Calcium channel blockers and cyclosporine metabolism

Travel to High Altitude Following Solid Organ Transplantation

Luks, Andrew M. Clinician's corner: travel to high altitude following solid organ transplantation. High Alt Med Biol. 17:147-156, 2016.-As they regain active lifestyles following successful organ transplantation, transplant recipients may travel to high altitude for a variety of activities, including skiing, climbing, and trekking. This review is intended to provide information for medical providers who may encounter transplant patients seeking advice before planned high altitude travel or care for medical issues that develop during the actual sojourn. There is currently limited information in the literature about outcomes during high-altitude travel following solid organ transplantation, but the available evidence suggests that the physiologic responses to hypobaric hypoxia are comparable to those seen in nontransplanted individuals and well-selected transplant recipients with no evidence of organ rejection can tolerate ascents as high as 6200 m. All transplant recipients planning high-altitude travel should undergo pretravel assessment and counseling with an emphasis on the recognition, prevention, and treatment of altitude illness, as well as the importance of preventing infection and limiting sun exposure. Transplant recipients can use the standard medications for altitude illness prophylaxis and treatment, but the choice and dose of medication should take into account the patient's preexisting medication regimen and current renal function. With careful attention to these and other details, the healthy transplant recipient can safely experience the rewards of traveling in the mountains.

Nifedipine improves immediate, and 6- and 12-month graft function in cyclosporin A (CyA) treated renal allograft recipients

To investigate the effect of oral nifedipine, a calcium channel blocker known not to modify cyclosporin A (CyA) pharmacokinetics, on immediate transplant function and CyA nephrotoxicity, 68 adult renal transplant recipients were pre-operatively randomized to one of three regimes: A (high-dose CyA, initial dose 17 mg/kg per day, maintenance dose 7 mg/kg per day); B (regime A plus oral nifedipine); C low-dose CyA, initial dose 10 mg/kg per day, maintenance 4 mg/kg per day plus azathioprine 1 mg/kg per day). All three groups received identical steroid regimes. Calcium channel blockers of all types were avoided in groups A and C. Delayed graft function (dialysis dependence by day 4) was seen least frequently in group B (P < 0.02). Group B had improved graft function at 6 months compared with group A, identified by differences in serum creatinine (P < 0.05), GFR (P < 0.01) and ERPF (P < 0.05). Similar differences in serum creatinine (P < 0.05) and GFR (P < 0.05) were also identified at 12 months. Group C also had better 6- and 12-month GFR values than group A (P < 0.05 each). The three groups did not differ in donor or recipient age, HLA matching, ischaemic or anastomosis times, frequency of early rejection or whole-blood CyA levels. These results indicate that nifedipine significantly improves immediate and medium-term graft function.

Prophylactic isradipine treatment after kidney transplantation: a prospective double-blind placebo-controlled randomized trial

There is evidence that calcium antagonists may have a beneficial effect on cyclosporine-induced nephropathy after transplantation. We treated 50 consecutive non-diabetic patients receiving their first cadaveric transplant with isradipine, a dihydropyridine calcium antagonist, or placebo in a double-blind, randomized, placebo-controlled trial. There were no significant differences between the two groups as regards age, weight, sex, HLA matching and ischaemic periods. To achieve optimal vasodilation, treatment was started intravenously 2 h before the transplantation procedure, and continued orally afterwards for 3 months. The immunosuppressive treatment included rabbit antithymocyte globulin on day 0, and oral cyclosporine from day 5. In both groups 7 patients had primary non-functioning grafts, but the incidence of never functioning kidneys due to vascular and thrombotic complications was significantly higher in the placebo group (0 vs 4 patients, P < 0.05). Hypertension was treated with oral labetolol in combination with guanfacine if necessary. In the placebo group antihypertensive medication had to be prescribed significantly more often (67% vs 33% of patients, P < 0.05), but resulted in similar blood pressure recordings in the two study groups. Cyclosporin A (CsA) plasma concentrations were also comparable but in the isradipine group a significantly higher dose of CsA was needed to achieve adequate levels (8.0 +/- 0.5 vs 6.2 +/- 0.5 mg/kg per day, P < 0.01). However, in the isradipine-treated patients creatinine clearance was significantly higher (66.1 +/- 4.5 vs 55.6 +/- 6.2 ml/min, P < 0.05) after 3 months. We conclude that isradipine is an effective antihypertensive agent after kidney transplantation. Isradipine ameliorates CsA-induced nephropathy and seems to protect against early postoperative vascular complications.

Amlodipine inhibits rat microsomal cytochrome P450-mediated drug biotransformation

Calcium channel antagonists have been shown to inhibit cytochrome P-450-mediated metabolism both in vitro and in vivo. The purpose of the present study was to examine the effect of amlodipine on a suite of rat hepatic microsomal cytochrome P-450 activities to determine the potential for drug interactions. In this study, amlodipine (0.05 and 0.5 mM) decreased CYP1A-mediated ethoxyresorufin O-deethylase activity in microsomes prepared from noninduced (56 and 73% inhibition) and pyridine-induced (30 and 51% inhibition) rats. Amlodipine reduced pentoxyresorufin O-deethylase activity (a marker for CYP2B) to 15% of control in incubations utilizing microsomes from phenobarbital-treated rats, but had no effect on this enzyme reaction in noninduced microsomes. The para-nitrophenol hydroxylase, erythromycin N-demethylase, and lauric acid omega and omega-1 hydroxylase activities were significantly inhibited by 1 mM amlodipine in both noninduced and induced microsomes. These results suggest that amlodipine inhibits a number of different P450 forms and therefore has the potential to inhibit the metabolism of a large number of drugs.

Nifedipine interaction with tacrolimus in liver transplant recipients

OBJECTIVE

To examine the possible drug interaction between nifedipine and tacrolimus in liver transplant recipients.

STUDY DESIGN

A retrospective study was done comparing two groups of liver transplant recipients. The starting time for comparison was the same after transplant. One group (n = 22) consisted of hypertensive patients who were treated with nifedipine; the other group (n = 28) did not receive nifedipine. The two groups were compared over 1 year. The effect of nifedipine on tacrolimus was measured in terms of tacrolimus whole blood trough concentrations, daily tacrolimus dosages, and cumulative tacrolimus dosages at 1, 3, 6, and 12 months. All patient charts were reviewed with regard to concurrent medication that could affect the metabolism of tacrolimus and eventually affect tacrolimus concentrations and dosages.

DATA COLLECTION

All required information was retrieved from medical records.

RESULTS

There was a statistically significant difference between daily dosage requirements of tacrolimus at 90 (p = 0.03), 180 (p = 0.004), and 365 (p = 0.0004) days between the nifedipine and no-nifedipine groups. The tacrolimus daily dosage in the nifedipine group was decreased by 26%, 29%, and 38% at 3, 6, and 12 months, respectively, compared with the dosage of the no-nifedipine group. Statistically significant differences in cumulative dosages of tacrolimus were observed at 180 (p = 0.02) and 365 (p = 0.003) days between the nifedipine and no-nifedipine groups, with cumulative dosage reduction of 25% and 31% by 6 and 12 months, respectively, in the nifedipine group compared with the no-nifedipine group.

CONCLUSIONS

Nifedipine decreased the daily and cumulative dosage requirement of tacrolimus. The interaction observed between nifedipine and tacrolimus is the first reported in humans and is clinically important. As a result of this drug interaction, it is recommended that blood concentrations of tacrolimus be monitored during coadministration of these drugs and that the tacrolimus dosage be adjusted accordingly.

The beneficial effects of oral nifedipine on cyclosporin-treated renal transplant recipients--a randomised prospective study

The aim of this study was to test the hypothesis that nifedipine will improve graft survival in cyclosporin A (CyA)-treated renal transplant recipients. One hundred and forty-seven patients were randomised to one of three regimens. Group A received CyA, 7 mg/kg per day, and prednisolone; group B followed the same regimen as group A plus oral nifedipine and group C received CyA, 4 mg/kg per day, prednisolone and azathioprine. Calcium channel blockers were avoided in groups A and C. The crude 2-year (P = 0.0223) and 4-year (P = 0.0181) graft survival was significantly better in group B (86% and 81%, respectively) than in group A (75% and 63%, respectively). Delayed initial function was seen least frequently in group B (10.2%) compared to groups A (31%) and C (28%; P < 0.01). Group B also experienced fewer rejection episodes than groups A and C (P < 0.05). We conclude that the combination of oral nifedipine and CyA significantly improves initial graft function, rejection frequency and long term graft survival.

Drug interactions in transplantation

Cyclosporine, tacrolimus, and mycophenolate are selective immunosuppressive agents commonly prescribed to prevent organ rejection. Drug interactions that increase their blood levels could expose transplant recipients to serious side effects, while drug interactions that decrease their blood levels may cause rejection episodes as a result of inadequate immunosuppression. Cyclosporine and tacrolimus are metabolized by the cytochrome P-450 enzyme system. Drugs that induce, inhibit, or compete for the same cytochrome P-450 enzyme could affect blood levels of these immunosuppressive agents.

Calcium antagonists. Drug interactions of clinical significance

The interaction of calcium antagonists, including the dihydropyridine calcium antagonists (e.g. nifedipine), verapamil and diltiazem, with drugs from other classes has major clinical ramifications as the use of drug combinations increases in frequency. Combinations are used in the treatment of disorders ranging from hypertension to cardiac rhythm disturbances, angina pectoris and peripheral vasospastic disease. In this era of organ transplantation, drugs like cyclosporin are coming into potential conflict with an ever-growing list of drugs. Drug combinations used as part of long term therapies are also making their appearance in toxic drug reactions, including antituberculous and anticonvulsant agents. Bronchodilators and H2-blockers also fall into this category of potential culprits of combined drug toxicity, and the interactions of calcium antagonists with beta-blockers and antiarrhythmic agents are also becoming a matter of concern.

The interaction of the calcium channel blockers verapamil and nifedipine with cyclosporin A in pediatric renal transplant patients

The elimination of cyclosporin A was assessed in eight pediatric renal transplant patients who received calcium channel blockers concomitantly with their immunosuppressive therapy. In three children, verapamil decreased the rate of elimination of cyclosporin A. In five children who received nifedipine, cyclosporin A elimination was also impaired, which contrasts with the reports in adult patients indicating that this calcium channel blocker has no effect on cyclosporin A elimination. When both calcium channel blockers were used on separate occasions in the same patient, nifedipine was less potent than verapamil in depressing cyclosporin A elimination. Although the number of subjects studied is small, these results likely indicate that nifedipine, as well as other calcium channel blocking drugs, must be used with caution in pediatric renal transplant patients.

Effect of nifedipine on renal transplant rejection

The effect of early nifedipine therapy on acute renal allograft rejection was studied in 170 adult cadaveric transplant recipients. Acute rejection occurring in the first 3 months after transplantation was diagnosed by Tru-cut biopsy and the severity of each rejection episode assessed histologically. The incidence of acute rejection was significantly lower in patients treated with nifedipine (29 of 80; 36 per cent) than in controls (52 of 90; 58 per cent) (P < 0.01) and there was a higher proportion of histologically mild rejection episodes in the former group (P < 0.01). Multivariate analysis confirmed that nifedipine exerted a significant independent effect on the incidence of early acute rejection. Other factors identified in the multivariate model as influencing rejection were human leucocyte antigen (HLA) matching at the DR locus, blood level of cyclosporin during the first week, HLA matching at the B locus, donor age and donor sex. The 1-year graft survival rate was 88.6 per cent in patients given nifedipine and 63.8 per cent in controls (P < 0.02). These data suggest that nifedipine therapy has a useful role in human renal transplantation.

Lack of effect of isradipine on cyclosporin pharmacokinetics

The influence of isradipine as a long acting form (IcazR LP 5 mg) on cyclosporin pharmacokinetics was studied in six hypertensive renal transplant patients (mean age 37 yrs; mean body weight 62 kg). These patients received a mean daily cyclosporin dose of 307 mg in two equal intakes. Isradipine was orally administered once a day at a dose of 5 mg before the morning cyclosporin intake. Cyclosporin kinetics was assessed over a 0-12-h period, the day before (D-1) and 13 days (D+13) after isradipine treatment. Whole blood concentrations of cyclosporin were determined by radioimmunoassay (RIA) using the SandimmuneR-RIA kit (specific and non-specific monoclonal antibodies). Area under the blood concentration-time curve (AUC), the maximum blood concentration (Cmax) and the time to reach Cmax (Tmax) on D-1 and D+13 were not significantly different whatever the specificity of the RIA method. For example, the mean AUC +/- sd values were 5,247 +/- 2,255 (D-1) vs 5,317 +/- 1,675 (D+13) microgram.1(-1).h for the specific and 20,905 +/- 8,317 vs 19,327 +/- 5,758 microgram.1(-1).h for the non-specific determinations. Therefore, the pharmacokinetics of cyclosporin is not influenced by co-administration of isradipine at a therapeutic dosage. Moreover, the clinical results show that isradipine treatment was effective after 13 days administration (mean systolic blood pressure 132 vs 158 mm Hg, P < 0.05 and mean diastolic blood pressure 77 vs 93 mm Hg, P < 0.05 in supine position), and well tolerated throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine: nephrotoxic effects and guidelines for safe use in patients with rheumatoid arthritis

Renal abnormalities occur frequently in patients with rheumatoid arthritis; they may be complications of the rheumatoid disease process itself (amyloidosis) or may result from various therapies including gold compounds, D-penicillamine, analgesics such as aspirin or phenacetin used long term, and nonsteroidal anti-inflammatory drugs. Cyclosporine, a highly effective immunosuppressive agent currently under investigation as a treatment for RA, is also known to produce renal dysfunction. Some forms of functional and structural tubular changes appear readily reversible. Others associated with renal vasculopathy and interstitial fibrosis can lead to irreversible nephrotoxicity. A clear understanding of the pharmacology, drug interactions, and types of renal side effects encountered with cyclosporine can lead to a reduction of adverse renal reactions. Similarly, an understanding of which patients are at high risk for renal dysfunction can lead to safer and more efficacious use of this potent immunosuppressive agent.

Pharmacokinetic interactions with calcium channel antagonists (Part II)

Since calcium channel antagonists are a diverse class of drugs frequently administered in combination with other agents, the potential for clinically significant pharmacokinetic drug interactions exists. These interactions occur most frequently via altered hepatic blood flow and impaired hepatic enzyme activity. Part I of the article, which appeared in the previous issue of the Journal, dealt with interactions between calcium antagonists and marker compounds, theophylline, midazolam, lithium, doxorubicin, oral hypoglycaemics and cardiac drugs. Part II examines interactions with cyclosporin, anaesthetics, carbamazepine and cardiovascular agents.

Pharmacokinetic drug interactions with cyclosporin (Part II)

Part I of this article, which appeared in the previous issue of the Journal, considered the potential mechanisms of drug interactions with cyclosporin, and divided the interacting drugs into 2 categories. Drugs that decrease cyclosporin concentrations (e.g. anti-convulsants, rifampicin, etc.) were dealt with first; the authors then moved on to consider the second category, those that increase cyclosporin concentration (macrolide antibiotics, azole antifungal drugs). Part II continues the survey of this category.