The population pharmacokinetics of citalopram after deliberate self-poisoning: a Bayesian approach

Chlorpromazine overdose: a case series

INTRODUCTION

Chlorpromazine, one of the oldest antipsychotic medications, remains widely available and is still taken in overdose. We aimed to investigate the clinical effects of chlorpromazine overdose and determine if there is a relationship between the reported dose ingested and intensive care unit admission or endotracheal intubation.

METHODS

We performed a retrospective analysis of patients admitted to our toxicology tertiary referral hospital with chlorpromazine overdose (reported dose ingested greater than 300 mg) between 1987 and 2023. We extracted demographic information, details of ingestion, clinical effects and complications (Glasgow Coma Scale, hypotension [systolic blood pressure less than 90 mmHg], delirium, dysrhythmias), length of stay, intensive care unit admission, and endotracheal intubation.

RESULTS

There were 218 chlorpromazine overdose cases, with presentations decreasing in frequency over the 36 years. The median age at presentation was 32 years (interquartile range: 25-40 years) and 143 (61 per cent) were female. The median reported dose ingested was 1,250 mg (interquartile range; 700-2,500 mg). The majority of presentations (135; 62 per cent) involved reported co-ingestion of other medications, typically benzodiazepines, paracetamol or antipsychotics. There were 76 (35 per cent) chlorpromazine alone ingestions in which there was a slightly higher median reported dose ingested of 1,650 mg (interquartile range: 763-3,000 mg) compared to the reported co-ingestion group, median reported dose ingested of 1,200 mg (interquartile range: 700-2,100 mg). Of all presentations, 36 (27 per cent) had a Glasgow Coma Scale less than 9, 50 (23 per cent) were admitted to the intensive care unit, and 32 (15 per cent) were endotracheally intubated. There was a significant difference in the median reported dose ingested between patients intubated (2,000 mg; interquartile range: 1,388-3,375 mg) and those not intubated (1,200 mg; interquartile range: 644-2,050mg; P < 0.001), and between those admitted to the intensive care unit and not admitted to the intensive care unit (P < 0.0001). The median reported dose ingested in seven chlorpromazine alone presentations who were intubated was 2,500 mg (interquartile range: 2,000-8,000 mg, range: 1,800-20,000 mg). Eighteen (8 per cent) patients developed delirium, eight (4 per cent) had hypotension, three had seizures, and there was one death.

DISCUSSION

Almost one quarter of cases were admitted to the intensive care unit and over half of these were intubated. Whist the decision to admit to an intensive care unit or intubate a patient is based on clinical need, there was a significant association between reported dose ingested and requirement for endotracheal intubation. Both the frequency of presentation and reported dose ingested declined after 2013. The major limitations of the study were a retrospective design and no analytical confirmation of ingestion.

CONCLUSIONS

We found that the most common effect of chlorpromazine overdose was central nervous system depression and that endotracheal intubation was associated with larger reported doses ingested, particularly in single chlorpromazine ingestions.

Pharmacokinetic analysis across studies to drive knowledge-integration: A tutorial on individual patient data meta-analysis (IPDMA)

Answering challenging questions in drug development sometimes requires pharmacokinetic (PK) data analysis across different studies, for example, to characterize PKs across diverse regions or populations, or to increase statistical power for subpopulations by combining smaller size trials. Given the growing interest in data sharing and advanced computational methods, knowledge integration based on multiple data sources is increasingly applied in the context of model-informed drug discovery and development. A powerful analysis method is the individual patient data meta-analysis (IPDMA), leveraging systematic review of databases and literature, with the most detailed data type of the individual patient, and quantitative modeling of the PK processes, including capturing heterogeneity of variance between studies. The methodology that should be used in IPDMA in the context of population PK analysis is summarized in this tutorial, highlighting areas of special attention compared to standard PK modeling, including hierarchical nested variability terms for interstudy variability, and handling between-assay differences in limits of quantification within a single analysis. This tutorial is intended for any pharmacological modeler who is interested in performing an integrated analysis of PK data across different studies in a systematic and thorough manner, to answer questions that transcend individual primary studies.

Predicting serotonin toxicity in serotonin reuptake inhibitor overdose

AIMS

We aimed to investigate the frequency of serotonin toxicity following overdose of antidepressants that inhibit serotonin reuptake and the factors that influence the probability of serotonin toxicity occurring.

METHODS

This was a retrospective cohort study of overdoses that included selective serotonin reuptake inhibitors (SSRIs) (70%) and serotonin norepinephrine reuptake inhibitors (SNRIs) (30%) admitted to a tertiary toxicology unit over 23 years. A multivariate mixed effects logistic regression model using NONMEM (7.2.0) was used to determine factors that influenced the probability of serotonin toxicity occurring.

RESULTS

There were 1978 overdoses in 1520 patients; median age 33 y (range: 13-86 years) and 64% female. Median defined daily dose equivalent (DDD) was 15 (1-420). Co-ingestants were taken in 1678/1978 (85%) overdoses: 11 co-ingested the monoamine oxidase-A inhibitor (MAOI) moclobemide, 99 (5%) co-ingested olanzapine, 58 (3%) co-ingested risperidone and 417 co-ingested a benzodiazepine (21%). Serotonin toxicity occurred in 269 overdoses (13.6%). The probability of serotonin toxicity increased slightly per 10 DDD units dose [OR, 1.01; 95% confidence intervals (CIs): 0.93-1.10], increased for an SNRI vs. an SSRI [OR, 1.07; 95% CI: 0.99-1.15], and markedly increased with co-ingestion of moclobemide [OR, 33.12; 95% CI: 7.5-147]. The probability decreased per 10 y age [OR, 0.84; 95% CI: 0.74-0.95], and with co-ingestion of the serotonin 2 A receptor (5-HT_2A) antagonists olanzapine [OR, 0.40; 95% CI: 0.17-0.94] or risperidone [OR, 0.13; 95% CI: 0.02-0.99]. The probability of serotonin toxicity was 12.5% at 1 DDD (therapeutic), 12.7% at 15 DDDs and 19% at 420 DDDs. In overdoses of the median dose of 15 DDDs, co-ingestion of moclobemide increased the probability to 83%, and co-ingestion of olanzapine or risperidone decreased it to 5.5% and 1.8%, respectively.

CONCLUSIONS

Serotonin toxicity is common following SSRI/SNRI overdose. Although dose increases probability, this was only a small effect. Co-ingestion with olanzapine or risperidone reduced the risk 2-6-fold, and moclobemide increased the risk 5-fold.

Duloxetine overdose causes sympathomimetic and serotonin toxicity without major complications

OBJECTIVE

Duloxetine is a commonly used antidepressant that is a serotonin and norepinephrine reuptake inhibitor. We aimed to investigate the frequency and severity of clinical effects following duloxetine overdose.

METHODS

We undertook a retrospective review of duloxetine overdoses (>120 mg) admitted to two tertiary toxicology units between March 2007 and May 2021. Demographic information, details of ingestion (dose, co-ingestants), clinical effects, investigations (ECG parameters including QT interval), complications (coma [GCS < 9], serotonin toxicity, seizures and cardiovascular effects), length of stay [LOS] and intensive care unit [ICU] admission were extracted from a clinical database.

RESULTS

There were 241 duloxetine overdoses (>120 mg), median age 37 years (interquartile range [IQR]: 25-48 years) and there were 156 females (65%). The median dose was 735 mg (IQR: 405-1200 mg). In 177 patients, other medications were co-ingested, most commonly alcohol, paracetamol, quetiapine, diazepam, ibuprofen, pregabalin and oxycodone. These patients were more likely to be admitted to ICU (12 [7%] vs. none; p = 0.040), develop coma (16 [9%] vs. none; p = 0.008) and hypotension [systolic BP < 90 mmHg] (15 [8%] vs. one; p = 0.076). Sixty four patients ingested duloxetine alone with a median dose of 840 mg (180-4200 mg). The median LOS, in the duloxetine only group, was 13 h (IQR:8.3-18 h), which was significantly shorter than those taking coingestants, 19 h (IQR:12-31 h; p = 0.004). None of these patients were intubated. Six patients developed moderate serotonin toxicity, without complications and one had a single seizure. Tachycardia occurred in 31 patients (48%) and mild hypertension (systolic BP > 140 mmHg) in 29 (45%). One patient had persistent sympathomimetic toxicity, and one had hypotension after droperidol. Two patients of 63 with an ECG recorded had an abnormal QT: one QT 500 ms, HR 46 bpm, which resolved over 3.5 h and a second with tachycardia (QT 360 ms, HR 119 bpm). None of the 64 patients had an arrhythmia.

CONCLUSION

Duloxetine overdose most commonly caused sympathomimetic effects and serotonin toxicity, consistent with its pharmacology, and did not result in coma, arrhythmias or intensive care admission, when taken alone in overdose.

Activated Charcoal and Bicarbonate for Aspirin Toxicity: a Retrospective Series

INTRODUCTION

Aspirin overdose causes acid-base disturbances and organ dysfunction. Management is guided by research reported over 50 years ago when chronic aspirin toxicity was common and accounted for significant morbidity. We investigate our experience of aspirin overdose and the effectiveness of charcoal and bicarbonate administration over 20 years.

METHODS

This is a retrospective series of acute aspirin overdose from two toxicology units from January 2000 to September 2019. Acute aspirin ingestions > 3000 mg were identified in each unit's database. Excluded were cases of chronic exposure, hospital presentation > 24 hours after ingestion, and cases without a salicylate concentration. Included in our analysis was demographic data, clinical effects, investigations, complications, and treatment.

RESULTS

There were 132 presentations in 108 patients (79 females (73%)). The median age was 28 years (range: 13-93 years). The median dose ingested was 7750 mg (IQR: 6000-14,400 mg). There were 44 aspirin-only ingestions. Mild toxicity (nausea, vomiting, tinnitus or hyperventilation) occurred in 22 with a median dose of 160 mg/kg. Moderate toxicity (acid-base disturbance, confusion) occurred in 16 with a median ingested dose of 297 mg/kg. There were no cases of severe toxicity (coma or seizures) due to aspirin alone. The median peak salicylate concentration was 276 mg/L (IQR: 175-400 mg/L, range: 14-814 mg/L). There was a moderate association between dose ingested and peak concentration (Pearson r = 0.58; 95% CI 0.45-0.68). Activated charcoal was administered in 36 (27%) cases, which decreased the median peak salicylate concentration (34.2 to 24.8 mg/L/g (difference: 9.4, 95% CI: 1.0-13.1)). Bicarbonate was administered in 34 (26%) presentations, decreasing the median apparent elimination half-life from 13.4 to 9.3 h (difference: 4.2 h, 95% CI: 1.0-6.5 h).

CONCLUSIONS

Acute aspirin overdose caused only mild to moderate effects in this series. Early administration of activated charcoal decreased absorption and use of bicarbonate enhanced elimination.

Approaches to handling missing or "problematic" pharmacology data: Pharmacokinetics

Missing or erroneous information is a common problem in the analysis of pharmacokinetic (PK) data. This may present as missing or inaccurate dose level or dose time, drug concentrations below the analytical limit of quantification, missing sample times, or missing or incorrect covariate information. Several methods to handle problematic data have been evaluated, although no single, broad set of recommendations for commonly occurring errors has been published. In this tutorial, we review the existing literature and present the results of our simulation studies that evaluated common methods to handle known data errors to bridge the remaining gaps and expand on the existing knowledge. This tutorial is intended for any scientist analyzing a PK data set with missing or apparently erroneous data. The approaches described herein may also be useful for the analysis of nonclinical PK data.

Population pharmacokinetics of Pseudechis porphyriacus (red-bellied black snake) venom in snakebite patients

OBJECTIVES

Understanding the time course of venom exposure in snakebite patients is important for the optimisation of treatment including antivenom dose and timing. We aimed to investigate the pharmacokinetics of red-bellied black snake (RBBS; Pseudechis porphyriacus) venom in envenomed patients.

METHODS

Timed venom concentration data were obtained from patients with RBBS envenomation recruited to the Australian Snakebite Project (ASP), including demographics and antivenom treatment. Venom concentrations were measured using an enzyme immunoassay. Data were modelled using NONMEM version 7.3. Uncertainty in venom "dose" was accounted for by arbitrarily fixing the average amount to 1 mg and incorporating between-subject variability on relative bioavailability. A scale parameter for venom clearance was implemented to account for the rapid venom clearance following antivenom dosing. A sensitivity analysis was performed to determine the magnitude of venom clearance amplification.

RESULTS

There were 457 venom concentrations in 114 patients (median age 41, 2-90 y; 80 male). Antivenom was administered to 54 patients a median of 4.2 h post-bite (0.67 to 32 h). A one-compartment model with first-order absorption and elimination provided the best description of the data. The estimated clearance and volume of distribution were 5.21 L/h and 39.9 L, respectively. The calculated elimination half-life of P. porphyriacus venom from the final pharmacokinetic model was 5.35 ± 0.36 h. The variability in the relative dose of injected venom was 140%. Antivenom administration increased venom clearance by 40-fold. Ten patients showed evidence of a double peak in the absorption profile.

CONCLUSION

The information on the exposure time of venom in the body following envenomation will help improve treatment and the timing of antivenom.

Application of Pharmacokinetic-Pharmacodynamic Modeling in Drug Delivery: Development and Challenges

With the advancement of technology, drug delivery systems and molecules with more complex architecture are developed. As a result, the drug absorption and disposition processes after administration of these drug delivery systems and engineered molecules become exceedingly complex. As the pharmacokinetic and pharmacodynamic (PK-PD) modeling allows for the separation of the drug-, carrier- and pharmacological system-specific parameters, it has been widely used to improve understanding of the in vivo behavior of these complex delivery systems and help their development. In this review, we summarized the basic PK-PD modeling theory in drug delivery and demonstrated how it had been applied to help the development of new delivery systems and modified large molecules. The linkage between PK and PD was highlighted. In particular, we exemplified the application of PK-PD modeling in the development of extended-release formulations, liposomal drugs, modified proteins, and antibody-drug conjugates. Furthermore, the model-based simulation using primary PD models for direct and indirect PD responses was conducted to explain the assertion of hypothetical minimal effective concentration or threshold in the exposure-response relationship of many drugs and its misconception. The limitations and challenges of the mechanism-based PK-PD model were also discussed.

The Use of Activated Charcoal to Treat Intoxications

BACKGROUND

In 2016, according to the German Federal Statistical Office, 178 425 cases of intoxication (poisoning) were treated in German hospitals. The poison control centers in the German-speaking countries gave advice in a total of 268 787 instances of poisoning in that year, and use of activated charcoal was recommended in 4.37% of cases. The application of activated charcoal plays a major role in both primary and secondary detoxification. This article serves as an overview of the mechanism of action, indications, contraindications, modes of application, and dosing of activated charcoal.

METHODS

This review is based on pertinent publications retrieved by a selective search in PubMed. The opinions of experts from the poison control centers in the German-speaking countries were considered in the interpretation of the data.

RESULTS

The administration of activated charcoal is indicated to treat moderately severe to life-threatening intoxication. It should be carried out as soon as possible, within the first hour of the ingestion; timed-release preparations can be given up to 6 hours after the ingestion. An important contraindication is impaired consciousness with the danger of aspiration in a patient whose air- way has not yet been secured. Activated charcoal is ineffective or inadequately effective in cases of poisoning with acids or bases, alcohols, organic solvents, inorganic salts, or metals. The proper dosage consists of an amount that is 10 to 40 times as much as that of the intoxicating substance, or else 0.5-1 g/kg body weight in children or 50 g in adults. Repeated application is indicated for intoxications with agents that persist for a longer time in the stomach and for intoxications with timed-release drugs or drugs with a marked enterohepatic or entero-enteric circulation. The routine combination of activated charcoal with a laxative is not recommended.

CONCLUSION

Even though intoxications are common, there is still no internationally valid guideline concerning the administration of activated charcoal. A precise analysis of the risks and benefits is needed for each administration, and a poison control center should be consulted for this purpose.

Restarting antidepressant and antipsychotic medication after intentional overdoses: need for evidence-based guidance

Intentional drug overdoses with antidepressant and antipsychotic medications are an increasingly common problem. Currently, there is little guidance with regard to reintroduction of these medications after intentional overdoses. We have used published toxicological and pharmacokinetic data to obtain factors which control the recovery from overdoses. From such data, we have proposed guidance regarding their reintroduction, provided there are no adverse effects or contraindications. Tentatively, we suggest that when adverse effects from the overdose are lost, treatment could recommence after a further mean half-life of elimination. Most antidepressant and antipsychotic drugs are metabolized by cytochrome P450 enzymes and, where cytochrome P450 inhibitors are co-ingested, serial plasma concentrations should optimally be obtained in order to assess a suitable time for reintroduction of the psychoactive drugs. We hope the proposals presented will stimulate research and discussion that lead to better guidance for clinicians concerning reintroduction of psychoactive medication after intentional overdose.

Fatal intoxication with antidepressants: a case with many culprits

Serotonin-specific reuptake inhibitors (SSRIs) are generally considered safe drugs but fatal adverse effects do sometimes occur, often as a consequence of interactions with other serotonin active drugs. Polypharmacy is usually a problem that the elderly encounter, but it can also have dire consequences for young people, especially when an underlying heart condition is present. Thus, failure to diagnose heart disease and the use of contraindicated medications can be a lethal combination, irrespective of age. Here we present a case of a young adult suffering from bipolar disorder who used a combination of two SSRIs (citalopram and fluoxetine) and a monoamine oxidase inhibitor (MAO; moclobemide) with tragic consequences. The deceased also suffered from undiagnosed hypertrophic cardiomyopathy and was carrier of a genotype that may have predisposed him to increased sensitivity to SSRIs. The apparent difficulty in establishing the manner of death in this case is also discussed.

Overdoses with Aripiprazole: Signs, Symptoms and Outcome in 239 Exposures Reported to the Danish Poison Information Centre

The aim of this study was to characterize the clinical signs and symptoms of exposures to aripiprazole overdoses. We retrospectively identified all aripiprazole exposures reported to the Danish Poison Information Centre (DPIC) from June 2007 to May 2015. Information concerning demographics, ingested dose and symptoms was extracted from the DPIC database and medical records. Information on death and admission to hospital was obtained from Danish national registers. We analysed 239 cases, 86 concerning single-drug exposures to aripiprazole, and 153 cases where aripiprazole had been taken with at least one other substance (mixed-drug). The median ingested aripiprazole dose was 105 mg (IQR: 50-1680 mg) in the single-drug exposure group and 120 mg (IQR: 60-225 mg) in the mixed-drug exposure group. The most commonly reported symptom was light sedation, reported in 63% of the single-drug group and 50% of the mixed-drug exposure group. There were no malignant arrhythmias or ECG abnormalities after single-drug exposures. No deaths were recorded in relation to the intake. We found a long-term mortality rate of 13 deaths per 1000 person-years (95% CI: 7; 23 per 1000 person-years), which is significantly higher than in an age- and gender-matched background population. In conclusion, we found that aripiprazole overdoses had few and mild symptoms predominantly related to the sedative properties. We detected a benign cardiovascular safety profile and no new safety concerns. Our findings may support an increased threshold of 300 mg for hospital admission after a single-drug exposure with aripiprazole and symptoms not worse than light sedation.

The pharmacokinetics of dexmedetomidine during long-term infusion in critically ill pediatric patients. A Bayesian approach with informative priors

The purpose of this study was to assess the pharmacokinetics of dexmedetomidine in the ICU settings during the prolonged infusion and to compare it with the existing literature data using the Bayesian population modeling with literature-based informative priors. Thirty-eight patients were included in the analysis with concentration measurements obtained at two occasions: first from 0 to 24 h after infusion initiation and second from 0 to 8 h after infusion end. Data analysis was conducted using WinBUGS software. The prior information on dexmedetomidine pharmacokinetics was elicited from the literature study pooling results from a relatively large group of 95 children. A two compartment PK model, with allometrically scaled parameters, maturation of clearance and t-student residual distribution on a log-scale was used to describe the data. The incorporation of time-dependent (different between two occasions) PK parameters improved the model. It was observed that volume of distribution is 1.5-fold higher during the second occasion. There was also an evidence of increased (1.3-fold) clearance for the second occasion with posterior probability equal to 62 %. This work demonstrated the usefulness of Bayesian modeling with informative priors in analyzing pharmacokinetic data and comparing it with existing literature knowledge.

The antipsychotic story: changes in prescriptions and overdose without better safety

AIMS

Morbidity and mortality from drug overdose has decreased over three decades. This is credited to safer drugs and therefore better outcomes in overdose. We aimed to investigate changing prescriptions of antipsychotic medications and associated changes in antipsychotic overdoses over a 26-year period.

METHODS

All antipsychotic poisoning presentations to a tertiary referral toxicology unit between 1987 and 2012 were reviewed. Data were collected prospectively on demographics, ingestion information, clinical effects, complications and treatment. Rates of antipsychotic drug use in Australia were obtained from Australian government publications for 1990-2011 and linked to overdose admissions by postcode.

RESULTS

There were 3180 antipsychotic overdoses: 1235 first generation antipsychotics, 1695 'atypical' second generation antipsychotics and 250 lithium overdoses. Over 26 years, antipsychotic overdoses increased 1.8-fold, with first generation antipsychotics decreasing to one-fifth of their peak (≈80/year to 16) and second generation antipsychotics increasing to double this (≈160/year), olanzapine and quetiapine accounting for 78%. All antipsychotic overdoses had a median length of stay of 18.6 h, 15.7% admitted to intensive care unit, 10.4% ventilated and 0.13% died in hospital, which was the same for first generation compared to second generation antipsychotics. There was a 2.3-fold increase in antipsychotic prescriptions over the same period; first generation antipsychotics declined whereas there was a dramatic rise in second generation antipsychotics, mainly olanzapine, quetiapine and risperidone (79%).

CONCLUSION

Over 26 years there was an increase in antipsychotic prescribing associated with an increase in antipsychotic overdoses. Although the type of antipsychotics changed, the morbidity and mortality remained the same, so that antipsychotics are an increasing proportion of overdose admissions.

A novel approach for estimating ingested dose associated with paracetamol overdose

AIM

In cases of paracetamol (acetaminophen, APAP) overdose, an accurate estimate of tissue-specific paracetamol pharmacokinetics (PK) and ingested dose can offer health care providers important information for the individualized treatment and follow-up of affected patients. Here a novel methodology is presented to make such estimates using a standard serum paracetamol measurement and a computational framework.

METHODS

The core component of the computational framework was a physiologically-based pharmacokinetic (PBPK) model developed and evaluated using an extensive set of human PK data. Bayesian inference was used for parameter and dose estimation, allowing the incorporation of inter-study variability, and facilitating the calculation of uncertainty in model outputs.

RESULTS

Simulations of paracetamol time course concentrations in the blood were in close agreement with experimental data under a wide range of dosing conditions. Also, predictions of administered dose showed good agreement with a large collection of clinical and emergency setting PK data over a broad dose range. In addition to dose estimation, the platform was applied for the determination of optimal blood sampling times for dose reconstruction and quantitation of the potential role of paracetamol conjugate measurement on dose estimation.

CONCLUSIONS

Current therapies for paracetamol overdose rely on a generic methodology involving the use of a clinical nomogram. By using the computational framework developed in this study, serum sample data, and the individual patient's anthropometric and physiological information, personalized serum and liver pharmacokinetic profiles and dose estimate could be generated to help inform an individualized overdose treatment and follow-up plan.

Activated charcoal for acute overdose: a reappraisal

Sometimes mistakenly characterized as a 'universal antidote,' activated charcoal (AC) is the most frequently employed method of gastrointestinal decontamination in the developed world. Typically administered as a single dose (SDAC), its tremendous surface area permits the binding of many drugs and toxins in the gastrointestinal lumen, reducing their systemic absorption. Like other decontamination procedures, the utility of SDAC attenuates with time, and, although generally safe, it is not free of risk. A large body of evidence demonstrates that SDAC can reduce the absorption of drugs and xenobiotics but most such studies involve volunteers and have little generalizability to clinical practice. Few rigorous clinical trials of SDAC have been conducted, and none validate or refute its utility in those patients who are intuitively most likely to benefit. Over the past decade, a growing body of observational data have demonstrated that SDAC can elicit substantial reductions in drug absorption in acutely poisoned patients. The challenge for clinicians rests in differentiating those patients most likely to benefit from SDAC from those in whom meaningful improvement is doubtful. This is often a difficult determination not well suited to an algorithmic approach. The present narrative review summarizes the data supporting the benefits and harms of SDAC, and offers pragmatic suggestions for clinical practice.

The pharmacokinetics of sertraline in overdose and the effect of activated charcoal

AIMS

To investigate the pharmacokinetics (PK) of sertraline in overdose and the effect of single dose activated charcoal (SDAC).

METHODS

Patients presenting to a toxicology unit with sertraline overdoses had demographic and clinical information recorded, and serial serum collected for measurement of sertraline concentrations. Monolix® version 4.2 was used to develop a population PK model of sertraline overdose and the effect of SDAC. Uncertainty in dose time was accounted for by shifting dose time using lag time with between subject variability (BSV). BSV on relative fraction absorbed was used to model uncertainty in dose.

RESULTS

There were 77 timed sertraline concentrations measured in 28 patients with sertraline overdoses with a median dose of 1550 mg (250-5000 mg). SDAC was given to seven patients between 1.5 and 4 h post-overdose. A one compartment model with lag time of 1 h and first order input and elimination adequately described the data. Including BSV on both lag time and relative fraction absorbed improved the model. The population PK parameter estimates for absorption rate constant, volume of distribution and clearance were 0.895 h(-1) , 5340 l and 130 l h(-1) , respectively. The calculated half-life of sertraline following overdose was 28 h (IQR 19.4-30.6h). When given up to 4 h post-overdose, SDAC significantly increased the clearance of sertraline by a factor of 1.9, decreased the area under the curve and decreased the maximum plasma concentration (Cmax ).

CONCLUSIONS

Sertraline had linear kinetics in overdose with parameter values similar to those in therapeutic use. SDAC is effective in increasing clearance when given 1.5 to 4 h post-overdose.

Effect of activated charcoal on apixaban pharmacokinetics in healthy subjects

Background

Activated charcoal is commonly used to manage overdose or accidental ingestion of medicines. This study evaluated the effect of activated charcoal on apixaban exposure in human subjects.

Methods

This was an open-label, three-treatment, three-period, randomized, crossover study of single-dose apixaban (20 mg) administered alone and with activated charcoal given at 2 or 6 h post-dose to healthy subjects. Blood samples for assay of plasma apixaban concentration were collected up to 72 h post-dose. Pharmacokinetic parameters, including peak plasma concentration (C_max), time to C_max (T_max), area under the concentration–time curve from time 0 to infinity (AUC_INF), and terminal half-life (T_½), were derived from apixaban plasma concentration–time data. A general linear mixed-effect model analysis of C_max and AUC_INF was performed to estimate the effect of activated charcoal on apixaban exposure.

Results

A total of 18 subjects were treated and completed the study. AUC_INF for apixaban without activated charcoal decreased by 50 and 28 %, respectively, when charcoal was administered at 2 and 6 h post-dose. Apixaban C_max and T_max were similar across treatments. The mean T_½ for apixaban alone (13.4 h) decreased to ~5 h when activated charcoal was administered at 2 or 6 h post-dose. Overall, apixaban was well tolerated in this healthy population, and most adverse events were consistent with the known profile of activated charcoal.

Conclusion

Administration of activated charcoal up to 6 h after apixaban reduced apixaban exposure and facilitated the elimination of apixaban. These results suggest that activated charcoal may be useful in the management of apixaban overdose or accidental ingestion.

How to combine non-compartmental analysis with the population pharmacokinetics? A study of tobacco smoke's influence on the bioavailability of racemic citalopram in rats

BACKGROUND

Citalopram (CIT) is an antidepressant drug from the group of selective serotonin reuptake inhibitors in which it is the most potent selective inhibitor of serotonin uptake currently available. Patients treated with CIT are often heavy cigarette smokers. Individual pharmacokinetic parameters cannot be directly estimated if full pharmacokinetic profiles are not available for each subject. Sparse sampling is common to experiments using small animals, such as the case that our study is concerned with.

METHODS

The aim of the study was to demonstrate how the two (non-compartmental analysis (NCA) and nonlinear mixed-effect (NLME)) approaches, used simultaneously, can help overcome specific limitations of these separate methods whilst at the same time preserve their respective benefits.

RESULTS

Despite the ultra-sparse design, the NLME approach enabled us to develop a pharmacostatistic model with the required covariate--exposition to the tobacco smoke.

CONCLUSIONS

A tobacco smoke slows down the absorption of the CIT and at the same time makes it more effective. The consistency of results obtained both with NCA and NLME decreased the risk of model misspecification and increased confidence in the final conclusions. Combining NLME with NCA may therefore be recommended for investigating pharmacokinetic properties of the drug in the sparse designs.

Mirtazapine overdose is unlikely to cause major toxicity

OBJECTIVE

There is limited information on mirtazapine overdose, but cases of severe effects (seizures, serotonin toxicity and coma) have been reported. We aimed to investigate the clinical effects and complications of mirtazapine overdose.

METHODS

This was an observational case series of mirtazapine overdoses (> 120 mg) identified from admissions to a toxicology unit between January 1987 and August 2013. Demographic information, details of ingestion, clinical effects, ECG parameters (HR, QT and QRS), and length of stay were extracted from a clinical database.

RESULTS

From 267 mirtazapine overdoses, there were 89 single-agent mirtazapine ingestions and 178 cases where mirtazapine was taken with at least one other drug. The median age of the 89 single-agent mirtazapine ingestions was 36 years [interquartile range (IQR): 26-49 years; Range: 15-81 years]; 45 were female (51%). The median ingested dose was 420 mg (IQR: 270-750 mg; Range: 150-1350 mg) and 41 patients (46%) had a Glasgow coma score (GCS) < 15, but the minimum GCS was 10. There were no seizures, serotonin toxicity or delirium. Tachycardia occurred in 29 patients (33%) and hypertension in 32 patients (36%). The median QRS was 80 ms (Range: 80-120 ms) and there were no cases with QT prolongation. There were no arrhythmias and no deaths. The median length of stay was 14 h (IQR: 8.8-18.2 h; Range:2.2-75 h). No single-agent mirtazapine patient was admitted to intensive care. The 178 patients taking co-ingestants had more severe toxicity depending on the co-ingested drug.

CONCLUSION

Mirtazapine appears to be relatively benign in overdose, associated with tachycardia, mild hypertension and mild CNS depression not requiring intervention.

Antidepressant and QT interval prolongation, how should we look at this issue? Focus on citalopram

INTRODUCTION

Evidence increasingly points to the potential development of harmful cardiac side effects concomitant with the use of a number of psychotropic drugs, primarily traditional antipsychotics and tricyclic antidepressants.

AREAS COVERED

The US Food and Drug Administration announced safety warnings associated with the use of citalopram with QT interval prolongation in 2011 and 2012. This paper explores the clinical background of QT interval prolongation, clinical data related to antidepressants and QT interval prolongation, the clinical implications of safety issues associated with the use of antidepressants and future research directions.

EXPERT OPINION

Currently available evidence proposes that citalopram may not be definitely associated with the increase of cardiac mortality, although it should be related with increase of QT prolongation. A firm consensus regarding the cardiac safety issues associated with antidepressants has to be established in near future. Hence, the choice of an individual antidepressant regarding cardiac safety issues should be based on multiple factors; clinicians may need to select the best available antidepressant for each individual based on that patient's vulnerability, the proven efficacy and safety of each agent and a reasonable benefit:risk ratio, based on currently available findings.

Estimation of CYP2D6*10 genotypes on citalopram disposition in Chinese subjects by population pharmacokinetic assay

WHAT IS KNOWN AND OBJECTIVE

There is great interindividual variability in citalopram (CIT) pharmacokinetics. We attempted to establish a population pharmacokinetic (PPK) model of CIT in Chinese healthy subjects, to evaluate the effect of genetic polymorphism on CIT pharmacokinetics and to compare the PPK and non-compartmental (NCA) assays in the estimation of CIT bioequivalence.

METHODS

Blood samples of 23 healthy subjects were collected after administration of CIT; plasma concentration of CIT was analysed using LC/MS-MS. CYP2C19 and CYP2D6*10 genotypes were determined. PPK model was established by using nonlinear mixed-effect modelling (NONMEM). The model was evaluated using goodness-of-fit plots and relative error measurements. Bioequivalence of CIT was evaluated by both PPK and NCA method.

RESULTS AND DISCUSSION

The estimated population absorption rate constant (ka ), clearance (CL/F) and volume of distribution (Vd/F) in Chinese healthy subjects are 0.64 L/h, 12.7 L/h and 705 L, respectively. Different CYP2C19 and CYP2D6 genotypes have impacts on CIT pharmacokinetics. There is about 5.5% decrement of CL/F for each CYP2C19*2 or CYP2D6*10 allele. The 90% confidence interval of CIT bioavailability obtained from NCA and PPK model were 96.4-105.4% and 92.5-103.4%, respectively.

WHAT IS NEW AND CONCLUSION

The PPK of CIT is best characterized by a one-compartment disposition model with first-order absorption. CYP2C19 and CYP2D6 genotypes have impacts on the CL/F of CIT. Bioequivalence of CIT can be estimated by both NCA and PPK model.

Predicting the requirement for N-acetylcysteine in paracetamol poisoning from reported dose

Context

There is contention over whether reported dose correlates with toxicity in paracetamol poisoning and risk assessment is currently based on serum paracetamol concentration compared to a nomogram, irrespective of reported dose.

Objective

To determine if reported dose predicts the need for N-acetylcysteine (NAC).

Methods

Data were taken from paracetamol overdoses presenting to a tertiary toxicology service. Age, sex, reported dose, ingestion time, timed paracetamol concentrations between 4 and 16 h, hepatotoxicity (peak alanine transaminase > 1000 U/L) and treatment (single dose-activated charcoal [SDAC] and NAC) were analysed. Data were analysed within a repeated measures logistic regression framework using NONMEM (ver 7.2). The primary outcome was administration of NAC, which was determined based on a serum paracetamol concentration greater than the nomogram line.

Result

There were 1571 admissions in 1303 patients, with a median age of 27 years (12–96 years) and 1140 (73%) were females. The median dose was 10 g (1–100 g). The paracetamol concentration was above the nomogram line in 337 of 1571 (22%) patients. Patients presenting later (first paracetamol concentration between 7 and 16 h post-overdose) compared to those presenting earlier (4–7 h post-overdose) were more likely to have hepatotoxicity (5.5% vs. 0.4%; p < 0.0001), have a toxic paracetamol concentration (34% vs. 18%; p < 0.0001) and receive NAC (48% vs. 23%; p < 0.0001). SDAC reduced the probability of the paracetamol concentration being above the nomogram. Based on SDAC not being administered there was a 5% probability of requiring NAC at a dose of 6–9 g, a 10% chance of requiring NAC at a dose of 13–16 g, a 50% chance of requiring NAC at a dose of 30–34 g and a 90% chance for needing NAC at 48–50 g.

Conclusion

Reported dose was a good predictor of a toxic paracetamol concentration and SDAC reduced the probability of the concentration being above the nomogram. These predictions may assist in determining which patients could be started on NAC immediately.

Acute calcineurin inhibitor overdose: analysis of cases reported to a national poison center between 1995 and 2011

Transplant recipients and other patients requiring immunosuppression with calcineurin inhibitors or their household contacts may be exposed to overdose. This study investigated the circumstances, pharmacokinetics and outcomes of overdose with cyclosporine and tacrolimus reported to the Swiss Toxicological Information Centre between 1995 and 2011. Of 145,396 reports by healthcare professionals, 28 (0.02%) concerned enteral or parenteral overdose with these calcineurin inhibitors. Thirteen (46%) were iatrogenic errors, 12 (43%) were with suicidal intent and 3 (11%) were accidental. Iatrogenic overdoses usually involved noncapsule drug formulations. Acute enteral overdoses caused symptoms in a dose-dependent fashion but were generally well tolerated; the mean multiple of patient's usual dose was 20.8 ± 28.8 for symptomatic versus 4.4 ± 3.4 for asymptomatic cases (p = 0.037). The most common symptoms were nausea, headache, somnolence, confusion, hypertension and renal impairment. In contrast, acute intravenous overdoses were often poorly tolerated and resulted in one fatality due to cerebral edema after a cyclosporine overdose. Enteral decontamination measures were performed in six cases involving oral ingestion and appeared to reduce drug absorption, as shown by pharmacokinetic calculations. In the one case where it was used, pharmacoenhancement appeared to accelerate tacrolimus clearance after intravenous overdose.

Oxycodone overdose causes naloxone responsive coma and QT prolongation

BACKGROUND

Although there are limited data on oxycodone overdose, it has been suggested that, in addition to central nervous system (CNS) depression, oxycodone may cause QT prolongation. Given the high prescription rate and increasing use of oxycodone, an understanding of its effects and treatment in overdose is necessary.

AIM

To investigate the clinical features, electrocardiogram (ECG) parameters and treatment of oxycodone overdose.

DESIGN

Retrospective review of a clinical database.

METHODS

One hundred and thirty-seven oxycodone overdoses were identified from admissions to a toxicology unit between January 2001 and May 2011. Demographic information, details of ingestion, clinical effects, ECG parameters [heart rate (HR), QT and QRS], naloxone use and length of stay (LOS) were extracted from a clinical database. QT was measured manually and plotted on a QT nomogram. LOS was extracted for all overdoses over the same period.

RESULTS

From 137 oxycodone overdoses, 79 (58%) ingested immediate release (IR) and 58 (42%) ingested sustained release (SR) or a combination of IR and SR. The median age was 40 years [interquartile range (IQR): 33-49 years], and 87 were female (64%). The median ingested dose of IR oxycodone was 70 mg (IQR: 40-100, range: 5-200), compared to 240 mg (IQR: 80-530, range: 30-1600) for SR oxycodone. Benzodiazepines were the most frequent co-ingested drug in 52 (38%) cases. No arrhythmias were recorded. Twenty-four patients (18%) had bradycardia of which five had a HR < 50 beats/min. From 116 available ECGs, the median QRS was 95 ms (IQR: 90-102 ms), and there were 20 (17%) abnormal QT-HR pairs. Naloxone boluses were required in 65 admissions (47%), and 34 (25%) required a naloxone infusion. There was higher overall naloxone use with SR and IR + SR (32/58, 55%) compared to IR oxycodone (33/79, 42%). The median LOS was 18 h (IQR: 12-35), which was greater than the median LOS for all toxicology admissions at 15 h (IQR: 8-24) over the same period. Patients requiring a naloxone infusion had an even greater LOS of 36 h (IQR: 20-62 h).

CONCLUSION

In addition to the expected CNS depression, the opioid oxycodone can cause bradycardia and QT prolongation in overdose. The SR formulation is associated with the use of naloxone infusions and a longer LOS.

Population pharmacokinetics and pharmacodynamics of escitalopram in overdose and the effect of activated charcoal

AIMS

To describe the pharmacokinetics and pharmacodynamics (PKPD) of escitalopram in overdose and its effect on QT prolongation, including the effectiveness of single dose activated charcoal (SDAC).

METHODS

The data set included 78 escitalopram overdose events (median dose, 140mg [10-560mg]). SDAC was administered 1.0 to 2.6 h after 12 overdoses (15%). A fully Bayesian analysis was undertaken in WinBUGS 1.4.3, first for a population pharmacokinetic (PK) analysis followed by a PKPD analysis. The developed PKPD model was used to predict the probability of having an abnormal QT as a surrogate for torsade de pointes.

RESULTS

A one compartment model with first order input and first-order elimination described the PK data, including uncertainty in dose and a baseline concentration for patients taking escitalopram therapeutically. SDAC reduced the fraction absorbed by 31% and reduced the individual predicted area under the curve adjusted for dose (AUC(i) /dose). The absolute QT interval was related to the observed heart rate with an estimated individual heart rate correction factor (α= 0.35). The heart rate corrected QT interval (QT(c) ) was linearly dependent on predicted escitalopram concentration [slope = 87ms/(mgl(-1) )], using a hypothetical effect-compartment (half-life of effect-delay, 1.0h). Administration of SDAC significantly reduced QT prolongation and was shown to reduce the risk of having an abnormal QT by approximately 35% for escitalopram doses above 200mg.

CONCLUSIONS

There was a dose-related lengthening of the QT interval that lagged the increase in drug concentration. SDAC resulted in a moderate reduction in fraction of escitalopram absorbed and reduced the risk of the QT interval being abnormal.

Patterns of toxicity and factors influencing severity in acute adult trimipramine poisoning

AIMS

To analyze the clinical features of trimipramine poisoning, identify a minimal toxic dose, and the dose bearing a 50% risk of developing a moderate, severe or fatal outcome.

METHODS

All acute adult trimipramine monointoxications reported by physicians to the Swiss Toxicological Information Centre between January 1992 and December 2009 were identified.

RESULTS

Two hundred and thirty cases (26 confirmed and 204 probable) were analyzed, the mean age was 35.7 years and 74% were females. One hundred and thirty-seven patients showed mild, 54 moderate and 21 severe symptoms. Three cases were fatal due to refractory cardiovascular collapse. Ninety-three per cent of the events were attempted or completed suicides. The most common symptoms were central nervous system depression (79.2%), tachycardia (19.1%) and QT(c) prolongation (13.9%). The severity of poisoning depended significantly on the ingested dose (P < 0.001). The minimal dose for moderate symptoms was 250 mg (median dose 1.2 g) and 850 mg for severe symptoms (median dose 2.7 g). The dose for a 50% risk of developing a moderate, severe or fatal outcome was 5.11 g. In 38 patients early gastrointestinal decontamination was performed. Overall, these patients ingested higher trimipramine doses than the late- or not-decontaminated patients (P = 0.113). The median doses were also higher in the decontaminated group within each severity category except in the fatal cases.

CONCLUSIONS

We demonstrated that moderate trimipramine poisoning can already occur after ingestion of doses in the high therapeutic range. Poisoned patients have to be monitored for central nervous system depression, dysrhythmias and QT(c) prolongation. Early decontamination might be beneficial.

Introduction to pharmacokinetics in clinical toxicology

In clinical toxicology, a better understanding of the pharmacokinetics of the drugs may be useful in both risk assessment and formulating treatment guidelines for patients. Pharmacokinetics describes the time course of drug concentrations and is a driver for the time course of drug effects. In this chapter pharmacokinetics is described from a mathematical modeling perspective as applied to clinical toxicology. The pharmacokinetics of drugs are described using a combination of input and disposition (distribution and elimination) phases. A description of the time course of the input and disposition of drugs in overdose provides a basis for understanding the time course of effects of drugs in overdose. Relevant clinical toxicology examples are provided to explain various pharmacokinetic principles. Throughout this chapter we have taken a pragmatic approach to understanding and interpreting the time course of drug effects.

Mechanism-based pharmacodynamic modeling

Pharmacodynamic modeling is based on a quantitative integration of pharmacokinetics, pharmacological systems, and (patho-) physiological processes for understanding the intensity and time-course of drug effects on the body. Application of such models to the analysis of meaningful experimental data allows for the quantification and prediction of drug-system interactions for both therapeutic and adverse drug responses. In this chapter, commonly used mechanistic pharmacodynamic models are presented with respect to their important features, operable equations, and signature profiles. In addition, literature examples showcasing the utility of these models to adverse drug events are highlighted. Common model types that are covered include simple direct effects, biophase distribution, indirect effects, signal transduction, and irreversible effects.

Indications for single-dose activated charcoal administration in acute overdose

PURPOSE OF REVIEW

Gastrointestinal decontamination in overdose patients remains a controversial problem in emergency medicine. There has been a significant decrease in the use of single-dose activated charcoal (SDAC) in recent years based on little new evidence and possibly because the overall mortality in overdose patients is low.

RECENT FINDINGS

Human volunteer studies suggest SDAC is effective and this effect occurs for up to 4 h after ingestion, but the magnitude of the reduction in area under the curve (AUC) decreases over time. Two randomized controlled trials including one recent large study did not find SDAC to be beneficial. Pharmacokinetic and pharmacodynamic studies of specific drugs in overdose suggest that for most drugs SDAC decreases drug exposure, but this does not translate to clinical benefit in all cases. The administration of SDAC is a low-risk intervention.

SUMMARY

Although SDAC is unlikely to be beneficial in many overdose patients, for some subgroups with severe poisoning, the benefits will outweigh the low risk of administration. The use of SDAC should be based on the potential toxicity of the drug ingested and the potential benefit of SDAC balanced against the willingness of the patient to take SDAC and the low risk of administration.

How do we use drug concentration data to improve the treatment of overdose patients?

The role of drug assays for screening, diagnosis, and guiding treatment decisions in overdose patients remains unclear. The use of drug concentration data in clinical toxicology research is more problematic, with studies using drug concentrations to simply confirm ingestion in observational studies or others report drug concentration time profiles with simplified pharmacokinetics. The reasons for the lack of more substantial pharmacokinetic and/or pharmacodynamic analysis in overdose patients include problems with uncertainty in dose, uncertainty in the time of ingestion, and limited sampling in the absorption phase. Many of these can be overcome by using population pharmacokinetic and pharmacokinetic-pharmacodynamic analysis in prospective studies of overdose patients to understand dose-concentration-effect relationships. Uncertainty in dose and dose time can be included using population analysis techniques, which may involve a clinical assessment of the veracity of the patient history. The pharmacokinetic-pharmacodynamic model can then be used as the basis for predicting toxicity and clinical outcomes from historical information such as dose and early clinical effects. Using such an approach means that the use of drug concentration data in research will improve the risk assessment in overdose patients, without requiring these assays to be rapidly available in the acute health setting.

Risperidone overdose causes extrapyramidal effects but not cardiac toxicity

OBJECTIVE

The aim of this study was to describe the clinical and electrocardiographic features of risperidone overdose, including the frequency of dystonic reactions.

METHODS

A consecutive series of admissions for risperidone overdose (>6 mg) were identified from a prospective database of poisoning admissions to a regional toxicology service. Data extracted included patient demographics, details of ingestion, clinical features including neurological findings and evidence of dystonias, electrocardiographic parameters (heart rate [HR], QRS, and QT intervals), complications, and medical outcomes including intensive care unit admission. In addition to descriptive statistics, visual inspection of plots of QT-HR pairs compared with the QT nomogram was performed.

RESULTS

There were 107 patients with 157 presentations, including 38 patients with 45 risperidone-alone overdoses. Of the 38 patients who ingested risperidone alone, the median age was 25 years (interquartile range [IQR],16-31 years), and 19 (50%) were female. The median dose ingested was 33 mg (IQR, 15-75 mg; range, 8-248 mg). Median length of stay was 16 hours (IQR, 8-18 hours), and none was ventilated or admitted to the intensive care unit. There were 5 cases (11%) with dystonic reactions, 26 (58%) with tachycardia (HR >or=100 beats/min), and no cases with hypotension (blood pressure <90 mm Hg). Only 1 patient (2%) recorded a decreased Glasgow Coma Scale score of 14, and there were no seizures or deaths. On review of electrocardiograms in 41 of the 45 cases where risperidone was ingested alone, there were no acute dysrhythmias. In 4 electrocardiograms (10%), there was an abnormal QT-HR pair, but all bar one were associated with an HR of greater than 110 beats/min. The median maximum QRS width was 80 milliseconds (IQR, 80-80 milliseconds; range, 40-120 milliseconds).

CONCLUSIONS

Risperidone taken alone in overdose causes minimal effects. Tachycardia and dystonic reactions were the main features of toxicity. Significant cardiac and other neurological features seem to be uncommon.

Amisulpride overdose is frequently associated with QT prolongation and torsades de pointes

This study aimed to describe the effects of the antipsychotic amisulpride in overdose, including the frequency of QT prolongation and torsades de pointes. Cases of amisulpride overdose (>1 g) were recruited from 2 state poison centers and a tertiary toxicology unit over 5 years. A 1-page clinical research form was used to collect clinical information. Copies of all electrocardiograms were obtained. Electrocardiogram parameters (QRS and QT intervals) were manually measured as previously described, and plots of QT-heart rate (HR) pairs were compared with the QT nomogram. There were 83 patients with amisulpride overdoses with a median age of 29 years (interquartile range [IQR], 23-40 years), and 42 (51%) were female. The median dose ingested was 6 g (IQR, 3-13 g, range, 1.2-120 g). The median HR was 66 beats/min (IQR, 60-81 beats/min). Bradycardia occurred in 20 cases (24%), and hypotension in 19 (23%). From 440 electrocardiograms (average of 5 per case; range, 1-15), an abnormal QT-HR pair occurred in 61 cases (73%). Torsades de pointes developed in 6 cases (7%), with doses of 4, 4.6, 18, 24, 32, and 80 g. The patient taking 32 g died after a cardiac arrest. Widened QRS did not occur except transient rate-dependent bundle-branch block in 3 cases. There were significant associations of bradycardia, hypokalemia, and hypocalcaemia, with QT prolongation and torsades de pointes. Central nervous system effects were uncommon with coma in 7 cases, seizures in 2, and dystonic reactions in 2. Amisulpride overdose commonly causes QT prolongation, bradycardia, and hypotension. Torsades de pointes occurred commonly enough to suggest that amisulpride is highly cardiotoxic in overdose.

Quetiapine overdose: predicting intubation, duration of ventilation, cardiac monitoring and the effect of activated charcoal

To investigate factors that predict the probability and duration of mechanical ventilation in quetiapine overdose, and if cardiac toxicity occurs, this cohort study involved 176 patients presenting to a toxicology unit on 286 occasions with quetiapine overdose. Patient demographics, dose, coingestants, single dose activated charcoal (SDAC) administration, requirement for and duration of mechanical ventilation and electrocardiogram parameters (heart rate, QT, QRS) were obtained. A fully Bayesian approach using logistic regression and time-to-event analysis was undertaken to investigate the relationship between predictor variables and the requirement for and duration of intubation. QT versus heart rate was plotted on a QT nomogram to investigate QT prolongation. The commonest clinical effects were central nervous system depression on 136 occasions (48%) and tachycardia (67%). There were no malignant arrhythmias and an abnormal QT occurred in only 24 admissions (8.4%), all with tachycardia. Hypotension (systolic blood pressure <90 mmHg) occurred on 35 occasions (12%). The logistic regression model supported dose and SDAC (<2 h) influencing the probability of intubation, but not age, sex, therapeutic use of quetiapine or coingestants. The probability of intubation was 10% after 2 g, 22% after 5 g, 37% after 10 g and 55% after 20 g and SDAC resulted in a reduced probability of intubation of 7% for 2 g ingestion. The median duration of ventilation was 22 h (interquartile: 19-28 h), which was not affected by SDAC. Ingested dose can inform early decision making about requirements for intensive care unit admission and intubation. SDAC seems to have only modest effects on outcomes but may be considered within 2 h for large ingestions. Electrocardiogram monitoring is unlikely to be necessary.

Electrocardiogram changes and arrhythmias in venlafaxine overdose

AIMS

To investigate serial electrocardiogram (ECG) parameters, haemodynamic changes and arrhythmias following venlafaxine overdose.

METHODS

The study included 369 venlafaxine overdoses in 273 patients presenting to a toxicology unit where an ECG was available. Demographic information, details of ingestion, haemodynamic effects [heart rate and blood pressure (BP)] and complications (arrhythmias and conduction defects) were obtained. ECG parameters (QT, QRS) were measured manually and analysed by visual inspection, including plotting QT-HR pairs on a QT nomogram.

RESULTS

The median ingested dose was 1500 mg [interquartile range (IQR) 600-3000 mg; range 75-13 500 mg). Tachycardia occurred in 54% and mild hypertension (systolic BP >140 mmHg) in 40%. Severe hypertension (systolic BP >180 mmHg) and hypotension (systolic BP <90 mmHg) occurred in 3% and 5%, respectively. No arrhythmias occurred based on continuous telemetry, and conduction defects were found in only seven of 369 admissions; five of these conduction defects were pre-existing abnormalities. In 22 admissions [6%, 95% confidence interval (CI) 4-10] there was an abnormal QT-HR pair, with larger doses being more likely to be associated with an abnormal QT. The median maximum QRS width was 85 ms (IQR 80-90 ms; range 70-145 ms) and the QRS was greater than 120 ms in only 24 admissions (7%, 95% CI 4-10).

CONCLUSIONS

Venlafaxine overdose causes only minor abnormalities in the QT and QRS intervals, unlikely to be associated with major arrhythmias, except possibly with large doses.

Promethazine overdose: clinical effects, predicting delirium and the effect of charcoal

OBJECTIVE

The aim of this study was to describe the clinical effects of promethazine in overdose and explore the relationship between delirium and possible predictor variables.

METHODS

A case series of promethazine poisonings was identified from a prospective database of poisoning admissions to a regional toxicology service. Data were extracted including demographics, details of ingestion, clinical features including delirium, complications and medical outcomes. In addition to descriptive statistics, a fully Bayesian approach using logistic regression was undertaken to investigate the relationship between predictor variables and delirium.

RESULTS

There were 199 patients with 237 presentations, including 57 patients with 78 promethazine alone overdoses. Of these 57 patients who ingested promethazine alone the median age was 22 years [interquartile range (IQR): 17-31] and 42 were female (74%). The median dose ingested was 625 mg (IQR: 350-1250 mg). Median length of stay was 19 h (IQR: 13-27 h), ten were admitted to the intensive care unit (ICU) and four were ventilated. Delirium occurred in 33 patients (42%), tachycardia (HR>100) occurred on 44 occasions (56%) and hypotension only twice. There were no seizures, dysrhythmias or deaths. Multivariate analysis of 215 presentations (in 181 patients) where dose of promethazine ingested was known demonstrated that dose, administration of charcoal within 2 h and co-ingestants predicted whether patients developed delirium. No relationship was shown for sex and age. A plot of probability that a patient will develop delirium vs. dose was constructed which showed the probability of delirium for 250 mg was 31%, 500 mg was 42% and for 1 g was 55% for promethazine alone overdoses.

CONCLUSION

The main feature of promethazine toxicity is delirium, the probability of which can be predicted from the dose ingested. The administration of charcoal and the presence of co-ingestants appears to reduce the probability of delirium in a predictable manner.

Activated Charcoal Decreases the Risk of QT Prolongation After Citalopram Overdose

STUDY OBJECTIVE

We determine whether single-dose activated charcoal (SDAC) administration after citalopram overdose reduces the proportion of patients developing abnormal QT prolongation.

METHODS

Data were collected retrospectively for citalopram overdose patients presenting to 8 emergency departments. Demographics, dose, coingested drugs, SDAC administration, and serial ECGs were extracted from medical records. The primary outcome was the proportion of patients who had an observed QT,RR combination at any time above an abnormal threshold, established as a predictor of torsade de pointes. We compared the proportion of patients with QT prolongation who received or did not receive SDAC. These data were analyzed within a Bayesian framework, using probabilities of abnormal QT,RR combinations with and without derived from a previous single-center study. WinBUGS was used to generate posterior estimates and credible intervals of the relative risk by combining the prior probabilities and the study data.

RESULTS

SDAC was administered on average 2.1 hours (range, 0.5 to 6.25 hours) after ingestion in 48 of 254 admissions, and abnormal QT,RR combinations occurred in 2 cases (4.2%), compared with 23 of 206 (11.2%) cases not receiving SDAC. There did not appear to be any clinically important difference in age, sex, dose, and cardiotoxic coingestants between the 2 groups. No cases of torsade de pointes occurred. The estimated relative risk of having an abnormal QT,RR combination for SDAC compared to no SDAC was 0.28 (0.06 to 0.70) (median with 2.5% and 97.5% credible limits). The probability that the relative risk was less than 1.0 was 0.99, which can be interpreted as very strong evidence in favor of a beneficial effect of SDAC. The absolute risk difference was estimated as 7.5% and the median number needed to treat as 13.3.

CONCLUSION

SDAC may be effective in reducing the risk of a prolonged QT in patients after citalopram overdose. Current trends toward nonuse of activated charcoal should be evaluated to determine whether patients poisoned by specific agents may benefit from activated charcoal administration.