Loss of Function ABCG2 c.421C>A (rs2231142) Polymorphism Increases Steady-State Exposure to Mycophenolic Acid in Stable Renal Transplant Recipients: An Exploratory Matched Cohort Study.

INTRODUCTION: Polymorphism ABCG2 c.421C>A (rs2231142) results in reduced activity of the important drug efflux transporter breast cancer-resistance protein (BCRP/ABCG2). One study has suggested that it may affect enterohepatic recirculation of mycophenolic acid (MPA). We evaluated the effect of rs2231142 on steady-state exposure to MPA in renal transplant recipients. METHODS: Consecutive, stable adult (age ≥ 16 years) renal transplant recipients on standard MPA-based immunosuppressant protocols (N = 68; 43 co-treated with cyclosporine, 25 with tacrolimus) underwent routine therapeutic drug monitoring after a week of initial treatment, and were genotyped for ABCG2 c.421C>A and 11 polymorphisms in genes encoding enzymes and transporters implicated in MPA pharmacokinetics. ABCG2 c.421C>A variant versus wild-type (wt) patients were matched with respect to demographic, biopharmaceutic, and genetic variables (full optimal combined with exact matching) and compared for dose-adjusted steady-state MPA pharmacokinetics [frequentist and Bayes (skeptical neutral prior) estimates of geometric means ratios, GMR]. RESULTS: Raw data (12 variant versus 56 wt patients) indicated around 40% higher total exposure (frequentist GMR = 1.45, 95% CI 1.10-1.91; Bayes = 1.38, 95% CrI 1.07-1.81) and around 30% lower total body clearance (frequentist GMR = 0.66, 0.58-0.90; Bayes = 0.71, 0.53-0.95) in variant carriers than in wt controls. The estimates were similar in matched data (11 variant versus 43 wt patients): exposure GMR = 1.41 (1.11-1.79) frequentist, 1.39 (1.15-1.81) Bayes, with 90.7% and 85.5% probability of GMR > 1.20, respectively; clearance GMR = 0.73 (0.58-0.93) frequentist, 0.71 (0.54-0.95) Bayes. Sensitivity analysis indicated low susceptibility of the estimates to unmeasured confounding. CONCLUSIONS: Loss-off-function polymorphism ABCG2 c.421C>A increases steady-state exposure to MPA in stable renal transplant patients.

Development and Validation of an HPLC Method for Simultaneous Determination of Capsaicinoids and Camphor in Over-the-Counter Medication for Topical Use.

A reverse-phase high-performance liquid chromatography method was developed to determine and quantify capsaicin (trans-8-methyl-N-vanillyl-6- nonenamid), dihydrocapsaicin (8-methyl-N-vanillylnonanamide), and camphor (trimethylbicyclo[2.2.1]heptan-2-one). It is applicable in analyses of over-the-counter (OTC) medications for topical use and raw materials such as chili pepper oleoresin. Chromatographic separation was carried out on a C18 column using an isocratic flow of the mobile phase containing acetonitrile and ultrapure water in a ratio of 2:3, with pH adjusted to 3.2 using glacial acetic acid, and a flow rate of 1.5 mL/min. The concentration of the eluting compounds was monitored by a diode-array detector at a wavelength of 281 nm. The method was evaluated for several validation parameters, including selectivity, accuracy (confidence intervals < 0.05%), repeatability, and intermediate precision. The limit of detection (LOD) was determined to be 0.070 µg/mL for capsaicin, 0.211 µg/mL for dihydrocapsaicin, and 0.060 µg/mL for camphor. The limit of quantification (LOQ) was determined to be 0.212 µg/mL for capsaicin, 0.640 µg/mL for dihydrocapsaicin, and 0.320 µg/mL for camphor. Linearity was set in the range of 2.5-200 µg/mL for capsaicin and dihydrocapsaicin and 25-2000 µg/mL for camphor. The suggested analytical method can be used for quality control of formulated pharmaceutical products containing capsaicinoids, camphor, and propolis.

Effect of cyclosporine on steady-state pharmacokinetics of MPA in renal transplant recipients is not affected by the MPA formulation: analysis based on therapeutic drug monitoring data.

BACKGROUND: Two oral mycophenolic acid (MPA) formulations, immediate-release mycophenolate mofetil and enteric-coated mycophenolate sodium, have been shown to differ regarding some drug-drug interactions. The aim was to assess whether the effects of cyclosporine (CsA) on steady-state pharmacokinetics (PK) of MPA in renal transplant patients were affected by MPA formulation. METHODS: A prospective, stratified observational study based on therapeutic drug monitoring of MPA (6 total plasma concentrations over a 12-hour dosing interval, τ) in consecutive stable adult renal transplant recipients (n = 68). RESULTS: Patients treated with enteric-coated mycophenolate sodium (n = 45) or mycophenolate mofetil (n = 23) and with either CsA (microemulsion, n = 43) or tacrolimus (Tac) (immediate release, n = 25) were comparable regarding demographics, comorbidity, renal and liver functions, comedication, corticosteroid dose, CsA or Tac dose, and trough concentrations. Based on dose-normalized MPA concentrations and with adjustment for age, sex, body mass index, estimated glomerular filtration rate, and corticosteroid dose, CsA (as compared with Tac) consistently reduced MPA area under the concentration-time curve during the dosing interval at steady state overall [geometric mean ratio (GMR), 0.78; 95% confidence interval, 0.62-0.99] and by MPA formulation (by 22% and 21%, respectively), increased CLT/F,ss overall (1.31; 1.00-1.70) and by formulation (by 25% and 36%, respectively), reduced morning predose MPA concentration overall (0.59; 0.38-0.92) and by formulation (by 34% and 47%, respectively), increased peak-trough fluctuation overall (1.51; 1.06-2.17) and by formulation (by 58% and 45%, respectively), and prolonged tmax,ss overall (adjusted median difference 0.58, 0.04-1.12 hours) and by formulation (by 0.6 and 0.5 hours, respectively). CONCLUSIONS: Qualitatively and quantitatively, the effect of CsA on steady-state PK of MPA is not conditional on MPA formulation.

Association between lamotrigine concentrations and ABCB1 polymorphisms in patients with epilepsy.

BACKGROUND: Epilepsy is treated with a variety of anticonvulsants that are often used concomitantly. Therefore, therapeutic drug monitoring is often necessary. Along with clinical and environmental factors, genetic predisposition has been recognized to be relevant for interindividual variability in drug response. Polymorphic transporter proteins such as P-glycoprotein significantly influence pharmacokinetics and bioavailability of many structurally unrelated drugs. The aim of the study was to evaluate the impact of polymorphisms in the P-glycoprotein-encoding gene ABCB1 (C1236T, G2677T/A, C3435T) on antiepileptic drug disposition. METHODS: We recruited 222 patients with epilepsy who were prescribed lamotrigine in monotherapy or polytherapy. Lamotrigine plasma concentrations were analyzed and compared with ABCB1 gene variants. The ABCB1 genotyping was performed by real-time polymerase chain reaction methods. The therapeutic drug monitoring was performed by high-performance liquid chromatography-diode array detector (DAD) and immunoassay. RESULTS: A significant correlation was confirmed between lamotrigine concentration and additional drugs (P < 0.001). In the whole group, statistical analysis showed correlations between lamotrigine concentrations and ABCB1 C1236T variants: 10.1 and 6.5 µmol/L for CC versus CT + TT, respectively (P = 0.021), and for dose corrected lamotrigine 0.068 and 0.053 µmol·L·mg, for CC versus CT + TT, respectively (P = 0.017). Analysis of a specific haplotype showed that 1236C-2677G-3435C carriers had higher lamotrigine concentrations than 1236T-2677G-3435T carriers (P < 0.001), followed by 1236T-2677T-3435C carriers (P < 0.001). CONCLUSIONS: ABCB1 C1236T, G2677T/A, C3435T polymorphisms have an influence on lamotrigine serum concentrations.

Ethylene glycol poisoning.

A 40-year-old man was admitted to the emergency department after a suicide attempt. The patient was found at home unconscious, with an open bottle of antifreeze near him. The patient was in a coma on admission, but neurological examination excluded intracranial changes. Results of initial urine and serum toxicological screening tests were negative. Laboratory values indicated metabolic acidosis, leukocytosis, urinalysis revealed hematuria and unrecognized crystals. Osmolality and osmol gap were not determined on patient admission. Treatment with ethanol as an antidote and hemodialysis were started because of metabolic acidosis, anamnestic data and clinical status of the patient, and subsequently led to improvement of his condition. Further toxicological analyses of glycolic and oxalic acids in serum and urine samples were performed by ion-chromatography (IC) method and showed high values in spot urine and serum ultrafiltrate at admission, but during therapy the values progressively decreased. Treatment of poisoned patient for 3 weeks resulted in complete recovery.

Genetic polymorphisms of cytochromes P450: CYP2C9, CYP2C19, and CYP2D6 in Croatian population.

AIM: To determine the prevalence of most common mutations of cytochrome P450 (CYP), ie, allelic variants of CYP2C9, CYP2C19, and CYP2D6, and to predict genotype frequency in the Croatian population. METHODS: CYP genotype was determined in 200 non-related Croatian citizens. DNA isolated from blood samples was used for the analysis of the most common allelic variants of CYP2C9, CYP2C19, and CYP2D6 by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. RESULTS: For 200 subjects genotyped for CYP2C9, the allele frequencies of CYP2C9*1 (wt), CYP2C9*2, and CYP2C9*3 were 0.74, 0.165, and 0.095, respectively. Among them, 3.5% of subjects were predicted to be poor metabolizers. For CYP2C19, the most frequent alleles were CYP2C19*1 and CYP2C19*2, with frequencies of 0.85 and 0.15, respectively; 3% of subjects were predicted to be poor metabolizers. For CYP2D6, the most frequent alleles were CYP2D6*1 (frequency 0.765), CYP2D62* (0.04), CYP2D6*3 (0.0275), CYP2D6*4 (0.14), CYP2D6*5 ( 0.01), and CYP2D6*6 (0.015). Out of these, 3% were predicted to be poor metabolizers, and 4% were predicted to be ultra-rapid metabolizers. CONCLUSION: The prevalence of allelic variants and predicted genotypes in the Croatian population is in accordance with the other European populations, and it can be interpolated between the values for mid-European and Mediterranean populations.