Katrin M. Kirschbaum

Brain and Plasma Pharmacokinetics of Aripiprazole in Patients With Schizophrenia: An [ 18 F]Fallypride PET Study

OBJECTIVE Aripiprazole at clinically effective doses occupies some 90% of striatal dopamine 2 and 3 (D(2)/D(3)) receptors. In order to further characterize its extrastriatal and time-dependent binding characteristics, the authors conducted positron emission tomography (PET) studies with the D(2)/D(3) antagonist [(18)F]fallypride at varying time points after the last aripiprazole administration in patients with schizophrenia. METHOD Sixteen inpatients with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder receiving treatment with aripiprazole underwent an [(18)F]fallypride PET scan. Receptor occupancy was calculated as the percentage reduction in binding potential relative to unblocked values measured in eight age-matched, medication-free patients with schizophrenia. In addition, aripiprazole serum concentrations were determined as part of a routine therapeutic drug monitoring program in a large group of patients (N=128) treated with aripiprazole. RESULTS Mean dopamine D(2)/D(3) receptor occupancy was high in all brain regions investigated, with no binding difference across brain regions. Nonlinear regression analysis revealed maximum attainable receptor occupancy (E(max)) values close to saturation. The values for serum concentration predicted to provide 50% of E(max) (EC(50)) were in the range of 5-10 ng/ml in all brain regions. The D(2)/D(3) receptors were completely saturated when serum aripiprazole concentration exceeded 100-150 ng/ml. The mean concentration in the large clinical patient sample was 228 ng/ml (SD=142). CONCLUSIONS Because of its high affinity for D(2)/D(3) receptors and its long elimination half-life, aripiprazole at clinical doses occupies a high fraction of its target receptor everywhere in the brain. Its dissociation from those receptors is very slow, such that the authors calculate from the results that in patients with serum aripiprazole concentrations in the range typical for clinical practice, D(2)/D(3) receptors must remain nearly saturated for as long as 1 week after the last dose.

Serum levels of aripiprazole and dehydroaripiprazole, clinical response and side effects.

Aripiprazole, a novel antipsychotic drug, is metabolized by CYP3A4 and CYP2D6 forming mainly its active metabolite dehydroaripiprazole. In this study, aripiprazole and dehydroaripiprazole serum levels of psychiatric patients were measured and related to dose, comedication, and clinical effects including therapeutic and side effects. Patients were treated with mean doses of 20±8 mg/day of aripiprazole (median 15 mg, range 7.5–60 mg). Serum levels correlated significantly with the dose (r=0.419; P<0.01), with a mean value of aripiprazole of 214±140 ng/ml. Mean concentrations of the active metabolite dehydroaripiprazole amounted to 40% of the parent compound. Comedication with CYP3A4 and CYP2D6 inducers or inhibitors changed serum levels up to 51%. Improvement was best in patients with a serum level between 150 to 300 ng/ml. No or only mild side effects were detected in patients, with aripiprazole plasma concentrations between 110 and 249 ng/ml. A total of 32% of the patients who received no other antipsychotic drug besides aripiprazole reported side effects; tension being the most frequent one. Since serum levels of aripiprazole and dehydroaripiprazole were highly variable between individuals, and distinct ranges were associated with good therapeutic response and minimal side effects, it seems likely that therapeutic drug monitoring can be helpful to improve the antipsychotic drug therapy.

Pharmacokinetics of acute and sub-chronic aripiprazole in P-glycoprotein deficient mice

BACKGROUND P-glycoprotein (P-gp), an efflux transporter localized in the blood-brain barrier, limits the access of multiple xenobiotics to the central nervous system (CNS). For the new antipsychotic aripiprazole and its active metabolite dehydroaripiprazole differences in disposition in blood and brain were investigated after acute and sub-chronic administration in a P-gp knockout mouse model. METHODS Serum and brain concentrations of both drugs were measured at several time points 1-24h after i.p. injection of 10mg/kg aripiprazole and after 11 days of sub-chronic administration in several tissues. Moreover, the expression of P-gp was determined by Western blot analysis after sub-chronic administration of the drug. RESULTS In both wild type and abcb1ab (-/-) mice concentration of aripiprazole in brain were up to 9 fold higher than in serum. For dehydroaripiprazole the mean brain to serum ratios were below two. Brain to serum concentrations of both substances were significantly higher after acute and sub-chronic administration in connection to the expression of P-gp indicated by higher levels in abcb1ab (-/-) mice especially for dehydroaripiprazole. Sub-chronic aripiprazole treatment in WT animals had no effect on P-gp expression in the blood-brain barrier. CONCLUSIONS Aripiprazole and, even more pronounced its active metabolite dehydroaripiprazole could be identified as substrates of P-gp. The efflux transporter P-gp must therefore be considered as a relevant factor that contributes to wanted or unwanted clinical effects in patients treated with aripiprazole.

Two cases of suicide by asphyxiation due to helium and argon

Numerous death cases due to suffocation in a toxic or oxygen deficient gas atmosphere have been described in the literature, but unfortunately especially cases involving inert gases like helium are often presented without detailed toxicological findings. Observations on two suicides are reported, one by helium and the other by argon inhalation. During autopsies gas samples from the lungs were collected directly into headspace vials by a procedure ensuring minimal loss and dilution. Qualitative gas analyses were performed using headspace gas chromatography-mass spectrometry (HS-GC/MS). For carrier gas the commonly used helium was replaced by hydrogen. Qualitative positive results were obtained in the argon case, but the case involving helium revealed negative findings. The use of HS-GC/MS enables in principle to detect inert gases like argon or helium. However, a number of factors may later influence the results as, e.g. a longer period of time between death and sampling or pre-analytical artefacts during sampling of such highly volatile substances. In absence of analytical data supporting helium exposure, the causes of death in the actual cases were found to be asphyxia and in both cases the manner was suicide.

Direct ELISA kits as a sensitive and selective screening method for abstinence control in urine

In 2009 cutoff values of assessment criteria to testify abstinence control in order to estimate driving ability were standardized in Germany. The cutoff values are lower than required in existing guidelines like SAMHSA and there is critical discussion about detection of low concentrations by using immunoassay, especially concerning amphetamines in urine (50 ng/ml). In this study Direct ELISA kits were tested for their applicability to identify the absence of amphetamines, cannabinoids, opiates, cocaine, methadone and benzodiazepines in urine. Results were confirmed by LC/MS or GC/MS analyses. Sensitivity, specificity, predictive values (positive as well as negative) and overall misclassification rates were evaluated by contingency tables and were compared to ROC-analyses. Sensitivity results as well as specificity results were satisfying showing sensitivity values higher than 96% for each analyte. The amphetamine test we used showed sensitivity and specificity of 100% and 88%, respectively, even if amphetamine tests usually react with high cross-reactivity. Our study results include high discrimination at required cutoff values between positives and negatives for each drug group and demonstrate that immunological tests complying with requirements of current decreased urine cutoff values for assessment of driving ability do exist.

Optimization and validation of CEDIA drugs of abuse immunoassay tests in serum on Hitachi 912.

Due to sensitive limits of detection of chromatographic methods and low limit values regarding the screening of drugs under the terms of impairment in safe driving (§ 24a StVG, Street Traffic Law in Germany), preliminary immunoassay (IA) tests should be able to detect also low concentrations of legal and illegal drugs in serum in forensic cases. False-negatives should be avoided, the rate of false-positive samples should be low due to cost and time. An optimization of IA cutoff values and a validation of the assay is required for each laboratory. In a retrospective study results for serum samples containing amphetamine, methylenedioxy derivatives, cannabinoids, benzodiazepines, cocaine (metabolites), methadone and opiates obtained with CEDIA drugs of abuse reagents on a Hitachi 912 autoanalyzer were compared with quantitative results of chromatographic methods (gas or liquid chromatography coupled with mass spectrometry (GC/MS or LC/MS)). Firstly sensitivity, specificity, positive and negative predictive values and overall misclassification rates were evaluated by contingency tables and compared to ROC-analyses and Youden-Indices. Secondly ideal cutoffs were statistically calculated on the basis of sensitivity and specificity as decisive statistical criteria with focus on a high sensitivity (low rates of false-negatives), i.e. using the Youden-Index. Immunoassay (IA) and confirmatory results were available for 3014 blood samples. Sensitivity was 90% or more for nearly all analytes: amphetamines (IA cutoff 9.5 ng/ml), methylenedioxy derivatives (IA cutoff 5.5 ng/ml), cannabinoids (IA cutoff 14.5 ng/ml), benzodiazepines (IA cutoff >0 ng/ml). Test of opiates showed a sensitivity of 86% for a IA cutoff value of >0 ng/ml. Values for specificity ranged between 33% (methadone, IA cutoff 10 ng/ml) and 90% (cocaine, IA cutoff 20 ng/ml). Lower cutoff values as recommended by ROC analyses were chosen for most tests to decrease the rate of false-negatives. Analyses enabled the definition of cutoff values with good values for sensitivity. Small rates of false-positives can be accepted in forensic cases.

Unclear loss of consciousness after clobutinol intake

The case of a 13-month-old boy with a diagnosis of unclear unconsciousness is reported on. As the physical examination did not lead to any explanation of his condition, the administration of drugs in the context of Munchausen syndrome by proxy was suspected. Complex forensic-toxicological analyses using HPLC/UV, LC/MS/MS, and GC/MS identified ambroxol and clobutinol, two drugs that are indicated for acute respiratory diseases. No other central active compounds were detected. The accusation of intentional bodily injury raised against the parents could be rebutted, since the boys unconsciousness could be explained with a rare but harmful side effect of the antitussive clobutinol.

Illegal drugs and delinquency

An interrelation between consumption of illegal drugs and committing an indictable offence has been repeatedly discussed in literature. In a retrospective study serum concentrations of illegal and legal drugs as well as data originating from police reports and examinations by physicians taking blood from individuals being suspected to be under the influence of drugs were evaluated. Results from 4816 cases were available. Property offences were the most frequent type (36%) as well as consumption of cannabinoids (55%). Psychophysiological conditions of consumers were compared with according serum concentrations. Close correlations between stimulating drugs and violence associated crime could not be found. Stimulated as well as sedated behaviour occurring following the consumption of various drugs might be the reason for no clear correlation between types of offence and consumed illegal or legal drugs in this study.

Another Suicide Using the Veterinary Drug T61 and Distribution of Drugs in the Body

The authors recently reported about the complex suicide of a former veterinarian who injected xylazine and levomethadone together with T61, which is normally used for the euthanasia of domestic and laboratory animals (1). Furthermore, various analgesics were detected in biological samples, probably taken as painkillers for an existing cancer disease. The quaternary ammonium compound mebezonium iodide, an acetylcholine inhibitor, is an active ingredient of T61, in addition to embutramide and tetracaine (2). Embutramide has narcotic properties and induces deep anesthesia and an inhibition of the respiratory center located in the brainstem. Tetracaine is a local anaesthetic substance and decreases painful reactions at injection sites. A recent report by the authors summarized cases of suicides or homicides involving the use of T61 (1). However, in most cases, embutramide, which is exclusively used in T61, was the only substance analyzed because of analytical difficulties when analyzing quarternary ammonium compounds like mebezonium. Before this report, mebezonium was only analyzed in two cases, once by thin-layer chromatography followed by ultraviolet spectrophotometry after elution from silica gel (3), and later by liquid-chromatography –mass spectrometry with quantification by a specific ion, m/z 294 (4). Because there are relatively few authentic cases reported in the literature, the distribution and concentration of all three ingredients of T61 in the body of a new case appears worthwhile to communicate. A 40-year-old male was found dead in the gateway of his home. In a garage 15 m away, opened bottles of wine, sherry and rum were found, as were a depleted 20 mL syringe, an opened pharmaceutical vial of T61 (50 mL with a rest of 5 mL) and a suicide note. Three years ago, T61 had been used for euthanasia of the Saint Bernard dog of the family and the veterinary surgeon had forgotten the rest of the drug, which was stored in the cellar. Autopsy findings The body weight was 84.1 kg and body height was 174.5 cm. No signs of external violence were observed. An injection mark was found over the back of the left hand with edema of the subcutaneous tissues. Another skin injection mark was noted on the palm of the left wrist, also with edema of the subcutaneous tissues. The subcutaneous tissues of both injection sites were dark black with discoloration. Edematous swelling of the subcutaneous tissues of the left forearm was observed, as were extreme congestion of internal organs, cerebral and pulmonary edema, acute pulmonary emphysema and advanced coronary atherosclerosis.