Dose-dependent pharmacokinetics of aprindine in healthy volunteers

In vivo evaluation of drug dialyzability in a rat model of hemodialysis

It is important to calculate the drug removal by hemodialysis (HD) for drug dosing regimens in HD patients. However, there are limited and inconsistent information about the dialyzability of drugs by HD. Therefore, the aim of our study is to evaluate drug removal by utilizing a rat model of HD (HD rat) and to extrapolate this result to the drug removal rate in HD patients. HD rats received bilateral nephrectomy and HD for 2 h. The dialysis removal of 6 drugs was evaluated in HD rats. Dialysis efficiency, plasma protein binding rate (PBR) and distribution volume (Vd) of drugs were also measured. Furthermore, we examined the correlation between the dialyzability of drug in HD rats and humans and constructed the prediction formula of the drug dialyzability in HD patients. The clearance of urea and creatinine and normalized dialysis dose in HD rats were 0.83 ± 0.07 mL/min, 0.70 ± 0.08 mL/min, and 0.13 ± 0.06, respectively. The drug dialyzability in HD rats was similar to reported clinical data except for doripenem. A higher correlation was observed between drug dialyzability in reported clinical data and HD rats which were adjusted for PBR (r² = 0.936; p < 0.001) compared to unadjusted (r² = 0.812; p = 0.009). Therefore, we constructed the prediction formula of the drug dialyzability in HD patients by utilizing the HD rat model and PBR. This study is useful for evaluating the dialyzability of high-risk drugs in a clinical setting and might provide appropriate preclinical dialyzability data for new drug.

Simple Formula for Predicting Drug Removal Rates During Hemodialysis

The present study sought to derive a simple formula for predicting the drug removal rates during hemodialysis. We examined the relationship between drug removal rates during hemodialysis and the molecular weights or pharmacokinetic parameters of injectable drugs (N = 90) obtained from pharmaceutical interview forms in Japan. Stepwise multiple regression analysis with the removal rate by hemodialysis as the objective variable adjusted for molecular weight or pharmacokinetic parameters as explanatory variables, showed that the logarithm of molecular weight (B = -18.87), the protein binding rate (B = -0.40), and the fraction of the unchanged drug excreted into the urine/volume of distribution (B = 0.05) were significantly and independently associated with drug removal rate by hemodialysis (α = 90.78, adjusted R²  = 0.64, P = 2.2e^-16 ). Our data demonstrated that molecular weight, protein binding rate, and volume of distribution were important factors affecting drug removal during hemodialysis, and that our simple regression equation could be used to predict the drug removal rate during hemodialysis.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Nonlinear Pharmacokinetics of Aprindine in Guinea Pigs

After intravenous bolus administration of aprindine (AP) to conscious guinea pigs, the semilogarithmic plasma concentration versus time curve was linear at a dose of 2 mg/kg, but convex at doses of 5 and 10 mg/kg. AP concentrations immediately after administration (C(p0)) were almost identical, irrespective of the dose received. The areas under the plasma concentration-time curves (AUCs) were proportional to the AP doses. At 2 mg/kg, the plasma total clearance (CL(tot)) of AP was high (279+/-80 mL/h), and its volume of distribution (Vd(ss)) was large (245+/-99 mL). Total blood clearance and time-averaged blood clearance (CL(ave)) values for AP were similar to those for R(+) propranolol (PL) after intravenous coadministration of R(+) PL (0.25 mg/kg) and AP (2 or 10 mg/kg). An in vitro serum protein binding study showed that the unbound fraction of AP was concentration-dependent. In guinea pigs pretreated with turpentine oil (2 mL/kg/day), the elimination of AP after intravenous doses of 2 and 5 mg/kg closely followed first-order kinetics, while C(p0) and AUC increased in proportion to the AP doses. The bound fraction of AP in the serum was larger after turpentine oil pretreatment than in normal guinea pig serum in vitro. From these observations, the nonlinear pharmacokinetics of AP observed in guinea pigs can be attributed to nonlinear serum protein binding.

The metabolism of aprindine in relation to the sparteine/debrisoquine polymorphism

1. Incubation of the class I antiarrhythmic drug aprindine (AP) with human liver microsomes resulted in the formation of two hydroxylated metabolites (HA1 and HA2) and desethylaprindine which were identified by GC-mass spectrometry. In liver microsomes isolated from a poor metaboliser (PM) of sparteine no hydroxylated metabolites of AP were detected whereas AP N-dealkylation was unimpaired. Thus hydroxylation of AP is mediated by cytochrome P450 2D6 (CYP2D6). 2. AP was found to be a competitive inhibitor of CYP2D6 as indicated by its ability to impair the formation of (2S)-hydroxysparteine, 5,6-didehydrosparteine and 5-hydroxypropafenone by human liver microsomes. 3. These in vitro findings are consistent with a major role of CYP2D6 in the clearance of AP in vivo, with its ability to impair the metabolism of other CYP2D6 substrates in vivo, and an ability to cause phenocopying (conversion of extensive metaboliser phenotypes for sparteine/debrisoquine to apparent 'poor metabolisers).

Rapid and sensitive determination of aprindine in serum by gas chromatography using a surface ionization detector

A rapid and highly sensitive method for the determination in serum of aprindine, an antiarrhythmic drug, was developed employing gas chromatography with a surface ionization detector. No interfering peak from endogenous substances appeared when an organic phase was directly injected into the system after single extraction from a serum sample. A standard curve obtained was linear up to the serum level of 6 micrograms/ml, and the limit of sensitivity was 16 pg. The method described is applicable to routine therapeutic monitoring of serum concentrations of aprindine.

Dose independent pharmacokinetics of mexiletine in healthy volunteers

In 12 healthy volunteers who received orally 100, 200, 300, 400 and 600 mg mexiletine at weekly intervals, the maximum plasma concentration of mexiletine and AUC increased linearly with the dose of mexiletine. Between doses there were no significant differences in the values for clearance and volume of distribution of mexiletine but there were for plasma elimination half-life. These results indicate that the kinetics of mexiletine are linear.