Diltiazem-cyclosporin pharmacokinetic interaction--dose-response relationship

To hit a home run as a heterotopic heart recipient-living with two hearts for over three decades: a case report

Heterotopic heart transplantation (HHT) is an alternative to the orthotopic technique in selected patients with terminal heart failure. We report the case of the longest survival after HHT, with an uneventful follow-up for over three decades after transplantation. At the age of 25 years, endomyocardial fibrosis following myocarditis rendered the patient's native heart unable to maintain the body's needs. An allograft provided a second chance at life. The HHT technique was favoured due to severe pulmonary hypertension. The patient had an uneventful follow-up since then. The scarcity of donors and the revolutionary advances in the mechanical circulatory device field restricted the utilization of the HHT technique, but it has the potential to provide an excellent prognosis with a good quality of life.

Diltiazem as a cyclosporine A-sparing agent in heart transplantation: Benefits beyond dose reduction

Diltiazem (DZ) is widely prescribed in transplant recipients because of its drug-drug interactions with calcineurin inhibitors (CNI). However, these interactions have been primarily investigated in renal transplantation, and data regarding the long-term efficacy and safety of DZ in orthotopic heart transplantation (OHT) are still sparse. Our study aimed to elucidate the extent to which the co-prescription of DZ reduces the dose required to maintain adequate blood levels of cyclosporine A (CsA) and the resulting effect on morbidity and mortality in OHT recipients. We performed a retrospective single-center analysis of OHT recipients on a long-term immunosuppressive regimen based on CsA and mycophenolate mofetil (MMF). The study population consisted of 95 adult OHT recipients with a mean follow-up of 15.8 ± 6.7 years. DZ was co-prescribed in 39 subjects (41.1%) and was associated with a 28.6% reduction of the mean CsA daily dose (P < .001). Patients on DZ had less frequent rejection episodes (P = .002), better renal function (P = .009) and a lower rate of end-stage renal disease (P = .008). Additionally, they developed later cardiac allograft vasculopathy (CAV). We observed no prognostic relevance of DZ co-prescription in univariate and multivariate Cox-regression analyses. In addition to reducing the CsA dose required to maintain adequate blood through levels, DZ may have nephroprotective properties in OHT. The co-administration of DZ may decelerate the development of CAV and reduce the frequency of the rejection episodes. However, the beneficial influence on morbidity has no impact on mortality.

Drug Interactions Affecting Antiarrhythmic Drug Use

Antiarrhythmic drugs (AAD) play an important role in the management of arrhythmias. Drug interactions involving AAD are common in clinical practice. As AADs have a narrow therapeutic window, both pharmacokinetic as well as pharmacodynamic interactions involving AAD can result in serious adverse drug reactions ranging from arrhythmia recurrence, failure of device-based therapy, and heart failure, to death. Pharmacokinetic drug interactions frequently involve the inhibition of key metabolic pathways, resulting in accumulation of a substrate drug. Additionally, over the past 2 decades, the P-gp (permeability glycoprotein) has been increasingly cited as a significant source of drug interactions. Pharmacodynamic drug interactions involving AADs commonly involve additive QT prolongation. Amiodarone, quinidine, and dofetilide are AADs with numerous and clinically significant drug interactions. Recent studies have also demonstrated increased morbidity and mortality with the use of digoxin and other AAD which interact with P-gp. QT prolongation is an important pharmacodynamic interaction involving mainly Vaughan-Williams class III AAD as many commonly used drug classes, such as macrolide antibiotics, fluoroquinolone antibiotics, antipsychotics, and antiemetics prolong the QT interval. Whenever possible, serious drug-drug interactions involving AAD should be avoided. If unavoidable, patients will require closer monitoring and the concomitant use of interacting agents should be minimized. Increasing awareness of drug interactions among clinicians will significantly improve patient safety for patients with arrhythmias.

Baicalin reduces ciclosporin bioavailability by inducing intestinal p-glycoprotein in rats

Objectives

To investigate the effects of multiple doses of baicalin (BG) on the pharmacokinetics of ciclosporin (CsA) in rats and the potential mechanisms.

Methods

Pharmacokinetic parameters of CsA were determined in male rats after administration of CsA (3 mg/kg, i.g. or i.v.) to rats in the presence and absence of BG (80 mg/kg, i.g. or i.v.) for 7 days. The livers and intestines of rats were isolated and the CYP3A and p-glycoprotein (P-gp) expression were analysed. The effect of BG on the intestinal absorptive behaviour of CsA was also investigated using in-vitro everted rat gut sac model.

Key findings

Baicalin (80 mg/kg, i.v., 7 days) had no effect on the intravenously administered CsA. However, BG (80 mg/kg, i.g., 7 days) significantly decreased the Cmax, AUC0–t and AUC0–∞ of orally administered CsA by 38, 26 and 25%, respectively (P &lt; 0.01 or P &lt; 0.05). Further study revealed that the expression of P-gp in intestine increased in oral multiple doses of BG-treated rats. The in-vitro everted rat gut sac model demonstrated BG (10 μm) significantly decreased the absorption of CsA (10 μm) in intestine (P &lt; 0.05).

Conclusions

Multiple doses of BG decreased the oral bioavailability of CsA in rats significantly, which may be mainly attributable to inhibition of absorption of CsA in intestine and induction of P-gp. The interaction between BG and CsA may occur when BG and CsA were co-administered for long-term use. The dosage adjustment and blood concentration monitoring of CsA may be required in clinic.

Population Pharmacokinetic Modeling of Diltiazem in Chinese Renal Transplant Recipients

BACKGROUND AND OBJECTIVES

Diltiazem is a benzothiazepine calcium blocker and widely used in renal transplant patients since it improves the level of tacrolimus or cyclosporine A concentration. Several population pharmacokinetic (PopPK) models had been established for cyclosporine A and tacrolimus but no specific PopPK model was established for diltiazem. The aim of the study is to develop a PopPK model for diltiazem in renal transplant recipients and provide relevant pharmacokinetic parameters of diltiazem for further pharmacokinetic interaction study.

METHODS

Patients received tacrolimus as primary immunosuppressant agent after renal transplant and started administration of diltiazem 90 mg twice daily on 5th day. The concentration of diltiazem at 0, 0.5, 1, 2, 8, and 12 h was measured by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Genotyping for CYP3A4*1G, CYP3A5*3, and MDR1 3435 was conducted by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). 25 covariates were considered in the stepwise covariate model (SCM) building procedure.

RESULTS

One-compartment structural pharmacokinetic model with first-order absorption and elimination was used to describe the pharmacokinetic characteristics of diltiazem. Total bilirubin (TBIL) influenced apparent volume of distribution (V/F) of diltiazem in the forward selection. The absorption rate constant (K _a), V/F, and apparent oral clearance (CL/F) of the final population pharmacokinetic (PopPK) model of diltiazem were 1.96/h, 3550 L, and 92.4 L/h, respectively.

CONCLUSION

A PopPK model of diltiazem is established in Chinese renal transplant recipients and it will provide relevant pharmacokinetic parameters of diltiazem for further pharmacokinetic interaction study.

Diltiazem co treatment with cyclosporine for induction of disease remission in sight-threatening non-infectious intraocular inflammation

PURPOSE

To investigate the effects of diltiazem co-treatment with microemulsified cyclosporine-A (CsA) on dosage, blood concentrations of CsA, as well as therapeutic and side effects in patients with sight-threatening non-infectious intraocular inflammation.

METHODS

A prospective, randomized, placebo-controlled, open-label trial of 39 patients with sight-threatening non-infectious intraocular inflammation. The change in visual acuity (LogMAR), the grade of inflammatory activity, therapeutic concentration of CsA in the blood and systemic and renal toxicity were determined after comparing two groups, one treated with CsA and diltiazem (treatment group), and the other without diltiazem (control group).

RESULTS

Compared with the control group, the concentration of CsA in the blood of the treatment group significantly increased (P < 0.05) requiring a reduction in dosage of CsA (P < 0.05).

CONCLUSION

In patients with severe intraocular inflammation treated with CsA and diltiazem, blood concentrations of CsA increased as the dosage decreased. This efficient combination therapy reduced patient's economic burden, at the same time decreasing systemic and renal toxicity which in turn may promote the use of CsA for longer periods.

Pharmacokinetic drug-drug interaction and their implication in clinical management

Drug-drug interactions (DDIs) are one of the commonest causes of medication error in developed countries, particularly in the elderly due to poly-therapy, with a prevalence of 20-40%. In particular, poly-therapy increases the complexity of therapeutic management and thereby the risk of clinically important DDIs, which can both induce the development of adverse drug reactions or reduce the clinical efficacy. DDIs can be classify into two main groups: pharmacokinetic and pharmacodynamic. In this review, using Medline, PubMed, Embase, Cochrane library and Reference lists we searched articles published until June 30 2012, and we described the mechanism of pharmacokinetic DDIs focusing the interest on their clinical implications.

The effects of diltiazem in renal transplantation patients treated with cyclosporine A

OBJECTIVE

To investigate the effects of diltiazem and cyclosporine A (CsA) combination therapy on protecting the kidney, promoting graft functioning and improving post-transplanted kidney recovery.

METHODS

The blood concentrations of CsA, the condition of the post-transplant kidney, the rate of acute rejection (AR), as well as hepatic and renal toxicity in 636 cases of renal transplant recipients were determined after being treated by CsA, with or without diltiazem.

RESULTS

Compared with the control group which received CsA, mycophenolate mofetil (MMF) and prednisolone (Pred) but lacked diltiazem, the group receiving these agents together with diltiazem required reduced dosage of CsA (P < 0.01), while blood concentrations of CsA were significantly increased (P < 0.01); the recovery time of graft function was reduced from (6.2±1.5) d to (3.9±1.4) d (P < 0.01), and the rate of AR was decreased from 13.2% to 7.9% (P < 0.01).

CONCLUSION

In renal transplantation patients treated with CsA and diltiazem, blood concentrations of CsA were increased while the dosage was decreased. This efficient combination therapy reduced patients' economic burden, at the same time retained kidney function, promoted graft function recovery and decreased hepatic and renal toxicity and the rate of AR.

Influence of Everolimus on Steady-State Pharmacokinetics of Cyclosporine in Maintenance Renal Transplant Patients

To investigate possible interactions of the novel immunosuppressant everolimus with cyclosporine, a multicenter, randomized, double-blind, placebo-controlled, dose-escalating phase I study was performed. Everolimus regimens (0.75-10 mg/d) were administered for 28 days to stable renal allograft recipients receiving the microemulsion form of cyclosporine. Steady-state cyclosporine profiles were assessed at baseline on day 0 (cyclosporine alone) and on day 21 with everolimus on steady state. By day 21, mean dose-normalized cyclosporine AUC0-12 increased by 15% in patients receiving placebo. In everolimus-treated patients, mean increases in cyclosporine AUC0-12 ranged from 7% to 43%, which were not significantly different across all dosing cohorts including placebo. Linear regression of everolimus AUC on day 21 versus the increase in cyclosporine AUC0-12 yielded a slope not significantly different from a horizontal line (P = ns). In conclusion, these results suggest that steady-state everolimus exposure over the wide range assessed in this study did not affect steady-state cyclosporine pharmacokinetics.

Updates on cytochrome p450-mediated cardiovascular drug interactions

Cytochrome P (CYP) 450 is a superfamily of hemoproteins that play an important role in the metabolism of steroid hormones, fatty acids, and many medications. Many agents used for management of cardiovascular diseases are substrates, inhibitors, or inducers of CYP450 enzymes. When two agents that are substrates, inhibitors, or inducers of CYP450 are administered together, drug interactions with significant clinical consequences may occur. This review discusses CYP450-mediated cardiovascular drug interactions as well as noncardiovascular drug interactions that produced significant cardiovascular side effects. The principles in predicting drug interactions are also discussed.

Updates on cytochrome P450-mediated cardiovascular drug interactions

Cytochrome P (CYP) 450 is a superfamily of hemoproteins that play an important role in the metabolism of steroid hormones, fatty acids, and many medications. Many agents used for management of cardiovascular diseases are substrates, inhibitors, or inducers of CYP450 enzymes.When two agents that are substrates, inhibitors, or inducers of CYP450 are administered together, drug interactions with significant clinical consequences may occur. This review discusses CYP450-mediated cardiovascular drug interactions as well as noncardiovascular drug interactions that produced significant cardiovascular side effects. The principles in predicting drug interactions are also discussed.

Role of cytochrome P450 in drug interactions

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues. Many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Population Pharmacokinetics of Cyclosporine in Chinese Cardiac Transplant Recipients

STUDY OBJECTIVE

To characterize the population pharmacokinetics of cyclosporine in Chinese patients undergoing cardiac transplantation and to identify the demographic and clinical covariates affecting cyclosporine clearance.

DESIGN

Population pharmacokinetic analysis using data from a retrospective chart review.

SETTING

Specialty hospital in Hong Kong for treatment of cardiac and pulmonary diseases.

PATIENTS

Thirty-eight Chinese adult patients (mean age 46 yrs) who had undergone routine cyclosporine therapeutic drug monitoring after cardiac transplantation between January 1, 1991, and December 31, 2003.

MEASUREMENTS AND MAIN RESULTS

Data regarding dosing, demographics, clinical laboratory values, and concurrent drugs were collected retrospectively. Data were included if patients had blood cyclosporine concentrations determined for at least 12 weeks after transplantation; an average of 18 blood samples/patient were collected. Population modeling was performed using a one-compartment linear model with first-order absorption and elimination. Various demographic and clinical covariates were tested for their significant effects on the apparent oral clearance (Cl/F) of cyclosporine. The stability of the final population model was evaluated by using the bootstrap resampling method. Statistically significant associations were observed between Cl/F and each of the following covariates: body weight (BW), use of diltiazem (DIL), and hematocrit value (HCT). The final model was Cl/F=5.00*(1-DIL)+365/HCT+(0.144*BW). The interindividual variabilities of Cl/F and apparent volume of distribution were 14.5% and 40.2%, respectively. The mean parameter estimates obtained from bootstrap analyses were highly consistent with those obtained with the original data set.

CONCLUSION

The estimated Cl/F values of cyclosporine in our Chinese cardiac transplant recipients appeared to be similar to those reported for Caucasian cardiac transplant recipients. Thus, our data provide support that a cyclosporine dosage regimen similar to that in Caucasian patients may be needed in Chinese cardiac transplant recipients. However, further studies are required to determine the optimum cyclosporine dosage regimen in the Chinese population.

Effects of berberine on the blood concentration of cyclosporin A in renal transplanted recipients: clinical and pharmacokinetic study

OBJECTIVE

To study the effects of berberine (BBR) on the blood concentration and pharmacokinetics of cyclosporin A (CsA) in renal-transplant recipients.

METHODS

In a randomized and controlled clinical trial, 52 renal-transplant recipients were treated with CsA and 0.2 g BBR three times daily for 3 months, while another 52 subjects received CsA without BBR co-administration. Blood trough concentration of CsA and biochemistry indexes for hepatic and renal functions were determined. For the pharmacokinetic study, six renal-transplant recipients were included with a 3-mg/kg dosage of CsA twice daily before and after oral co-administration of 0.2 g BBR three times daily for 12 days.

RESULTS

The trough blood concentrations and the ratios of concentration/dose of CsA in the BBR-treated group increased by 88.9% and 98.4%, respectively, compared with those at baseline (P < 0.05). As for the BBR-free group, they rose by 64.5% and 69.4%, respectively, relative to those at baseline (P < 0.01). Nevertheless, the final blood concentrations and the ratios of concentration/dose of CsA in BBR-treated patients were still 29.3% and 27.8%, respectively, higher than those in BBR-free patients (P < 0.05). No significant effects on liver or renal functions were observed under coadministration of BBR. After co-administration of BBR in six patients for 12 days, the mean AUC of CsA was increased by 34.5% (P < 0.05). The mean time taken to reach the peak blood concentration (t(max)) and the mean half-life (t(1/2)) of CsA were increased by 1.7 h and 2.7 h, respectively (P < 0.05). The average percentage increases in the steady-state drug concentration (Css) and minimum blood concentration (Cmin) were 34.5% and 88.3%, respectively (P < 0.05). In addition, the average percentage decrease in CL/F was 40.4% (P < 0.05) and the peak-to-through fluctuation index was significantly reduced (P < 0.01).

CONCLUSION

The BBR can markedly elevate the blood concentration of CsA in renal-transplant recipients in both clinical and pharmacokinetic studies. This combination may allow a reduction of the CsA dosage. The mechanism for this interaction is most likely explained by inhibition of CYP3A4 by BBR in the liver and/or small intestine.

Population pharmacokinetics of cyclosporine in clinical renal transplant patients

Population pharmacokinetics of cyclosporine (CsA) in clinical renal transplant patients has been reported in the present study. A total of 2,548 retrospective drug monitoring data points were collected from 120 renal transplant patients receiving CsA. Population modeling was performed using the NONMEM (nonlinear mixed-effect modeling) program, using a one-compartment model with first-order absorption and elimination. The final regression model for CsA clearance (CL/F) with the influence of six significant covariates, comprising postoperative days (POD), total bilirubin level (TBIL, micromolar concentration), current body weight (CBW, kilograms), age (years), concurrent metabolic inhibitors of cyclosporine (INHI), and hematocrit (HCT, percentage), has been established and expressed as CL/F=28.5 -- 1.24 . POD -- 0.252 . (TBIL -- 11)+0.188 . (CBW -- 58) --0.191 . (Age -- 42) -- 2.45 . INHI -- 0.212 . (HCT-- 28) (liters per hour). The values in parentheses represent the median level for each of the corresponding covariates. The population estimates for CL/F (28.5 l/h), V/F (volume of distribution, 133 l), and interpatient variability (CV%=19.7%) for CL/F were achieved, respectively. The population model was further validated by internal and external approaches, and was demonstrated to be effective and stable. Moreover, simulation was conducted to facilitate the individualized treatment based on patient information and the final model.

Immunosuppressant Drug Monitoring: Is the Laboratory Meeting Clinical Expectations?

OBJECTIVE:

To review the literature relating to immunosuppressant drug measurement as performed in therapeutic drug monitoring laboratories associated with transplantation centers and consider whether the assay methods widely used for patient dosage management achieve acceptable quality criteria in the context of other sources of variability with these drugs.

DATA SOURCES:

Articles used were accessed primarily through MEDLINE, as well as references cited in related publications. Searches were restricted to organ transplantation in humans.

STUDY SELECTION AND DATA EXTRACTION:

Emphasis was placed on the literature relating to the quality of immunosuppressant drug assays, their limitations, and evidence of clinical benefit in dosage individualization.

DATA SYNTHESIS:

There is a dilemma evident between the quality of the analytical services offered by some diagnostic immunoassay manufacturers and the ability of a significant number of clinical laboratories globally to select only appropriate assay methods.

CONCLUSIONS:

In many cases, clinical laboratories fail to meet the reasonable clinical expectations required for interpretation of immunosuppressant drug assay results as an adjunct to optimal dosage individualization and patient care.

The interaction of the diltiazem with oral and intravenous cyclosporine in rats

This study investigated the effect of diltiazem on the bioavailability of oral and intravenous cyclosporine (CsA) in rats. While control rats received normal saline, experimental groups received 60 or 90 mg/kg diltiazem orally for 3 days. Each group divided into 2 equal groups that received a single oral dose or i.v. injection of CsA. Pharmacokinetic parameters were analyzed by nonparametric analysis of variance. Pretreatment with 60 or 90 mg/kg diltiazem decreased the area under the blood CsA concentration-time curve (AUC) of oral CsA compared to control group (54.5% and 65.5% for AUC(0-24), 57.6% and 62.2% for AUC(0-infinity), respectively, p<0.05). Mean CsA maximum concentration (Cmax) decreased from 0.4 +/- 0.1 microg/ml to 0.1 +/- 0.0 microg/mL in rats pretreated with 90 mg/kg diltiazem (p<0.05). The absolute bioavailability after oral administration (F(p.o.)) in the 60 or 90 mg/kg diltiazem groups were lower than the control group (9.6% and 8.5% versus 22.6%). Pretreatment with 90 mg/kg but not 60 mg/kg of diltiazem increased the AUC(0-infinity), elimination half-life (t1/2) of intravenous CsA (116.0%, 219.2%, respectively, p<0.05) and decreased the intravenous CsA clearence (CL(i.v.)) (62.9%, p<0.05). Diltiazem decreased the bioavailability of oral CsA, while it increased the bioavailability of intravenous CsA. One must consider this interaction when administering oral or intravenous CsA concomitantly with diltiazem.

Antihypertensive therapy: special focus on drug interactions

Today, the lifetime risk of patients aged 55-65 years to receive antihypertensive drugs approaches 60%. Yet, recent trials suggest that hypertension is not adequately controlled in the majority of patients. The prevalence of hypertension increases with advancing age, as does the prevalence of comorbid conditions and the total number of medications taken. Multi-drug therapy, advancing age and comorbid conditions are also key risk factors for adverse drug reactions and drug interactions. In this review, the authors evaluate the most frequently used antihypertensive drugs (diuretics, beta-adrenergic blockers, angiotensin-converting enzyme inhibitors, calcium channel blockers, angiotensin II receptor Type 1 blockers and alpha-adrenergic blockers) with special reference to pharmacodynamic and pharmacokinetic drug interactions. As the spectrum of drugs prescribed is constantly changing, safety yesterday does not imply safety today and safety today does not imply safety tomorrow. Furthermore, therapeutic efficacy should not be neglected over concerns regarding drug interactions. Many patients are at risk of clinically relevant drug interactions involving antihypertensive drugs but, presently, even more patients may be at risk of suffering from the consequences of their inadequately treated hypertension. In this respect, the authors discuss controversial viewpoints on the overall clinical relevance of drug interactions occurring at the level of cytochrome P450 metabolism.

Diltiazem co-treatment in renal transplant patients receiving microemulsion cyclosporin

BACKGROUND

Usage of cyclosporin (the Hong Kong Hospital Authority's single largest item of drug expenditure) continues to increase, mainly due to increasing numbers of renal allograft patients taking it as long-term antirejection therapy. Diltiazem, an antihypertensive agent, interferes with the first pass extraction of oral cyclosporin, thus serving to conserve its dosage.

AIMS

In renal transplant patients, to assess whether diltiazem co-treatment could achieve worthwhile dosage conservation of Neoral (a relatively new microemulsified cyclosporin formulation), safely.

METHODS

A randomized, placebo-controlled, double-blind clinical trial was undertaken at three local hospitals. Renal transplant recipients receiving Neoral as prophylactic immunosuppression were randomized to two treatment arms. Active treatment consisted of diltiazem tablets 30 or 60 mg twice daily for patients weighing < 60 or >or= 60 kg, respectively. One hundred and ten eligible patients gave their informed consent, and were followed up for at least six months. The mean difference in the dollar cost in the sixth month was the primary outcome. Secondary/ancillary outcomes included changes in cyclosporin dosage and blood level, and untoward clinical events including rejection. Outcomes were evaluated by intention to treat analyses.

RESULTS

During weeks 23-26 (sixth month) post randomization, diltiazem co-treatment yielded an estimated average cost saving per patient on drugs of 15%[the 95% confidence interval (CI) of the difference being HK dollars 609 +/- 517 or pound 50 +/- 42], with no apparent excess of untoward or adverse events, complications, hospitalization, outpatient visits, or inferior quality of life.

CONCLUSIONS

This diltiazem co-treatment regime applied to the nearly 1800 surviving renal allograft patients followed up in Hospital Authority hospitals could have saved approximately HK dollars 14.3 million ( pound 1.17 million) annually, without adverse sequelae.

The effect of ketoconazole and diltiazem on oestrogen metabolism in postmenopausal women after single dose oestradiol treatment

AIMS

The effect of the CYP3A4 inhibitors ketoconazole and diltiazem on the pharmacokinetics of oestrone was studied in six healthy postmenopausal women after treatment with a single oral dose of oestradiol.

METHODS

Plasma oestrone concentrations were measured following the administration of 1) oestradiol, 2) oestradiol and ketoconazole and 3) oestradiol and diltiazem.

RESULTS

Treatment with ketoconazole increased the AUC of oestrone (+ 4029 nmol l-1 h; 95% CI on the difference: 1588, 6471) and its Cmax (+ 306 nmol l-1; 95% CI on the difference: 117, 496). The AUC and Cmax of oestrone tended to increase on treatment with diltiazem although this did not reach the level of statistical significance.

CONCLUSIONS

The small increase in the plasma concentrations of oestrone formed from 17beta-oestradiol during co-administration with ketoconazole is unlikely to be clinically significant.

Cyclosporin monitoring in Australasia: 2002 update of consensus guidelines

Therapeutic drug monitoring of cyclosporin (CsA) has been established as part of the routine clinical treatment of patients following organ transplantation for more than 20 years, and based on contemporary knowledge, many consensus guidelines have been published to assist clinics and laboratories attain optimal strategies for patient care. This article addresses the newer directions in CsA monitoring, with particular reference to the Australasian situation that has evolved since the 1993 Australasian guideline. These changes have included the introduction of alternative assay methodologies, changed CsA formulation from Sandimmun to Neoral throughout Australasia, and alternatives to trough concentration (C0) monitoring, especially 2-hour concentration (C2) monitoring and associated validated dilution protocols to accurately quantitate the higher whole blood CsA concentrations. The revision was prepared following a recent survey of all Australasian CsA-monitoring laboratories where discordant practices were evident.

Pharmacokinetic interaction between tacrolimus and diltiazem: dose-response relationship in kidney and liver transplant recipients

OBJECTIVE

To study the dose-response relationship of the pharmacokinetic interaction between diltiazem and tacrolimus in kidney and liver transplant recipients.

DESIGN

Nonrandomised seven-period stepwise pharmacokinetic study.

PATIENTS

Stable kidney (n = 2) and liver (n = 2) transplant recipients maintained on oral tacrolimus twice daily but not taking diltiazem.

METHODS

Patients were treated with seven incremental dosages of diltiazem (0 to 180 mg/day) at > or = 2-weekly intervals. At the end of each interval, 13 blood samples were taken over a 24-hour period to allow determination of morning (AUC(12)), evening (AUC(12-24)) and 24-hour (AUC(24)) areas under the concentration-time curve for tacrolimus, as well as AUC(24) for diltiazem and three of its metabolites.

RESULTS

There was considerable interpatient variability in tacrolimus-sparing effect. In the two kidney transplant recipients, an increase in tacrolimus AUC(24) occurred following the 20 mg/day dosage of diltiazem (26 and 67%). The maximum increase in tacrolimus AUC(24) occurred at the maximum diltiazem dosage used (180 mg/day), when the increase was 48 and 177%. In the two liver transplant recipients, an increase in tacrolimus AUC(24) did not occur until a higher diltiazem dosage (60 to 120 mg/day) was given. The increase at the maximum diltiazem dosages used (120 mg/day in one and 180 mg/day in the other) was also lower (18 and 22%) than that exhibited by the kidney transplant recipients. The increase in tacrolimus AUC(12) was similar to the increase in AUC(12-24) when diltiazem was given in the morning only (dosages < or = 60 mg/day). Hence, diltiazem affects blood tacrolimus concentrations for longer than would be predicted from the half-life of diltiazem in plasma.

CONCLUSIONS

The mean tacrolimus-sparing effect of diltiazem was similar in magnitude to the cyclosporin-sparing effect previously reported. Whether the lesser tacrolimus-sparing effect with diltiazem seen in the liver transplant recipients was due to functional differences in the transplanted liver is not known, but it was not due to lower plasma diltiazem concentrations. Diltiazem makes a logical tacrolimus-sparing agent because of the potential financial savings and therapeutic benefits. Because of interpatient variability, the sparing effect should be demonstrated in each patient and not merely assumed.

Transient bone marrow edema in renal transplantation: a distinct post-transplantation syndrome with a characteristic MRI appearance

We describe four patients who developed severe knee pain within 3 months of renal transplantation. Plain radiographs were normal and inflammatory markers (CRP, ESR) were all within normal ranges. Magnetic resonance imaging (MRI) showed a distinctive pattern in all four cases of bone marrow signal changes, extending from the epiphyseal region into the metaphyseal region in two cases. The appearances were different from those of avascular necrosis (AVN) and reflex sympathetic dystrophy and showed no progression to develop AVN during the follow-up period of 36 months. In all cases the pain resolved over a period of 3 months without specific therapy. Follow-up MRI scans were obtained in all patients after the pain had subsided, which revealed resolution of the MRI changes. We suggest that MRI be the investigation in such patients and that bone marrow edema changes will regress without the need to withdraw cyclosporin.

Pharmacokinetics of cyclosporine in heart transplant recipients receiving metabolic inhibitors

BACKGROUND

Inhibitors of cyclosporine metabolism are commonly co-administered with cyclosporine in transplant recipients. The aim of this study was to compare cyclosporine pharmacokinetics using the conventional formulation (Sandimmune) and after switching to the microemulsion (Neoral) formulation, in stable heart transplant recipients receiving various cyclosporine metabolic inhibitors.

METHODS

Steady-state blood concentration-time profiles of Sandimmune were studied in 47 transplant recipients receiving either cyclosporine alone (Group A, n = 11) or in combination with diltiazem (120 mg/day, Group B, n = 11), ketoconazole (200 mg/day, Group C, n = 13), or both ketoconazole and diltiazem (200 and 120 mg/day, respectively, Group D, n = 12), and restudied 1 week after switching to Neoral.

RESULTS

Neoral resulted in more rapid cyclosporine absorption as judged by the shorter absorption half-lives in all groups (p < 0.05). The mean percentage increase in the values of area-under-the-concentration-time curve was 42% and 37.5% higher for Neoral compared with Sandimmune for Groups A and B, respectively, but only 5.4% higher for Group C and 9.5% higher for Group D. The mean morning trough concentration of cyclosporine was not significantly different after administration of Neoral compared with Sandimmune in any of the groups studied (179 vs. 167 microg/liter for Group A; 171 vs. 147 microg/liter for Group B; 189 vs. 194 microg/liter for Group C; and 181 vs 201 microg/liter for Group D). Neoral did not alter serum concentrations of sodium, potassium, creatinine, and urea in any of the study groups.

CONCLUSIONS

The faster absorption and improved bioavailability of cyclosporine (around 40%) with Neoral compared with Sandimmune was not seen in patients receiving ketoconazole, where in fact cyclosporine bioavailability was already maximal. Mean morning trough levels of cyclosporine did not reflect the improvement in bioavailability seen in patients switching from Sandimmune to Neoral. Cyclosporine dose adjustment may be needed when switching from Sandimmune to Neoral for patients not receiving sparing agents or who receive diltiazem, but trough levels cannot necessarily be relied upon to determine the degree of adjustment needed. For patientson ketoconazole, the absorption profile is already optimized and no dosage alteration seems necessary.

The clinical and economic potential of cyclosporin drug interactions

The introduction of cyclosporin significantly improved solid organ transplantation outcomes. However, the costs associated with immunosuppressive therapy increased from approximately $US1000 to $US2000 per patient per year with azathioprine (AZA) and prednisone to $US5000 to $US8000 per patient per year with the addition of cyclosporin (1997 values). Because of the financial demands placed on medical care in the current era, research has been directed towards developing drug combinations which potentiate the therapeutic effect of cyclosporin whereby reducing the amount of drug administered and consequently the costs of long term immunosuppressive therapy. To date, many drugs that interact with cyclosporin have been recognised. Included in this list are the azole antifungal drugs, ketoconazole, fluconazole and itraconazole; the calcium channel blockers, diltiazem, verapamil and nicardipine; and the macrolide antibacterials, erythromycin and related compounds. Although all of these drugs increase cyclosporin drug concentrations when used concomitantly, ketoconazole and diltiazem appear to be the best candidates on the basis of reducing financial pressures of chronic immunosuppressive therapy without sacrificing patients' well-being. Studies of various regimens involving the combined use of ketoconazole and cyclosporin have shown that cyclosporin dosages can be reduced by approximately 70 to 85% while maintaining therapeutic blood concentrations in renal, cardiac and liver transplant recipients. The calcium channel blocker, diltiazem, allows a decrease in cyclosporin dosage by approximately 30 to 50% in this same group of organ transplant patients. These reductions in cyclosporin dosage have been achieved with no reported severe adverse effects that would discourage the use of these agents concurrently in practice. The combined use of cyclosporin and ketoconazole or diltiazem could reduce medication costs by approximately $US915 to $US3000 per year per patient. If all patients treated with cyclosporin are considered, these combinations could reduce medication costs by hundreds of millions of dollars per year in the US alone. While these are promising approaches, further characterisation of these drug interactions is necessary before this practice is adopted as standard protocol worldwide. The objective of this paper is to review the clinical and economic potential of cyclosporin-sparing agents such as the azole antifungal drugs and calcium channel blockers in an attempt to decrease the costs associated with this expensive immunosuppressive agent.

Clinically important pharmacokinetic drug-drug interactions: role of cytochrome P450 enzymes

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues and many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In the future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Effect of metabolic inhibitors on cyclosporine pharmacokinetics using a population approach

Drugs known to inhibit the metabolism of cyclosporine are administered concomitantly to those who undergo cardiothoracic transplantation. The aim of this study was to examine in quantitative terms the relationship between cyclosporine oral dose rate and the trough concentration (Css(trough)) at steady state in patients who undergo cardiothoracic transplantation and are administered cyclosporine alone or in combination with drugs known to inhibit its metabolism. Dose and whole blood cyclosporine Css(trough) observations measured using the enzyme-multiplied immunoassay technique (EMIT) (396 observations) or the TDx assay (435 observations) were collected as part of routine blood concentration monitoring from 182 patients who underwent cardiothoracic transplantation. Data were analyzed using a linear mixed-effects modeling approach to examine the effect of metabolic inhibitors on dose-rate-Css(trough) ratio. The mean (and 95% confidence interval) dose-rate-Css(trough) ratio for cyclosporine generated from concentrations measured using EMIT was 94 (82.5-105.5) Lh(-1) for patients administered cyclosporine alone, 66.7 (58.1-75.3) Lh(-1) for patients administered concomitant diltiazem, 47.9 (15.4 -80.4) Lh(-1) for patients administered concomitant itraconazole, 21.7 (14.8-28.5) Lh(-1) for patients administered concomitant ketoconazole, and 14.9 (11.8-18.1) Lh(-1) for patients concomitantly administered diltiazem and ketoconazole. For patients administered concomitant cyclosporine, ketoconazole, and diltiazem, the dosage of cyclosporine, if it is administered alone, should be 20% to achieve the same blood concentrations. This will allow safer drug concentration targeting of cyclosporine after cardiothoracic transplantation.

Diltiazem disposition and metabolism in recipients of renal transplants

Diltiazem is widely prescribed in Australasia as a cyclosporine-sparing agent. On seven separate occasions at 2-week intervals, the authors studied eight patients who had undergone renal transplantation, were treated with cyclosporin A, and were in stable condition. The patients were administered escalating doses of conventional-release diltiazem, and (in an extension study) controlled-diffusion diltiazem, to consider the disposition and metabolism of diltiazem. Blood samples were drawn during a 24-hour period, and the AUC(0)(24) of diltiazem and three major metabolites was determined. Results demonstrated that seven patients had comparable diltiazem metabolite AUC(0)(24) profiles, despite considerable variability in parent diltiazem areas under the curve (AUCs), with DM-DTZ > DA-DTZ > DMDA-DTZ. The eighth patient displayed a different metabolite profile. The controlled-diffusion formulation reduced the interpatient variability in diltiazem AUC(0)(24) from 46-fold to <3-fold, but it did not appear to have release characteristics consistent with the manufacturer's specifications. The apparent bioavailability of the conventional-release diltiazem formulation appeared to be highly variable, and this has implications for its use in recipients of organ transplants. The dosage escalation demonstrated a linear relationship between dose and AUC for diltiazem and for each of the metabolites. There may be a subset of patients who display a different diltiazem metabolite profile.