Antidotal Effects of the Antihistamine Diphenhydramine Against Cholinesterase Inhibitor Poisoning: A Meta-Analysis of Median Lethal Doses in Experimental Animals.

The H1-antihistamine diphenhydramine antagonizes cholinesterase inhibitor poisoning in various animal species. One aspect of acute antidotal actions of diphenhydramine is increasing the median lethal doses (LD50) of toxicants. The objective of this meta-analysis was to assess the antidotal action of diphenhydramine against short-term toxicity (LD50) of cholinesterase inhibitors in experimental animals. The experimental studies selected were according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. They were conducted in laboratory animals (mice, rats, and chicks) to determine acute LD50 values of cholinesterase inhibitors (organophosphates, carbamates, and imidocarb) under the influence of diphenhydramine vs. controls. Twenty-eight records were selected from 12 studies on mice (n= 242), rats (n= 27), and young chicks (n= 128). The forest plot of randomized two-group meta-analysis assessed effect size, subgroup analysis, drapery prediction, heterogeneity, publication bias-funnel plot as well as one-group proportions meta-analysis of percent protection. Diphenhydramine significantly increased the combined effect size (i.e. increased LD50) in intoxicated experimental animals in comparison to controls (-3.71, standard error (SE) 0.36, 95%CI -4.46, -2.97). The drapery plot proposed a wide range of confidence intervals. The I2 index of heterogeneity of the combined effect size was high at 81.03% (Q= 142.3, p < 0.0001). Galbraith regression also indicated data heterogeneity; however, the normal quantile plot indicated no outliers. Subgroup analysis indicated significantly high heterogeneity with organophosphates (I2 = 63.72%) and carbamates (I2 = 76.41%), but low with imidocarb (I2 = 51.48%). The funnel plot and Egger regression test (t= -13.7, p < 0.0001) revealed publication bias. The median of the diphenhydramine protection ratio was 1.655, and the related forest plot of one group proportion meta-analysis revealed a statistically high level of protection (0.594, SE 0.083, 95%CI 0.432, 0.756), with high heterogeneity (I2= 99.86). The risk of bias assessment was unclear, while the total score (16 out of 20) of each study leaned towards the side of the low risk of bias. In conclusion, the meta-analysis of LD50 values indicated that diphenhydramine unequivocally protected experimental animals from the acute toxicity of cholinesterase inhibitors. The drug could be an additional antidote against acute poisoning induced by cholinesterase inhibitors, but a word of caution: it is not to be considered as a replacement for the standard antidote atropine sulfate. Further studies are needed to examine the action of diphenhydramine on adverse chronic effects of cholinesterase inhibitors.

Effect of memantine hydrochloride on cisplatin-induced neurobehavioral toxicity in mice.

Cisplatin is an anticancer agent widely used in the treatment of malignant tumors. One of the major adverse effects of cisplatin is its neurotoxicity. Memantine, an uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, has been reported to have neuroprotective effects against neurological deficits. This study therefore investigated the possible protective role of memantine as an agent to minimize the neurobehavioral toxic side effects of cisplatin. Two different therapeutic doses of memantine (5 mg/kg) and (10 mg/kg) were orally administered for 30 days to 50 male BALB/c mice divided into 5 groups: G1: no treatment; G2: cisplatin treatment; G3: memantine treatment; G4: pretreatment of (5 mg/kg) memantine with cisplatin (4 mg/kg); G5: pretreatment of 10 mg/kg memantine with cisplatin (4 mg/kg). Weekly neurobehavioral investigations were conducted using the following battery of tests: open field activity, negative geotaxis, hole-board test, swimming test, and calculation of weight. At the end of the experimental period the mice were euthanized, and immunohistochemistry was then used to measure the expression scores of nicotinic acetylcholine receptors (nAChRs) in the muscles and brain. Results revealed that mice in G2 showed a significant decrease in the ability to perform neurobehavioral tasks. The mice in G5 exhibited a significantly improved ability on these tests, indicating a complete neurobehavioral protective effect, while the mice in G4 showed partial protection. The nAChRs score showed higher expression in the case of G2 in comparison with G3, G4, and G5. Weight loss was exhibited in G2, while in G3 and G1 these values were normal. A therapeutic dose of memantine 10 mg/kg yielded more protection than 5 mg/kg in the treatment of neuropathy; this highlights the importance of using memantine to decrease the main side effects of cisplatin.

Antinociception by metoclopramide, ketamine and their combinations in mice.

BACKGROUND: Metoclopramide is a centrally acting antiemetic and ketamine is a general anesthetic used with sedatives, tranquilizers and analgesics. Metoclopramide has analgesic effects and its combination with ketamine causes sedation and hypnosis. The contribution of metoclopramide to the analgesic effect of ketamine is not known. The purpose of the present study was to explore the analgesic effects of metoclopramide and ketamine alone or in combination in mice. METHODS: The up-and-down method was used to determine the median effective analgesic dosages (ED(50)s) of metoclopramide and ketamine administered intraperitoneally (ip) either alone or concomitantly in male albino Swiss mice. Analgesia was measured by using a hot plate. The ED(50)s of both drugs were analyzed isobolographically to determine the type of interaction between them. The analgesic effect of metoclopramide-ketamine combination (62.3 and 4.3 mg/kg, ip) was also monitored by the hot plate and acetic acid writhing methods. RESULTS: The analgesic ED(50)s for metoclopramide and ketamine in mice were 30.15 and 2.15 mg/kg, ip, respectively. Concomitant administration of the drugs reduced their ED(50)s to 10.17 and 0.68 mg/kg, ip, respectively. Isobolographic analysis of these ED(50)s for both drugs revealed synergistic analgesic effect. Further, the combination of the drugs was effective analgesic as seen by the hot plate test and by another analgesic test paradigm, the acetic acid-induced writhings in mice. CONCLUSIONS: The data suggest that the combination of metoclopramide and ketamine synergistically controls acute pain in mice. This combination could be used clinically for restraint and minor surgical interventions in mice.