2-Adamantanamine produces prolonged spinal block in rats

Electrochemiluminescence of an iridium complex doped with SiO2 nanoparticles to detect 2-adamantanamine based on the host-guest interaction of cucurbit[7]uril

The poor solubility of iridium complexes severely hampers its application in the electrochemiluminescence (ECL) sensing field. The doping of an iridium complex with silica (SiO2) nanospheres provides feasible solution for this problem. Herein, one kind of water insoluble iridium complex ([Ir(dFppy)2(d(CF3)bpy)](PF6)) was doped with SiO2 nanoparticles to obtain a luminescent nanocomposite (SiO2@Ir) which could generate strong ECL signals to act as a beacon molecule. An "off-on-off" mode ECL sensor was proposed based on the competitive host-guest interactions between 2-adamantanamine (2-ADA), ferrocene (Fc) and cucurbit[7]uril (Q[7]). Fc could be used as an inhibitor to decrease the ECL signal, while Q[7] could wrap Fc to recover the ECL signal. Q[7] has a stronger binding ability with 2-ADA than Fc. As a result, 2-ADA could replace Fc from the cavity of Q[7], and the ECL signal was inhibited again. Under the optimal conditions, the ECL intensity varied linearly with 2-ADA concentration in the range of 1.0 × 10-8 to 1.0 × 10-6 mol L-1 with a detection limit of 2.5 × 10-10 mol L-1. The results not only provided a new avenue for the application of water insoluble iridium complexes in ECL sensing, but also revealed the attractive potential of host-guest interactions in the fabrication of biosensors.

Antimalarial primaquine for spinal sensory and motor blockade in rats

OBJECTIVES

The purpose of the experiment was to estimate whether intrathecal antimalarial drugs could provoke spinal block, and their comparison with lidocaine.

METHODS

Rats were intrathecally administrated with antimalarial agents (primaquine, chloroquine, hydroxychloroquine and amodiaquine) and lidocaine, and neurobehavioural examinations (nociception, proprioception and motor function) were assessed; n = 8 per group. One-way and two-way analysis of variance were designed to analyse data.

KEY FINDINGS

At a concentration of 20 mM, primaquine (0.46 mg/rat) exhibited the longest duration and the most potent effect of nociceptive, proprioceptive and motor blockade (P < 0.01) among five drugs, whereas the other antimalarial drugs displayed a lesser or similar potency of spinal blockade compared with lidocaine (0.29 mg/rat). In dose-dependent studies, primaquine was more potent (P < 0.01) than lidocaine for spinal block. At ED25, ED50 and ED75 equipotent doses, primaquine produced a greater duration of spinal motor, proprioceptive and nociceptive blockade when compared with lidocaine (P < 0.01).

CONCLUSIONS

Primaquine, chloroquine, hydroxychloroquine and amodiaquine produced spinal blockade. Primaquine was more potent and displayed a prolonged life of local anaesthetic effect compared with lidocaine, whereas the other antimalarial drugs displayed a lesser or similar potency compared with lidocaine.

Antimalarial primaquine for skin infiltration analgesia in rats

OBJECTIVES

The purpose of this study was to estimate the ability of antimalarial medications to induce local infiltration analgesia.

METHODS

Using a rat model of skin infiltration anaesthesia, the effects of antimalarial medications (primaquine, chloroquine, hydroxychloroquine and amodiaquine) were compared with the application of lidocaine.

KEY FINDINGS

At a dose of 3 μmol, primaquine and chloroquine displayed better potency (all P < 0.05) and greater duration (all P < 0.01) of cutaneous analgesia than lidocaine, whereas the other antimalarial medications showed a similar potency and duration of cutaneous analgesia when compared with lidocaine. When a dose of 3 μmol antimalarial medication was used, primaquine was the most potent and had the longest duration of action among four antimalarial medications. The relative potency ranking (ED50, 50% effective dose) has been found to be primaquine [2.10 (1.87 - 2.37) μmol] > lidocaine [6.27 (5.32 -7.39) μmol] (P < 0.01). Infiltration analgesia of skin with primaquine had a greater duration of action than did lidocaine on the equipotent (ED25, ED50, ED75) basis (P < 0.01).

CONCLUSIONS

Primaquine and chloroquine have greater potency and longer lasting skin analgesia when compared with lidocaine, while the other antimalarials display a similar potency in comparison with lidocaine.

Chloroquine for prolonged skin analgesia in rats

The purpose of this study was to investigate the ability of chloroquine and chloroquine in combination with vasoconstrictor epinephrine to act as a local anesthetic in skin analgesia. After subcutaneous injection of drugs in rats, the inhibition of the cutaneous trunci muscle reflex (CTMR) is designed for evaluation of the cutaneous analgesic effect. The analgesic effect of chloroquine was compared with that of bupivacaine or coadministration of chloroquine and epinephrine. Chloroquine produced exactly the same local anesthesia as bupivacaine did in a dose-dependent manner. On the ED₅₀ (50 % effective dose) basis, the analgesic potency was chloroquine (4.81 [4.45-5.20] μmol) < bupivacaine (0.46 [0.40‒0.52] μmol) (p <  0.01). At every equipotent dose tested (ED₂₅, ED₅₀ and ED₇₅), chloroquine had a longer duration of cutaneous analgesia than bupivacaine (p <  0.01). Epinephrine enhanced the potency and duration of chloroquine-induced cutaneous analgesia. We found that chloroquine and bupivacaine elicit dose-dependent cutaneous analgesia. Chloroquine is not as potent as bupivacaine, but acts as an infiltrative anesthetic for a longer duration of time and is more potent and effective when used in combination with epinephrine.

Dopamine enhancement of dextrorphan-induced skin antinociception in response to needle pinpricks in rats

BACKGROUND

Dextrorphan with long-acting local anesthetic effects did not cause system toxicity as fast as bupivacaine, while catecholamines (i.e., epinephrine) with the vasoconstrictive characteristics enhanced the effects of local anesthetic drugs. The objective of the experiment was to examine the synergistic effect of local dopamine (a catecholamine) injection on cutaneous antinociception of dextrorphan.

METHODS

The panniculus reflex in response to skin stimulation with a needle was used as the primary endpoint when dextrorphan (1.50, 2.61, 5.46, 10.20 and 20.40 μmol) alone, dopamine (16.20, 32.40, 51.60, 60.00 and 81.60 μmol) alone, or dopamine + dextrorphan (a ratio of ED₅₀vs. ED₅₀) was injected subcutaneously on the rat's back. We used an isobolographic modelling approach to determine whether a synergistic effect would be observed.

RESULTS

We showed that dextrorphan, dopamine, or the mixture of dopamine and dextrorphan produced dose-related skin antinociception. The potency (ED₅₀, 50% effective dose) for cutaneous antinociception was dextrorphan [6.02 (5.93-6.14) μmol] greater than dopamine [48.91 (48.80-49.06) μmol] (p < 0.01). The duration of nociceptive inhibition induced by dopamine was longer than that induced by dextrorphan (p <  0.01) based on their equipotent doses (ED₂₅, ED₅₀, and ED₇₅). Enhancement and prolongation of skin antinociception occurred after co-administration of dopamine with dextrorphan.

CONCLUSIONS

When compared to dopamine, dextrorphan was more potent and had a shorter duration of skin nociceptive block. Dopamine produced a synergistic effect on dextrorphan-mediated antinociception, and prolonged dextrorphan's antinociceptive duration.

Skin nociceptive block with pramoxine delivery by subcutaneous injection in rats

BACKGROUND

Pramoxine has been shown to produce spinal anesthesia, while cutaneous analgesia (peripheral) of pramoxine is not established. The experimental goal was to examine cutaneous antinociception produced by a local anesthetic (LA) pramoxine and compare this result with that of another well-known LA lidocaine.

METHODS

Cutaneous antinociception was evaluated by blockade of pinprick- induced cutaneous trunci muscle reflex (CTMR) on the skin of rat's back. After the dose-related curves were constructed, the quality and duration of drug's (lidocaine and pramoxine) cutaneous antinociception were compared.

RESULTS

We showed that pramoxine, as well as lidocaine produced skin antinociception in a dose-related fashion. The relative potency (ED₅₀ [50% effective dose] basis) was lidocaine (5.44 [4.67-6.35] μmol) greater than pramoxine (42.1 [38.8-45.7] μmol) (p < 0.01). On the basis of equianalgesic doses (ED₇₅, ED₅₀, and ED₂₅), pramoxine caused equivalent duration of cutaneous antinociception to lidocaine.

CONCLUSIONS

These preclinical data indicated that pramoxine elicits skin antinociception dose-relatedly. Pramoxine exhibits a potency less than that of lidocaine while they have a comparable duration of skin antinociceptive action.

Intrathecal pramoxine causes long-lasting spinal sensory and motor block in rats

OBJECTIVES

The objective of this experiment was to investigate spinal anaesthetic effects of pramoxine and its comparison with bupivacaine, a long-lasting local anaesthetic.

METHODS

After intrathecal injection, three neurobehavioural assessments, which consisted of nociceptive, proprioceptive and motor block, were constructed in rats. The effects of bupivacaine and pramoxine (four doses of each drug) in a dose-related manner were conducted to obtain the ED₅₀ (50% effective dose). Pramoxine potency and duration at provoking spinal nociceptive, proprioceptive and motor block were compared with those of bupivacaine.

KEY FINDINGS

We manifested that pramoxine provoked dose-relatedly spinal blockades of nociception, proprioception and motor function. Based on the ED₅₀ , the rank potency at producing spinal nociceptive, proprioceptive and motor block was bupivacaine (0.90 (0.82-1.02), 1.00 (0.92-1.08) and 1.16 (1.02-1.34) μmol/kg) greater (P < 0.01 for the differences) than pramoxine (15.47 (14.04-17.05), 16.46 (15.06-17.99), and 17.77 (16.48-19.15) μmol/kg). The spinal block duration created by bupivacaine was not predominantly different (P > 0.05 for the differences) from that created by pramoxine at the equipotent doses (ED₇₅ , ED₅₀ and ED₂₅ ).

CONCLUSIONS

Our preclinical experiment indicated that pramoxine elicited a dose-related spinal block, was less potent than bupivacaine and had a similar duration of spinal block compared with bupivacaine.