Human Therapeutic Plasma Concentrations Research Articles

Therapeutic Drugs that Slow the Heart Rate of Early Rat Embryos. Is there a Risk for the Human?

During the organogenic period of development the cardiovascular system of the embryo fulfills several functions including delivery of oxygen and nutrients and a hemodynamic role necessary for cardiac morphogenesis, angiogenesis and hematopoiesis. It is expected that at each stage of embryonic development there is an ideal embryonic heart rate and contractility that maintains the optimal blood flow and pressure to fulfill these various functions. In vitro rat embryo culture studies have revealed that many therapeutic drugs (antiarrhythmics, antidepressants, antipsychotics and anticonvulsants), that may be taken during human pregnancy, cause a concentrationdependent slowing of the embryonic heart and irregular heart rate at higher concentrations. The concentrations causing bradycardia in vitro are often close to human therapeutic plasma concentrations and raise concern that these drugs can potentially cause embryonic death or malformations, and that current reproductive toxicity testing does not adequately examine possible effects of drugs on the embryo's cardiac function.

Establishment and Assessment of a New Human Embryonic Stem Cell‐Based Biomarker Assay for Developmental Toxicity Screening

A metabolic biomarker-based in vitro assay utilizing human embryonic stem (hES) cells was developed to identify the concentration of test compounds that perturbs cellular metabolism in a manner indicative of teratogenicity. This assay is designed to aid the early discovery-phase detection of potential human developmental toxicants. In this study, metabolomic data from hES cell culture media were used to assess potential biomarkers for development of a rapid in vitro teratogenicity assay. hES cells were treated with pharmaceuticals of known human teratogenicity at a concentration equivalent to their published human peak therapeutic plasma concentration. Two metabolite biomarkers (ornithine and cystine) were identified as indicators of developmental toxicity. A targeted exposure-based biomarker assay using these metabolites, along with a cytotoxicity endpoint, was then developed using a 9-point dose-response curve. The predictivity of the new assay was evaluated using a separate set of test compounds. To illustrate how the assay could be applied to compounds of unknown potential for developmental toxicity, an additional 10 compounds were evaluated that do not have data on human exposure during pregnancy, but have shown positive results in animal developmental toxicity studies. The new assay identified the potential developmental toxicants in the test set with 77% accuracy (57% sensitivity, 100% specificity). The assay had a high concordance (≥75%) with existing in vivo models, demonstrating that the new assay can predict the developmental toxicity potential of new compounds as part of discovery phase testing and provide a signal as to the likely outcome of required in vivo tests.

Does ketoprofen or diclofenac pose the lowest risk to fish?

Ketoprofen and diclofenac are non-steroidal anti-inflammatory drugs (NSAIDs) often used for similar indications, and both are frequently found in surface waters. Diclofenac affects organ histology and gene expression in fish at around 1μg/L. Here, we exposed rainbow trout to ketoprofen (1, 10 and 100μg/L) to investigate if this alternative causes less risk for pharmacological responses in fish. The bioconcentration factor from water to fish blood plasma was <0.05 (4 for diclofenac based on previous studies). Ketoprofen only reached up to 0.6‰ of the human therapeutic plasma concentration, thus the probability of target-related effects was estimated to be fairly low. Accordingly, a comprehensive analysis of hepatic gene expression revealed no consistent responses. In some contrast, trout exposed to undiluted, treated sewage effluents bioconcentrated ketoprofen and other NSAIDs much more efficiently, according to a meta-analysis of recent studies. Neither of the setups is however an ideal representation of the field situation. If a controlled exposure system with a single chemical in pure water is a reasonable representation of the environment, then the use of ketoprofen is likely to pose a lower risk for wild fish than diclofenac, but if bioconcentration factors from effluent-exposed fish are applied, the risks may be more similar.

Using the fish plasma model for comparative hazard identification for pharmaceuticals in the environment by extrapolation from human therapeutic data

Thousands of drugs are currently in use, but only for a few of them experimental chronic fish data exist. Therefore, Huggett et al. (Human Ecol Risk Assess 2003; 9:1789–1799) proposed the fish plasma model (FPM) to extrapolate the potential of unintended long-term effects in fish. The FPM compares human therapeutic plasma concentrations (HPCT) with estimated fish steady-state concentrations (FPCss), under the assumption that biological drug targets may be conserved across the species. In this study, the influence of using different input parameters on the model result was characterised for 42 drugs. The existence of structurally and functionally conserved protein targets in zebrafish could not be refuted. Thus, the FPM model application was not in contradiction to its basic assumption. Further, dissociation of drugs was shown to be important in determining the output and model robustness. As the proposed model for FPCss estimation was considered to predict accurate values for neutral and lipophilic chemicals only, a modified bioconcentration model was used with DOW as predictor. Using reasonable worst case assumptions, a hazard was indicated for one third of the selected drugs. Our results support the notion that this approach might help to prioritise among in use drugs to identify compounds where follow up evidence should be considered.

Developmental effects of coumarin and the anticoagulant coumarin derivative warfarin on zebrafish (Danio rerio) embryos

Coumarin and warfarin, two substances which are intensively metabolized in animals and humans, were tested for teratogenicity and embryo lethality in a 3-day in vitro assay using zebrafish embryos. Warfarin is a coumarin derivative, but in contrast to the mother substance warfarin has anticoagulant properties. Both substances produced teratogenic and lethal effects in zebrafish embryos. The LC50 and EC50 values for coumarin are 855μM and 314μM, respectively; the corresponding values for warfarin are 988μM and 194μM. For coumarin, three main or fingerprint endpoints (malformation of head, tail and growth retardation) were identified, whereas malformation of tail was the only fingerprint endpoint of warfarin. The analysis of the ratios between the zebrafish embryo effect concentrations of both substances and human therapeutic plasma concentrations confirmed the teratogenic potential of warfarin, as well as the equivocal status of coumarin.

Therapeutic Levels of Levonorgestrel Detected in Blood Plasma of Fish: Results from Screening Rainbow Trout Exposed to Treated Sewage Effluents

Pharmaceuticals are found in surface waters worldwide, raising concerns about effects on aquatic organisms. Analyses of pharmaceuticals in blood plasma of fish could provide means to assess risk for pharmacological effects, as these concentrations could be compared with available human therapeutic plasma levels. In this study we investigated if fish exposed to sewage effluents have plasma concentrations of pharmaceuticals that are approaching human therapeutic levels. We also evaluated how well the bioconcentration of pharmaceuticals into fish blood plasma can be predicted based on lipophilicity. Rainbow trout were exposed to undiluted, treated sewage effluents at three sites in Sweden for 14 days. Levels of 25 pharmaceuticals in blood plasma and effluents were analyzed with liquid chromatography-mass spectrometry/mass spectrometry and gas chromatography-high resolution mass spectrometry. The progestin pharmaceutical levonorgestrel was detected in fish blood plasma at concentrations (8.5-12 ng mL(-1)), exceeding the human therapeutic plasma level. In total 16 pharmaceuticals were detected in fish plasma at concentrations higher than 1/1000 of the human therapeutic plasma concentration. Twenty-one pharmaceuticals were detected in either plasma or effluent, and 14 were detected in both compartments, allowing plasma bioconcentration factors to be determined. For 11 of these, theoretically calculated and experimentally measured values were in reasonably good agreement. However a few drugs, including levonorgestrel, did not bioconcentrate according to the screening model used. This study shows that rainbow trout exposed to sewage effluents have blood plasma levels of pharmaceuticals similar to human therapeutic concentrations, suggesting a risk for pharmacological effects in the fish. There is a particular concern about effects of progestin pharmaceuticals. For levonorgestrel, the measured effluent level (1 ng/L) was higher than water levels shown to reduce the fertility of fish.

Drug–drug interaction between oxycodone and adjuvant analgesics in blood–brain barrier transport and antinociceptive effect

To examine possible blood–brain barrier (BBB) transport interactions between oxycodone and adjuvant analgesics, we firstly screened various candidates in vitro using [3H]pyrilamine, a substrate of the oxycodone transporter, as a probe drug. The uptake of [3H]pyrilamine by conditionally immortalized rat brain capillary endothelial cells (TR-BBB13) was inhibited by antidepressants (amitriptyline, imipramine, clomipramine, amoxapine, and fluvoxamine), antiarrhythmics (mexiletine, lidocaine, and flecainide), and ketamine. On the other hand, antiepileptics (carbamazepine, phenytoin, and clonazepam) and corticosteroids (dexamethasone and prednisolone) did not inhibit [3H]pyrilamine uptake, with the exception of sodium valproate. The uptake of oxycodone was significantly inhibited in a concentration-dependent manner by amitriptyline, fluvoxamine and mexiletine with Ki values of 13, 65, and 44 µM, respectively. These Ki values are 5–300 times greater than the human therapeutic plasma concentrations. Finally, we evaluated in vivo interaction between oxycodone and amitriptyline in mice. Antinociceptive effects of oxycodone were increased by coadministration of amitriptyline. The oxycodone concentrations in plasma and brain were not changed by coadministration of amitriptyline. Overall, the results suggest that several adjuvant analgesics may interact with the BBB transport of oxycodone at relatively high concentrations. However, it is unlikely that there would be any significant interaction at therapeutically or pharmacologically relevant concentrations. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:467–474, 2010

Chronic effects assessment and plasma concentrations of the β-blocker propranolol in fathead minnows ( Pimephales promelas)

The presence of many human pharmaceuticals in the aquatic environment is now a worldwide concern, yet little is known of the chronic effects that these bioactive substances may be having on aquatic organisms. Propranolol, a non-specific beta adrenoreceptor blocker (β-blocker), is used to treat high blood pressure and heart disease in humans. Propranolol has been found in surface waters worldwide at concentrations ranging from 12 to 590 ng/L. To test the potential for ecologically relevant effects in fish in receiving waters, short-term (21 days) adult reproduction studies were conducted, in which fathead minnows were exposed to nominal concentrations of propranolol hydrochloride [CAS number 318-98-9] ranging from 0.001 to 10 mg/L (measured concentrations typically from 78 to 130%). Exposure of fish to 3.4 mg/L (measured) over 3 days caused 100% mortality or severe toxicity requiring euthanasia. The most sensitive endpoints from the studies were a decrease in hatchability (with regard to the number of days to hatch) and a concentration-related increase in female gonadal somatic index (GSI), giving LOEC hatchability and LOEC female GSI values of 0.1 mg/L. Concentration-related decreases in weights of male fish were also observed, with LOEC male wet weight value of 1.0 mg/L, and the LOEC reproduction value was 1.0 mg/L. Collectively, these data do not suggest that propranolol was acting as a reproductive toxin. Plasma concentrations of propranolol in male fish exposed to nominal concentrations of 0.1 and 1.0 mg/L were 0.34 and 15.00 mg/L, respectively, which constitutes 436 and 1546% of measured water concentrations. These compare with predicted concentrations of 0.07 and 0.84 mg/L, and thus to a degree support the use of partition coefficient models for predicting concentrations in plasma in fish. In addition, propranolol plasma concentrations in fish exposed to water concentrations of 0.1 and 1.0 mg/L were greater than the human therapeutic plasma concentration and hence these data very strongly support the fish plasma model proposed by Huggett et al. [Huggett, D.B., Cook, J.C., Ericson, J.F., Williams, R.T., 2003a. A theoretical model for utilizing mammalian pharmacology and safety data to prioritize potential impacts of human pharmaceuticals to fish. Hum. Ecol. Risk Assess. 9, 1789–1799].

Risks to aquatic organisms posed by human pharmaceutical use

In order to help prioritize future research efforts within the US, risks associated with exposure to human prescription pharmaceutical residues in wastewater were estimated from marketing and pharmacological data. Masses of 371 active pharmaceutical ingredients (APIs) dispensed in the US in 2004 were estimated from marketing data, and then divided by therapeutic dose rate to normalize for potency. Metabolic inactivation of the 50 most dispensed APIs was estimated from published data, and active metabolites were tabulated. Comparing maximum likely average wastewater concentrations of API-associated activity to exposure rates that produce therapeutic effects in humans suggests that the threat to healthy human adults from aquatic exposure is low, even when likely mixture effects are considered. Comparing predicted wastewater concentrations to human therapeutic plasma concentrations suggests that some APIs may be present at sufficient concentrations to affect organisms which eliminate them inefficiently. Comparing predicted antimicrobial concentrations to published minimum inhibitory concentrations suggests that antibacterial APIs in wastewater, but probably not antifungal APIs, may select for low-level antimicrobial resistance. The taxonomic distribution of molecular targets of the 50 most dispensed APIs suggests that potential effects of some APIs are likely restricted to vertebrates, while other APIs can probably affect many eukaryotic and prokaryotic clades.

Variations in bioconcentration of human pharmaceuticals from sewage effluents into fish blood plasma

The “Fish Plasma Model” has been proposed for prioritizing pharmaceuticals for in-depth environmental risk assessment efforts. The model compares estimated drug concentrations in fish plasma with human therapeutic plasma concentrations in order to assess the risk for a pharmacological interaction in the fish. In this study the equation used to estimate bioconcentration from water to fish blood plasma was field-tested by exposing rainbow trout in situ to sewage effluents from three treatment plants. Measured plasma levels of diclofenac, naproxen, ketoprofen and gemfibrozil were similar or lower than those modelled, which is acceptable for an early tier. However, measured levels of ibuprofen were >200 times higher than modelled for the largest plant (Gryaab Göteborg). Comparing measured fish plasma concentrations to the human therapeutic concentrations ranked the relative risks from the pharmaceuticals. Diclofenac and gemfibrozil, followed by ibuprofen, presented the highest risk for target interactions, whereas naproxen and ketoprofen presented little risk. Remarkably, measured bioconcentration factors varied considerably between sites. This variation could not be attributed to differences in water concentrations, temperatures, pH or exposure times, thereby suggesting that chemical characteristics of effluents and/or recipient waters strongly affected the uptake/bioconcentration of the pharmaceuticals.

QT PRODACT: Comparison of Non-clinical Studies for Drug-Induced Delay in Ventricular Repolarization and Their Role in Safety Evaluation in Humans

Drug concentrations that would prolong repolarization parameters by 10%, including action potential duration (APD90, APD30–90), in in vitro assays using guinea-pig papillary muscle and QTc intervals in in vivo assays using conscious dogs, conscious monkeys, and anesthetized dogs were compared. Although, both the in vitro and in vivo assays showed concentration-dependent responses for compounds that have been classified as torsadogenic in humans, only a weak correlation in EC10 values was observed between the in vitro and in vivo assays. Among the in vivo QT assays, the EC10 values obtained from conscious dogs, conscious monkeys, and anesthetized dogs correlated well with each other, but the EC10 values in monkeys were some-what lower in comparison to those in dogs. When in vivo QT assay EC10 values were compared to the respective human effective therapeutic plasma concentration (ETPC), the ratios of EC10 values to ETPCs were less than 20 for most torsadogenic compounds. In conclusion, the relationships between the extent of QTc interval prolongation and the concentration of drugs was highly consistent among the three in vivo models, suggesting that the ratios of EC10 values in in vivo QT assays are useful for estimating the safety margin of drugs that prolong the QTc interval.

A Theoretical Model for Utilizing Mammalian Pharmacology and Safety Data to Prioritize Potential Impacts of Human Pharmaceuticals to Fish

Due to the potential for long-term, low-level exposure of environmental species to pharmaceuticals in the environment, concerns over chronic ecotoxicity have been raised. Pharmaceuticals typically have specific enzyme and receptor-based modes of action, which are extensively studied in mammals during drug development. A survey of the literature demonstrated that there is conservation of many enzyme/receptor systems between mammalian and teleost systems. Based on this conservation of enzyme/receptor systems across teleost species, a model has been developed to utilize the information from mammalian pharmacology and toxicology studies to evaluate the potential for chronic receptor mediated responses in fish. In this model, a measured human therapeutic plasma concentration (HTPC) is compared to a predicted steady state plasma concentration (FSSPC) in fish, and an effect ratio (ER = HTPC/FSSPC) is computed. The lower the ER, the greater the potential for a pharmacological response in fish. Data collection and model validation will strengthen the applicability of this approach as a viable tool for prioritizing research initiatives that examine the potential impact of pharmaceuticals on fish.

Pharmacologically induced embryonic dysrhythmia and episodes of hypoxia followed by reoxygenation: a common teratogenic mechanism for antiepileptic drugs?

Antiepileptic drugs (AEDs), such as phenytoin (PHT), carbamazepine (CBZ), trimethadione (TMD), and phenobarbital (PB), have all been associated with a similar pattern of malformations, as well as growth retardation and developmental delay. Valproic acid (VPA) has been associated with a different pattern of malformations. Recent studies suggest that PHT's fetal adverse effect is related to its membrane stabilizing pharmacological properties (blockage of voltage-dependent ion channels). During a restricted sensitive period, this results in induction of concentration-dependent bradyarrhythmia in the embryo and episodes of hypoxia/reoxygenation. The aim of this study was to compare the potential of PHT, CBZ, PB, TMD, and dimethadione (DMD; the active metabolite of TMD) to cause bradyarrhythmias. All of these AEDs exert mainly their pharmacological effect via blockage of ion channels. VPA and vigabatrin (VGB), which are pharmacologically active mainly by other mechanisms, were also tested. C57 Bl/6J mouse embryos were cultured in vitro on gestation day 10 in vitro (in 20% rat serum). The drugs were suspended in either water or dimethylsulfoxide and administered into the culture medium in increasing concentrations up to 20 times the human therapeutic plasma concentration. A scoring system was employed in order to rank the drugs based on their potential to cause bradycardia, ventricular arrhythmia, and cardiac arrest in relation to human therapeutic concentrations. Based on this system, the drugs were ranked as follows: DMD = PHT >> PB = CBZ > TMD = VPA >> VGB (no potential). The results correlate well with the available clinical/experimental data of the tested AED's potential to induce hypoxia-related fetal adverse effects, such as oral clefts, distal limb defects, growth retardation, and developmental delay. The results support the idea that adverse fetal effects after in utero exposure to PHT, PB, CBZ, and TMD (via the active metabolite DMD) are initiated via a common pharmacological mechanism: blockage of ion channels in the developing heart in the early embryo resulting in bradyarrhythmias, hemodynamic alterations, and hypoxia/reoxygenation damage.

The Use and Abuse of Toxicokinetics: What Does Actual Data Tell Researchers?

Pharmacokinetic data obtained in 71 toxicity studies on 38 compounds were investigated. Twenty-four studies (33%) were of “I-type” nonlinear kinetics where the plasma concentration did not increase as much as the dose increased, while 14 studies (20%) were of “S-type” nonlinear kinetics where the plasma concentration increased super-proportionally. Some marked increase in plasma concentrations during repeated administration occurred exclusively in “S-type” nonlinear kinetics cases, while decreases were found in some “I-type” kinetics cases. Plasma concentrations at dose levels which produced toxicity were less than the human therapeutic plasma concentrations in 6% of studies and in 18% for those compounds which did not produce toxicity. The intertest compounds difference in items investigated seemed to be much greater than the interstudies (animal species) difference. It should be stressed from these results that the well-designed assessment of systemic exposure in toxicity studies should be requested onl...