Distribution of amitriptyline and nortriptyline in fatal amitriptyline intoxications with different survival times

Just say no to postmortem drug dose calculations

For years, a number of professional groups have warned forensic and clinical toxicologists against calculating an administered dose of a drug based on postmortem blood drug concentrations. But to date, there has been limited information as to how unreliable these dose calculations may actually be. Using amitriptyline as a model drug, this study used empirically determined pharmacokinetic variables for amitriptyline from clinical studies coupled with clinical overdoses (where the individual survived), and death case studies (ascribed to amitriptyline toxicity) in which the dose of amitriptyline was known. Using these data, standard pharmacokinetic equations, and general error propagation, it was possible to estimate the accuracy of calculated doses of amitriptyline, compared with the doses that were consumed. As was expected in postmortem cases, depending on the pharmacokinetic equation used, the accuracy (mean +128% to +2347%) and precision (SD ± 383% to 3698%) were too large to allow reliable estimations of the dose of amitriptyline consumed prior to death based on postmortem blood drug concentrations. This work again reinforces that dose calculations from postmortem blood drug concentrations are unreliable.

Physiologically based pharmacokinetic-quantitative systems toxicology and safety (PBPK-QSTS) modeling approach applied to predict the variability of amitriptyline pharmacokinetics and cardiac safety in populations and in individuals

The physiologically based pharmacokinetic (PBPK) models allow for predictive assessment of variability in population of interest. One of the future application of PBPK modeling is in the field of precision dosing and personalized medicine. The aim of the study was to develop PBPK model for amitriptyline given orally, predict the variability of cardiac concentrations of amitriptyline and its main metabolite-nortriptyline in populations as well as individuals, and simulate the influence of those xenobiotics in therapeutic and supratherapeutic concentrations on human electrophysiology. The cardiac effect with regard to QT and RR interval lengths was assessed. The Emax model to describe the relationship between amitriptyline concentration and heart rate (RR) length was proposed. The developed PBPK model was used to mimic 29 clinical trials and 19 cases of amitriptyline intoxication. Three clinical trials and 18 cases were simulated with the use of PBPK-QSTS approach, confirming lack of cardiotoxic effect of amitriptyline in therapeutic doses and the increase in heart rate along with potential for arrhythmia development in case of amitriptyline overdose. The results of our study support the validity and feasibility of the PBPK-QSTS modeling development for personalized medicine.

Limitations of the Anticholinergic Activity Assay and Assay-Based Anticholinergic Drug Scales

OBJECTIVE

The anticholinergic activity (AA) assay is a common method to determine a patient's anticholinergic load. Several limitations, however, are expected when applying the AA assay to patients or using drug scales to estimate anticholinergic burden based on AA levels. This study aims to demonstrate common pitfalls in an experimental setting and outline their clinical consequences.

METHODS

The AA was analyzed for five drugs with reported interaction with muscarinic receptors. Concentration-response curves were constructed for furosemide (weak anticholinergic), diphenhydramine (moderate anticholinergic), the strong anticholinergic amitriptyline and its metabolite nortriptyline, and the cholinergic pilocarpine. The Combination Index (CI) was used to assess the interaction of three drug combinations with amitriptyline.

RESULTS

All compounds displaced the radioactive tracer from its receptor binding site in a concentration-dependent manner, and full displacement was reached for all compounds except furosemide (E_max 16%). The CI indicated that amitriptyline and thioridazine have antagonistic effects (CI = 1.46) at low and synergistic effects (CI = 0.88) at higher concentrations (p < 0.0001), whereas synergistic effects (CI = 0.47-0.48) were observed for amitriptyline in any concentration combined with pilocarpine (p < 0.001).

CONCLUSION

When the patient's anticholinergic load is estimated using AA levels, the actual exposure, combination of anticholinergic drugs, their active metabolites, and also drugs with an opposite pharmacologic action will contribute to AA levels, whereas weak anticholinergic drugs in therapeutic concentrations are rather negligible.

Fatal blood and tissue concentrations of more than 200 drugs

Fatal drug concentrations in body fluids and tissue samples are presented for more than 200 drugs and chemicals of toxicologic interest. Additionally, a reference list is added with more than 600 original papers concerning intoxications with a lethal outcome. The data can be helpful for the interpretation and plausibility control in own cases of intoxication. However, they should be used with caution, because use of drug data without sufficient knowledge about the patient or victim, the circumstances of the case, and about toxicokinetics and toxicodynamics might give a wrong interpretation in a special case.

Aspiration of nortriptyline

Unintentional aspiration of medication capsules is a rare event. A case report of a neurologically impaired 23-year-old woman who aspirated a 50-mg nortriptyline capsule is presented. This resulted in progressive respiratory distress necessitating ventilatory support. Bronchoscopy showed severe airway inflammation and edema.

Toxicological findings after fatal amitriptyline self-poisoning

A case of fatal self-poisoning with amitriptyline is reported. Both the drug and its metabolite nortriptyline were quantified in several post-mortem tissues and fluids, including vitreous humor. Results are discussed in the light of the existing literature.

A collection of therapeutic, toxic and fatal blood drug concentrations in man

In order to assess the significance of drug concentrations measured in clinical and toxicological investigations, it is essential that good collections of data are readily available. As a guide to interpreting findings, the present work provides a compilation of therapeutic, toxic and fatal blood concentration ranges of 298 drugs of interest to clinical pharmacologists, clinical toxicologists, and forensic toxicologists. Wherever possible, ranges are expressed concisely in terms of the maximum blood concentrations which account for 10, 50 and 90% of the data collected. They provide easy access to the most reliable information which relates the blood drug concentration to the biological response it produces. Where appropriate, the different toxic effects of a drug and/or the different degrees of severity of toxic symptoms associated with different drug levels are clearly defined. The original sources of all data used are provided to allow the analyst to obtain further analytical, pharmacokinetic and toxicological information should this be necessary. Those factors (e.g. age, capacity for drug metabolism, drug interactions, etc) which can modify the relationship between a drug concentration and the response it produces are briefly discussed.

Drug deaths in St. Louis City and County: a brief survey, 1977-1979

The vast majority of drug deaths in St. Louis City and County through 1977-1979 were of adults who ingested multiple drugs with suicidal intent. In this 3-year survey, seven deaths were due to accidental overdose of ethanol, seven to "over-the-counter" products or laboratory reagents, eight from "classic poisons," and only eight to drug abuse. The remaining 117 deaths (80%) resulted from ingestion of legally obtained prescription drugs. Sixty-two percent of all deaths were due to multiple drug administration. Only one child was fatally poisoned. Barbiturates, benzodiazepines, ethanol, propoxyphene, and tricyclic antidepressants were the most common agents encountered.

The human distribution of some barbiturate sedatives in combination with miscellaneous CNS-active drugs

This paper presents 14 cases in which the distribution of barbiturates and the hydroxylated metabolites in combination with miscellaneous CNS-active drugs was studied. In 7 of these cases the other drug present was methadone, and in the remainder dihydrocodeine, morphine, propoxyphene, amitriptyline, meprobamate, cyclizine and dipipanone, diphenhydramine and methaqualine. Amitriptyline, methadone, cyclizine and dipipanone, methaqualone and diphenhydramine appeared to modify the distribution of amylorbarbitone and quinalbarbitone. Likewise, the barbituates seemed to alter the distribution of amitriptyline, propoxyphene and, in one instance, methadone.