Plasma Concentrations Of Active Metabolite Research Articles

Evaluation of the effect of CYP2D6*3, *4,*10, and *17 polymorphisms on the pharmacokinetic of tamoxifen and its metabolites in patients with hormone-positive breast cancer

Background and objectiveA high rate of interindividual variability in response to tamoxifen (TAM) in breast cancer patients with CYP2D6 polymorphism has been reported, which affects the patient’s therapeutic outcome. The objective of this study was to investigate the pharmacogenomics of CYP2D6 genotyping in Iranian patients with breast cancer treated with adjuvant TAM. MethodsA peripheral blood sample was obtained to determine the steady-state plasma concentrations of TAM and its metabolites (Endoxifen (EN) and 4-Hydroxytamoxifen (4-OHT)) using high-performance liquid chromatography with fluorescence detection (HPLC-FLU) assay. We detected CYP2D6 * 3, * 4, * 10, and * 17 single nucleotide polymorphisms via polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method. ResultsA total of 84 Iranian estrogen receptor‑positive breast cancer patients receiving the daily dose of 20 mg tamoxifen were recruited. Although a consequent decrease in the median EN and 4-OHT concentrations was observed by comparing poor or intermediate metabolizer patients with an extensive metabolizer population, this difference did not reach a significant level. The mean plasma EN concentrations in poor and intermediate metabolizers were 46.1% (95% CI, 7.4–27.8%) and 59.4% (95% CI, 11.9–37.3%) of extensive metabolizer subjects, respectively. Poor and intermediate metabolizers had the mean plasma 4-OHT concentrations that were 46.6% (95% CI, 0.9–61.7%) and 73.2% (95% CI, 2.7–93.1%) of those of subjects who were extensive metabolizer, respectively. ConclusionsThe possible role of genotyping in Iranian patients' response to treatment may explain inter-individual differences in the plasma concentrations of active metabolites of TAM.

Assessment of Oral Bioavailability of Vitamin D 3 and Its Metabolite, 25-hydroxy (OH) Vitamin D 3 in Male Sprague Dawley Rats Following a Single Oral Dose of Biofield Energy Treated Vitamin D 3

The present study was performed to determine the effects of The Trivedi Effect ® -Energy of Consciousness Healing Treatment on vitamin D 3 and rats through the pharmacokinetic parameters measurement of both plasma level of vitamin D 3 and 25-hydroxy (OH)-vitamin D 3 after the oral administration of vitamin D 3 in rats. The test item, vitamin D 3 was divided into two parts. One part was denoted as the control (without Biofield Energy Healing Treatment), while the other part was defined as the Biofield Energy Treated sample, which received the Biofield Energy Healing Treatment by renowned Biofield Energy Healer, Mahendra Kumar Trivedi. Additionally, one group of animals also received Consciousness Energy Healing Treatment per se by the Healer under similar conditions. Vitamin D 3 oral formulations were administrated by oral gavage at a dose of 500 μg per kg in groups viz. G1 (untreated Vitamin D 3 ), G2 (Biofield Energy Treated Vitamin D 3 ) and G3 (Biofield Energy Treated animals received untreated Vitamin D 3 ) group. The results showed that the relative oral exposure (AUC 0 –t) of vitamin D 3 was significantly increased by 155.62% and 111.73% in G2 and G3 groups, respectively as compared to the control group. Biofield Energy Treatment also significantly improved the plasma peak concentration (C max ) of vitamin D 3 by 223.84% and 187.5% in G2 and G3 groups, respectively as compared to the control group. This study results also showed that the relative oral exposure (AUC 0 –t) of 25-hydroxy (OH)-vitamin D 3 (metabolite) was significantly increased by 161.28% and 113.96% in G2 and G3 groups, respectively as compared to the control group (G1). Biofield Energy Treatment also significantly improved the plasma peak concentration (C max ) of 25-hydroxy (OH)-vitamin D 3 by 174.25% and 111.77% in G2 and G3 groups, respectively as compared to the control group. After oral administration, plasma concentrations of active metabolite, 25-hydroxy (OH)-vitamin D 3 in all three groups were declined slowly. The mean residence time (MRT last ) and elimination rate constant (K el ) for this metabolite were unaltered in all three groups. These data suggest that Biofield Energy Treated vitamin D 3 might be influenced in vivo biological activity of vitamin D 3 due to increased plasma exposure (AUC) of both vitamin D 3 and metabolite level, 25-hydroxy (OH)-vitamin D 3 in rats. There was significant improvement (>100%) of relative oral bioavailability of both vitamin D 3 and 25-hydroxy (OH)-vitamin D 3 that might be due to the alteration of physicochemical properties and thermal properties of vitamin D 3 by the Biofield Energy Treatment. Biofield Energy Healing Treatment could be an innovative strategy that opens new avenues to overcome poorly absorbed pharmaceuticals/nutraceuticals/herbal extracts and can also improve the therapeutic performance of orally active molecules.

High on-treatment platelet reactivity (HPR): What does it mean, and does it matter?

2013; 109: 347-355. In this issue of Thrombosis and Haemostasis, Saucedo et al. (1) demonstrate that the prevalence of high on-treatment platelet reactivity was decreased after changing clopidogrel to prasugrel. It is perhaps appealing that the patients with adverse “high on-treatment platelet reactivity (HPR)” with clopidogrel was reduced when switched to prasugrel. From a scientific point of view, the meaning of “HPR” is still unclear. This uncertainty is derived from an arguably confusing clinical development history of the thienopyridine-type antiplatelet agents (ticlopidine, clopidogrel, and prasugrel). Indeed, the use of these agents was greatly expanded based on the clinical experience, rather than on their mechanistic understanding. A randomised, blinded, trial of clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE)was published in 1996 (2). However, the precise mechanism of antiplatelet action exerted by clopidogrel was clarified only after cloning the target ADP receptor of P2Y12 in 2001 (3). Moreover, the extent of P2Y12 ADP receptor blockade by active metabolite of clopidogrel in an individual patient, which should be a real bio-marker for this drug, has been measured in a very limited number of studies only (4). Nonetheless, some uncertainty remains about how much percentage of P2Y12 receptor should be blocked to achieve appropriate antithrombotic effects in individual patients. Obviously, the goal is not to achieve 100% inhibition of P2Y12 because P2Y12 deficiency manifests as a bleeding disorder (5). Perhaps some focus should be on the drugs per se. Both clopidogrel and prasugrel are pro-drugs. The chemical structure of active metabolite(s) of clopidogrel was detected in 2002 (6). Since the active metabolite(s) of clopidogrel are very labile in character with a reactive thiol function, it is most likely that the majority of produced active metabolite(s) easily binds to P2Y12 receptors on platelets circulating in liver, where it is produced (▶ Figure 1A) Thus, plasma concentrations of active metabolite(s) per se would not necessarily be good pharmaco-dynamic marker(s) for the antiplatelet effects of clopidogrel (8). Thus, the extent of P2Y12 receptor blockage, once achieved in the liver circulation, would be the same in platelet circulating in peripheral blood.

High dose of buprenorphine in terminally ill patient with liver failure: Efficacy and tolerability

Pain in terminally ill patients with cancer can be often hard to manage, due to the unpredictable kinetics of drugs caused by progressive kidney and liver dysfunction. Plasma concentrations of active metabolites-also a cause of dangerous side effects--could be difficult to estimate. This case report holds the idea that buprenorphine, a partial agonist of m-receptors, even at high dosage, may be effective and safe to use in terminally ill patients with significant liver and kidney impairment.

Activity Levels of Tamoxifen Metabolites at the Estrogen Receptor and the Impact of Genetic Polymorphisms of Phase I and II Enzymes on Their Concentration Levels in Plasma

The therapeutic effect of tamoxifen depends on active metabolites, e.g., cytochrome P450 2D6 (CYP2D6) mediated formation of endoxifen. To test for additional relationships, 236 breast cancer patients were genotyped for CYP2D6, CYP2C9, CYP2B6, CYP2C19, CYP3A5, UGT1A4, UGT2B7, and UGT2B15; also, plasma concentrations of tamoxifen and 22 of its metabolites, including the (E)-, (Z)-, 3-, and 4'-hydroxymetabolites as well as their glucuronides, were quantified using liquid chromatography-tandem mass spectrometry (MS). The activity levels of the metabolites were measured using an estrogen response element reporter assay; the strongest estrogen receptor inhibition was found for (Z)-endoxifen and (Z)-4-hydroxytamoxifen (inhibitory concentration 50 (IC50) 3 and 7nmol/l, respectively). CYP2D6 genotypes explained 39 and 9% of the variability of steady-state concentrations of (Z)-endoxifen and (Z)-4-hydroxytamoxifen, respectively. Among the poor metabolizers, 93% had (Z)-endoxifen levels below IC90 values, underscoring the role of CYP2D6 deficiency in compromised tamoxifen bioactivation. For other enzymes tested, carriers of reduced-function CYP2C9 (*2, *3) alleles had lower plasma concentrations of active metabolites (P < 0.004), pointing to the role of additional pathways.

Paraoxonase-1 is a major determinant of clopidogrel efficacy

Clinical efficacy of the antiplatelet drug clopidogrel is hampered by its variable biotransformation into the active metabolite. The variability in the clinical response to clopidogrel treatment has been attributed to genetic factors, but the specific genes and mechanisms underlying clopidogrel bioactivation remain unclear. Using in vitro metabolomic profiling techniques, we identified paraoxonase-1 (PON1) as the crucial enzyme for clopidogrel bioactivation, with its common Q192R polymorphism determining the rate of active metabolite formation. We tested the clinical relevance of the PON1 Q192R genotype in a population of individuals with coronary artery disease who underwent stent implantation and received clopidogrel therapy. PON1 QQ192 homozygous individuals showed a considerably higher risk than RR192 homozygous individuals of stent thrombosis, lower PON1 plasma activity, lower plasma concentrations of active metabolite and lower platelet inhibition. Thus, we identified PON1 as a key factor for the bioactivation and clinical activity of clopidogrel. These findings have therapeutic implications and may be exploited to prospectively assess the clinical efficacy of clopidogrel.

ACCF/AHA Clopidogrel Clinical Alert: Approaches to the FDA “Boxed Warning”

The recent US Food and Drug Administration (FDA) “boxed warning” on clopidogrel raises important questions for practitioners and patients. The warning addresses the need for pharmacogenomic testing to identify patients’ altered clopidogrel metabolism and thus their risk for a suboptimal clinical response to clopidogrel. Although there is an expanding database on genetic polymorphisms that may affect clopidogrel metabolism and thus clinical outcomes, there are no evidence-based data upon which todevelop specific recommendations on the role of genetic testing in routine care nor strategies proven to improve the safety/efficacy of specific pharmacologic approaches. To provide guidance on this issue, the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) convened a writing committee. The ACCF and AHA adhere to a rigorous policy regarding relationships with industry and other entities (RWI) of authors and peer reviewers for clinical document development (see http://www.cardiosource.org/Science-And-Quality/Practice-Guidelines-and-Quality-Standards/Relationships-With-Industry-Policy.aspx). This policy requires that a majority of writing committee members have no relevant relationships with industry to this topic, a standard that has been achieved for this document as indicated in Appendix 1. In the spirit of full disclosure, comprehensive RWI (RWI not relevant to this document) for all authors is available online for public view. RWI …

CYP2D6 genotypes in association with steady state plasma concentrations of active metabolites of tamoxifen in patients with breast cancer

634 Background: Tamoxifen is a prodrug that is metabolized to active metabolites, Z-4-hydroxy-N-desmethyltamoxifen (BX) and Z-4-hydroxy-tamoxifen (4OH) where CYP2D6 plays a major role in the conversion. Genetic polymorphisms of CYP2D6 by ethnicities are well known with CYP2D6*10 in Asians (up to 50% in Koreans), and CYP2D6 *2 and *4 in American Whites as major variant alleles. We analyzed the steady state plasma concentrations of tamoxifen and its metabolites in patients (pts) with breast cancer to evaluate their associations with various CYP2D6 genotypes. Methods: Blood samples were collected from 219 pts on tamoxifen, 20 mg daily as adjuvant therapy for more than 3 months at National Cancer Center, Korea. Plasma tamoxifen, N-desmethyltamoxifen, BX, 4OH were measured by validated HPLC with fluorescence detector, and analyzed according to CYP2D6 genotype groups by Wilcoxon rank sum test. CYP2D6*10, CYP2D6*5 and CYP2D6*2×2 were identified by PCR-RFLP methods, and the rests were classified as CYP2D6*1 (wild type). This study was approved by IRB at National Cancer Center Hospital (NCCNHS04–033) and conducted after informed consent obtained by the patients. Results: Thus far, we measured plasma concentration of tamoxifen and its metabolites for 158 pts among 198 pts genotyped. 59 pts (29.8%) carried CYP2D6*1/*1, 84 pts (42.4%) *1/*10 and 49 pts (24.7%) *10/*10. Other types were CYP2D6*1/*5 (8.6%), *5/*5 (1.0%), *1/*2×2 (2.5%). Pts with CYP2D6 *10/*10 (n=40) demonstrated significantly lower steady state plasma concentrations of BX and 4OH than those with other genotypes (n=118) (BX: 7.9 vs.19.2. ng/ml [95 % CI; 5.5–10.4 vs. 15.8–22.7 ng/ml] p&lt;0.0001; 4OH: 1.5 vs. 2.8 ng/ml [95 % CI; 1.1–2.0 vs. 2.3–3.3 ng/ml] p&lt;0.0001), whereas there were no differences with *1/*10 (n=64) vs. without *10 allele (n=54) (BX: 20.6 vs. 18.1 ng/ml; 4OH: 2.9 vs. 2.7 ng/ml). Basically no significant differences in BX/4OH or other compounds by various CYP2D6*2 ×2 and *5 alleles were observed. Conclusions: The steady state plasma concentrations of BX and 4OH were significantly low with CYP2D6 *10/*10 genotype, and their clinical implications need to be explored.(Supported by a grant NCC-0410590). No significant financial relationships to disclose.

Absorption, Metabolization, and Antiplatelet Effects of 300-, 600-, and 900-mg Loading Doses of Clopidogrel

For patients undergoing percutaneous coronary intervention, the administration of a clopidogrel loading dose ranging from 300 to 600 mg is currently recommended. It is unknown, though, whether loading doses higher than 600 mg exert additional suppression of platelet function. Sixty patients with suspected or documented coronary artery disease admitted to our hospital for coronary angiography were included in this trial. They were allocated to 1 of 3 clopidogrel loading doses (300, 600, or 900 mg) in a double-blinded, randomized manner. Plasma concentrations of the active thiol metabolite, unchanged clopidogrel, and the inactive carboxyl metabolite of clopidogrel were determined before and serially after drug administration. Optical aggregometry was performed before and 4 hours after administration of clopidogrel. Loading with 600 mg resulted in higher plasma concentrations of the active metabolite, clopidogrel, and the carboxyl metabolite compared with loading with 300 mg (P< or =0.03) and lower values for adenosine diphosphate-induced (5 and 20 micromol/L) platelet aggregation 4 hours after drug administration (P=0.01 and 0.004). With administration of 900 mg, no further increase in plasma concentrations of active metabolite and clopidogrel (P> or =0.38) and no further suppression of adenosine diphosphate-induced (5 and 20 micromol/L) platelet aggregation 4 hours after drug administration was achieved when compared with administration of 600 mg (P=0.59 and 0.39). Single doses of clopidogrel higher than 600 mg are not associated with an additional significant suppression of platelet function because of limited clopidogrel absorption.

Pharmacokinetics of the Active Metabolites of Ethyl Loflazepate in Elderly Patients Who Died of Asphyxia Associated with Benzodiazepine-Related Toxicity

We determined the pharmacokinetics of ethyl loflazepate (Lof) in elderly patients who died of benzodiazepine-related toxicity. Three elderly patients with body mass indexes of less than 17 kg/m2 died of asphyxia after having taken maintenance doses of Lof for 2 to 3 weeks. We measured serum concentrations of the active metabolites of Lof using gas chromatography-mass spectrometry and a benzodiazepine receptor assay to determine the pharmacokinetics of each. On admission, the serum concentrations of the active metabolites of Lof ([Lofl) were 256 ng/mL, 425 ng/mL, and 177 ng/mL in cases 1, 2, and 3, respectively. Serum benzodiazepine-receptor binding activities, expressed as diazepam equivalent concentrations ([Bz]), were 1800 ng/mL, 2200 ng/mL, and 1500 ng/mL. The T1/2(beta) of [Lof] were 124 and 121 h in cases 1 and 2 and the T1/2(beta) of [Bz] were 75 and 87 h. The distribution volume in the elderly was reduced due to a small lipid compartment, and total drug clearance was decreased due to the decline in liver and kidney function. These changes did not prolong T1/2(beta) but did increase plasma concentrations of active metabolites, especially in case 2, and a slight decrease in protein binding increased the amount of free active metabolites greatly.

Different accumulation of temocapril and enalapril during repeated dosing in elderly patients

Angiotensin-converting enzyme (ACE) inhibitors, temocapril and enalapril, are prodrugs that are converted to the active metabolites, temocaprilat and enalaprilat, respectively. Temocaprilat is eliminated by renal and biliary routes, while enalaprilat is mainly excreted in urine [1, 2]. This difference explains a 2-fold increase in plasma temocaprilat and a 13-fold increase in plasma enalaprilat in patients with renal insufficiency [3]. Because renal function is physiologically decreased with age, it is hypothesized that, compared with temocaprilat, accumulation of enalaprilat during repeated dosing is greater and blood pressure (BP)-lowering effect is enhanced in elderly hypertensive patients. In this study, temocapril or enalapril was given once daily for 14 days to elderly hypertensive patients. Pharmacokinetic profiles and BP-lowering effects after single and repeated dosings of these drugs were determined.

The pharmacokinetics and activation of proguanil in man: consequences of variability in drug metabolism.

1. Based on the ratio of drug to active metabolite excreted in urine approximately 3% of a healthy Caucasian population showed a reduced ability to convert proguanil to cycloguanil. 2. Pharmacokinetic analysis showed that this observation resulted from a reduced oral clearance of proguanil in these individuals (245, 534 and 552 ml min-1) compared with the rest of the population (858 +/- 482 ml min-1). 3. Peak plasma concentrations of active metabolite were significantly lower in these subjects (54.2, 26.8 and 51.7 ng ml-1) compared with the rest of the population (141 +/- 45.2 ng ml-1). 4. The observed variability may result from the polymorphic metabolism of proguanil in man.

Clinical pharmacokinetics of encainide.

The disposition kinetics of the new antiarrhythmic agent encainide are a function of the genetic polymorphism which also controls debrisoquin 4-hydroxylation. In the majority of subjects (extensive metabolisers) encainide undergoes extensive first-pass hepatic biotransformation to the active metabolites O-desmethyl encainide (ODE) and 3-methoxy-O-desmethyl encainide (MODE). The plasma concentrations of these metabolites are higher than those of encainide, and pharmacological effects correlate better with plasma metabolite concentrations than they do with those of encainide itself. In poor metabolisers, who make up to 7% of the population, a first-pass effect is absent, encainide clearance is lower, and plasma encainide concentrations are higher than those in extensive metabolisers. In poor metabolisers, plasma concentrations of active metabolites are low or undetectable, and the effects of encainide therapy can be closely correlated with plasma concentrations of the parent drug. Despite the marked differences in encainide disposition between extensive and poor metabolisers, the dosages which produce pharmacological effects (QRS prolongation and arrhythmia suppression) are similar in both groups. Encainide biotransformation is impaired in hepatic disease, but no major dosage changes are required. On the other hand, excretion of encainide and its metabolites is impaired in individuals with renal disease, and starting dosages should be decreased. The time required to achieve steady-state concentrations of metabolites (in extensive metabolisers) and of encainide itself (in poor metabolisers) is similar (3 to 5 days); therefore, the dosage should be increased no more often than every 3 to 5 days.(ABSTRACT TRUNCATED AT 250 WORDS)

The natural history of tolerance to the benzodiazepines.

Dependence on benzodiazepines following continued use is by now a well-documented clinical phenomenon. Benzodiazepines differ in their dependence potential. The present studies were aimed at examining the possibility that differential rates of tolerance development might account for differences in dependence risk. Four studies are reported. The first three studies concerned normal subjects. The development of tolerance over a fifteen day period was demonstrated for three different benzodiazepines (ketazolam, lorazepam and triazolam) using two paradigms. Tolerance in terms of a reduction in effectiveness of a repeated given dose was most notable for the benzodiazepine with a medium elimination half-life (lorazepam) for physiological, behavioural and subjective measures. In the case of the drug with the longest elimination half-life (ketazolam) reduction in effectiveness could only be assumed to be occurring if account was taken of the steady increase in plasma concentrations of active metabolites. For this drug it seemed that the physiological measures were those most likely to demonstrate the development of tolerance. Although triazolam showed few significant drug effects on this paradigm (testing being 12 hours after ingestion of this short half-life benzodiazepine), tolerance was seen to develop on some subjective measures. Using an alternative method of testing tolerance, assessing responses to a diazepam challenge dose, a high degree of tolerance on two-thirds of the measures was observed in subjects when pretreated with the benzodiazepine with the most marked accumulation of active metabolites (ketazolam). The other two drugs also led to tolerance development on a range of measures; this was more marked for lorazepam than triazolam. Blunting of the growth hormone response to diazepam was the most sensitive and reliable method of detecting tolerance to the benzodiazepines. Symptoms on discontinuation of the two weeks' intake of the benzodiazepines were marked for all the drugs but unrelated to either the tolerance induced or the elimination half-life of the particular drug. A further clinical study revealed that tolerance persisted in a group of long-term benzodiazepine users for between four months and two years following complete abstinence from the drug. These patients appeared to be less affected by diazepam in terms of its commonly observed subjective effects, regardless of their original medication. These ex-long-term users of benzodiazepines were, however, more likely to manifest two specific types of effects--immediate 'symptom' reduction and exacerbation of 'withdrawal symptoms' over the subsequent week.(ABSTRACT TRUNCATED AT 400 WORDS)