Modified high-performance liquid chromatographic method to measure both dextromethorphan and proguanil for oxidative phenotyping

Simultaneous quantification of dextromethorphan and its metabolites dextrorphan, 3-methoxymorphinan and 3-hydroxymorphinan in human plasma by ultra performance liquid chromatography/tandem triple-quadrupole mass spectrometry

A rapid and sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method has been developed and validated for the simultaneous quantitative determination of dextromethorphan (DM) and its metabolites dextrorphan (DX), 3-methoxymorphinan (3MM) and 3-hydroxymorphinan (3HM), in human lithium heparinized plasma. The extraction involved a simple liquid-liquid extraction with 1 ml n-butylchloride from 200μl aliquots of plasma, after the addition of 20 μl 4% (v/v) ammonium hydroxide and 100 μl stable labeled isotopic internal standards in acetonitrile. Chromatographic separations were achieved on an Aquity UPLC(®) BEH C(18) 1.7 μm 2.1 mm x 100mm column eluted at a flow-rate of 0.250 ml/min on a gradient of acetonitrile. The overall cycle time of the method was 7 min, with elution times of 1.3min for DX and 3HM, 2.8 min for 3MM and 2.9min for DM. The multiple reaction monitoring transitions were set at 272>215 (m/z), at 258>133 (m/z), at 258>213 (m/z) and at 244>157 (m/z) for DM, DX, 3MM and 3HM, respectively. The calibration curves were linear (r²≥0.995) over the range of 0.500-100 nM with the lower limit of quantitation validated at 0.500 nM for all compounds, which is equivalent to 136, 129, 129 and 122 pg/ml for DM, DX, 3MM and 3HM, respectively. Extraction recoveries were constant, but ranged from 39% for DM to 83% for DX. The within-run and between-run precisions were within 11.6%, while the accuracy ranged from 92.7 to 110.6%. The applicability of the bioanalytical method was demonstrated and is currently implemented in a clinical trial to study DM as probe-drug for individualized tamoxifen treatment in breast cancer patients.

The effect of Shoseiryuto, a traditional Japanese medicine, on cytochrome P450s, N-acetyltransferase 2 and xanthine oxidase, in extensive or intermediate metabolizers of CYP2D6

OBJECTIVE

Shoseiryuto (TJ-19) contains eight herbal components, including Ephedra sinica, and has been used for treating asthma and allergic rhinitis in Asian countries for several centuries. In this study, we investigated the potential herb-drug interaction of TJ-19 in healthy volunteers and attempted to ascertain whether or not the interaction might be affected by the cytochrome P450 (CYP) 2D6 genotype.

METHODS

We assessed the effect of TJ-19 on the activities of CYP1A2, CYP2D6, CYP3A, xanthine oxidase (XO), and N-acetyltransferase 2 (NAT2) in 37 healthy subjects. The subject pool consisted of 19 extensive metabolizers (EMs) with CYP2D6*Wild/*Wild, and 18 intermediate metabolizers (IMs) with CYP2D6*10/*10. The baseline activities of five enzymes were ascertained by their respective urinary metabolic ratios from an 8-h urine sample, after an oral 150-mg and 30-mg dose of caffeine and dextromethorphan were administrated, respectively. Thereafter, the subjects received 4.5 g of TJ-19 twice daily for 7 days, and underwent the same phenotyping test on postdose day 7.

RESULTS

The activities of all enzymes examined did not differ before or after the 7-day administration of TJ-19. Consequently, the influence of the CYP2D6 genotype on the herb-drug interaction remained unsolved.

CONCLUSION

Our results indicate that TJ-19 at the generally recommended dosage is unlikely to cause pharmacokinetic interaction with co-administered medications primarily dependent on the CYP1A2, CYP2D6, CYP3A, XO, and NAT2 pathways for elimination.

Comparative bioavailability of the microemulsion formulation of cyclosporine (Neoral) with a generic dispersion formulation (Cicloral) in young healthy male volunteers

The aim of this study was to compare the bioavailability of cyclosporine (CyA) from the generic dispersion formulation Cicloral (CIC) with the microemulsion formulation Neoral (NEO) and the original Sandimmune (SIM) capsules after single doses of 100, 300, or 600 mg of drug, respectively. The study was performed according to an open 3-period cross-over design with 12 young healthy male volunteers for each dosage. The concentrations of CyA and its main metabolites were determined by high performance liquid chromatography in whole blood and urine up to 48 hours postdosing. Peak concentrations and area under the time-concentration curve were greater for the NEO and CIC formulations compared with SIM, and the mean bioavailability of CIC was significantly (P<0.05) lower compared with NEO. The bioavailability of SIM compared with NEO was 54% to 71%, in agreement with previous results. Bioequivalence was not demonstrated between CIC (test) and NEO (reference) as the 90% confidence intervals were outside the 80% to 125% guidelines based on log-transformed AUCs, and were 75.2% to 87.7% at 100 mg, 79.2% to 91.8% at 300 mg, and 76.6% to 94.5% at 600 mg doses. The respective values for Cmax were 78.9% to 94.6%, 80.7% to 95.0%, and 71.4% to 84.1%. A good correlation was demonstrated between the urinary recovery of CyA and the AUC4. Therefore, the urinary recovery of CyA may be helpful as a surrogate parameter for the systemic exposure of patients to CyA. Whereas the relative amount of hydroxylated metabolites (AM1, AM9, AM1c) was similar for all formulations and doses, the urinary recovery of the N-demethylated metabolite AM4N decreased with increasing dose indicating saturable metabolism. No relationship could be demonstrated between CYP3A activity using dextromethorphan as a probe for the metabolic clearance of CyA.

Multiple night-time doses of valerian (Valeriana officinalis) had minimal effects on CYP3A4 activity and no effect on CYP2D6 activity in healthy volunteers

Valerian (Valeriana officinalis) is a popular dietary supplement. The objective of this study was to assess the influence of a valerian extract on the activity of the drug-metabolizing enzymes cytochrome P450 2D6 (CYP2D6) and 3A4. Probe drugs dextromethorphan (30 mg; CYP2D6 activity) and alprazolam (2 mg; CYP3A4 activity) were administered orally to healthy volunteers (n = 12) at baseline and again after exposure to two 500-mg valerian tablets (1000 mg) nightly for 14 days. The valerian supplement contained a total valerenic acid content of 5.51 mg/tablet. Dextromethorphan to dextorphan metabolic ratios (DMRs) and alprazolam pharmacokinetics were determined at baseline and after valerian treatment. The DMR was 0.214 +/- 0.025 at baseline and 0.254 +/- 0.026 after valerian supplementation (p > 0.05). For alprazolam, the maximum concentration in plasma was significantly increased after treatment with valerian (25 +/- 7 ng/ml versus 31 +/- 8 ng/ml; p < 0.05). There were no significant differences in other pharmacokinetic parameters at baseline and after valerian exposure (all p values > or = 0.05; time to reach maximum concentration in plasma, 3.0 +/- 3.2 versus 3.1 +/- 2.1 h; area under the plasma concentration versus time curve, 471 +/- 183 versus 539 +/- 240 hx ng x ml(-1); half-life of elimination, 13.5 +/- 4.3 versus 12.2 +/- 5.6 h). Our results indicate that although a modest increase was observed in the alprazolam Cmax, typical doses of valerian are unlikely to produce clinically significant effects on the disposition of medications dependent on the CYP2D6 or CYP3A4 pathways of metabolism.

Green tea (Camellia sinensis) extract does not alter cytochrome p450 3A4 or 2D6 activity in healthy volunteers

Green tea extract is a widely used dietary supplement. The objective of this study was to assess the influence of a decaffeinated green tea (DGT; Camellia sinensis) extract on the activity of the drug-metabolizing enzymes cytochrome P-450 2D6 and 3A4. Probe drugs dextromethorphan (30 mg, CYP2D6 activity) and alprazolam (ALPZ; 2 mg, CYP3A4 activity) were administered orally to healthy volunteers (n = 11) at baseline, and again after treatment with four DGT capsules/day for 14 days. Each DGT capsule contained 211 +/- 25 mg of green tea catechins and <1 mg of caffeine. Dextromethorphan metabolic ratios (DMRs) and alprazolam pharmacokinetics were determined at baseline and after DGT treatment. There were no significant differences in ALPZ pharmacokinetics at baseline and after DGT treatment (all P values >/= 0.05; maximum concentration in plasma, 33 +/- 8 versus 34 +/- 13 ng/ml; time to reach maximum concentration in plasma, 1.4 +/- 1.2 versus 1.4 +/- 1.2 h; area under the plasma concentration versus time curve, 480 +/- 119 versus 510 +/- 107 h. ng. ml(-1); half-life of elimination, 12.3 +/- 1.7 versus 13.1 +/- 3.4 h). The DMR was 0.053 +/- 0.045 at baseline and 0.041 +/- 0.032 after DGT supplementation (P > 0.05). The plasma concentration of the green tea flavonoid, (-)-epigallocatechin gallate, reached 1.3 +/- 1.8 microM 2 h after DGT treatment. Our results indicate that DGT is unlikely to alter the disposition of medications primarily dependent on the CYP2D6 or CYP3A4 pathways of metabolism.

Development of a chromatographic bioreactor based on immobilized β-glucuronidase on monolithic support for the determination of dextromethorphan and dextrorphan in human urine

We here reported the development and application of an immobilized enzyme reactor (IMER) based on beta-glucuronidase to the on-line determination of urinary molar ratios of dextromethorphan (DOMe)/dextrorphan (DOH) for the assessment of the metabolic activity of CYP2D6, a genetically variable isoform of cytochrome P-450 (CYP). beta-Glucuronidase was immobilized on an HPLC monolithic aminopropyl silica support. Catalytic activity and stability of the chromatographic reactor were evaluated using 8-hydroxyquinoline glucuronide (8-HQG) as substrate. The IMER was coupled through a switching valve to a reversed-phase column (C8) for the simultaneous determination of dextromethorphan and its main metabolite dextrorphan. On purpose a selective reversed-phase ion pair HPLC method coupled with fluorescence detection was developed. Urine samples were first centrifuged to remove insoluble materials and then aliquots of the supernatants were injected into the coupled-column analyser. Linearity, precision and accuracy of the method were established. The method reliability was verified by comparing our data with previous data of a phenotyping study carried out by the Poison Control Centre of Pavia-Clinical Toxicology Division.

Comparative CYP3A4 inhibitory effects of venlafaxine, fluoxetine, sertraline, and nefazodone in healthy volunteers

An antidepressant for use in the patient receiving concomitant drug treatment, over-the-counter medications, or herbal products should lack cytochrome P-450 (CYP) 3A4 inductive or inhibitory activity to provide the least likelihood of a drug-drug interaction. This study addresses the potential of 4 diverse antidepressants (venlafaxine, nefazodone, sertraline, and fluoxetine) to inhibit or induce CYP3A4. In a 4-way crossover design, 16 subjects received clinically relevant doses of venlafaxine, nefazodone, or sertraline for 8 days or fluoxetine for 11 days. Treatments were separated by a 7- to 14-day washout period and fluoxetine was always the last antidepressant taken. CYP3A4 activity was evaluated for each subject at baseline and following each antidepressant using the erythromycin breath test (EBT) and by the pharmacokinetics of alprazolam (ALPZ) after 2-mg dose of oral ALPZ. Compared to baseline, venlafaxine, sertraline, and fluoxetine caused no apparent inhibition or induction of erythromycin metabolism (P > 0.05). For nefazodone, a statistically significant inhibition was observed (P < 0.0005). Nefazodone was also the only antidepressant that caused a significant change in ALPZ disposition, decreasing its area under the concentration-versus-time curve (AUC; P < 0.01), and increasing its elimination half-life (16.4 vs. 12.3 hours; P < 0.05) compared with values at baseline. No significant differences were found in the pharmacokinetics of ALPZ with any of the other antidepressants tested. These results demonstrate in vivo that, unlike nefazodone, venlafaxine, sertraline, and fluoxetine do not possess significant metabolic inductive or inhibitory effects on CYP3A4.

Multiple-dose administration of Ginkgo biloba did not affect cytochrome P-450 2D6 or 3A4 activity in normal volunteers

Standardized extracts from the Ginkgo biloba tree are purported to exert positive neurocognitive effects and may also be useful in the treatment of a variety of vascular and other disorders. This dietary supplement is among the most commonly used herbal preparations in the world. The objective of this study was to assess in normal volunteers (n = 12) the influence of standardized Ginkgo biloba (GB) on the activity of cytochrome P-450 (CYP) 2D6 and 3A4 normal volunteers phenotyped as CYP2D6 extensive metabolizers. Probe substrates dextromethorphan (CYP2D6 activity) and alprazolam (CYP 3A4 activity) were co-administered orally at baseline, and following treatment with GB (120 mg twice daily) for 14 days. Urinary concentrations of dextromethorphan and dextrorphan were quantified and dextromethorphan metabolic ratios (DMRs) were determined at baseline and after GB treatment. Likewise, plasma samples were collected (0-60 hrs) for alprazolam pharmacokinetics at baseline and after GB treatment to assess effects on CYP 3A4 activity. Validated HPLC methods were used to quantify all compounds and relevant metabolites. No statistically significant differences were found between baseline and post-GB treatment DMRs indicating a lack of effect on CYP2D6. For alprazolam there was a 17% decrease in the area under the plasma concentration versus time curve (AUC); (P<0.05). However, the half-life of elimination was not significantly different after GB administration indicating a lack of hepatic CYP3A4 induction. We conclude that standardized extracts of GB at recommended doses are unlikely to significantly alter the disposition of co-administered medications primarily dependent on the CYP2D6 or CYP3A4 pathways for elimination.

Dietary levels of quinine in tonic water do not inhibit CYP2D6 in vivo

Quinine is a bitter alkaloid that is used as a flavoring agent in tonic water. Studies suggest that quinine can inhibit cytochrome P450 2D6 (CYP2D6) which could have implications for the metabolism of co-ingested drugs. We conducted a study with 11 healthy volunteers (7 men, 4 women; aged 26-54). After urinary void, each subject consumed either 1000 ml of carbonated water or 1000 ml of tonic water containing 80 mg quinine in a crossover design. Following each beverage subjects ingested an oral dose of 30 mg dextromethorphan (DM). Urine was collected for 8 h and analyzed for DM and dextrophran, its CYP2D6 mediated metabolite. The ratio of DM and its metabolite is an established measure of CYP2D6 activity. All subjects metabolized the vast majority of DM to its metabolite after both the carbonated water and the tonic water. The ratio (mean+/-S.D.) of DM to its metabolite was 0.013+/-0.028 after the carbonated water and 0.032+/-0.067 after the quinine containing water. No significant difference in the ratios was observed between the two beverages (P>0.05). We conclude that quinine as consumed in tonic water does not inhibit CYP2D6 activity in vivo. Thus, quinine should not alter the metabolism of CYP2D6 substrates taken concomitantly with tonic water.

Siberian ginseng (Eleutheroccus senticosus) effects on CYP2D6 and CYP3A4 activity in normal volunteers

Siberian ginseng ([SG]; Eleutherococcus senticosus) is a commonly used herbal preparation. The objective of this study was to assess in normal volunteers (n = 12) the influence of a standardized SG extract on the activity of cytochrome P450 CYP2D6 and 3A4. Probe substrates dextromethorphan (CYP2D6 activity) and alprazolam (CYP3A4 activity) were administered orally at baseline and again following treatment with SG (1 x 485 mg twice daily) for 14 days. Urinary concentrations of dextromethorphan and dextorphan were quantified, and dextromethorphan metabolic ratios (DMRs) were determined at baseline and after SG treatment. Likewise, plasma samples were collected (0-60 h) for alprazolam pharmacokinetics at baseline and after SG treatment to assess effects on CYP3A4 activity. Validated high performance liquid chromatography methods were used to quantify all compounds and relevant metabolites. There were no statistically significant differences between pre- and post-SG treatment DMRs indicating a lack of effect on CYP2D6 (P > 0.05). For alprazolam there also were no significant differences in the pharmacokinetic parameters determined by noncompartmental modeling (C(max), T(max), area under the curve, half-life of elimination) indicating that SG does not significantly induce or inhibit CYP3A4 (P > 0.05). Our results indicate that standardized extracts of SG at generally recommended doses for over-the-counter use are unlikely to alter the disposition of coadministered medications primarily dependent on the CYP2D6 or CYP3A4 pathways for elimination.

Differential time course of cytochrome P450 2D6 enzyme inhibition by fluoxetine, sertraline, and paroxetine in healthy volunteers

The selective serotonin reuptake inhibitors (SSRIs) paroxetine, sertraline, and fluoxetine have varying degrees of potency in inhibiting the hepatic cytochrome P450 (CYP) 2D6 enzyme. However, the time course for maximum inhibition to occur or for inhibition to dissipate when dosing is discontinued, requires clarification. In an open label, parallel group study of 45 healthy volunteers, the time course of CYP2D6 inhibition of the above SSRIs was evaluated. Subjects were randomized to receive paroxetine at 20 mg/day for 10 days; sertraline at 50 mg/day for 3 days, followed by sertraline at 100 mg/day for 10 days; or fluoxetine at 20 mg/day for 28 days. CYP2D6 activity was assessed using the dextromethorphan metabolic ratio (DMR) on antidepressant days 5 and 10 for sertraline and paroxetine and at weekly intervals for fluoxetine. Following SSRI discontinuation, calculation of a CYP2D6 inhibition half-life (t(1/2)inh) revealed the time course of fluoxetine inhibition (t(1/2)inh = 7.0 +/- 1.5 days) to be significantly longer than either paroxetine (t(1/2)inh = 2.9 +/- 1.9) or sertraline (t(1/2)inh = 3.0 +/- 3.0) (p < 0.01), but the latter were not significantly different from each other (p > 0.05). Time for the extrapolated DMR versus time log-linear plots to return to baseline was significantly different between fluoxetine (63.2 +/- 5.6 days) and both paroxetine (20.3 +/- 6.4 days) and sertraline (25.0 +/- 11.0 days) (p < 0.01), making the rank order (from longest to shortest) of time for CYP2D6 inhibition to dissipate: fluoxetine > sertraline >or= paroxetine. Differences between mean baseline DMR values and measured values obtained after drug discontinuation for each drug group became nonsignificant on discontinuation day 5 for both paroxetine and sertraline and on discontinuation day 42 for fluoxetine. These data define the time course of a persistent effect that fluoxetine, sertraline, and paroxetine have on CYP2D6 following drug discontinuation and should be considered when initiating therapy with a CYP2D6 substrate.

Relationship between proguanil metabolic ratio and CYP2C19 genotype in a Caucasian population

AIMS

To investigate the relationship between proguanil metabolic ratio (MR, proguanil/cycloguanil) and CYP2C19 genotype in a Caucasian population.

METHODS

Ninety-nine Caucasians (age range: 18-55 years, 54 female, 45 male) were genotyped for CYP2C19 and phenotyped for proguanil oxidation by collecting urine for 8 h after taking 100 mg proguanil hydrochloride. Proguanil and cycloguanil concentrations were measured by h.p.l.c. PCR was employed for CYP2C19 genotyping.

RESULTS

The three (3%) individuals who were homozygous for CYP2C19*2 (*2/*2) had the highest proguanil MRs (range: 8.0-134.6). Seventy-three (74%) individuals were homozygous for the wild-type allele (*1/*1) and 23 (23%) were heterozygous (*1/*2). The *1/*1 individuals had lower MRs (median=1.4, range: 0.23-5.9, P=0.003, Mann-Whitney U-test) than the *1/*2 subjects (median=2.5, range: 0.88-7.3).

CONCLUSIONS

A CYP2C19 gene-dose effect for proguanil oxidation to cycloguanil was observed, confirming a role for CYP2C19 in cycloguanil formation in vivo. However, there was substantial overlap of proguanil MRs in subjects of different CYP2C19 genotypes, due possibly to variability in the activity of other enzymes contributing to the formation of cycloguanil.