Local Anesthetics Transfer Across the Membrane: Reproducing Octanol-Water Partition Coefficients by Solvent Reaction Field Methods

Local anesthetics are one of the most widely used drug classes in clinical practice. Like many other biological molecules, their properties are altered depending on their protonation status, which is dependent on the pH of the environment. We studied the transport energetics of seven local anesthetics from the extracellular fluid across the biological membrane to the axoplasm in order to understand the effect of pH value on their efficacy and other pharmaco-dynamic roperties. In this we applied three different methods of solvent reaction field in conjunction with quantum chemical calculations to reproduce experimental values of n-octanol/water partition coefficients for both neutral and protonated forms. Only the SMD method of Cramer and Truhlar was able to reproduce experimental partition coefficient values. The results are discussed in terms of the function of local anesthetics under physiological conditions and in the case of local acidosis.

Local Anesthetics Transfer Across the Membrane: Reproducing Octanol-Water Partition Coefficients by Solvent Reaction Field Methods

Local anesthetics are one of the most widely used drug classes in clinical practice. Like many other biological molecules, their properties are altered depending on their protonation status, which is dependent on the pH of the environment. We studied the transport energetics of seven local anesthetics from the extracellular fluid across the biological membrane to the axoplasm in order to understand the effect of pH value on their efficacy and other pharmaco-dynamic properties. In this we applied three different methods of solvent reaction field in conjunction with quantum chemical calculations to reproduce experimental values of n-octanol/water partition coefficients for both neutral and protonated forms. Only the SMD method of Cramer and Truhlar was able to reproduce experimental partition coefficient values. The results are discussed in terms of the function of local anesthetics under physiological conditions and in the case of local acidosis.

Level of Depression, Anxiety and Impairment of Social Relations with Regard to Pain Intensity in a Naturalistic Sample of Patients at the Outpatient Chronic Pain Clinic

BACKGROUND

A high rate of concurrent depression and anxiety has been identified among the patients of pain clinics. Evaluation of own pain can appear as a perception of being negatively impacted by pain-related suffering in social relations.

SUBJECTS AND METHODS

A questionnaire with 228 variables was applied to 109 randomly chosen patients at outpatient pain clinic of the Ljubljana University Clinical Centre. Following summative scores were treated as a set of dependent variables in MANOVA, as a set of predictors in discriminant analysis: level of depression (Zung), level of anxiety (Zung), evaluation of the nature of pain and perceptions of negatively impacted social relations. Actual pain has been self-evaluated on a visual-analogue pain scale from 0 to 10 and recorded in subgroups with a low, middle and high intensity of actual pain (criterion variable).

RESULTS

The average age of the participants was M=52.7 years (SD 13.9), 70.9 % of them female. Participants with a high intensity of pain were found to have the highest level of depression, the highest level of anxiety and were negatively impacted in their social relations to the greatest extent. Only the first discriminant function was found to be significant (p<0.05). The structure matrix showed a high correlation between anxiety level (0.88) and depression level (0.86), and a low correlation with the perception of negatively impacted social relations (0.57).

CONCLUSIONS

The results emphasize the connection between pain intensity, anxiety, depression and interpersonal relational issues in the context of patients with chronic pain at an outpatient pain clinic. Anxiety and mood were found to be the best predictors for the perception of pain intensity. The results are preliminary, but significantly support the multidisciplinary collaboration of treatment at a pain clinic with mental health professionals.

Dopamine Autoxidation Is Controlled by Acidic pH

We studied the reaction mechanism of dopamine autoxidation using quantum chemical methods. Unlike other biogenic amines important in the central nervous system, dopamine and noradrenaline are capable of undergoing a non-enzymatic autoxidative reaction giving rise to a superoxide anion that further decomposes to reactive oxygen species. The reaction in question, which takes place in an aqueous solution, is as such not limited to the mitochondrial membrane where scavenging enzymes such as catalase and superoxide dismutase are located. With the experimental rate constant of 0.147 s⁻¹, the dopamine autoxidation reaction is comparably as fast as the monoamine oxidase B catalyzed dopamine decomposition with a rate constant of 1 s⁻¹. By using quantum chemical calculations, we demonstrated that the rate-limiting step is the formation of a hydroxide ion from a water molecule, which attacks the amino group that enters intramolecular Michael addition, giving rise to a pharmacologically inert aminochrome. We have shown that for dopamine stability on a time scale of days, it is essential that the pH value of the synaptic vesicle interior is acidic. The pathophysiologic correlates of the results are discussed in the context of Parkinson's disease as well as the pathology caused by long-term amphetamine and cocaine administration.

Intra-articular patient-controlled analgesia improves early rehabilitation after knee surgery

The influence of patient-controlled intra-articular analgesia with ropivacaine, morphine and ketorolac (RMK) on postoperative pain relief and early rehabilitation after anterior cruciate ligament reconstruction was studied. Twenty six patients, randomized into two groups, were enrolled in a placebo-controlled, double-blind study. At the end of surgery a catheter was placed intra-articularly and connected to a patient-controlled pump, programmed to deliver 10 mL bolus and 60 min lockout interval. RMK group received 0.25% ropivacaine, morphine 0.2 mg/mL and ketorolac 1 mg/mL; P group saline. Pain was measured with 10 cm visual analog scale. At pain scores > 3 cm, all patients were instructed to self-administer morphine intravenously using a patient-controlled pump. Daily rescue morphine consumption was noted and 48 h rehabilitation programme was evaluated. Daily morphine consumption was significantly lower in the RMK group (p < 0.001). At 24h after surgery, the patients in the RMK group experienced significantly less pain (p < 0.05). The patients in the RMK group achieved higher maximum degree of knee flexion in supine (p < 0.001) and in prone position (p < 0.05) compared to placebo group and better pain free flexion with assistance on day 1 (p < 0.05) and 2 (p > 0.05). The results show that patient-controlled intra-articular analgesia with RMK combination provides effective pain relief following anterior cruciate ligament reconstruction and improves early physical rehabilitation.

Intraarticular Patient-Controlled Regional Anesthesia After Arthroscopically Assisted Anterior Cruciate Ligament Reconstruction: Ropivacaine/Morphine/Ketorolac Versus Ropivacaine/Morphine

Anterior cruciate ligament reconstruction (ACLR) is associated with moderate to severe postoperative pain. We compared the intraarticular analgesic effects of ropivacaine and morphine with or without ketorolac and the need for rescue IV morphine at rest and during movement in patients undergoing anterior cruciate ligament reconstruction during spinal anesthesia. Thirty-nine patients receiving intraarticular patient-controlled regional analgesia with a 10-mL bolus and a 60-min lockout interval were randomized into 3 groups: the RM group received 0.25% ropivacaine and morphine 0.2 mg/mL; the RMK group received 0.25% ropivacaine, morphine 0.2 mg/mL and ketorolac 1 mg/mL; the P group received saline. Analgesic mixtures were prepared in 100-mL bags and coded. If needed, rescue morphine 2 mg was self-administered IV with 10-min lockout intervals. Pain scores and patient satisfaction were assessed at rest and during movement. There were no significant differences among the groups in pain scores and patient satisfaction. Daily morphine consumption was significantly smaller in the RMK group (8 +/- 8 mg) compared with the RM group (23 +/- 20 mg; P = 0.002) and in both groups compared with control (46 +/- 21 mg; P < 0.001). We conclude that intraarticular patient-controlled regional analgesia provides effective pain relief after anterior cruciate ligament reconstruction. The combination of intraarticular ropivacaine, morphine, and ketorolac was superior to control or to a combination of ropivacaine and morphine.

IMPLICATIONS

This study showed the feasibility and efficacy of intraarticular patient-controlled regional analgesia technique for pain relief after anterior cruciate ligament reconstruction. The combination of intraarticular ropivacaine, morphine, and ketorolac was superior to control or to a combination of ropivacaine and morphine.

Incisional self-administration of bupivacaine or ropivacaine provides effective analgesia after inguinal hernia repair

PURPOSE

To evaluate the safety and applicability of two local anesthetic (LA) solutions self-administered for pain treatment after inguinal hernia repair (IHR) by balloon-pumps via catheters placed in the surgical wound. Effectiveness of analgesia was also compared.

METHODS

Two groups of patients for IHR were included in the randomized, double-blind study. An epidural catheter was placed in the surgical wound, tunneled subcutaneously and connected to a balloon-pump containing either 0.25% bupivacaine (B) or 0.25% ropivacaine (R). Postoperatively, the patient self-administered the LA into the wound. Administration could be repeated after 20 min. If moderate to severe pain still persisted, rescue medication (piritramid) was given intravenously. The variables recorded in both groups were: visual analogue scale (VAS), pain scores at rest and with movement, number of applications, wound healing, patients' satisfaction.

RESULTS

During the first 24 hr, median number of LA applications in 26 B patients was 4 (range 1-6) and in 25 R patients 3 (range 1-5). Both groups showed low VAS pain scores: less than 2 at rest, less than 4 with movement. Eighty percent of patients of each group would choose this type of analgesia again. Two patients from B Group and three from R Group needed rescue medication. No wound infection was observed. There were no statistically significant differences between the groups.

CONCLUSION

Self-administration of the LA solution via a catheter in the surgical wound is an effective method of pain relief after IHR with little side-effects.