Diltiazem-cyclosporin pharmacokinetic interaction--dose-response relationship

AIMS

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

METHODS

Eight stable kidney transplant recipients maintained on cyclosporin but not taking diltiazem, were given increasing doses of diltiazem to a maximum dose of 180 mg day(-1). Following a 2 week period on each dose of diltiazem, thirteen blood samples were taken over a 24 h period to allow morning and evening AUCs to be determined for cyclosporin, diltiazem and three metabolites of diltiazem.

RESULTS

Mean cyclosporin AUC(0, 24 h) increased sharply following the lowest dose of diltiazem used (10 mg day(-1)), the rate of increase slowed after 30-60 mg day(-1) but continued to increase up to the maximum dose tested. The effect of a single morning dose of DTZ was evident over both morning (0-12 h) and evening (12-24 h) cyclosporin AUCs. There was considerable interpatient variation in response to DTZ.

CONCLUSIONS

The dose of diltiazem required to increase cyclosporin AUC (and hence allow significant reduction in cyclosporin dose) is less than that currently used for many patients. Lower doses of diltiazem should result in fewer adverse effects and may allow its use in situations where it was hitherto contraindicated. Because of the significant interpatient variation in response, we recommend individual patient blood cyclosporin concentration monitoring both before and after the introduction of diltiazem.

The use of other drugs to allow a lower dosage of cyclosporin to be used. Therapeutic and pharmacoeconomic considerations

Since its discovery in 1970, and introduction into clinical practice in 1978, cyclosporin has become the most important immunosuppressive drug used to prevent organ transplant rejection. This has been achieved by virtue of the improved graft survival rates and adverse effect profiles in patients when compared with that of the older agents. Cyclosporin is substantially more expensive (both to provide and to monitor) however, and the magnitude of these costs may preclude its use, particularly where the transplant recipient is required to pay. Cyclosporin has a complex pharmacokinetic profile with poor absorption, extensive metabolism to more than 30 metabolites and considerable inter- and intrapatient variability. Many transplant centres routinely use drugs ("cyclosporin-sparing agents') to allow a reduction in the dosage of cyclosporin while maintaining therapeutic blood cyclosporin concentrations. The use of a second drug to affect the pharmacokinetic profile of a primary drug is not new, but the use of cyclosporin-sparing agents is a departure from previous practices in that this coprescription is primarily for economic reasons. The decision to use these agents (and the choice of agent) is based upon economic and other factors including the extent of the cyclosporin-sparing effect, the potential for additional therapeutic benefit and/or adverse effects. The coprescription of cyclosporin-sparing agents is ethically more acceptable where the transplant recipient is the economic beneficiary but where the savings accrue to a third party it is more difficult. Benefits to the community at large must be balanced against the risk of adverse effects to the patient. The use of cyclosporin-sparing agents may reduce compliance and hence, jeopardise transplant and/or recipient outcomes. The transplant recipient must be informed about the reasons for their use and advised to consult an experienced physician or pharmacist before altering the established drug regimen.

Formulation of diltiazem affects cyclosporin-sparing activity

OBJECTIVE

To consider the effect of changing from a conventional release formulation of diltiazem to the controlled diffusion diltiazem formulation on the cyclosporin-sparing effect in kidney transplant recipients.

METHODS

Seven stable renal transplant recipients were studied on two separate occasions following at least 2 weeks stabilisation on either formulation. The order of administration of the two formulations was not randomised as all patients were already prescribed lower dosages of diltiazem before entering this phase of a larger study. The doses of diltiazem used were 90 mg (conventional release diltiazem) taken twice daily and 180 mg controlled diffusion diltiazem taken in the morning.

RESULTS

Whilst there were no overall significant differences between the two formulations, the study demonstrated considerable interpatient variability when changing to the controlled diffusion formulation, particularly following the morning cyclosporin dose, with three patients showing a reduced cyclosporin AUC (30-60%) and one an increased cyclosporin AUC of 36%.

CONCLUSION

A change in formulation of the cyclosporin-sparing agent may result in unpredictable alterations in cyclosporin concentrations and resultant clinical sequelae.

Survey of cyclosporin-sparing agent use in Australasian transplant centres

BACKGROUND

The co-prescription of drugs which elevate cyclosporin blood concentration has been advocated to reduce the costs associated with use of this expensive immunosuppressive drug. This is the first time that drugs have been widely prescribed for an economic purpose and while it is thought to be widespread, there are little published data on the extent of this practice in Australia and New Zealand.

AIMS

To determine the extent to which cyclosporin sparing agents are used by Australian and New Zealand organ transplant centres, to determine which agents are used and why these agents are used by some but not all centres.

METHODS

Organ transplant centres were surveyed via a questionnaire.

RESULTS

Considerable variation in use of cyclosporin sparing agents exists both within and across organ transplant types by Australian and New Zealand transplant centres. Diltiazem use is more widespread than ketoconazole.

CONCLUSIONS

Little of the variability in use of cyclosporin sparing agents can be explained by scientific considerations. While the central government benefits from the significant cost savings achieved by the use of cyclosporin sparing agents, individual transplant units may not. Transplant units may however be the major target in the event of litigation arising as a result of adverse effects. The availability of generic brands and improved formulations of cyclosporin may affect the viability of using cyclosporin sparing agents.

Diltiazem does not always increase blood cyclosporin concentration

The pharmacokinetic interaction between the calcium channel blocking drug, diltiazem (DTZ), the antifungal agent itraconazole (ICZ) and the immunosuppressive drug cyclosporin (CsA) was studied in a patient with a single lung transplant. The CsA area under curve estimations demonstrated a significant increase when ICZ was co-prescribed (5836 micrograms l-1 h vs 8159 micrograms l-1 h) but no increase when DTZ was co-prescribed with CsA (5836 micrograms l-1 h vs 5069 micrograms l-1 h). Despite widespread use as a CsA-sparing agent, DTZ does not always increase CsA concentrations.

Dextromoramide pharmacokinetics following sublingual administration

The extent of absorption and other pharmacokinetic parameters of dextromoramide following sublingual administration were assessed in five patients receiving chronic opioid analgesia. The use of the standard 5 mg tablet formulation was associated with negligible absorption in two patients, a prolonged time to peak concentration in the other three and substantial variability in clearance. The study concluded that the standard tablet formulation cannot be recommended for sublingual use where reliable, rapid onset analgesia is required.

Membrane depolarization induces calcium-dependent secretion of tissue plasminogen activator

Tissue plasminogen activator (tPA), a serine protease that converts inactive plasminogen to active plasmin, is produced in the rat and mouse hippocampus and participates in neuronal plasticity. To help define the role of tPA in the nervous system, we have analyzed the regulation of its expression in the neuronal cell line PC12. In control cultures, tPA activity is exclusively cell-associated, and no activity is measurable in the culture medium. When the cells are treated with depolarizing agents, such as KCI, tPA activity becomes detectable in the medium. The increased secreted tPA activity is not accompanied by an increase in tPA mRNA levels, and it is not blocked by protein synthesis inhibitors. In contrast, tPA release is abolished by Ca2+ channel blockers, suggesting that chemically induced membrane depolarization stimulates the secretion of preformed enzyme. Moreover, KCI has a similar effect in vivo when administered to the murine brain via an osmotic pump: tPA activity increases along the CA2-CA3 regions and dentate gyrus of the hippocampal formation. These results demonstrate a neuronal activity-dependent secretory mechanism that can rapidly increase the amount of tPA in neuronal tissue.

Hydration assessment during cold-weather military field training exercises

To quantify the magnitude of dehydration and to identify predictors of dehydration by utilizing changes in total body water (TBW), 24 male Marines were studied during an 8d moderately cold-weather (1-3 degrees C) training exercise. Training consisted of approximately 12 h/d of moderately intense activity. Variables examined included body composition, TBW, and various blood and urinary parameters indicative of hydration. Dietary food and fluid records were also maintained. Body composition changes were consistently with the high energy expenditure and insufficient energy intake. Despite a decrease in TBW, significant dehydration as assessed by blood and urinary parameters did not occur over the 8d period, therefore no relationships were found between TBW and any of the clinical indicators of dehydration. The change in TBW was reflective of a decrease in lean body mass. These data suggest that during cold-weather military field exercise, despite high activity levels and a negative energy balance, body fluid balance can be maintained when particular attention is paid to fluid intake.

Relationship between resistance of salmonids to furunculosis and recovery of Aeromonas salmonicida from external mucus

Fish were sampled at the Ed Weed State Fish Hatchery (South Hero, Vermont, USA) in September 1992. Aeromonas salmonicida was common, with concentrations as high as 10(5) to 10(7) colony-forming units per gram of mucus, and readily recovered from most mucus samples obtained from furunculosis-sensitive populations of brook trout (Salvelinus fontinalis), lake trout (Salvelinus namaycush), and Atlantic salmon (Salmo salar). The pathogen was the predominant microorganism and accounted for greater than 85% of the total number of bacteria isolated from the mucus of these fish. By comparison, A. salmonicida was recovered only from two rainbow trout (Oncorhynchus mykiss), and bacterial frequencies did not exceed 10(3) colony-forming units per gram of mucus. The pathogen was not recovered from the mucus of steelhead (O. mykiss) or Rome brown trout (Salmo trutta) selectively bred for resistance to furunculosis, even though there was widespread contagion throughout the hatchery and fish were cultured on a common, unprotected water supply.

Doubly labeled water measurement of human energy expenditure during exercise at high altitude

Estimates of total daily energy expenditure (TDEE) by the doubly labeled water (DLW, 2H(2)18O) and intake balance (I-B) methods were compared in six male soldiers studied over 6 days that included 5 days of strenuous winter exercise at 2,500- to 3,100-m elevation. Use of body energy stores [-9.54 +/- 1.54 (SD) MJ/day or -2,280 +/- 368 kcal/day] was estimated from changes in body weight, body density (hydrodensitometry), and total body water (H(2)18O dilution). The subjects wore computerized activity monitors and kept daily records of ration consumption (9.87 +/- 3.60 MJ/day or 2,359 +/- 860 kcal/day). Accuracy of individual DLW and I-B TDEE values was estimated from the correlations of TDEE with fat-free mass (FFM) or total weight (body wt + load). The DLW and I-B estimates of TDEE differed by -12.0 to 15.2% but provided comparable estimates of group mean TDEE (DLW = 19.07 +/- 2.37 MJ/day or 4,558 +/- 566 kcal/day; I-B = 19.41 +/- 3.72 MJ/day or 4,639 +/- 889 kcal/day; P > 0.05). The DLW TDEE was correlated with both FFM (r2 = 0.89, P < 0.01, power = 0.95) and total weight (r2 = 0.95, P < 0.01, power = 0.99), whereas I-B TDEE was correlated only with total weight (r2 = 0.75, P < 0.03, power = 0.81). Under adverse field conditions the DLW method provided individual TDEE estimates that were probably more accurate than those provided by the I-B method.

Novel nematocidal agents from Curcuma comosa

Curcuma comosa is a member of the economically important plant family, Zingiberaceae. A methanolic extract of C. comosa was shown to be nematocidal when tested against the free-living nematode Caenorhabditis elegans. Five diphenylheptanoids [1-5], one new and four known, have been isolated and shown to be responsible for the activity. This is the first report of three of these compounds [1, 2, 4] being isolated from a natural source.

Dopamine receptor antagonists increase markedly the quantity of retrograde transport of HRP in the rat masseteric motoneuron

Horseradish peroxidase (HRP) was injected, bilaterally, into the rat masseter muscle, subsequent to an intramuscular or intraperitoneal injection of one of five dopamine antagonists (chlorpromazine and haloperidol as the D1 and D2 receptor antagonist, SCH 23390 as the specific D1 receptor antagonist, sulpiride and domperidone as the specific D2 receptor antagonist). Control rats received an injection of a corresponding vehicle solution. After a survival period of 16 h, the brainstem was cut into 60 microns cryosections and processed with the TMB technique. The amount of retrogradely transported HRP was quantitatively measured in terms of the amount of HRP reaction product present in the motoneuron by the method which we have developed using an image processing system combined with a light microscope and a TV camera. Chlorpromazine, haloperidol, SCH 23390 and sulpiride significantly raised the quantity of retrograde transport of HRP. On the contrary, domperidone which can not penetrate the blood-brain barrier showed no significant change in the amount of the retrograde transport. In addition, an intravenous injection of chlorpromazine (8 mg/kg) was found to increase the amplitude of monosynaptic masseteric reflex EMG activity evoked by stimulations of the mesencephalic trigeminal nucleus. These results suggest that a possible regulatory system involving the dopamine receptor in the uptake and retrograde transport of HRP from axon terminals to cell bodies of the masseteric motoneuron exists in higher order neurons which make synaptic contact with the motoneuron.

The differentiation of the skin and its appendages. I. Normal development of papillary ridges

In the present study, the normal development of papillary ridges was studied in the volar pads of both fore and hindpaws of the opossum, Monodelphis domesticus. At birth, the developmental state of the opossum's paws is equivalent to that of a six-week human embryo. The development of papillary ridges in the opossum occurs entirely postnatally and the hindpaw lags behind the forepaw by at least four days in most developmental parameters. Papillary ridge formation is preceded by four events: skin innervation, Merkel cell differentiation, mesenchymal condensation, and epidermal proliferation. The apical pads at the tips of the digits and the interdigital pads between the heads of the metacarpals (or metatarsals) have a unique pattern of innervation and mesenchymal content as compared to the non-pad skin. Each pad is innervated by a prominent nerve trunk and axons ascend towards the epidermis providing a density of innervation that exceeds that in the non-pad epidermis. Merkel cells are absent in non-pad epidermis but present in the pads prior to the onset of formation of papillary ridges. A loose aggregation of mesenchyme forms the core of the pads and the superficial dermis is more cellular in the pads as compared to the equivalent dermis in surrounding non-pad skin. Developing papillary ridges always contained Merkel cell-axon complexes. Merkel cell axon complexes serve as the anatomical substrate of slowly adapting (SA) mechanoreceptors. The presence of these complexes during early skin differentiation is consistent with the use of the opossum's forepaw in climbing to the nipple, but also suggests other possible functions. We hypothesize that the nervous system might play a role in the timing or patterning of the formation of papillary ridges.

The differentiation of the skin and its appendages. II. Altered development of papillary ridges following neuralectomy

In order to test the hypothesis that the nervous system is an important determinant of skin differentiation, deletions of the left lumbosacral dorsal root ganglia (DRGs), the sources of cutaneous afferents to the left hindpaw, were performed on opossum pups at day 1 when hindpaws have just begun to be innervated. At birth, each lumbosacral DRG measures about 200 microns rostrocaudally and a deletion measuring 1 mm would span 4-5 DRGs. Following survival periods of 5-24 days, serial sections through the trunk documented partial left lumbosacral DRG deletion and a variable degree of spinal cord destruction. The blood supply to the trunk and hindpaws was preserved. Bilateral enlargement of residual DRGs was observed and regenerating skin at the site of the deletion was hyperplastic and hyperinnervated. The skin of the plantar pads of the hindpaws was studied following the neuralectomies. Statistically significant differences were observed between the left (experimental) and right (control) hindpaws. The density of innervation of the left hindpaw was reduced compared to the right hindpaw, development of papillary ridges was retarded by 3-4 days, and non-innervated Merkel cells were hypogranulated. This period of delay in ridge development is probably a reflection of the expansion of residual DRGs into the peripheral domains of deleted DRGs. The present study confirms a role for afferent nerves in the timing of cutaneous differentiation and a mutual trophic dependence between cutaneous nerves and Merkel cells in the epidermis.

Doubly labeled water measurement of human energy expenditure during strenuous exercise

The energy expenditures (EE) of 23 adult male Marines were measured during a strenuous 11-day cold-weather field exercise at 2,200- to 2,550-m elevation by both doubly labeled water (2H2 18O, DLW) and intake balance methods. The DLW EE calculations were corrected for changes in baseline isotopic abundances in a control group that did not receive 2H2 18O. Intake balance EE was estimated from the change in body energy stores and food intake. Body energy-store changes were calculated from anthropometric [-1,574 +/- 144 (SE) kcal/day] and isotope dilution (-1,872 +/- 293 kcal/day) measurements made before and after the field exercise. The subjects kept daily logbook records of ration consumption (3,132 +/- 165 kcal/day). Mean DLW EE (4,919 +/- 190 kcal/day) did not differ significantly from intake balance EE estimated from food intake and either anthropometric (4,705 +/- 181 kcal/day) or isotope dilution (5,004 +/- 240 kcal/day) estimates of the change in body energy stores. The DLW method can be used with at least the same degree of confidence as the intake balance method to measure the EE of active free-living humans.

Immunization against learned helplessness in the cockroach (Periplaneta americana)

Cockroaches exposed to one day of escapable shock prior to three days of inescapable shock did not become helpless on a shuttlebox-escape task. Like dogs and rats, cockroaches are immunized against learned helplessness by prior experience with escapable shock.

Yield loss assessments for cultivars of broccoli, lettuce, and onion exposed to ozone

The effects of the photochemical oxidant air pollutant ozone (O(3)) on growth and yield of three garden crops, broccoli (Brassica oleracea L.), lettuce (Lactuca sativa L.), and onion (Allium cepa L.) were studied in an open-top chamber experiment conducted in the field in southern California. Four cultivars each of leaf lettuce, broccoli, and globe onion were exposed to charcoal-filtered air (CF), non-filtered (NF) air, or NF plus 1.5 times ambient O(3) concentration from 4 weeks after germination in January or February until harvest. Exposures lasted 31 days for lettuce, 55 to 78 days for broccoli, and 105 days for onion. Results showed that despite severe O(3) injury to outer leaves, lettuce yields were not affected by O(3). Broccoli also was resistant to O(3) and no growth reduction was observed at ambient O(3) concentrations. Onions were more susceptible to O(3), but only one cv. 'Rio Bravo' had significant yield losses (ca. 5%) at ambient O(3) levels. These results suggest that, in general, concentrations of O(3) in the winter and spring may be below the threshold for adverse effects on yields of broccoli, lettuce and onion.

Innervation of the tooth pulp by the mesencephalic trigeminal nucleus in the cat: a retrograde horseradish peroxidase study

HRP was applied to the tooth pulp of 8 cats. Six were subjected to postoperative administration of the anti-inflammatory drug, prednisolone, whereas the remaining two were not. In all prednisolone-treated cats, labeled neurons were found in both the mesencephalic trigeminal nucleus and trigeminal ganglion, ipsilaterally. On the other hand, no labeled neurons were observed in the mesencephalic nucleus in cats receiving no steroid.

The morphogenesis of the posterior neural tube and tail in Monodelphis domesticus

The process of secondary neuralation has been studied in the Brazilian opossum, Monodelphis domesticus. Secondary neuralation in this mammal was found to have qualities of secondary neuralation that were present in both the chick and the mouse. In this study, four stages of secondary neuralation were found beginning with the medullary cord stage. Other stages in the differentiation of the secondary neural tube were: differentiation of the neuroepithelium, cavitation of the medullary cord, and proliferation of the neural tube. The process of secondary neuralation proceeded in a rostral-to-caudal direction and was found to be independent of age. Diastematomyelia (doubling of the tube) was found in several animals. The process of cavitation was completed by the joining of several small, focal cavities in a rostral-to-caudal direction. The most distinctive feature of secondary neuralation in this animal was the finding of axons within the secondary neural tube, a feature not characteristic of either the chick or the mouse.