Donald F. LeGatt

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression in renal transplant recipients

The combination of pharmacokinetic and pharmacodynamic monitoring of immunosuppressive drugs provides a novel method for the optimization of drug dosing. We chose to investigate this with the use of mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. The relationship between MPA concentration in plasma, IMPDH activity in whole blood, and nucleotide concentration in lymphocytes was investigated in renal-transplant recipients, who were randomized to receive either mycophenolate mofetil (MMF) (n = 5) or azathioprine (AZA) (n = 7), in combination with cyclosporine and prednisone. Blood samples were collected throughout the dosing interval. Pharmacokinetic analysis revealed substantial variability among the patients in the absorption and clearance of MPA. An inverse relationship was found between the MPA concentration of IMPDH activity in whole blood. The peak concentration of MPA achieved at 1 hr after dosing resulted in approximately 40% inhibition of IMPDH activity. As the MPA concentration decreased throughout the dosing interval, there was a gradual restoration of IMPDH activity. The inhibition of IMPDH activity (P < 0.05) in MMF-treated patients as compared with the AZA-treated controls was maintained for approximately 8 hr after dosing. No statistically significant (P > 0.05) difference between the predose and the 12 hr postdose activity was observed. The concentrations of guanine nucleotides, GDP and GMP, were significantly lower than in the AZA-treated group at most of the time points after dosing; however, considerable variability was observed. The measurement of the pharmacodynamic response to immunosuppressive drugs may provide not only a mechanism to predict the most appropriate dosing regimen, but also a viable alternative to traditional therapeutic drug monitoring, by assessing the overall state of immunosuppression.

RAPAMYCIN : DISTRIBUTION, PHARMACOKINETICS AND THERAPEUTIC RANGE INVESTIGATIONS : AN UPDATE

Based on the findings above, a number of conclusions can be made regarding the distribution, pharmacokinetics, and therapeutic range investigations with RAPA: (a) the majority of the drug is sequestered in erythrocytes, resulting in whole blood concentrations being considerably higher than plasma concentrations; (b) the drug is metabolized by the same cytochrome P450 3A enzyme involved in the metabolism of CsA and FK506. Metabolites are primarily simple demethylations and hydroxylations with 41-O-demethyl RAPA being the major metabolite both in vivo and in vitro; (c) the drug has a relatively long half-life in both humans and animals with 24-h trough concentrations being within the analytical range of HPLC when immunosuppressive doses are administered; (d) the drug exhibits a degree of proportionality between trough concentrations and dose; (e) a strong correlation exists between area under the concentration-time curve and trough blood concentration at steady state; (f) trough concentrations of the drug appear to be related to immunosuppressive efficacy and drug-related side effects; (g) the nephro- and neurotoxic properties of CsA are not augmented by concurrent treatment with RAPA; and (h) phase IIB trial results have shown a decrease of acute rejection episodes from 40% to < 10% among patients treated with full-dose CsA plus RAPA. The studies described here should provide a basis for the establishment of therapeutic monitoring protocols for RAPA. In addition, new derivatives of RAPA, such as SDZ RAD, designed to overcome formulation problems associated with RAPA, while maintaining similar pharmacokinetics and in vivo activity, show promise as alternatives to RAPA.

Levamisole tainted cocaine causing severe neutropenia in Alberta and British Columbia

BackgroundFive cases of severe neutropenia (neutrophil counts < 0.5 per 109 cells/L) associated with exposure to cocaine and levamisole, an antihelimithic agent no longer available in Canada, were identified in Alberta in 2008. Alberta and British Columbia (BC) public health officials issued an advisory and urged health care professionals to report cases to public health. This paper presents the findings of the public health investigations.MethodsCases were identified prospectively through reporting by clinicians and a retrospective review of laboratory and medical examiners data from January 1, 2006 to March 31, 2009. Cases were categorized as confirmed, probable or suspect. Only the confirmed and probable cases are included in this paper.ResultsWe compare cases of severe neutropenia associated with tainted cocaine (NATC) identified in Alberta and BC between January 1, 2008 to March 31, 2009. Of the 42 NATC cases: 23(55%) were from Alberta; 19(45%) were from British Columbia; 57% of these cases reported crack cocaine use (93% of those who identified type of cocaine used); 7% reported using cocaine powder; and the main route of cocaine administration was from smoking (72%). Fifty percent of the NATC cases had multiple episodes of neutropenia associated with cocaine use. Cases typically presented with bacterial/fungal infections and fever. One Alberta NATC case produced anti-neutrophil antibodies, and four were positive for anti-neutrophil cytoplasmic antibody (ANCA). Analysis of two crack pipes and one drug sample obtained from NATC cases confirmed the presence of both cocaine and levamisole. A further 18 cases were identified through the retrospective review of laboratory and medical examiner data in AlbertaInterpretationOur findings support a link between neutropenia and levamisole tainted cocaine; particularly from smoking the crack form of cocaine. Some patients may be genetically predisposed to develop levamisole-related neutropenia. Awareness of the differential diagnosis will assist clinicians with case timely detection and appropriate management.

Comparison of the efficacy, safety, and pharmacokinetics of controlled release and immediate release metoclopramide for the management of chronic nausea in patients with advanced cancer

Background. The short elimination half‐life of met‐oclopramide necessitates frequent administration for optimal relief of nausea. This study compares a newly developed controlled release preparation of metoclopram‐ide (CRM) and immediate release metoclopramide (IRM) with respect to efficacy, safety, and pharmacokinetics in patients with chronic nausea associated with advanced cancer.

Pharmacodynamic assessment of mycophenolic acid-induced immunosuppression by measurement of inosine monophosphate dehydrogenase activity in a canine model

The combination of pharmacokinetic and pharmacodynamic (measurement of the biological effect) monitoring of immunosuppressive drugs provides a method for the optimization of drug dosing. We chose to investigate this using mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. Using an assay developed for measurement of IMPDH activity in whole blood, the concentration required for 50% inhibition of IMPDH activity was approximately 200 mg/L (58 +/- 8.3% for whole blood [n = 6] and 55 +/- 10.0% for isolated lymphocytes). To ascertain the relationship between MPA concentration and IMPDH inhibition in vivo, dogs were administered a single dose of mycophenolate mofetil, the pro-drug of MPA, at 20 or 40 mg/kg orally. Pharmacokinetic analysis revealed that the Cmax of the 40-mg/kg group was statistically greater than that of the 20-mg/kg group (P < 0.05). There were no statistical differences in the other parameters investigated (area under the curve, beta half-life, mean residence time, volume of distribution at steady state, and clearance) between the two treatment groups. The half-life was calculated at approximately 8 hr for both dose groups. There was also substantial variability among the dogs in the absorption and clearance of MPA. An inverse relationship was found between the MPA concentration and IMPDH. Maximal inhibition of IMPDH activity of 30-40% occurs approximately 2-4 hr after dosing, followed by a gradual restoration in enzyme activity. After 24 hr, there is an increase in IMPDH activity that exceeds the pre-dosing levels in some cases by 3-fold. Evaluation of the pharmacokinetic and the pharmacodynamic responses to MPA in the canine model suggests that the drug should be administered ever 8 hr to optimize its immunosuppressive efficacy. This combined approach can be used for optimization of doses of this and other immunosuppressive drugs.

Blood distribution and single-dose pharmacokinetics of leflunomide.

Summary Leflunomide (HWA 486, LEF) is a novel isoxazole derivative with potent immunosuppressive properties. LEF is converted to its active metabolite (A77 1726) after absorption. Presently, the blood distribution and pharmacokinetics of LEF have not been reported. Such information would prove invaluable in determining the appropriate medium for analysis and optimal immunosuppressive dosing regimes. In this study, A77 1726 was found to be primarily associated (>95%) with the lipoprotein free fraction of plasma at all tested concentrations ranging from 0.4 to 100 mg/L. Detectable levels of A77 1726 (0.34 ± 0.18 mg/L), analyzed by HPLC, were found in the plasma free fraction only at the highest tested concentration (100 mg/L). Single-dose phar-macokinetics of A77 1726 (i.v.) and HWA 486 (p.o.) were investigated in five healthy New Zealand white rabbits. The half-lives (t1/2) of A77 1726 i.v. and HWA 486 p.o. administration were 3.88 ± 2.3 and 3.18 ± 1.6 h, respectively. The volume of distribution by both routes of administration indicates minimal distribution into tissues (Vdssp.o. = 0.14 ± 0.03 L/kg and Vdssi.v. = 0.09 ± 0.02 L/kg). The mean residence time of A77 1726 was greater after oral administration of LEF (MRTp.o. = 10.54 ± 2.6 h and MRTi.v. = 6.76 ± 1.0 h). Identical areas under the curve suggest bioavailability was 100% (AUCp.o. = 421.16 ± 204.5 mg ± h/L and AUCi.v. = 399.75 ± 126.9 mg ± h/L).

Blood distribution of mycophenolic acid.

RS-61443 (RS) a morpholinoethyl ester of mycophenolic acid (MPA), can be considered a prodrug, as immunosuppressive activity is expressed only after hydrolysis to MPA upon absorption. Little is known about the blood distribution of MPA; such information would have an impact on the medium used for analysis of the drug in clinical trials. This was investigated by spiking whole blood having an initial temperature of either 4° or 22°C with increasing amounts of MPA ranging from 100 to 10,000 μg/L. These drug concentrations span the range seen when immunosuppressive doses of the RS are administered. This was followed by incubation of the blood at 37°C for 0–120 min prior to separation of the cells. The drug concentration was measured in the plasma and whole blood fractions by high-performance liquid chromatography. MPA was almost exclusively found in the plasma fraction and did not exhibit any temperature or concentration dependence. The free or unbound fraction of MPA over the same concentration range was determined by ultracentrifugation and demonstrated a concentration dependence ranging from 7.2 to 16.5% of total drug for a concentration range spanning 500–10,000 μg/L. The drug was found to be primarily associated with the non-albumin proteins in the plasma. Less than 10% of the drug was found to be bound to lipoproteins. The data suggest that from an analytical standpoint, plasma, rather than whole blood, would be the most suitable medium for analysis because of the higher concentrations of the drug found in this fraction.

Metoclopramide Infusion with a Disposable Portable Pump

Excerpt To the editor: Chronic nausea and anorexia are frequent symptoms in patients with advanced cancer (1, 2). In patients who have no mechanical obstruction of the gastrointestinal tract or who...

Screening for amines of psychiatric interest in urine using gas chromatography with electron-capture detection

Abstract 1. 1. An electron-capture gas chromatographic procedure for the simultaneous quantitation of urinary levels of amines of psychiatric interest has been developed. 2. 2. The amines were isolated from urine using a liquid ion exchanger, then acetylated and perfluoroacylated for analysis. This procedure improved extraction efficiency and analytical sensitivity. 3. 3. The developed procedure was rapid, simple, specific and sensitive. 4. 4. Urinary levels of 5-hydroxytryptamine, 3-methoxytyramine, normetanephrine, 2-phenylethylamine, tryptamine, m - and p -tyramine in control subjects were determined using this analytical procedure and agreed with literature values.

Pharmacodynamic Monitoring of Mycophenolic Acid in Rabbit Heterotopic Heart Transplant Model

Pharmacodynamic (PD) monitoring of immunosuppressive drugs provides a novel approach to optimization of drug therapy in transplant recipients. We chose to investigate this using mycophenolic acid (MPA), an immunosuppressive drug that mediates its effect by the inhibition of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the de novo biosynthesis of purines. A comparison of the relationship between PD versus drug level monitoring was performed using a heterotopic cardiac transplant in New Zealand white rabbits. The animals were divided into four different treatment groups. Control animals were administered the drug vehicle, the treatment groups were administered mycophenolate mofetil (MMF) at doses of 40, 80, and 160 mg/kg/day. Statistically significant (p < 0.05) prolongation of graft survival was obtained at the 160 mg/kg/day dose group. The mean MPA concentration at this dose was approximately 2.5 mg/l, suggesting that this concentration may provide adequate immunosuppression. An increase in IMPDH activity appeared a few days prior to rejection, suggesting that measurement of enzyme activity may have potential for use as a marker of graft rejection. A significant (p < 0.05) relationship exists between MPA concentration and graft survival and the former with dose of MMF. There was a negative correlation (p = 0.17) between MPA concentration and IMPDH activity, while a trend (p = 0.37) to inverse relationship between graft survival and IMPDH activity was found. The data suggests that the measurement of the biological response may provide a useful adjunct to traditional therapeutic drug monitoring (TDM) for optimization of dosing of immunosuppressive drugs.