Bioavailability and kinetics of maprotiline

Mechanism of maprotiline-induced apoptosis: role of [Ca2+](i), ERK, JNK and caspase-3 signaling pathways

Antidepressants are generally used for treatment of various mood and anxiety disorders. Several studies have shown the anti-tumor and cytotoxic activities of some antidepressants, but the underlying mechanisms were unclear. Maprotiline is a tetracyclic antidepressant and possesses a highly selective norepinephrine reuptake ability. We found that maprotiline decreased cell viability in a concentration- and time-dependent manner in Neuro-2a cells. Maprotiline induced apoptosis and increased caspase-3 activation. The activation of caspase-3 by maprotiline appears to depend on the activation of JNK and the inactivation of ERK. Maprotiline also induced [Ca(2+)](i) increases which involved the mobilization of intracellular Ca(2+) stored in the endoplasmic reticulum. Pretreatment with BAPTA/AM, a Ca(2+) chelator, suppressed maprotiline-induced ERK phosphorylation, enhanced caspase-3 activation and increased maprotiline-induced apoptosis. In conclusion, maprotiline induced apoptosis in Neuro-2a cells through activation of JNK-associated caspase-3 pathways. Maprotiline also evoked an anti-apoptotic response that was both Ca(2+)- and ERK-dependent.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Cytochrome P450 enzymes contributing to demethylation of maprotiline in man

From case reports of patients treated with the tetracyclic antidepressant drug maprotiline, it appears that this drug is subject to polymorphic metabolism. Thus, we studied formation of the major maprotiline metabolite desmethylmaprotiline to identify the human cytochrome P-450 enzymes (CYP) involved. In incubations with human liver microsomes from two different donors, the substrate maprotiline was used at five different concentrations (5 to 500 microM). For selective inhibition of CYPs, quinidine (0.5-50 microM; CYP2D6), furafylline (0.3-30 microM; CYP1A2), ketoconazole (0.2-20 microM; CYP3A4), mephenytoin (20-200 microM; CYP2C19), chlorzoxazone (1-100 microM; CYP2E1), sulphaphenazole (0.2-100 microM; CYP2C9) and coumarin (0.2-100 microM; CYP2A6) were used. Desmethylmaprotiline concentrations were measured by HPLC, and enzyme kinetic parameters were estimated using extended Michaelis-Menten equations with non-linear regression. Relevant inhibition of the desmethylmaprotiline formation rate was observed in incubations with quinidine, furafylline and ketoconazole only. Formation rates of desmethylmaprotiline were consistent with a two enzyme model with a high (K(M)=71 and 84 microM) and a low (K(M)=531 and 426 microM) affinity site for maprotiline in the two samples, respectively. The high affinity site was competitively inhibited by quinidine (K(i,nc) 0.13 and 0.61 microM), the low-affinity site was non-competitively inhibited by furafylline (K(i,nc) 0.11 and 1.3 microM). Thus it appears that CYP2D6 and CYPIA2 contribute to maprotiline demethylation. Based on the parameters obtained, for plasma concentrations of 1 microM 83% (mean) of desmethylmaprotiline formation in vivo is expected to be mediated by CYP2D6 while 17% only may be attributed to CYPIA2 activity.

Pharmacokinetic optimisation of therapy with newer antidepressants

Since the early 1950s, when imipramine was first introduced, a whole series of antidepressants with differences in structures, neurochemical effects and pharmacokinetics have been developed. Structurally or functionally, they have been classified as tricyclic antidepressants (TCAs), tetracyclic antidepressants, monoamine oxidase inhibitors (MAOIs), or selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors (SSRIs). In addition, there is a series of antidepressants with unique structures. Many of the newer TCAs appear to have shorter half-lives than the standard TCAs (e.g. imipramine), allowing for the possibility of a more rapid response, but requiring the drugs to be given in multiple daily doses, which may reduce patient compliance. The short time to peak plasma concentration (tmax) can also lead to rapid onset of adverse effects. The tetracyclic antidepressants have longer elimination half-lives (t1/2) than the TCAs, but there is only very minimal evidence for a relationship between drug concentrations in the blood and clinical response. The triazolopyridines, like the newer TCAs, show pharmacokinetic evidence for rapid onset of adverse effects and the need for multiple daily doses due to short tmax and t1/2. The newer MAOIs are a significant addition to therapy, as the rapid binding action of these medications increases their safety margin with regard to tyramine interactions. Further information in this area is required. In addition, moclobemide has pharmacokinetic features that are clinically beneficial (e.g. aging and renal dysfunction have little effect on the elimination of the drug), but also features that are not beneficial (e.g. nonlinear pharmacokinetics). Among the SSRIs, there are a range of t1/2 values for the parent drugs, from relatively short t1/2 values of less than 24 hours (paroxetine, fluvoxamine) to among the longest found (e.g. 2 days for fluoxetine). Only 2 of the agents (sertraline and citalopram) have linear pharmacokinetics, and 1 drug has nonlinear pharmacokinetics within the usual therapeutic range (fluvoxamine). Once a therapeutic blood concentration is established, linearity is helpful in avoiding the small dose changes and repeated rechecking of concentrations of medications that would be required for those agents with nonlinear pharmacokinetics. Sertraline stands out as having the best effects on behaviour among all antidepressants. However, fluoxetine and fluvoxamine are least likely to penetrate into breast milk. All 3 of the structurally unique newer antidepressants [amfebutamone (bupropion), viloxazine venlafaxine] have relatively short tmax values (1 to 2 hours), which may relate to the early onset of adverse effects. Amfebutamone has the benefits of linear pharmacokinetics with potential for defined therapeutic blood concentrations, lack of effect of liver enzymes on metabolism of the drug, and lack of significant effects of either aging or hepatic dysfunction on elimination of the drug. Thus, the antidepressants best suited for pharmacokinetic optimisation of therapy are the following: desipramine, sertraline, fluvoxamine, citalopram and amfebutamone.

Assay for maprotiline in human serum with improved sensitivity and selectivity

The use of a photoreactor and fluorescence detection enables measurement of the tetracyclic antidepressant drug 3-(9,10-dihydro-9,10-ethanoanthracene-9-yl)-N-methylpropylamine (maprotiline) with a sensitivity of 100 pg/ml serum. This detection system is highly specific and enables the measurement of very low concentrations in the presence of high concentrations of other drugs that are often found in patient samples. The mean free portions of maprotiline and desmethylmaprotiline were found to be 2.2% and 1.5%, respectively.

Maprotiline metabolism appears to co-segregate with the genetically-determined CYP2D6 polymorphic hydroxylation of debrisoquine

The plasma concentrations of the tetracyclic antidepressant maprotiline and its effect on histamine-induced bronchoconstriction were measured after single (50 mg) and multiple (50 mg twice daily) oral doses in healthy subjects. Histamine-induced bronchoconstriction was abolished after a single dose of maprotiline and this effect persisted throughout multiple dose treatment. The mean Cmax of maprotiline in six poor metabolisers (PM) of debrisoquine was 2.7-fold greater than that in six extensive metabolisers (EM) and the mean AUC(0,48 h) was 3.5 times higher. The duration of the pulmonary effect of maprotiline after cessation of multiple dose treatment in EM was less than 3 weeks compared with at least 4 weeks in PM.

Long-term effects of two principally different antidepressant drugs on saliva secretion and composition

In a double-blind, controlled, cross-over trial on 10 healthy volunteers, the effects of daily doses of maprotiline (75 mg) and zimelidine (100 mg) over a 14-day period were tested on saliva secretion rate and saliva composition. Based on current knowledge of salivary gland physiology and the difference in specificity between the two drugs, differences in salivary gland response could be expected. Since both drugs have anticholinergic effects which influence saliva secretion rate, the measured component concentrations had to be recalculated with regard to dependencies of secretion rate. Maprotiline, but not zimelidine, caused strong inhibition of secretion rate and accommodation ability. Maprotiline consistently caused around 50% increases in concentrations of the following saliva components: protein, amylase, fucose, hexose, sialic acid and potassium. The effects of zimelidine were less pronounced and resulted in initial increases of most organic components. 14 and 18 h after the intake of the drug these increases had disappeared and some of the components instead showed decreased concentrations. The results are consistent with current theories about facilitated serotoninergic and noradrenergic transmissions during treatment with antidepressants.

The application of stable isotopes to studies of drug bioavailability and bioequivalence

The increased availability of chemical intermediates and automated instrumentation has resulted in expanded use of stable isotopes for bioavailability and bioequivalence studies in recent years. Initially, stable isotopes were confined to the labeling of mass internal standard compounds for gas chromatography/mass spectrometry. More recently, their in vivo use has expanded and proved to be a powerful pharmacologic tool. The lack of toxicity of stable isotopes, particularly deuterium and carbon-13, make them ideally suited for human studies. The primary advantage of the isotopic methods is that the drug can be administered concomitantly either by two routes (e.g., parenteral and oral) or in two formulations (e.g., solution and solid dosage). Thus, a single set of blood samples serves to describe the time course of the routes or formulations being compared. The concomitant administration reduces variability inherent in dual administration, the single assay for both forms further reduces variation, and the method minimizes both drug exposure and discomfort to the subject. In addition to single-dose administration, in which two routes or dosage forms are compared, the technique is well suited to "pulse" administration, wherein the kinetics of a single dose, during multiple or chronic dosing regimens, can be compared with single-dose kinetics.

Stable-isotope methodology in the bioavailability study of 17 alpha-methyltestosterone using gas chromatography-mass spectrometry

The application of a stable-isotope coadministration technique for estimating the relative bioavailability of 17 alpha-methyltestosterone is described. Eight healthy male subjects were administered orally a single 10-mg 17 alpha-methyltestosterone tablet together with a 10-mg 17 alpha-methyltestosterone-d3 solution. The serum concentrations of 17 alpha-methyltestosterone and 17 alpha-methyltestosterone-d3 were determined by gas chromatography-mass spectrometry with selected ion monitoring using 17 alpha-methyltestosterone-d6 as an internal standard. The extent of absorption from the tablet formulation was comparable to that from the oral solution. The stable-isotope methodology was compared with the conventional cross-over method for evaluating the bioavailability of 17 alpha-methyltestosterone.

Quantitative determination of methyltestosterone and methyltestosterone-d3 in serum by gas chromatography-mass spectrometry

A method for the quantitative estimation of methyltestosterone and methyltestosterone-d3 in biological fluids has been developed using gas chromatography-mass spectrometry-selected-ion monitoring. Methyltestosterone-d6 was used as an internal standard. Methyltestosterone and methyltestosterone-d3 in serum were determined based on the peak height ratios of the molecular ions of methyltestosterone, methyltestosterone-d3 and methyltestosterone-d6. Sensitivity, specificity, precision, accuracy and reproducibility of the present method were demonstrated to be satisfactory for application to pharmacokinetic and bioavailability studies.

Isolation and identification of hydroxylated maprotiline metabolites

Lipophilic maprotiline metabolites were extracted from human urine and animal excreta, with or without prior enzymic hydrolysis, purified by repeated t.l.c. and their structures determined by u.v., n.m.r. and mass spectrometry. Urine from patients under treatment with maprotiline contained the isomeric phenols, 2- and 3-hydroxymaprotiline, the 2,3-dihydrodiol, and an alcoholic metabolite, besides smaller quantities of the corresponding N-demethylated compounds. In dog urine and/or faeces the same products of aromatic hydroxylation were present as in human urine and in addition 3-hydroxy-2-methoxymaprotiline; alcohols were not detected. The only metabolites identified in rabbit urine and rat bile were 3-hydroxy- and 3-hydroxy-2-methoxymaprotiline.

Determination of orally coadministered nadolol and its deuterated analogue in human serum and urine by gas chromatography with selected-ion monitoring mass spectrometry

A cartridge serum and urine extraction procedure of the beta-adrenergic antagonist, nadolol, employing a cross-linked styrene-divinyl benzene macroreticular resin is described. Samples were analyzed as the silylated derivative by gas chromatography-mass spectrometry (GC-MS) using selected-ion monitoring. When nadolol was orally coadministered with its deuterated analogue, relative bioavailability could be demonstrated with six or fewer subjects. Employing a base-deactivated GC phase, the limit of detection is 1 ng and 0.5 ng/mL of serum for nadolol and the deuterated analogue, respectively. For levels of less than 10 ng/mL, the respective coefficients of variation are 4 and 2%. For concentrations of greater than 10 ng/mL, the CV is 1% for nadolol and nadolol-d9.

Fatal maprotiline intoxication

We report a fatal case of drug toxicity associated with torsade de pointes following an overdose of the tetracyclic antidepressant, maprotiline (Ludiomil). Tissue and plasma levels were obtained at autopsy and are noted. In addition, the cardiovascular effects, pharmacokinetics, and toxicity of maprotiline are reviewed and compared with that of tricyclic antidepressants.

Synthesis of deuterium labeled 17-methyl-testosterone

The synthesis of two forms of selectively deuterated 17-methyl-testosterone is described. 17-Methyl-d3-testosterone was prepared by the Grignard reaction of dehydroepiandrosterone with deuterium labeled methyl magnesium iodide followed by an Oppenauer oxidation. 17-Methyl-d3-testosterone-19,19,19-d3 was prepared by treating 3,3-ethylenedioxy-5,10-epoxy-5 alpha, 10 alpha-estran-17-one with deuterium labeled methyl magnesium bromide followed by hydrolysis and dehydration of the 5 alpha-hydroxyandrostane derivative.

Does viloxazine have epileptogenic properties?

Six cases of convulsive seizures occurring during treatment with viloxazine notified to the Committee on Safety of Medicines (CSM) and two other cases from Japan were reviewed. A critical study of the patient's histories suggests a possible causal connection between drug and seizures in only two of these cases. The occurrence of convulsions is not in keeping with the results of animal experiments and of clinical trials in which epileptic patients were included, both of which suggest that viloxazine does not have epileptogenic properties and may have anticonvulsant actions. A worldwide review of clinical trials in which unwanted effects have been recorded suggests that viloxazine, even if possessing convulsive properties like other anti-depressants, is probably less epileptogenic than conventional tricyclics and is not contraindicated in epileptic patients requiring antidepressant medication.

Determination of captopril in human blood and urine by GLC-selected ion monitoring mass spectrometry after oral coadministration with its isotopomer

A modified electron-impact GLC-selected ion monitoring mass spectrometric method for captopril is described. Positive chemical ionization GLC-selected ion monitoring and direct chemical ionization confirms the specificity of this procedure for captopril and establishes the chemical ionization techniques as potential analytical methods. This procedure has been adapted to the simultaneous measurement of captopril and its isotopomer. The results of a pilot oral bioavailability study of four subjects receiving either 100 mg of captopril as a direct compression tablet or a solution concomitantly with a 100-mg solution of isotopomer is discussed.