Extension de temps QT
Effets indésirables des médicaments
Variantes ✨Pour l'évaluation intensive en calcul des variantes, veuillez choisir l'abonnement standard payant.
Explications pour les patients
Les changements d'exposition mentionnés sont liés aux changements de la courbe concentration plasmatique en fonction du temps [ASC]. L'exposition à la simvastatine est réduite à 13%, lorsqu'il est associé à la amiodarone (157%) et à la rifampicine (12%). Étant donné que la substance est une prodrogue, nous nous attendrions à plus d'effets secondaires ici. Nous n'avons détecté aucune modification de l'exposition à la amiodarone. Nous ne pouvons actuellement pas estimer l'influence de la simvastatine et de la rifampicine. Nous n'avons détecté aucune modification de l'exposition à la rifampicine. Nous ne pouvons actuellement pas estimer l'influence de la simvastatine et de la amiodarone.
Les paramètres pharmacocinétiques de la population moyenne sont utilisés comme point de départ pour calculer les changements individuels d'exposition dus aux interactions.
La simvastatine a une faible biodisponibilité orale [ F ] de 5%, c'est pourquoi la concentration plasmatique maximale [Cmax] a tendance à changer de manière significative avec une interaction. La demi-vie terminale [ t12 ] est de 7.9 heures et les taux plasmatiques constants [ Css ] sont atteints après environ 9 999 heures. La liaison aux protéines [ Pb ] est 96.5% forte et le volume de distribution [ Vd ] est de 46 litres dans la fourchette moyenne, Le métabolisme s'effectue principalement via le CYP3A4 et le transport actif s'effectue en partie via BCRP, MRP2 et PGP.
La amiodarone a une biodisponibilité orale moyenne [ F ] de 55%, raison pour laquelle les concentrations plasmatiques maximales [Cmax] ont tendance à changer avec une interaction. La demi-vie terminale [ t12 ] est assez longue à 1884 heures et des taux plasmatiques constants [ Css ] ne sont atteints qu’après plus de 7536 heures. La liaison aux protéines [ Pb ] est 96% forte. Le métabolisme a lieu via le CYP2C8 et le CYP3A4, entre autres et le transport actif se fait notamment via PGP.
La rifampicine a une biodisponibilité orale élevée [ F ] de 90%, raison pour laquelle les concentrations plasmatiques maximales [Cmax] ont tendance à peu changer pendant une interaction. La demi-vie terminale [ t12 ] est assez courte à 3.5 heures et des taux plasmatiques constants [ Css ] sont atteints rapidement. La liaison aux protéines [ Pb ] est modérément forte à 75% et le volume de distribution [ Vd ] est très important à 101 litres. Le métabolisme ne se fait pas via les cytochromes communs et le transport actif s'effectue en partie via OATP1B1, OATP1B3 et PGP.
|Les scores||∑ Points||sim||ami||rif|
|Effets sérotoninergiques a||0||Ø||Ø||Ø|
Évaluation: Selon nos connaissances, ni la simvastatine, amiodarone ni la rifampicine n'augmentent l'activité sérotoninergique.
|Les scores||∑ Points||sim||ami||rif|
Évaluation: Selon nos résultats, ni la simvastatine, amiodarone ni la rifampicine n'augmentent l'activité anticholinergique.
Extension de temps QT
|Les scores||∑ Points||sim||ami||rif|
Évaluation: La amiodarone peut déclencher des arythmies ventriculaires potentiellement de torsades de pointes. Nous ne connaissons aucun potentiel d'allongement de l'intervalle QT pour la simvastatine et la rifampicine.
Effets secondaires généraux
|Effets secondaires||∑ la fréquence||sim||ami||rif|
|La nausée||26.5 %||5.4↓||21.5||+|
|Phosphatase alcaline élevée||10.0 %||n.a.||n.a.||10.0|
|GGT élevé||10.0 %||n.a.||n.a.||10.0|
|Transaminases élevées||10.0 %||n.a.||n.a.||10.0|
|Perte d'appétit||7.4 %||n.a.||6.5||+|
|Douleur abdominale||7.3 %||7.3↓||n.a.||n.a.|
Ataxie (6.5%): amiodarone
Problème de coordination (6.5%): amiodarone
Vertiges (6.5%): amiodarone
Paresthésie (6.5%): amiodarone
Mal de crâne (5%): simvastatine
Neuropathie périphérique: amiodarone
Pseudotumeur cérébrale: amiodarone
Vision floue (6.5%): amiodarone
Névrite optique: amiodarone, rifampicine
Perte visuelle: amiodarone
Hyperthyroïdie (2%): amiodarone
Syndrome de détresse respiratoire aiguë (2%): amiodarone
Fibrose pulmonaire: amiodarone
Insuffisance cardiaque: amiodarone
Arythmie ventriculaire: amiodarone
La diarrhée: rifampicine
Réaction d'hypersensibilité: amiodarone
Réaction anaphylactique: rifampicine
Syndrome de Stevens-Johnson: amiodarone
Nécrolyse épidermique toxique: amiodarone
Purpura thrombotique thrombotique: rifampicine
Hépatite cholestatique: simvastatine
Jaunisse: simvastatine, rifampicine
Insuffisance hépatique: simvastatine, rifampicine
Pancréatite: simvastatine, rifampicine
Insuffisance rénale: amiodarone
Rupture du tendon: simvastatine
Sur la base de vos
Abstract: We investigated the pharmacokinetics of rifampicin and its major metabolites, 25-desacetylrifampicin and 3-formylrifampicin, in two groups of six patients with active pulmonary tuberculosis, who received either multiple oral or intravenous rifampicin therapy in combination with intravenous isoniazid and ethambutol. Serum concentrations of rifampicin were each determined after a single oral and intravenous test dose of 600 mg rifampicin at the beginning and after 1 and 3 weeks of tuberculostatic treatment. Analysis of rifampicin and its metabolites was performed by high-pressure liquid chromatography. It was found that, due to autoinduction of its metabolizing hepatic enzymes, the systemic clearance of rifampicin increased from 5.69 to 9.03 l/h after 3 weeks of multiple dosing. The volume of distribution of the drug was constant over the period of this study. The bioavailability of the active, orally administered rifampicin decreased from 93% after the first single oral dose to 68% after 3 weeks of oral and intravenous rifampicin therapy. Relating to the increase in systemic (hepatic) clearance, a bioavailability no lower than 90% can be predicted. The reduction to 68% indicates that, in addition to an increase of hepatic metabolism, an induction of a prehepatic "first-pass" effect resulted from multiple rifampicin doses. Our study of rifampicin metabolites confirm that prehepatic metabolism was induced, since a higher metabolic ratio resulted after the oral doses than after the intravenous rifampicin test doses. A preabsorptive process can therefore be excluded as a cause of reduced bioavailability.
Abstract: Amiodarone is considered to be safe in patients with prior QT prolongation and torsades de pointes taking class I antiarrhythmic agents who require continued antiarrhythmic drug therapy. However, the safety of amiodarone in advanced heart failure patients with a history of drug-induced torsades de pointes, who may be more susceptible to proarrhythmia, is unknown. Therefore, the objective of this study was to assess amiodarone safety and efficacy in heart failure patients with prior antiarrhythmic drug-induced torsades de pointes. We determined the history of torsades de pointes in 205 patients with heart failure treated with amiodarone, and compared the risk of sudden death in patients with and without such a history. To evaluate the possibility that all patients with a history of torsades de pointes would be at high risk for sudden death regardless of amiodarone treatment, we compared this risk in patients with a history of torsades de pointes who were and were not subsequently treated with amiodarone. Of 205 patients with advanced heart failure, 8 (4%) treated with amiodarone had prior drug-induced torsades de pointes. Despite similar severity of heart failure, the 1-year actuarial sudden death risk was markedly increased in amiodarone patients with than without prior torsades de pointes (55% vs 15%, p = 0.0001). Similarly, the incidence of 1-year sudden death was markedly increased in patients with prior torsades de pointes taking amiodarone compared with such patients who were not subsequently treated with amiodarone (55% vs 0%, p = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: OBJECTIVE: To study the effects of erythromycin and verapamil on the pharmacokinetics of simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. METHODS: A randomized, double-blind crossover study was performed with three phases separated by a washout period of 3 weeks. Twelve young, healthy volunteers took orally either 1.5 gm/day erythromycin, 240 mg/day verapamil, or placebo for 2 days. On day 2, 40 mg simvastatin was administered orally. Serum concentrations of simvastatin, simvastatin acid, erythromycin, verapamil, and norverapamil were measured for up to 24 hours. RESULTS: Erythromycin and verapamil increased mean peak serum concentration (Cmax) of unchanged simvastatin 3.4-fold (p < 0.001) and 2.6-fold (p < 0.05) and the area under the serum simvastatin concentration-time curve from time zero to 24 hours [AUC(0-24)] 6.2-fold (p < 0.001) and 4.6-fold (p < 0.01). Erythromycin increased the mean Cmax of active simvastatin acid fivefold (p < 0.001) and the AUC(0-24) 3.9-fold (p < 0.001). Verapamil increased the Cmax of simvastatin acid 3.4-fold (p < 0.001) and the AUC(0-24) 2.8-fold (p < 0.001). There was more than tenfold interindividual variability in the extent of simvastatin interaction with both erythromycin and verapamil. CONCLUSIONS: Both erythromycin and verapamil interact considerably with simvastatin, probably by inhibiting its cytochrome P450 (CYP) 3A4-mediated metabolism. Concomitant administration of erythromycin, verapamil, or other potent inhibitors of CYP3A4 with simvastatin should be avoided. As an alternative, the dosage of simvastatin should be reduced considerably, that is, by about 50% to 80%, at least when a simvastatin dosage higher than 20 mg/day is used. Possible adverse effects, such as elevation of creatine kinase level and muscle tenderness, should be closely monitored when such combinations are used.
Abstract: BACKGROUND: Simvastatin is a cholesterol-lowering agent that is metabolized through CYP3A4. We studied the effect of grapefruit juice on the pharmacokinetics of orally administered simvastatin. METHODS: In a randomized, 2-phase crossover study, 10 healthy volunteers took either 200 mL double-strength grapefruit juice or water 3 times a day for 2 days. On day 3, each subject ingested 60 mg simvastatin with either 200 mL grapefruit juice or water, and an additional 200 mL was ingested 1/2 and 1 1/2 hours after simvastatin administration. Serum concentrations of simvastatin and simvastatin acid were measured by liquid chromatography-tandem mass spectrometry (LC-MS-MS) and those of active (naive) and total (after hydrolysis) 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors by a radioenzyme inhibition assay. RESULTS: Grapefruit juice increased the mean peak serum concentration (Cmax) of unchanged simvastatin about 9-fold (range, 5.1-fold to 31.4-fold; P < .01) and the mean area under the serum simvastatin concentration-time curve [AUC(0-infinity)] 16-fold (range, 9.0-fold to 37.7-fold; P < .05). The mean Cmax and AUC(0-infinity) of simvastatin acid were both increased about 7-fold (P < .01). Grapefruit juice increased the mean AUC(0-infinity) of active and total HMG-CoA reductase inhibitors 2.4-fold (P < .01) and 3.6-fold (P < .01), respectively. The time of the peak concentration of active and total HMG-CoA reductase inhibitors was increased by grapefruit juice (P < .05). CONCLUSION: Grapefruit juice greatly increased serum concentrations of simvastatin and simvastatin acid and, to a lesser extent, those of active and total HMG-CoA reductase inhibitors. The probable mechanism of this interaction was inhibition of CYP3A4-mediated first-pass metabolism of simvastatin by grapefruit juice in the small intestine. Concomitant use of grapefruit juice and simvastatin, at least in large amounts, should be avoided, or the dose of simvastatin should be greatly reduced.
Abstract: A novel human organic transporter, OATP2, has been identified that transports taurocholic acid, the adrenal androgen dehydroepiandrosterone sulfate, and thyroid hormone, as well as the hydroxymethylglutaryl-CoA reductase inhibitor, pravastatin. OATP2 is expressed exclusively in liver in contrast to all other known transporter subtypes that are found in both hepatic and nonhepatic tissues. OATP2 is considerably diverged from other family members, sharing only 42% sequence identity with the four other subtypes. Furthermore, unlike other subtypes, OATP2 did not transport digoxin or aldosterone. The rat isoform oatp1 was also shown to transport pravastatin, whereas other members of the OATP family, i.e. rat oatp2, human OATP, and the prostaglandin transporter, did not. Cis-inhibition studies indicate that both OATP2 and roatp1 also transport other statins including lovastatin, simvastatin, and atorvastatin. In summary, OATP2 is a novel organic anion transport protein that has overlapping but not identical substrate specificities with each of the other subtypes and, with its liver-specific expression, represents a functionally distinct OATP isoform. Furthermore, the identification of oatp1 and OATP2 as pravastatin transporters suggests that they are responsible for the hepatic uptake of this liver-specific hydroxymethylglutaryl-CoA reductase inhibitor in rat and man.
Abstract: BACKGROUND: Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase that is used as a cholesterol-lowering agent and is metabolized by cytochrome P450 3A (CYP3A) enzymes. Diltiazem is a substrate and an inhibitor of CYP3A enzymes and is commonly coadministered with cholesterol-lowering agents such as simvastatin. The objective of this study was to quantify the effect of diltiazem on the pharmacokinetics of simvastatin. METHOD: A fixed-order study was conducted in 10 healthy volunteers with a 2-week washout period between the phases. In one arm of the study, a single 20-mg dose of simvastatin was administered orally; the second arm entailed administration of a single 20-mg dose of simvastatin orally after 2 weeks of treatment with 120 mg diltiazem twice a day. RESULTS: Diltiazem significantly increased the mean peak serum concentration of simvastatin by 3.6-fold (P < .05) and simvastatin acid by 3.7-fold (P < .05). Diltiazem also significantly increased the area under the serum concentration-time curve of simvastatin 5-fold (P < .05) and the elimination half-life 2.3-fold (P < .05). There was no change in the time to peak concentration for simvastatin and simvastatin acid. CONCLUSION: Diltiazem coadministration resulted in a significant interaction with simvastatin, probably by inhibiting CYP3A-mediated metabolism. Concomitant use of diltiazem or other potent inhibitors of CYP3A with simvastatin should be avoided, or close clinical monitoring should be used.
Abstract: BACKGROUND: Concomitant treatment with simvastatin and gemfibrozil, two lipid-lowering drugs, has been associated with occurrence of myopathy in case reports. The aim of this study was to determine whether gemfibrozil affects the pharmacokinetics of simvastatin and whether it affects CYP3A4 activity in vitro. METHODS: A double-blind, randomized crossover study with two phases (placebo and gemfibrozil) was carried out. Ten healthy volunteers were given gemfibrozil (600 mg twice daily) or placebo orally for 3 days. On day 3 they ingested a single 40-mg dose of simvastatin. Plasma concentrations of simvastatin and simvastatin acid were measured up to 12 hours. In addition, the effect of gemfibrozil (0 to 1,200 micromol/L) on midazolam 1'-hydroxylation, a CYP3A4 model reaction, was investigated in human liver microsomes in vitro. RESULTS: Gemfibrozil increased the mean total area under the plasma concentration-time curve of simvastatin [AUC(0-infinity)] by 35% (P < .01) and the AUC(0-infinity) of simvastatin acid by 185% (P < .001). The elimination half-life of simvastatin was increased by 74% (P < .05), and that of simvastatin acid was increased by 51% (P < .01) by gemfibrozil. The peak concentration of simvastatin acid was increased by 112%, from 3.20 +/- 2.73 ng/mL to 6.78 +/- 4.67 ng/mL (mean +/- SD; P < .01). In vitro, gemfibrozil showed no inhibition of midazolam 1'-hydroxylation. CONCLUSIONS: Gemfibrozil increases plasma concentrations of simvastatin and, in particular, its active form, simvastatin acid, suggesting that the increased risk of myopathy in combination treatment is, at least partially, of a pharmacokinetic origin. Because gemfibrozil does not inhibit CYP3A4 in vitro, the mechanism of the pharmacokinetic interaction is probably inhibition of non-CYP3A4-mediated metabolism of simvastatin acid.
Abstract: BACKGROUND: Rifampin (rifampicin) is a potent inducer of several cytochrome P450 (CYP) enzymes, including CYP3A4. The cholesterol-lowering drug simvastatin has an extensive first-pass metabolism, and it is partially metabolized by CYP3A4. This study was conducted to investigate the effect of rifampin on the pharmacokinetics of simvastatin. METHODS: In a randomized cross-over study with two phases and a washout of 4 weeks, 10 healthy volunteers received a 5-day pretreatment with rifampin (600 mg daily) or placebo. On day 6, a single 40-mg dose of simvastatin was administered orally. Plasma concentrations of simvastatin and its active metabolite simvastatin acid were measured up to 12 hours with a sensitive liquid chromatography-ion spray tandem mass spectrometry method. RESULTS: Rifampin decreased the total area under the plasma concentration-time curve of simvastatin and simvastatin acid by 87% (P < .001) and 93% (P < .001), respectively. Also the peak concentrations of both simvastatin and simvastatin acid were reduced greatly (by 90%) by rifampin (P < .001). On the other hand, rifampin had no significant effect on the elimination half-life of simvastatin or simvastatin acid. CONCLUSIONS: Rifampin greatly decreases the plasma concentrations of simvastatin and simvastatin acid. Because the elimination half-life of simvastatin was not affected by rifampin, induction of the CYP3A4-mediated first-pass metabolism of simvastatin in the intestine and the liver probably explains this interaction. Concomitant use of potent inducers of CYP3A4 can lead to a considerably reduced cholesterol-lowering efficacy of simvastatin.
Abstract: The antibiotics rifamycin SV and rifampicin substantially reduce sulfobromophthalein (BSP) elimination in humans. In rats, rifamycin SV and rifampicin were shown to interfere with hepatic organic anion uptake by inhibition of the organic anion transporting polypeptides Oatp1 and Oatp2. Therefore, we investigated the effects of rifamycin SV and rifampicin on the OATPs of human liver and determined whether rifampicin is a substrate of 1 or several of these carriers. In complementary RNA (cRNA)-injected Xenopus laevis oocytes, rifamycin SV (10 micromol/L) cis-inhibited human organic anion transporting polypeptide C (SLC21A6) (OATP-C), human organic anion transporting polypeptide 8 (SLC21A8) (OATP8), human organic anion transporting polypeptide B (SLC21A9) (OATP-B), and human organic anion transporting polypeptide A (SLC21A3) (OATP-A) mediated BSP uptake by 69%, 79%, 89%, and 57%, respectively, as compared with uptake into control oocytes. In the presence of 100 micromol/L rifamycin SV, BSP uptake was almost completely abolished. Approximate K(i) values were 2 micromol/L for OATP-C, 3 micromol/L for OATP8, 3 micromol/L for OATP-B and 11 micromol/L for OATP-A. Rifampicin (10 micromol/L) inhibited OATP8-mediated BSP uptake by 50%, whereas inhibition of OATP-C-, OATP-B-, and OATP-A-mediated BSP transport was below 15%. 100 micromol/L rifampicin inhibited OATP-C- and OATP8-, OATP-B- and OATP-A-mediated BSP uptake by 66%, 96%, 25%, and 49%, respectively. The corresponding K(i) values were 17 micromol/L for OATP-C, 5 micromol/L for OATP8, and 51 micromol/L for OATP-A. Direct transport of rifampicin could be shown for OATP-C (apparent K(m) value 13 micromol/L) and OATP8 (2.3 micromol/L). In conclusion, these results show that rifamycin SV and rifampicin interact with OATP-mediated substrate transport to different extents. Inhibition of human liver OATPs can explain the previously observed effects of rifamycin SV and rifampicin on hepatic organic anion elimination.
Abstract: Rifampin, a member of the rifamycin class of antibiotics, is well known for its ability to induce drug-metabolizing enzymes and transporters, through activation of the pregnane X receptor. Available data suggest rifampin entry into hepatocytes may be transporter-mediated. Accordingly, it is therefore plausible that modulation of the achievable intracellular concentration of rifampin by drug uptake transporters would influence the degree of induction. In this study, we expressed an array of known hepatic uptake transporters to show the key hepatic rifampin uptake transporters are liver-specific members of the organic anion transporting polypeptide family (OATP). Indeed, both OATP-C and OATP8 seemed capable of mediating rifampin uptake into HeLa cells. OATP-C, however, seemed to have far greater affinity and capacity for rifampin transport. In addition, several allelic variants of OATP-C known to be present among European and African Americans were found to have markedly decreased rifampin transport activity. In cell-based, transactivation assays, OATP-C expression was associated with increased cellular rifampin retention as well as potentiation of PXR reporter gene activity. This is the first demonstration of an uptake transporter such as OATP-C, in modulating PXR function, and sheds important new insight into our understanding of the molecular determinants of PXR-mediated inductive processes.
Abstract: OBJECTIVE: The aim of this study was to examine the effect of carbamazepine on the pharmacokinetics of orally administered simvastatin in healthy volunteers. METHODS: In a randomised, two-phase crossover study and a wash out of 2 weeks, 12 healthy volunteers took carbamazepine for 14 days (600 mg daily except 200 mg daily for the first 2 days) or no drug. On day 15, each subject ingested 80 mg simvastatin. Serum concentrations of simvastatin and its active metabolite simvastatin acid were measured up to 24 h. RESULTS: Carbamazepine decreased the mean total area under the serum concentration-time curve of simvastatin and simvastatin acid by 75% ( P<0.001) and 82% ( P<0.001), respectively. The mean peak concentrations of both simvastatin and simvastatin acid were reduced by 68% ( P<0.01), and half-life of simvastatin acid was shortened from 5.9+/-0.3 h to 3.7+/-0.5 h ( P<0.01) by carbamazepine. CONCLUSION: Carbamazepine greatly reduces the serum concentrations of simvastatin and simvastatin acid, probably by inducing their metabolism. Concomitant administration of carbamazepine and simvastatin should be avoided or the dose of simvastatin should be considerably increased.
Abstract: The aim of this pharmacokinetic evaluation was to show the effect of the extra methyl group in simvastatin on esterase hydrolysis between lovastatin and simvastatin in male and female volunteers. This study was based on the plasma concentration-time curves and the pharmacokinetics of lovastatin and simvastatin with its respective active metabolite statin-beta-hydroxy acid obtained from two different bioequivalence studies, each with 18 females and 18 males. Results were: The group of female volunteers showed a higher yield of the active metabolite beta-hydroxy acid than the group of males (p < 0.002) for both lovastatin and simvastatin. This difference was not related to the body weight of both groups. In the male/female groups, subject-dependent yield of active metabolite beta-hydroxy acid was demonstrated, which was independent of the formulation. The variation in plasma/liver hydrolysis resulted in a fan-shaped distribution of data points when the AUCt lovastatin was plotted vs. that of the beta-hydroxy acid metabolite. In the fan of data points, subgroups could be distinguished, each showing a different regression line and with a different Y-intercept (AUCtbeta-hydroxy acid). Lovastatin hydrolysis was higher than simvastatin hydrolysis. It was possible to discriminate between hydrolysis of both lovastatin and simvastatin by plasma/liver or tissue esterase activity. The three subgroups of subjects (males/females) showing different but high yield of statin beta-hydroxy acid can be explained by variable hydrolysis of plasma and hepatic microsomal and cytosolic carboxyesterase activity. This study showed clearly that despite the subject-dependent hydrolysis of lovastatin/simvastatin to the active metabolite, males tend to hydrolyse less than females. The extra methyl group in simvastatin results in less hydrolysis due to steric hindrance.
Abstract: PURPOSE: In this study, P-glycoprotein (P-gp) mediated efflux of simvastatin (SV), simvastatin acid (SVA), and atorvastatin (AVA) and inhibition of P-gp by SV, SVA, and AVA were evaluated to assess the role of P-gp in drug interactions. METHODS: P-gp mediated efflux of SV, SVA, and AVA was determined by directional transport across monolayers of LLC-PK1 cells and LLC-PK1 cells transfected with human MDR1. Inhibition of P-gp was evaluated by studying the vinblastine efflux in Caco-2 cells and in P-gp overexpressing KBV1 cells at concentrations of SV, SVA, and AVA up to 50 microM. RESULTS: Directional transport studies showed insignificant P-gp mediated efflux of SV, and moderate P-gp transport [2.4-3.8 and 3.0-6.4 higher Basolateral (B) to Apical (A) than A to B transport] for SVA and AVA, respectively. Inhibition studies did not show the same trend as the transport studies with SV and AVA inhibiting P-gp (IC50 -25-50 microM) but SVA not showing any inhibition of P-gp. CONCLUSIONS: The moderate level of P-gp mediated transport and low affinity of SV, SVA, and AVA for P-gp inhibition compared to systemic drug levels suggest that drug interactions due to competition for P-gp transport is unlikely to be a significant factor in adverse drug interactions. Moreover, the inconsistencies between P-gp inhibition studies and P-gp transport of SV, SVA, and AVA indicate that the inhibition studies are not a valid means to identify statins as Pgp substrates.
Abstract: Statins are the treatment of choice for the management of hypercholesterolaemia because of their proven efficacy and safety profile. They also have an increasing role in managing cardiovascular risk in patients with relatively normal levels of plasma cholesterol. Although all statins share a common mechanism of action, they differ in terms of their chemical structures, pharmacokinetic profiles, and lipid-modifying efficacy. The chemical structures of statins govern their water solubility, which in turn influences their absorption, distribution, metabolism and excretion. Lovastatin, pravastatin and simvastatin are derived from fungal metabolites and have elimination half-lives of 1-3 h. Atorvastatin, cerivastatin (withdrawn from clinical use in 2001), fluvastatin, pitavastatin and rosuvastatin are fully synthetic compounds, with elimination half-lives ranging from 1 h for fluvastatin to 19 h for rosuvastatin. Atorvastatin, simvastatin, lovastatin, fluvastatin, cerivastatin and pitavastatin are relatively lipophilic compounds. Lipophilic statins are more susceptible to metabolism by the cytochrome P(450) system, except for pitavastatin, which undergoes limited metabolism via this pathway. Pravastatin and rosuvastatin are relatively hydrophilic and not significantly metabolized by cytochrome P(450) enzymes. All statins are selective for effect in the liver, largely because of efficient first-pass uptake; passive diffusion through hepatocyte cell membranes is primarily responsible for hepatic uptake of lipophilic statins, while hydrophilic agents are taken up by active carrier-mediated processes. Pravastatin and rosuvastatin show greater hepatoselectivity than lipophilic agents, as well as a reduced potential for uptake by peripheral cells. The bioavailability of the statins differs greatly, from 5% for lovastatin and simvastatin to 60% or greater for cerivastatin and pitavastatin. Clinical studies have demonstrated rosuvastatin to be the most effective for reducing low-density lipoprotein cholesterol, followed by atorvastatin, simvastatin and pravastatin. As a class, statins are generally well tolerated and serious adverse events, including muscle toxicity leading to rhabdomyolysis, are rare. Consideration of the differences between the statins helps to provide a rational basis for their use in clinical practice.
Abstract: If tuberculosis therapy is to be shortened it is imperative that the sterilising activity of current and future anti-tuberculosis drugs is enhanced. Intracellular Mycobacterium tuberculosis (MTB) phagocytosed by macrophages may be a key subpopulation of bacteria that are less readily eliminated by therapy. Here we investigate whether macrophages provide MTB with a pharmacological sanctuary site, making them less susceptible to chemotherapy than extracellular bacilli. Intracellular drug activity was determined by a novel colorimetric method that measures the ability of a drug to protect A-THP1 cells from infection-mediated cell death by H37Rv. Extracellular bactericidal activity was determined by the microplate alamar blue assay (MABA). Further, the effect of P-glycoprotein (P-gp) expressed on macrophages on the intracellular kill of H37Rv was assessed. To screen the anti-tuberculosis drugs for P-gp substrate specificity, their toxicity and cellular accumulation were determined in CEM and CEM(VBL100) cells. Intracellular and extracellular anti-tuberculosis drug activity following 7-day treatment with isoniazid (mean EC(50)+/-SD: 36.7+/-2.2 and 57.2+/-2.5 ng/mL, respectively) and ethambutol (243+/-95 and 263+/-12 ng/mL, respectively) were similar. However, for rifampicin a higher concentration was required to kill intracellular (148+/-32 ng/mL) versus extracellular (1.27+/-0.02 ng/mL) bacilli. The P-gp inhibitor tariquidar, significantly increased intracellular kill of H37Rv by ethambutol and rifampicin and both of these drugs were shown to be substrates for P-gp using the P-gp overexpressing CEM(VBL100) cells. We observed a large discrepancy between intracellular and extracellular activity of rifampicin (but not with isoniazid or ethambutol). Several factors could have accounted for this including inoculum size, media and cell-mediated metabolism. These factors make the comparison of intracellular and extracellular drug activity complex. However, the intracellular assay described here has potential for studying the impact of host proteins (such as drug transporters) on the intracellular activity of drugs, and has been used successfully here to demonstrate that both rifampicin and ethambutol are substrates for P-gp.
Abstract: The human organic anion and cation transporters are classified within two SLC superfamilies. Superfamily SLCO (formerly SLC21A) consists of organic anion transporting polypeptides (OATPs), while the organic anion transporters (OATs) and the organic cation transporters (OCTs) are classified in the SLC22A superfamily. Individual members of each superfamily are expressed in essentially every epithelium throughout the body, where they play a significant role in drug absorption, distribution and elimination. Substrates of OATPs are mainly large hydrophobic organic anions, while OATs transport smaller and more hydrophilic organic anions and OCTs transport organic cations. In addition to endogenous substrates, such as steroids, hormones and neurotransmitters, numerous drugs and other xenobiotics are transported by these proteins, including statins, antivirals, antibiotics and anticancer drugs. Expression of OATPs, OATs and OCTs can be regulated at the protein or transcriptional level and appears to vary within each family by both protein and tissue type. All three superfamilies consist of 12 transmembrane domain proteins that have intracellular termini. Although no crystal structures have yet been determined, combinations of homology modelling and mutation experiments have been used to explore the mechanism of substrate recognition and transport. Several polymorphisms identified in members of these superfamilies have been shown to affect pharmacokinetics of their drug substrates, confirming the importance of these drug transporters for efficient pharmacological therapy. This review, unlike other reviews that focus on a single transporter family, briefly summarizes the current knowledge of all the functionally characterized human organic anion and cation drug uptake transporters of the SLCO and the SLC22A superfamilies.
Abstract: Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.
Abstract: This study aimed to construct a physiologically based pharmacokinetic (PBPK) model of rifampicin that can accurately and quantitatively predict complex drug-drug interactions (DDIs) involving its saturable hepatic uptake and auto-induction. Using in silico and in vitro parameters, and reported clinical pharmacokinetic data, rifampicin PBPK model was built and relevant parameters for saturable hepatic uptake and UDP-glucuronosyltransferase (UGT) auto-induction were optimized by fitting. The parameters for cytochrome P450 (CYP) 3A and CYP2C9 induction by rifampicin were similarly optimized using clinical DDI data with midazolam and tolbutamide as probe substrates, respectively. For validation, our current PBPK model was applied to simulate complex DDIs with glibenclamide (a substrate of CYP3A/2C9 and hepatic organic anion transporting polypeptides (OATPs)). Simulated results were in quite good accordance with the observed data. Altogether, our constructed PBPK model of rifampicin demonstrates the robustness and utility in quantitatively predicting CYP3A/2C9 induction-mediated and/or OATP inhibition-mediated DDIs with victim drugs.
Abstract: BACKGROUND: The most common acquired cause of Long QT syndrome (LQTS) is drug induced QT interval prolongation. It is an electrophysiological entity, which is characterized by an extended duration of the ventricular repolarization. Reflected as a prolonged QT interval in a surface ECG, this syndrome increases the risk for polymorphic ventricular tachycardia (Torsade de Pointes) and sudden death. METHOD: Bibliographic databases as MEDLINE and EMBASE, reports and drug alerts from several regulatory agencies (FDA, EMEA, ANMAT) and drug safety guides (ICH S7B, ICH E14) were consulted to prepare this article. The keywords used were: polymorphic ventricular tachycardia, adverse drug events, prolonged QT, arrhythmias, intensive care unit and Torsade de Pointes. Such research involved materials produced up to December 2017. RESULTS: Because of their mechanism of action, antiarrhythmic drugs such as amiodarone, sotalol, quinidine, procainamide, verapamil and diltiazem are associated to the prolongation of the QTc interval. For this reason, they require constant monitoring when administered. Other noncardiovascular drugs that are widely used in the Intensive Care Unit (ICU), such as ondansetron, macrolide and fluoroquinolone antibiotics, typical and atypical antipsychotics agents such as haloperidol, thioridazine, and sertindole are also frequently associated with the prolongation of the QTc interval. As a consequence, critical patients should be closely followed and evaluated. CONCLUSION: ICU patients are particularly prone to experience a QTc interval prolongation mainly for two reasons. In the first place, they are exposed to certain drugs that can prolong the repolarization phase, either by their mechanism of action or through the interaction with other drugs. In the second place, the risk factors for TdP are prevalent clinical conditions among critically ill patients. As a consequence, the attending physician is expected to perform preventive monitoring and ECG checks to control the QTc interval.
Abstract: Amiodarone is one of the most commonly used antiarrhythmic drugs. Despite its well-known side effects, amiodarone is considered to be a relatively safe drug, especially in short-term usage to prevent life-threatening ventricular arrhythmias. Our case demonstrates an instance where short-term usage can yield drug side effect.
Abstract: The introduction of rifampicin (rifampin) into tuberculosis (TB) treatment five decades ago was critical for shortening the treatment duration for patients with pulmonary TB to 6 months when combined with pyrazinamide in the first 2 months. Resistance or hypersensitivity to rifampicin effectively condemns a patient to prolonged, less effective, more toxic, and expensive regimens. Because of cost and fears of toxicity, rifampicin was introduced at an oral daily dose of 600 mg (8-12 mg/kg body weight). At this dose, clinical trials in 1970s found cure rates of ≥ 95% and relapse rates of < 5%. However, recent papers report lower cure rates that might be the consequence of increased emergence of resistance. Several lines of evidence suggest that higher rifampicin doses, if tolerated and safe, could shorten treatment duration even further. We conducted a narrative review of rifampicin pharmacokinetics and pharmacodynamics in adults across a range of doses and highlight variables that influence its pharmacokinetics/pharmacodynamics. Rifampicin exposure has considerable inter- and intra-individual variability that could be reduced by administration during fasting. Several factors including malnutrition, HIV infection, diabetes mellitus, dose size, pharmacogenetic polymorphisms, hepatic cirrhosis, and substandard medicinal products alter rifampicin exposure and/or efficacy. Renal impairment has no influence on rifampicin pharmacokinetics when dosed at 600 mg. Rifampicin maximum (peak) concentration (C) > 8.2 μg/mL is an independent predictor of sterilizing activity and therapeutic drug monitoring at 2, 4, and 6 h post-dose may aid in optimizing dosing to achieve the recommended rifampicin concentration of ≥ 8 µg/mL. A higher rifampicin Cis required for severe forms TB such as TB meningitis, with C≥ 22 μg/mL and area under the concentration-time curve (AUC) from time zero to 6 h (AUC) ≥ 70 μg·h/mL associated with reduced mortality. More studies are needed to confirm whether doses achieving exposures higher than the current standard dosage could translate into faster sputum conversion, higher cure rates, lower relapse rates, and less mortality. It is encouraging that daily rifampicin doses up to 35 mg/kg were found to be safe and well-tolerated over a period of 12 weeks. High-dose rifampicin should thus be considered in future studies when constructing potentially shorter regimens. The studies should be adequately powered to determine treatment outcomes and should include surrogate markers of efficacy such as C/MIC (minimum inhibitory concentration) and AUC/MIC.