Recent antiarrhythmic drugs

Repurposing DrugBank compounds as potential Plasmodium falciparum class 1a aminoacyl tRNA synthetase multi-stage pan-inhibitors with a specific focus on mitomycin

Plasmodium falciparum aminoacyl tRNA synthetases (PfaaRSs) are potent antimalarial targets essential for proteome fidelity and overall parasite survival in every stage of the parasite's life cycle. So far, some of these proteins have been singly targeted yielding inhibitor compounds that have been limited by incidences of resistance which can be overcome via pan-inhibition strategies. Hence, herein, for the first time, we report the identification and in vitro antiplasmodial validation of Mitomycin (MMC) as a probable pan-inhibitor of class 1a (arginyl(A)-, cysteinyl(C), isoleucyl(I)-, leucyl(L), methionyl(M), and valyl(V)-) PfaaRSs which hypothetically may underlie its previously reported activity on the ribosomal RNA to inhibit protein translation and biosynthesis. We combined multiple in silico structure-based discovery strategies that first helped identify functional and druggable sites that were preferentially targeted by the compound in each of the plasmodial proteins: Ins1-Ins2 domain in Pf-ARS; anticodon binding domain in Pf-CRS; CP1-editing domain in Pf-IRS and Pf-MRS; C-terminal domain in Pf-LRS; and CP-core region in Pf-VRS. Molecular dynamics studies further revealed that MMC allosterically induced changes in the global structures of each protein. Likewise, prominent structural perturbations were caused by the compound across the functional domains of the proteins. More so, MMC induced systematic alterations in the binding of the catalytic nucleotide and amino acid substrates which culminated in the loss of key interactions with key active site residues and ultimate reduction in the nucleotide-binding affinities across all proteins, as deduced from the binding energy calculations. These altogether confirmed that MMC uniformly disrupted the structure of the target proteins and essential substrates. Further, MMC demonstrated IC50 < 5 μM against the Dd2 and 3D7 strains of parasite making it a good starting point for malarial drug development. We believe that findings from our study will be important in the current search for highly effective multi-stage antimalarial drugs.

Survey of Pharmacological Activity and Pharmacokinetics of Selected β-Adrenergic Blockers in Regard to Their Stereochemistry

The present survey concentrates on pharmacodynamics and pharmacokinetics of selected β-adrenergic blockers from the point of view of their stereochemistry. It could be shown that the activity in the arylaminoethanol and aryloxyaminopropanol group of β-blockers is higher in their (–)-enantiomers as compared with the (+)-enantiomers. The stereoisomers differ also in other types of bioactivity as well as in toxicity. The particular pharmacokinetic stages such as resorption, distribution, and metabolism are discussed in regard to their stereochemistry.

Evaluation of the CorInnova Heart Assist Device in an Acute Heart Failure Model

While the number of patients supported with temporary cardiac assist is growing, the existing devices are limited by a multitude of complications, mostly related to contact with the blood. The CorInnova epicardial compressive heart assist device was tested in six sheep using an acute heart failure model. High esmolol dose, targeting a 50% reduction in CO from healthy baseline, resulted in a failure state with mean CO 1.9 L/min. Heart assist with the device during failure state resulted in an average absolute increase in CO of 1.0 L/min, along with a decline in ventricular work to 67.5% of the total LV SW. Combined with repeated success of minimally invasive device implant, the resulting increases in cardiac hemodynamics achieved while still unloading the heart demonstrate the potential of the CorInnova device for temporary heart assist.

Effects of verapamil and procainamide on acute atrial electrical remodeling induced by short-term rapid atrial pacing in humans

Atrial electrical remodeling (ER) after spontaneous or pacing-induced atrial fibrillation has been previously described in humans. We investigated atrial ER induced by a 5-minute period of rapid atrial pacing and the pharmacologic effects of verapamil and procainamide on this atrial ER phenomenon. The atrial effective refractory periods (ERPs) at drive cycle lengths of 400 (ERP 400 ) and 600 (ERP 600 ) ms, at five representative atrial sites (high right atrium [HRA]; proximal, middle and distal coronary sinus; interatrial septum), were determined in 20 patients at baseline and immediately after cessation of a 5-minute period of rapid pacing from the HRA at a rate of 150 bpm. The degrees of atrial ERP 400 and ERP 600 shortening after pacing were calculated as acute atrial ER. The same protocol was repeated in another 15 patients after intravenous administration of verapamil (0.15 mg/kg) and in another 15 patients after intravenous administration of procainamide (15 mg/kg). The results demonstrated that, in the control state acute atrial ER can be significantly demonstrated at each atrial representative site ( p < 0.001). The mean ERP 400 and ERP 600 shortenings were 9 +/- 4% and 8 +/- 4%, respectively. After procainamide infusion, but not after verapamil, baseline ERP 400 and ERP 600 values were significantly prolonged at the five representative atrial sites ( p < 0.01). Acute atrial ER could still be demonstrated at each atrial site after procainamide or verapamil infusion ( p < 0.001). In conclusion, acute atrial ER can be demonstrated after only a 5-minute period of rapid atrial pacing in humans. Intravenous verapamil or procainamide does not abolish this ER process.

Electrophysiologic effects of procainamide, mexiletine, and amiodarone on the transplanted heart. Experimental study

The effects of procainamide, mexiletine, and amiodarone on automaticity, conduction, and refractoriness were studied in a model of heterotopic heart transplantation in dogs that combined an innervated heart (recipient) and a denervated transplanted heart (donor). After the surgical procedure, 500 mg procainamide (n = 13), 200 mg plus 0.1 mg/kg per minute mexiletine (n = 10), or 150 mg amiodarone (n = 10) was administered intravenously. During a baseline period and after drug administration, each heart was assessed for atrioventricular interval; cycle length; sinoatrial conduction time; atrioventricular node anterograde and retrograde block points; atrioventricular node and ventricular antegrade effective refractory periods; PR, QRS, and QT intervals on electrocardiogram; systemic arterial, pulmonary arterial, central venous, and pulmonary capillary wedge pressures; and cardiac output. In recipients, procainamide reduced cardiac output, depressed sinus automaticity, slowed conduction time without affecting the QRS interval, and prolonged the nodal and ventricular refractoriness; in donor hearts, it depressed automaticity and prolonged nodal refractoriness, but did not modify conduction or ventricular refractoriness. Mexiletine only moderately depressed sinus automaticity in recipient hearts; it did not affect the other parameters either in recipient or transplanted hearts, nor did it alter the hemodynamic situation. Amiodarone produced hypotension, reduced cardiac output, and prolonged all the electrophysiologic intervals except the QRS interval in recipient hearts. These changes were even more pronounced in the transplanted hearts and led to extreme sinus bradycardia in four cases. Of these three drugs, mexiletine appears to be the safest should treatment for arrhythmias be necessary in transplant recipients.

Antiarrhythmic drug classifications and the clinician: a gambit in the land of chaos

Several classifications of antiarrhythmic drugs have appeared and all suffer considerable limitations. Recently a Task Force of the Working Group on Arrhythmias of the European Society of Cardiology proposed a novel classification of antiarrhythmic drugs (the so-called Sicilian Gambit) based on their action on the most vulnerable parameter of an arrhythmogenic mechanism. The present article attempts a critical reappraisal of the antiarrhythmic drug actions and the relationship of vulnerable parameters with cellular mechanisms such as ion channels. The clinical applicability of these concepts, the implications of the new classification in the pharmacologic therapy of arrhythmias, and its potential limitations are discussed.

Encainide overdose in an infant

Ingestion of as little as a single tablet of encainide resulted in life-threatening ventricular arrhythmias in a child. Insertion of an intraosseous line permitted prompt delivery of medications and fluids. Prehospital care providers must be aware that apparently trivial amounts of some adult dosage forms can be toxic to small children.

Influence of lorcainide on microsomal Na+, K(+)-ATPase in guinea-pig isolated heart preparations

1. The effects of lorcainide on the myocardial Mg2(+)-dependent, Na+ and K(+)-activated adenosine triphosphatase (Na+, K(+)-ATPase) were compared in guinea-pig heart preparations with those of ouabain, a specific inhibitor of the enzyme activity. 2. Both ouabain and lorcainide inhibited the microsomal Na+, K(+)-ATPase activity in a concentration-dependent fashion. Their inhibitory effective ranges were 0.05-100 microM and 0.15-125 microM, respectively, and the concentrations for half maximal inhibition (IC50 values) were 2.1 +/- 0.3 and 33.5 +/- 7.3 microM, respectively. 3. In a second series of experiments, the combined effects of the two drugs on the enzyme activity were studied. In these experiments, lorcainide produced a concentration-dependent potentiation of the inhibitory effects of ouabain on Na+, K(+)-ATPase activity. 4. The present study demonstrates that lorcainide is a potent inhibitor of myocardial Na+, K(+)-ATPase.