PDE7-Selective and Dual Inhibitors: Advances in Chemical and Biological Research

Phosphodiesterase 7 (PDE7) is an intracellular enzyme that specifically hydrolyzes the second messenger, cyclic-3',5'-adenosine monophosphate (cAMP), into inactive noncyclic nucleotide, 5'-AMP. To date, many structurally diverse compounds with PDE7 inhibitory properties have been described, including selective PDE7 inhibitors, dual PDE4/PDE7, PDE7/PDE8, and PDE7/GSK-3 inhibitors, and non-selective PDE inhibitors with high affinity for PDE7. Inhibitors of PDE7 have provided beneficial effects in animal models of inflammatory and neurological disorders, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and many others. This review is a comprehensive summary of the current state-of-the-art in the field of design and synthesis of PDE7 inhibitors, their physicochemical properties, biological evaluation, and structure-activity relationships as well as it highlights the updated evidence for a potential therapeutic utility of these compounds. Moreover, new approaches to obtain more effective and safer PDE7 inhibitors than those available now are presented.

ANTI-INFLAMMATORY AND ANTIOXIDANT ACTIVITY OF 8-METHOXY-1,3-DIMETHYL-2,6-DIOXO-PURIN-7-YL DERIVATIVES WITH TERMINAL CARBOXYLIC, ESTER OR AMIDE MOIETIES IN ANIMAL MODELS

The previous studies in a series of 8-methoxy-1,3-dimethyl-2,6-dioxo-purin-7-yl derivatives revealed their analgesic properties. We extended the study with these compounds in aim to assess their impact on inflammatory process. For this purpose we used: the zymosan-induced peritonitis and the carrageenan-induced edema model. Furthermore, the antioxidant activity of the investigated compounds by the FRAP assay was determined. For the most active derivatives from evaluated series their influence on plasma TNF-α level was also tested in vivo. All investigated purine-2,6-dione derivatives 1-11 decreased neutrophils count and inhibited intensity of early vascular permeability. Furthermore, all evaluated compounds reduced the volume of edema caused by subcutaneous injection of carrageenan. Derivatives 1 (with ester moiety), 3 and 4 (with carboxylic group) showed the highest activity in the zymosan-induced peritonitis. In addition, a significant inhibition of plasma TNF-α level in rats with endotoxemia was observed following intraperitoneal administration of these compounds. In turn, compounds 6 and 8-11 containing amide moiety showed the greatest anti-inflammatory (antiedematous) effect in the carrageenan-induced paw edema model. All compounds did not show significant antioxidant properties. The present studies revealed that the presented purine-2,6-dione derivatives exhibit a significant anti-inflammatory activity and this effect may result from their ability to lower TNF-α level.

Pharmacokinetic modelling of pentoxifylline and lisofylline after oral and intravenous administration in mice

The aim of this study was to develop pharmacokinetic models for pentoxifylline (PTX) and the R(-)-enantiomer of the PTX metabolite 1, lisofylline (LSF), in order to identify some factors influencing the absorption of these compounds from the intestines and to clarify mechanisms involved in their non-linear pharmacokinetics. Serum samples were collected after oral and intravenous administration of PTX and LSF to male CD-1 mice at two different doses. In addition, both compounds under investigation were coadministered with a modulator of drug transporters, verapamil, and an inhibitor of cytochrome P450 (CYP) 3A4, ketoconazole. Pharmacokinetic analysis revealed that a one-compartment model with Michaelis-Menten type absorption and elimination best described the pharmacokinetics of PTX, whereas the LSF concentration-time data were adequately fitted to a two-compartment model with a first-order absorption and Michaelis-Menten type elimination process. Both coadministered compounds significantly decreased the area under the concentration-time curve from 0 to 60 min calculated for PTX and increased the value of this parameter for LSF. The results of this study indirectly suggest that saturation of drug transport across intestinal cells and elimination from the central compartment may be responsible for the non-linear pharmacokinetics of PTX, whereas in the case of LSF, the dose dependency in the pharmacokinetics is solely related to the elimination from the central compartment. It seems that the observed changes in PTX and LSF concentrations after coadministration with verapamil and ketoconazole may be clinically significant, especially after chronic treatment, however further studies are necessary to assess the importance of these interactions in humans.

Pharmacokinetic interaction between verapamil and methylxanthine derivatives in mice

The aim of this study was to assess the impact of a P-glycoprotein and CYP3A inhibitor, verapamil on the pharmacokinetics of two methylxanthines, pentoxifylline and lisofylline in male CD-1 mice. To differentiate the effects of verapamil, both methylxanthines were also given to male CF-1 mdr1a (-/-) and mdr1a (+/+) mice. CD-1 mice received a single dose (50 mg/kg) of pentoxifylline or lisofylline intravenously, whereas mutant animals were given the same dose of both compounds intravenously and orally. Blood and tissue samples were collected at different time points following drug administration and concentrations of pentoxifylline and lisofylline were measured by a chiral HPLC method. Verapamil significantly increased concentrations of both methylxanthines in murine serum and tissues. In contrast to lisofylline, pentoxifylline concentrations were also significantly higher in mutant mice 30 min following intravenous administration. Due to the fact that pentoxifylline is not a good P-glycoprotein substrate, a possible mechanism of this interaction might be that in the presence of verapamil, pentoxifylline elimination is inhibited by its metabolites that are normally eliminated through P-glycoprotein-mediated transport. This hypothesis was supported by the outcomes of pharmacokinetic analysis. In conclusion, the interaction between verapamil and pentoxifylline is, at least partially, P-glycoprotein-mediated, whereas alterations in lisofylline pharmacokinetics are caused by inhibition of drug metabolising enzymes.

Pretreatment with R(+)-verapamil significantly reduces mortality and cytokine expression in murine model of septic shock

It is well known that cytokines play an important role in the pathogenesis of sepsis and septic shock. There is evidence indicating that the membrane transporter, P-glycoprotein (P-gp), may be involved in the release of cytokines, such as IL-2, IL-4 or IFN-gamma. The aim of this study was to assess the influence of P-gp inhibitor, R(+)-verapamil, on cytokine expression in serum and tissues as well as survival rate of mice with LPS-induced septic shock. These effects were compared with the response to treatment with pentoxifylline, lisofylline, and prednisolone administered alone or after pretreatment with R(+)-verapamil. When given as a single agent, R(+)-verapamil significantly decreased serum levels of TNF-alpha and IFN-gamma and protected mice from endotoxin lethality. Moreover, it decreased up-regulated by LPS TNF-alpha gene expression in the liver and lungs. Given concomitantly with immunomodulatory compounds, it enhanced their beneficial impact on the survival of mice with septic shock. The highest increase in survival rate was observed in combination with pentoxifylline (7% vs. 67%). The most striking differences observed between saline and R(+)-verapamil pretreated animals on combination therapy included down-regulation of TNF-alpha, higher levels of IL-6, and decreased IFN-gamma concentrations. These results suggest that P-gp may be involved in the release of IFN-gamma, and possibly also TNF-alpha, in mice with septic shock. R(+)verapamil improves survival of mice receiving a lethal dose of LPS and significantly potentiates the protective effect of pentoxifylline and prednisolone against LPS-induced lethality, probably as a result of both P-gp inhibition and a synergistic interaction at the gene level.

Pharmacokinetics and pharmacodynamics of erythropoietin receptor in healthy volunteers

The purpose of this study was to apply the target-mediated drug disposition (TMDD) pharmacokinetic (PK) model to describe binding, internalization, and turnover of erythropoietin receptor (EPOR). This model allows one to determine from free drug (C) PK data not only parameters describing linear disposition of EPO such as the elimination rate constant (kel) and volume of distribution (Vc), but also the total receptor concentration (Rtot0), drug-receptor complex (RC) internalization rate constant (kint), as well as synthesis and degradation rate constants (ksyn and kdeg) for the receptor turnover. The previously published data on PK of recombinant EPO (rHuEPO) in humans and the results of EPOR binding studies were used for analysis. The estimated PK parameters were used to simulate time courses of free and bound EPOR after IV administration of clinically relevant rHuEPO doses. The estimates of kel=0.106 h(-1) and Vc=0.032 l/kg are consistent with reported in the literature values of rHuEPO linear disposition parameters. The determined value of Rtot0 was 66.35 pM and the half-life for EPOR degradation was 8.8 h. Computer simulations showed a very rapid binding phase in the EPOR time profile followed by a decline to a nadir, and a subsequent return to the baseline. The nadir values decreased with increasing doses and resulted in the maximum values of the bound fractions of the total EPOR in the ranges 33-99%. At the baseline conditions, only 3.1% of EPOR were occupied. The saturation of EPOR was correlated with the time C remained above the KD level. In conclusion, the time courses of serum rHuEPO concentrations contain information about internalization and turnover of EPOR. Kinetics of EPOR can be utilized to determine the relationship between the pharmacologic effect and exposure to rHuEPO.

Sevoflurane increases fade of neuromuscular response to TOF stimulation following rocuronium administration in children. A PK/PD analysis

BACKGROUND

Sevoflurane enhances neuromuscular block produced by rocuronium, affecting not only single twitch response but also the response to high-frequency stimulation, increasing tetanic [or train-of-four (TOF)] fade.

METHODS

We compared the degree of fade during spontaneous recovery from rocuronium-induced neuromuscular block in 24 children (3-11 years old, ASA groups I and II), anesthetized with nitrous oxide-sevoflurane (one MAC, endtidal concentration) or nitrous oxide-fentanyl. Neuromuscular transmission was monitored electromyographically (EMG), stimulating the ulnar nerve at the wrist with TOF, 2 Hz for 2 s, repeated at 20-s intervals and recording EMG potential from adductor pollicis brevis. Depression of the fourth twitch, T4, was used as a measure of fade. Following an intubating dose of rocuronium, 0.6 mgxkg(-1), continuous infusion of rocuronium was given to maintain stable 90-99% T1 depression. Plasma concentration of rocuronium was determined with high performance liquid chromatography with electrochemical detection (HPLC-EC) method at the moment of discontinuation of rocuronium infusion and 10, 20, 30, 40, 50, 60, and 75 min afterwards. A two compartment model was used for pharmacokinetic (PK) calculations. PK parameters were fixed and pharmacodynamic data were fitted to effect compartment model proposed by Sheiner.

RESULTS

Sevoflurane reduced rocuronium concentration in effect compartment producing 50% inhibition of both T1 and T4 response and significantly delayed not only T1, but also T4 recovery.

CONCLUSIONS

Potentiating effect of sevoflurane on rocuronium-induced neuromuscular block influences not only postsynaptic, but also the presynaptic part of the neuromuscular junction, enhancing fade of neuromuscular response to high-frequency stimulation. The intensity of this latter effect is clinically relevant.

Immobility stress induces depression-like behavior in the forced swim test in mice: effect of magnesium and imipramine

Previously, we demonstrated antidepressant-like effect of magnesium (Mg) in the forced swim test (FST). Moreover, the joint administration of Mg and imipramine (IMI) at ineffective doses per se, resulted in a potent reduction in the immobility time in this test. In the present study, we examined the effect of immobility stress (IS), and Mg and/or IMI administration on FST behavior. IS induced enhancement of immobility time, which was reversed by Mg or IMI at doses ineffective in non-stressed mice (10 mg/kg and 15 mg/kg, respectively). The joint administration of Mg and IMI was effective in both IS and non-stressed animals in FST. IS did not significantly alter locomotor activity, while IMI or Mg + IMI treatment in IS mice reduced this activity. We also measured serum and brain Mg, IMI and its metabolite desipramine (DMI) concentration in mice subjected to FST and injected with Mg + IMI, both restrained and non-restrained. In the present study we demonstrated a significant increase (by 68%) in the brain IMI and a slight, non-significant reduction in DMI concentration in IS + Mg + IMI + FST vs. Mg + IMI + FST groups, which might indicate the reduction in brain IMI metabolism. The IS-induced reduction in brain IMI metabolism did not participate in the activity in FST, since no differences in such activity were noticed between IS + Mg + IMI + FST and Mg + IMI + FST groups. The present data suggest that IS-induced increase in immobility time in FST is more sensitive for detection antidepressant-like activity. However, further studies are needed to examine the effect of other antidepressants in such an experimental paradigm.

Pharmacokinetic-pharmacodynamic relationship of rocuronium under stable nitrous oxide-fentanyl or nitrous oxide-sevoflurane anesthesia in children

BACKGROUND

The aim of this study was to compare pharmacokinetics and pharmacokinetic-pharmacodynamic (PK-PD) relationship of rocuronium in children anesthetized with nitrous oxide (N2O) and fentanyl or with N2O and sevoflurane.

METHODS

Twenty-four children (3-11 years old, ASA PS I or II) were randomized to receive N2O/O2-fentanyl or N2O/O2-sevoflurane (one MAC) anesthesia. Neuromuscular transmission was monitored electromyographically. Initial bolus dose of rocuronium, 0.6 mg x kg(-1) was followed by continuous infusion, targeting at steady-state 95% T1 depression. Neuromuscular transmission was allowed to recover spontaneously. Plasma samples were collected at the moment of discontinuation of infusion, and 10, 20, 30, 50, 60 and 75 min afterwards. Concentrations of rocuronium were measured using high-performance liquid chromatography with electrochemical detection (HPLC-EC). Rocuronium PK was described by a two-compartment model and PD parameters were estimated using effect compartment and sigmoidal E(max) models.

RESULTS

No differences in rocuronium PK parameters were observed between study groups. Clearance was 3.91 +/- 2.07 and 3.62 +/- 0.80 ml x min(-1) x kg(-1) in sevoflurane and fentanyl groups, respectively (P < 0.65). Effect compartment concentrations corresponding to 50% inhibition of T1 (EC50) were 1.41 +/- 0.45 and 2.32 +/- 1.00 microg x ml(-1) (P < 0.02), and rate constants for equilibration between plasma and effect compartment (k(e0)) values were 0.10 +/- 0.04 and 0.24 +/- 0.14 min(-1) (P < 0.009) in sevoflurane and fentanyl groups, respectively.

CONCLUSIONS

Disposition of rocuronium was similar under stable N2O-fentanyl and N2O-sevoflurane anesthesia. Sevoflurane reduced rocuronium requirements as well as decreased EC50 relevant to inhibition of T1 and rocuronium transfer to effect compartment. Therefore, the potentiating effect of sevoflurane seems to be mainly of PD origin, probably due to an increased sensitivity of the neuromuscular junction.

Interconversion and tissue distribution of pentoxifylline and lisofylline in mice

The aim of this study was to assess the interconversion pharmacokinetics and tissue distribution of pentoxifylline and the active (R)-enantiomer of its metabolite M1, lisofylline in male CD-1 mice. Both compounds were administered intravenously at a dose of 50 mg/kg on two separate occasions. Serum and tissues were collected at different time points following drug administration. In addition, the (S)-enantiomer of M1 was administered to a group of mice and serum samples were obtained. Analyte concentrations were measured by chiral HPLC. All serum concentration versus time data were fitted simultaneously to a pharmacokinetic model incorporating interconversion processes of parent drug and metabolites. The estimated conversion clearance of (-)-(R)-M1 to pentoxifylline (CL21) was six times greater than that for the reverse process (CL12). The interconversion of pentoxifylline and (+)-(S)-M1 was faster as reflected by the values of conversion clearances CL13 and CL31 which were approximately 16 and 7 times greater in comparison with the corresponding clearances for the interconversion of pentoxifylline and (-)-(R)-M1. When fitting pharmacokinetic data of both parent compounds to a one-compartment model, the values of elimination clearances assessed were close to those obtained on the basis of the interconversion model. After administration of pentoxifylline, tissue-to-serum AUC ratios ranged from 0.1 for liver and lungs to 0.32 for brain tissue. Serum levels of its metabolite, (-)-(R)-M1 were very low, whereas its tissue levels exceeded serum concentrations. The highest value of metabolite-to-parent AUC ratio (4.98) was observed in lungs. When (-)-(R)-M1 was given as a parent drug, tissue-to-serum AUC ratios in liver, kidney, and lungs were very close and ranged from 0.64 to 0.72. At the same time, levels of its metabolite, pentoxifylline were relatively low both in serum and all tissues studied. In consequence, metabolite-to-parent AUC ratios did not exceed the value of 0.27. In conclusion, reversible metabolism plays a modest role in the disposition of pentoxifylline and (-)-(R)-M1. It seems that pentoxifylline has less favourable pharmacokinetic properties than (-)-(R)-M1 due to lower concentrations attained in target organs. High levels of (-)-(R)-M1 observed after pentoxifylline administration in certain tissues such as liver or lungs suggest that pentoxifylline may constitute an effective prodrug for (-)-(R)-M1 in these organs.

[Application of real-time PCR to pharmacokinetic studies]

Pharmacokinetics is a discipline dealing with processes describing the fate of a drug in the body, starting from its absorption at the site of administration, through its distribution to tissues, metabolism via enzymes, mainly those of the cytochrome P450 family, and to its elimination from the body. In both drug absorption and distribution processes, membrane transporters are often involved, among which P-glycoprotein and organic anion transporting polypeptides (OATP) are probably the best known. Genes coding these proteins as well as many drug metabolizing enzymes are not only highly polymorphic, but their expression may also be significantly altered by the administered drugs. Real-time polymerase chain reaction (real-time PCR) is a sensitive and reliable technique enabling quantitative determination of mRNA levels in cells and tissues. It may also be used for rapid genotyping, and is thus especially useful in a clinical setting as well as for validating microarray data.The aim of this review is to present the utility of real-time PCR in pharmacokinetic studies with special attention paid to the analysis of the expressions of genes coding drug-metabolizing enzymes and membrane transporters as well as to recent studies concerning the impact of genotype on drug pharmacokinetics. Moreover, possibilities of applying this method to collect data for pharmacokinetic and pharmacokinetic-pharmacodynamic modeling (PK/PD) are indicated.

Enhancement of antidepressant-like activity by joint administration of imipramine and magnesium in the forced swim test: Behavioral and pharmacokinetic studies in mice

The effect of joint administration of imipramine (IMI) and magnesium (Mg) on antidepressant-like activity was studied in mice using forced swim test (FST). Mg doses ineffective per se (5 and 10 mg/kg) given jointly with IMI also at ineffective doses (10 and 15 mg/kg) resulted in a potent reduction in the immobility time. Since these combined treatments did not influence locomotor activity, the antidepressant-like activity was not due to non-specific behavioral activation. Moreover, we estimated the effect of joint administration of magnesium and IMI in FST on serum and brain magnesium, IMI and its active metabolite desipramine (DMI) concentrations in mice. Swim stress (mice subjected to FST) increased the magnesium concentration in serum and decreased it in the brain compared to naive animals. Moreover administration of IMI increased (normalized) magnesium brain concentration, without influence on the serum level. Joint administration of IMI and magnesium did not influence magnesium (compared with FST) or IMI and DMI (compared with IMI treatment alone) concentrations in both examined tissues. The present data demonstrated an enhancement of the antidepressant-like effect by joint administration of IMI and magnesium in the FST, and further indicate the particular role of magnesium in the antidepressant action. Since there was no increase in IMI, DMI or magnesium concentration after joint administration of magnesium and IMI, the data suggest that pharmacodynamic rather than pharmacokinetic interaction between magnesium and IMI is accountable for behavioral effect in the FST.

Pharmacokinetic interaction after joint administration of zinc and imipramine in forced swim test in mice

Recent preclinical and clinical data indicate beneficial role of zinc in the antidepressant treatment. To evaluate the mechanism of interaction between zinc and antidepressants, in the present study we examined the brain zinc, imipramine and desipramine concentrations in mice treated with combinations of zinc and imipramine and subjected to the forced swim test. We have chosen doses of zinc (10 mg/kg) and imipramine (15 mg/kg) which we have previously found to be ineffective in the forced swim test when given alone. However, when administered jointly, a significant reduction in the immobility time in this test was demonstrated. In the present study, we demonstrated a significant ca. 60% reduction in the brain desipramine and non-significant reduction (ca. 40%) in brain imipramine concentrations in the group of animals treated with zinc plus imipramine compared with animals treated with imipramine alone. The brain zinc concentration in the zinc plus imipramine group was reduced when compared with the group treated with zinc or imipramine alone. Since there was no increase in brain imipramine/desipramine or zinc brain concentration after combined zinc and imipramine treatment, the data suggest that pharmacodynamic rather than pharmacokinetic interaction between zinc and imipramine is responsible for behavioral effect in the forced swim test.

Methods of estimation of IC50 and SC50 parameters for indirect response models from single dose data

The basic indirect response models are described by several pharmacodynamic parameters of which IC(50) (drug concentration eliciting 50% of the maximum inhibition) and SC(50) (drug concentration eliciting 50% of the maximum stimulation) are not readily derived from the response versus time or response versus concentration plots. We discuss limitations of existing methods of IC(50) and SC(50) estimation from single dose data. A novel approach to such estimations based on the area between the baseline and effect curve is introduced. The effects of pharmacokinetic profile, dose, data variability, and number of data on the parameter estimation are analyzed for the new and one of the previously described methods. Our analysis is based on reconstruction of true IC(50) and SC(50) values from rich and sparse computer-generated data sets modified by two noise levels. Extensions of these methods to two dose data sets are presented. Both methods yielded IC(50) and SC(50) close to the known true values. Depending on the factors mentioned above, these methods exhibited different levels of accuracy.

Diversity of mechanism-based pharmacodynamic models

Pharmacodynamics is the study of the time course of pharmacological effects of drugs. The field of pharmacodynamic modeling has made many advances, due in part to the relatively recent development of basic and extended mechanism-based models. The purpose of this article is to describe the classic as well as contemporary approaches, with an emphasis on pertinent equations and salient model features. In addition, current methods of integrating various system complexities into these models are discussed. Future pharmacodynamic models will most likely reflect an assembly of the basic components outlined in this review.

Approaches to pharmacokinetic/ pharmacodynamic modeling during pregnancy

The modern approach in the field of pharmacokinetics/pharmacodynamics is the development of models based on the mechanisms of drug action and their alteration of physiologic processes. Such models often require consideration of the input and disposition kinetics of the drug, distribution to sites of action (biophase), processes controlling receptor binding or mediator turnover, mechanisms of drug activity, and signal transduction steps. Responses can often be categorized as: Direct (rapidly or slowly reversible), Indirect (inhibitory or stimulatory), or Irreversible. Further, there may be alterations in the system owing to tolerance, counter-regulation, pathophysiology, or physiological changes such as gender or pregnancy. Mathematical and computational tools are necessary for processing data. This article overviews many available pharmacodynamic models with an indication of the diverse approaches for quantitation of pharmacologic responses. Examples from the literature are illustrated with emphasis on changes occurring in kinetics and dynamics during pregnancy.

Pharmacokinetic interaction between imipramine and carbamazepine in patients with major depression

RATIONALE

Despite the fact that carbamazepine (CBZ) is frequently added to the existing tricyclic antidepressant (TCA) therapy, to date little is known about serum levels of pharmacologically active hydroxy metabolites of TCAs, as well as about possible changes in free (non-protein-bound) concentrations of these drugs and their metabolites during such combination treatment of depression.

OBJECTIVE

The aim of this study was to evaluate the effect of CBZ on steady-state total and free serum concentrations of imipramine (IMI) and its metabolites, desipramine (DMI), 2-hydroxyimipramine and 2-hydroxydesipramnine, in depressed patients. In addition, the free and total serum concentrations of CBZ and 10,11-epoxycarbamazepine were measured.

METHOD

Thirteen patients with DSM-III-R diagnosis of major depression were enrolled in the study. All patients hospitalised at the Department of Psychiatry, Collegium Medicum, Jagiellonian University were treated with IMI at a dose of 2 mg/kg per day for 3 weeks, after which CBZ at a dose of 400 mg/day was added. Steady-state serum concentrations of IMI, CBZ and their metabolites were assayed by HPLC. Free drug concentrations were measured by ultrafiltration.

RESULTS

After 2 weeks of combination therapy a significant decrease in mean steady-state total serum concentrations of IMI (from 168.84 +/- 102.18 to 98.12 +/- 43.79 ng/ml) and DMI (from 293.89 +/- 171.93 to 221.85 +/- 153.21 ng/ml) was observed. Simultaneously, steady-state serum concentrations of total hydroxy metabolites and free IMI and its metabolites, measured just before and 2 weeks after CBZ were started, did not differ significantly. In consequence, a significant increase in free fraction of the parent drug was observed (3.36 +/- 3.24% vs 5.75 +/- 3.60%). Also free fraction of DMI tended to be higher after CBZ addition.

CONCLUSION

CBZ affects not only the metabolism of IMI and its metabolites, but also their protein binding. Therefore, despite considerable reductions in total serum levels of IMI and DMI, but when the unchanged free fraction concentration of these compounds is maintained, a dosage elevation of IMI does not seem to be necessary after CBZ addition to TCA therapy.

[Clinical pharmacokinetics of tricyclic antidepressants Part II. Drug therapy monitoring]

Large interindividual variation in steady-state TCA plasma concentrations, the presence of active metabolites, narrow therapeutic range and life-threatening results of TCA overdosage constitute indications for therapeutic drug monitoring. Conditions which must be fulfilled in order that serum concentration measurements may be taken into consideration in routine practice were discussed. The most important ones are: relationship between TCA concentration and antidepressant effect, the knowledge of therapeutic TCA range and availability of rapid and sensitive analytical method. Pharmacokinetic methods of TCA dosage individualization were also described. TCA serum concentration monitoring and dosage individualization of these drugs allows the clinician to optimize treatment of depression.

[Clinical pharmacokinetics of tricyclic antidepressants. Part I. Pharmacokinetic properties]

Pharmacokinetic properties of tricyclic antidepressants (TCA) and factors changing pharmacokinetics of these drugs were presented. The following factors were discussed: age, genetically determined rate of metabolism and TCA interaction with co-administered drugs. As a consequence of these factors alterations mainly in elimination of TCA are observed. It leads to large interindividual variation in TCA plasma concentrations and lack of correlation between TCA concentration and dosage.