Espen Molden

Impact of the Ultrarapid CYP2C19*17 Allele on Serum Concentration of Escitalopram in Psychiatric Patients

Recently, a novel allelic variant of cytochrome P450 2C19 encoding ultrarapid enzyme activity was described (denoted CYP2C19*17). The objective of this study was to evaluate the impact of CYP2C19*17 on serum concentration of escitalopram in psychiatric patients. One hundred and sixty‐six patients treated with escitalopram were divided into the following subgroups according to CYP2C19 genotype: CYP2C19*17/*17 (n=7), CYP2C19*1/*17 (n=43), CYP2C19*1/*1 (n=60), CYP2C19*17/def (n=16), CYP2C19*1/def (n=34), and CYP2C19def/def (n=6) (def=defective allele, i.e., CYP2C19*2 or *3). Dose‐adjusted serum concentrations of escitalopram were compared using the CYP2C19*1/*1 subgroup as reference. Geometric mean of the escitalopram serum concentration was 42% lower in patients homozygous for CYP2C19*17 (P<0.01) and 5.7‐fold higher in subjects homozygous for defective CYP2C19 alleles (P<0.001). Of the heterozygous subgroups, only CYP2C19*1/def was significantly different from CYP2C19*1/*1 (P<0.001). In conclusion, a homozygous CYP2C19*17 genotype is associated with lower serum concentration of escitalopram, which might imply increased risk of therapeutic failure.

Exposure of atorvastatin is unchanged but lactone and acid metabolites are increased several‐fold in patients with atorvastatin‐induced myopathy

The most serious side effect from statin treatment is myopathy, which may proceed to rhabdomyolysis. This is the first study to investigate whether the pharmacokinetics of either atorvastatin or its metabolites, or both, is altered in patients with atorvastatin‐related myopathy compared with healthy controls.

The effect of variable cigarette consumption on the interaction with clozapine and olanzapine

ObjectiveCigarette smoking has been shown in several studies to induce the metabolism of the cytochrome P4501A2 (CYP1A2) substrates clozapine and olanzapine. The aim of the present study was to investigate the dose-dependent effect of cigarette smoking on serum concentrations of these drugs in a naturalistic setting.MethodsIn 73 schizophrenic patients recruited from psychiatric nursing homes, patient characteristics, smoking habits, drug dosing and serum concentrations of clozapine (n=33) and olanzapine (n=40) were registered. Concentration to dose (C/D) ratios of clozapine and olanzapine in non-smokers and subgroups of smokers were compared.ResultsFifty-nine patients (80%) were smokers and these were stratified into the following groups according to smoking habits: 1–6 (n=0), 7–12 (n=13), 13–19 (n=18) and ≥20 (n=28) cigarettes daily. While the mean ratio was twice as high in non-smokers compared to smokers for both drugs (p<0.01), the C/D ratios of clozapine and olanzapine were not significantly different between the subgroups of smokers (p >0.15). Absolute serum concentrations were also higher in non-smokers compared to smokers: 50% for clozapine (p=0.058) and 67% for olanzapine (p<0.01).ConclusionA daily consumption of 7–12 cigarettes is probably sufficient for maximum induction of clozapine and olanzapine metabolism. A 50% lower starting dose of both drugs in non-smokers seems rational to avoid side effects.

Pharmacokinetic variability of aripiprazole and the active metabolite dehydroaripiprazole in psychiatric patients.

Aripiprazole is a new atypical antipsychotic drug with a partial agonist activity at dopamine 2 and serotonin 1A receptors. The metabolism of aripiprazole involves both cytochrome P450 2D6 (CYP2D6) and CYP3A4. This study investigated the pharmacokinetic variability of aripiprazole and the active metabolite dehydroaripiprazole on the basis of 155 drug monitoring samples from psychiatric patients treated with therapeutic doses of aripiprazole (10-30 mg/day). Serum concentrations of drug and metabolite were determined by liquid chromatographic and tandem mass spectrometric detection. Pharmacokinetic variability was expressed as the range in concentration/dose (C/D) ratios, and the effect of sex and occasionally coprescribed CYP2D6 or CYP3A4 inhibitors/inducers was studied. In addition, the dose-concentration relationship and combined interquartile range of concentrations obtained at low dose (10-15 mg/day) and high dose (20-30 mg/day) were described. Individual C/D ratios ranged 37-fold for aripiprazole, 78-fold for dehydroaripiprazole, and 27-fold for the active sum of aripiprazole + dehydroaripiprazole. Median C/D ratios in male and female patients differed by less than 15%, and none of the differences were significant (P > 0.14). Cases of concurrent CYP3A4 inducers/inhibitors were not found, but three patients were coprescribed the potent CYP2D6 inhibitors paroxetine or fluoxetine. No consistent difference in C/D ratio was observed in these three patients compared with the rest of the patients. There was a proportional dose-concentration relationship in the population, and the combined interquartile ranges were 230 to 960 nmol/L for aripiprazole and 330 to 1210 nmol/L for aripiprazole + dehydroaripiprazole. In conclusion, pharmacokinetic variability of aripiprazole is extensive in psychiatric patients but apparently not dependent on dose or sex. The variability of the pharmacologic active sum of aripiprazole + dehydroaripiprazole is 25% to 30% less than aripiprazole, suggesting that variability of aripiprazole is partly determined by metabolism to dehydroaripiprazole.

Cognitive Effects of Reducing Anticholinergic Drug Burden in a Frail Elderly Population: A Randomized Controlled Trial

BACKGROUND Observational studies report a relationship between anticholinergic drug scale (ADS) score and cognitive function. This study investigated whether a reduced ADS score improved cognitive function in a frail elderly population. METHODS This randomized, controlled, single-blinded trial, recruited long-term residents with an ADS score of greater than or equal to 3 from 22 nursing homes in Norway. The participants were randomly allocated (1:1) to intervention or control. The intervention was a pharmacist-initiated reduction of ADS score after multidisciplinary drug reviews. Primary end point was Consortium to Establish a Registry for Alzheimers Disease 10-wordlist test for immediate recall. Secondary end points were Mini-Mental Sate Examination, delayed recall and recognition of words, saliva flow, and serum anticholinergic activity (SAA).The participants were retested after 4 and 8 weeks, and the study groups were compared after adjusting for baseline differences. RESULTS Eighty-seven patients were included. The median ADS score was reduced by 2 units (p < .0001) in the intervention group and remained unchanged in the control group. After 8 weeks, the adjusted mean difference in immediate recall was 0.54 words between the intervention and control group (95% confidence interval [CI]: -0.91, 2.05; p = .48). The study groups did not differ significantly in any of the other cognitive end points, salvia flow, or SAA at either follow-up (p > .18). CONCLUSION Pharmacist-initiated drug changes significantly reduced ADS score but did not improve cognitive function in nursing home residents. Moreover, the drug changes did not reduce SAA or mouth dryness significantly, which might indicate limited applicability of the ADS score to prevent prescription risks in this population.

Serum concentrations of sertraline and N-desmethyl sertraline in relation to CYP2C19 genotype in psychiatric patients

ObjectiveTo investigate the impact of CYP2C19 genotype on serum concentrations of sertraline and N-desmethyl sertraline in psychiatric patients.MethodsPatients treated with sertraline (n = 121) were divided into six subgroups according to CYP2C19 genotype: CYP2C19*17/*17, CYP2C19*1/*17, CYP2C19*1/*1, CYP2C19*17/def, CYP2C19*1/def and CYP2C19def/def (def = allele encoding defective CYP2C19 metabolism, i.e. *2 and *3). Dose-adjusted serum concentrations were compared by linear mixed model analyses using the CYP2C19*1/*1 subgroup as reference.ResultsSubgroups carrying one or two alleles encoding defective CYP2C19 metabolism achieved significantly higher mean dose-adjusted serum concentrations of sertraline and N-desmethyl sertraline compared to the CYP2C19*1/*1 subgroup (P < 0.05). The effect of CYP2C19 genotype was expressed as 3.2-fold (sertraline) and 4.5-fold (N-desmethyl sertraline) higher dose-adjusted serum concentrations in the CYP2C19def/def subgroup compared to the CYP2C19*1/*1 subgroup (P < 0.01). The CYP2C19*17 allele had no influence on the dose-adjusted serum concentrations of sertraline and N-desmethyl sertraline.ConclusionThe significantly higher serum concentrations associated with alleles encoding defective CYP2C19 metabolism might be of relevance for the clinical outcome of sertraline treatment.

Impact of OATP1B1, MDR1, and CYP3A4 Expression in Liver and Intestine on Interpatient Pharmacokinetic Variability of Atorvastatin in Obese Subjects

Individual variability in expression and function of organic anion‐transporting polypeptide 1B1 (OATP1B1), multidrug resistance protein 1 (MDR1), and/or cytochrome P450 3A4 (CYP3A4) may impact the clinical response of many drugs. We investigated the correlation between expression of these proteins and pharmacokinetics of atorvastatin, a substrate of all three, in 21 obese patients with paired biopsies from liver and intestinal segments. The patients were also screened for the SLCO1B1 c.521T→C variant alleles. Approximately 30% (r2 = 0.28) of the variation in oral clearance (CL/F) of atorvastatin was explained by hepatic OATP1B1 protein expression (P = 0.041). Patients carrying the SLCO1B1 c.521C variant allele (homozygous, n = 4; heterozygous, n = 2) exhibited 45% lower CL/F of atorvastatin than the c.521TT carriers (P = 0.067). No association between hepatic and intestinal expression of MDR1 or CYP3A4 and atorvastatin pharmacokinetics was found (P > 0.149). In conclusion, this study suggests that OATP1B1 phenotype is more important than CYP3A4 and MDR1 phenotypes for the individual pharmacokinetic variability of atorvastatin.

Pharmacokinetics of diltiazem and its metabolites in relation to CYP2D6 genotype

Recently, it was shown in vitro that the polymorphic enzyme cytochrome P450 (CYP) 2D6 mediates O‐demethylation of diltiazem. The aim of this study was to compare the pharmacokinetics of diltiazem and its major metabolites in healthy human volunteers representing different CYP2D6 genotypes.

Probable warfarin-simvastatin interaction.

Objective: To report and discuss a case of fatal cerebral hemorrhage following a switch from atorvastatin to simvastatin in a patient taking warfarin. Case Summary: An 82-year-old white female was admitted to the hospital because of an international normalized ratio (INR) value greater than 8, which was detected at a routine follow-up visit to monitor warfarin therapy. Four weeks earlier her lipid-lowering therapy had been switched from atorvastatin 10 mg daily to simvastatin 10 mg daily. She had been treated with 2.5 mg of warfarin daily for almost 30 years due to episodes of deep venous thrombosis and lung embolism. Her INR had been stable within the treatment range (2.0–3.5) for more than 2 years before the INR increase. Upon hospitalization, she was given 5 mg of vitamin K orally, A few hours later she lost the feeling and movement of her right arm and a computed tomography scan showed major bleeding in the left cerebral hemisphere. She died the following day. Discussion: One study has shown a lack of interaction between warfarin and atorvastatin. In comparison, 3 studies have shown significant increases (10–30%) in warfarin effect and/or reductions in dose requirement after starling concomitant simvastatin treatment. The interaction mechanism between simvastatin and warfarin is not known but is possibly associated with reduced elimination of warfarin. Use of the Naranjo probability scale showed that the likelihood of warfarin-induced INR increase following the switch to simvastatin was probable. Conclusions: Atorvastatin and simvastatin appear to differ in their potential to interact with warfarin. Clinicians should be aware of the interaction risk when starting simvastatin treatment in patients on warfarin therapy.

Heterozygous mutation in CYP2C19 significantly increases the concentration/dose ratio of racemic citalopram and escitalopram (S-citalopram)

There is limited documentation of the importance of heterozygous cytochrome P450 (CYP) mutations on drug exposure. This study was designed to evaluate the influence of heterozygous mutations in CYP2C19 on the serum concentration of racemic citalopram and escitalopram (S-citalopram). Eighty-three samples from subjects with determined CYP2C19 and CYP2D6 genotype receiving racemic citalopram or S-citalopram as part of their clinical treatment were collected from a routine therapeutic drug monitoring database. Concentration/dose (C/D) ratios, parent drug/metabolite ratios, and serum concentrations in CYP2C19 homozygous extensive metabolizers (EMs) and heterozygous extensive metabolizers (HEMs) were compared. The median C/D ratio was significantly higher in the HEM group compared with the EM group, both for racemic citalopram (8.0 vs. 4.9, P < 0.01) and S-citalopram (5.3 vs. 2.6, P < 0.01). The median parent drug/metabolite ratio was significantly higher in the HEM group compared with the EM group, both for racemic citalopram (2.9 vs. 1.6, P < 0.01) and for S-citalopram (2.4 vs. 1.2, P < 0.01). A higher median non-dose-corrected serum concentration also was observed in HEMs compared with EMs both for S-citalopram (P < 0.01) and racemic citalopram (P = 0.066). This study shows that the metabolism of racemic citalopram and S-citalopram is significantly impaired in CYP2C19 HEMs. Higher absolute serum concentrations indicate that this is not compensated for by dose reductions in clinical practice.