Therapeutic monitoring of antipsychotics with a focus on lurasidone and its dosing.

Dose-response relationships are not fully understood for antipsychotics. Especially in the case of multimodal antipsychotics, these relationships cannot be simplified to the level of dopaminergic receptor occupancy alone. In general, for most antipsychotics, there is no linear dose-response relationship. Reasons for this include, among others, pharmacokinetic factors affecting plasma levels. Based on meta-analyses, the doseresponse curve appears to be bell-shaped. However, in the case of some antipsychotics, it appears that even increasing the dose beyond the recommended range could yield further increases in efficacy. It should be stressed that this is an off-label procedure and cannot generally be recommended and there is not enough valid information for general conclusions for these antipsychotics either. Mini-invasive sampling and alternative matrices such as saliva or dry blood spots could open the way to more frequent monitoring of antipsychotics and a better understanding of doseresponse relationships.

Therapeutic monitoring of antipsychotics with a focus on lurasidone and its dosing.

Dose-response relationships are not fully understood for antipsychotics. Especially in the case of multimodal antipsychotics, these relationships cannot be simplified to the level of dopaminergic receptor occupancy alone. In general, for most antipsychotics, there is no linear dose-response relationship. Reasons for this include, among others, pharmacokinetic factors affecting plasma levels. Based on meta-analyses, the doseresponse curve appears to be bell-shaped. However, in the case of some antipsychotics, it appears that even increasing the dose beyond the recommended range could yield further increases in efficacy. It should be stressed that this is an off-label procedure and cannot generally be recommended and there is not enough valid information for general conclusions for these antipsychotics either. Mini-invasive sampling and alternative matrices such as saliva or dry blood spots could open the way to more frequent monitoring of antipsychotics and a better understanding of doseresponse relationships.

Assessment of delta-9-tetrahydrocannabinol (THC) in saliva and blood after oral administration of medical cannabis with respect to its effect on driving abilities.

Medical cannabis has recently been legalized in many countries, and it is currently prescribed with increasing frequency, particularly for treatment of chronic pain resistant to conventional therapy. The psychoactive substance delta-9-tetrahydro-cannabinol (THC) contained in cannabis may affect driving abilities. Therefore, the aims of this study (open-label, monocentric, nonrandomized) were to evaluate blood and saliva concentrations of THC after oral administration of medical cannabis and to assess the time needed for THC levels to decline below a value ensuring legal driving. The study involved 20 patients with documented chronic pain using long-term medical cannabis therapy. They were divided into two groups and treated with two different doses of cannabis in the form of gelatin capsules (62.5 mg or 125 mg). In all patients, the amount of THC was assessed in saliva and in blood at pre-defined time intervals before and after administration. THC levels in saliva were detected at zero in all subjects following administration of both doses at all-time intervals after administration. Assessment of THC levels in blood, however, showed positive findings in one subject 9 h after administration of the lower dose and in one patient who had been given a higher dose 7 h after administration. Our finding suggested that for an unaffected ability to drive, at least 9-10 h should elapse from the last cannabis use.

CYP2C19 and CYP3A4 activity and ADP-induced platelet reactivity in prasugrel- or ticagrelor-treated STEMI patients: monocentric study in PRAGUE-18 trial participants.

We assessed the contribution of CYP2C19 and CYP3A4 metabolic activity to the ADP-induced platelet aggregation 1h and 24h after a loading dose of 60 mg prasugrel or 180 mg ticagrelor in patients with ST-elevation myocardial infarction (STEMI). Further, we assessed the contribution of CYP2C19 polymorphisms and medication to the CYP enzymatic activity.Patients with STEMI were randomly assigned to the treatment with prasugrel (n = 51) or ticagrelor (n = 46). Metabolic activity of CYP2C19 and CYP3A4 was assessed by the rate of 5-hydroxylation and sulfoxidation of lansoprazole. Further, patients were genotyped for CYP2C19 *2 and *17 alleles.In prasugrel-treated patients, high ADP-induced platelet reactivity 1h after the loading dose positively correlated with 5OH-lansoprazole/lansoprazole ratio (r = 0.44, p = 0.002), a marker of CYP2C19 metabolic activity, and negatively with lansoprazole-sulfone/lansoprazole ratio, which reflects CYP3A4 metabolic activity (r = -0.35, p = 0.018).CYP2C19 poor metabolizers had lower 5OH-lansoprazole/lansoprazole ratio and higher lansoprazole-sulfone/lansoprazole ratio, but without any effect on the ADP-induced platelet reactivity. The treatment with amiodarone, a CYP3A4 inhibitor, influenced neither the metabolic ratios nor the ADP-induced platelet reactivity.The CYP3A4 and CYP2C19 metabolic activity is associated with ADP-induced platelet reactivity in prasugrel-treated, but not ticagrelor-treated patients with STEMI.

Bile acids, nuclear receptors and cytochrome P450.

This review summarizes the importance of bile acids (BA) as important regulators of various homeostatic mechanisms with detailed focus on cytochrome P450 (CYP) enzymes. In the first part, synthesis, metabolism and circulation of BA is summarized and BA are reviewed as physiological ligands of nuclear receptors which regulate transcription of genes involved in their metabolism, transport and excretion. Notably, PXR, FXR and VDR are the most important nuclear receptors through which BA regulate transcription of CYP genes involved in the metabolism of both BA and xenobiotics. Therapeutic use of BA and their derivatives is also briefly reviewed. The physiological role of BA interaction with nuclear receptors is basically to decrease production of toxic non-polar BA and increase their metabolic turnover towards polar BA and thus decrease their toxicity. By this, the activity of some drug-metabolizing CYPs is also influenced what could have clinically relevant consequences in cholestatic diseases or during the treatment with BA or their derivatives.

The effect of (-)-linalool on the metabolic activity of liver CYP enzymes in rats.

(-)-Linalool is the major floral scent occurring mainly in families Lamiaceae, Lauraceae and Rutaceae and is the main active compound of lavender oil. The purpose of this study was to reveal the influence of subchronic systemic treatment with (-)-linalool on the metabolic activity of CYP2A, 2B, 2C6, 2C11 and 3A in rat liver microsomes (RLM). The second aim was to reveal possible inhibitory effect of (-)-linalool on CYP2C6 in vitro. Wistar albino male rats were treated with (-)-linalool intragastrically at the doses of 40, 120, and 360 mg/kg/day for 13 days. Treatment with (-)-linalool at the dose of 360 mg/kg increased the metabolic activity of CYP2A assessed with testosterone as a probe substrate. (-)-Linalool showed weak competitive inhibition of CYP2C6 in rat liver microsomes, with IC(50) of 84 microM with use of diclofenac as a probe substrate.

Can bioactive compounds of Crocus sativus L. influence the metabolic activity of selected CYP enzymes in the rat?

Safranal and crocin are biologically active compounds isolated from Crocus sativus L., commonly known as saffron. Clinical trials confirm that saffron has antidepressant effect, thus being a potential valuable alternative in the treatment of depression. The aim of the present study was to determine, whether systemic administration of safranal and crocin can influence the metabolic activity of CYP3A, CYP2C11, CYP2B, and CYP2A in rat liver microsomes (RLM). The experiments were carried out on male Wistar albino rats intragastrically administered with safranal (4, 20, and 100 mg/kg/day) or with intraperitoneal injections of crocin (4, 20, and 100 mg/kg/day). Our results demonstrate the ability of safranal and crocin to increase the total protein content and to change the metabolic activity of several CYP enzymes assessed as CYP specific hydroxylations of testosterone in RLM. Crocin significantly decreased the metabolic activity of all selected CYP enzymes, while safranal significantly increased the metabolic activity of CYP2B, CYP2C11 and CYP3A enzymes. Therefore, both substances could increase the risk of interactions with co-administered substances metabolized by cytochrome P450 enzymes.

[Potential clinical benefit of therapeutic drug monitoring of imatinib in oncology]. / Mozný klinický prínos terapeutického monitorování hladin imatinibu v onkologii.

Imatinib mesylate is a competitive inhibitor of BCR/ ABL tyrosine kinase and inhibits also several receptor tyrosin kinases. Since its launch to the market, imatinib has proven to be very valuable in the treatment of Philadelphia chromosome (BCR/ ABL) -  positive (Ph+) chronic myeloid leukemia and Kit (CD117) positive gastrointestinal stromal tumors. The drug is metabolized by cytochrome P450, and there are many clinically important pharmacokinetic drug-drug interactions described in the literature. Frequent polypharmacy in oncological patients increases probability of such interactions, and also adherence may play its role during longterm treatment. Fixed dosing therapeutic regimens fail to respect known interindividual variability in pharmacokinetics of the drug and thus, some patients may not achieve sufficient plasma concentrations. Based on current evidence, there seems to be a relationship between plasma concentration and clinical response to imatinib. Therefore, imatinib appears to be suitable candidate for therapeutic drug monitoring. Here, we present an overview of pharmacokinetics, drug-drug interactions and current knowledge and suggestions on therapeutic drug monitor-ing of imatinib, its potential benefits and limitations.

Dynamics and persistence of CYP2D6 inhibition by paroxetine.

WHAT IS KNOWN AND OBJECTIVE: Paroxetine is both a substrate and an inhibitor of CYP2D6. The objective of the presented study was to determine the persistence of CYP2D6 inhibition after short term (6 weeks) and long term (18·7 ± 10·6 weeks) paroxetine treatment. METHODS: Two the studies consisted of 30 depressive/anxiety patients each. In the first study, patients were subdivided into three groups treated with paroxetine (A1), alprazolam (A2) and paroxetine + alprazolam (A3). After 6 weeks, all the patients (A1+A2+A3) were switched to alprazolam treatment; metabolic activity was evaluated at the beginning, after 6 weeks of paroxetine/alprazolam/alprazolam + paroxetine treatment (A1/A2/A3) and 4 weeks after the switch to alprazolam treatment (Week 0, 6, 10). In the second study patients on previous long term paroxetine treatment were subdivided into two groups treated with mirtazapine (B1) or paroxetine (B2); metabolic activity of CYP2D6 was evaluated at the beginning and after 6 weeks of therapy. RESULTS AND DISCUSSION: Metabolic ratio of dextromethorphan to dextrorphan has normalized in all subjects after 4 weeks of paroxetine wash out in the first study. In the second study, 6 weeks after paroxetine discontinuation, restoration of metabolic activity of CYP2D6 was observed in only five of eight originally poor metabolizers. WHAT IS NEW AND CONCLUSION: We conclude that a wash-out period of 4 weeks seems to be sufficient for CYP2D6 disinhibition after short-term paroxetine treatment (6 weeks). On the other hand, treatment with a CYP2D6 substrate less than 6 weeks after long-term paroxetine treatment (18·7 weeks on average) could result in elevated drug plasma levels and occasionally also in drug toxicity.

Alternative reliable method for cytochrome P450 2D6 poor metabolizers genotyping.

High-resolution melting curve analysis (HRM) of polymerase chain reaction (PCR) amplicons has been described as a fast, cheap, and reliable closed-tube method of genotyping with no need for labeled primers or labeled probes. We adapted this melting analysis assay for the detection of the most common nonfunctional alleles of cytochrome P-450 (CYP) 2D6 in the Caucasian population that affect the metabolism of many commonly used drugs. We used this method to genotype 91 patients under paroxetine therapy. The presence and the constitution of the most common single-nucleotide polymorphisms (1846G>A, 2988G>A, 100C>T, 2549delA, 2615_2617delAAG, and 1707delT) in poor and intermediate metabolizers from the Caucasian population were detected in short amplicons (≤148 bp). After fluorescence normalization, the wild-type, homozygous, and heterozygous samples were easily distinguishable from each other by their specific melting curve shape. A total of 92.6% of the 1846G>A heterozygotes, 96% of the 100C>T heterozygotes, and 100% of the 2988G>A, 2549delA, 2615_2617delAAG, and 1707delT heterozygotes have been correctly distinguished from the wild types. One hundred percent of all the homozygotes in this group of patients have been detected without any error. HRM of short amplicons is a simple tool for effective, rapid, and reliable CYP2D6 genotyping that does not require real-time PCR, labeled probes, processing or any separations after PCR. The reaction is performed in a closed-tube system and is highly specific and sensitive. We proved that this technique is highly reliable for use in routine diagnostics.

Serum dextromethorphan/dextrorphan metabolic ratio for CYP2D6 phenotyping in clinical practice.

WHAT IS KNOWN AND OBJECTIVE: Accurate prediction of actual CYP2D6 metabolic activity may prevent some adverse drug reactions and improve therapeutic response in patients receiving CYP2D6 substrates. Dextromethorphan-to-dextrorphan metabolic ratio (MR(DEM/DOR)) is well established as a marker of CYP2D6 metabolizer status. The relationship between urine and plasma or serum MR(DEM/DOR) is not well established nor is there evidence of antimode for separation of intermediate and especially poor metabolizers (PM) from extensive metabolizers (EM). This study addressed whether CYP2D6 phenotyping using molar metabolic ratio of dextromethorphan to dextrorphan (MR(DEM/DOR)) in serum is usable and reliable in clinical practice as urinary MR(DEM/DOR). METHODS: We measured MR(DEM/DOR) in serum and CYP2D6 genotype in 51 drug-naive patients and 30 volunteers. Receiver-operator characteristic (ROC) analysis was used for the evaluation of optimum cut-off value for discriminating between extensive, intermediate and PM. In addition, we studied the correlation of serum MR(DEM/DOR) with urine MR(DEM/DOR) in the 30 healthy volunteers. RESULTS AND DISCUSSION: A trimodal distribution of log MR(DEM/DOR) in serum was observed, with substantial overlap between extensive and intermediate metabolizer groups. We obtained an acceptable cut-off serum MR(DEM/DOR) value to discriminate between PM and either extensive or extensive + intermediate metabolizers. Using serum MR(DEM/DOR), it seems to be unreliable to discriminate EM from intermediate metabolizers (IM). A strong correlation between serum MR(DEM/DOR) and urine MR(DEM/DOR) was found. WHAT IS NEW AND CONCLUSION: Serum MR(DEM/DOR) (3 h) correlated with MR(DEM/DOR) in urine (0-8 h). Serum MR(DEM/DOR) discriminated between extensive and PM and between extensive + intermediate and PM. Our CYP2D6 phenotyping using serum dextromethorphan/dextrorphan molar ratio appears reliable but requires independent validation.

Effect of methamphetamine on cytochrome P450 activity.

Amphetamine-based drugs, including methamphetamine, are some of the most widely used illegal drugs in the world. Methamphetamine is metabolized by the cytochrome P450s, the latter also being involved in the metabolism of many drugs and other xenobiotics. The effect of methamphetamine pretreatment (10 mg kg-1, intraperitoneally once daily for 6 days) on the activity of the P450 enzymes was assessed both in the rat isolated perfused liver and in vivo. The rate of 4-hydroxydiclofenac production was significantly enhanced in vivo, indicating a possible stimulatory effect on P4502C6. Similarly, the kinetics of tolbutamide and dextromethorphan in isolated perfused rat liver indicate a significant increase in both P4502C6 and the P4502D subfamily. No significant changes in midazolam kinetic in the isolated perfused rat liver were observed. The potential for methamphetamine to cause drug interactions is of clinical relevance and, therefore, it warrants further investigation. Until further drug interaction experiments are accomplished, the co-administration of drugs with methamphetamine should be conducted with caution.

Protective effects of osajin in ischemia-reperfusion of laboratory rat kidney.

The aim of this study was to analyze the antioxidative effect of osajin during prophylactic administration. The pathological model for in vivo experiment was the unilateral ischemia-reperfusion of kidney of the laboratory rat. The animals were randomly divided into five groups. Osajin was administrated orally in doses of 5, 10 and 20 mg/kg once a day to three premedicated groups. Placebo--0.5% solution of Avicel--was given to the fourth group and the fifth group was completely intact. The premedication lasted 15 days and subsequently the ischemia of the left kidney was incited in general anaesthesia for 60 min. The reperfusion lasted 10 min and it was finished by blood collection from the left ventricle and the reperfused kidney was recovered. Selected biochemical markers were assessed in blood: superoxide dismutase, glutathion peroxidase, total antioxidative capacity and malondialdehyde. The kidney tissue samples were used for histopathological examination. Laboratory and histopathological results confirmed supposed effects of osajine. The dependence between the effect and the applied dose of osajin was linear. The best biochemical results were reached after administration of osajin at the dose of 5 mg/kg. The best histopathological results were reached after administration of osajin at the dose of 10 mg/kg.

[Morin in the therapy of the ischemia-reperfusion damage model of the rat kidney]. / Morin v terapii ischemicko-reperfuzního poskození ledvinné tkáne laboratorního potkana.

The aim of this study was to analyze the protective effects of morin administered during the therapy of reperfusion injury of the laboratory rat kidney. Animals were randomly divided into five groups (n= 10). One group was left intact. Three medicated groups and one placebo group were subjected to ischemia (60 min) and reperfusion of the left kidney. Morin was suspended in a 2 ml of 0.5% Avicel solution and administered orally by a gastric probe at doses of 5, 10, and 20 mg.kg(-1) once a day for 15 days. The placebo group was given only 2 ml of 0.5% Avicel in the same way. On the 15th day, all the animals were exsanguinated and the reperfused kidneys were recovered. Selected biochemical markers in blood were assessed: superoxide dismutase, glutathion peroxidase, total antioxidative capacity, malondialdehyde, creatinine, urea, and uric acid. Creatinine, urea, and total protein were analyzed in urine, and a 24-hour diuresis was recorded. The kidney tissue samples were used for histopathological examination. Morin supported the organism's own defensive reactions against free radicals and decreased lipid peroxidation in the cell membranes and contributed to the recovery of kidney functions. The histopathological results confirm 20 mg x kg(-1) as the most effective dose.

Effect of methamphetamine on the pharmacokinetics of dextromethorphan and midazolam in rats.

Methamphetamine is the fourth most frequently reported compound associated with drug abuse on admission of patients to treatment centres after cocaine, heroin and marijuana. It is metabolized in the organism with a reaction that is catalyzed by cytochrome P450, mainly by the CYP2D and CYP3A subfamily, 4-hydroxyamphetamine and amphetamine being dominant metabolites. The present pharmacokinetic study was undertaken to investigate the possible influence of methamphetamine (10 mg/kg, i.p., once daily for six days) on the pharmacokinetics of dextromethorphane as a model substrate for rat cytochrome P-4502D2 and midazolam as a model substrate for CYP3A1/2. Animals received a single injection of dextromethorphane (10 mg/kg) or midazolam (5 mg/kg) in the tail vein 24 h after the last dose of methamphetamine or administration of placebo. The results of pharmacokinetic analysis showed a significantly increased rate of dextrorphane and 3-hydroxymorphinan formation, and a marked stimulatory effect of methamphetamine on CYP2D2 metabolic activity. Similarly, the kinetics of midazolam's metabolic conversion to hydroxy derivates of midazolam indicated a significant increase in CYP3A1/2 activity. The results showed that the administration of methamphetamine significantly stimulated the metabolic activity of CYP2D2 as well as that of CYP3A1/2. With regard to the high level of homology between human and rat CYP isoforms studied, the results may have a clinical impact on future pharmacotherapy for methamphetamine abuse.

Effect of St John's wort (Hypericum perforatum) on cytochrome P-450 activity in perfused rat liver.

St. John's wort (Hypericum perforatum) is a popular over-the-counter dietary supplement and a herbal antidepressant that has been implicated in drug interactions with substrates of several cytochrome P-450 (CYP) isozymes. The effects of the St. John's wort extract (100 mg/kg, i.p., once daily for 10 days) on metabolic activity of CYP450 were assessed in the system of isolated perfused rat liver. The substrates used in this study were tolbutamide (CYP2C6), dextromethorphan (CYP2D2) and midazolam (CYP3A2). Validated HPLC method was used to quantify all compounds of interest. St. John's wort administration affected CYP activity, causing a significant decline in AUC of dextromethorphan [F(4,31)=1511, p<0.001; PLSD, p<0.001] and AUC of midazolam [F(3,25)=221, p<0.001; PLSD, p=0.035] and a significant increase in AUC of tolbutamide [F(3,26)=200, p<0.001; PLSD, p<0.001]. St. John's wort administration resulted in a significant induction of CYP2D2 and CYP3A2, and in a significant inhibition of CYP2C6 metabolic activities.

Graded exercise stress test training in family practice and internal medicine residencies.

A mail survey of upper Midwest family practice and internal medicine residency program directors was performed to determine the prevalence and characteristics of exercise stress test training. Two mailings provided a 68% response rate for the 184 programs surveyed. Internal medicine programs were significantly more likely to offer exercise stress test training than family practice programs (57% vs 34%). Overall, an estimated 31% of family practice and internal medicine residency graduates are performing exercise stress tests in their practice. Programs provided an average of 7.3 hours of didactic instruction and 32.7 stress tests per resident. A minority (43%) had an established minimum number of exercise stress tests recommended for competency. Programs with and without exercise stress test training did not differ significantly with respect to age, size of program, or size of community. There were some interstate differences in the extent of exercise stress test training provided by family practice residency programs. Internal medicine programs were more likely to require a minimum number of treadmill tests. Otherwise there were few differences between family practice and internal medicine program instruction in exercise stress test training. Family practice program directors were more likely to believe that their residents should be taught this procedure and to include family physicians in their panel of instructors. Specific guidelines should be created to assure adequate stress test training for interested residents.

Chlamydia and incidental carcinoid tumor in spontaneous abortion.

Maternal Chlamydia trachomatis infections have been associated with premature rupture of the membranes, preterm labor, premature birth, and fetal wastage. Women with acute infection may be at particular risk. We report the case of an unexplained second trimester spontaneous abortion with serologic evidence of recent infection with C. trachomatis. Serum IgG antibody titer ultimately exceeded 1:10,240. This patient also had an incidental finding of appendiceal carcinoid tumor. While treatment of asymptomatic chlamydial infections in early pregnancy is controversial, we suggest that delaying treatment may result in fetal loss.