Isobolographic analysis of non-depolarising muscle relaxant interactions at their receptor site

Donepezil-related inadequate neuromuscular blockade during laparoscopic surgery: A case report

BACKGROUND

Donepezil is an acetylcholinesterase inhibitor used to improve cognition and delay disease progression in dementia patients by increasing acetylcholine levels. This drug may potentially interact with neuromuscular blocking agents (NMBAs) that act on muscular acetylcholine receptors during general anesthesia. Herein, we present a case of inadequate neuromuscular blockade with rocuronium, a nondepolarizing NMBA, in a dementia patient who had taken donepezil.

CASE SUMMARY

A 71-year-old man was scheduled for laparoscopic gastrectomy. He had been taking donepezil 5 mg for dementia. General anesthesia was induced with propofol and remifentanil. The depth of neuromuscular blockade was monitored by train-of-four (TOF) stimulation. After the administration of rocuronium, the TOF ratio decreased at an unusually slow rate, and a TOF count of 0 was detected 7 min later. After intubation, a TOF count of 1 was detected within 1 min, and a TOF ratio of 12% was detected within 2 min. The TOF count remained at 4 even with an additional bolus and continuous infusion of rocuronium, suggesting resistance to this NMBA. Instead of propofol, an inhalation anesthetic was administered alongside another NMBA (cisatracurium). Then, the quality of neuromuscular blockade improved, and the TOF count remained at 0-1 for the next 70 min. No further problems were encountered with respect to surgery or anesthesia.

CONCLUSION

Donepezil may be responsible for inadequate neuromuscular blockade during anesthesia, especially when total intravenous anesthesia is used.

Optimal dose of combined rocuronium and cisatracurium during minor surgery: A randomized trial

BACKGROUND

Combined rocuronium and cisatracurium have synergistic effects. We investigated whether reduced doses are effective during coadministration, by monitoring neuromuscular relaxation during surgery.

METHODS

This randomized, controlled clinical trial was registered at http://clinicaltrials.gov (registration number NCT02495038). The participants were 81 patients scheduled for elective mastoidectomy and tympanoplasty. Participants were assigned to groups, including the intubating dose group (Group I, n = 27; combined ED95 rocuronium and ED95 cisatracurium), the small reduction group (Group S, n = 27; dose reduced by 10% of each ED95), or the large reduction group (Group L, n = 27; dose reduced by 20% of each ED95). Drugs were administered to patients and a timer was started using TOF-Watch monitoring. TOF (train-of-four) was monitored at the ulnar nerve, at a setting of 2 Hz/12 s. We recorded the time to TOF ratio = 0 (onset), time to first TOF ratio > 25% (duration 25%), and TOF 25-75% (recovery index) under total intravenous anesthesia. One-way analysis of variance was used for statistical analyses (α = 0.05, β = 0.2).

RESULTS

There were no significant demographic differences between groups. Group L had a longer duration to onset (mean ± standard deviation, 399.3 ± 147.8 seconds) and shorter duration 25% (39.4 ± 6.8 minutes) compared to Group I (212.8 ± 56.0 s and 51.3 ± 8.47 minutes, respectively) and Group S (230.7 ± 60.6 s and 47.9 ± 10.7 minutes, respectively). There were no other significant differences between groups.

CONCLUSION

Our findings contribute to determining clinically effective combinations of rocuronium and cisatracurium, as well as to predicting the pharmacokinetic characteristics of the synergistic effects. We suggest that reducing doses of both drugs by approximately 10% of their respective ED95 values is sufficient to maintain neuromuscular relaxation during minor surgery.

In Vitro Antimalarial Activity of Different Inhibitors of the Plasmodial Isoprenoid Synthesis Pathway

Previous studies have shown that fosmidomycin, risedronate, and nerolidol exert antimalarial activity in vitro. We included squalestatin, an inhibitor of the isoprenoid metabolism in Erwinia uredovora, and found that combinations of compounds which act on different targets of the plasmodial isoprenoid pathway possess important supra-additivity effects.

Drug interaction: focusing on response surface models

Anesthesiologists have been aware of the importance of optimal drug combination long ago and performed many investigations about the combined use of anesthetic agents. There are 3 classes of drug interaction: additive, synergistic, and antagonistic. These definitions of drug interaction suggest that a zero interaction model should exist to be used as a reference in classifying the interaction of drug combinations. The Loewe additivity has been used as a universal reference model for classifying drug interaction. Most anesthetic drugs follow the sigmoid E(max) model (Hill equation); this model will be used for modeling response surface. Among lots of models for drug interaction in the anesthetic area, the Greco model, Machado model, Plummer model, Carter model, Minto model, Fidler model, and Kong model are adequate to be applied to the data of anesthetic drug interaction. A model with a single interaction parameter does not accept an inconsistency in the classes of drug interactions. To solve this problem, some researchers proposed parametric models which have a polynomial interaction function to capture synergy, additivity, and antagonism scattered all over the surface of drug combinations. Inference about truth must be based on an optimal approximating model. Akaike information criterion (AIC) is the most popular approach to choosing the best model among the aforementioned models. Whatever the good qualities of a chosen model, it is uncertain whether the chosen model is the best model. A more robust inference can be extracted from averaging several models that are considered relevant.

Analysis of the rocuronium-vecuronium interaction on tetanic fade based on a generalized response surface model with varying relative potencies

BACKGROUND

Some studies have shown that rocuronium and vecuronium have additive, or synergistic effects on muscle relaxation based on the Loewe additivity. Therefore, we performed a fit of tetanic fade data to a generalized response surface model with varying relative potencies proposed by Kong and Lee (KLGRS) to evaluate the usefulness of KLGRS for capturing the interspersed drug interactions and to characterize the interaction between the two drugs.

METHODS

Left phrenic nerve-hemidiaphragms (Male Sprague-Dawley rats, 150-250 g) were mounted in Krebs solution. Supramaximal electrical stimulation (0.2 ms, rectangular) of 50 Hz for 1.9 s to the phrenic nerve evoked tetanic contractions that were measured with a force transducer. Each preparation was exposed to one of 4 vecuronium concentrations (0.0, 1.5, 2.5, and 3.0 microM), or one of 4 rocuronium concentrations (0.0, 3.0, 4.5, and 5.5 microM). Subsequently the adequate amount of rocuronium was added to a vecuronium bath and that of vecuronium was added to a rocuronium until an 80-90% increase in tetanic fade was achieved. We then fitted the modified KLGRS models to the above data, after which we selected the best model, based on 5 methods for determining goodness of fit. Using this method, we obtained the response surface, as well as contour plots for the response surface (i.e. isoboles), the polynomial function and the interaction index.

RESULTS

The model with the constant relative potency ratio and 8 parameters was found to best describe the results, and this model reflected well the characteristics of the raw data. In addition, the two drugs showed a synergistic interaction in almost every area and an antagonistic one in a very narrow area.

CONCLUSIONS

KLGRS was found to be a useful method of analyzing data describing interspersed drug interactions. The interaction between rocuronium and vecuronium was found to be synergistic.

Site selectivity of competitive antagonists for the mouse adult muscle nicotinic acetylcholine receptor

The muscle-type nicotinic acetylcholine receptor has two nonidentical binding sites for ligands. The selectivity of acetylcholine and the competitive antagonists (+)-tubocurarine and metocurine for adult mouse receptors is known. Here, we examine the site selectivity for four other competitive antagonists: cisatracurium, pancuronium, vecuronium, and rocuronium. We rapidly applied acetylcholine to outside-out patches from transfected BOSC23 cells and measured macroscopic currents. We have reported the IC(50) of the antagonists individually in prior publications. Here, we determined inhibition by pairs of competitive antagonists. At least one antagonist was present at a concentration producing > or =67% receptor inhibition. Metocurine shifted the apparent IC(50) of (+)-tubocurarine in quantitative agreement with complete competitive antagonism. The same was observed for pancuronium competing with vecuronium. However, pancuronium and vecuronium each shifted the apparent IC(50) of (+)-tubocurarine less than expected for complete competition but more than expected for independent binding. The situation was similar for cisatracurium and (+)-tubocurarine or metocurine. Cisatracurium did not shift the apparent IC(50) of pancuronium or vecuronium, indicating independent binding of these two pairs. The data were fit to a two-site, two-antagonist model to determine the antagonist binding constants for each site, L(alphaepsilon) and L(alphadelta). We found L(alphaepsilon)/L(alphadelta) = 0.22 (range, 0.14-0.34), 20 (9-29), 21 (4-36), and 1.5 (0.3-2.9) for cisatracurium, pancuronium, vecuronium, and rocuronium, respectively. The wide range of L(alphaepsilon)/L(alphadelta) for some antagonists may reflect experimental uncertainties in the low affinity site, relatively poor selectivity (rocuronium), or possibly that the binding of an antagonist at one site affects the affinity of the second site.

Synergy between pairs of competitive antagonists at adult human muscle acetylcholine receptors

BACKGROUND

Synergistic neuromuscular blocking effects have been observed clinically with certain pairs of nicotinic acetylcholine receptor (nAChR) competitive antagonists. The mechanism for synergy has not been elucidated. We tested the hypothesis that synergy arises from a differential selectivity of antagonists for the two ligand binding sites on adult human nAChR.

METHODS

We expressed nAChR in BOSC23 cells. We applied ACh with or without antagonists to outside-out patches and measured macroscopic currents at room temperature. We determined the IC(90) for (+)-tubocurarine, metocurine, pancuronium, vecuronium, cisatracurium, rocuronium, and atracurium. For 15 combinations of two antagonists, we determined the IC(90) for one antagonist in the presence of the IC(70) of a second antagonist. We constructed isobolograms for 90% inhibition. For single antagonists, we measured inhibition of receptors containing mutations in the epsilon- and delta-subunits to determine site selectivity.

RESULTS

Two pairs of antagonists, metocurine+cisatracurium and cisatracurium+ atracurium exhibited additive inhibition. Ten combinations, including (+)-tubocurarine+ pancuronium and pancuronium+vecuronium, were highly synergistic such that the combination was two to three times more effective than expected for additivity. Three combinations were 1.5-1.6 times more effective than expected for additivity. Inhibition by (+)-tubocurarine and metocurine was sensitive to mutations in the epsilon-subunit only. Vecuronium was affected by the delta-subunit mutation only. Inhibition by other antagonists was decreased by mutations in either subunit.

CONCLUSIONS

Many combinations of antagonists exhibited synergistic effects on adult human nAChR. Synergy was observed with structurally similar and dissimilar antagonists. The degree of synergy did not always correlate well with site specificity assayed with mutants. In some, but not all cases, the synergy at the receptor level correlated with clinical determinations of synergy. We conclude that the synergistic actions of muscle relaxants can be partially explained by direct interactions with adult human nAChR.

Roles of amino acids and subunits in determining the inhibition of nicotinic acetylcholine receptors by competitive antagonists

BACKGROUND

Binding sites for agonists and competitive antagonists (nondepolarizing neuromuscular blocking agents) are located at the alpha-delta and alpha-epsilon subunit interfaces of adult nicotinic acetylcholine receptors. Most information about the amino acids that participate in antagonist binding comes from binding studies with (+)-tubocurarine and metocurine. These bind selectively to the alpha-epsilon interface but are differentially sensitive to mutations. To test the generality of this observation, the authors measured current inhibition by five competitive antagonists on wild-type and mutant acetylcholine receptors.

METHODS

HEK293 cells were transfected with wild-type or mutant (alphaY198F, epsilonD59A, epsilonD59N, epsilonD173A, epsilonD173N, deltaD180K) mouse muscle acetylcholine receptor complementary DNA. Outside-out patches were excised and perfused with acetylcholine in the absence and presence of antagonist. Concentration-response curves were constructed to determine antagonist IC50. An antagonist-removal protocol was used to determine dissociation and association rates.

RESULTS

Effects of mutations were antagonist specific. alphaY198F decreased the IC50 of (+)-tubocurarine 10-fold, increased the IC50 of vecuronium 5-fold, and had smaller effects on other antagonists. (+)-Tubocurarine was the most sensitive antagonist to epsilonD173 mutations. epsilonD59 mutations had large effects on metocurine and cisatracurium. deltaD180K decreased inhibition by pancuronium, vecuronium, and cisatracurium. Inhibition by these antagonists was increased for receptors containing two delta subunits but no epsilon subunit. Differences in IC50 arose from differences in both dissociation and association rates.

CONCLUSION

Competitive antagonists exhibited different patterns of sensitivity to mutations. Except for pancuronium, the antagonists were sensitive to mutations at the alpha-epsilon interface. Pancuronium, vecuronium, and cisatracurium were selective for the alpha-delta interface. This suggests the possibility of synergistic inhibition by pairs of antagonists.

Endogenous adenosine prevents post-tetanic release facilitation mediated by alpha3beta2 nicotinic autoreceptors

We investigated the modulatory role of endogenous adenosine on tetanic-induced (50 Hz for 5 s) nicotinic facilitation of [3H]acetylcholine release (5 Hz for 50 s) from rat motoneurons. Adenosine deaminase (0.5 U/ml) and the adenosine A(2A) receptor antagonist, 3,7-dimethyl-1-propargyl xanthine (DMPX, 30 microM), facilitated post-tetanic [3H]acetylcholine release. Release inhibition caused by tubocurarine (1 microM), dihydro-beta-erythroidine (1 microM) and alpha-conotoxin MII (0.1 microM) was attenuated after tetanic preconditioning. Nicotinic inhibitory action was fully restored after adenosine A(2A) receptor block by DMPX or adenosine deaminase. DMPX (10 microM) caused a leftward shift of the inhibitory dose-response curves for d-tubocurarine (0.1-1 microM), dihydro-beta-erythroidine (0.03-10 microM) and alpha-conotoxin MII (1-300 nM) on post-tetanic twitch amplitude. In contrast, the post-tetanic twitch depression caused by alpha-bungarotoxin (3-100 nM, which had no effect on transmitter release) was attenuated by DMPX (10 microM). It is concluded that activation of adenosine A(2A) receptors by endogenously generated adenosine prevents the post-tetanic release facilitation mediated by nicotinic alpha3beta2 autoreceptors.