Metabolic disposition of ajmaline

The Mechanism of Ajmaline and Thus Brugada Syndrome: Not Only the Sodium Channel!

Ajmaline is an anti-arrhythmic drug that is used to unmask the type-1 Brugada syndrome (BrS) electrocardiogram pattern to diagnose the syndrome. Thus, the disease is defined at its core as a particular response to this or other drugs. Ajmaline is usually described as a sodium-channel blocker, and most research into the mechanism of BrS has centered around this idea that the sodium channel is somehow impaired in BrS, and thus the genetics research has placed much emphasis on sodium channel gene mutations, especially the gene SCN5A, to the point that it has even been suggested that only the SCN5A gene should be screened in BrS patients. However, pathogenic rare variants in SCN5A are identified in only 20–30% of cases, and recent data indicates that SCN5A variants are actually, in many cases, prognostic rather than diagnostic, resulting in a more severe phenotype. Furthermore, the misconception by some that ajmaline only influences the sodium current is flawed, in that ajmaline actually acts additionally on potassium and calcium currents, as well as mitochondria and metabolic pathways. Clinical studies have implicated several candidate genes in BrS, encoding not only for sodium, potassium, and calcium channel proteins, but also for signaling-related, scaffolding-related, sarcomeric, and mitochondrial proteins. Thus, these proteins, as well as any proteins that act upon them, could prove absolutely relevant in the mechanism of BrS.

Scope and limitations of a general unknown screening by gas chromatography-mass spectrometry in acute poisoning

The gold standard for the diagnosis of acute poisoning is toxicological analysis. Because information on the incorporated toxic substance provided by the patient or his relatives is known from experience to be unreliable in about 40% of all intoxications, a screening procedure that covers most relevant drugs and toxicants is required rather than an analytical procedure optimized for the identification of a single class of substances. The special task for a general unknown screening procedure is to identify a toxic substance among endogenous or food-derived substances as well as environmental toxicants in a biological matrix on an emergency basis. Because the unknown toxic substance may vary considerably in its physicochemical properties and its concentration range, a universally applicable screening procedure is required. Although gas chromatography-mass spectrometry has been used for three decades, it still offers many unique advantages in terms of sensitivity, specificity, reliability, and coverage of a large number of toxic substances. Because the procedure has to be kept as simple and as short as possible, compromises have to be made with respect to extraction, derivatization, and mass-spectral techniques. The specimen of choice for a general unknown screening is-if available-urine. The standard mode of ionization is electron impact. The identification of unknown substances is highly challenging because, in our experience, previously unknown metabolites may be detected rather frequently in acute poisoning. Although an automated mass spectra library search considerably facilitates the identification process, expert knowledge on the identification of substances not included in the library as well as knowledge in clinical toxicology and metabolism is indispensable.

Fatal poisoning with detajmium: identification of detajmium and its metabolites and artifacts by gas chromatography-mass spectrometry and quantification by high-performance liquid chromatography

After ingestion of an unknown dose of detajmium, a 14-year-old female collapsed with asystolia. Resuscitation efforts were not successful. A medicolegal autopsy was carried out, and blood, liver and gastric content were extracted and analyzed by gas chromatography-mass spectrometry (GC-MS). After derivatization with acetic anhydride, detajmium and twelve of its derivatives and metabolites were identified. The main metabolic pathways include hydroxylation and subsequent O-methylation of the indol ring, and oxidation as well as reduction of the C-21 hydroxyl function. Cleavage of the N-alkyl side-chain is a further, possibly non-enzymatic degradation pathway. Artifact formation induced by acetylation included dehydratation of the hydroxyl function of C-21 and the N-alkyl side-chain. The detajmium concentration in blood of the decreased was determined by high-performance liquid chromatography with fluorimetric detection (12 micrograms/ml).

Rapid determination of functional liver plasma flow in ICU patients by a modified hepatic D-sorbitol plasma clearance method

Changes in liver perfusion may have a substantial influence on the pharmacokinetics of drugs with flow-controlled metabolism. This may have important implications for drug dosage in patients in an intensive care unit (ICU). The hepatic D-sorbitol plasma clearance has been suggested as a non-invasive test for evaluating functional liver plasma flow, which is in reasonable agreement with the direct blood measurement. However, its determination requires D-sorbitol infusion for 3 h or administration of a D-sorbitol bolus and withdrawal of blood specimens every 3-5 min. Since both variants are impractical in the ICU setting, a bolus/infusion technique was tested. A combined technique applying a bolus (0.85 mg/kg) and steady-state infusion (0.0014 mg/kg/min) of D-sorbitol was tested in 10 ICU patients without hepatic disease (group 1) and in 10 ICU patients with liver disease (group 2). Steady-state plasma levels (+/- 9%, P < 0.05) could be achieved within 60 min in all patients. The modified D-sorbitol clearance method requires a bolus and an infusion of D-sorbitol and withdrawal of a single blood specimen after 60 min. The lowest values of functional liver plasma flow were determined in patients with decompensated liver cirrhosis, acute fatty degeneration of the liver or Budd-Chiari syndrome. The method for routine determination of functional hepatic plasma perfusion proved to be rapid, safe and non-invasive in ICU patients. Hepatic D-sorbitol clearance may be especially useful for assessing the functional aspect of liver perfusion.

Monitoring of ajmaline in plasma with high-performance liquid chromatography

A rapid, reliable and sensitive assay for routine determination of ajmaline in plasma by high-performance liquid chromatography with fluorimetric detection is presented. A low limit of detection in plasma (less than 1 ng/ml ajmaline) could be achieved by the extraction of plasma samples and the use of fluorimetric detection. Deproteinization of the plasma sample instead of extraction, or the use of an ultraviolet detector, yielded a higher limit of detection (less than 50 ng/ml). Two different eluents were studied. Eluent 1 allowed clear separation of ajmaline from isoajmaline and sandwicine, but did not separate isoajamaline from sandwicine. With eluent 2, separation of isoajmaline and sandwicine was achieved, but separation of ajmaline from sandwicine was less optimal than with eluent 1. Therefore, eluent 1 was used for further clinical studies. No interference was observed from therapeutic doses of other commonly co-administered drugs, such as acetylsalicylic acid, digoxin, digitoxin, ranitidine, dopamine, dobutamine, furosemide, captopril or glycerol trinitrate. In addition, the chemical stability of ajmaline and a possible rearrangement of ajmaline to its stereoisomers isoajmaline and sandwicine was studied in vivo and in vitro. Ajmaline proved to be unusually stable under both in vivo and in vitro conditions.

Clinical course and outcome in class IC antiarrhythmic overdose

120 cases of class IC antiarrhythmic overdose, including propafenone, flecainide, ajmaline and prajmaline overdose, were evaluated with respect to clinical course, therapy and outcome. Whereas drug overdose in general has an overall mortality of less than 1%, intoxication with antiarrhythmic drugs of class IC was associated with a mean mortality of 22.5%. Nausea, which occurred within the first 30 minutes after ingestion, was the earliest symptom. Spontaneous vomiting probably led to self-detoxication in about half the patients. Cardiac symptoms including bradycardia and, less frequently, tachyrhythmia occurred after about 30 minutes to 2 hours. Therapeutic measures included administration of activated charcoal, gastric lavage and a saline laxative, catecholamines, and in some patients, hypertonic sodium bicarbonate, insertion of a transvenous pacemaker and hemoperfusion. Fatal outcome was mainly due to cardiac conduction disturbances progressing to electromechanical dissociation or asystolia. Resuscitation, which had to be performed in 29 patients, was successful in only two of them. No correlation was found between fatal outcome, the type of antiarrhythmic, and ingested dose. Since a specific treatment is not available and resuscitive procedures including sodium bicarbonate and insertion of a pacemaker are of limited therapeutic value, early diagnosis and primary detoxification are most important for prevention of fatal outcome.