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Aims: Metamizole is quite an old drug with analgesic, antipyretic and spasmolytic properties. Recent findings have shown that it may induce several cytochrome P450 (CYP) enzymes, especially CYP3A4 and CYP2B6. The clinical relevance of these properties is uncertain. We aimed to unravel potential pharmacokinetic interactions between metamizole and the CYP3A4 substrate quetiapine., Methods: Plasma concentrations of quetiapine from a large therapeutic drug monitoring database were analysed. Two groups of 33 patients, either receiving quetiapine as a monotherapy (without CYP modulating comedications) or with concomitantly applied metamizole, were compared addressing a potential impact of metamizole on the metabolism of quetiapine being reflected in differences of plasma concentrations of quetiapine and dose-adjusted plasma concentrations., Results: Patients comedicated with metamizole showed >50% lower plasma concentrations of quetiapine (median 45.2 ng/mL, Q 1  = 15.5; Q 3  = 90.5 vs. 92.0 ng/mL, Q 1  = 52.3; Q 3  = 203.8, P = .003). The dose-adjusted plasma concentrations were 69% lower in the comedication group (P = .001). Subgroup analyses did not suggest a dose dependency of the metamizole effect or an influence of quetiapine formulation (immediate vs. extended release). Finally, the comedication group exhibited a significantly higher proportion of patients whose quetiapine concentrations were below the therapeutic reference range (78.8% in the metamizole group vs. 54.4% in the control group, P = .037) indicating therapeutically insufficient drug concentrations., Conclusion: The combination of metamizole and quetiapine leads to significantly lower drug concentrations of quetiapine, probably via an induction of CYP3A4. Clinicians must consider the risk of adverse drug reactions, especially treatment failure under quetiapine when adding metamizole., (© 2024 The Author(s). British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Drug-drug interactions (DDI) are a major topic in programs for continuous medical education (CME). Many physicians are afraid of being trapped into charges of malpractice; however, DDI cannot be avoided in many cases. They belong to routine medical practice and it is often impossible to avoid them. Moreover, they do not just occur between drugs but between any kind of foreign substance (xenobiotica), such as food (e.g. grapefruit juice, broccoli, barbecue) as well as legal (e.g. tobacco smoke, caffeine and alcohol) and illegal drugs. Therefore, the medical challenge is not just to avoid any interaction. Instead the physician faces the question of how to proceed with drug treatment in the presence of such interactions. Based on the medical education a physician has to judge first of all whether there is a risk for interactions in the prescription being planned for an individual patient. The classification of interactions proposed in this article (PD1-PD4, PK1-PK3) might help as a sort of check list. For more detailed information the physician can then consult one of the many databases available on the internet, such as PSIAConline (http://www.psiac.de) and MediQ (http://www.mediq.ch). Pharmacokinetic interactions can be easily assessed, monitored and controlled by therapeutic drug monitoring (TDM). Besides these tools it is important to keep in mind that nobody knows everything; even physicians do not know everything. So take pride in asking someone who might help and for this purpose AGATE offers a drug information service AID (http://www.amuep-agate.de). Just good for nothing, without being based on any kind of medical approach are computer programs that judge prescriptions without taking into account a patient's individual peculiarities. In case these types of programs produce red exclamation marks or traffic lights to underline their judgment, they might even work in a contrapuntal way by just eliciting insecurity and fear.

Delirium may be induced by a variety of reasons, among them drugs and in particular the combination of drugs. In elderly people a delirium is often misinterpreted as dementia. Anticholinergic activity is the mode of action by which drugs cause delirium. Antipsychotic drugs, antidepressants, antihistamines, and of course anticholinergic drugs themselves are the major anticholinergic classes of drugs. In addition some opioids have anticholinergic effects. Other drugs may induce delirium by dehydration (loop diuretics like furosemide) or sedation (benzodiazapines like lorazepam). Elderly people are at especially high risk to develop delirium, because of the multitude of drugs often prescribed to them, because they tend to drink to little, and because their brain is more sensitive to psychoactive drugs.

The quantification and pharmacological interpretation of drug concentrations in blood (serum or plasma) is widely known as therapeutic drug monitoring (TDM). In clinical practice, TDM is an established precision tool that provides the fundamental prerequisites for personalized treatment. Specifically, in neurology and psychiatry, TDM can be used as part of the process of prescription of medications in specific patient subgroups, including children and adolescents, pregnant women, elderly patients, patients with intellectual disabilities, patients with substance abuse disorders, individuals with pharmacokinetic idiosyncrasies and forensic patients. Clinicians may consider TDM in the case of lack of clinical response to therapeutic doses of medication, assessment of drug adherence, tolerability and drug-drug interactions. This is the Greek translation of a short summary of the updated consensus guidelines compiled by the TDM task force of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP). It includes therapeutic reference ranges, laboratory alert levels, recommendation levels for prescribing TDM for dosage optimization without specific indications, conversion factors, factors for calculation of dosage-related drug concentrations and metabolite-to-parent ratios. [ABSTRACT FROM AUTHOR]

Introduction: The main objective of this study was to investigate the influence of the use of multiple medications and other risk factors on citalopram plasma concentrations. Methods: A retrospective cohort study with a naturalistic population of 957 patients for whom routine therapeutic drug monitoring (TDM) of citalopram had been requested between 2006 and 2013 was conducted. Results: Concomitant drugs inhibiting at least 2 different CYP subtypes involved in the metabolism of citalopram decreased statistically significantly the total clearance (Clt). Compared to younger patients over 64-year-old patients had on average a 4.5 times higher risk rate of supratherapeutic plasma concentrations. However, binary logistic regression showed that age, sex and co-medication accounted only for 26 % of the inter-individual variability of citalopram plasma concentrations. Discussion: Due to pharmacokinetic interactions, citalopram plasma concentrations are often higher than expected with a given dose. Especially in geriatric and often multimorbid patients who are usually prescribed high numbers of concomitant drugs and are at higher risk for adverse drug reactions (ADR), restriction of the maximal dose of citalopram is not sufficient to prevent supra-therapeutic plasma concentrations. [ABSTRACT FROM AUTHOR]

Drug-drug interactions (DDI) are a major topic in programs for continuous medical education (CME). Many physicians are afraid of being trapped into charges of malpractice; however, DDI cannot be avoided in many cases. They belong to routine medical practice and it is often impossible to avoid them. Moreover, they do not just occur between drugs but between any kind of foreign substance (xenobiotica), such as food (e.g. grapefruit juice, broccoli, barbecue) as well as legal (e.g. tobacco smoke, caffeine and alcohol) and illegal drugs. Therefore, the medical challenge is not just to avoid any interaction. Instead the physician faces the question of how to proceed with drug treatment in the presence of such interactions. Based on the medical education a physician has to judge first of all whether there is a risk for interactions in the prescription being planned for an individual patient. The classification of interactions proposed in this article (PD1-PD4, PK1-PK3) might help as a sort of check list. For more detailed information the physician can then consult one of the many databases available on the internet, such as PSIAConline (http://www.psiac.de) and MediQ (http://www.mediq.ch). Pharmacokinetic interactions can be easily assessed, monitored and controlled by therapeutic drug monitoring (TDM). Besides these tools it is important to keep in mind that nobody knows everything; even physicians do not know everything. So take pride in asking someone who might help and for this purpose AGATE offers a drug information service AID (http://www.amuep-agate.de). Just good for nothing, without being based on any kind of medical approach are computer programs that judge prescriptions without taking into account a patient's individual peculiarities. In case these types of programs produce red exclamation marks or traffic lights to underline their judgment, they might even work in a contrapuntal way by just eliciting insecurity and fear. [ABSTRACT FROM AUTHOR]

Evidence-based therapeutic drug monitoring (TDM), which may be successfully employed to guide drug therapy in clinical routine, supplies all the information from laboratory determination of a drug concentration in a patient's blood specimen. This value is interpreted first of all in relation to a therapeutic reference range that must be established according to the same rules that are generally accepted for clinical studies aimed to license a new drug. The drug concentration may be furthermore interpreted in reference to a dose-related reference range. Thereby a signal is created to alert for individual abnormalities such as drug/drug interactions, gene polymorphisms that give rise to slow/rapid metabolizers, altered function of the excretion organs liver and kidneys by age and/or disease, compliance problems, a missing pharmacokinetic steady state, and even signal overlay in the laboratory analysis. We return all information available and clinical pharmacological comments to physicians who send specimens to our laboratory. [ABSTRACT FROM AUTHOR]