A retrospective assessment of safety, efficacy, and pharmacoeconomics of generic azathioprine in heart-transplant recipients.

Although a generic formulation of azathioprine (AZA) has been available since 1996, safety, efficacy and pharmacoeconomic implications following conversion from Imuran (AZA) to generic AZA in heart-transplant patients remains to be determined. A retrospective, safety and efficacy assessment, in addition to a cost comparison, was performed in 30 heart-transplant patients who had been switched from Imuran to generic AZA. In heart-transplant patients converted from Imuran to generic AZA, no compromise in safety and efficacy, as measured by white blood cell (WBC) count, infections, rejections, malignancies, and hospitalizations was observed. Generic substitution of Imuran results in an annual cost savings of $318 per patient.

Immunosuppressive drugs and novel strategies to prevent acute and chronic allograft rejection.

Maintenance immunosuppression for lung transplantation includes cyclosporine or tacrolimus, mycophenolate mofetil or azathioprine, and prednisone. Some centers rely on induction agents including OKT3 (murine monoclonal antibody, OKT3), ATG (antithymocyte globulin), or thymoglobulin. In addition, a number of new agents including sirolimus (SRL) and the interleukin (IL)-2 receptor antagonists, daclizumab and basiliximab, have become available. Management of chronic rejection typically consists of augmented immunosuppression using many of the standard agents, and other potent agents such as methotrexate or cytoxan or more novel strategies including photopheresis, radiation, and total lymphoid irradiation (TLI).

Elevated free fractions of valproic acid in a heart transplant patient with hypoalbuminemia.

OBJECTIVE: To report a case demonstrating the importance of monitoring unbound valproic acid (VPA) serum concentrations in a patient with hypoalbuminemia. CASE SUMMARY: A 53-year-old white woman status-post heart transplantation was admitted to the hospital for declining cardiac function, possible rejection, and increased lethargy requiring intubation. An extensive workup of the patient's profound lethargy was initiated, including an evaluation of her VPA regimen. Initially, VPA dosages were adjusted based on the total serum concentration of VPA. Hypoalbuminemia compounded with increased lethargy prompted the measurement of unbound serum concentrations of VPA. The VPA dosage was then adjusted based on the unbound rather than the total VPA serum concentration; the patient eventually improved and was discharged from the hospital. DISCUSSION: Lethargy is a concentration-related adverse effect of VPA. The nonlinear pharmacokinetic and protein saturation characteristics of VPA may result in nonproportional elevations in unbound drug, and subsequent increases in adverse effects, when dosage adjustments are based solely on measurement of total VPA serum concentrations in patients with hypoalbuminemia. CONCLUSIONS: This case report suggests that appropriate monitoring of unbound drug concentrations of VPA may prevent unrecognized concentration-related adverse effects. Awareness of the pharmacokinetic relationship and adverse effects of VPA will aid clinicians in identifying the etiology of symptoms.

Cannabinoid-induced mesenteric vasodilation through an endothelial site distinct from CB1 or CB2 receptors.

Cannabinoids, including the endogenous ligand arachidonyl ethanolamide (anandamide), elicit not only neurobehavioral but also cardiovascular effects. Two cannabinoid receptors, CB1 and CB2, have been cloned, and studies with the selective CB1 receptor antagonist SR141716A have implicated peripherally located CB1 receptors in the hypotensive action of cannabinoids. In rat mesenteric arteries, anandamide-induced vasodilation is inhibited by SR141716A, but other potent CB1 receptor agonists, such as HU-210, do not cause vasodilation, which implicates an as-yet-unidentified receptor in this effect. Here we show that "abnormal cannabidiol" (Abn-cbd) is a neurobehaviorally inactive cannabinoid that does not bind to CB1 receptors, yet causes SR141716A-sensitive hypotension and mesenteric vasodilation in wild-type mice and in mice lacking CB1 receptors or both CB1 and CB2 receptors. Hypotension by Abn-cbd is also inhibited by cannabidiol (20 microgram/g), which does not influence anandamide- or HU-210-induced hypotension. In the rat mesenteric arterial bed, Abn-cbd-induced vasodilation is unaffected by blockade of endothelial NO synthase, cyclooxygenase, or capsaicin receptors, but it is abolished by endothelial denudation. Mesenteric vasodilation by Abn-cbd, but not by acetylcholine, sodium nitroprusside, or capsaicine, is blocked by SR141716A (1 microM) or by cannabidiol (10 microM). Abn-cbd-induced vasodilation is also blocked in the presence of charybdotoxin (100 nM) plus apamin (100 nM), a combination of K(+)-channel toxins reported to block the release of an endothelium-derived hyperpolarizing factor (EDHF). These findings suggest that Abn-cbd and cannabidiol are a selective agonist and antagonist, respectively, of an as-yet-unidentified endothelial receptor for anandamide, activation of which elicits NO-independent mesenteric vasodilation, possibly by means of the release of EDHF.

Nefazodone and cyclosporine drug-drug interaction.

Depression is a significant post-transplant complication often necessitating drug therapy. Many of the newer selective serotonin reuptake inhibitor (SSRI) antidepressants are metabolized by the same cytochrome P450IIIA isoenzyme system that is responsible for the metabolism of cyclosporine, and these agents pose an interactive risk in transplant patients. We have observed nearly a 10-fold increase in whole blood cyclosporine concentrations in a cardiac transplant patient shortly after the addition of nefazodone antidepressant therapy. We suggest there is a clinically significant drug-drug interaction between nefazodone and cyclosporine due to inhibition of cytochrome P-450 IIIA4 isoenzymes by nefazodone.

Adenovirus-mediated gene transfer in vivo to cerebral blood vessels and perivascular tissue in mice.

BACKGROUND AND PURPOSE: Gene transfer to cerebral blood vessels has been accomplished in rats and dogs by injection of replication-deficient adenovirus into cerebrospinal fluid. In this study we examined transgene expression after injection of adenovirus into the cerebrospinal fluid of mice. Responses were observed in ICR mice and C57BL/6 mice, which are outbred and inbred strains, respectively. METHODS: We injected replication-deficient recombinant adenovirus expressing nuclear targeted beta-galactosidase, driven by either the Rous sarcoma virus promoter (AdRSV-betaGal) or the cytomegalovirus promoter (AdCMV-betaGal), into the cisterna magna of anesthetized ICR and C57BL/6 strains of mice. The brains were examined from 1 to 21 days after injection by chemiluminescent enzyme activity assay or histochemical staining. RESULTS: After injection of AdRSV-betaGal, expression of beta-galactosidase in ICR mice peaked on day 7 and returned to basal by day 14. Expression of beta-galactosidase in C57BL/6 mice was maximal on days 7 to 14 and was minimal by day 21 after injection of AdRSV-betaGal. After injection of AdCMV-betaGal in C57BL/6 mice, peak expression of transgene occurred on day 1 and was greatly diminished by day 3. Transgene expression was observed primarily on the ventral surface of the brain, with preferential expression in leptomeninges and adventitia along the major cerebral arteries of that region. CONCLUSIONS: Injection of recombinant adenovirus in the cisterna magna resulted in transgene expression in leptomeninges and perivascular tissue of cerebral blood vessels in two strains of mice. The CMV promoter elicited rapid but short-lived expression of the transgene, while the RSV promoter elicited slower, more sustained transgene expression. Expression of AdRSV transgene was prolonged in C57BL/6 mice compared with ICR mice. This approach for gene transfer may be useful to study cerebral vascular biology in genetically altered strains of mice.

Policies regarding the transplantation of hepatitis C-positive candidates and donor organs.

Whether hepatitis C virus (HCV)-positive candidates or donor organs should undergo transplantation remains controversial. Seventy-two thoracic transplantation centers responded to a survey soliciting specific information about policies regarding the listing of HCV-positive candidates and the use of HCV-positive donor organs. Most centers (64%) list HCV-positive candidates for heart transplantation. Twenty-six percent of centers refuse to use HCV-positive organs, whereas the remainder restrict the use of HCV-positive organs to status 1 recipients or HCV-positive candidates. More information is needed regarding the clinical outcomes of HCV-positive candidates and recipients of HCV-positive organs before clear-cut candidate selection and organ allocation policies can be established.

Cannabinoid-induced hypotension and bradycardia in rats mediated by CB1-like cannabinoid receptors.

Previous studies indicate that the CB1 cannabinoid receptor antagonist, N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-met hyl-1H-pyrazole-3-carboxamide HCl (SR141716A), inhibits the anandamide- and delta9-tetrahydrocannabinol- (THC) induced hypotension and bradycardia in anesthetized rats with a potency similar to that observed for SR141716A antagonism of THC-induced neurobehavioral effects. To further test the role of CB1 receptors in the cardiovascular effects of cannabinoids, we examined two additional criteria for receptor-specific interactions: the rank order of potency of agonists and stereoselectivity. A series of cannabinoid analogs including the enantiomeric pair (-)-11-OH-delta9-THC dimethylheptyl (+)-11-OH-delta9-THC dimethylheptyl were evaluated for their effects on arterial blood pressure and heart rate in urethane anesthetized rats. Six analogs elicited pronounced and long lasting hypotension and bradycardia that were blocked by 3 mg/kg of SR141716A. The rank order of potency was (-)-11-OH-delta9-THC dimethylheptyl > or = (-)-3-[2-hydroxy-4-(1,1-dimethyl-heptyl)phenyl]-4-[3-hydroxy-propyl]c yclohexan-1-ol > (-)-3-[2-hydroxy-4-(1,1-dimethyl-heptyl)phenyl]-4-[3-hydroxy-propyl]c yclohexan-1-ol > THC > anandamide > or = (-)-3-[2-hydroxy-4-(1,1-dimethyl-heptyl)phenyl]-4-[3-hydroxy-propyl]c yclohexan-1-ol, which correlated well with CB1 receptor affinity or analgesic potency (r = 0.96-0.99). There was no hypotension or bradycardia after palmitoylethanolamine or (+)-11-OH-delta9-THC dimethylheptyl. An initial pressor response was also observed with THC and anandamide, which was not antagonized by SR141716A. We conclude that the similar rank orders of potency, stereoselectivity and sensitivity to blockade by SR141716A indicate the involvement of CB1-like receptors in the hypotensive and bradycardic actions of cannabinoids, whereas the mechanism of the pressor effect of THC and anandamide remains unclear.

Cardiovascular effects of anandamide in anesthetized and conscious normotensive and hypertensive rats.

We previously showed that in anesthetized rats anandamide elicits bradycardia and a triphasic blood pressure response: transient hypotension secondary to a vagally mediated bradycardia, followed by a brief pressor and prolonged depressor response, the latter two effects being similar to those of delta 9-tetrahydrocannabinol (THC). The prolonged depressor but not the pressor response was reduced after alpha-adrenergic receptor blockade or cervical spinal cord transection and was inhibited by the cannabinoid type 1 (CB1) receptor antagonist SR141716A, suggesting CB1 receptor-mediated sympathoinhibition as the underlying mechanism. Here we examined the relationship between sympathetic tone and the cardiovascular effects of anandamide by testing these effects in both conscious and anesthetized, normotensive and spontaneously hypertensive rats. In urethane-anesthetized normotensive rats, SR141716A inhibited the prolonged depressor and bradycardic effects of anandamide and THC with similar potency, whereas it did not affect the pressor response to either agent. Anadamide caused similar hypotension in spontaneously breathing and in paralyzed, mechanically ventilated rats, suggesting that the hypotension is not secondary to respiratory effects. In conscious normotensive rats, anandamide elicited transient vagal activation and a brief pressor response, but the prolonged hypotensive component was absent. SR141716A potentiated and prolonged the brief pressor response to anandamide, suggesting that the depressor response may have been masked by an increased pressor response. All three phases of the anadamide response were present in both anesthetized and conscious spontaneously hypertensive rats, and the hypotensive component, inhibited by SR141716A in both, was more prolonged in the absence (> 50 minutes) than the presence (10 to 15 minutes) of anesthesia. We conclude that anandamide causes a non-CB1 receptor-mediated pressor and a CB1 receptor-mediated prolonged depressor response. The depressor response can be elicited in both conscious and anesthetized animals, but its magnitude depends on preexisting sympathetic tone.

Mechanism of the hypotensive action of anandamide in anesthetized rats.

We studied the effects of the endogenous cannabinoid ligand anandamide on blood pressure, single unit activity of barosensitive neurons in the rostral ventrolateral medulla, and postganglionic splanchnic sympathetic nerve discharge in urethane-anesthetized rats. In rats with an intact baroreflex, an intravenous bolus of 4 mg/kg anandamide caused a triphasic blood pressure response: transient hypotension, followed by a brief pressor and more prolonged depressor phase. Anandamide evoked a "primary" increase in neuronal firing coincident with its pressor effect and a "secondary," baroreflex-mediated rise coincident with its depressor effect at both sites. Pretreatment of rats with phentolamine or trimethaphan did not inhibit either the pressor response or the primary increase in splanchnic nerve discharge elicited by anandamide. In barodenervated rats, electrical stimulation of the rostral ventrolateral medulla increased blood pressure and splanchnic nerve discharge. Anandamide treatment blunted the rise in blood pressure without affecting the increase in splanchnic nerve discharge. Anandamide did not affect the rise in blood pressure in response to an intravenous bolus dose of phenylephrine. The results indicate that (1) the brief pressor response to anandamide is not sympathetically mediated, and (2) the prolonged hypotensive response to anandamide is not initiated in the central nervous system, in ganglia, or at postsynaptic adrenergic receptors but is due to a presynaptic action that inhibits norepinephrine release from sympathetic nerve terminals in the heart and vasculature.

Treatment of hyperlipidemia after heart transplantation and rationale for the Heart Transplant Lipid Registry.

Hyperlipidemia occurs frequently after heart transplantation, and accelerated coronary artery disease remains the major cause of morbidity and mortality in patients who survive more than 1 year after heart transplantation. However, the risks and benefits of lipid-lowering therapy after heart transplantation remain poorly defined, and national guidelines for lipid-lowering drug therapy do not specifically address treatment of dyslipidemia in transplant recipients. Since the initial reports in the 1980s of rhabdomyolysis in heart transplant patients receiving high-dosage lovastatin, results of 11 post-transplantation series that used lovastatin, simvastatin, or pravastatin at lower dosages as drug monotherapy have been published. These studies have shown an overall 1% incidence of rhabdomyolysis, defined as creatine kinase > 10 times the upper limit of normal plus muscle symptoms. One randomized, controlled prospective trial has investigated the effects of lipid-lowering pharmacotherapy on patient outcome in cardiac transplant recipients. At 1-year follow-up in this nonblinded, single-center trial, patients treated with pravastatin (20 or 40 mg/day) initiated within 2 weeks of transplantation had a significant reduction in mortality rate and a significantly lower incidence of transplant arteriopathy. A number of important issues remain unanswered regarding treatment guidelines in patients with hyperlipidemia after heart transplantation. In January 1995 we began the Heart Transplant Lipid Registry, with 12 participant centers, to gather data prospectively on the efficacy and safety of lipid-lowering drugs in the treatment of dyslipidemia after heart transplantation.

Azathioprine and allopurinol: the price of an avoidable drug interaction.

OBJECTIVE: To report the price of a drug interaction between azathioprine and allopurinol that resulted in pancytopenia in a patient who had undergone a heart transplant. CASE SUMMARY: A 63-year-old white man who received an orthotopic heart transplant in 1987 was hospitalized in June 1991 with a diagnosis of pancytopenia. His immunosuppressive medications on admission included cyclosporine 125 mg bid, azathioprine (AZA) 200 mg/d, and prednisone 2.5 mg/5 mg every other day. Six weeks prior to admission, the patient's local physician prescribed allopurinol for left wrist pain suspected to be gout. It was determined that the pancytopenia was caused by the drug interaction between AZA and allopurinol, both of which were withheld on admission. During hospitalization, the patient's white blood cell count dropped to 1.1 x 10(3)/mm3 with an absolute neutrophil count of less than 0.5 x 10(3)/mm3, a platelet count of less than 20 x 10(3)/mm3, and a hemoglobin of 3.7 g/dL. Four units of packed red blood cells were transfused and regramostim (GM-CSF) therapy was begun on hospital day 3 to speed the marrow recovery process. The patient was discharged on hospital day 8 and AZA, which had been withheld since admission, was restarted. The dosage was titrated to 200 mg/d over the following 2 weeks. The price of this patient's hospital stay was $13,042. DISCUSSION: Not included in this price was the effect this drug interaction had on the patient's quality of life. Even after discharge from the hospital, it was estimated that it would take up to 3 months for the patient to fully recover his previous level of strength and functional capability. This interaction between AZA and allopurinol could easily have been avoided. Both the physician and the pharmacist missed this well-documented and potentially life-threatening drug interaction. Also, the patient failed to notify the transplant team when allopurinol was prescribed by his local physician. The importance of patient responsibility for medication therapy must be stressed to help avoid unnecessary drug interactions. CONCLUSIONS: Undetected drug interactions can be life-threatening to patients as well as costly to the healthcare system. Drug interactions also can have a profound negative effect on the patients' quality of life, the price of which cannot be measured in dollars alone. It is vital that the physician, pharmacist, and patient work together to optimize therapeutic outcomes and avoid unnecessary drug interactions.

Considerations for using ketoconazole in solid organ transplant recipients receiving cyclosporine immunosuppression.

Drug interactions involving cyclosporine following transplantation are a challenging issue for the transplant clinician. This is especially true when ketoconazole is the second agent used in conjunction with cyclosporine. Because both agents are metabolized by the cytochrome P-450 IIIA4 enzyme system, cyclosporine levels rise dramatically in the presence of ketoconazole. Many other agents interact with ketoconazole, either by competitive enzyme inhibition in the liver and gastrointestinal tract, or by reducing the absorption of ketoconazole by agents that increase the pH of the gastrointestinal tract. Despite the potential cost savings when using ketoconazole to reduce cyclosporine doses, adverse effects associated with ketoconazole put patients at risk when using this combination. Close monitoring of cyclosporine levels is imperative when adding ketoconazole to cyclosporine, and once the dosage adjustments are complete, the addition of a third drug that interacts with either cyclosporine or ketoconazole could result in an unexpected rejection episode or toxic cyclosporine side effect.

Inhibition of exocytotic noradrenaline release by presynaptic cannabinoid CB1 receptors on peripheral sympathetic nerves.

1. Activation of CB1 receptors by plant cannabinoids or the endogenous ligand, anandamide, causes hypotension via a sympathoinhibitory action in anaesthetized rats. In mouse isolated vas deferens, activation of CB1 receptors inhibits the electrically evoked twitch response. To determine if these effects are related to presynaptic inhibition of noradrenaline (NA) release, we examined the effects of delta 9-tetrahydrocannabinol (delta 9-THC), anandamide and the CB1 antagonist, SR141716A, on exocytotic NA release in rat isolated atria and vasa deferentia. 2. In isolated atria and vasa deferentia preloaded with [3H]-NA, electrical field stimulation caused [3H]-NA release, which was abolished by tetrodotoxin 0.5 microM and concentration-dependently inhibited by delta 9-THC or anandamide, 0.3-10 microM. The inhibitory effect of delta 9-THC and anandamide was competitively antagonized by SR 141716A, 1-10 microM. 3. Tyramine, 1 microM, also induced [3H]-NA release, which was unaffected by tetrodotoxin, delta 9-THC or anandamide in either atria or vasa deferentia. 4. CB1 receptor mRNA is present in the superior cervical ganglion, as well as in whole brain, cerebellum, hypothalamus, spleen, and vas deferens and absent in medulla oblongata and atria, as demonstrated by reverse transcription-polymerase chain reaction. There was no evidence of the presence of CB1A receptor mRNA in ganglia, brain, or cerebellum. These results suggest that activation of presynaptic CB1 receptors located on peripheral sympathetic nerve terminals mediate sympathoinhibitory effects in vitro and in vivo.

Important interactions of drugs with immunosuppressive agents used in transplant recipients.

Solid organ transplant recipients depend on multiple immunosuppressive drugs, given in combination, to prevent rejection of their allografts. These patients often require many other therapeutic agents to treat underlying illnesses or concurrent diseases. Whenever a new medication is administered to a transplant patient, the potential exists for increasing or decreasing the tissue concentrations of immunosuppressive agents. This can lead to serious complications, such as over-immunosuppression and infection, under-immunosuppression and acute rejection, or additive toxicities, including nephrotoxicity. New immunosuppressants are under development and in clinical use, such as FK506, deoxyspergualin, OG 37-325, rapamycin, brequinar, and mycophenolate mofetil, thereby creating the possibility of many new drug-drug interactions.

Chronic manipulation of dietary salt modulates renal physiology and kidney dopamine receptor subtypes: functional and autoradiographic studies.

1. Compared to rats maintained on the normal NaCl (0.33%) diet, animals maintained on the low NaCl (0%) diet for 4 weeks exhibited increased plasma aldosterone and chloride and decreased urinary sodium excretion. 2. Rats maintained on the high NaCl (8%) diet for 4 weeks showed increased systolic blood pressure, water intake, urine volume, sodium and dopamine excretion and decreased plasma aldosterone and glomerular filtration rate. 3. Administration of SCH 23390 (10 mg/kg, po), but not domperidone to the high salt diet rats attenuated the diuretic effect, indicating the involvement of DA1 rather than DA2 receptors. The dopamine decarboxylase inhibitor, carbidopa (30 mg/kg, i.p.), also reduced the high salt-induced diuresis. 4. Kidney sections from rats fed the low NaCl diet showed a 63-100% decrease (P < 0.001-0.02) in cortical and medullary DA1 and DA2 binding sites, while rats fed the high NaCl diet demonstrated only a 70% decrease (P < 0.01-0.02) in cortical DA1 binding, without affecting DA2 binding. 5. These data indicate that chronic modification of dietary salt profoundly affects the sodium, water and dopamine excretion and leads to selective modulation of renal dopamine receptor subtypes.