Effect of oral contraceptives on triazolam, temazepam, alprazolam, and lorazepam kinetics

Pharmacological interactions and menopausal hormone therapy: a review

IMPORTANCE AND OBJECTIVE

Menopausal hormone therapy (HT) is widely used, and there are several statements of international scientific societies to guide prescribers; however, a summary of existing literature about possible drug interactions with HT does not exist, although many midlife women take medications for other conditions. Therefore, our objective was to create a document that presents and synthesizes the most relevant interactions. The impact of the interaction itself and the number of candidates for HT who are likely to use other treatments are considered based on the best available evidence.

METHODS

A systematic review was performed to determine the best evidence of interaction effects on relevant outcomes of interest for decision making. A working framework was developed to formulate explicit and reasoned recommendations according to four predefined categories for coadministration: (1) can be used without expected risks, (2) acceptable use (no evidence of negative interaction), (3) alternative treatment should be considered, and (4) nonuse without express justification. The project protocol was registered in the Open Science Framework platform (doi: 10.17605/OSF.IO/J6WBC) and in PROSPERO (registration number CRD42020166658).

RESULTS

Studies targeting our objective are scarce, but 23 pharmacological groups were assigned to one of the predefined categories of recommendation for concomitant use of HT. Vaginal HT was assigned to category 1 for 21 of the analyzed pharmacological groups. For oral and transdermal HT (estrogen-only or combined) and tibolone, there were 12 pharmacological groups assigned to category 1, 12 to category 2, 5 to category 3, and 4 to category 4. Results are shown in crossed-tables that are useful for counseling and prescription.

DISCUSSION AND CONCLUSIONS

Available evidence of HT interactions with other drugs is scarce and mainly indirect. It comes from biological plausibility, knowledge of extensive concomitant use without reported incidents, and/or extrapolation from hormonal contraception, but there are pharmacological groups in all categories showing that information is useful. These eligibility criteria summarize it and can help in the decision process of HT coadministration with other drugs. Decisions should be taken based on these recommendations but also individualized risk/benefit evaluation, according to underlying pathology, patient's clinical requirements, and the existence or nonexistence of alternatives.

Navigating the complex landscape of benzodiazepine- and Z-drug diversity: insights from comprehensive FDA adverse event reporting system analysis and beyond

Introduction

Medications which target benzodiazepine (BZD) binding sites of GABAA receptors (GABAARs) have been in widespread use since the nineteen-sixties. They carry labels as anxiolytics, hypnotics or antiepileptics. All benzodiazepines and several nonbenzodiazepine Z-drugs share high affinity binding sites on certain subtypes of GABAA receptors, from which they can be displaced by the clinically used antagonist flumazenil. Additional binding sites exist and overlap in part with sites used by some general anaesthetics and barbiturates. Despite substantial preclinical efforts, it remains unclear which receptor subtypes and ligand features mediate individual drug effects. There is a paucity of literature comparing clinically observed adverse effect liabilities across substances in methodologically coherent ways.

Methods

In order to examine heterogeneity in clinical outcome, we screened the publicly available U.S. FDA adverse event reporting system (FAERS) database for reports of individual compounds and analyzed them for each sex individually with the use of disproportionality analysis. The complementary use of physico-chemical descriptors provides a molecular basis for the analysis of clinical observations of wanted and unwanted drug effects.

Results and Discussion

We found a multifaceted FAERS picture, and suggest that more thorough clinical and pharmacoepidemiologic investigations of the heterogenous side effect profiles for benzodiazepines and Z-drugs are needed. This may lead to more differentiated safety profiles and prescription practice for particular compounds, which in turn could potentially ease side effect burden in everyday clinical practice considerably. From both preclinical literature and pharmacovigilance data, there is converging evidence that this very large class of psychoactive molecules displays a broad range of distinctive unwanted effect profiles - too broad to be explained by the four canonical, so-called "diazepam-sensitive high-affinity interaction sites". The substance-specific signatures of compound effects may partly be mediated by phenomena such as occupancy of additional binding sites, and/or synergistic interactions with endogenous substances like steroids and endocannabinoids. These in turn drive the wanted and unwanted effects and sex differences of individual compounds.

Drug-drug interactions that alter the exposure of glucuronidated drugs: Scope, UDP-glucuronosyltransferase (UGT) enzyme selectivity, mechanisms (inhibition and induction), and clinical significance

Drug-drug interactions (DDIs) arising from the perturbation of drug metabolising enzyme activities represent both a clinical problem and a potential economic loss for the pharmaceutical industry. DDIs involving glucuronidated drugs have historically attracted little attention and there is a perception that interactions are of minor clinical relevance. This review critically examines the scope and aetiology of DDIs that result in altered exposure of glucuronidated drugs. Interaction mechanisms, namely inhibition and induction of UDP-glucuronosyltransferase (UGT) enzymes and the potential interplay with drug transporters, are reviewed in detail, as is the clinical significance of known DDIs. Altered victim drug exposure arising from modulation of UGT enzyme activities is relatively common and, notably, the incidence and importance of UGT induction as a DDI mechanism is greater than generally believed. Numerous DDIs are clinically relevant, resulting in either loss of efficacy or an increased risk of adverse effects, necessitating dose individualisation. Several generalisations relating to the likelihood of DDIs can be drawn from the known substrate and inhibitor selectivities of UGT enzymes, highlighting the importance of comprehensive reaction phenotyping studies at an early stage of drug development. Further, rigorous assessment of the DDI liability of new chemical entities that undergo glucuronidation to a significant extent has been recommended recently by regulatory guidance. Although evidence-based approaches exist for the in vitro characterisation of UGT enzyme inhibition and induction, the availability of drugs considered appropriate for use as 'probe' substrates in clinical DDI studies is limited and this should be research priority.

Eligibility criteria for Menopausal Hormone Therapy (MHT): a position statement from a consortium of scientific societies for the use of MHT in women with medical conditions. MHT Eligibility Criteria Group

This project aims to develop eligibility criteria for menopausal hormone therapy (MHT). The tool should be similar to those already established for contraception A consortium of scientific societies coordinated by the Spanish Menopause Society met to formulate recommendations for the use of MHT by women with medical conditions based on the best available evidence. The project was developed in two phases. As a first step, we conducted 14 systematic reviews and 32 metanalyses on the safety of MHT (in nine areas: age, time of menopause onset, treatment duration, women with thrombotic risk, women with a personal history of cardiovascular disease, women with metabolic syndrome, women with gastrointestinal diseases, survivors of breast cancer or of other cancers, and women who smoke) and on the most relevant pharmacological interactions with MHT. These systematic reviews and metanalyses helped inform a structured process in which a panel of experts defined the eligibility criteria according to a specific framework, which facilitated the discussion and development process. To unify the proposal, the following eligibility criteria have been defined in accordance with the WHO international nomenclature for the different alternatives for MHT (category 1, no restriction on the use of MHT; category 2, the benefits outweigh the risks; category 3, the risks generally outweigh the benefits; category 4, MHT should not be used). Quality was classified as high, moderate, low or very low, based on several factors (including risk of bias, inaccuracy, inconsistency, lack of directionality and publication bias). When no direct evidence was identified, but plausibility, clinical experience or indirect evidence were available, "Expert opinion" was categorized. For the first time, a set of eligibility criteria, based on clinical evidence and developed according to the most rigorous methodological tools, has been defined. This will provide health professionals with a powerful decision-making tool that can be used to manage menopausal symptoms.

Evaluation of a rapid, generic human gestational dose model

Chemical risk assessment considers potentially susceptible populations including pregnant women and developing fetuses. Humans encounter thousands of chemicals in their environments, few of which have been fully characterized. Toxicokinetic (TK) information is needed to relate chemical exposure to potentially bioactive tissue concentrations. Observational data describing human gestational exposures are unavailable for most chemicals, but physiologically based TK (PBTK) models estimate such exposures. Development of chemical-specific PBTK models requires considerable time and resources. As an alternative, generic PBTK approaches describe a standardized physiology and characterize chemicals with a set of standard physical and TK descriptors - primarily plasma protein binding and hepatic clearance. Here we report and evaluate a generic PBTK model of a human mother and developing fetus. We used a published set of formulas describing the major anatomical and physiological changes that occur during pregnancy to augment the High-Throughput Toxicokinetics (httk) software package. We simulated the ratio of concentrations in maternal and fetal plasma and compared to literature in vivo measurements. We evaluated the model with literature in vivo time-course measurements of maternal plasma concentrations in pregnant and non-pregnant women. Finally, we prioritized chemicals measured in maternal serum based on predicted fetal brain concentrations. This new model can be used for TK simulations of 859 chemicals with existing human-specific in vitro TK data as well as any new chemicals for which such data become available. This gestational model may allow for in vitro to in vivo extrapolation of point of departure doses relevant to reproductive and developmental toxicity.

Benzodiazepines Remain Important Therapeutic Options in Psychiatric Practice

Benzodiazepines and medications acting on benzodiazepine receptors that do not have a benzodiazepine structure (z-drugs) have been viewed by some experts and regulatory bodies as having limited benefit and significant risks. Data presented in this article support the use of these medications as treatments of choice for acute situational anxiety, chronic anxiety disorders, insomnia, alcohol withdrawal syndromes, and catatonia. They may also be useful adjuncts in the treatment of anxious depression and mania, and for medically ill patients. Tolerance develops to sedation and possibly psychomotor impairment, but not to the anxiolytic effect of benzodiazepines. Sedation can impair cognitive function in some patients, but assertions that benzodiazepines increase the risk of dementia are not supported by recent data. Contrary to popular opinion, benzodiazepines are not frequently misused or conduits to misuse of other substances in patients without substance use disorders who are prescribed these medications for appropriate indications; most benzodiazepine misuse involves medications that are obtained from other people. Benzodiazepines are usually not lethal in overdose except when ingested with other substances, especially alcohol and opioids. Benzodiazepines comprise one of the few classes of psychotropic medication the mechanisms of action of which are clearly delineated, allowing for greater precision in their clinical use. These medications, therefore, belong in the therapeutic armamentarium of the knowledgeable clinician.

Drug Interactions Involving 17α-Ethinylestradiol: Considerations Beyond Cytochrome P450 3A Induction and Inhibition

It is widely acknowledged that drug-drug interactions (DDIs) involving estrogen (17α-ethinylestradiol (EE))-containing oral contraceptives (OCs) are important. Consequently, sponsors of new molecular entities (NMEs) often conduct clinical studies with priority given to OCs as victims of cytochrome P450 (CYP) 3A (CYP3A) induction and inhibition. Such scenarios are reflected in the US Food and Drug Administration-issued guidance documentation related to OC DDI studies. Although CYP3A is important, OCs such as EE are metabolized by sulfotransferase 1E1 and UDP-glucuronosyltransferase (UGT) 1A1, expressed in the gut and liver, and so both can also serve as loci of victim OC DDI. Therefore, for any NME, one should carefully consider its induction and inhibition profile involving CYP3A4/5, UGT1A1, and SULT1E1. As DDI perpetrators, available clinical DDI data indicate that EE-containing OCs can induce (e.g., UGT1A4 and CYP2A6) and inhibit (CYP1A2 ≥ CYP2C19 > CYP3A4/5 > CYP2C8, CYP2B6, CYP2D6, and CYP2C9) various CYP forms. Although available in vitro CYP inhibition data do not explain such a graded inhibitory effect in vivo, it is hypothesized that EE differentially modulates CYP expression via potent agonism of the estrogen receptor expressed in the gut and liver. From the standpoint of the NME as potential OC DDI victim, therefore, it is important to assess its projected (pre-phase I) or known therapeutic index and pharmacokinetic profile (fraction absorbed, absolute oral bioavailability, clearance/extraction class, fraction metabolized by CYP1A2, CYP2C19, CYP2A6, and UGT1A4). Such information can enable the prioritization, design, and interpretation of NME-OC DDI studies.

Drug-Drug Interaction Studies With Oral Contraceptives: Pharmacokinetic/Pharmacodynamic and Study Design Considerations

Oral contraceptives (OCs) are the most widely used form of birth control among women of childbearing potential. Knowledge of potential drug-drug interactions (DDIs) with OCs becomes imperative to provide information on the medication to women of childbearing potential and enable their inclusion in clinical trials, especially if the new molecular entity is a teratogen. Although a number of DDI guidance documents are available, they do not provide recommendations for the design and conduct of OC DDI studies. The evaluation of DDI potential of a new molecular entity and OCs is particularly challenging because of the availability of a wide variety of combinations of hormonal contraceptives, different doses of the ethinyl estradiol, and different metabolic profiles of the progestin component. The aim of this review is to comprehensively discuss factors to be considered such as pharmacokinetics (PK), pharmacodynamics (PD), choice of OC, and study population for the conduct of in vivo OC DDI studies. In this context, metabolic pathways of OCs, the effect of enzyme inhibitors and inducers, the role of sex hormone-binding globulin in the PK of progestins, current evidence on OC DDIs, and the interpretation of PD end points are reviewed. With the emergence of new tools like physiologically based PK modeling, the decision to conduct an in vivo study can be made with much more confidence. This review provides a comprehensive overview of various factors that need to be considered in designing OC DDI studies and recommends PK-based DDI studies with PK end points as adequate measures to establish clinical drug interaction and measurement of PD end points when there is basis for PD interaction.

Sex-Related Differences in Pharmacokinetics and Pharmacodynamics of Frequently Prescribed Drugs: A Review of the Literature

While there is considerable evidence about sex-related differences between men and women in drug metabolism, efficacy and safety of frequently prescribed drugs such as analgesics, tranquillizers, statins and beta-blockers, clinicians' awareness of the implications on dosing and adverse event monitoring in routine practice is inadequate. Some drugs are more effective in men than women (e.g. ibuprofen) or vice versa (e.g. opioids, benzodiazepine), typically owing to pharmacodynamic causes. The 5-hydroxytryptamine (5-HT) receptor 3 antagonist alosetron is approved for women only since it largely lacks efficacy in men. For statins, equal efficacy was demonstrated in secondary prevention of cardiovascular events, but primary prevention is still under debate. For some drugs (e.g. paracetamol, metoprolol), women are at significantly higher risk of adverse effects. Therefore, considering sex-specific features in clinical trials and therapeutic guidelines is warranted to ensure efficacy and safety of medicines.

Estradiol and weight are covariates of paracetamol clearance in young women

AIM

Paracetamol clearance differs between pregnant and non-pregnant women and between women with or without specific oral contraceptives (OCs). However, an association between female sex hormones and paracetamol clearance has never been explored.

METHODS

In total, 49 women at delivery, 8 female control subjects without OC use, historical data of 14 women taking OCs, and 15 postpartum observations with and without OCs were pooled to explore covariates of paracetamol clearance. All received a single intravenous 2-gram paracetamol dose, and blood samples were collected up to 6 h after dosing. High-performance liquid chromatography was used to quantify paracetamol. The area under the curve to time infinity (AUC0-∞) was determined and clearance (l/h·m(2)) was calculated by dose/ AUC0-∞. In addition, estradiol and progesterone were quantified by ELISA with electro-chemiluminescence.

RESULTS

Median paracetamol clearance at delivery was significantly higher when compared to postpartum or non-pregnant women (11.9 vs. 6.42 and 8.4 l/h·m(2), at least p < 0.05), while an association between paracetamol clearance and estradiol was observed (R = 0.494, p < 0.0001). In non-pregnant subjects, there was no impact of OC exposure on paracetamol clearance. Multiple regression revealed a linear association (Radj = 0.41, p < 0.001) between paracetamol clearance and weight (p = 0.0462) and estradiol (p < 0.0001).

CONCLUSION

Estradiol and weight in part explain the variation in paracetamol clearance in young women.

Gender-dependent effects of gonadectomy on lung carcinogenesis by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in female and male A/J mice

The present study was conducted to investigate the effects of gonadectomy on lung carcinogenesis in female and male mice, and to determine an association between sex hormone and lung carcinogenesis. Female and male A/J mice were divided into gonadectomized and unoperated control groups and all animals were treated intraperitoneally with 1 or 2 injections of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) at the dose of 2 mg/mouse. The mice were sacrificed 18 or 56 weeks after surgery. Serum levels of estradiol in females and testosterone in males were confirmed to be decreased by gonadectomy. Lung white nodules were detected in all mice of all groups. In the control groups of 18- and 56-week studies, the multiplicities of lung nodules in females were significantly greater than in males. In males in the 56-week study, the multiplicity of macroscopical lung nodules, bronchiolo-alveolar hyperplasias, adenomas and tumors (adenomas and adenocarcinomas) showed significant increase with castration. In females in the 18-week study, the multiplicity of adenomas decreased significantly by ovariectomy. Based on the results of the present study, female A/J mice were confirmed to be more susceptible to NNK-induced lung carcinogenesis than males. Furthermore, it was suggested that the process is inhibited by testosterone and accelerated by estradiol. These findings indicate the possibility that sex hormones play important roles in determining sex differences in lung carcinogenesis in the A/J mice initiated by NNK.

Importance of multi-p450 inhibition in drug-drug interactions: evaluation of incidence, inhibition magnitude, and prediction from in vitro data

Drugs that are mainly cleared by a single enzyme are considered more sensitive to drug-drug interactions (DDIs) than drugs cleared by multiple pathways. However, whether this is true when a drug cleared by multiple pathways is coadministered with an inhibitor of multiple P450 enzymes (multi-P450 inhibition) is not known. Mathematically, simultaneous equipotent inhibition of two elimination pathways that each contribute half of the drug clearance is equal to equipotent inhibition of a single pathway that clears the drug. However, simultaneous strong or moderate inhibition of two pathways by a single inhibitor is perceived as an unlikely scenario. The aim of this study was (i) to identify P450 inhibitors currently in clinical use that can inhibit more than one clearance pathway of an object drug in vivo and (ii) to evaluate the magnitude and predictability of DDIs caused by these multi-P450 inhibitors. Multi-P450 inhibitors were identified using the Metabolism and Transport Drug Interaction Database. A total of 38 multi-P450 inhibitors, defined as inhibitors that increased the AUC or decreased the clearance of probes of two or more P450s, were identified. Seventeen (45%) multi-P450 inhibitors were strong inhibitors of at least one P450, and an additional 12 (32%) were moderate inhibitors of one or more P450s. Only one inhibitor (fluvoxamine) was a strong inhibitor of more than one enzyme. Fifteen of the multi-P450 inhibitors also inhibit drug transporters in vivo, but such data are lacking on many of the inhibitors. Inhibition of multiple P450 enzymes by a single inhibitor resulted in significant (>2-fold) clinical DDIs with drugs that are cleared by multiple pathways such as imipramine and diazepam, while strong P450 inhibitors resulted in only weak DDIs with these object drugs. The magnitude of the DDIs between multi-P450 inhibitors and diazepam, imipramine, and omeprazole could be predicted using in vitro data with similar accuracy as probe substrate studies with the same inhibitors. The results of this study suggest that inhibition of multiple clearance pathways in vivo is clinically relevant, and the risk of DDIs with object drugs may be best evaluated in studies using multi-P450 inhibitors.

Sex-dependent modulation of treatment response

The response to a psychotropic medication reflects characteristics of both the medication and the substrate, ie, the individual receiving the medication. Sex is an individual characteristic that influences all elements of the pharmacokinetic process - absorption, distribution, metabolism, and elimination. The effects of sex on these components of the pharmacokinetic process often counterbalance one another to yield minimal or varying sexual differences in blood levels achieved. However, sex also appears to influence pharmacodynamics, the tissue response to a given level of medication. Consideration by the practitioner of sex as a possible contributing factor to treatment nonresponse will enhance the efficacy and precision of clinical interventions.

CYP2A6 activity in a healthy Spanish population: effect of age, sex, smoking, and oral contraceptives

This study was performed to assess the influence of age, sex, smoking, and contraceptive use on CYP2A6 activity. In the metabolism of caffeine, the conversion of 1,7 dimethylxanthine (17X) to 1,7 dimethiylurate (17U) is catalyzed primarily by CYP2A6. CYP2A6 phenotype was determined by the urinary ratio 17U:17X in the interval of 4-5 h after caffeine intake in 179 healthy white Spaniards (102 women and 76 men). There were 99 non-smokers and 80 smokers. Among women, 26 were taking oral contraceptives. The age was the most important predictive factor of CYP2A6 activity (P < 0.001) with older subjects having higher activity. The influence of the gender was more modest (P = 0.07) with women exhibiting borderline increased values of the CYP2A6 marker than men. Tobacco smoking did not affect CYP2A6 activity. However, the CYP2A6 marker resulted to be strongly related to the use of oral contraceptives. The women users of oral contraceptives had higher values of CYP2A6 marker than both women not taking oral contraceptives and men (P < 0.001 in both comparisons). The results indicate that age, oral contraceptive use, and possibly gender should be controlled in epidemiological studies dealing with CYP2A6 activity and its relationship with xenobiotics exposure and genetic or pathological factor.

Microsomal prediction ofin vivoclearance and associated interindividual variability of six benzodiazepines in humans

The intrinsic clearances (CLint) of midazolam, triazolam, diazepam, nordiazepam, flunitrazepam and alprazolam were determined from two liver banks (n=21) by formation kinetics of ten metabolites. A literature-collated database of in vivo CLint values (811 subjects) was used to assess predictions and variability. The in vivo clearance of six benzodiazepines was generally underpredicted by in vitro data and the degree of bias was in agreement with a database of structurally diverse compounds (n=37). The variability observed for in vitro clearances (11--19--fold for midazolam, diazepam and nordiazepam in liver bank 1; 101--269--fold for triazolam, flunitrazepam and alprazolam in liver bank 2) exceeded the in vivo variability for the same compounds (4--59 and 10--29, respectively). This mismatch may contribute to the bias in microsomal predictions and it highlights the need for careful selection of representative livers for human liver banks.

Pharmacokinetics of the CYP 3A substrate simvastatin following administration of delayed versus immediate release oral dosage forms

PURPOSE

The study was designed to evaluate the effect of delayed release (DR) on absorption and bioavailability of intestinally metabolized drugs after oral dosing, using the HMG-CoA reductase inhibitor simvastatin, a CYP3A substrate, as a model drug.

MATERIALS AND METHODS

To target drug release and to assess regional gastrointestinal absorption of the CYP 3A substrate simvastatin from the distal parts of the intestine, delayed release film coated tableted oral dosage forms were developed. Simvastatin delayed release tablet, simvastatin immediate release capsule and simvastatin immediate release tablet Zocor were administered as single doses (20 mg) to fasting healthy volunteers in a crossover design.

RESULTS

Simvastatin bioavailability was increased by a factor of three, as compared to the reference formulation Zocor. The overall metabolite levels from the immediate release capsules tended to be higher throughout the period studied than the metabolite levels following administration of Zocor and simvastatin delayed release dosage form.

CONCLUSIONS

The interplay between gastrointestinal physiology (lower CYP 3A expression in the distal ileum and the colon) and formulation design (zero-order controlled release after a predetermined lag-time) resulted in successful absorption and bioavailability improvement and represent a viable strategy to reduce the dose of CYP 3A drugs.

Adverse events caused by drug interactions involving glucuronoconjugates of zidovudine, valproic acid and lamotrigine, and analysis of how such potential events are discussed in package inserts of Japan, UK and USA

BACKGROUND AND OBJECTIVE

As pharmacokinetic drug interactions frequently cause adverse events, it is important that the relevant information is given in package inserts (PIs). We previously analysed the provision of PIs for HMG-CoA reductase inhibitors and Ca antagonists, for which metabolism by cytochrome P450 could be a major interaction mechanism. In this article, we focus on interactions involving glucuronoconjugates because many drugs and their metabolites undergo this conjugation.

METHODS

We reviewed clinical drug interactions related to glucuronoconjugates, focusing on reports of adverse events. Then, we picked out three important drugs (zidovudine, valproic acid and lamotrigine), and examined how the literature information is reflected in the relevant PIs in Japan, UK and USA.

RESULTS AND DISCUSSION

Pharmacokinetic interactions related to glucuronoconjugates were found with 33 drug combinations. Of these, five combinations induced clear adverse events: (i) severe anaemia due to zidovudine and caused by interaction with valproic acid, (ii) recurrence/increased frequency of seizure or increased manic states from a reduction in therapeutic effects of valproic acid caused by panipenem, (iii) meropenem or (iv) ritonavir and (v) of lamotrigine caused by oral contraceptives. Analysis of PIs showed a lack of description of the interaction of zidovudine with valproic acid in the Japanese PI. The UK PI mentioned this interaction without quantitative data, whereas full information was given in the US PI. A lack of description was also present on the interaction between valproic acid with ritonavir, reported in 2006, in the PIs of all three countries. For the interactions involving valproic acid and panipenem or meropenem, even though marked reduction of blood valproic acid level has been reported, no quantitative data were provided in any of the PIs.

CONCLUSION

Five combinations were identified to cause severe adverse events because of interactions related to glucuronoconjugates. This information, including quantitative data, is not always properly provided in the relevant PIs in Japan, UK or USA. PIs should be improved to better inform healthcare providers and thereby help them and their patients.

Using pharmacokinetics to predict the effects of pregnancy and maternal-infant transfer of drugs during lactation

Knowledge of pharmacokinetics and the use of a mechanistic-based approach can improve our ability to predict the effects of pregnancy for medications when data are limited. Despite the many physiological changes that occur during pregnancy that could theoretically affect absorption, bioavailability does not appear to be altered. Decreased albumin and alpha(1)-acid glycoprotein concentrations during pregnancy will result in decreased protein binding for highly bound drugs. For drugs metabolised by the liver, this can result in misinterpretation of total plasma concentrations of low extraction ratio drugs and overdosing of high extraction ratio drugs administered by non-oral routes. Renal clearance and the activity of the CYP isozymes, CYP3A4, 2D6 and 2C9, and uridine 5'-diphosphate glucuronosyltransferase are increased during pregnancy. In contrast, CYP1A2 and 2C19 activity is decreased. The dose of a drug an infant receives during breastfeeding is dependent on the amount excreted into the breast milk, the daily volume of milk ingested and the average plasma concentration of the mother. The lipophilicity, protein binding and ionisation properties of a drug will determine how much is excreted into the breast milk. The milk to plasma concentration ratio has large inter- and intrasubject variability and is often not known. In contrast, protein binding is usually known. An extensive literature review was done to identify case reports including infant concentrations from breast-fed infants exposed to maternal drugs. For drugs that were at least 85% protein bound, measurable concentrations of drug in the infant did not occur if there was no placental exposure immediately prior to or during delivery. Knowledge of the protein binding properties of a drug can provide a quick and easy tool to estimate exposure of an infant to medication from breastfeeding.

The impact of sex and contraceptive therapy on the plasma and intracellular pharmacokinetics of zidovudine

OBJECTIVES

Zidovudine remains part of combination antiretroviral therapy. Pharmacological studies rely on quantitation of active triphosphates in peripheral blood mononuclear cells. This study evaluated the impact of female sex and contraceptive therapy on zidovudine plasma and intracellular pharmacokinetics and the impact of contraceptive therapy on HIV viral load.

METHODS

Serial plasma and intracellular zidovudine pharmacokinetics following oral and intravenous dosing were determined in 18 men and 20 women treated with zidovudine. Women could repeat pharmacokinetics assessment following 2 months oral or injectable contraceptive therapy. Zidovudine plasma and intracellular mono-, di- and triphosphate concentrations were determined by liquid chromatography tandem mass spectrometry. Plasma and cervical viral loads were determined preceding and following 2 months of contraceptive therapy in women.

RESULTS

Men exhibited higher area under the concentration versus time curve for intracellular zidovudine and zidovudine-monophosphate following oral and intravenous dosing and higher zidovudine triphosphate following oral dosing. There was no difference between men and women in plasma zidovudine parameters. Furthermore, contraceptive therapy had no effect on zidovudine plasma or intracellular pharmacokinetics or on plasma or cervical HIV-1 RNA levels.

CONCLUSIONS

Using an optimized pharmacokinetic design, this study indicated men exhibit significantly higher zidovudine-monophosphate and zidovudine-triphosphate exposure following zidovudine oral administration, having implications for drug toxicity and overall tolerance of zidovudine therapy. The lack of an effect of contraceptive therapy on zidovudine pharmacokinetics is surprising in light of previous pharmacokinetic studies for drugs eliminated primarily through glucuronidation. Contraceptive therapy had no effect on plasma or cervical viral load, results consistent with previous findings.

Pregnancy-induced changes in pharmacokinetics: a mechanistic-based approach

Observational studies have documented that women take a variety of medications during pregnancy. It is well known that pregnancy can induce changes in the plasma concentrations of some drugs. The use of mechanistic-based approaches to drug interactions has significantly increased our ability to predict clinically significant drug interactions and improve clinical care. This same method can also be used to improve our understanding regarding the effect of pregnancy on pharmacokinetics of drugs. Limited studies suggest bioavailability of drugs is not altered during pregnancy. Increased plasma volume and protein binding changes can alter the apparent volume of distribution (Vd) of drugs. Through changes in Vd and clearance, pregnancy can cause increases or decreases in the terminal elimination half-life of drugs. Depending on whether a drug is excreted unchanged by the kidneys or which metabolic isoenzyme is involved in the metabolism of a drug can determine whether or not a change in dosage is needed during pregnancy. The renal excretion of unchanged drugs is increased during pregnancy. The metabolism of drugs catalysed by select cytochrome P450 (CYP) isoenzymes (i.e. CYP3A4, CYP2D6 and CYP2C9) and uridine diphosphate glucuronosyltransferase (UGT) isoenzymes (i.e. UGT1A4 and UGT2B7) are increased during pregnancy. Dosages of drugs predominantly metabolised by these isoenzymes or excreted by the kidneys unchanged may need to be increased during pregnancy in order to avoid loss of efficacy. In contrast, CYP1A2 and CYP2C19 activity is decreased during pregnancy, suggesting that dosage reductions may be needed to minimise potential toxicity of their substrates. There are limitations to the available data. This analysis is based primarily on observational studies, many including small numbers of women. For some isoenzymes, the effect of pregnancy on only one drug has been evaluated. The full-time course of pharmacokinetic changes during pregnancy is often not studied. The effect of pregnancy on transport proteins is unknown. Drugs eliminated by non-CYP or non-UGT pathways or multiple pathways will need to be evaluated individually. In conclusion, by evaluating the pharmacokinetic data of a variety of drugs during pregnancy and using a mechanistic-based approach, we can start to predict the effect of pregnancy for a large number of clinically used drugs. However, because of the limitations, more clinical, evidence-based studies are needed to fully elucidate the effects of pregnancy on the pharmacokinetics of drugs.

Oral contraception does not alter single dose saquinavir pharmacokinetics in women

AIMS

Women experience more adverse drug reactions (ADR) to antiretroviral therapy than men. This may be attributed to higher plasma concentrations of protease inhibitors due to pharmacokinetic interactions with hormonal preparations. Thus, in the present study we aimed to investigate the influence of oral contraceptives (OC) on the pharmacokinetics of the protease inhibitor saquinavir.

METHODS

Saquinavir was administered in a hard gelatin capsule formulation (Invirase) to rule out confounding by pharmaceutical aids of the more frequently used soft gelatin capsule. After an overnight fast, eight healthy female participants ingested a single oral dose of 600 mg saquinavir immediately before and after the 19th dose of a combined, low dose OC (0.03 mg ethinylestradiol, 0.075 mg gestodene) in a prospective, fixed sequence study design. The first saquinavir application was scheduled on day 1, 2, or 3 of the individual menstrual cycle. Plasma concentrations of saquinavir and relative concentrations of its M2&M3-hydroxy metabolites were determined by LC/MS/MS for 48 h.

RESULTS

Intake of OC resulted in a significant decrease in morning serum concentrations (before intake of OC, compared to day 19 of OC therapy) of 17beta-estradiol by -23.4 pg ml-1 (57%, 95%CI: -76% to -37.4%); progesterone by -0.25 ng ml-1 (33%, 95%CI: -45.3% to -21.5%); follicle-stimulating hormone by -4.06 U l-1 (82%, 95%CI: -96.5% to -67.7%); and luteinizing hormone by -3.49 U l-1 (74%, 95%CI: -93 to -54.6%). Conversely, sexual hormone binding globulin serum concentrations increased by 83.6 nmol l-1 (205%, 95%CI: 32.2% to 377%). Pharmacokinetic parameters of saquinavir (AUC, Cmax, tmax, t1/2, CLR) were not affected by OC, nor was the relative metabolic ratio of saquinavir/M2&M3-hydroxy saquinavir. Furthermore, there was no association of serum hormone concentrations or MDR1-polymorphisms (C3435T and G2677T) with pharmacokinetic parameters of saquinavir.

CONCLUSIONS

There was no effect of OC on saquinavir pharmacokinetics. Thus, pharmacokinetic interactions of synthetic sexual steroids with saquinavir are not likely to account for the increased ADR to antiretroviral therapy seen in women.

The effect of ethinyloestradiol and levonorgestrel on the CYP2C19-mediated metabolism of omeprazole in healthy female subjects

AIMS

To study the effect of an oral contraceptive (OC) formulation containing ethinyloestradiol and levonorgestrel (LNG) (combination OC) or LNG alone on the CYP2C19-mediated hydroxylation of omeprazole in healthy females.

METHODS

This was an open crossover study with three phases. In phase one, 10 healthy females received a single 40-mg dose of omeprazole. Thereafter the subjects received in a random order either 40 micro g ethinyloestradiol and 75 micro g LNG or 60 micro g LNG alone once daily for 10 days. On day 10, 1 h after the last OC dose, subjects received a single 40-mg oral dose of omeprazole. The plasma concentrations of omeprazole, 5'-hydroxyomeprazole and omeprazole sulphone were determined for up to 8 h.

RESULTS

The use of combination OC increased the area under the curve (AUC) of omeprazole by 38% [95% confidence interval (CI) - 3.8, 80; P = 0.040] and caused a 48% increase (95% CI 28, 68) in the AUC ratio of omeprazole/5-hydroxyomeprazole. LNG alone did not effect the 5'-hydroxylation of omeprazole. Neither of the OC preparations seemed to have an inhibitory effect on the formation of omeprazole sulphone by CYP3A4.

CONCLUSIONS

Oral contraceptives containing ethinyloestradiol but not those containing only LNG decrease CYP2C19 activity.

Lack of gender differences and large intrasubject variability in cytochrome P450 activity measured by phenotyping with dextromethorphan

Gender-based differences in cytochrome P450 (CYP) activity may occur due to endogenous hormonal fluctuations with the menstrual cycle, which are altered by oral contraceptives. This study assessed the average activity and within-subject variability in CYP3A4 and CYP2D6 in men, women taking Triphasil, and regularly menstruating women not receiving oral contraceptives. Thirty-three healthy volunteers participated in this 28-day pilot study (12 women receiving Triphasil) (OCs), 11 regularly menstruating women not on exogenous progesterone or estrogen (no OCs), and 10 men. CYP3A4 and CYP2D6 activities were phenotyped with dextromethorphan (DM) on study days 7, 14, 21, and 28 using urinary ratios of DM:3-methoxymorphinan (3MM) and DM:dextrorphan (DX), respectively. Serial blood concentrations of estrogen and progesterone and menstrual diaries were used to determine menstrual phase in both groups of women. Average urinary DM:3MM and DM:DX in the 28 extensive metabolizers of CYP2D6 did not differ between the three study populations (p = 0.86 and 0.93, respectively). Post hoc power analysis indicated that more than 1000 subjects would be needed for 80% power (alpha = 0.05) to detect a +/- 15% difference from the population mean in the urinary ratios of dextromethorphan and its metabolites 3MM and DX. Variability in CYP3A4 and CYP2D6 activity, characterized by intrasubject standard deviation, also did not differ. The varying doses of levonorgesterol and ethinyl estradiol in Triphasil, fluctuations in estrogen and progesterone, and menstrual phase did not influence CYP3A4 or CYP2D6 activity. It was concluded that CYP3A4 and CYP2D6 activity and intrasubject variability were not different in the three study populations, and thus a clinically important difference between men, women on Triphasil, and women not receiving oral contraceptives is unlikely. High inter- and intrasubject variability in DM:3MM and DM:DX were clearly demonstrated and limit the use of dextromethorphan to phenotype endogenous CYP3A4 and CYP2D6 activity.

Generalized anxiety disorder in women

Women have a higher prevalence of GAD than do men. This ratio holds true in most clinical and general-population samples. Some variations exist, with evidence to suggest the strong impact of environment and life events. Women are sensitive to lifetime adversity and exacerbation of symptoms in conjunction with their menstrual cycle. Comorbidity is a crucial diagnostic factor when treating anyone with GAD, especially women. Most notably, high comorbidity with other anxiety disorders, MDD and alcohol-abuse disorder occurs for women. Overall, although the prevalence of women with GAD is greater than that of men with GAD, the course of illness and prognosis are not qualitatively different. Across varied methodology, data suggest gender-related differences in the metabolism and potentially in the effects and side effects of the various benzodiazepines and antidepressant psychopharmacologic treatments of GAD. Additional research is needed to better understand these differences.

Effect of an oral contraceptive preparation containing ethinylestradiol and gestodene on CYP3A4 activity as measured by midazolam 1'-hydroxylation

AIMS

To characterize the effect of an oral contraceptive (OC) containing ethinylestradiol and gestodene on the activity of CYP3A4 in vivo as measured by the 1'-hydroxylation of midazolam.

METHODS

In this randomised, double-blind, cross-over trial nine healthy female subjects received either a combined OC (30 microg ethinylestradiol and 75 microg gestodene) or placebo once daily for 10 days. On day 10, a single 7.5 mg dose of midazolam was given orally. Plasma concentrations of midazolam and 1'-hydroxymidazolam were determined up to 24 h and the effects of midazolam were measured with three psychomotor tests up to 8 h.

RESULTS

The combined OC increased the mean AUC of midazolam by 21% (95% CI 2% to 40%; P = 0.03) and decreased that of 1'-hydroxymidazolam by 25% (95% CI 10% to 41%; P = 0.01), compared with placebo. The metabolic ratio (AUC of 1'-hydroxymidazolam/AUC of midazolam) was 36% smaller (95% CI 19% to 53%; P = 0.01) in the OC phase than in the placebo phase. There were no significant differences in the Cmax, tmax, t(1/2) or effects of midazolam between the phases.

CONCLUSIONS

A combined OC preparation caused a modest reduction in the activity of CYP3A4, as measured by the 1'-hydroxylation of midazolam, and slightly increased the AUC of oral midazolam. This study suggests that, at the doses used, ethinylestradiol and gestodene have a relatively small effect on CYP3A4 activity in vivo.

Effects of triazolam at three phases of the menstrual cycle

This study investigated the subjective and behavioral effects of a commonly used benzodiazepine, triazolam, in healthy women at three phases of the menstrual cycle: follicular, periovulatory, and luteal. Ovarian hormones or their metabolites have direct and indirect actions on neuronal receptors, which may affect responses to psychoactive drugs acting on the same central nervous system receptors. This study explored the effect of menstrual cycle phase on the mood-altering and performance effects of a single oral dose of the benzodiazepine triazolam. Twenty women received triazolam (0.25 mg orally) or placebo at the follicular, periovulatory, and luteal phases of their menstrual cycles in a within-subject design. Dependent measures included self-reported mood states, psychomotor performance, and plasma levels of triazolam, estradiol, progesterone, and allopregnanolone. After administration of triazolam, most subjects reported the expected increases in fatigue and decreases in arousal and psychomotor performance. Neither plasma levels nor mood and performance effects of triazolam differed across the three phases. This study illustrates a useful methodology for assessing responses to psychoactive drugs in normally cycling women and shows that the effects of this drug were highly stable across the cycle.

Clinically significant pharmacokinetic drug interactions with benzodiazepines

The reports of interactions between benzodiazepines (BZPs) and other drugs (e.g., antidepressants, selective serotonin reuptake inhibitors, antiulcer drugs, antiepileptic drugs, macrolide antibiotics) during their combined use are reviewed. In general, metabolism of BZPs is delayed when combined with a number of other drugs but some reports have suggested otherwise. In recent years, the cytochrome P450 (P450 or CYP) isoenzyme that catalyses the metabolism of BZPs has also been identified. BZPs are mainly catalysed by CYP3A4. When published reports are studied, it appears necessary to be exceptionally careful about interactions mainly between BZPs and selective serotonin reuptake inhibitors, cimetidine, antiepileptic drugs, macrolide antibiotics and antimycotics. More information is necessary to identify individuals at greatest risk of drug interactions and adverse events.

Zolpidem: distinct from triazolam?

OBJECTIVE

To review the literature that compares zolpidem with triazolam, with an emphasis on efficacy and safety in humans.

DATA SOURCES

Information was retrieved from a MEDLINE search (1983-1996) of the English-language literature using the terms triazolam and zolpidem.

STUDY SELECTION

Reports of clinical trials comparing the safety and efficacy of zolpidem and triazolam were included in this review.

DATA EXTRACTION

Data were evaluated according to study design, efficacy, and adverse effects. Pertinent information was selected and the data synthesized into a review format.

DATA SYNTHESIS

Zolpidem and triazolam have similar pharmacokinetic and pharmacodynamic effects in humans. Clinical trials have shown that usually recommended, equipotent dosages of zolpidem and triazolam do not differ with respect to pharmacokinetics, efficacy, tolerability, residual effects, memory impairment, rebound insomnia, abuse potential, or other adverse effects.

CONCLUSIONS

Zolpidem offers no distinct therapeutic advantage over triazolam for the treatment of insomnia.

Influence of oral contraceptive use and cigarette smoking, alone and together, on antipyrine pharmacokinetics

The pharmacokinetics of antipyrine following a single 1-g intravenous dose was determined in 63 healthy women. Subjects were divided into 4 groups as follows: 1) cigarette smokers using low-dose oral contraceptives (n = 15); 2) nonsmokers using low-dose oral contraceptives (n = 12); 3) cigarette smokers not using oral contraceptives (n = 10); and 4) controls, neither cigarette smokers nor oral contraceptive users. Plasma antipyrine concentrations during 24 to 48 hours after dosage were measured by high-performance liquid chromatography. Mean kinetic variables in the nonsmoking, non-oral contraceptive using control group were: volume of distribution, 37.7 L; elimination half-life, 13.2 hours; and clearance, 34.4 mL/min. In cigarette smoking, non-oral contraceptive users versus controls, elimination half-life was reduced (8.0 vs. 13.2 hours, P < 0.05) and clearance increased (56.0 vs. 34.4 mL/min, P < 0.05). In nonsmoker oral contraceptive users, the reverse was true (elimination half-life was significantly increased: 16.6 vs. 13.2 hours, P < 0.05; and clearance was significantly decreased: 24.8 vs. 34.4 mL/min, P < 0.05). In smokers who were using oral contraceptives, values were not significantly different from controls (elimination half-life, 11.2 hours; clearance, 39.5 mL/min). Volume of distribution did not differ among the four groups. Thus the opposing effects on antipyrine clearance of the induction of metabolism by cigarette smoking and the inhibition due to low dose oral contraceptive use in effect negate each other when combined in humans.

Coadministration of nefazodone and benzodiazepines: III. A pharmacokinetic interaction study with alprazolam

This study was conducted to determine the potential for an interaction between nefazodone, a new antidepressant, and alprazolam after single- and multiple-dose administration in a randomized, double-blind, parallel-group, placebo-controlled study in 48 healthy male volunteers. A group of 12 subjects received either placebo twice daily, 1 mg of alprazolam twice daily, 200 mg of nefazodone twice daily, or the combination of 1 mg of alprazolam and 200 mg of nefazodone twice daily for 7 days. Serial blood samples were collected after dosing on day 1 and day 7 and before the morning dose on days 4, 5, and 6 for the determination of alprazolam and its metabolites alpha-hydroxyalprazolam (AOH) and 4-hydroxyalprazolam (4OH) and nefazodone and its metabolites hydroxynefazodone (HO-nefazodone), m-chlorophenylpiperazine (mCPP), and a triazole dione metabolite (dione) by validated high-performance liquid chromatography methods. Steady-state levels in plasma were reached by day 4 for alprazolam, 4OH, nefazodone, HO-nefazodone, mCPP, and dione. Noncompartmental pharmacokinetic analysis showed that at steady state, alprazolam Cmax and AUCtau values significantly increased approximately twofold and 4OH Cmax and AUCtau values significantly decreased by 40 and 26%, respectively, when nefazodone was coadministered with alprazolam. There was no effect of alprazolam on the single-dose or steady-state pharmacokinetics of nefazodone, HO-nefazodone, or dione after the coadministration of alprazolam and nefazodone. However, the mean steady-state mCPP Cmax and AUCtau significantly increased by approximately threefold and t1/2 values significantly increased by approximately twofold after the coadministration of alprazolam and nefazodone in comparison to those when nefazodone was given alone. Competitive inhibition between alprazolam and nefazodone metabolism at cytochrome P450 3A4 may be responsible for the pharmacokinetic interaction when alprazolam and nefazodone were coadministered. No adjustment of nefazodone dosage is required when nefazodone and alprazolam are coadministered. Because alprazolam concentrations in plasma are increased in the presence of nefazodone, a reduction in alprazolam dosage is recommended when the two agents are coadministered.

Coadministration of nefazodone and benzodiazepines: I. Pharmacodynamic assessment

One hundred two healthy men were evaluated in one of three studies conducted to evaluate the coadministration of nefazodone, 200 mg twice daily, and three benzodiazepines: triazolam, 0.25 mg; alprazolam, 1 mg twice daily; or lorazepam, 2 mg twice daily. In the first study, psychomotor performance, memory, and sedation were assessed at 0, 0.5, 1.5, 2.5, and 9 hours after single doses of triazolam alone and again after 7 days of nefazodone. Data from 6 of 12 subjects in this study were evaluable because of a dosing error in the other 6 subjects. In the subsequent two parallel design studies, groups of 12 volunteers received 7 days of either placebo; nefazodone, 200 mg; alprazolam, 1 mg twice daily; or alprazolam plus nefazodone or, in the second study, either placebo; nefazodone; lorazepam, 2 mg twice daily; or lorazepam plus nefazodone; the studies were identical, double-dummy, double-blind designs. Psychomotor performance, memory, and sedation were assessed at 0, 1, 3, and 8 hours after the 8 a.m. dose on days 1, 3, 5, and 7 of the studies. In all studies, blood samples were also obtained at testing times so that effect/concentration comparisons could be made and so full pharmacokinetic analyses could be done for separate studies. Nefazodone had no effect on psychomotor performance, memory, or sedation relative to placebo in any study. The mean maximum observed effect (MaxOE) on psychomotor performance and sedation were increased when triazolam was given after 7 days of nefazodone (p < 0.05); also, triazolam concentration was 60% higher at this time. Alprazolam and lorazepam impaired performance on day 1 (mean MaxOE, 34 and 30%, respectively) relative to placebo and nefazodone. By day 7 of alprazolam or lorazepam, psychomotor impairment decreased, indicating the development of tolerance. Alprazolam plus nefazodone increased psychomotor impairment (MaxOE, approximately 50%) and sedation relative to alprazolam alone on days 3, 5, and 7 (p < 0.05). Higher alprazolam concentrations explained the increased impairment in the alprazolam plus nefazodone treatment group; however, it is also possible that there was a delay in the development of tolerance. There were no differences in psychomotor impairment, memory, sedation, or lorazepam concentration detected between the lorazepam alone and lorazepam plus nefazodone treatments. This is consistent with the absence of a pharmacokinetic interaction between nefazodone and lorazepam. These results indicate that if the coadministration of a benzodiazepine is required in patients receiving nefazodone therapy, clinically significant interactions would be less likely with those eliminated by conjugative metabolism such as lorazepam. In cases where a benzodiazepine eliminated by oxidative metabolism is required, a reduction in initial dosage and careful clinical evaluation for signs of psychomotor impairment may be appropriate.

Pharmacokinetic and pharmacologic variation between different estrogen products

Due to the complex nature of endogenous and exogenous hormone concentration, formation, and metabolism and assay complexity, the pharmacokinetics of estrogen are difficult to study. Oral estrogens have minimal systemic bioavailability (2% to 10%) due to gut and liver (first-pass) metabolism. High concentrations of estrone are achieved with oral administration, whereas higher concentrations of estradiol are generally achieved after percutaneous absorption. Although vaginal products (such as gel, rings, etc.) are administered locally, they achieve high serum concentrations. Estradiol and estrone concentrations and estradiol-to-estrone ratios vary with different estrogen therapies. Approximately 95% to 98% of estradiol is bound loosely to albumin or tightly to sex hormone binding globulin, the major binding protein. The terminal half lives for the different estrogen compounds (after oral or intravenous administration) vary from 1-12 hours. Some conversion rates have been calculated between estrogen and its metabolites. Smoking decreases achievable estrogen concentrations, and has a greater effect on oral products. Oral contraceptives have been found to decrease antipyrine clearance. In the one study evaluating conjugated estrogens, antipyrine clearance was not altered. Oral contraceptives have a variable effect on the elimination of medications. Acetaminophen clearance is increased, whereas clearance of some benzodiazepines, caffeine,and prednisolone is decreased. Phenytoin increases the metabolism of conjugated estrogens. The various estrogen products may produce different clinical effects based on composition. The metabolites (minor components) of conjugated estrogens have been found to have significant effects on lipid concentrations, uterine weight, liver generated compounds, and bone resorption. Because transdermal products bypass the first-pass effect, delayed or decreased effects on lipid profiles and liver generated compounds have been observed.

Variables affecting nicotine metabolism

Nicotine metabolism is exceedingly sensitive to perturbation by numerous host factors. To reduce the large variations and discrepancies in the literature pertaining to nicotine metabolism, investigators in future studies need to recognize and better control these host factors. Recent advances in the understanding of nicotine metabolism have suggested new approaches to elucidating underlying mechanisms of certain toxic effects associated with cigarette smoking.

Factors and conditions affecting the glucuronidation of oxazepam

The aim of the present work was to investigate the impact of disease states and environmental and host factors on the glucuronidation of oxazepam. Glucuronidation represents quantitatively one of the most important metabolic conjugation pathways (phase II) in man for the inactivation and detoxication of xenobiotics and endogenous compounds and the liver is the major site for it to take place. Far less attention has been paid to the conjugation reactions in previous clinical research in this field compared to the immense interest in the oxidative biotransformation pathways (phase I). This fact is mainly due to the latter giving rise to active or reactive metabolites with a toxicological potential. The metabolism of oxazepam expresses exclusively the capacity for glucuronide formation. It was a prerequisite to establish the bioavailability of oxazepam prior to succeeding studies on the oral disposition of the drug. A preparation for intravenous administration was created. Clearance was chosen as measurement of the capacity to glucuronidate oxazepam. Severe decompensated liver disease was associated with a significant decrease in oxazepam clearance, that became even more obvious when corrected for by a diminished binding to plasma proteins. This increase in free fraction of oxazepam was substantial and could mainly be accounted for by low plasma albumin values. The results are in part a settlement with earlier studies on glucuronidation in liver disease and they may undoubtedly be ascribed to the severe degree of liver disease. For the first time it was shown that hypothyroidism led to a decline in the clearance and metabolism of oxazepam and paracetamol that is mainly biotransformed by glucuronidation. It was concluded that the enzymes responsible for glucuronidation in hypothyroidism are under the influence of thyroid hormones as is the case with oxidative enzymes. Further studies focused on the effect of host and environmental factors on glucuronidation. A commercially available very low calorie product for the treatment of obesity resulted in a decrease in oxazepam clearance and a lack of co-factors as a consequence of the low calorie intake was explanatorily proposed. Beta-adrenoceptor antagonists are often prescribed together with other drugs and close knowledge on interactions is mandatory but insufficient in regard of drugs being glucuronidated. Despite the mutual metabolic pathway labetalol exerted no dispositional alterations concerning oxazepam. It was moreover suggested that very elderly subjects between the age of 80 to 94 years had a reduced clearance of oxazepam.(ABSTRACT TRUNCATED AT 400 WORDS)

Lack of effect of oral contraceptive use on the pharmacokinetics of quinine

The pharmacokinetics of quinine after a single 600 mg oral dose of quinine sulphate were studied in seven female subjects who used oral contraceptives and in seven age-matched female controls who did not. There were no significant differences (P greater than 0.05) in the maximum plasma concentration (Cmax) and the time of peak concentration (tmax) between the subjects who used oral contraceptives (Cmax = 5.3 +/- 1.0 (s.d.) mg l-1; tmax = 1.4 +/- 0.7 h) and the control subjects (Cmax = 5.6 +/- 0.9 mg l-1; tmax = 2.1 +/- 0.9 h). The mean elimination half-life of quinine in the oral contraceptives user group (12.5 +/- 1.9 h) was similar (P greater than 0.05) to that in the control group (11.8 +/- 2.7 h). The oral clearance of quinine in the oral contraceptive user group was 0.133 +/- 0.055 l h-1 kg-1 (range 0.073-0.233) and was not significantly different (P greater than 0.05) from that observed in the control group (0.125 +/- 0.025 l h-1 kg-1, range 0.075-0.148).

Drug glucuronidation in humans

Glucuronidation is a major metabolic pathway for a large number of drugs in humans. Conjugation of drugs and other chemicals with glucuronic acid is catalyzed by the multigene UDP-glucuronosyltransferase family. It is believed that a number (unspecified at present) of glucuronosyltransferase isozymes, which probably differ in terms of substrate specificity and regulation, contribute to drug glucuronidation. Factors known to influence the pharmacokinetics of glucuronidated drugs in man, presumably via an effect on specific glucuronosyltransferases, include age (especially the neonatal period), cigarette smoking, diet, certain disease states, coadministered drugs, ethnicity, genetics and hormonal effects.

Propranolol does not alter flutoprazepam kinetics and metabolism in the rat

The influence of propranolol on the disposition of flutoprazepam, a benzodiazepine derivative extensively biotransformed by hepatic microsomal oxidation, was evaluated in the rat. Propranolol was infused subcutaneously with osmotic minipumps (5 mg/day) to obtain steady-state concentrations of about 200 ng/ml. Flutoprazepam (5 mg/kg) was given intraperitoneally on the third day of propranolol infusion. There was some variability in flutoprazepam disposition, consistent with the concept of an extensive first-pass metabolism of high-extraction drugs. Propranolol had no significant effects on the kinetics of flutoprazepam or norflutoprazepam, an active metabolite possibly accounting for a substantial part of the parent compound's pharmacological and clinical effects. It was concluded that there is no evidence of any pharmacokinetic interaction between this beta-adrenoceptor blocker and flutoprazepam in the rat.

Influence of oral contraceptives on drug therapy

Interferences between drugs and oral contraceptives are considered to alter pharmacokinetics and thus the efficacy of steroidal hormones. It should be noted, however, that steroids can also modify the metabolism and pharmacodynamic effects of various substances. To the present knowledge, phase I (i.e., oxidation, demethylation) and phase II reactions (conjugation) are concerned. Drugs sharing those enzymatic systems with oral contraceptives experience either an increase in bioavailability by inhibition of oxidative metabolism or undergo accelerated elimination by induced conjugation. Such interaction may be of practical interest in subjects who take oral contraceptives and are simultaneously treated with antidepressants, antihypertensives, insulin, synthetic glucocorticoids, theophylline, and caffeine.

Oxidative versus conjugative biotransformation of temazepam

Twenty-four healthy volunteers, aged 21-59 years, received single 30 mg oral doses of the benzodiazepine hypnotic temazepam. Levels of intact temazepam were determined in multiple plasma samples drawn during 48 h after dosage. Intact temazepam, its direct glucuronide conjugate, and the conjugate of its demethylated (oxidized) metabolite oxazepam were measured in two consecutive 24-h urine collections. Mean kinetic variables for temazepam in plasma were: peak plasma level (Cmax), 873 ng ml-1; time of peak, 1.36 h after dosage; volume of distribution, 0.961 kg-1; elimination half-life 9.9 h; clearance, 1.16 ml min-1 kg-1. Volume of distribution increased significantly with body weight (r = 0.67, p less than 0.001), and Cmax decreased with weight (r = -0.58, p less than 0.01). Only 0.2 per cent of the dose was excreted as intact temazepam, and negligible amounts as intact oxazepam. However, 39 per cent of the dose was recovered as temazepam glucuronide, and oxazepam glucuronide accounted for another 4.7 per cent of the dose. The remainder was not accounted for. Thus, a significant fraction of temazepam clearance occurs by direct glucuronide conjugation, with the conjugate temazepam glucuronide excreted in urine. A much smaller fraction undergoes parallel oxidation to form oxazepam, which is subsequently conjugated to oxazepam glucuronide and excreted in urine.

Effect of oral contraceptive steroids on the pharmacokinetics of phenprocoumon

1. The effect of chronic administration of oral contraceptive steroids (OCS) on the pharmacokinetics of the oral anticoagulant phenprocoumon was investigated in seven healthy females. 2. Plasma concentrations of phenprocoumon and the urinary recovery of unchanged as well as conjugated drug were measured following a single oral dose of 0.22 mg kg-1. A group of seven non-smoking, drug-free women matched for age and body weight served as controls. 3. Administration of OCS was associated with a significant increase in the clearance of phenprocoumon from 1.6 +/- 0.7 to 2.0 +/- 0.7 ml min-1 kg-1 (P less than 0.05). The urinary recovery of phenprocoumon glucuronide was significantly higher in OCS users (21.0 +/- 16 vs 14.0 +/- 10 (% of dose); P less than 0.05). No difference in plasma protein binding of phenprocoumon was observed, being 99.2 +/- 0.07 in both groups. 4. The accelerated glucuronidation of phenprocoumon in OCS users suggests the need for careful monitoring of the anticoagulatory response in these subjects, especially when the OCS are withdrawn.