Clinical pharmacology of pyridostigmine and neostigmine in patients with myasthenia gravis

Congenital Myasthenic Syndromes in Belgium: Genetic and Clinical Characterization of Pediatric and Adult Patients

BACKGROUND

Congenital myasthenic syndromes (CMS) are a group of genetic disorders characterized by impaired neuromuscular transmission. CMS typically present at a young age with fatigable muscle weakness, often with an abnormal response after repetitive nerve stimulation (RNS). Pharmacologic treatment can improve symptoms, depending on the underlying defect. Prevalence is likely underestimated. This study reports on patients with CMS followed in Belgium in 2022.

METHODS

Data were gathered retrospectively from the medical charts. Only likely pathogenic and pathogenic variants were included in the analysis.

RESULTS

We identified 37 patients, resulting in an estimated prevalence of 3.19 per 1,000,000. The patients harbored pathogenic variants in CHRNE, RAPSN, DOK7, PREPL, CHRNB1, CHRNG, COLQ, MUSK, CHRND, GFPT1, and GMPPB. CHRNE was the most commonly affected gene. Most patients showed disease onset at birth, during infancy, or during childhood. Symptom onset was at adult age in seven patients, caused by variants in CHRNE, DOK7, MUSK, CHRND, and GMPPB. Severity and distribution of weakness varied, as did the presence of respiratory involvement, feeding problems, and extraneuromuscular manifestations. RNS was performed in 23 patients of whom 18 demonstrated a pathologic decrement. Most treatment responses were predictable based on the genotype.

CONCLUSIONS

This is the first pooled characterization of patients with CMS in Belgium. We broaden the phenotypical spectrum of pathogenic variants in CHRNE with adult-onset CMS. Systematically documenting larger cohorts of patients with CMS can aid in better clinical characterization and earlier recognition of this rare disease. We emphasize the importance of establishing a molecular genetic diagnosis to tailor treatment choices.

Single fiber electromyography and measuring jitter with concentric needle electrodes

This monograph contains descriptions of the single fiber electromyography (SFEMG) method and of the more recently implemented method of recording jitter with concentric needle electrodes (CNEs). SFEMG records action potentials from single muscle fibers (SFAPs), which permits measuring fiber density (FD), a sensitive measure of reinnervation, and jitter, a sensitive measure of abnormal neuromuscular transmission (NMT). With voluntary activation, jitter is measured between two SFAPs with acceptable amplitude and rise time. With activation by axon stimulation, jitter is measured between the stimulus and individual SFAPs. Pitfalls due to unstable triggers and inconstant firing rates during voluntary activation and subliminal stimulation during axon stimulation should be identified and avoided. In CNE recordings, spikes with shoulders or rising phases that are not parallel are produced by summation of SFAPS; these should be excluded and reference values for CNE jitter should be used. CNE and SFEMG have similar and very high sensitivity in detecting increased jitter, as in myasthenia gravis and other myasthenic conditions. However, jitter is also seen in ongoing reinnervation and some myopathic conditions. With SFEMG, these can be identified by increased FD; however, FD cannot be measured with CNE, and conventional electromyography should be performed in muscles with increased jitter to detect neurogenic or myogenic abnormalities. Jitter is abnormal after injections of botulinum toxin, even in muscles remote from the injection site, and can persist for 6 mo or more. This can complicate the detection or exclusion of abnormal NMT.

Single fiber EMG and measuring jitter with concentric needle electrodes

This monograph contains descriptions of the single-fiber electromyography (SFEMG) method and of the more recently implemented method of recording jitter with concentric needle electrodes (CNE). SFEMG records action potentials from single muscle fibers (SFAPs), which permits measuring fiber density (FD), a sensitive measure of reinnervation, and jitter, a sensitive measure of abnormal neuromuscular transmission (NMT). With voluntary activation, jitter is measured between two SFAPs with acceptable amplitude and rise time. With activation by axon stimulation, jitter is measured between the stimulus and individual SFAPs. Pitfalls due to unstable triggers and inconstant firing rates during voluntary activation and subliminal stimulation during axon stimulation should be identified and avoided. In CNE recordings, spikes with shoulders or rising phases that are not parallel are produced by summation of SFAPS; these should be excluded and reference values for CNE jitter should be used. CNE and SFEMG have similar and very high sensitivity in detecting increased jitter, as in myasthenia gravis and other myasthenic conditions. However, jitter is also seen in ongoing reinnervation and some myopathic conditions. With SFEMG, these can be identified by increased FD; however, FD cannot be measured with CNE, and conventional EMG should be performed in muscles with increased jitter to detect neurogenic or myogenic abnormalities. Jitter is abnormal after injections of botulinum toxin, even in muscles remote from the injection site, and can persist for 6 mo or more. This can complicate the detection or exclusion of abnormal NMT.

[Investigations into the distribution of neohistamine methylsulfate in the organism of the warm blooded animals following its intragastric administration]

The objective - of the present study was to elucidate the specific features of the distribution of neohistamine methylsulfate (proserin) in the organism of the omnivorous warm blooded animals following its intragastric administration. The analytical methods included TLC, HPLC, and UV-spectrophotometry. Neohistamine methylsulfate was administered intrgastrically to the male Wistar rats at a dose equivalent to the triple LD₅₀ dose. The substance of interest was extracted by acetone from the biological matrices of the dead animals and purified by sequential treatment with the relevant solvents and chromatography in a thin layer of the reverse-phase sorbent (C₁₄-C₁₅ bonded phase model) with the elution in the buffer solution (pH 1.98) - acetone (8:2) system. The compound of interest was identified based on the Rf values (obtained by TLC), retention time (in HPLC), and the spectral characteristics. The quantitative determination of the analyte in the biomatrices was performed with the use of UV spectrophotometry. The analytical methods were validated based on the criteria for linearity, selectivity, correctness, and precision as well as detection threshold and results of quantitation. The largest amount of the study compound were determined in the heart (365.2±33.94 mcg/g), spleen (288.6±24.97 mcg/g), kidney (127.6±9.33 mcg/g), and the gastric walls (124.6±12.17 mcg/g) of the experimental animals.

gPKPDSim: a SimBiology®-based GUI application for PKPD modeling in drug development

Modeling and simulation (M&S) is increasingly used in drug development to characterize pharmacokinetic-pharmacodynamic (PKPD) relationships and support various efforts such as target feasibility assessment, molecule selection, human PK projection, and preclinical and clinical dose and schedule determination. While model development typically require mathematical modeling expertise, model exploration and simulations could in many cases be performed by scientists in various disciplines to support the design, analysis and interpretation of experimental studies. To this end, we have developed a versatile graphical user interface (GUI) application to enable easy use of any model constructed in SimBiology^® to execute various common PKPD analyses. The MATLAB^®-based GUI application, called gPKPDSim, has a single screen interface and provides functionalities including simulation, data fitting (parameter estimation), population simulation (exploring the impact of parameter variability on the outputs of interest), and non-compartmental PK analysis. Further, gPKPDSim is a user-friendly tool with capabilities including interactive visualization, exporting of results and generation of presentation-ready figures. gPKPDSim was designed primarily for use in preclinical and translational drug development, although broader applications exist. gPKPDSim is a MATLAB^®-based open-source application and is publicly available to download from MATLAB^® Central™. We illustrate the use and features of gPKPDSim using multiple PKPD models to demonstrate the wide applications of this tool in pharmaceutical sciences. Overall, gPKPDSim provides an integrated, multi-purpose user-friendly GUI application to enable efficient use of PKPD models by scientists from various disciplines, regardless of their modeling expertise.

Environmental effects of anticholinesterasic therapeutic drugs on a crustacean species, Daphnia magna

The presence of pharmaceutical drugs in the environment is an important field of toxicology, since such residues can cause deleterious effects on exposed biota. This study assessed the ecotoxicological acute and chronic effects of two anticholinesterasic drugs, neostigmine and pyridostigmine in Daphnia magna. Our study calculated 48 h-EC50 values for the immobilization assay of 167.7 μg L(-1) for neostigmine and 91.3 μg L(-1) for pyridostigmine. In terms of feeding behavior, we calculated a 5 h-EC50 for filtration rates of 7.1 and 0.2 μg L(-1) for neostigmine and pyridostigmine, respectively; for the ingestion rates, the calculated EC50 values were, respectively, 7.5 and 0.2 μg L(-1) for neostigmine and pyridostigmine. In the reproduction assay, the most affected parameter was the somatic growth rate (LOECs of 21.0 and 2.9 μg L(-1) for neostigmine and pyridostigmine, respectively), followed by the fecundity (LOECs of 41.9 and 11.4 μg L(-1) for neostigmine and pyridostigmine, respectively). We also determined a 48 h-IC50 for cholinesterase activity of 1.7 and 4.5 μg L(-1) for neostigmine and pyridostigmine, respectively. These results demonstrated that both compounds are potentially toxic for D. magna at concentrations in the order of the μg L(-1).

In vivo and in vitro effects of neostigmine on gastrointestinal tract motility of horses

OBJECTIVE

To determine the response to neostigmine of the contractile activity of the jejunum and pelvic flexure and the effects of a continuous rate infusion (CRI) of neostigmine in horses.

ANIMALS

7 adult horses and tissue from 12 adult horses.

PROCEDURES

A CRI of neostigmine (0.008 mg/kg/h) or placebo was administered to 6 horses in a crossover study design. Gastric emptying was evaluated by the acetaminophen test. The frequency of defecation and urination and the consistency and weight of feces were recorded throughout the experiment. The effect of neostigmine on smooth muscle contractile activity was evaluated in tissues from the jejunum and pelvic flexure. The effect of neostigmine and acetylcholine after incubation with muscarinic receptor antagonists (atropine and DAU 5884) and an acetylcholinesterase inhibitor (edrophonium) was also investigated in vitro.

RESULTS

No difference was observed between neostigmine and placebo for time to reach peak plasma acetaminophen concentration and absorption rate constant. A CRI of neostigmine increased fecal production and frequency of urination. Neostigmine induced a dose-dependent increase of contractile amplitude in jejunum and pelvic flexure muscle strips. Incubation of muscle strips with atropine and DAU 5884 inhibited the response to acetylcholine and neostigmine. Incubation of smooth muscle strips from the jejunum with edrophonium increased the response to acetylcholine and had no effect on the response to neostigmine in vitro.

CONCLUSIONS AND CLINICAL RELEVANCE

A CRI of neostigmine increased fecal production and urination frequency in horses. A CRI of neostigmine did not decrease gastric emptying. Neostigmine stimulated contractile activity of jejunum and pelvic flexure smooth muscle strips in vitro.

Treatment of myasthenia gravis: focus on pyridostigmine

Acquired myasthenia gravis (MG) is a chronic autoimmune disorder of the neuromuscular junction, characterized clinically by muscle weakness and abnormal fatigability on exertion. Current guidelines and recommendations for MG treatment are based largely on clinical experience, retrospective analyses and expert consensus. Available therapies include oral acetylcholinesterase (AChE) inhibitors for symptomatic treatment, and short- and long-term disease-modifying treatments. This review focuses on treatment of MG, mainly on the use of the AChE inhibitor pyridostigmine. Despite a lack of data from well controlled clinical trials to support their use, AChE inhibitors, of which pyridostigmine is the most commonly used, are recommended as first-line therapy for MG. Pyridostigmine has been used as a treatment for MG for over 50 years and is generally considered safe. It is suitable as a long-term treatment in patients with generalized non-progressive milder disease, and as an adjunctive therapy in patients with severe disease who are also receiving immunotherapy. Novel AChE inhibitors with oral antisense oligonucleotides have been developed and preliminary results appear to be promising. In general, however, AChE inhibitors provide only partial benefit and most patients eventually switch to long-term immunosuppressive therapies, most frequently corticosteroids and/or azathioprine. Although AChE inhibitors are known to be well tolerated and effective in relieving the symptoms of MG, further efforts are required to improve treatment options for the management of this disorder.

Electrophysiological signs and the prevalence of adverse effects of acetylcholinesterase inhibitors in patients with myasthenia gravis

The aim of this prospective study was to assess whether extra discharges (EDs), sometimes following the compound muscle action potential, could be used as a neurophysiological indicator of overdose of acetylcholinesterase inhibitors (AChEIs) in patients with myasthenia gravis (MG). The characteristics and frequency of EDs were explored and the correlation of EDs with cholinergic side effects was also determined. Twenty-two MG patients (14 women, 8 men; 61 +/- 16 years of age) with daily AChEI treatment were examined. The mean disease duration was 10 years (range 2-62 years) and all patients had been treated with AChEI since MG onset. Both single and repetitive stimulation of the ulnar and accessory nerves were performed before and 60 min after oral pyridostigmine bromide (PB) administration and after additional edrophonium injection. Fatigue, side effects, and AChE activity in blood were assessed before and 60 min after PB intake. The daily dose of PB ranged from 150 to 900 mg/day. Fourteen patients (64%) experienced daily cholinergic adverse effects, and muscarinic side effects correlated with AChE activity. Eleven patients (50%) developed EDs after oral PB. Among the eight patients with daily nicotinic side effects, EDs were significantly (P < 0.05) more common. Additionally, older patients were more prone to develop cholinergic side effects and EDs. Thus, when EDs are found, patients should be asked about daily muscular symptoms, which may be related to AChEI treatment and not solely to MG.

Pharmacodynamic analysis of contractile potentiation by cholinesterase inhibitors in rats

Pharmacological profiles of four cholinesterase (ChE) inhibitors: edrophonium, pyridostigmine, neostigmine, and ambenonium after to administration to rats were analyzed. A pharmacodynamic model was developed by considering acetylcholinesterase (AChE) inhibition, direct antagonism to the nicotinic receptor, and desensitization of the nicotinic receptor. Pharmacokinetics of these drugs are dose-independent and have similar volumes of distribution at steady state (0.4-0.6 L/kg various doses). The t1/2 increases in the order of neostigmine, edrophonium, pyridostigmine, and ambenonium. Inhibitory constants of ChE inhibitors to bovine erythrocyte AChE determined in vitro were 2019, 276, 26, and 3.7 nM for edrophonium, pyridostigmine, neostigmine, and ambenonium, respectively. The effect of ChE inhibitor was monitored as the increase of developed tension of triceps muscle induced by sciatic nerve stimulation. The maximum value of contractile tension after i.v. administration decreased at high doses of each drug and the dose-response curves were biphasic. Time courses of plasma concentration and contractile muscle tension were modeled to estimate the association/dissociation rate constants to AChE and the nicotinic receptor, desensitization rate constant of receptor and the dissociation constant of acetylcholine (ACh) to nicotinic receptor/basal acetylcholine level ratio (Kd/ACh0). The estimated Kd/ACh0 values were not dependent on the drug. A significant correlation between inhibitory constants of ChE inhibitors to AChE estimated by in vivo pharmacodynamic analysis and those determined by an in vitro enzyme kinetic study was shown, while the relationship between dissociation constants to nicotinic receptor estimated by in vivo pharmacodynamic analysis and those measured by an in vitro binding study was not clear. Other process such as desensitisization induced by endogenous ACh diffusion rate of drugs into the synaptic cleft, action of presynaptic receptors, etc., might contribute to the dose-effect relationship of ChE inhibitors.

Influence of food on serum ambenonium concentration in patients with myasthenia gravis

Influence of food on the serum concentration and kinetics ambenonium chloride (AMBC) has been examined in thirteen patients with myasthenia gravis (MG). Mean serum concentrations and Cmax during fasting were higher than those in the non-fasting state. The AUC (0-3 h) was also about four-times larger. The drug effects versus the serum concentration were observed to be anti-clockwise or clockwise. The effective range of the Cmax varied between patients. The unexpected increase in Cmax led to adverse muscarinic actions of AMBC, when the condition was changed from the nonfasting to the fasting state. It is recommended that the dose be changed during non-fasting treatment when adjusting the optimum regimen for patients myasthenia gravis. Patients must be advised to keep to the dosing and dietary schedule in order to avoid unexpected adverse actions to AMBC.

Efficacy of intranasal administration of neostigmine in myasthenic patients

The efficacy of intranasally administered neostigmine was tested in 22 patients with generalized myasthenia gravis (MG). Topical therapy to the highly vascularized oropharynx proved to be quickly effective in 5-15 min both clinically and electrophysiologically. Twenty-eight MG patients were then recruited from different centres and their morning doses of oral pyridostigmine were substituted with intranasal neostigmine over a period of 2 or 3 weeks. Intranasal neostigmine proved to be equally efficacious in this regimen. No side-effect was noted even in 4 patients treated in this way for 1 year. Intranasal administration of anti-acetylcholinesterase may be very beneficial: (1) for patients with irregular absorption of oral doses; (2) early in the morning and every time a fast and temporary effect is needed; (3) in bulbar impairment and emergencies, in which a handy atomizer may be life-saving.

Ten years experience with therapeutic apheresis in a community hospital

A retrospective study was carried out on 2,500 therapeutic hemapheresis procedures performed at a community teaching hospital from 1980 to 1990. Seventy-six percent of the procedures consisted of plasmapheresis (PE). The most frequently treated conditions were myasthenia gravis (MG), Guillain-Barré syndrome (GB), hyperviscosity (HV), and thrombotic thrombocytopenia purpura (TTP). Therapeutic results and clinical implications for these four conditions are discussed.

Pharmacokinetics of ambenonium, a reversible cholinesterase inhibitor, in rats

The pharmacokinetics of ambenonium, a reversible cholinesterase inhibitor, in rats was investigated following intravenous administration of the drug. Mean residence time and steady state volume of distribution were 23-36 min and 0.20-0.311 kg-1, respectively, and were dose independent at the dose of 0.3-3 mumole kg-1. Total body clearance of 8.2 ml min-1 kg-1 over 0.3 mumole kg-1 was slightly increased to 11.3 ml min-1 kg-1 at 3 mumole kg-1. Renal clearance was also increased with the increase of the dose, while hepatobiliary clearance was substantially constant. Ambenonium was highly concentrated in the liver, kidney, spleen, and lung. About 30 per cent of the dose is concentrically stored in the liver at 6 h after administration, and had not disappeared after 24 h.

Pharmacokinetic studies of ambenonium chloride in patients with myasthenia gravis

Serum levels of ambenonium chloride (AC) were monitored in 4 myasthenic patients. This determination revealed important intraindividual variations (up to 10-fold) over a period of 24 h. Levels varied considerably between different patients (maximum serum concentration of ambenonium chloride ranged from 0.129 to 0.812 micrograms/ml) and no correlation between the daily dose and the AUC was found. These characteristic properties of ambenonium chloride could explain the erratic pattern of bioavailability observed as well as the difficulty in controlling the disease in some patients.

Neuromuscular function and plasma drug levels in pyridostigmine treatment of myasthenia gravis

In 18 patients with generalised myasthenia treated with oral pyridostigmine, muscular strength, decrement of neuromuscular transmission in the trapezius muscle on repetitive accessory nerve stimulation, and pyridostigmine plasma level were measured repeatedly during 1-3 dosing intervals. Significant correlations between pyridostigmine concentrations and functional parameters were present in three out of 11 cases in which plasma levels changed by at least 25 ng/ml during the investigational period and peak levels did not exceed 100 ng/ml. Several other observations indicated that pyridostigmine at levels above 100 ng/ml may impair neuromuscular function.

New treatment approaches to myasthenia gravis

Myasthenia gravis is an autoimmune disorder in which neuromuscular transmission is impaired by autoantibodies to the acetylcholine receptor (AChR). There are 3 varieties of generalised myasthenia with differing genetic susceptibilities. There is also a purely ocular form in which the weakness is confined to the extraocular muscles, and a neonatal variety which occurs in 20% of babies born to myasthenic mothers due to transplacental passage of the acetylcholine receptor antibody. Another variety of myasthenia occurs several months after treatment with D-penicillamine. The role of the thymus is suggested by abnormal histology in patients with myasthenia and by the beneficial effects of thymectomy in more than two-thirds of patients. Thymectomy is indicated in most patients unless the symptoms are minimal or the weakness is confined to the extraocular muscles. Most patients require treatment with anticholinesterase drugs to prolong the action of acetylcholine at the muscle end-plate. Overdosage of these drugs can provoke a cholinergic weakness. Remissions can be achieved with corticosteroids in 80% of patients. Immunosuppression with azathioprine is used mainly in patients who do not respond to thymectomy or in those patients who are considered unsuitable for operation. Plasma exchange can cause a rapid but temporary improvement in myasthenia, and has no long term place in its treatment.

Clinical pharmacokinetics of cholinesterase inhibitors

This review deals mainly with the pharmacokinetics of the reversible quaternary cholinesterase inhibitors neostigmine, pyridostigmine and edrophonium, which are mainly used to antagonise non-depolarising neuromuscular blockade in general anaesthesia and in the symptomatic treatment of myasthenia gravis. Only in the last few years, since the introduction of highly sensitive and selective analytical procedures based on gas and liquid chromatography, have proper pharmacokinetic studies of these drugs become possible. Rapid cooling and addition of internal standard to samples before freezing are important precautions in view of the poor stability of the cholinesterase inhibitors in plasma and blood. Plasma clearances of the reversible quaternary cholinesterase inhibitors are in the range 0.5 to 1.0 L/h/kg and their apparent volumes of distribution range from 0.5 to 1.7 L/kg. Accordingly, the drugs have short plasma elimination half-lives, in the order of 30 to 90 minutes. One to two hours after oral administration of 60 mg pyridostigmine, peak plasma concentrations of 40 to 60 micrograms/L are observed, whereas the plasma concentrations of neostigmine after a 30 mg oral dose are only 1 to 5 micrograms/L. The oral bioavailability of these hydrophilic ionised compounds is low: that of pyridostigmine is approximately 10% and the value for neostigmine is even lower. In spite of the short elimination half-life of pyridostigmine, intraindividual variations in plasma concentration during a dose interval are small in myasthenic patients receiving oral maintenance therapy, probably as a result of slow absorption from the gastrointestinal tract. Severely impaired renal function has been shown to prolong the elimination of neostigmine and pyridostigmine, while methylcellulose has been reported to inhibit the absorption of the latter drug completely. Other pharmacokinetic drug interactions suggested so far do not seem to be of clinical significance. Although a positive correlation has been demonstrated between the plasma concentrations of these drugs and their pharmacological effects as measured by a decrement in muscle response to repetitive nerve stimulation in a single muscle, this relationship is less clear when a global evaluation of muscular function in myasthenia gravis is used. Pharmacokinetic studies of the tertiary reversible cholinesterase inhibitor physostigmine, an important tool in experimental cholinergic neuropharmacology, are still in their initial stages. This drug too is characterised by a short plasma elimination half-life of 20 to 30 minutes.(ABSTRACT TRUNCATED AT 400 WORDS)