Subcutaneous infiltration of doxylamine on cutaneous analgesia in rats

BACKGROUND

We aimed to evaluate the effect of doxylamine, a first generation antihistamine, as a local analgesic agent by comparing its effect to bupivacaine.

METHODS

After blocking the cutaneous trunci muscle reflex (CTMR) by subcutaneous injection of doxylamine, we assessed doxylamine's cutaneous analgesic effect in rats. The dose-related effect and duration of doxylamine on infiltrative cutaneous analgesia were compared with that of bupivacaine.

RESULTS

We demonstrated that doxylamine, as well as the local anesthetic bupivacaine produced the cutaneous analgesic effects in a dose-related fashion. At the equipotent dose (50% effective doses (ED₅₀)), the relative potency was bupivacaine (0.41 (0.36-0.48) mmol)> doxylamine (7.39 (6.91-7.91)mmol) (p<0.01). On an equipotent basis (ED₂₅, ED₅₀ and ED₇₅), subcutaneous doxylamine resulted in greater duration of action (p<0.01) than bupivacaine at producing cutaneous analgesia.

CONCLUSIONS

The result of this experiment indicated that doxylamine has the local anesthetic property less potent than bupivacaine, but its nociceptive block duration is longer than that of bupivacaine at an equianalgesic dose.

Isobolographic analysis of the cutaneous antinociceptive interaction between bupivacaine co-injected with serotonin in rats

BACKGROUND

The aim of this experiment was to investigate a long-lasting local anesthetic bupivacaine combined with serotonin at inducing cutaneous antinociception.

METHODS

The skin antinociception, characterized by an inhibition of the cutaneous trunci muscle reflex (CTMR) following the pinprick on the dorsal skin of rats, was evaluated. The cutaneous antinociceptive effects of bupivacaine alone, serotonin alone, or bupivacaine co-injected with serotonin in a dose-dependent fashion were constructed, while the drug-drug interactions were evaluated by isobologram.

RESULTS

Subcutaneous serotonin, as well as the local anesthetic bupivacaine provoked dose-related cutaneous antinociception. On an equipotent basis (50% effective dose [ED₅₀]), the relative potency was bupivacaine (0.43 [0.37-0.50] μmol)>serotonin (1.27 [1.15-1.40] μmol) (p<0.01). At the equi-anesthetic doses (ED₇₅, ED₅₀ and ED₂₅), the duration of bupivacaine was similar to that of serotonin at producing cutaneous antinociceptive effects. Co-administration of bupivacaine and serotonin displayed a synergistic antinociception.

CONCLUSIONS

The preclinical data demonstrated that serotonin is less potent in eliciting cutaneous antinociceptive effects but has the similar duration of action, compared with bupivacaine. We also found a more significant depth of the sensory block with bupivacaine+serotonin than bupivacaine alone.

Efficacy of Magnesium Sulphate as an Adjunct to Ropivacaine in Local Infiltration for Postoperative Pain Following Lower Segment Caesarean Section

INTRODUCTION

Intravenous and peri-articular magnesium has been shown to reduce perioperative analgesic consumption. With this background, subcutaneous infiltration was hypothesized to potentiate the subcutaneous infiltration of local anaesthetic agent.

AIM

To comparatively evaluate the efficacy of magnesium sulphate as an adjunct to ropivacaine in local infiltration for postoperative pain following lower segment cesarean section.

MATERIALS AND METHODS

Sixty parturients undergoing cesarean delivery were randomized to either group A or B in a double blinded manner. After uterine and muscle closure but before skin closure, Group A was administered local subcutaneous wound infiltration of Injection (Inj) ropivacaine 0.75% 150 milligram (mg) or 20 millilitres(ml) whereas, group B patients were given a local subcutaneous wound infiltration of Inj magnesium sulphate 750 mg (1.5 ml of Inj 50% Magnesium sulphate) added to Inj ropivacaine 0.75% (18.5 ml) making a total volume of 20 ml. In postoperative period, Heart rate (HR), Mean Arterial Pressure (MAP), Visual Analogue Score (VAS), supplemental analgesic consumption and timing of each subsequent analgesic was noted for the initial 24 hours.

RESULTS

There was no difference in the timings for the requirement of first Intravenous (IV) rescue analgesic among both the groups (p=0.279). However, the need for 2(nd) and 3(rd) doses of rescue analgesics was significantly later in group B and the difference was statistically significant with p-value of 0.034 and 0.031 respectively. The number of patients who were administered 2(nd), 3(rd) and 4(th) doses of rescue analgesics was significantly greater in group A as compared to group B. None of the patients in group B needed more than 4 doses of rescue analgesia while in group A, 5 patients were administered a rescue analgesic for 5(th) time. The cumulative analgesic requirement in the initial 24 hours was also greater in group A as compared to group B and the difference was statistically significant (p =0.01). The incidence of adverse effects was similar in both the groups.

CONCLUSION

Subcutaneous infiltration of magnesium along with local anaesthetic prolongs the analgesic efficacy of local anaesthetic and is not associated with any significant adverse effects.