal analgesia.

RESULTS

The onset time of sensory and motor block was significantly shorter in Groups K and F than in Group S (P < 0.014). Their duration was significantly longer in Group F than in Groups K and S (P < 0.009). The time to reach the maximal dermatomal level of sensory block was significantly shorter in Groups K and F than in Group S (P < 0.001). The duration of spinal analgesia was significantly longer in Group F than in Groups K and S (P < 0.001).

CONCLUSION

In patients undergoing Caesarean section with spinal analgesia, the addition of S(+) ketamine (0.05 mg kg-1) IT to 10 mg of spinal plain bupivacaine (0.5%) led to rapid onset of both sensory and motor blockade and enhanced the segmental spread of spinal block without prolonging the duration of spinal analgesia, whereas fentanyl provided prolonged analgesia.

Beneficial Effect of Low-Dose Ketamine Addition to Epidural Administration of Morphine–Bupivacaine Mixture for Cancer Pain in Two Cases

Two patients experiencing cancer pain with neuropathic components were treated with epidural administration of a mixture of ketamine (1 mg/mL) + morphine (1 mg/mL) + bupivacaine (1 mg/mL) injected daily by epidural port. No serious adverse effect was observed throughout the therapy. The patients were mostly pain-free and have gotten better quality of life during 110- and 48-day follow-up when the therapy was given by epidural route. Low doses of epidural ketamine added to morphine and bupivacaine increase the mean duration of satisfactory analgesia without severe adverse effects and restore quality of life when traditional therapy fails.

Beneficial effect of trimebutine and N-monodesmethyl trimebutine on trinitrobenzene sulfonic acid-induced colitis in rats

The use of local anesthetics, such as lidocaine, has been proposed in the treatment of distal ulcerative colitis. Trimebutine maleate (TMB) displays a local anesthetic activity higher than that of lidocaine in rabbit corneal reflex. TMB and nor-TMB its main metabolite in human show similar affinity to that of bupivacaine toward sodium channel labeled by [3H]batrachotoxin and block sodium currents in sensory neurons from rat dorsal root ganglia. The aim of this study was to evaluate the effects of TMB and nor-TMB in comparison to lidocaine and bupivacaine in a rat model of acute colonic inflammation induced by trinitrobenzene sulfonic acid (TNBS). A single intracolonic instillation of TNBS (50 mg/kg dissolved in ethanol 30%) led to early plasma extravasation then macroscopic damage (hyperemia and necrosis), increased colonic weight and tissular MPO, a marker of neutrophilic infiltration. Local administration of TMB at dose of 3 to 60 mg/kg, 30 min before, 24 and 48 h after colitis induction, significantly reduced the severity of colitis. Nor-TMB (1, 3, 10, 30 mg/kg) as well as lidocaine (1, 3, 10 mg/kg) dose-dependently reduced colitis while bupivacaine at 10 mg/kg did not affect it significantly. In contrast systemic administration of TMB, nor-TMB and lidocaine at 10 mg/kg had no significant effect. Furthermore, local administration of TMB (30 mg/kg) and lidocaine (10 mg/kg) significantly reduced plasmatic extravasation. In conclusion, intracolonic treatment with TMB and nor-TMB improved acute experimental TNBS-induced colitis in rat and these effects could be explained by their local anesthetic activity.

Encapsulation of mepivacaine prolongs the analgesia provided by sciatic nerve blockade in mice

PURPOSE

Liposomal formulations of local anesthetics (LA) are able to control drug-delivery in biological systems, prolonging their anesthetic effect. This study aimed to prepare, characterize and evaluate in vivo drug-delivery systems, composed of large unilamellar liposomes (LUV), for bupivacaine (BVC) and mepivacaine (MVC).

METHODS

BVC and MVC hydrochloride were encapsulated into LUV (0.4 micro m) composed of egg phosphatidylcholine, cholesterol and alpha-tocopherol (4:3:0.07 molar ratio) to final concentrations of 0.125, 0.25, 0.5% for BVC and 0.5, 1, 2% for MVC. Motor function and antinociceptive effects were evaluated by sciatic nerve blockade induced by liposomal and plain formulations in mice.

RESULTS

Liposomal formulations modified neither the intensity nor the duration of motor blockade compared to plain solutions. Concerning sensory blockade, liposomal BVC (BVC(LUV)) showed no advantage relatively to the plain BVC injection while liposomal MVC (MVC(LUV)) improved both the intensity (1.4-1.6 times) and the duration of sensory blockade (1.3-1.7 times) in comparison to its plain solution (P < 0.001) suggesting an increased lipid solubility, availability and controlled-release of the drug at the site of injection.

CONCLUSION

MVC(LUV) provided a LA effect comparable to that of BVC. We propose MVC(LUV) drug delivery as a potentially new therapeutic option for the treatment of acute pain since the formulation enhances the duration of sensory blockade at lower concentrations than those of plain MVC.

Effects of S(+) ketamine added to bupivacaine for spinal anaesthesia for prostate surgery in elderly patients

BACKGROUND AND OBJECTIVE

Intrathecal ketamine as the sole anaesthetic agent has demonstrated a lack of cardiovascular depression that should be of advantage in an elderly population. S(+) ketamine has three-times the analgesic potency of R(-) ketamine and its antinociceptive effects after intrathecal administration in rats are known. We decided to evaluate the effects of intrathecal S(+) ketamine added to a small dose of spinal bupivacaine in elderly patients undergoing transurethral prostate surgery.

METHODS

Forty males over 60 yr old, scheduled for transurethral prostate resection under spinal anaesthesia, were studied in a prospective, double-blinded, randomized way. Patients were allocated to receive either bupivacaine 10 mg or bupivacaine 7.5 mg combined with S(+) ketamine 0.1 mg kg(-1). Spinal block onset time, maximum sensory level, duration of blockade, haemodynamic variables, postoperative analgesic requirements and adverse events were recorded.

RESULTS

Onset times of motor and sensory block were shorter in the bupivacaine plus S(+) ketamine group. Incomplete motor block of the lower extremities was seen in 80% of the patients in bupivacaine plus S(+) ketamine group. Duration of complete motor block and spinal analgesia was shorter in the bupivacaine plus S(+) ketamine group. There was no significant difference in arterial pressure. Heart rate decreased after spinal anaesthesia in the bupivacaine plus S(+) ketamine group and was significantly lower until the end of anaesthesia. The incidence of adverse effects was not different between groups.

CONCLUSIONS

Intrathecal S(+) ketamine administered with a low dose of bupivacaine provides shorter motor and sensory block onset time, shorter duration of action and less motor blockade in elderly males.

Reduction of tissue concentration of cocaine in rat by ketamine

The coabuse of cocaine and ketamine occurs with high frequency. The presence of another active substance with cocaine allows for the potential of various drug-drug interactions to occur. This study investigated the tissue distribution after the administration of cocaine or ketamine alone and their combination in rat. Cocaine (5 mg/kg iv), ketamine (100 mg/kg by gavage), or ketamine followed by cocaine (same doses and routes of administration) was utilized. Tissue contents of cocaine and norcocaine were significantly lowered at 5, 15, and 30 min following ketamine administration versus cocaine alone. However, tissue contents of benzoylecgonine were significantly higher in the combination group compared to cocaine alone. On the other hand, cocaine administration did not affect the tissue disposition of ketamine. The results suggest that ketamine decreased cocaine tissue content, which may affect its pharmacological and toxicological profiles.

The role of ketamine on plasma cocaine pharmacokinetics in rat

Ketamine has gained attention recently because of re-emergence of its abuse especially in combination with cocaine. When more than one drug is present simultaneously, the potential for drug--drug interaction exists, which can be pharmacokinetic, pharmacodynamic or both in nature. The objective of this study was to investigate the effect of ketamine on plasma cocaine pharmacokinetics to assess the role that the kinetic component may play in the interaction of these agents. Moreover, the effect of repetitive administration of ketamine pretreatment on the pharmacokinetics of cocaine was addressed. Male Sprague-Dawley rats were treated with cocaine alone (5 mg/kg i.v.), ketamine alone (100 mg/kg by gavage), or ketamine followed by cocaine (the same routes and doses). Blood samples were withdrawn at different time points post-injection and analyzed for determination of cocaine, its metabolites (benzoylecgonine and norcocaine) and ketamine. The results demonstrated that ketamine caused a significant decrease in cocaine's area under the curve (AUC) and elimination half-life while its total clearance was increased. The AUC of benzoylecgonine was increased by 1.5-fold after the combination compared with cocaine alone. However, cocaine did not affect ketamine's pharmacokinetic parameters. In the pretreatment study, ketamine was given orally for 3 days, followed 18 h later by a single i.v. of cocaine. Further enhancement of cocaine metabolism occurred with the appearance of norcocaine. This investigation revealed that ketamine enhances cocaine metabolism and may affect its toxicological profile.

Simultaneous analysis of ketamine and bupivacaine in plasma by high-performance liquid chromatography

A reversed-phase HPLC technique for the simultaneous measurement of both bupivacaine and ketamine in plasma is described. Plasma samples (0.5 ml) were prepared using a rapid and simple back-extraction technique. Resolution of both analytes and the internal standard, desipramine, from medicines coadministered to surgical paediatric patients was obtained using a 5 microm cyano (CN) (250x4.6 mm) column and a mobile phase comprising methanol-acetonitrile-orthophosphoric acid-0.01 M sodium dihydrogenphosphate (200:80:2:718). Good sensitivity for both analytes was observed using UV detection at a wavelength of 215 nm. The method has been validated according to the criteria established by the Journal of Chromatography B.