[Influence of ORM1 polymorphism on serum concentration of free nortriptyline]

To study the effect of alpha1-acid glycoprotein 1 (ORM1) polymorphism on the concentration of free nortriptyline in serum, genotyping analysis was employed in ORM1 by sequencing. Eighteen unrelated male adults were chosen and given a single dose of 25 mg nortriptyline orally, then the blood samples were taken at 0, 1, 2, 3, 4, 6, 8, 12, 24, 32, 48, 72, 96 and 168 hours after drug administration. Nortriptyline and 10-OH-nortriptyline in serum and ultrafiltrate were detected for the total and free concentration by using HPLC-MS/MS. Pharmacokinetic parameters were compared among different ORM1 genotypes. No significant differences were shown in the pharmacokinetic parameters of total nortriptyline and 10-OH-nortriptyline. The mean AUC(0-infinity) of free nortritpyline in ORM1 * F/ * F1 subjects was significantly higher than that in ORM1 * F1/ * S and ORM1 * S/ * S subjects [(119.1 +/- 74.4) ng x mL(-1) x h vs (51.4 +/- 23.2) ng x mL(-1) x h and (42.4 +/- 11.6) ng x mL(-1) x h]. The percentage of protein binding in subjects with ORM1 * F1/ * F1 genotype at 2, 3, 4, 6, 8 and 12 h after administration was slightly lower than in those with ORM1 * F1/ * S and ORM1 * S/ * S genotypes while the distinct difference was shown at 4 h (P < 0.05). Different ORM1 genotypes might affect the protein binding percentage and the concentration of serum free nortriptyline. The ability binding to the drug was higher in subjects with ORM1 * S/ * S genotype than in those with other two genotypes, so as to cause the lower concentration of free nortriptyline.

Placental passage of tricyclic antidepressants

BACKGROUND

The use of antidepressants during pregnancy continues to garner considerable attention, though there are limited investigations that have sought to quantify fetal exposure.

METHODS

Maternal and umbilical cord sera were collected at delivery from ten women taking nortriptyline and seven taking clomipramine. Placental passage was calculated as the ratio of umbilical cord to maternal serum concentration. Obstetrical outcome data were gathered from subjects at delivery.

RESULTS

The placental passage ratio of nortriptyline and its active metabolite, cis-10-hydroxynortriptyline, were .68 +/- .40, 1.40 +/- 2.40, respectively. Clomipramine and desmethylclomipramine ratios were .60 +/- .50, .80 +/- .60. Obstetrical complications, such as pre-term delivery and pregnancy induced hypertension, were increased compared to the national average.

CONCLUSIONS

The in vivo ratios of umbilical cord to maternal serum drug concentrations demonstrate considerable fetal exposure and differ greatly from previous results utilizing ex vivo perfusion.

Influence of P-glycoprotein inhibition on the distribution of the tricyclic antidepressant nortriptyline over the blood-brain barrier

The distribution of the antidepressant drug nortriptyline (NT) and its main metabolite E-10-hydroxy-nortriptyline (E-10-OH-NT) across the blood-brain barrier was considered in relation to inhibition of the multidrug transporter P-glycoprotein (P-gp). Rats received NT in doses of 25 mg/kg orally, 10 mg/kg i.p. or 25 mg/kg i.p. Half the rats were treated with the P-glycoprotein inhibitor cyclosporine A (CsA) (200 mg/kg) 2 h prior to NT administration, and the other half served as a control group. NT and the metabolite were extracted from brain and serum by liquid-liquid extraction and analysed by HPLC with UV-detection. The brain to serum ratio of NT was increased in the CsA treated groups (22.3-26.8) compared with the control groups (16.5-22.7), the difference being statistically significant in two of the three experiments (p<0.05). Increased brain-serum ratios were also found for E-10-OH-NT, but the differences were not statistically significant. These results suggest that inhibition of P-gp by CsA increases the accumulation of NT in the brain. Administration of the antipsychotic drug risperidone (0.5 mg/kg s.c.), which is a P-gp substrate, instead of CsA did not exert any measurable influence on the blood-brain ratio of NT concentrations. In conclusion, the results show that drug-drug interaction at P-gp may influence the intracerebral NT concentration, but apparently, a major inhibition of P-gp is necessary to attain a measurable effect.

The role of metabolites in bioequivalence

The role of metabolites in bioequivalence studies has been a contentious issue for many years. Many papers have published recommendations for the use of metabolite data based on anecdotal evidence from the results of bioequivalence studies. Such anecdotal evidence has validity, but the arguments lack weight because the "correct" answers are always unknown. A more promising area of exploration is recommendations based on simulated bioequivalence studies for which the "correct" answers are known, given the assumptions. A review of the literature, however, reveals scant evidence of attempts to apply to real data the pharmacokinetic principles on which the recommendations from simulated studies relied. We therefore applied those principles (based on estimates of intrinsic clearance after oral administration of the parent drug) to four bioequivalence studies from our archives, in which the parent drug and at least one metabolite were monitored. In each case, the outcome is discussed in the context of the complexity of the metabolic processes that impact on the parent drug and the metabolite(s) during the first passage from the intestinal lumen to the systemic circulation. Our observation is that no simple generalization can be made such that each drug/metabolite combination must be examined individually. Our recommendation, however, is that in the interests of safety, bioequivalence decision-making should be based on the parent drug whenever possible.

Inhibition of cytochrome P4502D6 activity with paroxetine normalizes the ultrarapid metabolizer phenotype as measured by nortriptyline pharmacokinetics and the debrisoquin test

BACKGROUND

The ultrarapid metabolizer phenotype of the cytochrome P4502D6 (CYP2D6) enzyme has been considered a relevant cause of nonresponse to antidepressant drug therapy. Prescribing high doses of antidepressants to such patients leads to high concentrations of potentially toxic metabolites and an increased risk for adverse reactions. Normalization of the metabolic status of ultrarapid metabolizers by inhibition of CYP2D6 activity could offer a clinically acceptable method to successfully treat such patients with antidepressants.

METHODS

Five ultrarapid metabolizers with a CYP2D6 gene duplication or triplication were treated with 25 mg nortriptyline twice a day for 3 consecutive weeks, alone during the first week and concomitantly with the CYP2D6 inhibitor paroxetine 10 mg or 20 mg twice a day, respectively, during the second and third weeks. After the third week, nortriptyline was discontinued and the subjects were treated with paroxetine 20 mg twice a day during the fourth study week. At the end of each study week, the steady-state pharmacokinetic parameters of nortriptyline or paroxetine were determined within the dose interval. In addition, the CYP2D6 phenotype was determined by debrisoquin (INN, debrisoquine) test at baseline and at the end of each study phase. Treatment-related adverse events were recorded during drug administration and for 1 week thereafter.

RESULTS

All 5 subjects had very low (subtherapeutic) nortriptyline concentrations after 7 days' treatment with nortriptyline only. Addition of paroxetine 10 mg twice a day to the nortriptyline regimen resulted in a change in all individuals to the "normal" extensive debrisoquine metabolizer phenotype, and therapeutic plasma nortriptyline concentrations were achieved in 4 of 5 subjects after a 3 times mean increase in nortriptyline trough concentration (P =.0011). Doubling the paroxetine dose caused a 15 times mean increase in paroxetine trough concentration (P <.001), indicating strong inhibition by paroxetine of its own metabolism. The high paroxetine concentrations in 2 subjects caused them to have the poor debrisoquine metabolizer phenotype and resulted in a further increase in plasma nortriptyline trough concentration (P =.0099). A strong correlation (rank correlation coefficient [r(s)] = 0.89; P <.0001) was observed between paroxetine and nortriptyline trough concentrations. Paroxetine also significantly decreased the fluctuation of nortriptyline concentrations within the dose interval. One subject discontinued the study after the second study week because of adverse effects; otherwise, the study drugs were well tolerated.

CONCLUSIONS

Paroxetine, with a daily dosage from 20 to 40 mg, is an effective tool in normalizing the metabolic status of CYP2D6 ultrarapid metabolizers.

Steady-state plasma levels of nortriptyline and its hydroxylated metabolites in Japanese patients: impact of CYP2D6 genotype on the hydroxylation of nortriptyline

The authors investigated the impact of the CYP2D6 genotype on steady-state concentrations of nortriptyline (NT) and its metabolites, trans-10-hydroxynortriptyline (EHNT) and cis-10-hydroxynortriptyline in a Japanese population of psychiatric patients. Forty-one patients (20 men and 21 women) were orally administered nortriptyline hydrochloride. The allele frequencies of the CYP2D6*5 and CYP2D6*10 were 4.9% and 34.1%, respectively. Significant differences in NT concentrations corrected for dose and weight were observed between the subjects with no mutated alleles and those with one mutated allele (mean +/- SD for no mutated alleles vs. one mutated allele: 70.3 +/- 25.4 vs. 98.4 +/- 36.6 ng/mL x mg(-1) x kg(-1); t = 2.54, dcf = 33, p < 0.05) and between the subjects with no mutated alleles and two mutated alleles (no mutated alleles vs. two mutated alleles: 70.3 +/- 25.4 vs. 147 +/- 31.1 ng/mL x mg(-1) x kg(-1); t = 5.87, df = 19, p < 0.0001). Also, a significant difference in the NT/EHNT ratio, which is representative of the hydroxylation ratio of NT, was observed between the subjects with no mutated alleles and those with two mutated alleles (no mutated alleles vs. two mutated alleles: 0.82 +/- 0.30 vs. 2.71 +/- 0.84; t = 7.86, df = 19, p < 0.0001). Multiple regression analysis showed that the number of mutated alleles of CYP2D6, which was the only significant factor, accounted for 41% and 48% of the variability in log(NT corrected for dose and weight) and log(NT/EHNT), respectively.

Pharmacokinetics of nortriptyline and its 10-hydroxy metabolite in Chinese subjects of different CYP2D6 genotypes

OBJECTIVES

To study the impact of the CYP2D6*10 allele on the disposition of nortriptyline in Chinese subjects.

METHODS

A single dose of 25 mg nortriptyline was given orally to 15 healthy Chinese volunteers who were classified as extensive metabolizers after phenotyping with debrisoquin (INN, debrisoquine) and who were genotyped by allele-specific polymerase chain reaction. Five subjects were homozygous for CYP2D6*1, 5 subjects were homozygous for CYP2D6*10, and 5 subjects were heterozygous for these 2 alleles. Plasma concentrations of nortriptyline and its main metabolite 10-hydroxynortriptyline were measured by liquid chromatography-mass spectrometry, and the pharmacokinetics were studied during 168 hours after the dose.

RESULTS

Subjects who were homozygous for CYP2D6*10 had significantly higher total areas under the plasma concentration-time curve (AUC), lower apparent oral clearances, and longer mean plasma half-life of nortriptyline than subjects in the CYP2D6*1/*1 and the heterozygous groups. For 10-hydroxynortriptyline, the AUC was lower and the plasma half-life was longer in subjects who were homozygous for CYP2D6*10 than in subjects in the other 2 groups.

CONCLUSION

The CYP2D6*10 allele in Chinese subjects was associated with significantly higher plasma levels of nortriptyline compared with the CYP2D6*1 allele because of an impaired metabolism of nortriptyline to 10-hydroxynortriptyline, particularly in the subjects with the CYP2D6*10/*10 genotype. The results suggest that genotyping of CYP2D6 may be a useful tool in predicting the pharmacokinetics of nortriptyline.

High-performance liquid chromatography-mass spectrometry for the quantification of nortriptyline and 10-hydroxynortriptyline in plasma

A highly sensitive and selective method for the quantification of nortriptyline and its major 10-hydroxy metabolite in plasma is described. The method is based on liquid-liquid extraction in combination with acid dehydration of the 10-hydroxy metabolite to the less polar 10,11-dehydronortriptyline. Deuterium labelled internal standards ([2H4]NT and [2H3]10-OH-NT) were used and the compounds were separated by reversed-phase HPLC and detected using atmospheric pressure chemical ionisation and mass spectrometry. The limit of quantification was 0.8 ng/ml for both compounds. A 1-ml volume of plasma was used for analysis in the concentration range 0.8-32 ng/ml. The within- and between-day coefficients of variation were 11% in the low, 1.6 ng/ml range, and 7% at 8 ng ml/ml. Using this method it was possible to quantify plasma concentrations for 168 h following a single oral dose of 25 mg of nortriptyline with good accuracy and precision.

10-Hydroxylation of nortriptyline in white persons with 0, 1, 2, 3, and 13 functional CYP2D6 genes

OBJECTIVE

To investigate the disposition and effects of nortriptyline and its major metabolite 10-hydroxy-nortriptyline line in panels of white subjects with different CYP2D6 genotypes, including those with duplicated and multiduplicated CYP2D6*2 genes and to evaluate the contribution of the number of functional C gamma P2D6 alleles to the metabolism of nortriptyline, used here as a model drug for CYP2D6 substrates.

METHODS

Oral single doses of 25 to 50 mg nortriptyline were given to five poor metabolizers of debrisoquin (INN; debrisoquine) with no functional CYP2D6 gene, five extensive metabolizers with one functional CY2D6 gene, five extensive metabolizers with two functional CYP2D6 genes, five ultrarapid metabolizers with duplicated CYP2D6*2 genes, and one ultrarapid metabolizer with 13 copies of the CYP2D6*2 gene. Plasma kinetics of nortriptyline and 10-hydroxynortriptyline were analyzed. Anticholinergic effects (inhibition of salivation and accommodation disturbances), sedation, blood pressure, and effect on supine and erect pulse rate were measured.

RESULTS

There was a clear relation between the C gamma P2D6 genotype and the plasma kinetics of nortriptyline and 10-hydroxynortriptyline. The proportion between the apparent oral clearances of nortriptyline in the groups with 0, 1, 2, 3, and 13 functional genes was 1:1:4:5:17. The proportions between AUC(nortriptyline) to AUC(10-hydroxynortriptyline) ratios in the groups with 0, 1, 2, 3, and 13 functional genes were 36:25:10:4:1. Oral plasma clearance of nortriptyline and AUC(nortriptyline) to AUC(10-hydroxynortriptyline) ratio both correlated significantly with the debrisoquin metabolic ratio (rS = -0.89, p = 0.0001; rS = 0.92, p = 0.0001). Although ultrarapid metabolizer subjects were given double the nortriptyline dose (50 mg), inhibition of salivation was not more pronounced compared with the other genotype groups given 25 mg nortriptyline.

CONCLUSION

The results of this study show the quantitative importance of the CYP2D6 genotype, especially the presence of multiple functional CYP2D6 genes for the pharmacokinetics of nortriptyline and 10-hydroxynortriptyline. Genotyping of subjects with multiple copies of functional genes may be of great value for differentiating ultrarapid metabolizers from patients who do not comply with the prescription and for assuring adequate drug choice and dosage for these patients.

Metabolism of amitriptyline with CYP2D6 expressed in a human cell line

1. Expressed human cytochrome P450 enzyme CPY2D6 was used to metabolize amitriptyline (AMI). It was established that CYP2D6 not only catalyzed ring 10-hydroxylation of AMI, but also mediated its N-demethylation to nortriptyline (NT), as well as the formation of 10-hydroxy-NT from NT. When the metabolism of AMI by CYP2D6 was repeated in the presence of quinidine, none of the metabolites, 10-hydroxy-AMI, NT and 10-hydroxy-NT, was formed. 2. Biochemical parameters of NT formation from AMI were determined, yielding Km = 47.48 +/- 1.32 microM; Vmax = 3.95 +/- 0.11 nmol/h/mg protein. The same parameters were calculated for the formation of 10-hydroxy-AMI (E + Z-isomers) from AMI, yielding Km = 10.70 +/- 0.20 microM; Vmax = 8.99 +/- 0.47 nmol/h/mg protein. 3. The formation of 10-hydroxy-NT from AMI proceeded primarily via NT and to a much lesser extent via 10-hydroxy-AMI. 4. Quantitative analyses of AMI and its metabolites were difficult to reproduce when the metabolites were analysed underivatized. Two derivatization procedures, acetylation and trifluoroacetylation, were employed to improve assay reproducibility.

Pharmacokinetics of amitriptyline and its demethylated and hydroxylated metabolites in streptozocin-induced diabetic rats

Plasma and brain levels of amitriptyline (AMI), its demethylated and hydroxylated metabolites were determined after acute IP administration of AMI (20 mg/kg) in streptozocin-induced diabetic Sprague-Dawley rats. Results showed 1. in plasma: rapid AMI absorption, but slow elimination; the proportion of AMI similar to those of the rest of compounds; the proportion of its demethylated metabolite, nortriptyline, 1.8-fold higher than that of 10-hydroxy-nortriptyline. 2. in brain: the proportions of AMI and nortriptyline were 9.5- and 2.6-fold higher respectively, than those of whole hydroxylated metabolites, which represented 7.4% of the total amount.

Plasma and brain pharmacokinetics of amitriptyline and its demethylated and hydroxylated metabolites after one and six half-life repeated administrations to rats

The purposes of the present study were as follows: 1. After an acute intraperitoneal (IP) administration of amitriptyline (AMI) to male Sprague-Dawley rats we found that: (i) its absorption rate is rapid; (ii) its elimination half-life is much shorter than in humans; and (iii) its levels largely exceeded those of its metabolites. The most important metabolites being 10-hydroxynortriptyline and nortriptyline in plasma and brain, respectively. 2. After six (every half-life) repeated IP administrations: (i) AMI kinetic parameters were unchanged; and (ii) amounts of metabolites were significantly increased and the levels of AMI were lowered both in plasma and brain.

Steady-state plasma levels of nortriptyline and its 10-hydroxy metabolite: relationship to the CYP2D6 genotype

The relationship between the CYP2D6 genotype and the steady state plasma levels of nortriptyline (NT), its main active metabolite 10-hydroxynortriptyline (10-OH-NT) and the NT/10-OH-NT ratio were studied in 21 Caucasian depressed patients treated with 100-150 mg NT daily. The patients had participated in a previously published study investigating the role of NT and 10-OH-NT for the therapeutic effect of NT, and the plasma level data were from that study. In the present follow-up study, the patients were genotyped with respect to the polymorphic CYP2D6 by allele-specific PCR amplification and EcoRI RFLP. One poor metabolizer (PM) was identified and she had the highest plasma concentration of NT. Among the 20 extensive metabolizers (EM), the genotype (homozygous versus heterozygous EM) alone was not found to explain the variance in dose-corrected NT concentrations, but contributed significantly when gender was also taken into account. Together, these factors accounted for 59% of the variability in NT levels. Female patients had higher plasma levels of NT than male patients. 10-OH-NT levels were influenced by genotype, and NT/10-OH-NT ratio by genotype and gender. The present follow-up study confirms a relationship between the CYP2D6 genotype and the plasma levels of NT and its active metabolite. Identification of PM by genotyping should be of value for the prediction of the plasma levels and, consequently, the lower than average dose of NT required for optimal therapy. Also among EM, the genotype contributes to the variability in NT and 10-OH-NT levels but alone is of limited practical value for the prediction of optimal dosage.

Stereoselective reversible ketone formation from 10-hydroxylated nortriptyline metabolites in human liver

1. E- and Z-10-hydroxynortriptyline are major metabolites of amitriptyline and nortriptyline in man. Upon incubation with human liver microsomes or cytosol, these metabolites were oxidized to the corresponding ketones, E- and Z-10-oxonortriptyline. (+)-E- and (+)-Z-10-hydroxynortriptyline were distinctly preferred over the (-)-isomers as substrates. NADP+ supported the oxidation in cytosol, whereas in microsomes NAD+ was the best cofactor. 2. Incubation of E- and Z-10-oxonortriptyline with NADPH and cytosol resulted in the nearly exclusive formation of (+)-E- and (+)-Z-10-hydroxynortriptyline. Kinetic analysis revealed high-affinity reduction (K(m) 1-2 microM) of the two ketones and an additional low-affinity component with the E-isomer. 10-Oxonortriptyline reduction was also catalysed by rabbit, but not by rat or guinea pig liver cytosol. 3. With [4-3H]NADPH as cosubstrate, tritium was incorporated into E- and Z-10-hydroxynortriptyline preferentially from the pro-4R position. Redox cycling of (+)-E- and (+)-Z-10-hydroxynortriptyline in cytosol in the presence of NAD- and NADPH was indicated by 3H incorporation from [pro-4R-3H]NADPH. 4. Recombinant human carbonyl reductase catalysed low-affinity reduction of E-10-oxonortriptyline with preferential transfer of the pro-4S-3H of labelled NADPH. 5. Ketone reduction in cytosol was strongly inhibited by 9,10-phenanthrenequinone and dehydrolithocholic acid and moderately by other 3-oxo steroids and some anti-inflammatory drugs. 6. The high-affinity reduction of E- and Z-10-oxonortriptyline and the oxidation of the alcohols in cytosol are probably mediated by a member of the aldo-keto reductase family of enzymes.

Interindividual variations of desmethylation and hydroxylation of amitriptyline in a Japanese psychiatric population

We measured the concentrations in plasma of amitriptyline and its metabolites, nortriptyline and geometric isomers of 10-hydroxynortriptyline and 10-hydroxyamitriptyline, in 73 Japanese psychiatric patients receiving amitriptyline hydrochloride (Tryptanol; Banyu Pharmaceutical Co. Ltd., Tokyo, Japan) by high-performance liquid chromatography. Although there were large interindividual variations of total drug concentrations and concentrations of parent or intermediate metabolic compounds in plasma, significant positive correlations were observed between these drug concentrations and daily doses of amitriptyline hydrochloride (milligrams per kilogram of body weight). The metabolic ratios for both hydroxylation and desmethylation varied substantially with approximately 8- to 19-fold interindividual variations. Frequency distribution histograms and probit analyses of these parameters identified neither definite poor hydroxylators nor poor desmethylators of amitriptyline.

Active hydroxymetabolites of antidepressants. Emphasis on E-10-hydroxy-nortriptyline

Hydroxymetabolites of the antidepressants nortriptyline and desipramine, like the parent drugs, inhibit neuronal uptake of noradrenaline (norepinephrine). In both plasma and cerebrospinal fluid (CSF), the concentrations of the 10-hydroxymetabolites of nortriptyline (10-OH-NT) are usually higher than those of the parent drugs, but there is a pronounced interindividual variation in the plasma concentrations. This shows that during treatment with nortriptyline, hydroxymetabolites exert, at least in some patients, major effects on brain noradrenaline neurons. Hydroxymetabolites of antidepressants are formed by the polymorphic cytochrome P450 enzyme CYP2D6. Nortriptyline is hydroxylated by this enzyme in a highly stereospecific way to the (-)-enantiomer of E-10-OH-NT. Among Caucasians, 7% are poor metabolisers of the CYP2D6 probe drug debrisoquine. These patients will form very little hydroxymetabolite. The affinity of E-10-OH-NT for muscarinic acetylcholine receptors in vitro was only one-eighteenth of the affinity of nortriptyline for these receptors. In healthy individuals, nortriptyline decreased saliva flow to a significantly greater extent than either E-10-OH-NT or placebo. In an ultrarapid hydroxylator of nortriptyline treated with very high doses of nortriptyline, the plasma concentration of unconjugated 10-OH-NT was very high without any sign of anticholinergic adverse effects. These results show that hydroxymetabolites of nortriptyline have much less anticholinergic effect than the parent drug. When racemic E-10-OH-NT per se was given to healthy individuals, the plasma concentration of the (-)-enantiomer was 5-fold higher than that of (+)-E-10-OH-NT. The 2 enantiomers were eliminated in parallel with an elimination half-life of 8 to 10 hours. A combined in vitro and in vivo investigation showed that a mean of 64% of (+)-E-10-OH-NT was glucuronidated in the liver and subsequently eliminated in urine. Of the administered (-)-enantiomer, a mean of 36% was eliminated as glucuronide formed in the intestine and 35% was actively secreted as unchanged form in urine. Plasma protein binding, determined by ultrafiltration, of the (+)- and (-)-enantiomers of E-10-OH-NT was 54 and 69%, respectively, which is less than that of nortriptyline (92%). The concentration of E-10-OH-NT in CSF was 50% of the concentration of unbound in plasma. There seems to be a stereoselective active transport of E-10-OH-NT from the CSF to blood. We administered racemic E-10-OH-NT to 5 patients during a major depressive episode.(ABSTRACT TRUNCATED AT 400 WORDS)

Mice plasma and brain pharmacokinetics of amitriptyline and its demethylated and hydroxylated metabolites after half-life repeated administration. Comparison with acute administration

Kinetics of amitriptyline (AMI), its demethylated metabolites nortriptyline (NOR) and demethylnortriptyline (DM-NOR), and its hydroxylated metabolites, the E and Z isomers or 10-hydroxy-amitriptyline (E- and Z-10-OH-AMI) and of 10-hydroxynortriptyline (E- and Z-10-OH-NOR) were studied in plasma and brain from Swiss CD1 mice after six successive intraperitoneal injections of amitriptyline (10 mg/kg) administered every elimination half-life time (t1/2 = 3.1 h) to obtain the steady state. In these conditions, AMI was metabolised rapidly. Compared with acute administration, hydroxylation reactions were saturated by the repeated AMI injections and demethylation became preponderant both in plasma and brain. Thus, plasma levels of demethylated metabolites, NOR and DM-NOR, increased (49% and 13% of total AUC against 22% and 7% in acute conditions, respectively), while levels of AMI and its hydroxylated metabolites, 10-OH-AMI and 10-OH-NOR, decreased (8%, 2.5% and 27.5% against 17%, 8% and 46% in acute conditions, respectively). Likewise in brain tissue, when AMI was repeatedly administered, NOR and DM-NOR increased (62% and 22% against 29% and 11%, respectively) while AMI and 10-OH-AMI decreased (11.5% and 1% against 47% and 9%, respectively). These differences may account for modified pharmacological effects seen after half-life repeated administration of AMI since demethylated metabolites exert a more marked inhibiting effect than AMI on noradrenaline reuptake.

CSF/plasma ratio of 10-hydroxynortriptyline is influenced by sex and body height

The CSF/plasma ratios of nortriptyline (NT) and its major metabolite 10-hydroxy-NT (10-OH-NT) were investigated retrospectively in 25 depressed patients. For 10-OH-NT (but not NT), a significant influence of sex and body height was found, most conspicuously in males, in whom the ratio related to body height curvilinearly (N = 8; R = 0.93; P < 0.01). In males, the NT/10-OH-NT ratio in plasma correlated with body height (N = 8; r = 0.80; P < 0.05). Hypothetically, CSF circulation is partly influenced by body height, which accounts for a steeper gradient of 10-OH-NT across the blood-brain barrier in taller persons. From the lumbar site, the more polar 10-OH-NT is assumed to be eliminated by bulk flow via the villi, while the less polar NT exits by diffusion in the choroid plexus. Prospective studies are urgently needed to further evaluate the distribution of antidepressants in the CSF.

Enantioselective amitriptyline metabolism in patients phenotyped for two cytochrome P450 isozymes

In 26 hospitalized patients with depression, a combined pharmacogenetic test with dextromethorphan, a substrate of cytochrome P450IID6, and mephenytoin, the S-form of which is hydroxylated by a P450IIC isozyme, was carried out before amitriptyline therapy. Metabolites were determined in 24-hour urine samples collected on treatment day 8, and the contributions of individual compounds, including the four isomers of 10-hydroxyamitriptyline and 10-hydroxynortriptyline to total excretion were calculated. Formation of (-)-E-10-hydroxyamitriptyline and (-)-E-10-hydroxynortriptyline apparently depends on the activity of cytochrome P450IID6 because negative correlations existed between the log metabolic ratio of dextromethorphan and the relative quantities of these enantiomers. In contrast, correlations were positive for nortriptyline, (+)-E-10-hydroxynortriptyline, (-)-Z-10-hydroxynortriptyline, and (+)-Z-10-hydroxynortriptyline. The mephenytoin hydroxylase seems to participate in side-chain demethylation to the secondary and primary amines, because the log metabolic ratio of mephenytoin correlated negatively with the relative quantity of E-10-hydroxydidesmethylamitriptyline and positively with that of amitriptyline and its N-glucuronide.

Molecular structure and dynamics of the four 10-hydroxynortriptyline isomers

The three-dimensional structures, molecular conformations, and electrostatic potentials of the R-E-, S-E-, R-Z-, and S-Z-isomers of 10-hydroxynortriptyline were examined by computer graphics, molecular mechanical energy calculations, and molecular dynamics simulations in vacuo and in aqueous solution. Molecular models of the isomers, based on the structure of nortriptyline, were refined by energy minimization and used as starting points in the simulations. R-E- and S-Z-10-hydroxynortriptyline formed intramolecular hydrogen bonds between the side-chain nitrogen atom and the hydroxyl group during the simulations in vacuo, and had the side chain folded over the ring system in the minimum energy conformations. Intramolecular hydrogen bonding was not observed for R-Z- and S-E-10-hydroxynortriptyline, which had extended side chains in the minimum energy conformations and stronger negative molecular electrostatic potentials around the hydroxyl group than the R-E- and S-Z-isomers.

Nortriptyline response in elderly depressed patients

1. Depressed geriatric patients were treated with nortriptyline (NT) for 6 weeks. The authors measured serum levels of NT and 10-hydroxynortriptyline (10-OH-NT) using a column-switching HPLC method, and examined aging effects on NT steady-state levels to NT doses (doses/kg) ratios and NT levels to 10-OH-NT levels ratios as well as clinical response and propensity for side effects. 2. There was no significant relationship between the ages and the NT serum levels to NT doses (doses/kg) ratios, the ages and the 10-OH-NT levels to NT levels ratios, or the ages and the clinical response or the %improvement of Hamilton Scores. 3. Then the authors divided the subjects into two groups: a younger group and an elderly group with the cut off age of 60. The elderly group received significantly smaller doses of NT and had significantly lower serum levels of NT. The elderly group had tendency to have lower serum levels of 10-OH-NT. However, no significant difference was found in the improvement scores or the %improvement of depression. The elderly patients did not have higher propensity for unnegligible side effects.

Sensitive method for the quantitation of nortriptyline and 10-hydroxynortriptyline in human plasma by capillary gas chromatography with electron-capture detection

A method for the determination of nortriptyline and 10-hydroxynortriptyline concentrations in human plasma by capillary gas chromatography with electron-capture detection is described. The procedure requires 1.0 ml of plasma and uses maprotiline as an internal standard. The compounds are extracted from alkalinized plasma with hexane-2-butanol (98:2) and back-extracted into hydrochloric acid. The acid solution is then made basic and the compounds are re-extracted into n-butyl chloride. The extract is evaporated to dryness, derivatized with heptafluorobutyric anhydride, and analyzed by gas chromatography on a fused-silica capillary column coated with phenylmethyl silicone. The calibration curves for nortriptyline and 10-hydroxynortriptyline are linear in the ranges 3-40 and 7-90 micrograms/l, respectively, with coefficients of variation for within-day and between-day precision of less than 12%. The quantitation limits for nortriptyline and 10-hydroxynortriptyline are 1 and 3 micrograms/l, respectively. This procedure was used to analyze more than 1400 samples following sub-therapeutic doses of nortriptyline in human subjects. The assay was sufficiently sensitive for use in pharmacokinetic analysis.

Comparative cardiotoxicity of nortriptyline and its isomeric 10-hydroxymetabolites

The potential cardiotoxicity of the hydroxymetabolites of nortriptyline (NT) has been raised by inferential data from clinical studies and by the experimentally demonstrated cardiac effects of 2-OH-imipramine. Cardiac output, arterial pressure, and a continuous electrocardiogram were assessed after intravenous de novo administration of NT or its hydroxymetabolites to 41 swine. NT at doses ranging from 3.5 to 7 mg base per kilogram caused significantly more arrhythmias than did E-10-hydroxynortriptyline (E-10-OH-NT) but was not significantly different from Z-10-hydroxynortriptyline (Z-10-OH-NT) in this effect. Z-10-OH-NT, in contrast, to its geometrical isomer caused marked bradycardia, and decrements in blood pressure and cardiac output. NT and Z-10-OH-NT, but not E-10-OH-NT, produced dose-correlated declines in cardiac output. The hydroxymetabolites had smaller volumes of distribution, shorter half-lives and larger free fractions compared with NT. The differing cardiotoxicity of the hydroxymetabolites could not be accounted for by differing pharmacokinetic properties.

Serum nortriptyline levels in nursing mothers and their infants

The nortriptyline levels of seven depressed mothers and their breast-fed infants were obtained. Nortriptyline was not detected in the infants' sera. However, two of four infants evaluated developed low concentrations of 10-hydroxynortriptyline. No adverse effects were observed.

Studies on active transport of (E)-10-hydroxynortriptyline in the kidney and brain of rats: effects of propranolol and quinidine

Studies in humans have given strong support of an active transport of (E)-10-hydroxynortriptyline [E)-10-OH-NT) in the kidney and from the cerebrospinal fluid. After 3 days of intraperitoneal injections of (E)-10-OH-NT (10 mg/kg t.i.d.) in a rat model, we investigated the effect of propranolol and quinidine (25 and 2.5 mg/kg injected 6 times during day 3) on the concentrations of (E)-10-OH-NT in urine, plasma (total and unbound) and brain. In a group of control rats the renal clearance of (E)-10-OH-NT varied 10-fold between rats, but was reproducible from Day 2 to Day 3 (r = 0.83; n = 8; p less than 0.05). Quinidine markedly decreased the renal clearance of both total and unbound (E)-10-OH-NT from plasma, while the effect of propranolol was less pronounced. There was no difference in the ratio of (E)-10-OH-NT concentrations in brain and plasma (unbound) between treated and control rats. We conclude that (E)-10-OH-NT is actively secreted in the rat proximal tubule and that the activity of this system varies between rats, but is constant in the individual rat. Quinidine, and to a less extent propranolol, inhibits this renal secretion. By the present methodology we could not demonstrate an active transport of (E)-10-OH-NT from brain to blood in the rat. Studies using other methods are needed to further elucidate this.

Enantioselective hydroxylation of nortriptyline in human liver microsomes, intestinal homogenate, and patients treated with nortriptyline

The enantioselectivity of hydroxylation of nortriptyline (NT) to E-10-hydroxynortriptyline (E-10-OH-NT) was studied in human liver microsomes, intestinal homogenate, and patients treated with NT. The rate of formation of (-)-E-10-OH-NT was higher than that of (+)-E-10-OH-NT both in the liver microsomes and in the intestinal homogenate. Quinidine, a prototype competitive inhibitor of the cytochrome P450IID6 ("debrisoquin hydroxylase"), inhibited the formation of (-)-E-10-OH-NT in a concentration-dependent manner in liver microsomes, while the formation of (+)-E-10-OH-NT was hardly affected. This indicates that P450IID6 catalyzes the hydroxylation of NT in a highly enantioselective manner to (-)-E-10-OH-NT in the liver. Another P450 isozyme besides IID6 seems to be responsible for the formation of the (+)-enantiomer in the liver. In intestinal homogenate, the formation of both enantiomers of E-10-OH-NT was inhibited to about the same extent by quinidine, the maximum inhibition being much less than in the liver. In the urine of six patients treated with NT, the (-)-enantiomer accounted for 91 +/- 2% of the unconjugated E-10-OH-NT, and for 78 +/- 6% of the glucuronide conjugates. The study shows that NT is hydroxylated in a highly enantioselective way, probably catalyzed by the polymorphic P450IID6, to (-)-E-10-OH-NT both in vitro in human liver as well as in vivo in patients treated with the drug.

Stereoselective efflux of (E)-10-hydroxynortriptyline enantiomers from the cerebrospinal fluid of depressed patients

In 5 patients treated with nortriptyline or amitriptyline for at least 9 months, the cerebrospinal fluid (CSF)/plasma ratio for 10-hydroxynortriptyline (10-OH-NT) ranged from 0.085 to 0.172, which is similar to the ratio previously measured in patients treated for 3 weeks. In 4 other patients treated with racemic (E)-10-OH-NT, the mean concentration ratio between (-)- and (+)-(E)-10-OH-NT was 3.56 in plasma, 2.39 in plasma ultrafiltrate and 1.42 in CSF (one-way ANOVA; P less than 0.001). The mean free fraction in plasma determined by ultrafiltration for (-)-(E)-10-OH-NT was 28.9 +/- S.D.1.1% and for the (+)-enantiomer 43.7 +/- 0.8% (P less than 0.001) confirming the difference in protein binding shown previously in healthy subjects. There was a correlation between the concentration of 10-OH-NT (sum of enantiomers) in CSF and plasma ultrafiltrate (r = 0.96; n = 7; P less than 0.001). The concentration in CSF was, however, only about 50% of that in the plasma ultrafiltrate and this seems to be due to a stereoselective transport of (E)-10-OH-NT out from the CSF. The secretion from the CSF is more pronounced for the (-)-compared to the (+)-enantiomer, which is consistent with the stereoselectivity of the renal secretion of these compounds.

Treatment of depression with E-10-hydroxynortriptyline--a pilot study on biochemical effects and pharmacokinetics

The major metabolite of nortriptyline, i.e. E-10-hydroxynortriptyline (E-10-OH-NT), was given as a racemate in increasing doses from 75 to 225 mg/day to five patients with major depressive episode. Plasma concentrations of both the (-)- and (+)-enantiomers were linearly related to the doses. The mean ratio between them was 3.6 +/- 0.53, indicating stereospecific kinetics during maintenance treatment. Lumbar punctures were performed in four of the patients before and after 3 weeks of E-10-OH-NT treatment. There was a 18% mean decrease (P less than 0.01) in the noradrenaline metabolite HMPG in cerebrospinal fluid (CSF), supporting previous in vitro data showing that E-10-OH-NT inhibits noradrenaline uptake in vivo. During treatment, the median depression score measured by the Montgomery-Asberg Depression Rating Scale declined from 32 to 14 (P less than 0.05). As the study was open, the clinical outcome is not conclusive but does not contradict the hypothesis that E-10-OH-NT has antidepressant properties. If present at all, side effects were mild and did not interfere with the treatment.

Affinity of nortriptyline and its E-10-hydroxy metabolite for muscarinic receptors

In the present investigation, the binding of nortriptyline and its active metabolite 10-hydroxynortriptyline (E-10-OH-NT) to muscarinic receptors was studied in the heart, parotid gland, cerebral cortex, urinary bladder and ileum from guinea pig. The affinity of E-10-OH-NT, as determined by competition with 1-quinuclidinyl (phenyl 4-3H)benzilate (-)3H-QNB), was about 10-12 times lower than that of nortriptyline in each tissue and none of the compounds seemed to exhibit any tissue selectivity. It is concluded that increased heart rate induced by E-10-OH-NT, but not by nortriptyline, cannot be attributed to a selective blockade of cardiac muscarinic receptors.

Relationship of hydroxynortriptyline to nortriptyline concentration and creatinine clearance in depressed elderly outpatients

Plasma concentration of E-10-hydroxynortriptyline is increased in the elderly and may be related to both renal clearance of hydroxynortriptyline and rate of liver hydroxylation of nortriptyline. In 25 ambulatory, depressed elderly outpatients treated with therapeutic doses of nortriptyline, relationships among plasma levels of nortriptyline and E-10-hydroxynortriptyline, and an estimate of creatinine clearance were examined. Plasma levels of E-10-hydroxynortriptyline (corrected for varying dosage) were significantly correlated with age and inversely correlated (r = -0.50) with creatinine clearance but not with notriptyline or Z-10-hydroxynortriptyline concentration. E-10-hydroxynortriptyline concentration was about 5 1/2 times that of Z-10-hydroxynortriptyline. By best subsets multiple regression analyses, the ratio of E-10-hydroxynortriptyline to nortriptyline level was best predicted by plasma nortriptyline concentration, creatinine clearance, and age, all of which accounted for 63% of the variance. These results corroborate and extend previous findings in elderly inpatients in whom creatinine clearance was measured directly. In addition, age had an effect on E-10-hydroxynortriptyline independently of creatinine clearance. Since E-10-hydroxynortriptyline concentration has been related to both therapeutic efficacy and toxicity during nortriptyline treatment, it may be important to assess nortriptyline hydroxymetabolites in elderly patients and in those with renal insufficiency.

An automated method for the determination of nortriptyline and its isomeric 10-hydroxylated metabolites in plasma by high pressure liquid chromatography

A high pressure liquid chromatography assay for determination of the tricyclic antidepressant nortriptyline (NT) and its two major metabolites, Z- and E-10-Hydroxy-NT, in plasma is described. Sample preparation included addition of internal standard and a single step extraction procedure. Run time was approximately 14 min. with a LC-18. 5 mu 250 x 4.6 mm column, a mobile phase consisting of aqueous ammonium: methanol: acetonitrile (0.8:6.2:93, v/v), and flow of 1.3 ml/min. NT, Z- and E-10-OH-NT, amitriptyline, Z- and E-10-OH-AT and the internal standard desipramine, were adequately separated within this time span. In our laboratory, the assay has been employed mainly for pharmacokinetic and toxicologic studies in experimental animals at relatively high concentrations.

The pupil response to E-10-hydroxynortriptyline in rabbits with ocular sympathetic paresis

E-10-hydroxynortriptyline, a metabolite of nortriptyline with half the norepinephrine re-uptake blocking potency of the parent drug, but only 5% of its anticholinergic effect, was as effective as cocaine in demonstrating ocular sympathetic paresis. In five rabbits with unilateral superior cervical ganglionectomies, bilateral 5% cocaine HCl or E-10-hydroxynortriptyline maleate eye drops increased (P less than 0.001) the mean +/- SE anisocoria at 1 h by 1.84 +/- 0.03 mm or 2.16 +/- 0.33 mm, respectively. A single drop of E-10-hydroxynortriptyline did not alter corneal thickness or endothelial cell count.

Steady-state plasma levels of E- and Z-10-OH-nortriptyline in nortriptyline-treated patients: significance of concurrent medication and the sparteine oxidation phenotype

Steady-state plasma levels of nortriptyline and E- and Z-10-OH-nortriptyline were determined in 55 depressed patients during long-term treatment. Dose-corrected steady-state levels varied by a factor of 20 for nortriptyline, a factor of 7 for E-10-OH-nortriptyline (sum of enantiomers), and a factor of 12 for Z-10-OH-nortriptyline (sum of enantiomers). The E-10-OH-nortriptyline levels were higher than the corresponding nortriptyline levels in about 50% of the patients and the nortriptyline/E-10-OH-nortriptyline ratio ranged from 0.27 to 4.8. In contrast to E-10-OH-nortriptyline, the steady-state levels of Z-10-OH-nortriptyline correlated significantly with the nortriptyline levels (rs = 0.68, n = 55, p less than 0.001) and the nortriptyline/Z-10-OH-nortriptyline ranged from 1.7 to 10. Patients on concurrent treatment with perphenazine or benzodiazepines had higher nortriptyline and nortriptyline/E-10-OH-nortriptyline ratios than patients taking lithium or no other psychotropic drugs. A sparteine test was carried out in 22 patients and the sparteine metabolic ratio correlated significantly with the dose-corrected steady-state levels of nortriptyline (rs = 0.62, p less than 0.01) and E-10-OH-nortriptyline (rs = -0.52, p less than 0.02) and particularly well with the ratio nortriptyline/E-10-OH-nortriptyline (rs = 0.83). The genetic variability in the sparteine/debrisoquine P-450 isozyme appeared to be clearly more important for the interindividual variation in 10-hydroxylation of nortriptyline than the possible interactions with concurrent medication.

Steady state pharmacokinetics of nortriptyline in the frail elderly

The frail elderly, for whom chronic disease and disability are essentially universal, are at high risk for depression and are specifically vulnerable to the adverse effects of antidepressant medication. There have, however, been few investigations of either the pharmacokinetics or the clinical investigations of either the pharmacokinetics or the clinical response to antidepressants in such patients. We report on the pharmacokinetics of nortriptyline at steady state in a group of 22 patients, average age 84, living within an institutional setting. Comparison of our findings with those previously reported for younger and healthier subjects suggests that there are no clinically significant group differences in nortriptyline kinetics. Plasma levels of nortriptyline and those of both the trans- and cishydroxylated metabolites are linear with daily dose. Mean (and SD) for the parameter (plasma level/dose) was 1.21 (0.63) ng/ml/mg/day for the parent compound, 1.41 (0.86) for the trans metabolite, and 0.30 (0.16) for the cis metabolite. There was no significant correlation across individuals between the accumulation of the parent compound and the metabolites. Based upon these data, the average dose of nortriptyline required to achieve a plasma level of 100 ng/ml is 80 mg/day. Dose requirements, however, vary between individuals by a factor of 20. Plasma levels measured 24 hours after a 25-mg test dose of nortriptyline can allow early identification of slow metabolizers. Twenty-four-hour plasma levels (mean 8.8 ng/ml, SD 3.2) were significantly correlated with steady state levels at 25 mg/day (r = 0.71), steady state levels at 50 mg/day (r = 0.73), and each individual's average (plasma level/dose) (r = 0.57).

Stereoselective disposition of racemic E-10-hydroxynortriptyline in human beings

The disposition and elimination kinetics of the enantiomers of E-10-hydroxynortriptyline (E-10-OH-NT) were studied in six rapid and four slow hydroxylators of debrisoquin after a single oral dose of 75 mg racemic E-10-OH-NT hydrogen maleate. The plasma levels and the AUC of unconjugated (-)E-10-OH-NT were two to five times higher than those of (+)E-10-OH-NT. The plasma half-lives of both enantiomers were 8 to 9 hours. A significantly higher proportion of the given dose of (+)E-10-OH-NT (64.4% +/- 12.1%) than of (-)E-10-OH-NT (35.3% +/- 9.7%) was recovered in urine as glucuronide conjugate, but more (-)E-10-OH-NT was recovered unchanged in urine. The total oral plasma clearance and the metabolic clearance by glucuronidation were significantly (p less than 0.0001) higher for (+)E-10-OH-NT than for (-)E-10-OH-NT. The findings indicate that first-pass glucuronidation of E-10-OH-NT is enantioselective in human beings in vivo, with preference for (+)E-10-OH-NT. The renal clearance of unbound (-)E-10-OH-NT (0.57 +/- 0.16 L.kg-1.hr-1), on the other hand, exceeded that of (+)E-10-OH-NT (0.44 +/- 0.14 L.kg-1.hr-1) (p less than 0.005), which suggests enantioselective tubular secretion. The debrisoquin hydroxylation status was not associated with any of the investigated kinetic processes that relate to E-10-OH-NT.

Relationships among nortriptyline, 10-OH(E)nortriptyline, and 10-OH(Z)nortriptyline steady-state plasma levels and nortriptyline dosage

The postulated therapeutic activity of nortriptyline metabolites has prompted investigation of dosage adjustments based on plasma levels of nortriptyline (NT) and its metabolites. The method assumes that metabolite concentrations vary independently of nortriptyline concentrations among patients. This study tests that assumption and investigates different means of obtaining metabolite concentrations. Forty-two psychiatric inpatients were divided into three maintenance dose groups: 50, 100, and 150 mg NT/day. After a 28-day study for each inpatient, steady-state plasma concentrations for days 14, 18, 21, 25, and 28 were determined. Concentrations were averaged for each patient. Nortriptyline concentrations did not correlate well with corresponding 10-OH(E)nortriptyline (p greater than 0.05) or 10-OH(Z)nortriptyline concentrations (r2 = 0.31, p less than 0.05). Concentrations of 10-OH(E)nortriptyline did not correlate well with corresponding 10-OH(Z)nortriptyline concentrations (r2 = 0.236, p less than 0.05). Neither dose/body weight nor obesity were good predictors of individual concentrations of nortriptyline, 10-OH(E)nortriptyline, or 10-OH(Z)nortriptyline or even the sum of the three. In conclusion, optimal drug therapy may involve dosage adjustments according to the combined plasma levels of nortriptyline and metabolites. Assurance of obtaining certain plasma concentrations requires plasma level monitoring.

Validation of a therapeutic plasma level range in amitriptyline treatment of depression

In the course of a double-blind study, 29 depressed patients received amitriptyline 150 mg/day for 4 weeks. Scores on the Hamilton Depression Rating Scale were assessed before treatment and after 2 and 4 weeks, and plasma levels of amitriptyline, nortriptyline, and (E)-10-hydroxynortriptyline were monitored weekly. Response reflected by percent reduction of Hamilton Depression Rating Scale score and by final score was better at steady-state amitriptyline + nortriptyline concentrations of 125-210 ng/ml than at lower and higher plasma levels. This applied to the total group and to the subgroup of 22 female patients. The data confirm the results of a previous study performed in the same hospital. An influence of the (E)-10-hydroxynortriptyline concentration in plasma on therapeutic outcome was not discernible. The results suggest that plasma level monitoring may be helpful when patients do not respond to conventional amitriptyline doses.

10-Hydroxynortriptyline and treatment effects in elderly depressed patients

Sixty-four elderly depressed outpatients were treated with nortriptyline for seven weeks. Plasma nortriptyline and its main metabolite, 10-hydroxynortriptyline, were measured weekly. No relationship was found between levels of 10-hydroxynortriptyline and clinical response. Plasma levels of the trans isomer, E-10-hydroxynortriptyline, were significantly lower when dizziness and symptoms of orthostatic hypotension were reported, although there was no significant correlation with actual orthostatic drop in systolic pressure. Plasma level of 10-hydroxynortriptyline was not significantly correlated with the other reported side effects.

Plasma levels of nortriptyline and 10-hydroxynortriptyline and treatment-related electrocardiographic changes in the elderly depressed

Thirty-one elderly depressed patients were treated for seven weeks with nortriptyline with plasma levels kept between 50-180 ng/ml. Electrocardiograms were taken at the third and seventh weeks of treatment. There were significant increases in the PR interval, QTc interval, and heart rate from before and after treatment. However, there were no consistent correlations between electrocardiographic changes during treatment and plasma levels of nortriptyline, 10-hydroxynortriptyline and either of its two isomers (E-10-hydroxynortriptyline, Z-10-hydroxynortriptyline). Increased QRS duration after seven weeks of treatment was correlated with daily dose of nortriptyline.

Electrocardiographic changes with nortriptyline and 10-hydroxynortriptyline in elderly depressed outpatients

Pharmacokinetic factors may contribute to altered nortriptyline effects in the elderly. Plasma concentrations of nortriptyline's principal metabolite, E-10-hydroxynortriptyline, tend to be greater than nortriptyline, increase with age, and may contribute to cardiotoxicity. Electrocardiogram changes were evaluated in 21 ambulatory, elderly, depressed outpatients who were treated with therapeutic doses of nortriptyline. Resting electrocardiograms were obtained before and after 6 weeks of treatment. Plasma samples were assayed simultaneously for nortriptyline, E-, and Z-10-hydroxynortriptyline. Three subjects developed a first degree atrioventricular block and one developed a right bundle branch block during treatment. Mean daily nortriptyline dose and steady state plasma level in these subjects did not differ from those who did not develop conduction defects, but E-10-hydroxynortriptyline levels were significantly higher. Overall, there were significant correlations between changes in the PR interval and QRS duration with plasma concentrations of nortriptyline, E-10-hydroxynortriptyline, Z-10-hydroxynortriptyline, and the sum of nortriptyline and its 10-hydroxynortriptyline metabolites. Multiple regression analyses suggested that increases in PR interval were associated with increasing nortriptyline concentration, while increases in QRS duration and Q-Tc intervals were associated with increasing Z-10-hydroxynortriptyline concentration. E- and Z-10-hydroxynortriptyline may contribute substantially to the cardiac conduction effects of nortriptyline treatment and may be of particular importance in the elderly.

Plasma 10-hydroxynortriptyline and therapeutic response in geriatric depression

Geriatric inpatients with major depression received nortriptyline for 4 weeks. Plasma E-10-hydroxynortriptyline concentrations were correlated positively with residual Hamilton depression ratings and negatively with changes in ratings.

Isomers of 10-hydroxynortriptyline in geriatric depression

In geriatric, depressed inpatients treated with nortriptyline (NT), total unconjugated plasma concentrations of the Z isomer of the 10-hydroxylated metabolite (10-OH-NT) were determined simultaneously with concentrations of the E isomer by high-performance liquid chromatography. Z-10-OH-NT concentrations averaged 14% of E-10-OH-NT concentrations.