Chlorpheniramine produces cutaneous analgesia in rats

Beta-blocker carteolol and oxprenolol produce cutaneous analgesia in response to needle pinpricks in the rat

BACKGROUND

This present study was undertaken to determine whether beta-blockers produce the cutaneous analgesic effect, comparing them with the long-acting local anesthetic bupivacaine.

METHODS

Using a rat model of infiltrative cutaneous analgesia, the effect of 5 beta-blockers (oxprenolol, carteolol, butaxamine, metoprolol, and acebutolol) and bupivacaine was compared and eventually combined with epinephrine.

RESULTS

Among 5 beta-blockers, oxprenolol exhibited the most potent and the longest duration of cutaneous analgesia. In dose-response studies, the rank order of efficacy (ED₅₀ [50% effective dose]) was bupivacaine (0.40 [0.35-0.47] μmol) > oxprenolol (2.33 [2.06-2.64] μmol) > carteolol (4.86 [4.27-5.53] μmol) (p< 0.01). Carteolol provoked a longer duration of analgesia (p< 0.01) than oxprenolol or bupivacaine on an equipotent basis (ED₂₅, ED₅₀, and ED₇₅). Adding epinephrine 1:200,000 to drug preparations (carteolol, oxprenolol, and bupivacaine) at ED₉₅ had a peripheral action in prolonging the duration of action.

CONCLUSIONS

Oxprenolol and carteolol had greater potencies and longer durations of cutaneous analgesia than butaxamine, metoprolol, and acebutolol. Oxprenolol produced a similar duration of action when compared to bupivacaine, while carteolol had a greater duration of action than bupivacaine. Cutaneous analgesia of oxprenolol (or carteolol) plus adrenaline was greater than that of bupivacaine plus adrenaline.

N(Omega)-nitro-l-arginine methyl ester potentiates lidocaine analgesic and anaesthetic effect in rats

OBJECTIVES

The purpose of the experiment was to study the effect of L-NAME (N(Omega)-nitro-L-arginine methyl ester) and its cotreatment with lidocaine on the spinal block and infiltrative cutaneous analgesia.

METHODS

The quality of cutaneous analgesia was examined by the block of the cutaneous trunci muscle reflexes following needle stimuli in the rat. Spinal anaesthetic potency was assessed by measuring three neurobehavioral examinations of nociceptive, proprioceptive and motor function following intrathecal injection in the rat.

KEY FINDINGS

L-NAME (0.6, 6 and 60 nmol) when cotreatment with lidocaine (ED50) produced dose-related cutaneous analgesia. Coadministration of L-NAME (0.6 μmol) with lidocaine intensified (P < 0.01) and prolonged (P < 0.001) cutaneous analgesia, whereas subcutaneous L-NAME (0.6 μmol) and saline did not provoke cutaneous analgesic effects. Adding L-NAME (2.5 μmol) to lidocaine intrathecally prolonged spinal sensory and motor block (P < 0.01), while intrathecal L-NAME (2.5 μmol) or 5% dextrose (vehicle) produced no spinal block.

CONCLUSIONS

L-NAME at 60 nmol (the minimum effective dose) increases and prolongs the effect of cutaneous analgesia of lidocaine. L-NANE at an ineffective dose potentiates lidocaine analgesic and anaesthetic effects.

Intrathecal pramipexole and selegiline for sensory and motor block in rats

BACKGROUND

The purpose of the study was to investigate spinal sensory and motor block by antiparkinsonian drugs (pramipexole and selegiline), and the combination of pramipexole and the local anesthetic lidocaine.

METHODS

Using a technique of spinal blockade in rats, the effects of pramipexole, selegiline, and coadministration of pramipexole and lidocaine on spinal blockades of motor and sensory function were investigated.

RESULTS

Under a concentration of 100 mM, pramipexole displayed more potent and had a longer duration of nociceptive, proprioceptive, and motor block than selegiline, whereas pramipexole and selegiline were less potent in comparison to lidocaine. Pramipexole produced spinal nociceptive, proprioceptive, and motor blocks in a dose-related manner. On the ED₅₀ (50% effective dose) basis, the rank-order potency on nociceptive, proprioceptive, and motor block was pramipexole < lidocaine. The spinal block duration of pramipexole was greater than lidocaine at every equipotent dose tested (ED₂₅, ED₅₀, and ED₇₅). Coadministration of lidocaine (ED₅₀ or ED₉₅) with pramipexole (4.5 μmol/kg) improved the effect (efficacy) and duration of the spinal block.

CONCLUSIONS

Pramipexole and selegiline were less potent than lidocaine to block sensory and motor responses. The duration of the spinal anesthetic effect of pramipexole was longer than lidocaine. At a non-effective dose, pramipexole increased the duration of efficacy of lidocaine.

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.