Pharmacokinetics of oral nifedipine in different populations

Design and characterisation of an amorphous formulation of nifedipine for the treatment of autonomic dysreflexia

OBJECTIVES

Current treatment for autonomic dysreflexia (AD) involves rupturing a liquid-filled soft capsule of nifedipine to aid rapid drug release and absorption, however, this application is not covered under the manufacturer's license. The objective of the current work was to design a rapidly dissolving solid dosage formulation for the treatment of AD as an alternative to the off-license "bite and swallow" use of currently available commercial products.

METHODS

Amorphous solid dispersions (ASDs) of nifedipine were prepared by spray-drying using three different polymers: hydroxypropyl methyl cellulose (HPMC), polyvinyl pyrrolidone (PVP) and polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol (Soluplus), at a 15% w/w drug loading and were formulated and compressed into tablets. Dissolution testing was performed in the paddle dissolution apparatus using either a monophasic or biphasic medium.

KEY FINDINGS

The PVP-nifedipine ASD tablets exhibited rapid dissolution, with 35% of the total nifedipine dose dissolving within 15 min in the monophasic dissolution medium. The HPMC-nifedipine ASD exhibited a very slow dissolution, while the Solupus-nifedipine system exhibited no nifedipine release over 120 min. When tested in the biphasic dissolution medium, the PVP-nifedipine ASD tablets exhibited a release profile comparable to that of the pre-split/ruptured nifedipine soft capsule product.

CONCLUSIONS

This study demonstrates that a nifedipine-PVP ASD is a promising formulation strategy in the treatment of AD.

Oral Ciprofloxacin Pharmacokinetics in Healthy Mexican Volunteers and Other Populations: Is There Interethnic Variability?

BACKGROUND

There is evidence that the pharmacokinetics of certain drugs in Mexicans may differ with respect to other ethnic groups. On the other hand, there is controversy about the existence of interethnic variability in the pharmacokinetics of ciprofloxacin.

AIM OF THE STUDY

To study oral ciprofloxacin pharmacokinetics in Mexicans at various dose levels and make comparisons with other populations in order to gain insight on interethnic variability.

METHODS

Healthy Mexican volunteers received oral ciprofloxacin as 250 mg and 500 mg immediate-release tablets or a 1,000 mg extended-release formulation. Plasma concentration against time curves were constructed, and pharmacokinetic parameters were compared with those reported for other populations.

RESULTS

Ciprofloxacin pharmacokinetics in Mexicans was linear and no significant differences between males and females were detected. When several populations were compared, it appeared that bioavailability in Mexicans was similar to that of Caucasians, being lower than that of Asians. These variations were attenuated when data were normalized by body weight.

CONCLUSIONS

Ciprofloxacin pharmacokinetics exhibit interethnic variability, Asians exhibiting an increased bioavailability with regard to Mexicans and Caucasians. Data suggest that these differences are due to body weight.

CYP3A5 polymorphism in Mexican renal transplant recipients and its association with tacrolimus dosing

BACKGROUND AND AIMS

Variability in CYP3A5 expression associated with differences in tacrolimus bioavailability has been documented. The wild-type allele CYP3A5*1 expresses the functional protein, whereas the CYP3A5*3 allele is a splice variant with a premature stop codon and encodes a truncated nonfunctional protein. The aim of the study was to determine the frequency of CYP3A5*1 and CYP3A5*3 in 291 (124 adults, 167 pediatric) Mexican renal transplant recipients, evaluate the tacrolimus dose requirements by genotype and compare genotype frequency data with that of other populations.

METHODS

We carried out a multicenter study. Patients were recruited from three institutions located in Mexico City. Genotyping of the CYP3A5*1 and CYP3A5*3 alleles was performed by direct DNA sequencing.

RESULTS

Eighteen patients (6.2%) were CYP3A5*1*1 homozygous carriers or functional protein expresser homozygous, 121 patients (41.6 %) were CYP3A5*1*3 were heterozygous carriers or heterozygous expressers, and 152 patients (52.2%) were CYP3A5*3*3 homozygous carriers or homozygous nonexpressers. There was a statistically significant difference in frequency of the functional and nonfunctional expresser phenotypes from those reported for Black and Caucasian, but not for South Asian populations. The CYP3A5 phenotype had a significant impact in tacrolimus bioavailability, as wild-type carriers required higher dosing compared to mutated carriers to achieve similar drug trough levels. Patients with CYP3A5*1*1 genotype had a median dose requirement of 0.16 mg/kg/day, CYP3A5*1*3 patients had a median tacrolimus dose of 0.13 mg/kg/day and CYP3A5*3*3 had a median dose of 0.07 mg/kg/day (Kruskal-Wallis, p <0.0001).

CONCLUSIONS

Of the Mexican transplant recipients, 52.2% were CYP3A5*3*3 and required significantly lower tacrolimus dose than those with CYP3A5*1 allele.

Impact of the haplotypes of the human pregnane X receptor gene on the basal and St John's wort-induced activity of cytochrome P450 3A4 enzyme

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Human pregnane X receptor (PXR/NR1I2) is a key regulator of cytochrome P450 3A4. To date, there are 198 reported SNPs for the human PXR/NR1I2 gene. Some of these SNPs are found to affect the inducing ability of PXR to CYP3A4.

WHAT THIS STUDY ADDS

This study, for the first time, has investigated the effect of PXR haplotype on basal and St John's wort-induced CYP3A4 activity in humans. H1/H1 of the PXR gene had weaker basal transcriptional activity but greater inducible transcriptional activity to CYP3A4 than H1/H2 and H2/H2.

AIMS

Human pregnane X receptor (PXR/NR1I2) is the master regulator of CYP3A4, which metabolizes >50% of drugs on the market. This study investigated the relationship between the two most frequent haplotypes [H1 (TCAGGGGCCACC) and H2 (CCGAAAACTAAT)] of PXR and basal and St John's wort (SJW)-induced CYP3A4 activity.

METHODS

Ten healthy subjects carrying H1 and H2 haplotypes (three subjects with H1/H1, four with H1/H2 and three with H2/H2) entered this study. The 10 subjects did not carry CYP3A4*4, *5 and *6. All subjects were administrated a 300-mg SJW tablet three times daily for 14 days, and CYP3A4 activity was measured using nifedipine (NIF) as a probe. The plasma concentrations of NIF and dehydronifedipine (DNIF) were determined by a validated liquid chromatography/mass spectrometry/mass spectrometry method.

RESULTS

After administration of SJW, the AUC(0-infinity) of NIF decreased significantly, and the AUC(0-infinity) of DNIF increased significantly (P < 0.05). For H1/H2, the AUC(0-infinity) of NIF decreased by 42.4%, and the AUC(0-infinity) of DNIF increased by 20.2%; for H2/H2, the AUC(0-infinity) of NIF decreased by 47.9%, and the AUC(0-infinity) of DNIF increased by 33.0%; for H1/H1, the AUC(0-infinity) of NIF decreased by 29.0%, yet the AUC(0-infinity) of DNIF increased by 106.7%. The increase of the AUC(0-infinity) of DNIF in H1/H1 was significantly different from the other two haplotype pairs (P < 0.05). Meanwhile, before administration of SJW, the ratio of AUC(0-infinity(DNIF))/AUC(0-infinity(NIF)) was the lowest for H1/H1 (22.1%), compared with H1/H2 (58.7%) and H2/H2 (30.0%).

CONCLUSIONS

H1/H1 of the human PXR gene had weaker basal transcriptional activity but greater inducible transcriptional activity to CYP3A4 than H1/H2 and H2/H2.

Rapid and simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography-tandem mass spectrometry: Application to a clinical herb-drug interaction study

Nifedipine (NIF), a calcium channel antagonist, is metabolized primarily by cytochrome P450 (CYP3A4) to dehydronifedipine (DNIF). As such, NIF is often used as a probe drug for determining CYP3A4 activity in human studies. A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated to simultaneously determine NIF and DNIF in human plasma using nitrendipine as the internal standard (IS). After extraction of the plasma samples by ether-n-hexane (3:1, v/v), NIF, DNIF and the IS were subjected to LC/MS/MS analysis using electro-spray ionization (ESI). Chromatographic separation was performed on a Hypersil BDS C(18) column (50 mm x 2.1 mm, i.d., 3 microm). The method had a chromatographic running time of approximately 2.5 min and linear calibration curves over the concentrations of 0.5-100 ng/mL for NIF and DNIF. The recoveries of the one-step liquid extraction method were 81.3-89.1% for NIF and 71.6-80.4% for DNIF. The lower limit of quantification (LLOQ) of the analytical method was 0.5 ng/mL for both analytes. The intra- and inter-day precision was less than 15% for all quality control samples at concentrations of 2, 10, and 50 ng/mL. The validated LC/MS/MS method has been successfully used to study pharmacokinetic interactions of NIF with the herbal antidepressant St. John's wort in healthy volunteers. These results indicated that the developed LC/MS/MS method was efficient with a significantly shorter running time (2.5 min) for NIF and DNIF compared to those methods previously reported in the literature. The presented LC/MS/MS method had acceptable accuracy, precision and sensitivity and was used in a clinical pharmacokinetic interaction study of NIF with St. John's wort, a known herbal inducer of CYP3A4. St. John's wort was shown to induce NIF metabolism with increased plasma concentrations of DNIF.

Pharmacokinetic properties of pravastatin in Mexicans: An open-label study in healthy adult volunteers

BACKGROUND

The pharmacokinetic properties of pravastatin, particularlyAUC and Cmax, are variable by population. A description of the pharmacokinetic properties of pravastatin in Mexican mestizos was not found in a search of MEDLINE/PubMed (key terms: pravastatin, Mexican, and pharmacokinetics; years: 1966-2005). Because Mexicans and Japanese have common ancestors (Mongoloid group), they also have a common gene pool. This gene pool was modified by genetic "bottlenecks" that occurred when these populations migrated to the Americas and when the Mexican population mixed with the Spanish population during the 16th and 17th centuries. Previous studies in Japanese subjects showed 5 main mutations on the hepatic drug transporter OATP-C, resulting in higher Cmax and AUC values compared with whites. In the Japanese population, the rates of expression of the (*) 1b and (*) 15 alleles were 46% and 15%, respectively.

OBJECTIVE

The aim of this study was to evaluate the pharmacokinetic propertiesof pravastatin in healthy Mexican mestizo volunteers and to compare them with those in white and Japanese populations described in the literature.

METHODS

This open-label, uncontrolled pilot study of the pharmacokineticproperties of pravastatin was conducted at the Division of Pharmacology, Center for Research and Advanced Studies, Mexico City, Mexico. Healthy, adult, Mexican volunteers received a single dose of pravastatin 10 mg PO (tablet). High-performance liquid chromatography was used to determine plasma pravastatin concentrations between 15 minutes and 12 hours after dosing.

RESULTS

Twenty-four subjects (15 women, 9 men; mean age, 30.6 years)participated in the study. The mean (SD) Cmax was 9.5 (2.4) ng/mL; Tmax, 0.8 (0.3) hours; AUC0-∞ 35.7 (19.7) ng/mL - h; t1/2, 2.7 (1.1) hours; and mean residence time, 3.1 (1.1) hours. One volunteer (4%) had an AUC value that differed substantially from the rest of the study population, producing a bimodal distribution of the pharmacokinetic parameters. No adverse events were observed or reported during the trial.

CONCLUSIONS

In this small pilot study of the pharmacokinetic properties of pravastatin in Mexican mestizos, AUC was not statistically significantly different from previous studies, either in a white or Japanese population. However, we did not find the high values reported for Cmax in some Japanese subjects carrying recently reported mutations on the pravastatin transporter.

Further Evidence for Interethnic Differences in the Oral Pharmacokinetics of Meloxicam

INTRODUCTION

Meloxicam is a nonsteroidal anti-inflammatory agent used widely in therapeutics. It is mainly metabolised by the cytochrome P450 enzyme (CYP) 2C9, with minor involvement of CYP3A4. So far, no information on the oral pharmacokinetics of this drug in adult Mexicans is available. The purpose of this study was to evaluate the oral pharmacokinetics of meloxicam in Mexican subjects.

METHODS

Twenty-four healthy male subjects received an oral dose of meloxicam 7.5mg after fasting for 10 hours. Blood samples were drawn from a suitable forearm vein and plasma obtained. The meloxicam concentration was evaluated by a high-performance liquid chromatographic method and pharmacokinetic parameters were obtained by non-compartmental techniques. Pharmacokinetic parameters obtained in this study were compared with those reported under similar conditions in other populations in order to establish if interethnic differences in the pharmacokinetics of meloxicam exist.

RESULTS

After administration of meloxicam, plasma levels increased to a maximum concentration (C(max)) of 0.702 +/- 0.027 (mean +/- SEM) microg/mL with a time to reach C(max) of 4.77 +/- 0.65h. The area under the plasma concentration versus time curve was 24.82 +/- 1.23 microg . h/mL. The clearance was about 4.8 mL/min and the volume of distribution 9.8 +/- 0.36L. When these parameters were compared with those reported in German and Indian subjects, a reduced clearance and volume of distribution were evident in Mexicans. However, clearance and volume of distribution obtained in this study were very similar to those reported in Chinese subjects.

CONCLUSIONS

The oral pharmacokinetic parameters of meloxicam in healthy Mexican subjects compared with historic controls reported in other populations showed a reduced clearance and volume of distribution when compared with German subjects, whereas no differences between Mexican and Chinese subjects were observed. These results suggest that there are interethnic differences in the pharmacokinetics of meloxicam.

Common allelic variants of cytochrome P4503A4 and their prevalence in different populations

Marked interindividual variability in expression of CYP3A4 influences the disposition of many endo- and xenobiotics, including the metabolism of steroids, environmental toxins and therapeutically useful drugs. The present study was designed to determine the genetic basis of CYP3A4 variability. We analysed DNA from 82 individuals with known CYP3A4 phenotype including 53 Caucasians and 21 African-American liver donors, seven individuals who were outliers in CYP3A4 metabolism and five individuals in a family of a poor nifedipine metabolizer. In addition, we analysed DNA from the eight person DNA Polymorphism Discovery Resource subset (Coriell Institute) and 89 individuals representing nine ethnic groups. Five non-synonymous mutations in the coding region of CYP3A4 were observed. CYP3A4*14 (T44C) in exon 1 resulted in an L15P change; CYP3A4*15 (G14387A) in exon 6 resulted in a R162Q substitution; CYP3A4*10 (G14422C) in exon 6 resulted in a D174H substitution; CYP3A4*16 (C15721G) in exon 7 resulted in a T185S amino acid substitution; and CYP3A4*12 (C22002T) in exon 11 resulted in a L373F change in the CYP3A4 protein. An additional six single nucleotide polymorphisms (SNPs) in the 5'-UTR, 13 SNPs in the introns and three SNPs in the 3'-UTR were observed. Extensive population differences were observed in the frequencies of various CYP3A4 alleles. None of the 28 CYP3A4 SNPs identified in CYP3A4 phenotyped persons (most individuals being heterozygous for any CYP3A4 variant) was associated with low hepatic CYP3A4 protein expression or low CYP3A4 activity in vivo.

Protease inhibitor-associated hyperglycemia in Mexican patients with HIV infection

BACKGROUND

The use of protease inhibitors has revolutionized the treatment of HIV infection. These agents are well tolerated, although the Federal Drug Administration (FDA) has warned U.S. doctors that protease inhibitors may precipitate hyperglycemia and diabetes (DM), based on isolated reports from physicians.

METHODS

Sixty-one patients with HIV infection with criterion of non-DM from the onset of the protease inhibitor therapy participated in the study. Plasma glucose levels were obtained every month during a 6-month period, with a basal determination prior to protease inhibitor therapy.

RESULTS

All Mexican patients enrolled in this study had the same Hispanic-American ethnic origin. Four patients (6.55%) developed hyperglycemia related with saquinavir. One had family history of DM type II. These patients were controlled with diet.

CONCLUSIONS

Based on present data, we believe the benefits of these drugs to patients suffering from HIV infection outweigh the various risks of taking protease inhibitors. However, physicians who use these drugs have to be on the alert for hyperglycemia in the Mexican population, while patients should know the warning symptoms of hyperglycemia and diabetes.

Bioavailability of oral cyclosporine in healthy Mexican volunteers: evidence for interethnic variability

The existence of population variations in cyclosporine pharmacokinetics could be expected, as this drug, similar to nifedipine, is biotransformed by cytochrome P-450 subfamily 3A4, and the existence of interethnic variability in nifedipine disposition has been demonstrated previously. The bioavailability of oral cyclosporine was studied in 23 healthy Mexican volunteers receiving 7.5-mg/kg doses of cyclosporine. Blood samples were drawn over 24 hours, and concentration of cyclosporine in whole blood was determined by a radioimmunoassay using monoclonal antibodies specific for the unchanged drug. The bioavailability of cyclosporine exhibited wide interindividual variability. Maximum concentration (Cmax) ranged from 528 ng/mL to 2,689 ng/mL, area under the concentration-time curve (AUC) ranged from 6,550 ng.hr/mL to 18,562 ng.hr/mL, and time to reach Cmax (tmax) ranged from 1 to 8 hours. Half-life (t1/2) exhibited less important variations, ranging from 4.4 to 9.1 hours. The bioavailability of oral cyclosporine in Mexicans was higher than that reported for white populations under similar conditions. The present results suggest the existence of interethnic variability in the pharmacokinetics of cyclosporine, as is the case with nifedipine.

Cytochrome P4503A (CYP3A) metabolism: prediction of in vivo activity in humans

CYP3A is one of the most important cytochrome P450 isoforms responsible for drug metabolism by humans because it is the major such enzyme in critical tissues such as the gastrointestinal tract and liver, and it is involved in the oxidative biotransformation of numerous clinically useful therapeutic agents. Many factors regulate CYP3A expression but these are being increasingly defined so that the disposition characteristics of a drug whose metabolism is importantly mediated by this isoform can be reasonably well predicted a priori. For example, metabolic clearance is distributed within a population in a unimodal fashion but marked (5- to 20-fold) interindividual variability is present as a consequence of both genetic and nongenetic factors. In addition, first-pass metabolism occurs following oral drug administration and this may be extensive so that bioavailability is low. CYP3A activity can also be readily modulated by inducers like rifampicin and several anticonvulsant agents, and many potent inhibitors exist such as azole antifungal agents and macrolide antibiotics. Accordingly, the potential for drug interactions with these drugs as well as other CYP3A substrates, when given concomitantly, is high. Metabolism involving CYP3A is also likely to be affected by liver disease as well as aging, and modest differences may be present between men and women but these are often clinically unimportant. Because of such predictability, knowledge of the role and importance of CYP3A in the metabolism of a putative drug candidate is becoming increasingly desirable at an early stage in the development process. In vitro studies using human liver preparations, including microsomes, cultured hepatocytes and heterologous expressed enzymes, can provide important insights in this regard. This is particularly the case for identifying potential drug interactions whose clinical significance can be subsequently assessed. Data with respect to terfenadine and cyclosporine obtained several years after their approval and marketing, indicate that, if available and applied during their development, the paradigm of using in vitro studies to rationally direct and prioritize clinical studies would have prospectively prevented the serious adverse effects and inefficacy that were only recognized during their empiric clinical use. Such examples, along with those associated with the genetic polymorphism of CYP2D6, provide strong justification for establishing the role and importance of individual CYP isoforms in a candidate drug's metabolism at an early stage.