Population pharmacokinetics of steady-state carbamazepine in Egyptian epilepsy patients

Uptake, elimination, and toxicokinetics of selected pharmaceuticals in multiple tissues of Nile tilapia (Oreochromis niloticus) exposed to environmentally relevant concentrations

Pharmaceuticals in aquatic environment displayed adverse effects to fish. The effects are usually related to the internal levels of pharmaceuticals accumulated in specific fish tissues. In this study, we investigated the uptake, elimination, and toxicokinetics of six pharmaceuticals, e.g. naproxen (NAX), diclofenac (DCF), ibuprofen (IBU), carbamazepine (CBZ), fluoxetine (FLX), and sertraline (SER), in 11 fish tissues of Nile tilapia. The experiments were conducted in a flow-through system with an 8-day uptake/8-day elimination periods. The fish exposure groups involved the control, single FLX, and mixture of six pharmaceuticals at environmentally relevant concentration of 4 μg/L. FLX and SER showed the maximum concentrations of 145 and 201 ng/g wet weight, respectively, in fish spleen tissue, while NAX and IBU were not detected in any tissue. The mean concentrations for the pharmaceuticals in Nile tilapia tissues generally followed the order: bile> kidney, gut, stomach, liver> brain, gill, spleen> plasma, skin, muscle. The steady-state bioconcentration factors in various tissues generally range at 0.74-437.58 L/kg. The uptake and elimination toxicokinetics illustrated the rapid accumulation and depuration of pharmaceuticals in fish tissues. The results help to understand the internal bioconcentration, tissue distribution, and toxicokinetics of pharmaceuticals in multiple fish biological compartments.

Iron supplements in nursing home patients associated with reduced carbamazepine absorption

Persons in nursing homes receive a number of medications that may interfere with the pharmacokinetics of carbamazepine (CBZ). The aim of our study was to determine factors that may affect the pharmacokinetics of CBZ in elderly nursing home patients.

METHODS

CBZ concentration data collected from 60 nursing homes across the US were evaluated. Inclusion criteria included residency in a nursing home for at least 2 months, age 65 years or older, a stable dosing regimen of CBZ for at least 4 weeks (considered steady state), available CBZ concentration, and complete information regarding all co-medications. Using a nonlinear mixed-effects model, the data were adequately described by a one-compartment model with first-order absorption and elimination. Goodness-of-fit plots, plausibility of parameter estimates, visual predictive check and nonparametric bootstrap were used to evaluate the models.

MAIN FINDINGS

The final data set consisted of 345 CBZ concentrations from 99 subjects (38 males, 61 females). The population estimate of apparent clearance (CL/F) for a 70-kg person was 3.69 L/hr (RSE 6.9%). Residents were receiving either immediate (93.9%) or extended release (6.1%) formulation of CBZ and the Ka of each formulation was fixed to literature values. Age, sex, and co-medications had no effect on CL/F and apparent volume of distribution. Iron supplementation, which was taken by 16% of the residents, resulted in a 33% decrease in bioavailability (p < 0.001). No other medications were found to have an effect.

CONCLUSIONS

Results from this pharmacokinetic study indicate that use of iron supplementation is associated with a reduction in absorption of CBZ and may need to be considered when dosing CBZ in patients taking iron supplementation.

The influence of CYP2C8*3 on carbamazepine serum concentration in epileptic pediatric patients

The aim of the present study was to investigate the distribution of CYP2C8 variants *3 and *5, as well as their effect on carbamazepine pharmacokinetic properties, in 40 epileptic pediatric patients on carbamazepine treatment. Genotyping was conducted using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), and allele-specific (AS)-PCR methods, and steady-state carbamazepine plasma concentrations were determined by high performance liquid chromatography (HPLC). The CYP2C8 *3 and *5 polymorphisms were found at frequencies of 17.5 and 0.0%, respectively. After dose adjustment, there was a difference in daily dose in CYP2C8*3 carriers compared to non carriers [mean ± standard deviation (SD): 14.19 ± 5.39 vs. 15.46 ± 4.35 mg/kg; p = 0.5]. Dose-normalized serum concentration of carbamazepine was higher in CYP2C8*3 (mean ± SD: 0.54 ± 0.18 vs. 0.43 ± 0.11 mg/mL, p = 0.04), and the observed correlation between weight-adjusted carbamazepine dose and carbamazepine concentration after dose adjustment was significant only in CYP2C8*3 non carriers (r = 0.52, p = 0.002). However, the population pharmacokinetic analysis failed to demonstrate any significant effect of CYP2C8 *3 polymorphism on carbamazepine clearance [CL L/h = 0.215 + 0.0696*SEX+ 0.000183*DD]. The results indicated that the CYP2C8*3 polymorphism might not be of clinical importance for epilepsy treatment in pediatric populations.

CYP1A2 genotype affects carbamazepine pharmacokinetics in children with epilepsy

PURPOSE

The purpose of this study is to investigate the effect of two of the most important functional CYP1A2 variations -3860G > A and -163C > A on carbamazepine pharmacokinetics in Serbian pediatric epileptic patients.

METHODS

The study involved 40 Serbian pediatric epileptic patients on steady-state carbamazepine treatment. Genotyping for -3860G > A and -163C > A was carried out using PCR-RFLP method, and carbamazepine plasma concentrations were determined by high pressure liquid chromatography (HPLC) method. For pharmacokinetic analysis, NONMEM software with implementation of ADVAN 1 subroutine was used.

RESULTS

CYP1A2 polymorphism -163C > A was found at the frequency of 65.0 %, while -3860G > A was not detected. The correlation between weight-adjusted carbamazepine dose and carbamazepine concentration after dose adjustment was significant only in carriers of -163C/C and C/A genotypes (r = 0.68, p = 0.0004). The equation that described population clearance (CL) was CL (l/h) = 0.176 + 0.0484 * SEX + 0.019 * CYP1A2 + 0.000156 * DD, where SEX has a value of 1 if male and 0 if female, CYP1A2 has a value of 1 if -163A/A and 0 if -163C/C or C/A, and DD is the total carbamazepine daily dose (mg/day).

CONCLUSIONS

CYP1A2 -163A/A genotype influence carbamazepine pharmacokinetics. In addition to sex and total carbamazepine daily dose, -163C > A CYP1A2 polymorphism should be considered as a predictor of carbamazepine clearance.

Carbamazepine

This chapter includes the aspects of carbamazepine. The drug is synthesized by the use of 5H-dibenz[b,f]azepine and phosgene followed by subsequent reaction with ammonia. Carbamazepine is generally used for the treatment of seizure disorders and neuropathic pain, it is also important as off-label for a second-line treatment for bipolar disorder and in combination with an antipsychotic in some cases of schizophrenia when treatment with a conventional antipsychotic alone has failed. Other uses may include attention deficit hyperactivity disorder, schizophrenia, phantom limb syndrome, complex regional pain syndrome, borderline personality disorder, and posttraumatic stress disorder. The chapter discusses the drug metabolism and pharmacokinetics and presents various methods of analysis of this drug such electrochemical analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.