A Comprehensive Review of Drug-Drug Interactions with Metformin

Metformin is the world's most commonly used oral glucose-lowering drug for type 2 diabetes, and this is mainly because it protects against diabetes-related mortality and all-cause mortality. Although it is an old drug, its mechanism of action has not yet been clarified and its pharmacokinetic pathway is still not fully understood. There is considerable inter-individual variability in the response to metformin, and this has led to many drug-drug interaction (DDI) studies of metformin. In this review, we describe both in vitro and human interaction studies of metformin both as a victim and as a perpetrator. We also clarify the importance of including pharmacodynamic end points in DDI studies of metformin and taking pharmacogenetic variation into account when performing these studies to avoid hidden pitfalls in the interpretation of DDIs with metformin. This evaluation of the literature has revealed holes in our knowledge and given clues as to where future DDI studies should be focused and performed.

Benefit-risk assessment of orlistat in the treatment of obesity

Orlistat, an inhibitor of intestinal lipase, has been available for the treatment of obesity for nearly two decades. In conjunction with a hypocaloric diet, orlistat treatment results in a placebo-subtracted reduction in body weight of around 3 kg at 1 year, and increases the likelihood of achieving clinically significant (≥5%) weight loss by around 20%. Orlistat-induced weight loss also confers modest improvements in systolic and diastolic blood pressure, low-density lipoprotein (LDL) cholesterol, glycemic parameters, and progression to diabetes in people with impaired glucose tolerance. Overall, it has a good safety profile, and serious adverse events (including reports of severe kidney and liver injury) are rare. However, a high rate of gastrointestinal side effects limits adherence to treatment.

Anti-obesity drugs: a review about their effects and their safety

INTRODUCTION

Amphetamines, rimonabant and sibutramine licenses as anti-obesity drugs have been withdrawn because of their adverse effects. In fact, orlistat is the only available long-term treatment for obesity.

AREAS COVERED

The efficacy and safety of long-term drug therapy is very important in the management obesity; for this reason, the authors decided to conduct a review on the efficacy and safety of current, past and future pharmacotherapies for weight loss.

EXPERT OPINION

Orlistat is a good choice for the treatment of obesity, because of its safety on cardiovascular events and its positive effects on diabetic control, even if it is not as effective as rimonabant or sibutramine in reducing body weight. Regarding emerging anti-obesity therapies in diabetic people, we currently have drugs that have already been marketed including the glucagon-like peptide-1 (GLP-1) receptor agonists exenatide and liraglutide; other than improving glycemic control, they also suppress appetite reducing body weight. Moreover, some other drugs are currently in study such as tesofensine, phentermine + topiramate, bupropion + naltrexone and bupropion + zonisamide. Furthermore, several additional gut hormone-based treatments for obesity are under investigation in Phase II and III clinical trials, with particular focus on ghrelin, peptide YY, pancreatic polypeptide, amylin and oxyntomodulin.

Age-related changes in antidepressant pharmacokinetics and potential drug-drug interactions: a comparison of evidence-based literature and package insert information

BACKGROUND

Antidepressants are among the most commonly prescribed psychotropic agents for older patients. Little is known about the best source of pharmacotherapy information to consult about key factors necessary to safely prescribe these medications to older patients.

OBJECTIVE

The objective of this study was to synthesize and contrast information in the package insert (PI) with information found in the scientific literature about age-related changes of antidepressants in systemic clearance and potential pharmacokinetic drug-drug interactions (DDIs).

METHODS

A comprehensive search of two databases (MEDLINE and EMBASE from January 1, 1975 to September 30, 2011) with the use of a combination of search terms (antidepressants, pharmacokinetics, and drug interactions) was conducted to identify relevant English language articles. This information was independently reviewed by two researchers and synthesized into tables. These same two researchers examined the most up-to-date PIs for the 26 agents available at the time of the study to abstract quantitative information about age-related decline in systemic clearance and potential DDIs. The agreement between the two information sources was tested with κ statistics.

RESULTS

The literature reported age-related clearance changes for 13 antidepressants, whereas the PIs only had evidence about 4 antidepressants (κ < 0.4). Similarly, the literature identified 45 medications that could potentially interact with a specific antidepressant, whereas the PIs only provided evidence about 12 potential medication-antidepressant DDIs (κ < 0.4).

CONCLUSION

The evidence-based literature compared with PIs is the most complete pharmacotherapy information source about both age-related clearance changes and pharmacokinetic DDIs with antidepressants. Future rigorously designed observational studies are needed to examine the combined risk of antidepressants with age-related decline in clearance and potential DDIs on important health outcomes such as falls and fractures in older patients.

Effects of 1-year orlistat treatment compared to placebo on insulin resistance parameters in patients with type 2 diabetes

WHAT IS KNOWN AND OBJECTIVE

  The behavioural approach is usually slow and not always sufficient to achieve optimal targets in weight and metabolic control in obese diabetic patients, and a pharmacological treatment is often necessary. The aim of this study was to compare the effects of orlistat and placebo on body weight, glycaemic and lipid profile and insulin resistance in patients with type 2 diabetes.

METHODS

Two hundred and fifty-four obese, diabetic patients were enrolled in this study and randomized to take orlistat 360mg or placebo for 1year. We evaluated at baseline and after 3, 6, 9 and 12months body weight, waist circumference (WC), body mass index (BMI), glycated haemoglobin (HbA(1c) ), fasting plasma glucose (FPG), post-prandial plasma glucose (PPG), fasting plasma insulin (FPI), homeostasis model assessment insulin resistance index (HOMA-IR), lipid profile, retinol-binding protein-4 (RBP-4), resistin, visfatin and high-sensitivity C-reactive protein (Hs-CRP).

RESULTS AND DISCUSSION

We observed a significant reduction in body weight, WC, BMI, lipid profile, RBP-4 and visfatin in the orlistat group but not in control group. Faster improvements in HbA(1c) , PPG, FPI, HOMA-IR, resistin and Hs-CRP were recorded with orlistat than with placebo. A similar decrease in FPG was seen in the two groups. Significant predictors of change in insulin resistance (HOMA-IR) were RBP-4 and resistin concentration in the orlistat group (r=-0·53, P<0·05, and r=-0·59, P<0·01, respectively).

WHAT IS NEW AND CONCLUSION

To the best of our knowledge, this is the first study investigating the effect of orlistat on insulin resistance and markers of inflammation. Orlistat improved lipid profile and led to faster glycaemic control and insulin resistance parameters than the control, without any serious adverse event. Orlistat also improved RBP-4 and visfatin, effects not observed with placebo.

Investigation of Orlistat effects on PXR activation and CYP3A4 expression in primary human hepatocytes and human intestinal LS174T cells

Drugs for weight loss have been in use for nearly hundred years. Orlistat (Xenical) is a non-centrally acting anti-obesity drug that inactivates gastric and intestinal lipases, thus, preventing absorption of dietary triglycerides. There are reports indicating that Orlistat reduces bioavailability of Cyclosporin to a clinically relevant degree. Since Cyclosporin is metabolized by cytochrome P450 CYP3A4, we examined whether interaction between Orlistat and Cyclosporin involves induction of CYP3A4. Human Caucasian colon adenocarcinoma cells LS174T and primary cultures of human hepatocytes were used, as in vitro models of intestinal and hepatic cells, respectively. Treatment of LS174T cells for 24h with Orlistat (1-100mg/L) did not cause induction of CYP3A4 mRNA levels as compared to control cells while Orlistat (100mg/L) slightly induced CYP3A4 mRNA in human hepatocytes. Rifampicin, a model CYP3A4 inducer, significantly induced CYP3A4 mRNA in both types of cells. The level of CYP3A4 protein in human hepatocytes was increased by Orlistat after 48h, while rifampicin strongly induced CYP3A4 protein level. In addition, Orlistat moderately dose-independently activated pregnane X receptor (PXR) in LS174T cells transiently transfected with p3A4-luc reporter construct containing the basal promoter (-362/+53) with proximal PXR response element and the distal xenobiotic responsive enhancer module (-7836/-7208) of the CYP3A4 gene 5'-flanking region. In conclusion, we report here that Orlistat is weak PXR activator and CYP3A4 inducer in human hepatocytes, but it has no effect on CYP3A4 in intestinal cells, implying no role of CYP3A4 induction in the interaction between Orlistat and Cyclosporin in absorption process.

Immunotherapy in elderly transplant recipients: a guide to clinically significant drug interactions

Currently, >50% of candidates for solid organ transplantation in Europe and the US are aged >50 years while approximately 15% of potential recipients are aged >or=65 years. Elderly transplant candidates are characterized by specific co-morbidity profiles that compromise graft and patient outcome after transplantation. The presence of coronary artery or peripheral vascular disease, cerebrovascular disease, history of malignancy, chronic obstructive lung disease or diabetes mellitus further increases the early post-transplant mortality risk in elderly recipients, with infections and cardiovascular complications as the leading causes of death. Not only are elderly patients more prone to developing drug-related adverse effects, but they are also more susceptible to pharmacokinetic and pharmacodynamic drug interactions because of polypharmacy. The majority of currently used immunosuppressant drugs in organ transplantation are metabolized by cytochrome P450 (CYP) or uridine diphosphate-glucuronosyltransferases and are substrates of the multidrug resistance (MDR)-1 transporter P-glycoprotein, the MDR-associated protein 2 or the canalicular multispecific organic anion transporter, which predisposes these immunosuppressant compounds to specific interactions with commonly prescribed drugs. In addition, important drug interactions between immunosuppressant drugs have been identified and require attention when choosing an appropriate immunosuppressant drug regimen for the frail elderly organ recipient. An age-related 34% decrease in total body clearance of the calcineurin inhibitor ciclosporin was observed in elderly renal recipients (aged >65 years) compared with younger patients, while older recipients also had 44% higher intracellular lymphocyte ciclosporin concentrations. Similarly, using a Bayesian approach, an inverse relationship was noted between sirolimus clearance and age in stable kidney recipients. Ciclosporin and tacrolimus have distinct pharmacokinetics, but both are metabolized by intestinal and hepatic CYP3A4/3A5 and transported across the cell membrane by P-glycoprotein. The most common drug interactions with ciclosporin are therefore also observed with tacrolimus, but the two drugs do not interact identically when administered with CYP3A inhibitors or inducers. The strongest effects on calcineurin-inhibitor disposition are observed with azole antifungals, macrolide antibacterials, rifampicin, calcium channel antagonists, grapefruit juice, St John's wort and protease inhibitors. Drug interactions with mycophenolic acids occur mainly through inhibition of their enterohepatic recirculation, either by interference with the intestinal flora (antibacterials) or by limiting drug absorption (resins and binders). Rifampicin causes a reduction in mycophenolic acid exposure probably through induction of uridine diphosphate-glucuronosyltransferases. Proliferation signal inhibitors (PSIs) such as sirolimus and everolimus are substrates of CYP3A4 and P-glycoprotein and have a macrolide structure very similar to tacrolimus, which explains why common drug interactions with PSIs are comparable to those with calcineurin inhibitors. Ciclosporin, in contrast to tacrolimus, inhibits the enterohepatic recirculation of mycophenolic acids, resulting in significantly lower concentrations and hence risk of underexposure. Therefore, when switching from tacrolimus to ciclosporin and vice versa or when reducing or withdrawing ciclosporin, this interaction needs to be taken into account. The combination of ciclosporin with PSIs requires dose reductions of both drugs because of a synergistic interaction that causes nephrotoxicity when left uncorrected. Conversely, when switching between calcineurin inhibitors, intensified monitoring of PSI concentrations is mandatory. Increasing age is associated with structural and functional changes in body compartments and tissues that alter absorptive capacity, volume of distribution, hepatic metabolic function and renal function and ultimately drug disposition. While these age-related changes are well-known, few specific effects of the latter on immunosuppressant drug metabolism have been reported. Therefore, more clinical data from elderly organ recipients are urgently required.

Head-to-head studies evaluating efficacy of pharmaco-therapy for obesity: a systematic review and meta-analysis

Randomized controlled trials (RCTs) directly comparing weight loss drugs approved in the European Union were reviewed and the results analysed by meta-analysis. Eight RCTs including 885 patients were found comparing weight loss of orlistat and sibutramine, while no study including rimonabant was found. The median study duration was 7 months (range 3-12). Four of the seven studies comparing sibutramine and orlistat mono-therapy showed that sibutramine was significantly more efficacious for weight loss, while the remaining three showed equivalence. The weighted mean difference in weight loss was 2.2 kg (95% CI 0.5-3.9) favouring sibutramine. Three studies investigated orlistat and sibutramine as combination therapy, and two found it to be significantly better than orlistat alone, but not better than sibutramine alone. Based on these head-to-head RCT data, sibutramine appears to be significantly more efficacious for achieving weight loss than orlistat. This is concordant with indirect evidence from previous meta-analyses, where the respective compounds were compared with placebo. Only four studies reported attrition, and the pooled risk ratio was 0.6 (0.3-1.4) indicating lower dropout for sibutramine. This information together with an understanding of the clinical properties of each drug should help to guide the prescribing physician in the selection of adequate drug therapy for obesity.

New agents in development for the management of obesity

Obesity is fast becoming the major cause of premature death in the developed world. The rising prevalence of obesity and obesity-related comorbidities also elevates healthcare costs, and reduced quality of life. The National Institute of Clinical Excellence in the UK recommends pharmacotherapy, in conjunction with lifestyle modification, for obese individuals [i.e. body mass index (BMI) of 30 kg/m(2)] and for overweight persons with a BMI greater than 27 kg/m(2), accompanied by at least one comorbidity. However, the current pharmaceutical treatment available to combat this epidemic remains limited. We review the efficacy and pharmacology of the anti-obesity agents currently used in clinical practice as well as some of the potential agents in phase II and III trials.

Orlistat for the management of overweight individuals and obesity: a review of potential for the 60-mg, over-the-counter dosage

Orlistat, in the 60-mg over-the-counter dose, was recently approved by the FDA. This lipase inhibitor blocks absorption of ~25% of ingested fat and has ~85% of the efficacy of the 120-mg dose for weight loss. Over 16 weeks weight loss with diet and orlistat 60 mg averages ~5% of initial body weight. The 60-mg dose is better tolerated than the 120-mg dose and the gastrointestinal side effects are minimal when individuals consume < 30% of their energy from fat. In addition to facilitating modest weight loss, orlistat use decreases serum LDL-cholesterol values by ~10%. When taken three times daily before meals, orlistat 60 mg modifies lifestyle behavior, encourages lower fat-consumption and sets the stage for other healthy lifestyle changes.

Obesity: which drug and when?

BACKGROUND

Obesity, with all its consequences, is audaciously confronting medical professionals and health service providers worldwide. Diet and exercise intervention is an essential part of any weight management strategy, but may not succeed in isolation. Effective approaches for routine practice are more likely to involve affordable, efficacious and well-tolerated drug therapy than the more expensive, case selective approach of bariatric surgery.

OBJECTIVES AND CONCLUSIONS

Advancement of pharmacotherapy is expanding the battery of available drugs; the clinician is faced with an increasingly complex therapeutic decision. Which drug to use, and when, is influenced by a range of factors, discussed here. There is a large body of high quality evidence in the literature to support the presently available drugs; however, many questions remain unanswered including duration of therapy and whether longer-term goals of improved morbidity and mortality are achievable. Clinician and patient awareness of these issues will provide a more informed therapeutic decision and ultimately improve the potential for reaching the weight management targets.

Drug treatments for obesity: orlistat, sibutramine, and rimonabant

Antiobesity treatment is recommended for selected patients in whom lifestyle modification is unsuccessful. Two antiobesity drugs are currently licensed for long-term use. Orlistat, a gastrointestinal lipase inhibitor, reduces weight by around 3 kg on average and decreases progression to diabetes in high-risk patients; adverse gastrointestinal effects are common. Sibutramine, a monoamine-reuptake inhibitor, results in mean weight losses of 4-5 kg, but is associated with increases in blood pressure and pulse rate. Rimonabant, the first of the endocannabinoid receptor antagonists, reduces weight by 4-5 kg on average and improves waist circumference and concentrations of HDL cholesterol and triglyceride; however, an increased incidence of mood-related disorders has been reported. To date, all antiobesity drug trials have been limited by their high attrition rates and lack of long-term morbidity and mortality data. Other promising antiobesity drugs, including those acting within the central melanocortin pathway, are in development, but are years away from clinical use. In light of the lack of successful weight-loss treatments and the public-health implications of the obesity pandemic, the development of safe and effective drugs should be a priority. However, as new drugs are developed we suggest that the assessment processes should include both surrogate endpoints (ie, weight loss) and clinical outcomes (ie, major obesity-related morbidity and mortality). Only then can patients and their physicians be confident that the putative benefits of such drugs outweigh their risks and costs.

Orlistat treatment is safe in overweight and obese liver transplant recipients: a prospective, open label trial

Obesity is a frequent complication following liver transplantation and is insufficiently responsive to dietary and life style advice. We studied the safety of orlistat treatment in obese and overweight liver transplant recipients (n = 15) on a stable tacrolimus-based immunosuppressive regimen. For safety reasons, the treatment period was restricted (6 months 120 mg t.i.d., 3 months 120 mg daily). Three patients dropped out, tacrolimus dose was adjusted in six of 12 remaining patients (dose reduction in 4, increase in 2, P = N.S.). All dose adjustments occurred during the 6 months of orlistat 120 mg t.i.d. therapy. No drug intolerance, adverse events or episodes of rejection occurred during the study. Efficacy of orlistat treatment in this population could not be shown, because a formal control population was not included in this safety trial. Moreover, only a significant decrease of waist circumference (P < 0.01 versus start of the study), but not of weight or body mass index, was achieved in the treated group. Orlistat treatment is well tolerated in liver transplant recipients and can be started safely, provided immunosuppressive drug levels and dietary adherence are closely monitored.

The use of orlistat in the treatment of obesity, dyslipidaemia and Type 2 diabetes

Orlistat (tetrahydrolipstatin) is an inhibitor of gastrointestinal lipases, especially pancreatic lipase. It is used as an adjunct to diet and exercise in order to achieve weight loss in obese individuals (body mass index > 30 kg/m2) or in overweight individuals (body mass index > 27 kg/m2) with other risk factors for atherosclerotic vascular disease, such as hypertension, dyslipidaemia or diabetes. Short- and long-term studies of up to 4 years duration have shown the drug to have significant benefits in weight loss, as well as in the reduction in lipids, glucose and haemoglobin A1c, and in time to onset of Type 2 diabetes compared with diet alone or placebo groups. The incremental amount of weight loss that orlistat produces is modest, but sufficient to result in improvement in obesity comorbidities such as elevated blood pressure, dyslipidaemia and hyperglycaemia compared with diet and exercise alone. Orlistat should only be prescribed for individuals who are motivated to adhere to lifestyle modifications, especially dietary fat restriction.

Orlistat

Orlistat (Xenical) is a reversible inhibitor of gastric and pancreatic lipases. In conjunction with a hypocaloric diet and moderate exercise, orlistat is an effective drug for use in the management of obesity in adults with or without comorbidities. Recent data have shown that orlistat is also effective as a component of weight management strategies in obese adolescents. In addition to its well established efficacy in achieving modest weight loss, orlistat has been shown to improve glycaemic parameters in obese adults with type 2 diabetes mellitus as well as some features of the metabolic syndrome. Orlistat is generally well tolerated. Thus, orlistat is an option for the treatment of obese patients with or without type 2 diabetes and also has a role in the management of obese patients with the metabolic syndrome, associated comorbidities or concomitant disorders.

Pharmacologic Agents for the Treatment of Obesity

Obesity guidelines state that pharmacologic therapy can be considered if a patient fails to lose 10 percent of their original body weight after 6 months of adhering to a low calorie diet, exercise, and behavior modification. Many published trials have shown sibutramine and orlistat to be effective for weight loss and weight maintenance when used with lifestyle modifications. However, few trials have studied the efficacy and safety of these medications in the elderly. This article provides a review of the FDA approved medications currently available for the treatment of obesity. Pertinent clinical trials are also reviewed and recommendations regarding the use of these agents in the elderly are discussed.

Biowaiver extension potential to BCS Class III high solubility-low permeability drugs: bridging evidence for metformin immediate-release tablet

The biopharmaceutics classification system (BCS) allows biowaiver for rapid dissolving immediate-release (IR) products of Class I drugs (high solubility and high permeability). The possibility of extending biowaivers to Class III high solubility and low permeability drugs is currently under scrutiny. In vivo bioequivalence data of different formulations of Class III drugs would support such an extension. The objective of this work was to demonstrate the bioequivalence of two marketed IR tablet products of a Class III drug, metformin hydrochloride, that are rapidly dissolving and have similar in vitro dissolution profiles. The effect of race on the systemic exposure of metformin was also explored. A randomized, open-label, two-period crossover study was conducted in 12 healthy Chinese male volunteers. Each subject received a single-dose of 500 mg of each product after an overnight fasting. The plasma concentrations of metformin were followed for 24 h. No significant formulation effect was found for the bioequivalence metrics: areas under concentration-time curve (AUC0-t, AUC0-infinity) and maximal concentration (Cmax). The 90% confidence intervals for the ratio of means were found within the acceptance range of 80-125% for the log-transformed data. Based on these results, it was concluded that the two IR products are bioequivalent. The pharmacokinetic parameters of metformin in Chinese for both products were similar and were in good agreement with those reported for metformin IR tablets in other ethnic populations. This study serves as an example for supporting biowaiver for BCS Class III drugs.

Efficacy and safety comparative evaluation of orlistat and sibutramine treatment in hypertensive obese patients

AIM

The aim of our study was to comparatively evaluate the efficacy and safety of orlistat and sibutramine treatment in obese hypertensive patients, with a specific attention to cardiovascular effects and to side effects because of this treatment.

METHODS

Patients were enrolled, evaluated and followed at three Italian Centres of Internal Medicine. We evaluated 115 obese and hypertensive patients. (55 males and 60 females; 26 males and 29 females, aged 50 +/- 4 with orlistat; 28 males and 30 females, aged 51 +/- 5 with sibutramine). All patients took antihypertensive therapy for at least 6 months before the study. We administered orlistat or sibutramine in a randomized, controlled, double-blind clinical study. We evaluated anthropometric variables, blood pressure and heart rate (HR) during 12 months of this treatment.

RESULTS

A total of 113 completed the 4 weeks with controlled energy diet and were randomized to double-blind treatment with orlistat (n = 55) or sibutramine (n = 58). Significant body mass index (BMI) improvement was present after 6 (p < 0.05), 9 (p < 0.02), and 12 (p < 0.01) months in both groups, and body weight (BW) improvement was obtained after 9 (p < 0.05) and 12 (p < 0.02) months in both groups. Significant waist circumference (WC), hip circumference (HC) and waist/hip ratio (W/H ratio) improvement was observed after 12 months (p < 0.05, respectively) in both groups. Significant systolic blood pressure (SBP) and diastolic blood pressure (DBP) improvement (p < 0.05) was present in orlistat group after 12 months. Lipid profile [total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C) and triglycerides] reduction (p < 0.05, respectively) was observed in orlistat group and triglyceride reduction (p < 0.05) in sibutramine group after 12 months. No significant change was observed in sibutramine group during the study. No significant HR variation was obtained during the study in both groups. Of the 109 patients who completed the study, 48.1% of patients in the orlistat group and 17.5% of patients in the sibutramine group had side effects (p < 0.05 vs. orlistat group). Side-effect profiles were different in the two treatment groups. All orlistat side effects were gastrointestinal events. Sibutramine caused an increase in blood pressure (both SBP and DBP) in two patients, but it has been controlled by antihypertensive treatment. The vitamin changes were small and all mean vitamin and beta-carotene values stayed within reference ranges. No patients required vitamin supplementation.

CONCLUSIONS

Both orlistat and sibutramine are effective on anthropometric variables during the 12-month treatment; in our sample, orlistat has been associated to a mild reduction in blood pressure, while sibutramine assumption has not be associated to any cardiovascular effect and was generically better tolerated than orlistat.

Effects of orlistat, a lipase inhibitor, on the pharmacokinetics of three highly lipophilic drugs (amiodarone, fluoxetine, and simvastatin) in healthy volunteers

To investigate the effect of orlistat on the pharmacokinetics of three highly lipophilic drugs (amiodarone, fluoxetine, and simvastatin), the authors performed double-blind, placebo-controlled, randomized two-period crossover (for fluoxetine and simvastatin) or parallel (for amiodarone) studies in healthy volunteers ages 18 to 65 years of a body mass index between 18 and 30 kg/m2. During treatment with orlistat or matching placebo for 5 to 13 1/3 days, a single oral dose of highly lipophilic drug was administered, followed by obtaining serial blood samples for measuring plasma (for fluoxetine and simvastatin) or serum (for amiodarone) concentrations of the lipophilic drug and its active metabolite. Treatments were compared for the pharmacokinetic parameters AUC0-infinity, Cmax, tmax, and t 1/2 of highly lipophilic drugs and active metabolites. Analysis of variance was performed to assess the significance of the sequence effect and provide the variance estimate for the 90% confidence intervals. Subjects were also evaluated for adverse events, vital signs, and clinical and laboratory safety. The absorption of amiodarone (and active metabolite) was significantly reduced by approximately one-quarter using parameters of Cmax and AUC, while no inhibition of absorption was observed for fluoxetine and simvastatin as well as their active metabolites. There were no clinically significant differences in t 1/2 and tmax for all three drugs tested. Due to expected gastrointestinal adverse events known to occur with orlistat, there was a higher incidence of adverse events under regimen B (highly lipophilic drugs and orlistat) than under regimen A (highly lipophilic drugs and placebo). Other adverse events were sporadic and unremarkable. There were no clinically relevant changes in vital signs or laboratory values. In conclusion, except for amiodarone, there was no effect of orlistat on the pharmacokinetics of highly lipophilic drugs when these drugs were taken concomitantly with orlistat.

Improvement of cyclosporin A determination in whole blood by reversed-phase high-performance liquid chromatography

A chromatographic method was developed for the determination of cyclosporin A in human whole blood using reversed-phase HPLC at room temperature. Most previous reports carried out this liquid chromatographic separation at temperatures above 70 degrees C. The present procedure greatly improves the detection limit by controlling peak broadening effects, as well as the lifetime of the column at room temperature. Under optimal conditions and using ketoconazole as an internal standard, the calibration graph was linear in the range of 16-1000 microg/L with a relative standard deviation of 3.72% at 150 microg/L and 2.45% at 300 microg/L (n = 11) of cyclosporin A. The detection limit was of 5.0 microg/L cyclosporin A. By this procedure, cyclosporin A pharmacokinetic parameters in healthy Chinese subjects were studied. The developed method could be applied to the quantification of cyclosporin A in human blood samples and allows the study of its pharmacokinetics in routine laboratories.