Effect of troglitazone on the pharmacokinetics of an oral contraceptive agent

Risk-Benefit Assessment of Ethinylestradiol Using a Physiologically Based Pharmacokinetic Modeling Approach

Current formulations of combined oral contraceptives (COC) containing ethinylestradiol (EE) have ≤35 μg due to increased risks of cardiovascular diseases (CVD) with higher doses of EE. Low‐dose formulations however, have resulted in increased incidences of breakthrough bleeding and contraceptive failure, particularly when coadministered with inducers of cytochrome P450 enzymes (CYP). The developed physiologically based pharmacokinetic model quantitatively predicted the effect of CYP3A4 inhibition and induction on the pharmacokinetics of EE. The predicted C_max and AUC ratios when coadministered with voriconazole, fluconazole, rifampicin, and carbamazepine were within 1.25 of the observed data. Based on published clinical data, an AUC_ss value of 1,000 pg/ml.h was selected as the threshold for breakthrough bleeding. Prospective application of the model in simulations of different doses of EE (20 μg, 35 μg, and 50 μg) identified percentages of the population at risk of breakthrough bleeding alone and with varying degrees of CYP modulation.

Drug-induced idiosyncratic hepatotoxicity: prevention strategy developed after the troglitazone case

Troglitazone induced an idiosyncratic, hepatocellular injury-type hepatotoxicity in humans. Statistically, double null genotype of glutathione S-transferase isoforms, GSTT1 and GSTM1, was a risk factor, indicating a low activity of the susceptible patients in scavenging chemically reactive metabolites. CYP3A4 and CYP2C8 were involved in the metabolic activation and CYP3A4 was inducible by repeated administrations of troglitazone. The genotype analysis, however, indicated that the metabolic idiosyncrasy resides in the degradation of but not in the production of the toxic metabolites of troglitazone. Antibody against hepatic aldolase B was detected in the case patients, suggesting involvement of immune reaction in the toxic mechanism. Troglitazone induced apoptotic cell death in human hepatocytes at a high concentration, and this property may have served as the immunological danger signal, which is thought to play an important role in activating immune reactions. Hypothesis is proposed in analogy to the virus-induced hepatitis. After the troglitazone-case, pharmaceutical companies implemented screening systems for chemically reactive metabolites at early stage of drug development, taking both the amount of covalent binding to the proteins in vitro and the assumed clinical dose level into consideration. At the post-marketing stage, gene analyses of the case patients, if any, to find pharmacogenetic biomarkers could be a powerful tool for contraindicating to the risky patients.

Hepatic Drug-Metabolizing Enzyme Induction and Implications for Preclinical and Clinical Risk Assessment

Hepatic drug metabolizing enzyme (DME) induction complicates the development of new drugs owing to altered efficacy of concomitant treatments, reduction in exposure resulting from autoinduction, and potential generation of toxic metabolites. Risk assessment of DME induction during clinical evaluation is confounded by several uncertainties pertaining to hazard identification and dose response analysis. Hepatic DME induction rarely leads to clinical evidence of altered metabolism and toxicity in the patient, which typically occur only if the DME induction is relatively severe. High drug doses are associated with a greater likelihood of hepatic DME induction and downstream effects; therefore, drugs of low potency requiring higher dosing tend to lead to a greater risk of drug–drug interactions. Vigilance in clinical trials for increased or diminished drug effect and, specifically, pharmacokinetic studies in the presence of other drugs and concomitant diseases are necessary for a drug risk assessment profile.

Efforts to remove hepatic DME-inducing drugs from development can be facilitated with current in vitro and in vivo assessments and will improve with the development of newer technologies. A carefully tailored case-by-case approach will lead to the development of efficacious drugs with an acceptable risk/benefit profile available to patients.

The effect of etoricoxib on the pharmacokinetics of oral contraceptives in healthy participants

The pharmacokinetics of oral contraceptive (OC) components, ethinyl estradiol (EE) and norethindrone (NET), were evaluated after coadministration with etoricoxib in 3 double-blind, randomized, 2-period crossover studies of healthy women. There were 16, 39, and 24 participants enrolled in studies 1 (part I, part II), and 2, respectively. Each participant received triphasic OC (EE 35 microg/NET 0.5 mgx7 days, 0.75 mgx7 days, 1.0 mgx7 days) throughout each 28-day period. OC was coadministered with 21 days of etoricoxib daily followed by placebo for 7 days; the alternate period followed the reverse regimen (placebo to etoricoxib). Study 1 (part I) examined concurrent (morning) administration of OC/etoricoxib 120 mg, study 1 (part II) examined staggered (morning/night) administration of OC/etoricoxib 120 mg, and study 2 examined concurrent (morning) administration of OC/etoricoxib 60 mg. Coadministration of OC and etoricoxib 120 mg once daily was associated with a approximately 50% to 60% increase in EE concentrations, whereas etoricoxib 60 mg once daily was associated with a approximately 37% increase in EE concentrations. Coadministration of OC and etoricoxib was generally well tolerated. A clinically important change in NET AUC0-24 h was not observed. Adverse events included dyspepsia, diarrhea, headache, nausea, fatigue, loss of appetite, and taste disturbance.

Application and interpretation of hPXR screening data: Validation of reporter signal requirements for prediction of clinically relevant CYP3A4 inducers

A human pregnane X receptor (PXR) reporter-gene assay was established and validated using 19 therapeutic agents known to be clinical CYP3A4 inducers, 5 clinical non-inducers, and 6 known inducers in human hepatocytes. The extent of CYP3A4 induction (measured as RIF ratio in comparison to rifampicin) and EC50 was obtained from the dose-response curve. All of the clinical inducers (19/19) and human hepatocyte inducers (6/6) showed positive responses in the PXR assay. One out of five clinical non-inducers, pioglitazone, also showed a positive response. An additional series of 18 commonly used drugs with no reports of clinical induction was also evaluated as putative negative controls. Sixteen of these were negative (89%), whereas two of these, flutamide and haloperidol showed 16-fold (RIF ratio 0.79) and 10-fold (RIF ratio 0.48) maximal induction, respectively in the reporter-gene system. Flutamide and haloperidol were further demonstrated to cause CYP3A4 induction in human cryopreserved hepatocytes based on testosterone 6beta-hydroxylation activity. The induction potential index calculated based on the maximum RIF ratio, EC50, and in vivo maximum plasma concentration was used to predict the likelihood of CYP3A4 induction in humans. When the induction potential index is greater than 0.08, the compound is likely to cause induction in humans. A high-throughput screening strategy was developed based on the validation results at 1microM and 10microM for the same set of drugs. A RIF ratio of 0.4 was set as more practical screening cut-off to minimize the possibility of generating false positives. Thus, a tiered approach was implemented to use the human PXR reporter-gene assay from early lead optimization to late lead characterization in drug discovery.

The effects of metformin and rosiglitazone, alone and in combination, on the ovary and endometrium in polycystic ovary syndrome

OBJECTIVE

To examine the effects of metformin and rosiglitazone, alone and in combination, on endometrial histology and ovarian steroid production.

STUDY DESIGN

Randomized open-label study of metformin and rosiglitazone in 16 women with polycystic ovary syndrome (PCOS) performed at a single academic health center. The study consisted of a 6-week baseline observation period, a 3-month treatment period of single-agent therapy (rosiglitazone or metformin), and then a 3-month period of combined therapy.

RESULTS

Abnormal endometrial histology was found in 3 subjects at baseline, including 1 case of adenocarcinoma of the endometrium in an asymptomatic subject, who was excluded from further study. The 2 other abnormal cases (simple hyperplasia) resolved with treatment. Three months of single-agent therapy showed a benefit of rosiglitazone (n = 9) over metformin (n = 6) in terms of reducing circulating unbound testosterone levels (-11.8; 95% CI: -21.7 to -2.0 ng/dL) and 2-hour glucose (-42.0; 95% CI: -76.2 to -7.8 mg/dL), 2-hour insulin (-150.4; 95% CI: -272.7 to -28.1 microU/mL) as well as a significant decrease in integrated levels of glucose and insulin by area under the curve analysis, all obtained from oral glucose tolerance testing. Daily urinary progestin-to-estrogen ratios improved on rosiglitazone compared to metformin therapy (0.08; 95% CI: 0.02 to 0.14). Ovulatory rates tended to improve on both single-agent and combined treatments (30/90 cycles, 33%), compared to baseline ovulatory rate (2/15, 13%). Despite 6 months of therapy alone or in combination, 5 women displayed no evidence of biochemical ovulation by urinary or serum progestin measurements.

CONCLUSION

This study provides preliminary evidence that insulin-sensitizing drugs may have beneficial effects on the endometrium, although the exact mechanism beyond improving ovulatory function is still unknown. In addition, we suggest that rosiglitazone may be more beneficial than metformin therapy on raised insulin and androgen levels in an obese PCOS population. Combined therapy did not demonstrate significant benefit above and beyond single-agent therapy.

Pharmacokinetic Drug Interactions Involving 17??-Ethinylestradiol

17alpha-Ethinylestradiol (EE) is widely used as the estrogenic component of oral contraceptives (OC). In vitro and in vivo metabolism studies indicate that EE is extensively metabolised, primarily via intestinal sulfation and hepatic oxidation, glucuronidation and sulfation. Cytochrome P450 (CYP)3A4-mediated EE 2-hydroxylation is the major pathway of oxidative metabolism of EE. For some time it has been known that inducers of drug-metabolising enzymes (such as the CYP3A4 inducer rifampicin [rifampin]) can lead to breakthrough bleeding and contraceptive failure. Conversely, inhibitors of drug-metabolising enzymes can give rise to elevated EE plasma concentrations and increased risks of vascular disease and hypertension. In vitro studies have also shown that EE inhibits a number of human CYP enzymes, such as CYP2C19, CYP3A4 and CYP2B6. Consequently, there are numerous reports in the literature describing EE-containing OC formulations as perpetrators of pharmacokinetic drug interactions. Because EE may participate in multiple pharmacokinetic drug interactions as either a victim or perpetrator, pharmaceutical companies routinely conduct clinical drug interaction studies with EE-containing OCs when evaluating new chemical entities in development. It is therefore critical to understand the mechanisms underlying these drug interactions. Such an understanding can enable the interpretation of clinical data and lead to a greater appreciation of the profile of the drug by physicians, clinicians and regulators. This article summarises what is known of the drug-metabolising enzymes and transporters governing the metabolism, disposition and excretion of EE. An effort is made to relate this information to known clinical drug-drug interactions. The inhibition and induction of drug-metabolising enzymes by EE is also reviewed.

Use of Immortalized Human Hepatocytes to Predict the Magnitude of Clinical Drug-Drug Interactions Caused by CYP3A4 Induction

Cytochrome P4503A4 (CYP3A4) is the principal drug-metabolizing enzyme in human liver. Drug-drug interactions (DDIs) caused by induction of CYP3A4 can result in decreased exposure to coadministered drugs, with potential loss of efficacy. Immortalized hepatocytes (Fa2N-4 cells) have been proposed as a tool to identify CYP3A4 inducers. The purpose of the current studies was to characterize the effect of known inducers on CYP3A4 in Fa2N-4 cells, and to determine whether these in vitro data could reliably project the magnitude of DDIs caused by induction. Twenty-four compounds were chosen for these studies, based on previously published data using primary human hepatocytes. Eighteen compounds had been shown to be positive for induction, and six compounds had been shown to be negative for induction. In Fa2N-4 cells, all 18 positive controls produced greater than 2-fold maximal CYP3A4 induction, and all 6 negative controls produced less than 1.5-fold maximal CYP3A4 induction. Subsequent studies were conducted to determine the relationship between in vitro induction data and in vivo induction response. The approach was to relate in vitro induction data (E(max) and EC(50) values) with efficacious free plasma concentrations to calculate a relative induction score. This score was then correlated with decreases in area under the plasma concentration versus time curve values for coadministered CYP3A4 object drugs (midazolam or ethinylestradiol) from previously published clinical DDI studies. Excellent correlations (r(2) values >0.92) were obtained, suggesting that Fa2N-4 cells can be used for identification of inducers as well as prediction of the magnitude of clinical DDIs.

Insulin-Lowering Agents Inhibit Synthesis of Testosterone in Ovaries of DHEA-Induced PCOS Rats

BACKGROUND

Insulin-lowering agents are reported to be useful in treating polycystic ovary syndrome (PCOS) anovulation. It has been suggested that lower insulin levels secondarily affect ovarian tissue, although the direct mechanism of action has not yet been verified. Here we investigated if these agents directly affect the ovary.

METHODS

Thirty female Wister rats were studied. Six control rats were injected subcutaneously with 0.2 ml sesame oil, while 24 rats used as PCOS models were injected subcutaneously with dehydroepiandrosterone (DHEA) and divided into four groups. Six rats were injected with only DHEA, while the remaining 18 rats received metformin, pioglitazone or troglitazone. The ovaries were immunohistochemically stained with anti- testosterone and anti-17beta-HSD antibodies, and then evaluated for morphological changes.

RESULTS

In the DHEA administration group, the number of atretic follicles significantly increased compared to that of control rats. The insulin-lowering agents did not improve the multicystic appearance. Serum testosterone concentrations significantly increased with DHEA administration, but the increase was inhibited by oral administration of insulin-lowering agents. Testosterone deposits in ovarian tissue were also reduced by feeding rats insulin-lowering agents.

CONCLUSION

Insulin-lowering agents affected ovarian tissue by inhibiting testosterone biosynthesis in vivo.

Troglitazone induces CYP3A4 activity leading to falsely abnormal dexamethasone suppression test

After evaluating a patient who appeared to have a falsely abnormal response to the dexamethasone suppression test while taking troglitazone, we examined the effects of troglitazone on the activity of hepatic CYP3A4 and the screening tests for Cushing's syndrome. We studied five healthy women and three healthy men, aged 25 +/- 2 yr, before and after treatment with troglitazone (600 mg daily) for 28 d. Baseline 0800 h cortisol and corticosterone were similar before and after troglitazone treatment. Before troglitazone treatment, all subjects suppressed 0800 h cortisol below 1.8 micro g/dl (mean, 0.66 +/- 0.08 micro g/dl) during the 1-mg overnight dexamethasone suppression test (DST), whereas during troglitazone treatment none of the subjects suppressed 0800 h cortisol below 1.8 micro g/dl (mean, 9.0 +/- 1.8 micro g/dl). Serum dexamethasone levels decreased by 66 +/- 4%, and the erythromycin breath test measurements increased by 27 +/- 8%, indicating increased CYP3A4 activity during troglitazone treatment. The hydrocortisone suppression test (HST) was performed by administering 50 mg hydrocortisone at 2300 h. Using the criterion of suppression of 0800 h plasma corticosterone by more than 50%, the specificity of the HST was 100% both before and after troglitazone treatment. In conclusion, troglitazone induced the activity of CYP3A4 leading to falsely abnormal DST. HST is a useful alternative to the DST in patients taking medications that increase the activity of CYP3A4.

Reduced production rates of testosterone and dihydrotestosterone in healthy men treated with rosiglitazone

The effect of the thiazolidinedione, rosiglitazone (8 mg/d for 7 days), on the production rates of testosterone (T), dihydrotestosterone (DHT), and cortisol (F) was studied in healthy men (n = 10) using the stable isotope dilution technique and mass spectrometry. Treatment with rosiglitazone resulted in a decrease in the production rates of T from, basal, 318 +/- 62 microg/h to 272 +/- 72 microg/h (P <.05). Production rates of DHT fell from, basal, 21 +/- 6 microg/h to 17 +/- 5 microg/h (P <.05). Hence, the ratio calcuated from the production rates of T and DHT was unchanged (basal, 17 +/- 7; rosiglitazone, 17 +/- 3). Production rates of cortisol were unchanged (basal, 577 +/- 136 microg/h; rosiglitazone, 627 +/- 141 microg/h). These results suggest that a clinically relevant dose of at least one thiazolidindione, rosiglitazone, impedes the production of testosterone in man.

Pioglitazone: effect on CYP3A4 activity

Clinical studies demonstrate CYP3A4 enzyme induction with troglitazone, a thiazolidinedione derivative structurally related to pioglitazone. The objective of this prospective, open-label study conducted in healthy volunteers was to evaluate the influence of multiple-dose pioglitazone therapy on the urinary excretion ratio of 6-beta-hydroxycortisol to cortisol, an endogenous marker of CYP3A4 activity. Twelve subjects were given pioglitazone hydrochloride 45 mg daily for 14 days. Urine was collected over a 24-hour period before pioglitazone and after administration of the last tablet. Baseline and posttreatment CYP3A4 activity was assessed with the urinary 6-beta-hydroxycortisol/cortisol ratio. The mean +/- SD 6-beta-hydroxycortisol/cortisol ratios before and after treatment were 8.3 +/- 4.4 and 9.4 +/- 4.0, respectively (p = 0.29). The mean change from baseline was a nonsignificant 20.2%. Nine subjects had a small increase and 3 subjects had a reduction in the ratio. Using the ratio as a marker of CYP3A4 activity, the data support a lack of inductive effect on CYP3A4 by multiple-dose pioglitazone therapy. Thus, administration of pioglitazone should not result in clinically significant effects on the pharmacokinetics of other CYP3A4 substrates.

Evaluation of liver function in type 2 diabetic patients during clinical trials: evidence that rosiglitazone does not cause hepatic dysfunction

OBJECTIVE

Troglitazone treatment has been associated with idiosyncratic hepatic reaction leading to hepatic failure and death in some patients. This raises questions regarding whether all thiazolidinediones or peroxisomal proliferator-activated receptor-gamma (PPAR-gamma) agonists are hepatotoxic and whether data from clinical trials are adequate to detect a signal of potentially serious drug-related hepatotoxicity. The purpose of this study was to assess whether the idiosyncratic liver toxicity reported with troglitazone is molecule-specific or a thiazolidinedione class effect, based on liver enzyme data collected prospectively during phase 2/3 clinical trials with rosiglitazone, a new, potent, and specific member of the thiazolidinedione class.

RESEARCH DESIGN AND METHODS

This is an analysis of liver function in type 2 diabetic patients at baseline and serially in 13 double-blind, 2 open-label active-controlled, and 7 open-label extension studies of rosiglitazone treatment conducted in outpatient centers throughout North America and Europe. The study comprised > 6,000 patients aged 30-80 years with type 2 diabetes. Patients underwent baseline liver function studies and were excluded from clinical trials if they had an alanine aminotransferase (ALT), aspartate aminotransferase (AST), or alkaline phosphatase value 2.5 times greater than the upper limit of the reference range. The main outcome measures were liver enzyme levels, which were assessed at screening, at baseline, and every 4 weeks for the first 3 months of treatment and at 6- to 12-week intervals thereafter. Patients with at least one on-therapy ALT value >3 times the upper limit of the reference range were identified, and their case records examined in detail.

RESULTS

At baseline, 5.6% of the patients with type 2 diabetes (mean HbA(1c) 8.5-9.0%) had serum ALT values between 1.0 and 2.5 times the upper limit of the reference range. On antidiabetic therapy, most of those patients ( approximately 83%) had a decrease in ALT values, many into the normal range. The percentages of all patients with an on-therapy ALT value >3 times the upper limit of the reference range during double-blind and open-label treatment were as follows: rosiglitazone-treated 0.32%, placebo-treated 0.17%, and sulfonylurea-, metformin-, or insulin-treated 0.40%. The respective rates of ALT values >3 times the upper limit of the reference range per 100 person-years of exposure were 0.29, 0.59, and 0.64.

CONCLUSIONS

No evidence of hepatotoxic effects was observed in studies that involved 5,006 patients taking rosiglitazone as monotherapy or combination therapy for 5,508 person-years. This is in keeping with hepatic data from clinical trials of another member of the class, pioglitazone, and in contrast to the clear evidence of hepatotoxic effects observed during the troglitazone clinical trial program. These findings suggest that the idiosyncratic liver toxicity observed with troglitazone is unlikely to be a thiazolidinedione or a PPAR-gamma agonist class effect. Poorly controlled patients with type 2 diabetes may have moderate elevations of serum ALT that will decrease with improved glycemic control during treatment with rosiglitazone or other antihyperglycemic agents.

A prospective, randomized comparison of the metabolic effects of pioglitazone or rosiglitazone in patients with type 2 diabetes who were previously treated with troglitazone

OBJECTIVE

To characterize potential differences in glycemic control, plasma lipid level, and weight in a cohort of patients previously treated with troglitazone (TROG) who were switched to either pioglitazone or rosiglitazone.

RESEARCH DESIGN AND METHODS

After a 2-week washout from TROG, 186 patients were randomly assigned to receive either pioglitazone (PIO) or rosiglitazone (ROSI). Weight, HbA(1c), and fasting lipid profile were documented before discontinuing TROG and at 4 months after starting either pioglitazone or rosiglitazone. Secondarily, the effect of concurrent medications on study outcomes was assessed.

RESULTS

A total of 127 patients completed follow-up: 67 individuals in the PIO group (32 women, 35 men) and 60 individuals in the ROSI group (33 women, 27 men). There were no significant differences in gender mix, age, weight, fasting lipid profile, or HbA(1c) between the ROSI and PIO groups. After 4 months of randomized treatment, no change in HbA(1c) from baseline between or within groups was noted. Both groups experienced an equal and significant increase in weight from baseline of approximately 2.0 kg. Thiazolidinedione and HMG-CoA reductase inhibitor therapy had significant and independent effects on lipid profile (P < 0.005). Significant improvements in lipid profile were noted in the PIO group (P < 0.01), whereas none were detected with conversion to ROSI. Specifically, the PIO group experienced an average decrease in total cholesterol of approximately 20 mg/dl.

CONCLUSIONS

Differing effects on lipid profile were apparent after random conversion from TROG to either PIO or ROSI, despite similar weight increase and glycemic control. The clinical significance of these differences remains to be determined, and further comparative research is warranted.

Interactions between simvastatin and troglitazone or pioglitazone in healthy subjects

Two randomized, two-period crossover studies were conducted to evaluate the effects of repeat oral dosing of troglitazone (Study I) and pioglitazone (Study II) on the pharmacokinetics of plasma HMG-CoA reductase inhibitors following multiple oral doses of simvastatin and of simvastatin on the plasma pharmacokinetics of troglitazone (Study I) in healthy subjects. In both studies, each subject received two treatments. Treatment A consisted of once-daily oral doses of troglitazone 400 mg (Study I) or pioglitazone 45 mg (Study II) for 24 days with coadministration of once-daily doses of simvastatin 40 mg (Study I) or 80 mg (Study II) on Days 15 through 24. Treatment B consisted of once-daily oral doses of simvastatin 40 mg (Study I) or 80 mg (Study II) for 10 days. In Study I, the area under the plasma concentration-time profiles (AUC) and maximum plasma concentrations (Cmax) of HMG-CoA reductase inhibitors in subjects who received both troglitazone and simvastatin were decreased modestly (by approximately 30% for Cmax and approximately 40% for AUC), but time to reach Cmax (tmax) did not change, as compared with those who received simvastatin alone. Simvastatin, administered orally as a 40 mg tablet daily for 10 days, did not affect the AUC or tmax (p > 0.5) but caused a small but clinically insignificant increase (approximately 25%) in Cmax for troglitazone. In Study II, pioglitazone, at the highest approved dose for clinical use, did not significantly alter any of the pharmacokinetic parameters (AUC, Cmax, and tmax) of simvastatin HMG-CoA reductase inhibitory activity. For all treatment regimens, side effects were mild and transient, suggesting that coadministration of simvastatin with either troglitazone or pioglitazone was well tolerated. The modest effect of troglitazone on simvastatin pharmacokinetics is in agreement with the suggestion that troglitazone is an inducer of CYP3A. The insignificant effect of simvastatin on troglitazone pharmacokinetics is consistent with the conclusion that simvastatin is not a significant inhibitor for drug-metabolizing enzymes. The lack of pharmacokinetic effect of pioglitazone on simvastatin supports the expectation that this combination may be used safely.

Implications and consequences of enzyme induction on preclinical and clinical drug development

1. Enzyme induction has traditionally been studied during drug development to assess the potential of drug entities to interact with concomitant medications and alter their pharmacological effects, and clearly it is an unwanted phenomenon. However, another hurdle caused by induction occurs during preclinical development via the attainment of safety data, obtained by dosing high quantities of compound to species used in toxicology assessment. This review considers the techniques that can now be utilized in drug discovery, their relevance, the pharmacokinetic aspects of this phenomenon, and it discusses the consequences and implications of induction during preclinical and clinical development. 2. It is becoming increasingly routine to employ hepatocyte cultures and novel techniques such as quantitative real-time reverse transcriptase PCR to identify enzyme inducers in vitro. The major challenge is to utilize these in vitro data to predict the consequences of induction in vivo. From an understanding of pharmacokinetic principles and low clinical doses relative to preclinical studies, there is limited potential for induction by a development candidate to significantly alter the pharmacological efficacy of a co-administered drug. 3. The most comprehensive approach when considering induction involves integrating quantitative in vitro data, information on the pharmacokinetic behaviour of the compound and the PK/PD) relationship in order to predict its consequences. The generation of this holistic strategy would enable more detailed and informed decision-making about both the suitability of molecules for development and the development strategy itself.

Lack of effect of rosiglitazone on the pharmacokinetics of oral contraceptives in healthy female volunteers

The effect of rosiglitazone (Avandia [BRL 49653C]) on the pharmacokinetics of ethinylestradiol and norethindrone was evaluated after repeat dosing of rosiglitazone with an oral contraceptive (OC; Ortho-Novum 1/35 containing norethindrone 1 mg and ethinylestradiol 0.035 mg) in a randomized, double-blind, placebo-controlled crossover study. Thirty-four healthy female volunteers received oral rosiglitazone (RSG) 8 mg + OC or matched placebo (P) + OC daily on days 1 to 14 of a 28-day OC dosing cycle; the alternate regimen was administered during a second cycle. Ethinylestradiol and norethindrone pharmacokinetics were determined from plasma concentrations on day 14. Lack of pharmacokinetic effect was prospectively defined as 90% CI for the point estimate (PE) of the ratio (RSG + OC):(P + OC) contained within a 20% equivalence range for both ethinylestradiol and norethindrone (analyzed by ANOVA). For RSG + OC and P + OC, respectively, mean ethinylestradiol AUC(0-24) was 1126 and 1208 pg.h/mL (PE: 0.92; 90% CI: 0.88-0.97), and mean norethindrone AUC(0-24) was 178 and 171 ng.h/mL (PE: 1.04; 90% CI: 1.00-1.07). Thus, rosiglitazone had no significant effects on the pharmacokinetics of ethinylestradiol or norethindrone. Coadministration of rosiglitazone with OCs does not induce metabolism of these synthetic sex steroids and is not expected to impair the efficacy of OCs or hormone replacement therapy.