Coordinated intrahepatic and extrahepatic regulation of cytochrome p4502D6 in healthy subjects and in patients after liver transplantation

Cytochrome p450 (CYP) 2D6 activity exhibits wide intersubject variation even among individuals with similar genotypes in whom the active enzyme is expressed. There is, therefore, a need to understand the mechanisms involved in determining its activity. The relationship of messenger ribonucleic acid (mRNA) expression to CYP2D6 activity has been evaluated in hepatic and extrahepatic tissues to test the hypothesis of coordinated regulation. In human liver microsomes, there was a greater than 25-fold variation in both bufuralol hydroxylation and concentration of mRNA for CYP2D6, with a significant association between variables (n = 20; Spearman correlation coefficient [r(s)] = 0.85, P <.001). In normal subjects, there was a similar extent of interindividual variation in in vivo activity of CYP2D6, measured as the debrisoquin (INN, debrisoquine) recovery ratio, and in mRNA for CYP2D6 in peripheral blood mononuclear cells, with a significant association between variables (n = 78; r(s) = 0.56 [95% confidence interval, 0.35 to 0.73], P <.001), whereas no association was found between mRNA for CYP2D6 and CYP2E1 activity. Recipients of liver transplants, at a time of stable liver function, had a similar relationship between debrisoquin recovery ratio and concentration of mRNA for CYP2D6 in peripheral blood mononuclear cells (n = 27; r(s) = 0.74 [95% confidence interval, -0.16 to 0.44], P <.001). Three recipients, who had CYP2D6*4/*4 genotypes, remained phenotypically poor metabolizers for CYP2D6 after liver transplantation. Collectively, these results imply that transcriptional regulation of mRNA for CYP is a major determinant of in vivo activity and that regulation of intrahepatic and extrahepatic enzymes is coordinated, possibly through a mechanism that is predominantly extrahepatic.

QTc interval lengthening is related to CYP2D6 hydroxylation capacity and plasma concentration of thioridazine in patients

Thioridazine cardiotoxicity has been associated with a prolonged heart-rate corrected QT (QTc) interval. However, no systematic studies have been performed on patients at therapeutic doses. The present study aimed to evaluate the influence of dose and plasma concentration of thioridazine and CYP2D6 enzyme status on the QTc interval in psychiatric patients. Sixty-five Spanish European psychiatric patients receiving thioridazine antipsychotic monotherapy were studied. The plasma levels of thioridazine and its metabolites were determined by high-performance liquid chromatography. All patients were phenotyped for CYP2D6 activity with debrisoquine during treatment. Thirty-five patients (54%) had a QTc interval over 420 ms. The lengthening of QTc interval was correlated with plasma concentration (p < 0.05) and daily dose (p < 0.05) of thioridazine. CYP2D6 enzyme hydroxylation capacity, evaluated by debrisoquine metabolic ratio (MR) (p < 0.05) and thioridazine/mesoridazine ratio (p < 0.05), was also correlated with QTc intervals. The present study shows the relationship between QTc interval lengthening among psychiatric patients treated at therapeutical doses with the dose and the plasma concentration of thioridazine. Since debrisoquine MR has been shown to be correlated with the QTc intervals, CYP2D6 enzyme hydroxylation capacity might be relevant in determining the risk for QTc interval lengthening. Patients with impaired CYP2D6 enzyme activity due to enzyme inhibition by thioridazine might be more prone to increased risk of sudden death due to torsade de pointes type cardiac dysrhythmia.

The African-specific CYP2D617 allele encodes an enzyme with changed substrate specificity

OBJECTIVE

The effects of the CYP2D6*17 and *29 alleles on substrate specificity and enzyme activity were studied by correlating CYP2D6 genotype to phenotype with 4 probe drugs (codeine, debrisoquine, dextromethorphan, metoprolol) in black Tanzanians and white Swedes.

METHODS

The black Tanzanian subjects represented the following 6 genotypic groups: A, (CYP2D6*1 or *2)/(*1 or *2) (n = 13); B, CYP2D6*17 /*17 (n = 5); C, CYP2D6*29 /*29 (n = 4); D, CYP2D6*1 /*17 (n = 5); E, CYP2D6*5/*17 (n = 4); and F, various genotypes (n = 4). The white subjects were from 4 groups, as follows: A, (CYP2D6*1 or *2)/(*1 or *2) (n = 7); B, (CYP2D6*1 or *2)/(*3, *4, or *5) (n = 7); C, homozygous for defect alleles (n = 7); and D, duplicated CYP2D6 gene (n = 2).

RESULTS

The metabolic ratios of the 4 probe drugs correlated significantly (r (s) = 0.69-0.92; P <.001) in both populations. Tanzanian subjects homozygous for the CYP2D6*17 allele were slower metabolizers when debrisoquine or dextromethorphan was used as the probe drug than when codeine or metoprolol was used, showing a different substrate specificity of CYP2D6.17 than of CYP2D6.1 and CYP2D6.2. This was confirmed with analysis of covariance of the different metabolic ratios for a subgroup of subjects carrying only the CYP2D6*17 mutated allele (n = 9) compared with all other subjects (n = 44). The metabolic ratios of dextromethorphan and metoprolol differed significantly among Tanzanian subjects homozygous for the CYP2D6*29 allele compared with those with CYP2D6*1 or *2 alleles.

CONCLUSION

We found differences in the disposition of 4 CYP2D6 probe drugs in black Tanzanians compared with Swedes. The differences were caused by the presence of CYP2D6.17 and CYP2D6.29. The results show that CYP2D6.17 exhibits altered substrate specificity compared with CYP2D6.1 and CYP2D6.2.

Therapeutic drug monitoring in depression

The difference between Therapeutic Drug Monitoring (TDM) and uncontrolled therapy consists in the fact that in TDM we can predict a certain scheme of treatment according to clinical and laboratory results. It is a method which serves to increase the efficacy and safety of pharmacotherapy in an individual patient. This paper presents the results of the treatment with tricyclic antidepressants based on the monitoring of serum drug level in 32 patients with indications for using pharmacogenetic as well as pharmacoelectroencephalographic tests. Clinical status of the patients was evaluated according to: Hamilton Depression Rating Scale (HDRS), Hamilton Anxiety Rating Scale (HARS), Clinical Global Impression Scale (CGIS), and TCA concentration in serum was determined using Fluorescence Polarization Immunoassay (FPIA). Hydroxylation phenotype was determined using debrisoquine as a model drug. EEG was recorded in four leads: F3-C3, F4-C4, P3-O1, P4-O2. In the present study, we did not found any significant correlation between clinical status and serum TCAs concentrations measured by FPIA method. Efficacy of antidepressant treatment and stabilization of serum TCA concentrations depended largely upon the time course of the treatment. Debrisoquine phenotyping revealed the presence of one poor metabolizer (MR = 15) in the examined group of patients. A significant improvement in the clinical status of the patients, the stabilization of therapeutic drug concentrations, the appearance of antidepressive profiles in the pharmaco-EEG profile after 14 days of therapy, as well as the starting value determined by SERS were shown to be prognostic factors for the further antidepressant therapy.

Similarities and/or dissimilarities of CYP2D6 polymorphism in three Tunisian ethnic groups: Arabs, Berbers, Numides

Using the validated probe drug debrisoquine and the 8 h urinary metabolic ratio debrisoquine/4 hydroxy-debrisoquine, we have determined the phenotype of the debrisoquine CYP2D6 dependent polymorphic metabolism in 464 Arabs, 227 Berbers and 215 Numides to elicit similarities or dissimilarities of poor metabolizer (PM) prevalence. We found 2.36 per cent of PM in Arabs, 3.08 per cent in Berbers and 2.33 per cent in Numides. These figures are similar to those observed in Middle East populations, and cannot be considered as different from those observed in Caucasians.

Validation of the five-drug "Pittsburgh cocktail" approach for assessment of selective regulation of drug-metabolizing enzymes

OBJECTIVES

To determine whether the probe drugs caffeine, chlorzoxazone, dapsone, debrisoquin (INN, debrisoquine), and mephenytoin can be simultaneously administered as a metabolic cocktail to estimate in vivo cytochrome P450 (CYP) and N-acetyltransferase enzyme activities.

METHODS

Fourteen healthy nonsmoking male volunteers (mean age +/- SD, 21.6 +/- 2.2 years) received 100 mg caffeine, 250 mg chlorzoxazone, 100 mg dapsone, 10 mg debrisoquin, and 100 mg mephenytoin individually and in four and five-drug combinations in a randomized manner using a 7 x 7 Latin square. Each drug or drug combination was given orally after an overnight fast, with a minimum 1-week washout between administrations. In each session, urine was collected from 0 to 8 hours and plasma was obtained at 4 and 8 hours after drug administration. Plasma and metabolite concentrations were used to estimate phenotypic trait measures for the efficiency of each drug's metabolism.

RESULTS

The phenotypic indexes determined for caffeine, chlorzoxazone, dapsone, debrisoquin, and mephenytoin were not significantly different when given alone than when given in combination. The median percentage change of the trait measures observed during administration of all five compounds compared with individual administration ranged from -10.7% for the 6-hydroxychlorzoxazone to chlorzoxazone plasma ratio to +2.2% for the debrisoquin recovery ratio.

CONCLUSIONS

The results of this study show that caffeine, chlorzoxazone, dapsone, debrisoquin, and mephenytoin in low doses can be simultaneously administered without metabolic interaction. This cocktail approach can thus simultaneously provide independent in vivo phenotypic measures for multiple CYP enzymes and N-acetyltransferase.

N-acetylation and hydroxylation polymorphisms in type II diabetics with microvascular disturbances

The N-acetylation and hydroxylation (CYP2D6) genetic polymorphisms were assessed in 43 healthy subjects and in 84 type II (non-insulin-dependent) diabetics. The proportions of slow and fast acetylators as well as poor and extensive metabolisers in a group of diabetics suffering from microvascular disturbances (nephropathy, retinopathy and neuropathy) were compared with the control group and with diabetics without such complications. Sulphadimidine was used as a probe for polymorphic acetylation and debrisoquine for CYP2D6. Debrisoquine and its 4-OH metabolite were assayed by means of HPLC, and sulphadimidine using a modified Bratton-Marshall procedure. The frequency of the slow phenotype (63%) was significantly higher in diabetics with microvascular disturbances than in patients without diabetic complications (P < 0.005). In patients with type II diabetes (84), only the extensive phenotype of hydroxylation was observed.

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.

Phenobarbital induces the 2-hydroxylation of desipramine

The kinetics of a single oral dose of desipramine (DMI; 100 mg) were studied in eight epileptic patients chronically treated with phenobarbital (PB) and in eight drug-free healthy controls. All subjects were extensive metabolizers with respect to the genetically determined CYP2D6-related metabolic polymorphism. Compared with controls, epileptic patients exhibited lower peak plasma DMI concentrations (74 +/- 24 vs. 107 +/- 32 nmol/L; means +/- SD, p < 0.05), smaller DMI area-under-the-curve values (1,943 +/- 461 vs. 3,234 +/- 1,145 nmol L-1 h; p < 0.01), and shorter DMI elimination half-lives (15.1 +/- 2.1 vs. 20.6 +/- 3.4 h; p < 0.01). The proportion of the dose excreted as 2-hydroxydesipramine (2-OH-DMI) was significantly higher in the patients (54 +/- 8 vs. 40 +/- 9%; p < 0.05). In one single poor metabolizer volunteer, a 3-week treatment with PB was associated with no major changes in DMI kinetics, but the urinary excretion of 2-OH-DMI tended to increase. These results suggest that PB is an inducer of the 2-hydroxylation of DMI, a reaction primarily catalyzed by CYP2D6, but do not provide further information on the specific P450 isoenzyme(s) being induced.

Prevalence of CYP2D6 gene duplication and its repercussion on the oxidative phenotype in a white population

The occurrence of multiple copies of the CYP2D6 gene was investigated 217 white healthy Spaniards by the combined use of Xba I and Eco RI restriction fragment length polymorphism (RFLP) analyses. About 3.5% of the alleles yielded an 12.1 kb Eco RI-RFLP product in combination with the 42 kb Xba I-RFLP product, which is indicative of multiple CYP2D6. The prevalence of subjects carrying multiple CYP2D6 was 7%. The 12.1 kb Eco RI-RFLP product was highly associated (60%) with the presence of the genotype 29wt/42wt, as characterized by mutation-specific polymerase chain reaction and Xba I-RFLP analyses. Six subjects who had multiple CYP2D6 had other genotypes, namely, 44wt/42wt (four subjects), 29C/42wt (one subject), and one subject had a 12.1 kb product plus the CYP2D6C mutation associated with the 44 kb/42 kb genotype. All subjects identified as carrying multiple CYP2D6 had only two CYP2D6 copies in the same chromosome and were classified as carriers of the (CYP2D6L)2 allelic variant. Phenotyping with debrisoquin indicated an increase in the oxidative capacity as a function of the number of functional CYP2D6 genes. The metabolic ratio and the 95% confidence limits were as follows: subjects lacking functional genes, 48.8 (95% confidence limits, 14.4 to 79.3); subjects with one functional gene, 2.14 (95% confidence limits, 0.61 to 3.67); subjects with two functional genes, 1.5 (95% confidence limits, 0.88 to 2.14); and subjects with three functional genes, 0.33 (95% confidence limits, 0.22 to 0.45).(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the central dopaminergic index of plasma HVA in schizophrenia

Under fasting conditions, the dopamine (DA) metabolite homovanillic acid (HVA) in plasma originates mainly from central DA neurons or from central and peripheral noradrenergic (NA) neurons. The latter source contributes, in addition to HVA, the norepinephrine metabolites, for example, 3-methoxy-4-hydroxyphenylglycol (MHPG). It has been shown in primates that the association between HVA and MHPG in plasma or urine under varying rates of NA metabolism can be used to obtain an estimate of the central DA neuronal contribution of HVA to plasma or urine. This estimate is called the central dopaminergic index (CDI). Two studies presented here examine the applicability of this model in schizophrenia patients. The results were consistent with the proposed model and suggested that only about 30 percent of the total plasma HVA concentrations in our patients were derived from central DA neurons. A convenient modification of this model is proposed for future studies. Since the CDI of plasma HVA is not likely to be confounded by NA activity, this tool may prove useful in disentangling the roles played by the DA and NA systems in schizophrenia.

Plasma HVA levels following debrisoquine administration do not reflect cerebral dopamine loss in early Parkinson's disease

Plasma levels of homovanillic acid (pHVA) following debrisoquine (DBQ) administration may be indicative of central dopaminergic activity. The effect of DBQ (10-20 mg) administration on pHVA in young healthy volunteers was studied to establish a protocol for use in de novo patients with Parkinson's disease. Subsequently, pHVA in de novo patients with Parkinson's disease were measured and compared to young healthy volunteers. Following DBQ (10 mg) administration to healthy volunteers, pHVA fell with time to a maximum of 62% of control values at 6 h. The decrease in pHVA was not affected by loading with DBQ (10 mg) 10 h previously (pHVA: 67.6 +/- 5.8% of preDBQ levels) or increasing the dose to 20 mg (56.1 +/- 11.8% of preDBQ levels) compared to a single 10 mg dose of debrisoquine (66.5 +/- 4.5% of preDBQ levels). pHVA was reduced in both de novo patients with Parkinson's disease and in healthy volunteers following DBQ (10 mg) administration. However, there was no difference in pHVA before or after DBQ administration when comparing the two groups. These results suggest that, following DBQ administration, pHVA does not reflect dopamine neuronal loss in de novo patients with Parkinson's disease, so it is unlikely to detect the disease before the clinical symptoms manifest themselves.

Studies of catecholamine metabolism in schizophrenia/psychosis--I

Acutely psychotic schizophrenic patients not taking antipsychotic medications and control subjects were studied before and during treatment with debrisoquin (DBQ), an inhibitor of monoamine oxidase, which does not penetrate into brain. Homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured in plasma, urine, and cerebrospinal fluid (CSF). Significant differences between patients and control subjects were more easily discerned during treatment with DBQ. In patients, HVA was increased in plasma but not in urine or CSF, although MHPG was increased in all three fluids. There were many significant correlations between plasma MHPG and HVA levels and clinical ratings of psychoticism. Plasma MHPG correlated positively with both the severity of positive and negative symptoms and plasma HVA correlated only with positive symptom severity. These data suggest that both dopamine and norepinephrine (NE) metabolism are disturbed in acutely psychotic schizophrenic patients; disturbed NE metabolism may relate to negative symptoms as well.

Utility of a one-point (3-hour postdose) plasma metabolic ratio as a phenotyping test using metoprolol in two east Asian populations

We examined the utility of the postdose 3-h plasma metabolic ratio (MR) as a phenotyping method for assessing genetically determined debrisoquine-type oxidation polymorphism after an oral dose of 100 mg of metoprolol tartrate administered to 402 unrelated, healthy, and native East Asian (218 Korean and 184 Japanese) subjects. All of them were phenotyped simultaneously with the reported MR employing urine samples collected during an 8-h postdose period. In the two populations, the distribution histograms and probit plots of log10plasma MRs derived from the metoprolol/alpha-hydroxymetoprolol concentration values indicated a large gap between the extensive and poor metabolizers who were phenotyped by the reported criteria of the 8-h urinary MR. There were statistically significant (p less than 0.001) correlations (rs = 0.688 and 0.810, respectively) between the postdose urinary and plasma MRs in the Korean and Japanese populations. Two poor metabolizers (one each included in the two racial groups) identified according to the 8-h urinary MR gave the greatest plasma MRs (i.e., 549.7 among the Koreans and 150.0 among the Japanese). The results suggest that the one-point, postdose 3-h plasma MR is also useful for the phenotyping purpose of oxidation pharmacogenetic polymorphism of metoprolol, a widely prescribed beta-adrenoceptor blocking drug.

Perhexiline maleate-induced hepatitis

We report on a case of perhexiline maleate-induced hepatitis secondary to a long-term administration of recommended daily dosages of 300 mg. The patient had a spectacular weight loss of 29 kg. He developed hepatitis, which subsided after drug withdrawal. Our electron-microscopic findings with the typical inclusion bodies and impaired hydroxylation capacity point to an underlying metabolic disorder as the pathogenetic mechanism.

Role of genetics and drug metabolism in human cancer risk

The research field concerning responses to drugs having a hereditary basis is called 'pharmacogenetics'. At least 5 dozen pharmacogenetic polymorphisms have been described in clinical medicine; many are responsible for marked differences in genetic predisposition toward toxicity or cancer. Three are detailed here: the acetylation, the debrisoquine, and the AH locus polymorphism. All 3 are very common among the United States' population: 1 in 2 is a 'slow acetylator', 1 in 12 is a 'poor metabolizer' for more than 2 dozen commonly prescribed drugs in the debrisoquine panel, and the CYP1A1 and CYP1A2 (cytochromes P(1)450 and P(3)450) genes are highly inducible by cigarette smoke in 1 of 10 patients. Differences in xenobiotic metabolism between individuals in the same family can be greater than 200-fold, suggesting that occupationally hazardous chemicals, as well as prescribed drugs having a narrow therapeutic window, might cause strikingly dissimilar effects between patients of differing genotypes. Our ultimate goal is 'preventive toxicology', i.e. the development of simple, inexpensive, unequivocal and sensitive assays to predict individual risk of toxicity or cancer. These tests could help the individual in choosing a safer life style or place of work and might aid the physician in deciding which drug to prescribe.

A new approach to biochemical evaluation of brain dopamine metabolism

1. Dopaminergic neurotransmission in brain is receiving increased attention because of its known involvement in Parkinson's disease and new methods for the treatment of this disorder and because of hypotheses relating several psychiatric disorders to abnormalities in brain dopaminergic systems. 2. Chemical assessment of brain dopamine metabolism has been attempted by measuring levels of its major metabolite, homovanillic acid (HVA), in cerebrospinal fluid, plasma, or urine. Because HVA is derived in part from dopamine formed in noradrenergic neurons, plasma levels and urinary excretion rates of HVA do not adequately reflect solely metabolism of brain dopamine. 3. Using debrisoquin, the peripheral contributions of HVA to plasma or urinary HVA can be diminished, but the extent of residual HVA formation in noradrenergic neurons is unknown. By measuring the levels of methoxy-hydroxyphenylglycol (MHPG) in plasma or of urinary norepinephrine metabolites (total MHPG in monkeys; the sum of total MHPG and vanillyl mandelic acid (VMA) in humans) along with HVA, it is possible to estimate the degree of impairment by debrisoquin of HVA formation from noradrenergic neuronal dopamine and thereby better assess brain dopamine metabolism. 4. This method was applied to a monkey before and after destruction of the nigrostriatal pathway by the administration of MPTP.

Acetylation of maprotiline and desmethylmaprotiline in depressive patients phenotyped with sulfamidine, debrisoquine, and mephenytoin

A gas chromatographic/mass spectrometric method (using either electron impact or chemical ionisation with methane or ammonia) is described for the quantitative analysis of maprotiline (MP, Ludiomil), N-acetylmaprotiline (AcMP) and N-acetyldesmethylmaprotiline (AcDMP) in whole blood or plasma. In two groups (A and B) of 82 and 53 depressive patients treated clinically with MP for 10 and 21 days, respectively, plasma and whole blood MP was monitored during the treatment. In group A, all subjects were phenotyped with debrisoquine and mephenytoin, and 44 with sulfamidine. 5 patients were poor metabolizers of debrisoquine and 2 of mephenytoin; 18 subjects were fast acetylators of sulfamidine. Traces of AcMP were found only in two patients. AcDMP was present in levels below 2 ng/ml in the plasma of most of the patients in group A. In group B, AcDMP levels between 2.4-14.6 ng/ml of whole blood were found in 9 patients. The mass spectral data suggest the presence of another, unknown MP metabolite interfering partly with the analysis of AcDMP. The presence of AcDMP seemed not to be related to the phenotype of the patients as determined by the pharmacogenetic tests.

[Pharmacogenetics of antidepressant metabolism. Value of the debrisoquin test]

The drug monitoring of antidepressants in blood plasma has revealed considerable interindividual differences in steady-state levels. For some compounds recent results strongly suggest that this phenomenon finds an explanation in genetic differences in the metabolism of the drugs by monooxygenases (cytochrome P-450) in the liver. Thus, a genetic deficiency has been described in 5-10% of the European population in the metabolism of debrisoquine and sparteine. Clinical experience shows that the separation of subjects into extensive metabolizers (EM) and poor metabolizers (PM) is also valid for drugs of interest in psychiatry, such as some betablockers and antidepressants like amitriptyline, nortriptyline and desipramine. Actually, PMs of debrisoquine may develop excessively high levels of these antidepressants in blood during the treatment. On the other hand, it is probable that, at least, one oxidative pathway of maprotiline belongs to the genetic polymorphism of debrisoquine, but a deficiency in the metabolism of this test substance does not necessarily mean high levels of maprotiline. Today's clinical experience shows that, in some cases, PMs of debrisoquine do not respond to a treatment with nortriptyline. However, this has not been demonstrated for amitriptyline. It is predicted that pharmacogenetic tests will find their place in psychopharmacotherapy, especially for subjects candidates for a long-term treatment or susceptible to suffer from side effects. However, the validity of the test remains to be demonstrated for other drugs, like benzodiazepines and neuroleptics, but also in the case of patients suffering from organic diseases or under treatment with potential competitors.

Brief debrisoquin administration to assess central dopaminergic function in children

Central dopaminergic (DA) function in children was assessed by monitoring plasma-free homovanillic acid (pHVA) levels after brief (18 hour) administration with debrisoquin sulfate, a peripherally active antihypertensive agent that blocks peripheral, but not central, HVA production. Brief debrisoquin administration resulted in marked reductions in pHVA in each of six patients studied. In five of the six patients, post-debrisoquin pHVA levels remained relatively stable over the six-hour period of observation. No significant cardiovascular or behavioral side effects of debrisoquin were observed. The brief debrisoquin administration method appears to be a safe, simple, and potentially valid peripheral technique for evaluating aspects of central dopaminergic function in children with neuropsychiatric disorders. Additional work is needed to further establish this method's validity and reliability.

Norepinephrine-related mechanism in hypertension accompanying renal failure

Various blood pressure (BP)-regulating factors were assessed before and after 4 weeks of selective norepinephrine (NE) inhibition with the sympathetic neurone blocker, debrisoquine, in nine hypertensive, nine normotensive hemodialysis patients (HDP), and 11 normal subjects. On placebo, hypertensive HDP had an increased total blood volume (P less than 0.05) and exchangeable sodium (P less than 0.001), while both HDP groups had increased (P less than 0.05) plasma clearances of NE and angiotensin II (AII), and tended to have higher basal plasma NE, renin, and AII levels, and lower BP responses to NE or AII than normal subjects. Plasma epinephrine and the chronotropic dose of isoproterenol (CDI) did not differ significantly among groups. Debrisoquine lowered supine BP markedly in hypertensive HDP (on average from 181/107 to 148/88 mm Hg) and slightly in normotensive HDP (143/78 to 131/76 mm Hg), but not in normal subjects (116/74 to 120/79 mm Hg). In all groups, plasma NE, CDI, and NE pressor dose were reduced in parallel (by 35 to 75%; P less than 0.05 to less than 0.001), and the relation between stepwise increasing plasma NE and BP changes during NE infusion was commensurably displaced to the left (P less than 0.01). The remaining parameters were not changed consistently.

CONCLUSION

HDP, as normal subjects, respond to decreased sympathetic outflow with increased alpha- and beta-receptor sensitivity. Hypertension in HDP depends strongly on a NE-related mechanism. The latter seems to complement renin-angiotensin, sodium and fluid volume in the pathogenesis of high BP.

[The use of low-dose amitriptyline in psychogeriatrics. A clinical, pharmacokinetic and pharmacogenetic study]

Two groups of six depressive psychogeriatric patients (age 69-93) have been treated for three weeks with either 25 mg or 50 mg of amitriptyline (AT) per day. Before the beginning of the treatment and after 8, 15 and 22 days of medication, the patients (7 outpatients and 5 hospitalized patients) underwent various psychopathological tests (Hamilton, Crichton) and biochemical investigations, i.e. clinical chemistry and hematology, analyses of AT and nortriptyline (NT), in the plasma. In some subjects the hydroxylated metabolites and the binding of these substances to plasma proteins were also measured. Except one patient, all responded favourably to the treatment. No difference between the two doses has been observed as regards their clinical efficacy and incidence of side effects. The plasma levels of AT and NT were below those generally recommended in the literature. The monitoring served to identify some cases of noncompliance and, in one patient, a deficiency of hydroxylation of AT, confirmed by the debrisoquine test. These results suggest that the "therapeutic window" needs redefinition and that low-dose medication with antidepressants is indicated in a psychogeriatric population.