Cutaneous Analgesia and Systemic Toxicity of Carbetapentane and Caramiphen in Rats:

Carbetapentane citrate

Carbetapentane citrate, a non-opioid centrally-acting antitussive drug, is a common treatment for cough associated with other diseases such as common cold and respiratory tract infections. Its mode of action is very close to that of atropine; since it acts at the level of the peripheral parasympathetic nerve endings. The drug reaches its maximum plasma concentration (C_max) 2h after administration, and it has a plasma half-life of 2.3h in case of oral administration. Due to its clinical importance, there are many analytical methods in the literature for carbetapentane determination. In addition, it is crucial to collect its analytical results in a single chapter so as to allow researchers to easily interpret their experimental data. Here, we provide the analytical profile of carbetapentane citrate with a brief description/interpretation of each analysis.

Naloxone prolongs cutaneous nociceptive block by lidocaine in rats

We aimed to investigate the local anesthetic properties of naloxone alone or as an adjunct for the local anesthetic lidocaine. After the block of the cutaneous trunci muscle reflex (CTMR) with drugs delivery by subcutaneous infiltration, cutaneous nociceptive block was tested on the ratsꞌ backs. We demonstrated that naloxone, as well as lidocaine, elicited cutaneous analgesia dose-dependently. The relative potency in inducing cutaneous analgesia was lidocaine [22.6 (20.1 - 25.4) μmol/kg] > naloxone [43.2 (40.3 - 46.4) μmol/kg] (P < 0.05). On an equianesthetic basis [50% effective dose (ED₅₀ ), ED₂₅ , and ED₇₅ ], naloxone displayed a greater duration of cutaneous analgesic action than lidocaine (P < 0.01). Coadministration of lidocaine (ED₉₅ or ED₅₀ ) and ineffective-dose naloxone (13.3 μmol/kg) intensifies sensory block (P < 0.01) with prolonged duration of action (P < 0.001) compared with lidocaine (ED₉₅ or ED₅₀ ) alone or naloxone (13.3 μmol/kg) alone on infiltrative cutaneous analgesia. The preclinical data showed that naloxone is less potent than lidocaine as an infiltrative anesthetic, but its analgesic duration was longer than that of lidocaine. Furthermore, naloxone prolongs lidocaine analgesia, acting synergistically for nociceptive block.

Synergistic Effects of Serotonin or Dopamine Combined With Lidocaine at Producing Nociceptive Block in Rats

BACKGROUND

The purpose of this experiment was to investigate the interactions of the local anesthetic lidocaine combined with an agent (serotonin or dopamine) as infiltrative anesthetics.

METHODS

Cutaneous analgesia was characterized by the blockade of the cutaneous trunci muscle reflex following 6 skin pinpricks on the rat back. Serotonin or dopamine at producing cutaneous analgesia in a dosage-dependent fashion was compared with lidocaine. Drug-drug interactions were calculated using the isobolographic analysis.

RESULTS

We revealed that serotonin, dopamine, and lidocaine provoked dose-related cutaneous analgesic effects. On the 50% effective dose basis, the rank of drugs' potency was found to be serotonin (1.70 [1.56-1.85] μmol) > lidocaine (5.18 [4.67-5.75] μmol) > dopamine (43.0 [40.9-45.2] μmol) (P < 0.01). At doses equivalent to their 25%, 50%, and 75% effective doses, serotonin or dopamine elicited a longer duration of action than lidocaine (P < 0.01) on producing cutaneous analgesia. Coadministration of serotonin or dopamine with lidocaine produced a synergistic effect.

CONCLUSIONS

The preclinical data showed that serotonin and dopamine produce dose-related cutaneous analgesic effects as an infiltrative anesthetic. Serotonin has a better potency with a much longer duration of action compared with lidocaine at provoking cutaneous analgesia. Serotonin or dopamine as an adjuvant increases the quality of lidocaine in cutaneous analgesia.

Ifenprodil for prolonged spinal blockades of motor function and nociception in rats

BACKGROUND

The aim of the study was to compare the proposed spinal anesthetic effect of ifenprodil, an a1 adrenergic receptor antagonist, with that of the long-acting local anesthetic bupivacaine.

METHODS

After intrathecally injecting the rats with five different doses of each drug, the dose-response curves of ifenprodil and bupivacaine were constructed to obtain the 50% effective dose (ED50). The spinal blockades of motor function and nociception of ifenprodil were compared with that of bupivacaine.

RESULTS

We showed that either ifenprodil or bupivacaine produced spinal blockades of motor function and nociception dose-dependently. On the ED50 basis, the potency of ifenprodil (0.42(0.38-0.46) μmol; 0.40(0.36-0.44) μmol) was equal (p>0.05) to that of bupivacaine (0.38(0.36-0.40) μmol; 0.35(0.32-0.38) μmol) in motor function and nociception, respectively. At the equianesthetic doses (ED25, ED50, and ED75), duration produced by ifenprodil was greater than that produced by bupivacaine in motor function and nociception (p<0.05 for the differences). Furthermore, both ifenprodil and bupivacaine showed longer duration of sensory blockade than that of motor blockade (p<0.05 for the differences).

CONCLUSIONS

The resulting data demonstrated that ifenprodil produces a dose-dependent local anesthetic effect in spinal anesthesia. Ifenprodil shows a more sensory-selective duration of action over motor block, whereas the duration of anesthesia is significantly longer with ifenprodil than with bupivacaine.

Clonidine as an adjuvant for propranolol enhances its effect on infiltrative cutaneous analgesia in rats

Clonidine prolongs duration of analgesia when used as an adjunct to local anesthetics for infiltrative cutaneous analgesia, and propranolol produces local anesthesia. The purpose of the experiment was to evaluate clonidine as an adjuvant for propranolol on the quality and duration of cutaneous analgesia. A rat model of cutaneous trunci muscle reflex (CTMR) in response to local skin pinprick was employed to evaluate the cutaneous analgesic effect of propranolol combined with clonidine. The long-lasting local anesthetic bupivacaine was used as control. Cutaneous analgesia elicited by propranolol and bupivacaine was dose-dependent, and both propranolol (9.0μmol) and bupivacaine (1.8μmol) produced 100% nociceptive blockade. On an 50% effective dose (ED50) basis, the relative potency was bupivacaine [0.48 (0.42-0.55) μmol] greater than propranolol [2.27 (1.98-2.54) μmol] (p<0.01). Subcutaneous saline and clonidine (0.12μmol) did not produce cutaneous analgesia. The mixture of an ineffective-dose clonidine (0.12μmol) and a drug (propranolol or bupivacaine) at ED50 or ED95 increased the potency and extended the duration at producing cutaneous analgesia. The resulting data demonstrated that propranolol is less potent than bupivacaine as an infiltrative anesthetic. Clonidine as an adjuvant for propranolol or bupivacaine has a significant peripheral action in increasing the depth and duration of action on infiltrative cutaneous analgesia.

Memantine elicits spinal blockades of motor function, proprioception, and nociception in rats

Although memantine blocks sodium currents and produces local skin anesthesia, spinal anesthesia with memantine is unknown. The purpose of the study was to evaluate the local anesthetic effect of memantine in spinal anesthesia and its comparison with a widely used local anesthetic lidocaine. After intrathecally injecting the rats with five doses of each drug, the dose-response curves of memantine and lidocaine were constructed. The potencies of the drugs and durations of spinal anesthetic effects on motor function, proprioception, and nociception were compared with those of lidocaine. We showed that memantine produced dose-dependent spinal blockades in motor function, proprioception, and nociception. On a 50% effective dose (ED50 ) basis, the rank of potency was lidocaine greater than memantine (P < 0.05 for the differences). At the equipotent doses (ED25 , ED50 , ED75 ), the block duration produced by memantine was longer than that produced by lidocaine (P < 0.05 for the differences). Memantine, but not lidocaine, displayed more sensory/nociceptive block than motor block. The preclinical data demonstrated that memantine is less potent than lidocaine, whereas memantine produces longer duration of spinal anesthesia than lidocaine. Memantine shows a more sensory-selective action over motor blockade.

Propranolol combined with dopamine has a synergistic action in intensifying and prolonging cutaneous analgesia in rats

BACKGROUND

The purpose of the experiment was to assess interactions of dopamine with propranolol as an infiltrative anesthetic.

METHODS

After injecting the rats with four doses of drugs subcutaneously, the cutaneous analgesic effect of propranolol was compared with dopamine through the blockade of cutaneous trunci muscle reflex (CTMR) in response to local skin pinprick. Drug-drug interactions were examined via an isobolographic analysis.

RESULTS

We demonstrated that the action of propranolol and dopamine was dose dependent to skin infiltrative analgesia. On the ED(50) (50% effective dose) basis, the rank of drug potency was propranolol (11.3 [10.6-12.2]μmol) > dopamine (195 [188-205]μmol) (p < 0.001). At the equi-anesthetic doses (ED(25), ED(50), ED(75)), the block duration caused by dopamine was equal to that caused by propranolol. Coadministration of dopamine and propranolol exhibited a synergistic effect on infiltrative cutaneous analgesia.

CONCLUSIONS

The preclinical data showed that dopamine produced a lesser potency but a comparable duration of cutaneous analgesia compared to propranolol. Adding dopamine to propranolol potentiated and prolonged propranolol's cutaneous analgesic effect.

Subcutaneous L-tyrosine elicits cutaneous analgesia in response to local skin pinprick in rats

The purpose of the study was to estimate the ability of L-tyrosine to induce cutaneous analgesia and to investigate the interaction between L-tyrosine and the local anesthetic lidocaine. After subcutaneously injecting the rats with L-tyrosine and lidocaine in a dose-dependent manner, cutaneous analgesia (by blocking the cutaneous trunci muscle reflex-CTMR) was evaluated in response to the local pinprick. The drug-drug interaction was analyzed by using an isobolographic method. We showed that both L-tyrosine and lidocaine produced dose-dependent cutaneous analgesia. On the 50% effective dose (ED50) basis, the rank of drug potency was lidocaine (5.09 [4.88-5.38] μmol)>L-tyrosine (39.1 [36.5-41.8] μmol) (P<0.05). At the equipotent doses (ED25, ED50, and ED75), the duration of cutaneous analgesia caused by L-tyrosine lasted longer than that caused by lidocaine (P<0.01). Lidocaine co-administered with L-tyrosine exhibited an additive effect on infiltrative cutaneous analgesia. Our pre-clinical study demonstrated that L-tyrosine elicits the local/cutaneous analgesia, and the interaction between L-tyrosine and lidocaine is additive. L-tyrosine has a lower potency but much greater duration of cutaneous analgesia than lidocaine. Adding L-tyrosine to lidocaine preparations showed greater duration of cutaneous analgesia compared with lidocaine alone.

Caramiphen edisylate: an optimal antidote against organophosphate poisoning

Potent cholinesterase inhibitors such as sarin, induce an array of harmful effects including hypersecretion, convulsions and ultimately death. Surviving subjects demonstrate damage in specific brain regions that lead to cognitive and neurological dysfunctions. An early accumulation of acetylcholine in the synaptic clefts was suggested as the trigger of a sequence of neurochemical events such as an excessive outpour of glutamate and activation of its receptors. Indeed, alterations in NMDA and AMPA central receptors' densities were detected in brains of poisoned animals. Attempts to improve the current cholinergic-based treatment by adding potent anticonvulsants or antiglutamatergic drugs produced unsatisfactory results. In light of recent events in Syria and the probability of various scenarios of military or terrorist attacks involving organophosphate (OP) nerve agent, research should focus on finding markedly improved countermeasures. Caramiphen, an antimuscarinic drug with antiglutamatergic and GABAergic facilitating properties, was evaluated in a wide range of animals and experimental protocols against OP poisoning. Its remarkable efficacy against OP exposure was established both in prophylactic and post-exposure therapies in both small and large animals. The present review will highlight the outstanding neuroprotective effect of caramiphen as the optimal candidate for the treatment of OP-exposed subjects.

Antitussive drugs--past, present, and future

Cough remains a serious unmet clinical problem, both as a symptom of a range of other conditions such as asthma, chronic obstructive pulmonary disease, gastroesophageal reflux, and as a problem in its own right in patients with chronic cough of unknown origin. This article reviews our current understanding of the pathogenesis of cough and the hypertussive state characterizing a number of diseases as well as reviewing the evidence for the different classes of antitussive drug currently in clinical use. For completeness, the review also discusses a number of major drug classes often clinically used to treat cough but that are not generally classified as antitussive drugs. We also reviewed a number of drug classes in various stages of development as antitussive drugs. Perhaps surprising for drugs used to treat such a common symptom, there is a paucity of well-controlled clinical studies documenting evidence for the use of many of the drug classes in use today, particularly those available over the counter. Nonetheless, there has been a considerable increase in our understanding of the cough reflex over the last decade that has led to a number of promising new targets for antitussive drugs being identified and thus giving some hope of new drugs being available in the not too distant future for the treatment of this often debilitating symptom.