Potent CYP3A4 Inhibitor Research Articles

Effect of Steady-State Enoxacin on Single-Dose Pharmacokinetics of Roflumilast and Roflumilast N-Oxide

Roflumilast is an oral phosphodiesterase 4 (PDE4) inhibitor for the treatment of chronic obstructive pulmonary disease (COPD). It is metabolized by CYP1A2 and CYP3A4 to its primary metabolite, roflumilast N-oxide, through which >90% total PDE4 inhibitory activity (tPDE4i) is mediated. Fluoroquinolones, of which enoxacin is the most potent CYP1A2 inhibitor, are used to treat COPD exacerbations. This phase I, open, nonrandomized, fixed-sequence, 2-period study evaluated the effects of steady-state enoxacin on the single-dose pharmacokinetics of roflumilast and roflumilast N-oxide. Twenty healthy participants received roflumilast, 500 µg once daily, on days 1 and 12, and enoxacin, 400 mg twice daily, on days 7 to 18. Pharmacokinetic profiles were obtained for days 1 to 6 and 12 to 19. The safety and tolerability of all treatments were also assessed. In 19 evaluable participants, coadministration led to 56% higher mean systemic exposure, 20% higher mean peak concentrations, and 36% lower mean apparent oral clearance compared with roflumilast alone. For roflumilast N-oxide, 23% higher mean systemic exposure and 14% lower mean peak concentrations were seen after coadministration. Roflumilast was well tolerated both alone and in combination with enoxacin. A weak interaction was shown between roflumilast and enoxacin, as mean tPDE4i increased by 25%, but is unlikely to have clinical relevance.

Pharmacokinetics of oral neratinib during co‐administration of ketoconazole in healthy subjects

The primary objective was to evaluate the pharmacokinetics of a single dose of neratinib, a potent, low-molecular-weight, orally administered, irreversible pan-ErbB (ErbB-1, -2, -4) receptor tyrosine kinase inhibitor, during co-administration with ketoconazole, a potent CYP3A4 inhibitor. This was an open-label, randomized, two-period, crossover study. Fasting healthy adults received a single oral dose of neratinib 240 mg alone and with multiple oral doses of ketoconazole 400 mg. Blood samples were collected up to 72 h after each neratinib dose. Plasma concentration data were analyzed using a noncompartmental method. The least square geometric mean ratios [90% confidence interval (CI)] of C(max) (neratinib+ketoconazole): C(max) (neratinib alone), and AUC(neratinib+ketoconazole): AUC(neratinib alone) were assessed. Twenty-four subjects were enrolled. Compared with neratinib administered alone, co-administration of ketoconazole increased neratinib C(max) by 3.2-fold (90% CI: 2.4, 4.3) and AUC by 4.8-fold (3.6, 6.5). Median t(max) was 6.0 h with both regimens. Ketoconazole decreased mean apparent oral clearance of neratinib from 346 lh(-1) to 87.1 lh(-1) and increased mean elimination half-life from 11.7 h to 18.0 h. The incidence of adverse events was comparable between the two regimens (50% neratinib alone, 65% co-administration with ketoconazole). Co-administration of neratinib with ketoconazole, a potent CYP3A inhibitor, increased neratinib C(max) by 3.2-fold and AUC by 4.8-fold compared with administration of neratinib alone. These results indicate that neratinib is a substrate of CYP3A and is susceptible to interaction with potent CYP3A inhibitors and, thus, dose adjustments may be needed if neratinib is administered with such compounds.

Extreme bradycardia due to multiple drug–drug interactions in a patient with HIV post‐exposure prophylaxis containing lopinavir–ritonavir

Extreme bradycardia due to multiple drug–drug interactions in a patient with HIV post‐exposure prophylaxis containing lopinavir–ritonavir

Thiomers: Inhibition of cytochrome P450 activity

The aim of the present study was to investigate the potential of different thiolated polymers (thiomers) on the catalytic activity of CYP450s on one hand and to explore new inhibitors for CYP activity on the other hand. Several thiolated polymers including poly(acrylic acid)–cysteine (PAA–cysteine), chitosan–thioglycolic acid (chitosan–TGA), and thiolated PEG- g-PEI copolymer along with brij® 35, myrj® 52 and the well-established CYPP450 inhibitor verapamil were screened for their CYP3A4 and CYP2A6 inhibitory activity, and their IC 50 values were determined. Both enzyme inhibition assays were performed in 96-well microtiter plates. 7-Benzyloxy-4-(trifluoromethyl)-coumarin (BFC) and 7-hydroxycoumarin (7-HC) were used as fluorescent substrates in order to determine CYP3A4 and CYP2A6 catalytic activity, respectively. All investigated compounds inhibited CYP3A4 as well as CYP2A6 activity. All tested (thiolated) polymers were found to be more potent inhibitors of CYP3A4 than of CYP2A6 catalytic activity. Apart from verapamil that is a known CYP3A4 inhibitor, brij® 35 and myrj® 52 were explored as potent inhibitors of CYP3A4 and CYP2A6 catalytic activity. Among the tested polymers, the rank order for CYP3A4 inhibition was PAA–cysteine (100 kDa) > brij® 35 > thiolated PEG- g-PEI copolymer (16 kDa) > myrj® 52 > PAA (100 kDa) > PAA–cysteine (450 kDa) > verapamil > PAA (450 kDa) > chitosan–TGA (150 kDa) > chitosan (150 kDa). On the other hand, the rank order of CYP2A6 inhibition was brij® 35 > PAA–cysteine (100 kDa) > chitosan–TGA (150 kDa) > PAA (100 kDa) > thiolated PEG- g-PEI copolymer (16 kDa) > PAA–cysteine (450 kDa) > chitosan (150 kDa) > verapamil > PAA (450 kDa) > myrj® 52. Thus, this study suggests that (thiolated) polymers display a promising potential to inhibit cytochrome P450s activity and might turn out to be potentially valuable tools for improving the oral bioavailability of actively secreted compounds by avoiding intestinal metabolism.

Chroman and tetrahydroquinoline ureas as potent TRPV1 antagonists

Novel chroman and tetrahydroquinoline ureas were synthesized and evaluated for their activity as TRPV1 antagonists. It was found that aryl substituents on the 7- or 8-position of both bicyclic scaffolds imparted the best in vitro potency at TRPV1. The most potent chroman ureas were assessed in chronic and acute pain models, and compounds with the ability to cross the blood-brain barrier were shown to be highly efficacious. The tetrahydroquinoline ureas were found to be potent CYP3A4 inhibitors, but replacement of bulky substituents at the nitrogen atom of the tetrahydroisoquinoline moiety with small groups such as methyl can minimize the inhibition.

Inhibitory Effects of Phyllanthus amarus and Its Major Lignans on Human Microsomal Cytochrome P450 Activities: Evidence for CYP3A4 Mechanism-Based Inhibition

Phyllanthus amarus has long been used as a herbal medicine in several countries. Phytochemicals in herbal medicine may interact with cytochromes P450 (CYP) and thus raise the potential of herb-drug interactions; therefore, the inhibitory effects of P. amarus and its major phytochemicals phyllanthin and hypophyllanthin on CYP isoforms were determined using human liver microsomes and selective substrates. Both ethanolic and aqueous extracts of P. amarus inhibited CYP1A2, CYP2D6, CYP2E1 and CYP3A4 in a dose-dependent manner. Compared to known CYP3A inhibitors, the IC(50) values of the ethanolic and aqueous extracts on testosterone 6β-hydroxylation were higher than that of ketoconazole but were lower than those of erythromycin and clarithromycin. Both extracts were weak inhibitors of CYP1A2, CYP2D6 and CYP2E1. In addition, phyllanthin and hypophyllanthin were potent mechanism-based inhibitors of CYP3A4 with K(I) values of 1.75 ± 1.20 µM and 2.24 ± 1.84 µM and k(inact) values of 0.18 ± 0.05 min(-1) and 0.15 ± 0.06 min(-1), respectively. The k(inact)/K(I) ratios of these lignans were higher than those reported for some therapeutic drugs that act as mechanism-based inhibitors of CYP3A4. These results suggest that co-administration of P. amarus with drugs that are metabolized by CYP3A4 may potentially result in herb-drug interactions.

Effect of Intrinsic and Extrinsic Factors on the Clinical Pharmacokinetics and Pharmacodynamics of Prasugrel

Thienopyridines are inactive prodrugs that are converted in vivo to active metabolites, which irreversibly bind to and inactivate platelet P2Y(12) receptors, and inhibit platelet activation and aggregation. Prasugrel is a third-generation thienopyridine, recently approved for prevention of thrombotic cardiovascular complications in patients with an acute coronary syndrome undergoing percutaneous coronary intervention. Prasugrel is converted to its active metabolite (Pras-AM; compound R-138727) in two sequential steps: (i) rapid and complete hydrolysis by intestinal human carboxylesterase-2 to form a thiolactone intermediate; and (ii) oxidation of the thiolactone by cytochrome P450 (CYP) enzymes in the gut and/or the liver. CYP3A and CYP2B6 are the primary CYPs contributing to Pras-AM formation, with smaller contributions from CYP2C9 and CYP2C19. Prasugrel is rapidly absorbed and metabolized, with Pras-AM plasma concentrations peaking at about 0.5 hours after oral administration; this helps to account for the rapid onset of inhibition of platelet aggregation (IPA) achieved by prasugrel. In the clinical pharmacology programme for prasugrel, bodyweight had the greatest effect of all covariates that were tested. In the phase III TRITON-TIMI 38 trial, the mean exposure to Pras-AM was 42% greater in patients weighing < 60 kg than in patients with the study population median bodyweight of 85 kg. In a pharmacodynamic meta-analysis of data from healthy subjects a decrease of 1 kg in bodyweight was associated with an increase in IPA of approximately 0.26 percentage points (p < 0.0001). Pras-AM exposure was greater in subjects aged ≥ 75 years, but exposure differences were not as large as those for bodyweight. Pras-AM exposure was greater in Asians than in Caucasians, but this appeared to result from a disproportionately greater exposure difference in Asian subjects with low bodyweight. Sex and allelic variation in CYPs 1A2, 2B6, 2C19, 2C9, 3A4 and 3A5 appeared to have no clinically relevant effect on Pras-AM exposure or IPA. Consistent with the lack of association between genetic status and these pharmacokinetic and pharmacodynamic results in healthy subjects, no significant association was detected between these allelic variants and the composite primary endpoint (cardiovascular death, non-fatal myocardial infarction or non-fatal stroke) in the TRITON-TIMI 38 trial. Studies in renally impaired subjects and subjects with mild or moderate hepatic impairment have indicated that dose adjustment is not required in these patient populations. Prasugrel has few clinically significant drug-drug interactions. Potent CYP3A inhibitors, gastric acid suppressants and food have been shown to reduce the rate of formation of Pras-AM but not its overall exposure. This pharmacokinetic effect reduced the rate of onset of IPA after a loading dose but did not affect the peak IPA after a loading dose or the IPA during maintenance dosing. Potent induction of CYP3A, as well as smoking--which induces CYP1A2--did not affect Pras-AM exposure or IPA. Prior treatment with clopidogrel did not influence tolerability to prasugrel and did not appear to alter IPA during prasugrel treatment. Prasugrel did not affect the activities of CYP2C9, CYP2C19 or P-glycoprotein, but it weakly inhibited CYP2B6. The inhibition of CYP2B6 is potentially clinically significant only for drugs that have a narrow therapeutic window and have CYP2B6 as the primary elimination pathway. No interaction was detected between prasugrel and heparin. Although prasugrel did not alter warfarin pharmacokinetics, prasugrel and warfarin should not be used together, because of an increased bleeding risk associated with their concomitant use.

Effect of ketoconazole on the pharmacokinetics of axitinib in healthy volunteers

Summary Objective Axitinib (AG-013736), an oral, potent, and selective inhibitor of vascular endothelial growth factor receptors 1, 2, and 3, is metabolized primarily by cytochrome P450 (CYP) 3A with minor contributions from CYP1A2, CYP2C19, and glucuronidation. Co-administration with CYP inhibitors may increase systemic exposure to axitinib and alter its safety profile. This study evaluated changes in axitinib plasma pharmacokinetic parameters and assessed safety and tolerability in healthy subjects, following axitinib co-administration with the potent CYP3A inhibitor ketoconazole. Methods In this randomized, single-blind, two-way crossover study, 32 healthy volunteers received placebo, followed by a single 5-mg oral dose of axitinib, administered either alone or on the fourth day of dosing with oral ketoconazole (400 mg/day for 7 days). Results Axitinib exposure was significantly increased in the presence of ketoconazole, with a geometric mean ratio for area under the plasma concentration–time curve from time zero to infinity of 2.06 (90% confidence interval [CI]: 1.84–2.30) and a geometric mean ratio for maximum plasma concentration (Cmax) of 1.50 (90% CI: 1.33–1.70). For axitinib alone or with ketoconazole, Cmax occurred 1.5 and 2.0 h after dosing, respectively. Adverse events were predominantly mild; the most commonly reported treatment-related adverse events were headache and nausea. Conclusions Axitinib plasma exposures and peak concentrations were increased following concurrent administration of axitinib and ketoconazole in healthy volunteers. Axitinib alone and in combination with ketoconazole was well tolerated. These findings provide an upper exposure for expected axitinib plasma concentrations in the presence of potent metabolic inhibition.

Major tanshinones of Danshen (Salvia miltiorrhiza) exhibit different modes of inhibition on human CYP1A2, CYP2C9, CYP2E1 and CYP3A4 activities in vitro

This study investigated the effects of tanshinones on human CYP1A2 (phenacetin O-deethylase), CYP2C9 (tolbutamide 4-hydroxylase), CYP2E1 (chlorzoxazone 6-hydroxylase) and CYP3A4 (testosterone 6beta-hydroxylase) activities in vitro using pooled human liver microsomes and specific human CYP isoforms. Tanshinone I, tanshinone IIA, and cryptotanshinone were potent competitive CYP1A2 inhibitors (K(i)=1.5-2.5 microM); medium competitive inhibitors of CYP2C9 (K(i)=22-62 microM); medium competitive inhibitors of CYP2E1 (K(i)=3.67 microM) for tanshinone I and 10.8 microM for crytotanshinone; but weak competitive inhibitors of CYP3A4 (K(i)=86-220 microM). Dihydrotanshinone was a competitive inhibitor of human CYP1A2 (K(i)=0.53 microM) and CYP2C9 (K(i)=1.92 microM), a noncompetitive inhibitor of CYP3A4 (K(i)=2.11 microM) but an uncompetitive CYP2E1 inhibitor. In conclusion, these results showed that tanshinones inhibited the metabolism of various CYP probe substrates in human liver microsomes and specific human CYP isoforms in vitro. Given that CYP1A2, 2C9, 2E1 and 3A4 are responsible for the metabolism and disposition of a large number of drugs currently used, the potential herb-drug interactions of Danshen preparations containing the major tanshinones with drugs which are substrates of these CYPs may be important.

Saxagliptin

Type 2 diabetes mellitus is a common chronic disease that causes significant morbidity and mortality worldwide. The primary goal of treatment is to target glycemic control by maintaining the glycosylated hemoglobin (HbA1c) level near 6% to 7% without predisposing patients to hypoglycemia. Currently available antidiabetic agents work by different mechanisms to lower blood glucose levels. Unfortunately, each of them has its tolerability and safety concerns that limit use and dose titration. Dipeptidyl peptidase-4 enzyme inhibitors are novel drugs that prolong the action of incretins, and lead to increased insulin secretion and reduced hepatic glucose production. Saxagliptin is another dipeptidyl peptidase-4 (after sitagliptin) that is approved for the management of type 2 diabetes. It can be used alone or in combination with metformin, sulfonylurea, or thiazolidinedione (pioglitazone or rosiglitazone) when treatment with one drug alone provides inadequate glucose control. The usual adult dose is 2.5 to 5 mg once daily regardless of meals. A daily dose of 2.5 mg is recommended for patients with moderate to severe renal impairment or those who are taking potent CYP 3A4 inhibitors. In randomized clinical trials, saxagliptin alone lowered HbA1c levels by about 0.5%; with better efficacy seen when combined with other agents. It is well tolerated with the most common side effects being upper respiratory tract infection, headache, and urinary tract infection. In summary, saxagliptin is an option as an adjunct to lifestyle modifications and other antidiabetic agents to target glycemic control. It is also an alternative therapy for patients who have contraindications or intolerability to other antidiabetic agents.

Drug Interaction Between Itraconazole and Bortezomib: Exacerbation of Peripheral Neuropathy and Thrombocytopenia Induced by Bortezomib

To investigate whether a drug interaction exists between bortezomib and the cytochrome P450 (CYP) 3A4 inhibitor itraconazole and/or the CYP2C19 inhibitor lansoprazole that results in increased severity of bortezomib-induced peripheral neuropathy and thrombocytopenia. Retrospective medical record review. Hematology-oncology ward of a university-affiliated hospital in Japan. Six adults with relapsed multiple myeloma who received intravenous bortezomib plus oral dexamethasone as the first course of a 21-day cycle between July 2007 and December 2008. Four of the six patients were treated concomitantly with itraconazole or lansoprazole: two with itraconazole, one with lansoprazole, and one with both itraconazole and lansoprazole. Using the National Cancer Institute's Common Terminology Criteria for Adverse Events, we identified the presence and graded the severity of peripheral neuropathy and thrombocytopenia before and during each patient's first 21-day course of bortezomib plus dexamethasone therapy. All three patients who received itraconazole experienced new or worsening peripheral neuropathy; they also experienced grade 4 thrombocytopenia. The patient who received lansoprazole alone, as well as the two patients who did not receive itraconazole or lansoprazole, had no changes in either adverse effect. We also evaluated the relationship between peripheral neuropathy and bortezomib plus dexamethasone therapy by using the Naranjo adverse drug reaction probability scale, and a probable relationship was found. We further assessed whether a drug interaction between bortezomib and itraconazole and/or lansoprazole had occurred involving the CYP3A4 and/or the CYP2C19 pathways, respectively-resulting in increased severity of the bortezomib-induced peripheral neuropathy and thrombocytopenia-by using the Horn drug interaction probability scale. We found that the occurrence of this drug interaction was strongly supported. Itraconazole appears to exacerbate peripheral neuropathy and thrombocytopenia induced by bortezomib; however, the mechanism of this drug interaction is unknown. Clinicians should closely monitor for bortezomib-induced adverse effects when itraconazole, or any other potent CYP3A4 inhibitor, is administered concomitantly with bortezomib.

Pharmacokinetics of dipeptidylpeptidase‐4 inhibitors

Type 2 diabetes (T2DM) is a complex disease combining defects in insulin secretion and insulin action. New compounds have been developed for improving glucose-induced insulin secretion and glucose control, without inducing hypoglycaemia or weight gain. Dipeptidylpeptidase-4 (DPP-4) inhibitors are new oral glucose-lowering agents, so-called incretin enhancers, which may be used as monotherapy or in combination with other antidiabetic compounds. Sitagliptin, vildaglipin and saxagliptin are already on the market in many countries, either as single agents or in fixed-dose combined formulations with metformin. Other DPP-4 inhibitors, such as alogliptin and linagliptin, are currently in late phase of development. The present paper summarizes and compares the main pharmacokinetics (PK) properties, that is, absorption, distribution, metabolism and elimination, of these five DPP-4 inhibitors. Available data were obtained in clinical trials performed in healthy young male subjects, patients with T2DM, and patients with either renal insufficiency or hepatic impairment. PK characteristics were generally similar in young healthy subjects and in middle-aged overweight patients with diabetes. All together gliptins have a good oral bioavailability which is not significantly influenced by food intake. PK/pharmacodynamics characteristics, that is, sufficiently prolonged half-life and sustained DPP-4 enzyme inactivation, generally allow one single oral administration per day for the management of T2DM; the only exception is vildagliptin for which a twice-daily administration is recommended because of a shorter half-life. DPP-4 inhibitors are in general not substrates for cytochrome P450 (except saxagliptin that is metabolized via CYP 3A4/A5) and do not act as inducers or inhibitors of this system. Several metabolites have been documented but most of them are inactive; however, the main metabolite of saxagliptin also exerts a significant DPP-4 inhibition and is half as potent as the parent compound. Renal excretion is the most important elimination pathway, except for linagliptin whose metabolism in the liver appears to be predominant. PK properties of gliptins, combined with their good safety profile, explain why no dose adjustment is necessary in elderly patients or in patients with mild to moderate hepatic impairment. As far as patients with renal impairment are concerned, significant increases in drug exposure for sitagliptin and saxagliptin have been reported so that appropriate reductions in daily dosages are recommended according to estimated glomerular filtration rate. The PK characteristics of DPP-4 inhibitors suggest that these compounds are not exposed to a high risk of drug-drug interactions. However, the daily dose of saxagliptin should be reduced when coadministered with potent CYP 3A4 inhibitors. In conclusion, besides their pharmacodynamic properties leading to effective glucose-lowering effect without inducing hypoglycaemia or weight gain, DPP-4 inhibitors show favourable PK properties, which contribute to a good efficacy/safety ratio for the management of T2DM in clinical practice.

Increased Glyburide Clearance in the Pregnant Mouse Model

Glyburide (GLB) is an oral sulfonylurea, commonly used for the treatment of gestational diabetes mellitus. It has been reported that the clearance of GLB in pregnant women is significantly higher than that in nonpregnant women. The molecular mechanism by which pregnancy increases the clearance of GLB is not known, but it may be caused by increased CYP3A activity. Because liver tissue from pregnant women is not readily available, in the present study, we investigated the mechanism of such pregnancy-related changes in GLB disposition in a mouse model. We demonstrated that the systemic clearance of GLB in pregnant mice was increased approximately 2-fold (p < 0.01) compared with nonpregnant mice, a magnitude of change similar to that observed in the clinical study. Plasma protein binding of GLB in mice was not altered by pregnancy. The half-life of GLB depletion in hepatic S-9 fractions of pregnant mice was significantly shorter than that of nonpregnant mice. Moreover, GLB depletion was markedly inhibited by ketoconazole, a potent inhibitor of mouse Cyp3a, suggesting that GLB metabolism in mice is primarily mediated by hepatic Cyp3a. These data suggest that the increased systemic clearance of GLB in pregnant mice is likely caused by an increase in hepatic Cyp3a activity during pregnancy, and they provide a basis for further mechanistic understanding and analysis of pregnancy-induced alterations in the disposition of GLB and drugs that are predominantly and extensively metabolized by CYP3A/Cyp3a.

Pharmacokinetics (PK) of PF-562271, a focal adhesion kinase (FAK) inhibitor, and its effect on CYP3A in patients with advanced nonhematologic malignancies.

2553 Background: FAK transduces signaling from integrins and growth factors to modulate tumor cell invasion, proliferation, and survival. PF-562271, a potent FAK inhibitor, is under development as an anticancer agent. Preclinical studies demonstrated that PF-562271 is an inhibitor of its primary metabolizing enzyme, CYP3A. PF-562271 PK and its effect on CYP3A were investigated in a dose-escalation trial in patients with nonhematologic malignancies. Methods: Escalating doses of PF-562271 were administered orally to a total of 67 patients twice a day (BID) or once a day (QD), with or without food. Serial serum samples were collected after the first dose and at steady state to determine PK of PF-562271. To evaluate the effect of PF-562271 on CYP3A activity, plasma PK of orally administered midazolam were determined prior to PF-562271 administration and after repeated PF-562271 dosing to steady state in 8 patients who received the recommended phase 2 dose of 125 mg BID. Serum PF-562271 and plasma midazolam concentrations were determined using validated HPLC-MS/MS methods. The concentration-time data for PF-562271 and midazolam were analyzed by noncompartmental methods. Results: After a single oral dose, PF-562271 was readily absorbed with the maximum serum concentration achieved in 0.5 to 6 hours. The increases in systemic exposure (AUCinf) were dose proportional over the 5 to 25 mg range, but greater than dose proportional from 35 to 225 mg. After multiple oral doses, PF-562271 demonstrated nonlinear accumulation in exposure; the mean ratio of steady state AUC during a dose interval to AUCinf after the first dose ranged from 1.3 to 5.3, indicating time-dependent PK. Similar PK parameters for PF-562271 were observed at comparable doses given with or without food. When co-administered, PF-562271 (125 mg BID) increased total midazolam plasma exposure approximately 5.9-fold. Conclusions: PF-562271 displayed time- and dose-dependent nonlinear PK, and is a potent CYP3A inhibitor. The nonlinear PK of PF-562271 likely resulted from auto-inhibition of CYP3A. In the limited number of subjects evaluated, food did not substantially alter the PK of PF-562271. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Pfizer Pfizer

Case Report: Drug Interaction Between Tacrolimus and Amiodarone With QT Prolongation

Both amiodarone (Cordarone; Wyeth, Philadelphia, PA) and tacrolimus (Prograf; Astellas, Markham, ON) are metabolized through the cytochrome (CYP) P450 3A metabolic pathway (1, 2). Amiodarone is known to be a potent inhibitor of CYP 3A4 and can increase serum concentrations of drugs that are substrates of this enzyme system (such as tacrolimus). Previous case reports recommend diligent serum tacrolimus concentration monitoring and prospective tacrolimus dose reductions when the two drugs are given in combination (3, 4). This case report provides further evidence to support the drug interaction between tacrolimus and amiodarone as well as evidence of QT prolongation seen in a renal transplant recipient on this drug combination. CASE REPORT A 65-year-old man underwent a living, nonrelated, renal transplant. His medical history was significant for end-stage renal disease secondary to diabetes, sleep apnea, obesity, and bilateral knee arthroscopy. In addition, he had known coronary artery disease and had undergone coronary artery bypass grafting 5 years before transplant. He had been started on amiodarone postoperatively for presumed atrial fibrillation and maintained on 200 mg daily, since then. Preoperatively, he was in sinus rhythm, and a stress test and echocardiogram were normal. QTc was 440 ms (2 days preoperatively). Posttransplant, he began taking tacrolimus 3 mg orally two times per day for immunosuppression in combination with corticosteroids and mycophenolate mofetil 1000 mg orally two times per day. His initial tacrolimus dose had been empirically reduced by approximately 50% because of an anticipated drug interaction with amiodarone. He was also receiving sulfamethoxazole/trimethoprim, metoprolol, nifedipine, simvastatin, insulin, lansoprazole, betahistine, calcium carbonate, and alfacalcidol. The doses of nifedipine and simvastatin, both of which can interact with tacrolimus, were unchanged during the transplant period. His serum tacrolimus levels are presented in Figure 1.FIGURE 1.: Serum tacrolimus concentrations and QTc.On postoperative day 1, his electrocardiogram revealed normal sinus rhythm, with no evidence of ischemia; however, his QTc was prolonged and equal to 535 ms. His troponins were negative. His magnesium, potassium, calcium, and liver enzymes levels were within the normal range. He was empirically treated with magnesium intravenously, and as the QTc was not improving, the amiodarone was discontinued on postoperative day 2. After withdrawal of the amiodarone, his QTc slowly fell over the next few days to 493 ms on postoperative day 5, when he was discharged with good kidney function (Fig. 1). His tacrolimus serum concentrations were maintained in the 12.3 to 14.9 ng/mL range and he was discharged on a dose of 1.5 mg two times per day orally (∼25% of the usual recommended starting dose). DISCUSSION Both amiodarone and tacrolimus have been implicated in prolonging the QT interval (5–8). Our patient's borderline prolongation of QTc preoperatively might be attributable to long-term amiodarone use. Both amiodarone and tacrolimus are substrates at CYP 3A for enzyme metabolism and could potentially be implicated in increasing the concentration of the other agent through competition for metabolism sites. Some studies suggest that the risk of QT prolongation and torsades de pointes with tacrolimus is concentration dependent (5) whereas others do not (6). Tacrolimus-induced QT prolongation is believed to be due to inhibition of the delayed rectifier K+ current (IK), inward rectifier K+ current (IKI), L-type Ca2+ current (ICaL), and prolongation of the action potential duration although other pharmacological mechanisms have been postulated (5, 6). QT prolongation is common with amiodarone but with a low incidence of proarrhythmic events (<1%) (9). Torsades de pointes may be provoked in patients on amiodarone, usually in conjunction with electrolyte imbalances, increased amiodarone doses, or in combination with other drugs that prolong the QT interval (9). The amiodarone-induced inhibition of tacrolimus metabolism resulted in markedly lower doses of tacrolimus than would usually be expected to achieve desired therapeutic serum concentrations. In our patient, despite adjustment and reduction in tacrolimus dose, the patient still had an elevated tacrolimus level. Even more concerning was that the amiodarone-tacrolimus interaction led to a sudden and marked prolongation of the QT interval when tacrolimus was commenced and improved when the amiodarone was discontinued. This is a significant interaction because a large percentage of patients with end-stage renal disease have left ventricular hypertrophy (10) and subsequently are at higher risk of atrial fibrillation especially in the posttransplant operative period. Amiodarone is a commonly used agent for atrial fibrillation and given the importance of the amiodarone-tacrolimus interaction, we suggest that patients who are on, or require, amiodarone while on tacrolimus be closely monitored through serial electrocardiograms or on telemetry. Otherwise, consideration should be given to use an alternative agent. Cathy I. Burger1 Catherine M. Clase2 Azim S. Gangji2 1Department of Pharmacy St. Joseph's Healthcare Hamilton, ON 2Department of Medicine McMaster University Department of Nephrology and Transplant St. Joseph's Healthcare Hamilton, ON

Furanocoumarin Derivatives in Kampo Extract Medicines Inhibit Cytochrome P450 3A4 and P-Glycoprotein

Furanocoumarins in grapefruit are known to show inhibitory effects against P-glycoprotein (P-gp) and CYP3A4 in intestinal epithelial cells; however, furanocoumarin derivatives are widely contained in the plants of Rutaceae and Umbelliferae families, which are used as components of Kampo extract medicines. In this study, we investigated the inhibitory effects of 12 furanocoumarins extracted from plants in the Umbelliferae family against P-gp and CYP3A4 activity. Furthermore, we studied their inhibitory effect on P-gp when furanocoumarins are used as Kampo extract medicine rather than as an isolated single compound. From screening of the CYP3A4 inhibitory effect, notopterol and rivulobirin A, the only dimer types of furanocoumarin, were found to be potent inhibitors of CYP3A4. On the other hand, byakangelicol and rivulobirin A showed strong P-gp inhibition from the screening of P-gp inhibitor evaluated by quinidine permeation through the Caco-2 monolayer; however, the chemical structural relationship of furanocoumarins between P-gp and CYP3A4 inhibitory effects could not be obtained. We also investigated the effect of these furanocoumarins on the transport of digoxin through the Caco-2 monolayer. The inhibitory effect of rivulobirin A was more potent than that of byakangelicol. Application of either Senkyu-cha-cho-san or Sokei-kakketsu-to, which are composed of herbal remedies in the Umbelliferae group, significantly decreased the efflux ratio of digoxin. In conclusion, it was found that some furanocoumarins extracted from the plants in the Umbelliferae family strongly inhibited P-gp and CYP3A4. Kampo extract medicines containing herbal remedies belonging to the Umbelliferae family may cause a drug-drug interaction with P-gp or a CYP3A4 substrate drug.

Pharmacokinetics and Pharmacodynamics of Tamsulosin in its Modified-Release and Oral Controlled Absorption System Formulations

Tamsulosin is an alpha(1)-adrenoceptor antagonist used for the treatment of lower urinary tract symptoms that are suggestive of benign prostatic hyperplasia. It is mostly used in a modified-release (MR) formulation, but an oral controlled absorption system (OCAS) and a 'without-water' tablet formulation are also available in some countries. The oral bioavailability of the MR formulation in the fasted state is close to 100%. Whereas absorption from the MR formulation is affected by concomitant food intake, that of the OCAS formulation is food independent. Tamsulosin exhibits high plasma-protein binding, largely to alpha(1)-acid glycoprotein. It is metabolized, mainly by cytochrome P450 (CYP) 3A4 and CYP2D6 to compounds with low abundance, and 8.7-15% of an oral dose is excreted renally as the parent compound. The pharmacokinetics of tamsulosin are not affected to a major extent by age, and pharmacokinetic alterations in renally impaired patients relate largely to an increased concentration of alpha(1)-acid glycoprotein. Pharmacokinetic alterations with hepatic impairment are also only moderate, thus neither renal nor mild to moderate hepatic impairment necessitates dose adjustment. Concomitant exposure to potent CYP3A4 inhibitors can more than double the exposure of tamsulosin. Clinical studies have indicated that despite its lower bioavailability, the OCAS formulation has the same treatment efficacy as the MR formulation but causes somewhat fewer cardiovascular adverse effects.

Effects of cranberry juice on nifedipine pharmacokinetics in rats

Little information is available about drug interactions with cranberry juice (CJ). Using microsomes from the human liver and rat small intestine, this study was designed to determine whether CJ could inhibit CYP3A-mediated nifedipine (NFP) oxidase activity; it showed that CJ was a potent inhibitor of human and rat CYP3A. Preincubation with 10% vol/vol of CJ and 1 mM NADPH for 10 min resulted in significant inhibition of the NFP oxidation activity of human and rat CYP3A (18.2 and 12.6% decreases, respectively, compared with preincubation experiments without NADPH). In addition, the pharmacokinetic interaction between CJ and NFP in vivo was confirmed in rats. In comparison with a control group, the area under the concentration-time curve (AUC) of NFP was approximately 1.6-fold higher when CJ (2 mL) was injected intraduodenally 30 min before the intraduodenal administration of NFP (30 mg kg(-1)). However, the mean residence time, the volume of distribution and the elimination rate constant were not changed significantly. These data suggest that CJ component(s) inhibit the function of enteric CYP3A. In conclusion, it was found that CJ inhibits the CYP3A-mediated metabolism of NFP in both rats and humans. Furthermore, CJ alters NFP pharmacokinetics in rats.

240: Everolimus (ERL) Drug-Drug Interaction (DDI) Management with Azole Antifungals (AF) in Lung Transplant Patients

Everolimus (ERL) was recently introduced as the second mTOR inhibitor immunosuppressant. Azoles are often prescribed for invasive fungal infection control in solid organ transplantation. Coadministration of azoles acting as potent CYP3A4 inhibitors with ERL leads to metabolic drug drug interaction (DDI). Therefore, we conducted a retrospective analysis (june 2006-april 2008) of concomitant ERL, introduced to control other immunossupressant tolerance, and azoles therapeutic drug monitoring (TDM) data to describe a quantitative evaluation of this coprescription.

In vitro inhibition of CYP3A4 and CYP2D6 activity by the horse chestnut constituents’ aescin and aesculetin

Event Abstract Back to Event In vitro inhibition of CYP3A4 and CYP2D6 activity by the horse chestnut constituents’ aescin and aesculetin Marios Spanakis1, Ioannis S. Vizirianakis1, Maria Mironidou-Tzouveleki1 and Ioannis Niopas1* 1 Aristotle University of Thessaloniki, Department of Pharmacognosy and Pharmacology, Greece Introduction. Herbal medicinal products (HMPs) are capable of modulating the metabolism through CYPs of several drugs. Horse chestnut seed extract (HCSE) derived from Aesculus hippocastanum has been found to inhibit CYP3A4 activity (Hellum and Nilsen, 2008). The aim of this study was to investigate two of the constituents of HCSE, aescin and aesculetin, for their in vitro inhibitory potential of CYP3A4 and CYP2D6. Aescin is the pharmacologically active compound of the herb and aescin is a secondary compound without attributed therapeutic properties. Methods. Dextromethorphan was used as a probe drug to simultaneously assess CYP3A4 and CYP2D6 activity. Incubations of recombinant CYPs and analysis of the formed metabolites, 3-methoxymorphinan trough CYP3A4 and dextrorphan through CYP2D6, were conducted as previously described using a validated SIM GC/MS method (Spanakis et al., 2009). Results: The mean basic control activity of dextromethorphan metabolism was estimated to be 820 ± 58 pmol/CYP pmol/min for CYP3A4 and 75.5 ± 3.7 pmol/CYP pmol/min for CYP2D6. The estimated IC50 values for aescin were 12.1 ± 1.6 μΜ for CYP3A4 and 24.3 ± 5.3 μΜ for CYP2D6 and for aesculetin were 6.18 ± 1.3 μΜ for CYP3A4 and 39.2 ± 5.7 μΜ for CYP2D6, respectively. Conclusion. The results of the present study showed that aesculetin is a more potent inhibitor of CYP3A4 than aescin suggesting that it may also contribute to the previously observed CYP3A4 inhibitory effect found for HCSE. Moreover, both compounds showed to be inhibitors of CYP2D6.