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.

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.

Clinical and biochemical effects during treatment of depression with nortriptyline: the role of 10-hydroxynortriptyline.

Plasma concentrations of nortriptyline (NT) and its major metabolite 10-hydroxy-NT (10-OH-NT) were measured in 30 patients with depression, treated with NT for 3 weeks. Nine patients who recovered completely had plasma concentrations of NT and 10-OH-NT ranging from 358 to 728 nmol/L and from 428 to 688 nmol/L, respectively. Of the 21 patients who did not recover completely, only four had plasma concentrations within the window limited by these two plasma concentration ranges. A correlation was found between the degree of amelioration and the plasma concentration of NT (rs = 0.469; P less than 0.01). Lumbar punctures were performed in 26 patients before and after 3 weeks of NT treatment. During treatment there was a 30.9% mean decrease in the noradrenaline metabolite 4-hydroxy-3-methoxyphenylglycol (HMPG) in cerebrospinal fluid (CSF). We could not evaluate the extent to which this decrease was caused by NT or 10-OH-NT, respectively, because both are strong inhibitors of noradrenaline uptake. The ratio between the concentration of NT and 10-OH-NT in CSF correlated to the reduction of HMPG in CSF (r = 0.397; P less than 0.05) and to the amelioration of depression (rs = 0.623; P less than 0.001). This might indicate that NT and 10-OH-NT interact on the noradrenaline system in a nonadditive way. During treatment there was a 15.2% decrease in CSF concentration of the serotonin metabolite 5-hydroxyindoleacetic acid. The reduction was significantly correlated to the CSF concentration of NT but not to that of 10-OH-NT. This is in accordance with the fact that NT is a more potent inhibitor of serotonin uptake than is 10-OH-NT. The dopamine metabolite homovanillic acid in CSF decreased significantly by 10.0%. The biochemical data indicate that noradrenergic, serotoninergic, and dopaminergic systems are affected by NT treatment and that 10-OH-NT might be more selective on noradrenergic neurons than the parent drug.

CSF and plasma levels of nortriptyline and its 10-hydroxy metabolite.

After 3 weeks' nortriptyline (NT) treatment the mean plasma concentration of its 10-hydroxy metabolite (10-OH-NT) (599 +/- 207 nmol l-1) was higher than that of the parent drug (433 +/- 199 nmol l-1) in 25 depressed patients. Also in the cerebrospinal fluid (CSF) the mean level of 10-OH-NT (67 +/- 20 nmol l-1) was higher than that of NT (39 +/- 23 nmol l-1). There was a strong correlation (P less than 0.001) between the CSF and plasma concentration of both NT (r = 0.92) and 10-OH-NT (r = 0.77). The interindividual variation in the CSF/plasma ratio of both compounds was small, compared to the variation in plasma levels. These results show that 10-OH-NT passes the blood-brain barrier as it is present in concentrations higher than those of NT in the CSF. 10-OH-NT has previously been shown to be a potent blocker of noradrenaline uptake and to have much less affinity for muscarinic receptors than NT itself. This active metabolite might therefore be a potential antidepressant with less disturbing anticholinergic side-effects.

Cerebrospinal fluid levels of amitriptyline, nortriptyline, imipramine and desmethylimipramine. Relationship to plasma levels and treatment outcome.

Fifty-five (55) depressed patients were treated with amitriptyline (AMI) or imipramine (IMI). Concentrations of AMI, IMI, and their metabolites, nortriptyline (NT) and desmethylimipramine (DMI), were measured in cerebrospinal fluid (CSF) and plasma at steady state by gas chromatography mass spectrometry (GC/MS). Highly significant correlations between CSF and plasma levels of AMI, NT, IMI, and DMI were found (r greater than 0.75; P less than 0.0001 in all cases). There were no significant sex, diagnostic subgroup, or geographic difference in any of the drug parameters measured. An evaluation of the relationship between CSF levels of drug variables and clinical response showed essentially no significant correlations between these various parameters. The results obtained do not support the concept of a 'therapeutic window' for levels of plasma NT in AMI-treated patients. Furthermore, the highly significant correlations between CSF and plasma compartments in terms of drug and metabolite levels would argue against the need to measure CSF levels of these parameters in clinical practice. Plasma level measurements should be equally informative, and simpler to obtain.