Concentrations Of Amitriptyline Research Articles

Ionic and Cellular Mechanisms Underlying the Development of Acquired Brugada Syndrome in Patients Treated with Antidepressants

Tricyclic antidepressants are known to induce cardiac arrhythmias at therapeutic or supratherapeutic doses. The tricyclic antidepressant, amitriptyline, is reported to induce ST segment elevation in the right precordial electrocardiogram (ECG) leads, thus unmasking Brugada syndrome (BrS). The mechanism by which antidepressants induce the BrS phenotype and associated sudden death is not well established. Action potentials (AP) were simultaneously recorded from epicardial and endocardial sites of isolated coronary-perfused canine right ventricular wedge preparations, together with a transmural pseudo-ECG. Amitriptyline alone (0.2 μM-1 mM) failed to induce a BrS phenotype. NS5806 (8 μM), a transient outward potassium channel current (I(to) ) agonist, was used to produce an outward shift of current mimicking a genetic predisposition to BrS. In the presence of NS5806, a therapeutic concentration of amitriptyline (0.2 μM) accentuated the epicardial AP notch leading to ST-segment elevation of the ECG. All-or-none repolarization at some epicardial sites but not others gave rise to phase-2-reentry and polymorphic ventricular tachycardia (VT) in 6 of 9 preparations. Isoproterenol (100 nM) or quinidine (10 μM) reversed the effects of amitriptyline aborting phase 2 reentry and VT (4/4). Using voltage-clamp techniques applied to isolated canine ventricular myocytes, 0.2 μM amitriptyline was shown to produce use-dependent inhibition of sodium channel current (I(Na) ), without significantly affecting I(to) (n = 5). Our data suggest that amitriptyline-induced inhibition of I(Na) unmasks the Brugada ECG phenotype and facilitates development of an arrhythmogenic substrate only in the setting of a genetic predisposition by creating repolarization heterogeneities that give rise to phase 2 reentry and VT.

Amitriptyline and clomipramine increase the concentration of administered L-tryptophan in the rat brain.

The tricyclic antidepressant amitriptyline has been shown to reduce concentrations of large neutral amino acids (LNAA) in rat plasma. Compounds with that property might interact with such amino acids used as therapeutic agents with a central site of action by causing a change in the relationship between the administered LNAA and its endogenous LNAA competitors for carrier-mediated transport through the blood-brain barrier into the brain. This study was performed to investigate if the antidepressant agents amitriptyline and clomipramine could, by such a mechanism, increase brain concentrations of administered tryptophan. Intraperitoneal administration of L-tryptophan alone (100 mg kg-1) resulted in an increase in the concentration of tryptophan in the rat brain from 14 +/- 0.7 to 100 +/- 4.3 nmol g-1 compared with rats given saline only. When rats were given tryptophan with amitriptyline (25 mg kg-1, i.p.) or clomipramine (25 mg kg-1, i.p.) brain concentrations of tryptophan were increased even further, to 150 +/- 4.5 and 157 +/- 10.2 nmol g-1, respectively. Administration of L-tryptophan alone resulted in an increase in the rat plasma tryptophan ratio [(concentration of tryptophan)/(total concentration of LNAAs)] from 0.14 +/- 0.003 to 0.42 +/- 0.011 compared with rats given saline only. When rats were given tryptophan with amitriptyline or clomipramine the plasma tryptophan ratios were increased even further to 0.52 +/- 0.017 and 0.54 +/- 0.025, respectively. All these effects were statistically significant (P < 0.001). These findings support the hypothesis that tricyclic antidepressants could interact with administered tryptophan by changing the relationship in plasma between tryptophan and its endogenous LNAA competitors for transport into the brain, resulting in higher concentrations of tryptophan in the brain. It is possible that this could be the mechanism of the previously reported finding that clomipramine and tryptophan potentiate each other in the treatment of depression.

Intrathecal injection of amitriptyline and doxepin for spinal anesthesia in animal studies.

Intrathecal injection of amitriptyline and doxepin for spinal anesthesia in animal studies.

Ionic and Cellular Mechanisms Underlying the Development of Acquired Brugada Syndrome in Patients Treated with Antidepressants

Background: Tricyclic antidepressants, such as amitriptyline, is reported to induce ST segment elevation in the right precordial ECG leads, thus unmasking Brugada syndrome (BrS). The mechanism by which antidepressants induce the BrS phenotype and associated sudden death is not well established. Methods and Results: Action potentials (AP) were recorded from epicardial and endocardial sites of coronary-perfused canine right ventricular wedge preparations, together with a transmural pseudo-ECG. Amitriptyline alone (0.2 µM–1 mM) failed to induce a BrS phenotype. In the presence of NS5806 (8 µM), a transient outward potassium channel current (Ito) agonist, a therapeutic concentration of amitriptyline (0.2 µM) accentuated the epicardial AP notch leading to ST-segment elevation of the ECG. All-or-none repolarization at some epicardial sites but not others gave rise to phase-2-reentry and polymorphic ventricular tachycardia (VT) in 6 of 9 preparations. Isoproterenol (100 nM) or quinidine (10 µM) reversed the effects of amitriptyline. Using voltage-clamp techniques applied to isolated cardiomyocytes, 0.2 µM amitriptyline was shown to produce use-dependent inhibition of sodium channel current (INa), without significantly affecting Ito (n=5). Conclusions: Our data suggest that amitriptyline-induced inhibition of INa unmasks the Brugada ECG phenotype and facilitates development of an arrhythmogenic substrate only in the setting of a genetic predisposition by creating repolarization heterogeneities that give rise to phase-2-reentry and VT.

Validated assay for studying activity profiles of human liver UGTs after drug exposure: inhibition and induction studies

UDP-glucuronsyltransferases (UGTs) are a family of conjugating enzymes that participate in the metabolism of many drugs. The study of potential drug-drug interactions involving UGTs has been largely hindered by the limited availability of selective functional assays for individual UGT enzymes. We propose a sensitive and reproducible procedure for the activity measurements of four major human hepatic UGT forms. The assays are based on analysis and quantification by high-performance liquid chromatography-tandem mass spectrometry of glucuronides formed from selective probe substrates, namely, beta-estradiol (UGT1A1, 3-glucuronide), 1-naphthol (UGT1A6), propofol (UGT1A9), and naloxone (UGT2B7). The analytical methods developed in the present study have been validated under good laboratory practice compliance following FDA recommendations. The assays can be easily applied to both phenotyping UGT reactions in liver-derived cellular and subcellular systems, and drug-drug interaction in vitro studies. Chemical inhibition of UGTs was tested in human liver microsomes at substrate concentrations lower than the corresponding K (M) values. Under these conditions, selective inhibition of UGT2B7 by fluconazole and low amitriptyline concentrations were observed, whereas diclofenac and quinidine were shown as non-enzyme-selective inhibitors of UGTs. Induction of UGTs was studied in primary human hepatocytes and HepG2 cells cultured in 96-well plates. Aryl hydrocarbon receptor ligands (except indirubin in hepatocytes) increased the UGT1A1 activity in both cell models. The highest effects were observed in HepG2 cells exposed to indirubin (21-fold over the control) and omeprazole or beta-naphthoflavone (about sixfold). Although variable effects were observed in other UGT enzymes, the degree of induction was generally lower than that for UGT1A1.

The rapid simultaneous tricyclic antidepressant determination by plasma deproteinization and liquid chromatography

Background: Imipramine, desipramine, amitriptyline and nortriptyline are widely prescribed antidepressant drugs in Asia because of their low price and high efficacy. The concentrations of these drugs in plasma need to be monitored for achieving efficient therapy. A simple, rapid and practical analytical method is required. Objective: To develop a plasma deproteinization process for rapid determination of imipramine, desipramine, amitriptyline or nortriptyline in plasma using high-performance liquid chromatography (HPLC). Methods: A deproteinizing agent, with an acceptable accuracy and sensitivity, to precipitate plasma protein containing imipramine, desipramine, amitriptyline and nortriptyline was investigated along with the HPLC condition for resolving each of these compounds. The developed method was verified by performing a bio-analytical method validation, and by analyzing plasma samples from volunteers who received imipramine or amitriptyline. Results: Using clomipramine as an internal standard, the concentrations of imipramine, desipramine, amitriptyline and nortriptyline in plasma could easily be determined by precipitating plasma protein with acetonitrile and concentrated aqueous potassium phosphate solution prior to HPLC analysis. The mobile phase comprised of acetonitrile and 70 mM phosphate buffer (pH 6.1) (60/40 v/v). A separation was achieved on a C 18 column, and the effluent was measured by UV absorption at 251 nm or by EC detection at +1.0 V of glassy carbon against silver/ silver chloride reference electrode. The chromatographic separation was excellent, without interference from endogenous plasma constituents. All compounds were resolved in a run time of 12 minutes. The method was suitable for quantifying drug concentrations in the ranges of 40-900 ng/ml for UV detection or 4-900 ng/mL for EC detection. The relative standard intra-day and inter-day deviations for each compound in the plasma were less than 8%. The percentage of bias was within ±4% which confirmed the accuracy of the method. The method proved to be efficient and practical for determining the plasma concentrations of each compound, following the administration of imipramine or amitriptyline to volunteers. Conclusion: This developed method is very simple, rapid and inexpensive and is practical for routine therapeutic drug monitoring and forensic toxicological screening.

Amitriptyline inhibits the activity of the rat glutamate transporter EAAT3 expressed in Xenopus oocytes

Abstract Objectives Evidence suggests that glutamatergic systems may be involved in the pathophysiology of major depression and the mechanism of action of antidepressants. We have investigated the effects of amitriptyline, a tricyclic antidepressant, on the activity of the excitatory amino acid transporter type 3 (EAAT3), a protein that can regulate extracellular glutamate concentrations in the brain. Methods EAAT3 was expressed in Xenopus oocytes. Using a two-electrode voltage clamp, membrane currents were recorded after application of 30 μM l-glutamate in the presence or absence of various concentrations of amitriptyline or after application of various concentrations of l-glutamate in the presence or absence of 0.64 μM amitriptyline. Key findings Amitriptyline concentration-dependently reduced EAAT3 activity. This inhibition reached statistical significance at 0.38–1.27 μM amitriptyline. Amitriptyline 0.64 μM reduced the pharmacokinetic parameter Vmax, but did not affect the pharmacokinetic parameter Km, of EAAT3 for l-glutamate. The amitriptyline inhibition disappeared after a 4-min washout. Phorbol-12-myristate-13-acetate, a protein kinase C activator, increased EAAT3 activity. However, 0.64 μM amitriptyline induced a similar degree of decrease in EAAT3 activity in the presence or absence of phorbol-12-myristate-13-acetate. Conclusions Our results suggested that amitriptyline at clinically relevant concentrations reversibly reduced EAAT3 activity via decreasing its maximal velocity of glutamate transporting function. The effects of amitriptyline on EAAT3 activity may have represented a novel site of action for amitriptyline to increase glutamatergic neuro-transmission. Protein kinase C may not have been involved in the effects of amitriptyline on EAAT3.

Low concentrations of amitriptyline inhibit nicotinic receptors in unmyelinated axons of human peripheral nerve

Amitriptyline is often prescribed as a first-line treatment for neuropathic pain but its precise mode of analgesic action remains uncertain. Amitriptyline is known to inhibit voltage-dependent ion channels and also to act as an antagonist at ligand-gated ion channels, such as nicotinic acetylcholine receptors (nAChRs). In the present study, we tested the effect of amitriptyline on nicotinic responses of unmyelinated axons in isolated segments of human peripheral nerve. In particular, a comparison was made between the concentrations of amitriptyline necessary for inhibition of nAChRs and those required for inhibition of the compound C-fibre action potential. Isolated axon fascicles were prepared from short segments of human sural nerve, and multiple measures of axonal excitability were recorded using computer-controlled threshold tracking software. Amitriptyline (EC(50) 2.6 microM) reduced the nicotine-induced increase in C-fibre excitability but only slightly altered the amplitude and latency to onset of the compound action potential. In contrast, tetrodotoxin produced a clear reduction in the amplitude and a prolongation of action potential onset latency but was without effect on the nicotine-induced increase in axonal excitability. These data demonstrate that low concentrations of amitriptyline suppress the response of human peripheral C-type axons to nicotine by directly inhibiting nAChRs. Blockade of tetrodotoxin-sensitive, voltage-dependent sodium channels does not contribute to this effect. An inhibitory action of amitriptyline on nAChRs in unmyelinated nociceptive axons may be an important component of amitriptyline's therapeutic effect in the treatment of neuropathic pain.

Interactions Between Herbal Medicines and Prescribed Drugs

The concomitant use of herbal medicines and pharmacotherapy is wide spread. We have reviewed the literature to determine the possible interactions between seven popular herbal medicines (ginkgo, St John's wort, ginseng, garlic, echinacea, saw palmetto and kava) and conventional drugs. Literature searches were performed using MEDLINE, Cochrane Library and EMBASE and we identified 128 case reports or case series, and 80 clinical trials. Clinical trials indicate that St John's wort (Hypericum perforatum), via cytochrome P450 (CYP) and/or P-glycoprotein induction, reduces the plasma concentrations (and/or increases the clearance) of alprazolam, amitriptyline, atorvastatin, chlorzoxazone, ciclosporin, debrisoquine, digoxin, erythromycin, fexofenadine, gliclazide, imatinib, indinavir, irinotecan, ivabradine, mephenytoin, methadone, midazolam, nifedipine, omeprazole, oral contraceptives, quazepam, simvastatin, tacrolimus, talinolol, verapamil, voriconazole and warfarin. Case reports or case series suggest interactions of St John's wort with adrenergic vasopressors, anaesthetics, bupropion, buspirone, ciclosporin, eletriptan, loperamide, nefazodone, nevirapine, oral contraceptives, paroxetine, phenprocoumon, prednisone, sertraline, tacrolimus, theophylline, tibolone, tryptophan, venlafaxine and warfarin. Ginkgo (Ginkgo biloba) decreases the plasma concentrations of omeprazole, ritonavir and tolbutamide. Clinical cases indicate interactions of ginkgo with antiepileptics, aspirin (acetylsalicylic acid), diuretics, ibuprofen, risperidone, rofecoxib, trazodone and warfarin. Ginseng (Panax ginseng) may interact with phenelzine and warfarin. Kava (Piper methysticum) increases the clearance of chlorzoxazone (a CYP2E1 substrate) and may interact with alprazolam, levodopa and paroxetine. Garlic (Allium sativum) interacts with chlorpropamide, fluindione, ritonavir and warfarin; it also reduces plasma concentrations of chlorzoxazone (a CYP2E1 probe). Echinacea might affect the clearance of caffeine (a CYP1A2 probe) and midazolam (a CYP3A4 probe). No interactions have been reported for saw palmetto (Serenoa repens). Numerous interactions between herbal medicines and conventional drugs have been documented. While the significance of many interactions is uncertain, several interactions, particularly those with St John's wort, may have serious clinical consequences.

Effects of amitriptyline, a tricyclic antidepressant, on smooth muscle reactivity in isolated rat trachea

This study was designed to investigate the action of amitriptyline, a tricyclic antidepressant, on airway smooth muscle reactivity and its underlying mechanisms. In isolated rat trachea, isometric force was recorded to examine the effects of amitriptyline on the contractile response to acetylcholine (ACh), electrical field stimulation (EFS), calyculin A (a myosin light chain phosphatase inhibitor), and sphingosylphosphorylcholine (SPC; a Rhokinase activator). In addition, inositol monophosphate (IP1) accumulation was measured to examine its effects on inositol 1, 4, 5-trisphosphate (IP(3)) production during stimulation with ACh. Amitriptyline inhibited the contractile responses to ACh, EFS, calyculin A, and SPC, with the concentrations of amitriptyline (mean +/- SD) required to exert 50% inhibition (IC(50)) being 4.3 +/- 1.3 microM, 3.2 +/- 1.6 microM, 256.4 +/- 106.4 microM, and 98.2 +/- 21.8 microM, respectively. In addition, amitriptyline (10 microM) eliminated the ACh (10 microM)-induced IP(1) accumulation. The results suggest that amitriptyline does not influence tracheal smooth muscle reactivity at clinical concentrations (<1 microM), but attenuates the reactivity at supraclinical concentrations (> or =1 microM). The attenuated response to ACh brought about by amitriptyline is presumably due, at least in part, to the inhibition of phosphatidylinositol (PI) metabolism. The ability of amitriptyline to inhibit the calyculin Ainduced contraction suggests that amitriptyline also inhibits the Ca(2+)-calmodulin-myosin light chain pathway independently of the inhibition of PI metabolism. Finally, the difference between the IC(50) values for SPC-induced contraction and those for calyculin A-induced contraction suggests that amitriptyline may also inhibit the Rho-kinase pathway.

Amitriptyline inhibits the activity of the rat glutamate transporter EAAT3 expressed in &lt;I&gt;Xenopus&lt;/I&gt; oocytes

Evidence suggests that glutamatergic systems may be involved in the pathophysiology of major depression and the mechanism of action of antidepressants. We have investigated the effects of amitriptyline, a tricyclic antidepressant, on the activity of the excitatory amino acid transporter type 3 (EAAT3), a protein that can regulate extracellular glutamate concentrations in the brain. EAAT3 was expressed in Xenopus oocytes. Using a two-electrode voltage clamp, membrane currents were recorded after application of 30 microM L-glutamate in the presence or absence of various concentrations of amitriptyline or after application of various concentrations of L-glutamate in the presence or absence of 0.64 microM amitriptyline. Amitriptyline concentration-dependently reduced EAAT3 activity. This inhibition reached statistical significance at 0.38-1.27 microM amitriptyline. Amitriptyline 0.64 microM reduced the pharmacokinetic parameter Vmax, but did not affect the pharmacokinetic parameter Km, of EAAT3 for L-glutamate. The amitriptyline inhibition disappeared after a 4-min washout. Phorbol-12-myristate-13-acetate, a protein kinase C activator, increased EAAT3 activity. However, 0.64 microM amitriptyline induced a similar degree of decrease in EAAT3 activity in the presence or absence of phorbol-12-myristate-13-acetate. Our results suggested that amitriptyline at clinically relevant concentrations reversibly reduced EAAT3 activity via decreasing its maximal velocity of glutamate transporting function. The effects of amitriptyline on EAAT3 activity may have represented a novel site of action for amitriptyline to increase glutamatergic neurotransmission. Protein kinase C may not have been involved in the effects of amitriptyline on EAAT3.

Roles of polymorphic enzymes CYP2D6 and CYP2C19 for in vitro metabolism of amitriptyline at therapeutic and toxic levels

The metabolism of the tricyclic antidepressant amitriptyline was studied in vitro in the presence of the main metabolite nortriptyline to simulate the steady state with amitriptyline and nortriptyline present in the ratio 1:1. The metabolism of the active metabolite nortriptyline in the presence of amitriptyline was also studied. The contribution of cytochrome P450 (CYP) 2D6, CYP2C19, and CYP3A4 was assessed by in vitro experiments at therapeutic (5 μM) and toxic (50 μM) concentrations for amitriptyline or nortriptyline with human liver microsomes (HLM). The results indicated that nortriptyline acted as a competitive inhibitor at the steady-state concentrations, lowering the amitriptyline metabolism, and thus changed the importance of different metabolic pathways. When the concentration of substrate amitriptyline was increased from therapeutic level to toxic level (in the steady state), the contribution of CYP2D6 significantly decreased for its demethylation and hydroxylation pathways. However, the contribution of CYP3A4 increased according to the increase in substrate concentration. Similar results could be obtained when nortriptyline was used as substrate in the presence and absence of the precursor amitriptyline. For CYP2C19 in the average HLM, its contribution to metabolism of both amitriptyline and nortriptyline was found to be small. However, it was also found that CYP2C19, in a “high activity” CYP2C19 HLM, was active for N-demethylation of both amitriptyline and nortriptyline and likewise the importance of CYP2C19 decreased when the concentration of substrate was increased. The above results indicate that CYP2D6 or CYP2C19 are generally not likely to be critical enzymes related to accidental intoxication under treatment with amitriptyline, but other contributing factors would be important; for example, low levels of various CYP enzymes and/or drug-drug interactions resulting in inhibition of several CYP enzymes may cause amitriptyline poisoning.

Plasma amitriptyline level after acute administration, and driving performance in healthy volunteers

Amitriptyline triggers the impairment of cognitive and motor functions and has been confirmed to have harmful effects on driving performance. Although interindividual differences in plasma concentration may cause variations in driving performance, the relationship between plasma amitriptyline concentration and its effect on driving performance has not been completely elucidated. Thus, the aim of the present study was to assess the influence of individual pharmacokinetic differences on driving performance and cognitive functions. In this double-blinded study, 17 healthy male volunteers were given an acute, single, 25-mg dose of amitriptyline. The subjects were assigned three driving simulator tasks, three cognitive tasks, and the questionnaire of the Stanford Sleepiness Scale at the baseline and at 4 h after dosing. The plasma amitriptyline concentrations were measured on high-performance liquid chromatography. A significant positive correlation was observed between the plasma amitriptyline concentration and road-tracking performance (r = 0.543, P < 0.05). There was no significant correlation between the plasma amitriptyline concentration and other driving performance, cognitive functions, and subjective somnolence. Amitriptyline produces a concentration-related impairment on road-tracking performance. Therapeutic monitoring of amitriptyline would be useful for predicting the difficulties involved while driving.

Tricyclic antidepressant amitriptyline alters sarcoplasmic reticulum calcium handling in ventricular myocytes

Tricyclic antidepressants such as amitriptyline (AMT) have been reported to have adverse side effects on cardiac performance. AMT effects on Ca handling in ventricular myocytes, however, are not well understood. Therefore, we investigated AMT action on sarcoplasmic reticulum (SR) Ca release in ventricular myocytes, ryanodine receptor (RyR) activity, and Ca uptake by SR microsomes. In permeabilized myocytes, AMT transiently increased free luminal Ca concentration ([Ca]) followed by marked depletion. AMT (10 microM) caused a rapid and a transient increase of Ca spark frequency, followed by a significant suppression of spark activity. The latter was associated with a decrease of Ca spark amplitude and SR Ca load to 87 and 60%, respectively. AMT (10 microM) completely abolished propagation of spontaneous Ca waves. Higher concentrations of AMT (0.1-1 mM) evoked SR Ca release reminiscent of the effect of caffeine (20 mM) and caused almost complete depletion of SR Ca content. Studies on single calsequestrin-free RyR channels revealed that AMT increased the mean open time and open probability (Po) in a dose-dependent fashion (dissociation constant = 4.2 microM). High concentrations of AMT (> 25 microM) evoked frequent long openings with Po reaching very high levels (> 0.70). In studies with cardiac SR microsomes, AMT slowed the rate of ATP-dependent Ca uptake. We conclude that AMT affects SR Ca handling in ventricular myocytes by multiple mechanisms, including direct stimulation of RyRs and inhibition of SR Ca uptake. These effects could contribute to AMT cardiotoxicity.

Influence of amitriptyline, chlorpromazine, and imipramine on the activity of phosphohydrolases

We have studied the effects of the antidepressants amitriptyline and imipramine and the neuroleptic chlorpromazine on the enzymatic function of Ca 2+ -activating-Mg 2+ -dependent ATPase of sarcoplasmic reticulum (SR), Na + , K + -dependent ATPase of endoplasmic reticulum (ER), and phosphodiesterase of cyclic adenosine monophosphate (cAMP). It is shown that interference with the enzymatic function (decrease of [Ca 2+ ]/[ATP]) or inhibition of active transport of calcium ions by Ca 2+ , Mg 2+ -ATPase of SR by the psychotropic drugs leads to impairment of Ca 2+ transport into the SR vesicule, which increases the force of muscle contraction. This effect decreases with increasing concentrations of amitriptyline and imipramine and with decreasing concentration of chlorpromazine, which is evidence for different mechanisms of action of Ca 2+ , Mg 2+ -ATPase of SR. Amitriptyline was a noncompetitive reversible inhibitor of Ca 2+ , Mg 2+ -ATPase of SR with an ATP hydrolysis inhibition constant K i = 1.8 × 10 −4 M and an active calcium transport inhibition constant K i = 0.7 × 10 −4 M. The goal of the investigation was to study the molecular mechanisms of action of amitriptyline, imipramine, and chlorpromazine.

Potential of Various Drugs to Inhibit Nucleoside Uptake in Rat Syncytiotrophoblast Cell Line, TR-TBT 18d-1

The placenta requires nucleosides as nutrients for fetal growth, so it is important to examine potential interactions between placental transports of nucleosides and drugs to ensure the safety of pharmacotherapy during pregnancy. The purposes of this study are to clarify the uptake mechanisms of nucleosides from the maternal side of the syncytiotrophoblast and to investigate the inhibitory effect of various drugs on nucleoside uptake, using the rat syncytiotrophoblast cell line TR-TBT 18d-1, which shows syncytial-like morphology and functional expression of several transporters. Initial uptake of [ 3H]uridine or [ 3H]adenosine from the apical side of TR-TBT 18d-1 was markedly reduced by an excess of the respective unlabelled compound, and was slightly reduced by replacement of Na + with N-methyl- d-glucamine, indicating that both uptakes were Na +-independent. [ 3H]Uridine and [ 3H]adenosine uptakes in the absence of Na + were significantly and concentration-dependently inhibited by both 0.1 μM and 100 μM nitrobenzylthioinosine, suggesting the involvement of equilibrative nucleoside transporters (ENTs, SLC29). Kinetic analysis of adenosine uptake yielded a K m value of approximately 17 μM. These results are consistent with the reported uptake characteristics of uridine and adenosine by ENT1 and ENT2. The uptakes were significantly reduced by high concentrations of several nucleoside drugs, including cytarabine, vidarabine, zidovudine, mizoribine, caffeine and amitriptyline, but the effects were small within the therapeutic concentration ranges. In summary, our results suggest that ENTs are involved in apical uptake of uridine and adenosine in the syncytiotrophoblast. However, therapeutic concentrations of the drugs tested in this study might have little influence on maternal-to-fetal nucleoside transfer.

Effects of adenosine receptor antagonists onamitriptyline-induced QRS prolongation in isolated rat hearts

Objective. We investigated the effects of adenosine receptor antagonists on amitriptyline-induced cardiotoxicity in isolated rat hearts. Methods. The amitriptyline concentrations that prolonged the QRS duration more than 150% (10−4 M) and 50–75% (5.5 × 10−5 M) were accepted as the control groups for two experimental protocols, respectively. In the first protocol, amitriptyline (10−4 M) was infused following pretreatment with a selective adenosine A1 receptor antagonist, DPCPX (8-cyclopentyl-1,3-Dipropylxanthine,10−4 to 10−6 M) or a selective adenosine A2a receptor antagonist, CSC (8-3-chlorostyryl-caffeine,10−4 to 10−6 M). In the second protocol, amitriptyline (5.5 × 10−5 M) was infused following pretreatment with DPCPX (10−4 M) or CSC (10−5 M). Left ventricular developed pressure (LVDP), dp/dtmax, QRS duration and heart rate (HR) were measured. Results. In the first protocol, 10−4 M DPCPX pretreatment shortened QRS duration at 50 minutes when compared to the control group (p < 0.05). In the second protocol, pretreatment with 10−4 M DPCPX shortened the QRS duration at 40, 50, and 60 minutes after amitriptyline infusion when compared to the control group (p < 0.05, p < 0.01 and p < 0.05, respectively). Pretreatment with 10−5 M CSC prolonged QRS duration at 20, 30, and 60 minutes (p < 0.05). Amitriptyline infusion following pretreatment with DPCPX or CSC did not change LVDP, dp/dtmax, or HR when compared to control in both protocols (p > 0.05). Conclusion. While 10−4 M DPCPX shortened QRS prolongation, 10−5 M CSC prolonged QRS duration in the isolated rat hearts with prolonged QRS duration induced by 5.5 × 10−5M amitriptyline. An adenosine A1 receptor antagonist, DPCPX, might shorten amitriptyline-induced QRS prolongation by activating beta adrenergic receptors.

Amitriptyline pharmacokinetics in experimental spinal cord injury in the rabbit.

Previous studies have demonstrated that pharmacokinetic behavior of several drugs such as paracetamol, theophylline, and aminoglycosides are significantly altered in spinal cord injured patients. No pharmacokinetic study of amitriptyline has been performed in patients and experimental models of spinal cord injury. Pharmacokinetic parameters of amitriptyline in orally treated rabbits subjected to laminectomy and spinal cord injury compared with those underwent laminectomy alone. Among twenty four male rabbits were included in this study, nine of them subjected to spinal cord injury at the 8th thoracic level by knife severance method and six rabbits underwent laminectomy alone (sham group) and nine rabbits treated as control. All received a single oral dose of amitriptyline (20 mg/kg) 24 h after injury. Blood sampling were done at predetermined times to 36 h after drug administration. Amitriptyline concentration in serum samples was determined by high-performance liquid chromatography. Pharmacokinetic parameters including maximum concentration (Cmax), time to reach maximum concentration (Tmax), half life, and the area under the curve to last detectable concentration time point (AUC0-t) were directly determined from the concentration-time curve. Maximum concentration was observed at 6.5 h after administration in sham group with a concentration of 439.6 ng/ml, whereas in SCI group Tmax was at 2.7 h with a concentration of 2763.9 ng/ml. In control group it was 3.3 h and 396 ng/ml, respectively. In SCI group, AUC was 9465.6 ng.h/ml and half life was 6 h and for control group it was 2817.4 ng.h/ml and 6.4 h, respectively. Statistical analysis of data showed that SCI didn't induce significant changes in amitriptyline pharmacokinetic parameters.

Uptake of amitriptyline and nortriptyline with liposomes, proteins, and serum: Implications for drug detoxification

Liposomes composed of DOPG and DMPC were studied for their ability to sequester amitriptyline and nortriptyline under physiological conditions. The liposomes reduced the free drug concentration in protein mixtures and in human serum, but the drug uptake efficiency of liposomes was reduced in the presence of plasma proteins, perhaps due to adsorption of proteins on the liposomes. The reduction was significantly more for the pure DOPG liposomes. The 50:50 DMPC:DOPG liposomes (0.72 mg lipid/mL) reduced the free amitriptyline concentration by 50–60% in the presence of 7% proteins (4% albumin (w/w), 2% fibrinogen (w/w), 1% globulins (w/w)). In human serum, the free drug reduction was 35–70% with the same 50:50 liposomes (0.72 mg lipid/mL). The liposomal systems were equally efficient at sequestering nortriptyline, which is a major metabolite of amitriptyline. The drug binding to liposomes in the presence of serum proteins is also quick and reversible and the likely mechanism of drug sequestration is adsorption of drug on the surface of liposomes. Accordingly, the drug uptake increases with increased charge and lipid loading. Even though the serum proteins reduced the effectiveness of the liposomes at sequestering the drug, the 50:50 DMPC:DOPG liposomes may be effective at treating amitriptyline overdose patients.

Massive intoxication involving unusual high concentration of amitriptyline

Amitriptyline is a tricyclic antidepressant widely used in the treatment of depression. Antidepressant drugs are among the most commonly encountered causes of self-poisoning, as illustrated by several published cases in the literature. This investigation reports a case of massive amitriptyline intoxication, involving a 44-year old female found dead in bed. The presence of this tricyclic antidepressant was revealed by a routine screening procedure. The concentration was calculated by gas chromatography/ electron ionization-mass spectrometry in the selected ion monitoring mode after solid-phase extraction using proadifen as internal standard and was in the post-mortem whole blood sample 85.9 mug/mL. This value was much higher than the reported toxic values ever found in the literature, and may therefore have caused the victim's death. Nortriptyline was also detected in the toxic concentration range, as well as therapeutic levels of diazepam and nor-diazepam. Taking into account both the available circumstantial information and toxicological results, it is very likely that death was caused by self-poisoning. Human & Experimental Toxicology (2007) 26, 667-670.