The law of mass action and the pharmacological concentration-effect curve: resolving the paradox of apparently non-dose-related adverse drug reactions

Evaluation of the antimalarial properties of Solanum incanum L. leaf extract fractions and its ability to downregulate delta aminolevulinate dehydratase to prevent the establishment of malaria infection

ETHNOPHARMACOLOGICAL RELEVANCE

Solanum incanum L. is commonly used in traditional herbal medicine (THM) in Kenya for treating various ailments. Recent developments in disease treatment have introduced the concept of host-directed therapy (HDT). This approach involves targeting factors within the host cell that can impede the growth or replication of a pathogen. One such host factor is delta aminolevulinate dehydratase (δ-ALAD), the second enzyme in the heme biosynthesis pathway utilized by Plasmodium for growth. Studies using mice models have shown an increase in δ-ALAD expression during Plasmodium berghei infection. Another plant in the Solanum genus, S. guaranticum, has been found to inhibit δ-ALAD in red blood cells in vitro and in the brain in vivo. Is it possible that the bioactive compounds in S. incanum extracts could also be effective in HDT for malaria treatment?

AIM OF STUDY

To better assess the effectiveness of S. incanum leaf extracts as a curative and prophylaxis in malaria parasite infection, and to test the plant's ability to decrease δ-ALAD expression.

MATERIALS AND METHODS

The leaves of S. incanum were collected, dried, and pulverized before being subjected to a successive extraction protocol to obtain crude, hexane, ethyl acetate, and aqueous extract fractions. Phytochemical analysis was conducted on all extract fractions, followed by GC-MS analysis of the fraction with the most potent antimalarial activity. An acute toxicity study was also performed on the extracted fractions. The potency of the extract fractions as curative and prophylactic antimalarial was then evaluated in THM using Plasmodium berghei-infected mice at a dose of 100 mg/kg. The extract fraction with the highest activity was further evaluated at varying doses and its effect on δ-ALAD was measured using RT-qPCR. The percentage of parasitemia and chemosuppression, and mean survival time were used as indices of activity.

RESULTS

Phytochemical analysis revealed that the ethyl acetate and aqueous extract fractions contained high terpenoids, flavonoids, and phenols levels. However, alkaloids were only present in moderate quantities in the aqueous extract, and quinones were found in high levels only in the crude extract. Additionally, all extract fractions contained saponins in high levels but lacked tannins. While the plant extracts were found to be non-toxic, they did not exhibit curative antimalarial activity. However, all extract fractions showed prophylactic antimalarial activity, with the ethyl acetate extract having the highest percentage of chemosuppression even at doses of 250 and 1000 mg/kg. In the negative control, the expression of δ-ALAD was 5.4-fold, but this was significantly reduced to 2.3-fold when mice were treated with 250 mg/kg of the ethyl acetate fraction. GC-MS analysis of the ethyl acetate fraction revealed high percentages of 2-methyloctacosane, tetracosane, and decane.

CONCLUSION

The fractions extracted from S. incanum leaves have been found to possess only antimalarial prophylactic properties, with the ethyl acetate extract fraction showing the most effective results. The activity of this fraction may be attributed to its ability to decrease the expression of δ-ALAD, as it contains an alkane compound implicated with enzyme-inhibitory activity.

Acute Oral Toxicological Profile of Croton membranaceus Mull. Arg. Aqueous Stem Extract, a Herbal Treatment for Benign Prostate Hyperplasia, in Male Sprague-Dawley Rats

Croton membranaceus Mull. Arg. is a traditional medicinal plant frequently employed in Ghana for the treatment of benign prostatic hyperplasia and prostate cancer. The objective of this study was to determine the acute oral toxicity of the aqueous stem extract of Croton membranaceus (CMASE) in male Sprague-Dawley (S-D) rats. The acute toxicity of CMASE was evaluated using S-D rats randomly divided into four groups of five animals each. Three groups (low dose, median dose, and high dose) of rats received single oral doses of CMASE (1000, 2500, and 5000 mg/kg body weight, respectively) using an oral gavage. The control group was given distilled water. After 14 days of daily observations, hematological, biochemical, and histopathological analyses were conducted on the rats. From the results obtained, doses of CMASE up to 5000 mg/kg did not cause death or induce any clinical indications of toxicity during the study period. Also, the mean body weight and the hematological indices assessed were not significantly affected by the various doses of CMASE compared to the control group. However, serum uric acid and creatinine levels decreased significantly (p < 0.001) 14 days after the extract administration. Serum liver function enzyme levels, including alkaline phosphatase (ALP), alanine aminotransferases (ALT), and aspartate aminotransferases (AST), and serum proteins (total proteins and albumin) exhibited significant (p < 0.001) non dose-dependent changes (increases and decreases) in treated groups compared to the controls. Other biochemical indices, however, did not differ significantly between the treated groups and the controls. The gross pathological and histological analysis of the heart, liver, and kidney tissues did not reveal any significant changes in histoarchitecture. The oral LD50 of CMASE in rats was greater than 5000 mg/kg, indicating that the extract was relatively safe. It must, however, be used with care as a substitute for the roots.

Enemies or Allies? Hormetic and Apparent Non-Dose-Dependent Effects of Natural Bioactive Antioxidants in the Treatment of Inflammation

This review aims to analyze the emerging number of studies on biological media that describe the unexpected effects of different natural bioactive antioxidants. Hormetic effects, with a biphasic response depending on the dose, or activities that are apparently non-dose-dependent, have been described for compounds such as resveratrol, curcumin, ferulic acid or linoleic acid, among others. The analysis of the reported studies confirms the incidence of these types of effects, which should be taken into account by researchers, discarding initial interpretations of imprecise methodologies or measurements. The incidence of these types of effects should enhance research into the different mechanisms of action, particularly those studied in the field of basic research, that will help us understand the causes of these unusual behaviors, depending on the dose, such as the inactivation of the signaling pathways of the immune defense system. Antioxidative and anti-inflammatory activities in biological media should be addressed in ways that go beyond a mere statistical approach. In this work, some of the research pathways that may explain the understanding of these activities are revised, paying special attention to the ability of the selected bioactive compounds (curcumin, resveratrol, ferulic acid and linoleic acid) to form metal complexes and the activity of these complexes in biological media.

The relationship between dose and serotonin transporter occupancy of antidepressants-a systematic review

Brain imaging techniques enable the visualization of serotonin transporter (SERT) occupancy as a measure of the proportion of SERT blocked by an antidepressant at a given dose. We aimed to systematically review the evidence on the relationship between antidepressant dose and SERT occupancy. We searched PubMed and Embase (last search 20 May 2021) for human in vivo, within-subject PET, or SPECT studies measuring SERT occupancy at any dose of any antidepressant with highly selective radioligands ([¹¹C]-DASB, [¹²³I]-ADAM, and [¹¹C]-MADAM). We summarized and visualized the dose-occupancy relationship for antidepressants across studies, overlaying the plots with a curve based on predicted values of a standard 2-parameter Michaelis-Menten model fitted using the observed data. We included seventeen studies of 10 different SSRIs, SNRIs, and serotonin modulators comprising a total of 294 participants, involving 309 unique occupancy measures. Overall, following the Michaelis-Menten equation, SERT occupancy increased with a higher dose in a hyperbolic relationship, with occupancy increasing rapidly at lower doses and reaching a plateau at approximately 80% at the usual minimum recommended dose. All the studies were small, only a few investigated the same antidepressant, dose, and brain region, and few reported information on factors that may influence SERT occupancy. The hyperbolic dose-occupancy relationship may provide mechanistic insight of relevance to the limited clinical benefit of dose-escalation in antidepressant treatment and the potential emergence of withdrawal symptoms. The evidence is limited by non-transparent reporting, lack of standardized methods, small sample sizes, and short treatment duration. Future studies should standardize the imaging and reporting procedures, measure occupancy at lower antidepressant doses, and investigate the moderators of the dose-occupancy relationship.

The PHARMACOM-EPI Framework for Integrating Pharmacometric Modelling Into Pharmacoepidemiological Research Using Real-World Data: Application to Assess Death Associated With Valproate

In pharmacoepidemiology, it is usually expected that the observed association should be directly or indirectly related to the pharmacological effects of the drug/s under investigation. Pharmacological effects are, in turn, strongly connected to the pharmacokinetic and pharmacodynamic properties of a drug, which can be characterized and investigated using pharmacometric models. Recently, the use of pharmacometrics has been proposed to provide pharmacological substantiation of pharmacoepidemiological findings derived from real-world data. However, validated frameworks suggesting how to combine these two disciplines for the aforementioned purpose are missing. Therefore, we propose PHARMACOM-EPI, a framework that provides a structured approach on how to identify, characterize, and apply pharmacometric models with practical details on how to choose software, format dataset, handle missing covariates/dosing data, how to perform the external evaluation of pharmacometric models in real-world data, and how to provide pharmacological substantiation of pharmacoepidemiological findings. PHARMACOM-EPI was tested in a proof-of-concept study to pharmacologically substantiate death associated with valproate use in the Danish population aged ≥ 65 years. Pharmacological substantiation of death during a follow-up period of 1 year showed that in all individuals who died (n = 169) individual predictions were within the subtherapeutic range compared with 52.8% of those who did not die (n = 1,084). Of individuals who died, 66.3% (n = 112) had a cause of death possibly related to valproate and 33.7% (n = 57) with well-defined cause of death unlikely related to valproate. This proof-of-concept study showed that PHARMACOM-EPI was able to provide pharmacological substantiation for death associated with valproate use in the study population.

What I have learnt from helping thousands of people taper off antidepressants and other psychotropic medications

Although psychiatric drug withdrawal syndromes have been recognized since the 1950s - recent studies confirm antidepressant withdrawal syndrome incidence upwards of 40% - medical information about how to safely go off the drugs has been lacking. To fill this gap, over the last 25 years, patients have developed a robust Internet-based subculture of peer support for tapering off psychiatric drugs and recovering from withdrawal syndrome. This account from the founder of such an online community covers lessons learned from thousands of patients regarding common experiences with medical providers, identification of adverse drug reactions, risk factors for withdrawal, tapering techniques, withdrawal symptoms, protracted withdrawal syndrome, and strategies to cope with symptoms, in the context of the existing scientific literature.

Nobody ever questions-Polypharmacy in care homes: A mixed methods evaluation of a multidisciplinary medicines optimisation initiative

BACKGROUND

Nurse-led monitoring of patients for signs and symptoms associated with documented 'undesirable effects' of medicines has potential to prevent avoidable harm, and optimise prescribing.

INTERVENTION

The Adverse Drug Reaction Profile for polypharmacy (ADRe-p) identifies and documents putative adverse effects of medicines commonly prescribed in primary care. Nurses address some problems, before passing ADRe-p to pharmacists and prescribers for review, in conjunction with prescriptions.

OBJECTIVES

We investigated changes in: the number and nature of residents' problems as recorded on ADRe-p; prescription regimens; medicines optimisation: and healthcare costs. We explored aetiologies of problems identified and stakeholders' perspectives.

SETTING AND PARTICIPANTS

In three UK care homes, 19 residents completed the study, December 2018 to May 2019. Two service users, three pharmacists, six nurses gave interviews.

METHODS

This mixed-method process evaluation integrated data from residents' ADRe-ps and medicines charts, at the study's start and 5-10 weeks later.

RESULTS

We recruited three of 27 homes approached and 26 of 45 eligible residents; 19 completed ADRe-p at least twice. Clinical gains were identified for 17/19 residents (mean number of symptoms 3 SD 1.67, range 0-7). Examples included management of: pain (six residents), seizures (three), dyspnoea (one), diarrhoea (laxatives reduced, two), falls (two of five able to stand). One or more medicine was de-prescribed or dose reduced for 12/19 residents. ADRe administration and review cost ~£30 in staff time. ADRe-p helped carers and nurses bring residents' problems to the attention of prescribers.

IMPLICATIONS

ADRe-p relieved unnecessary suffering. It supported carers and nurses by providing a tool to engage with pharmacists and prescribers, and was the only observable strategy for multidisciplinary team working around medicines optimisation. ADRe-p improved care by: a) regular systematic checks and problem documentation; b) information transfer from care home staff to prescribers and pharmacists; c) recording changes.

REGISTRATION

NLM Identifier NCT03955133; ClinicalTrials.gov.

Susceptibility to adverse drug reactions

The pharmacological effects of a drug depend on its concentration at the site of action, and therefore on the concentration in blood and on the dose. The relationship between the concentration or dose and the corresponding effect can usually be represented mathematically as a rectangular hyperbola; when effect is plotted against log concentration or log dose, the curve is sigmoidal. Inevitably, the effect size and the doses causing benefit and harm will differ among individuals, since they are biological phenomena: some individuals are more likely than others to suffer harm at any given dose. Some harmful effects can occur at much lower doses than those used in therapeutics; that is, the log dose-response curve for harm lies far to the left of the log dose-response curve for benefit. Those who suffer such reactions are hypersusceptible. When the dose-response curves for harm and therapeutic effect are in the same range, dose cannot separate the harmful effects from the therapeutic effects, and adverse reactions are collateral. Toxic effects occur when harmful doses are above the doses needed for benefit. In this review we consider factors that influence a subject's susceptibility to adverse drug reactions. Determinants of susceptibility include Immunological, Genetic, demographic (Age and Sex), Physiological and Exogenous factors (drug-drug interactions, for example), and Diseases and disorders such as renal failure, giving the mnemonic I GASPED. Some susceptibility factors are discrete (for example, all-or-none) and some are continuous; susceptibility can therefore be discrete or continuous; and the factors can interact to determine a person's overall susceptibility to harm.

New Insights in Computational Methods for Pharmacovigilance: E-Synthesis, a Bayesian Framework for Causal Assessment

Today’s surge of big data coming from multiple sources is raising the stakes that pharmacovigilance has to win, making evidence synthesis a more and more robust approach in the field. In this scenario, many scholars believe that new computational methods derived from data mining will effectively enhance the detection of early warning signals for adverse drug reactions, solving the gauntlets that post-marketing surveillance requires. This article highlights the need for a philosophical approach in order to fully realize a pharmacovigilance 2.0 revolution. A state of the art on evidence synthesis is presented, followed by the illustration of E-Synthesis, a Bayesian framework for causal assessment. Computational results regarding dose-response evidence are shown at the end of this article.

Adverse Drug Reactions, Power, Harm Reduction, Regulation and the ADRe Profiles

The power and influence of healthcare systems comes largely from the ability to prescribe efficacious medicine. However, medicine can sometimes cause harm rather than bring benefits. Systematically checking patients for the adverse effects of medicines, as listed in manufacturers' literature, would protect patients from iatrogenic harm, but this is rarely undertaken. We argue for the benefits of this approach using the example of the prescription of antipsychotics to older adults. Prescribing antipsychotics to control challenging behaviours associated with dementia is a controversial matter, and regulatory intervention is under discussion. Improved regulatory systems could protect against iatrogenic harm, such as over-sedation, falls, tremor, or drug-induced Parkinsonism. However, measuring the impact and outcomes of regulatory interventions has proved difficult, not least because there are rarely systematic records of all adverse effects of medicines. We indicate how regulatory initiatives to reduce antipsychotic prescribing can be supported by systematic monitoring and documentation of patients' signs and symptoms of putative adverse drug reactions. Monitoring documentation then provides the rationale and support for professionals' responses to identified problems. Longitudinal monitoring records would improve understanding of the impact and outcomes of adverse drug reactions (ADRs) on health and wellbeing, and the many costs of ADRs.

Ailanthone inhibits non-small cell lung cancer cell growth through repressing DNA replication via downregulating RPA1

Background:

The identification of bioactive compounds from Chinese medicine plays a crucial role in the development of novel reagents against non-small lung cancer (NSCLC).

Methods:

High throughput screening assay and analyses of cell growth, cell cycle, apoptosis, cDNA microarray, BrdU incorporation and gene expression were performed.

Results:

Ailanthone (Aila) suppressed NSCLC cell growth and colony formation in vitro and inhibited NSCLC tumour growth in subcutaneously xenografted and orthotopic lung tumour models, leading to prolonged survival of tumour-bearing mice. Moreover, Aila induced cell cycle arrest in a dose-independent manner but did not induce apoptosis in all NSCLC cells. Furthermore, 1222 genes were differentially expressed upon Aila administration, which were involved in 21 signal pathways, such as DNA replication. In addition, Aila dose-dependently decreased BrdU incorporation and downregulated the expression of replication protein A1 (RPA1).

Conclusions:

Aila inhibited the growth of NSCLC cells through the repression of DNA replication via downregulating RPA1, rather than through cell cycle arrest and apoptosis. Our findings suggested that Aila could be used as a promising therapeutic candidate for NSCLC patients.

Pharmacogenomics of off-target adverse drug reactions

Off-target adverse drug reactions (ADRs) are associated with significant morbidity and costs to the healthcare system, and their occurrence is not predictable based on the known pharmacological action of the drug's therapeutic effect. Off-target ADRs may or may not be associated with immunological memory, although they can manifest with a variety of shared clinical features, including maculopapular exanthema, severe cutaneous adverse reactions (SCARs), angioedema, pruritus and bronchospasm. Discovery of specific genes associated with a particular ADR phenotype is a foundational component of clinical translation into screening programmes for their prevention. In this review, genetic associations of off-target drug-induced ADRs that have a clinical phenotype suggestive of an immunologically mediated process and their mechanisms are highlighted. A significant proportion of these reactions lack immunological memory and current data are informative for these ADRs with regard to disease pathophysiology, therapeutic targets and biomarkers which may identify patients at greatest risk. Although many serious delayed immune-mediated (IM)-ADRs show strong human leukocyte antigen associations, only a small subset have successfully been implemented in screening programmes. More recently, other factors, such as drug metabolism, have been shown to contribute to the risk of the IM-ADR. In the future, pharmacogenomic targets and an understanding of how they interact with drugs to cause ADRs will be applied to drug design and preclinical testing, and this will allow selection of optimal therapy to improve patient safety.

A web resource for mining HLA associations with adverse drug reactions: HLA-ADR

Human leukocyte antigens (HLA) are an important family of genes involved in the immune system. Their primary function is to allow the host immune system to be able to distinguish between self and non-self peptides—e.g. derived from invading pathogens. However, these genes have also been implicated in immune-mediated adverse drug reactions (ADRs), presenting a problem to patients, clinicians and pharmaceutical companies. We have previously developed the Allele Frequency Net Database (AFND) that captures the allelic and haplotype frequencies for these HLA genes across many healthy populations from around the world. Here, we report the development and release of the HLA-ADR database that captures data from publications where HLA alleles and haplotypes have been associated with ADRs (e.g. Stevens–Johnson Syndrome/toxic epidermal necrolysis and drug-induced liver injury). HLA-ADR was created by using data obtained through systematic review of the literature and semi-automated literature mining. The database also draws on data already present in AFND allowing users to compare and analyze allele frequencies in both ADR patients and healthy populations. The HLA-ADR database provides clinicians and researchers with a centralized resource from which to investigate immune-mediated ADRs.

Database URL: http://www.allelefrequencies.net/hla-adr/.

The law of mass action and the pharmacological concentration-effect curve: resolving the paradox of apparently non-dose-related adverse drug reactions

BACKGROUND

Adverse drug reactions are sometimes described as being 'non-dose-related' because no relationship has been found between increasing doses and either the intensity of the response or the proportion of individuals in whom the response occurs; furthermore, hypersensitivity reactions are often regarded as being non-dose-related, even if different doses have not been studied. However, the law of mass action implies that all pharmacological effects are concentration related and should increase in intensity with increasing dose. We set out to explain this paradox.

METHODS

We searched for published adverse drug reactions that have been described as non-dose-related and analysed them.

RESULTS

We identified four categories of explanations that resolve the paradox: (i) the reaction is not real; it may have occurred by chance or there may be methodological problems, such as bias or confounding factors; (ii) the dose-response curve for the adverse effect reaches a maximum at doses lower than were studied (i.e. a hypersusceptibility reaction); this underpins the use of test doses to predict the possibility of an adverse reaction at therapeutic doses; (iii) susceptibility to the adverse reaction differs widely among individuals; and (iv) imprecision or inaccuracy in the measurement of either dose or effect obscures dose responsiveness. This last explanation encompasses: (a) reactions related to cumulative dose; (b) dissociation between dose and concentration through saturable pharmacokinetics; and (c) variability in the measurement of the effect.

CONCLUSIONS AND IMPLICATIONS

If an adverse drug reaction appears to be non-dose-related, the reasons should be sought, having these mechanisms in mind.

Cato Guldberg and Peter Waage, the history of the Law of Mass Action, and its relevance to clinical pharmacology

We have traced the historical link between the Law of Mass Action and clinical pharmacology. The Law evolved from the work of the French chemist Claude Louis Berthollet, was first formulated by Cato Guldberg and Peter Waage in 1864 and later clarified by the Dutch chemist Jacobus van 't Hoff in 1877. It has profoundly influenced our qualitative and quantitative understanding of a number of physiological and pharmacological phenomena. According to the Law of Mass Action, the velocity of a chemical reaction depends on the concentrations of the reactants. At equilibrium the concentrations of the chemicals involved bear a constant relation to each other, described by the equilibrium constant, K. The Law of Mass Action is relevant to various physiological and pharmacological concepts, including concentration-effect curves, dose-response curves, and ligand-receptor binding curves, all of which are important in describing the pharmacological actions of medications, the Langmuir adsorption isotherm, which describes the binding of medications to proteins, activation curves for transmembrane ion transport, enzyme inhibition and the Henderson-Hasselbalch equation, which describes the relation between pH, as a measure of acidity and the concentrations of the contributory acids and bases. Guldberg and Waage recognized the importance of dynamic equilibrium, while others failed to do so. Their ideas, over 150 years old, are embedded in and still relevant to clinical pharmacology. Here we explain the ideas and in a subsequent paper show how they are relevant to understanding adverse drug reactions.