The genetics of loop diuretic effects.

Little is known about the genetic impact on loop diuretic effects. We newly investigated five genetic polymorphisms in 95 healthy volunteers, who had ingested bumetanide, frusemide and torsemide. The subjects excreted means of 20.2 g sodium chloride, 2.87 g potassium and 261 mg calcium over 24 h. Concerning sodium chloride, the subjects excreted 2.2 g less per two T-alleles of C825T in the G nucleotide ß-subunit 3 (GNB3), 3.2 g less per two Met32-alleles of Val32Met in the atrial natriuretic peptide precursor (ANP) and 2.8 g more per two Arg152-alleles of Ter152Arg in ANP (P=0.007, 0.05 and 0.007). Concerning potassium, the subjects excreted 0.42 g more per two ANP Arg152-alleles (P=0.023). Concerning calcium, the subjects excreted 32 mg more per two deletion-alleles of the insertion/deletion polymorphism in the angiotensin-converting enzyme, 44 mg more per two Trp460-alleles of Gly460Trp in α-adducin (ADD1) and 42 mg less per two GNB3 T-alleles (P=0.006, 0.023 and 0.008). The common genetic impact together with three polymorphisms in the sodium chloride cotransporter and the epithelial sodium channel was 20, 15, 10 and 23% of the variation in the urinary excretion of sodium chloride, volume, potassium and calcium. This exceeded the fraction of variation explained by differences in the pharmacokinetics: 13, 10, 11 and 6%. Thus, genetic variation seems to be a stronger predictor of the loop diuretic drug response than pharmacokinetic variation.

The effects of genetic polymorphisms in the organic cation transporters OCT1, OCT2, and OCT3 on the renal clearance of metformin.

Organic cation transporters (OCTs) can mediate metformin transmembrane transport. We explored metformin pharmacokinetics in relation to genetic variations in OCT1, OCT2, OCT3, OCTN1, and MATE1 in 103 healthy male Caucasians. Renal clearance varied 3.8-fold and was significantly dependent on creatinine clearance (r(2) = 0.42, P < 0.0001), age (r(2) = 0.09, P = 0.002), and OCT1 polymorphisms. Carriers of zero, one, and two low-activity OCT1 alleles (Arg61Cys, Gly401Ser, 420del, or Gly465Arg) had mean renal clearances of 30.6, 33.1, and 37.1 l/h, respectively (P = 0.04, after adjustment for creatinine clearance and age). Immunohistochemical staining of human kidneys demonstrated OCT1 expression on the apical side of proximal and distal tubules. Increased renal clearance, in parallel with the known decreased hepatic uptake, may contribute to reduced metformin efficacy in low-activity genotypes. Renal OCT1 expression may be important not only in relation to metformin but with respect to other drugs as well.

Relative impact of genotype and enzyme induction on the metabolic capacity of CYP2C9 in healthy volunteers.

Pharmacokinetics in individual subjects is determined by genes and environment. The relative contributions of enzyme induction and inherited genomic variation to cytochrome P450 enzyme 2C9 (CYP2C9) activity are unknown. In 130 volunteers, CYP2C9 activity was measured in vivo using tolbutamide as a probe drug. Tolbutamide was administered orally, and the pharmacokinetics of the drug was analyzed twice--before and after four doses of 450 mg rifampin. Mean total apparent clearances (Cl/F) in the genotype groups CYP2C9*1/*1, *1/*2, *1/*3, *2/*3, and *3/*3 before rifampin were 0.78, 0.74, 0.52, 0.40, and 0.13 l/h, respectively. After rifampin administration, these clearances increased in all genotype groups by a median factor of 1.9 (range 1.1-4.8). The combined effects of genes and environment could be predicted by a simple additive model. Thus, enzyme induction resulted in an approximately twofold difference in CYP2C9 activity, irrespective of the CYP2C9 genotypes. But the difference in activity levels between the CYP2C9*1/*1 and *3/*3 genotypes before the administration of rifampin was sixfold.

The social phobia psychotherapy research network. The first multicenter randomized controlled trial of psychotherapy for social phobia: rationale, methods and patient characteristics.

This paper presents the Social Phobia Psychotherapy Research Network. The research program encompasses a coordinated group of studies adopting a standard protocol and an agreed-on set of standardized measures for the assessment and treatment of social phobia (SP). In the central project (study A), a multicenter randomized controlled trial, refined models of manualized cognitive-behavioral therapy and manualized short-term psychodynamic psychotherapy are compared in the treatment of SP. A sample of 512 outpatients will be randomized to either cognitive-behavioral therapy, short-term psychodynamic psychotherapy or waiting list. Assessments will be made at baseline, at the end of treatment and 6 and 12 months after the end of treatment. For quality assurance and treatment integrity, a specific project using highly elaborated measures has been established (project Q). Study A is complemented by 4 interrelated add-on projects focusing on attachment style (study B1), on cost-effectiveness (study B2), on variation in the serotonin transporter gene in SP (study C1) and on structural and functional deviations of the hippocampus and amygdala (study C2). Thus, the Social Phobia Psychotherapy Research Network program enables a highly interdisciplinary research into SP. The unique sample size achieved by the multicenter approach allows for studies of subgroups (e.g. comorbid disorders, isolated vs. generalized SP), of responders and nonresponders of each treatment approach, for generalization of results and for a sufficient power to detect differences between treatments. Psychological and biological parameters will be related to treatment outcome, and variables for differential treatment indication will be gained. Thus, the results provided by the network may have an important impact on the treatment of SP and on the development of treatment guidelines for SP.

Interindividual variation in the pharmacokinetics of Delta9-tetrahydrocannabinol as related to genetic polymorphisms in CYP2C9.

The impact of the CYP2C9 polymorphism on the pharmacokinetics of orally administered 9-tetrahydrocannabinol (THC) was studied in 43 healthy volunteers. THC pharmacokinetics did not differ by CYP2C9*2 allele status. However, the median area under the curve of THC was threefold higher and that of 11-nor-9-carboxy-9-tetrahydrocannabinol was 70% lower in CYP2C9*3/*3 homozygotes than in CYP2C9*1/*1 homozygotes. CYP2C9*3 carriers also showed a trend toward increased sedation following administration of THC. Therefore, the CYP2C9*3 variant may influence both the therapeutic and adverse effects of THC.

Genetic variation in the renal sodium transporters NKCC2, NCC, and ENaC in relation to the effects of loop diuretic drugs.

There is little data on genetic predictors of loop diuretic efficacy in humans. Therefore, we investigated the diuretic effects of single oral doses of bumetanide, frusemide, and torsemide in a crossover study in 97 healthy Caucasians in relation to genetic variation in the renal sodium transporters NKCC2 (coded by SLC12A1), NCC (SLC12A3), and ENaC (three subunits coded by SCNN1A, SCNN1B, and SCNN1G). The NCC alanine 264 allele (Gly264Ala) and the most frequent SCNN1B haplotype were associated with stronger diuresis, indicating lower reabsorbing function of these alleles. The variant alleles of the tightly coupled polymorphisms rs5723 (Leu649Leu) and rs5729 in SCNN1G were associated with weaker diuresis, indicating higher activity. Extended haplotype homozygosity implied evolutionary selection of the NCC alanine 264 allele. In conclusion, acute diuretic effects of loop diuretics were affected by genetic variation in sodium transporters that, in the nephron, are located distally from NKCC2.

Genetic variation at the CYP2C locus and its association with torsemide biotransformation.

In 97 unselected volunteers and two additional homozygous carriers of CYP2C9(*)3, we investigated the oral clearance of torsemide in relation to 37 polymorphisms at the CYP2C gene locus. Torsemide total oral clearance was linearly associated with the number of CYP2C9(*)3 alleles (geometric mean: 59, 40 and 20 ml/min in carriers of no, one and two alleles) and so were the methyl- and ring-hydroxylation but not the carboxylation clearance. Haplotypes including the CYP2C9(*)3 allele were similarly associated with the clearances but no other variant and no haplotype not including the CYP2C9(*)3 variant. The extended haplotype length (EHL) of the CYP2C9 haplotypes was positively associated with higher activity of the gene product. Torsemide total oral clearance was predictable with r(2)=82.1% using plasma concentrations at 0.5, 1, 2 and 24 h. In conclusion, torsemide's biotransformation strongly depended on the CYP2C9(*)3 variant but no other. Higher clearance CYP2C9 haplotypes appear to be evolutionarily selected.

The role of active metabolites in dihydrocodeine effects.

OBJECTIVE: The metabolism of dihydrocodeine to dihydromorphine, a high affinity mu-opioid receptor ligand in membrane homogenates, is catalyzed by CYP2D6. However, it is not clear whether an active CYP2D6 enzyme is required for opioid receptor-mediated effects in man after standard dihydrocodeine doses. METHODS: Whole cell opioid-receptor affinity and effects on cAMP accumulation of dihydrocodeine and its metabolites were determined in differentiated SH-SY5Y neuroblastoma cells. In a double-blind, 2-period, placebo-controlled randomized crossover pilot study the pharmacokinetics of dihydrocodeine (60 mg single dose) and its metabolites were examined in 5 phenotyped extensive (EMs) and 4 poor metabolizers (PMs) for CYP2D6, and pharmacodynamics were evaluated using a pain threshold model and dynamic pupillometry. RESULTS: Displacement binding and cAMP accumulation experiments showed clearly higher affinities (100- and 50-fold) and activities (180- and 250-fold) of dihydromorphine and dihydromorphine-6-glucuronide, respectively, whereas the other metabolites had similar or lower affinities and activities as compared to dihydrocodeine. The clinical study revealed no significant difference in plasma or urine pharmacokinetics between EMs and PMs for dihydrocodeine and its glucuronide. Dihydromorphine and its glucuronides were detectable in EMs only. A clear reduction of initial pupil diameters was observed up to 6 hours postdose in both PMs and EMs, with no obvious differences between CYP2D6 phenotypes. In the pain threshold model no effects were observed in either group. CONCLUSION: CYP2D6 phenotype has no major impact on opioid receptor-mediated effects of a single 60 mg dihydrocodeine dose, despite the essential role of CYP2D6 in formation of highly active metabolites.

Death attributed to methadone.

Besides its other effects, MMT (methadone maintenance treatment) reduces the high mortality of intravenous heroin addicts to about 30% of controls. On the other hand, deaths of patients and non-patients have been attributed to methadone. Here, we will report on the major reasons for deaths attributed to methadone and discuss suggestions for their prevention. 69% of deaths attributed to methadone occurred in subjects not on MMT at the time of their death. 51% of deaths attributed to methadone in subjects in MMT occurred during the dose-finding period of MMT. Further apparent risk situations are methadone intake in addition to that received for MMT, discharge from prison and intravenous injection of methadone. Intake of methadone in non-patients is almost entirely due to abuse of diverted take-home methadone. Not giving methadone as take-home should reduce methadone deaths most effectively. Replacing take-home methadone by substances acting longer than one day, such as LAAM (levacetylmethadol) or buprenorphine, should also be effective. Restriction of take-home prescriptions to substances with a slow onset of action, such as LAAM, or to partial agonists with an extended safety margin such as buprenorphine should be partly effective. Meticulous evaluation of substance history, slow dose increases and strict supervision of the patient by experienced personal should prevent methadone overdose during the dose-finding period. Discharge from prison closely corresponds to this situation; informing addicts shortly before discharge and psychosocial help during the first months out of prison may reduce this risk. Naloxone as an adjunct to oral agonist preparations should effectively prevent high-risk intravenous injection, for example of methadone syrup. This has been the case with tilidine plus naloxone in Germany. Reducing deaths attributable to methadone increases the net benefit of MMT. Also, reducing deaths attributable to methadone avoids decreases in the public acceptance of MMT.

Pharmacokinetics of cerivastatin in renal impairment are predicted by low serum albumin concentration rather than by low creatinine clearance.

The influence of renal impairment on the clearance of the new HMG-CoA reductase inhibitor cerivastatin was evaluated. A single oral dose of 300 microg cerivastatin was given to 18 patients with different degrees of renal impairment and 6 healthy controls. Concentrations of total cerivastatin, its fraction unbound, and the total concentrations of the active metabolites M1 and M23 were measured in plasma. Serum concentrations of unbound cerivastatin were calculated for each individual from the concentration of total cerivastatin and cerivastatin's fraction unbound at t = 2.5 hours. In contradiction to what had been expected, renal impairment significantly influenced the pharmacokinetics of cerivastatin. The best correlation to the AUC and Cmax of unbound cerivastatin was found with serum albumin concentration. Also, serum albumin concentration was the only factor significantly correlated to t 1/2 of cerivastatin. Significant but slighter correlation with the AUC and Cmax of unbound cerivastatin was also observed for creatinine clearance and cerivastatin's fraction unbound, while no correlation was observed with total plasma protein. No significant correlation of creatinine clearance, serum albumin concentration, fu, or total plasma protein concentration with the AUC and Cmax of total cerivastatin or the AUC, Cmax or t 1/2 of M1 and M23 was observed. The authors conclude that low serum albumin concentration rather than low creatinine clearance predicts the pharmacokinetics of cerivastatin in renal impairment.

Non-response to maprotiline caused by ultra-rapid metabolism that is different from CYP2D6?

CASE: We are reporting about a patient with major depression who failed to respond to pharmacotherapy due to ultra-rapid metabolism of maprotiline. Under daily oral doses of 175 mg maprotiline, the patient's metabolic ratio (MR) for maprotiline in plasma was 9.2 (expected MRp: 2.4) and the clearance of maprotiline (CLM) was 4190 ml.min-1 (expected CLM = 1220 in extensive metabolisers of CYP2D6). RESULTS: The patient's MRurine for sparteine was 0.5, which is within the range for extensive metabolisers of CYP2D6. Genotyping did not show a duplication of the CYP2D6L allele. The patient's caffeine half-life was 10 h, thus, precluding ultra-rapid metabolism for CYP1A2. The therapeutic regiment was changed to co-administration of 200 mg maprotiline and 20 mg fluoxetine once per day in order to inhibit metabolism via CYP2D6. Subsequently, MRP of maprotiline (4.9) and CLM were reduced (1900 ml.min-1; expected CLM in poor metabolisers: of CYP2D6 364). This regimen improved the clinical outcome of the underlying disease. CONCLUSION: We conclude that for the non-response seen with maprotiline, P450 isozymes other than CYP2D6 or CYP1A2 are responsible. As CYP2C19 is involved in the metabolism of a number of tricyclic antidepressants it may be a candidate for ultra-rapid metabolism in this patient.