The influence of cisapride and clarithromycin on QT intervals in healthy volunteers.

OBJECTIVE: Recently a few cases of long QT syndrome were reported during treatment with cisapride. In most of these cases, risk factors for cardiac arrhythmias or pharmacologic interactions might have been involved, and the role of cisapride remained unclear. Macrolides such as clarithromycin potentially interact with the metabolic elimination of cisapride and have overlapping indication areas. We therefore studied whether combined treatment with clarithromycin and cisapride leads to pharmacokinetic changes and increased QT intervals. METHODS: The study was an open, randomized, 2-way crossover study with washout periods of 1 week. Twelve healthy volunteers were recruited. Treatments were cisapride (10 mg 4 times a day) for 10 days with concomitant clarithromycin (500 mg twice a day) from days 6 through 10, or clarithromycin (500 mg twice a day) for 10 days combined with cisapride (10 mg 4 times a day) from days 6 through 10. Frequent ECG recordings were performed for 24 hours before drug treatment (baseline). After 5 days of monotherapy and combination therapy, frequent ECG recordings and assessments of plasma drug levels were performed for 24 hours. RESULTS: Clarithromycin alone was associated with a minimal increase in QTc intervals. Monotherapy with 10 mg cisapride 4 times a day led to a concentration-dependent QTc elevation, amounting to 6 ms during steady state. Combination of cisapride and clarithromycin caused an average QTc increase of 25 ms above pretreatment values and 3-fold increases in cisapride concentrations. CONCLUSIONS: QTc elevations after cisapride or clarithromycin alone remained within the normal range of diurnal variation. Coadministration of cisapride and clarithromycin produced a substantial QT prolongation. The data support the recently purported interaction between cisapride and clarithromycin and thus the filed contraindication to combine these drugs.

Hepatic cytochrome P450 induction in goats. Effects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels.

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with beta-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2-3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16 alpha-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA probe, rather than with a rat 3A1 probe. BNF selectively induced EROD, whereas TST hydroxylation and ETM dealkylation were inhibited. With BNF-treated animals, increased concentrations of a protein cross-reactive with anti-rat P450 1A1/1A2 and of an mRNA that showed homology with a human 1A1 cDNA probe, but not with a mouse 1A1/1A2 probe, were observed.

Cytochrome P450 induction and metabolism of alkoxyresorufins, ethylmorphine and testosterone in cultured hepatocytes from goats, sheep and cattle.

Very little is known of cytochrome P450 (P450) patterns and enzyme characteristics in food-producing animal species. Oxidative metabolism of alkoxyresorufins, ethylmorphine (EtM) and testosterone (TST) was used to monitor the effects of the P450 inducers phenobarbital (PB), beta-naphthoflavone (BNF), dexamethasone (DEX) and triacetyloleandomycin (TAO) in primary cultured hepatocytes from goats, sheep and cattle. BNF effectively and specifically induced ethoxyresorufin deethylase (> 20-fold), indicating the presence of an inducible P450 1A form, and down-regulated EtM demethylation and most selected TST hydroxylations. In non-induced hepatocyte cultures, TST was metabolized to 6 beta-, 2 beta-, 12 beta-, and 11 alpha-hydroxy-TST (OHT). PB and, to a lesser extent, DEX non-specifically induced all OHT formations, and EtM demethylation. TAO almost completely inhibited OHT formation and EtM demethylation. These results indicate the involvement of principally one P450 form, or a restricted number of related P450 forms, presumably belonging to the P450 3A subfamily. In western blot analysis, cross reactivity was found with rat anti-P450 3A1 and anti-sheep P450 3A. A more specific PB effect was observed for 16 alpha-OHT, which may be formed though a ruminant P450 2B form. None of the inducers influenced pentoxyresorufin depentylase (PROD) or EtM O-deethylation. Metabolite patterns and inducibility of selected activities in ruminant hepatocytes are in accordance with previous findings in goats in vivo. Cytochrome P450 characteristics in ruminants appear to differ from those in rats whereas similarities to the situation in humans appear to exist.

Induction of hepatic drug metabolizing enzymes and interaction with carbon tetrachloride in rats after a single oral exposure to atrazine.

A single oral dose (430 mg/kg) of atrazine, a widely employed s-triazine herbicide, was administered to young male rats. There was a significant increase of the in vivo elimination of hexobarbital and a significant induction of the activity of 7-pentoxyresorufin-O-dealkylase, while cytochrome P-450 content and other mixed function oxidase activities remained unaltered. The administration of carbon tetrachloride (CCl4) to atrazine pretreated rats did not substantially augment the impairment of drug metabolizing enzymes brought about by CCl4 alone. Results suggest that atrazine behaves like a relatively weak inducer of phenobarbital-inducible families of cytochrome P-450.

Primary bovine hepatocytes in the study of cytokine induced acute-phase protein secretion in vitro.

To investigate the utility of primary cultures of bovine hepatocytes for compartmentalized acute phase protein studies the secretion of serum amyloid-A (SAA) and haptoglobin (Hp) was measured after stimulation by pro-inflammatory cytokines (recombinant human IL-6 (rhIL-6) and recombinant human tumour necrosis factor-alpha (rhTNF-alpha)). During the incubation period of the experiment, the SAA and Hp secretion into the culture medium increased (P < 0.05). SAA concentrations showed an additional increase following treatment with each of the cytokines (P < 0.01). Hp concentrations remained unchanged, whereas incubation with a combination of both resulted in a significant increase of the medium concentration of both SAA (P < 0.01) and Hp (P < 0.05). From these findings it is concluded that primary bovine hepatocytes can be used for in vitro studies on acute-phase protein secretion.

Characterization of cytochrome P450 isoenzymes in primary cultures of pig hepatocytes.

Despite the fact that pigs are increasingly used in pharmacological and toxicological studies, knowledge on the enzymes which metabolize xenobiotics, in particular cytochrome P450 (CYP) enzymes, in pigs is still very limited. Primary cultures of pig hepatocytes were used to characterize CYP enzymes. The characterization was performed at the level of enzymatic activities, apoprotein and mRNA analyses. Enzyme inducers investigated were beta-naphthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX) and rifampicin (RIF). After 48hr of BNF treatment, CYP1A protein and mRNA levels were increased, and ethoxyresorufin O-deethylation and caffeine 3-demethylation were strongly induced. PB and RIF increased the levels of CYP3A apoprotein and mRNA, whereas BNF down-regulated CYP3A and related activities. PB and RIF treatment resulted in increased ethylmorphine N-demethylation and testosterone hydroxylation, which appears to be the result of CYP3A induction. Hybridization of pig RNA with a human CYP2C9 cDNA probe showed a PB and RIF inducible CYP, which was down-regulated by BNF. Similar inducing effects were observed for tolbutamide, a marker substrate for CYP2C. DEX was not a potent inducer, although some induction of CYP3A mRNA was observed. The present results indicate the absence of CYP2B and probably CYP2D enzymes and activities in pig liver. Despite some dissimilarities, the results indicate that pigs, apart from their very human-like physiology, might represent a more appropriate model species for oxidative drug metabolism in humans than rats.

The influence of nitrite, nitrate and nitric oxide on ammonia use and urea production in primary cultures of sheep hepatocytes.

Inorganic nitrite introduced into the living organism is rapidly converted into nitrate and nitric oxide (NO). It is known that nitrite decreases ammonia use and urea formation in vitro and it seems that nitrite also influences these processes in vivo. However, the mechanism underlying this effect is not known. Therefore, we decided to compare the influence of sodium nitrite (NaNO(2)), sodium nitrate (NaNO(3)) and NO on ammonia use and ureagenesis in monolayer cultures of sheep hepatocytes during 18 hr of cultivation. It was found that 0.5 and 2.5 mmNaNO(2) significantly reduced ammonia use in a dose-dependent manner for the first 6 hr of incubation; at higher concentrations (2.5 mm), it also decreased urea formation. Also, the presence of nitrite did not affect the lactate dehydrogenase (LDH) activity in the medium which indicates that the nitrite effect did not result from its cytotoxic action. NaNO(3) (0.5 and 2.5 mm) did not induce any changes in ammonia use and urea synthesis in hepatocytes. With sodium nitroprusside (SNP) (0.001, 0.01, 0.1, 0.5 and 1.0 mm) a decrease of ammonia use and urea production was observed corresponding to the nitrite effect, but contrary to nitrite exposure these changes in metabolism were persistent during the whole cultivation period. On the other hand, potassium cyanide (KCN) (0.1 and 0.5 mm) did not influence either urea formation or ammonia use. Thus, it can be concluded that in isolated hepatocytes nitrate and/or NO are not the mediators of nitrite effects on nitrogen metabolism. Furthermore, there is no evidence that nitrite effects are mediated by impaired mitochondrial respiration and energy production.

Epidemiological assessment of rinderpest surveillance and control in Uganda between 1990 and 1998.

Based on passive and active data, we report on an epidemiological assessment of surveillance and control of rinderpest (RP) in Uganda between 1990 and 1998. Active data were collected by administration of questionnaires to animal health personnel and their auxiliaries and to stockowners in six selected districts of eastern and northeastern Uganda. Passive data were extracted from vaccination and seromonitoring reports, and from field and laboratory reports. RP events were classified as "confirmed outbreaks", "suspected outbreaks" and "rumours". The classification of 56% of the RP events as "suspected outbreaks" indicates the difficulty in investigating disease outbreaks in Uganda. Although vaccination coverage and seroprevalence were <85% (the recommended target), they nevertheless corresponded well-reflecting effective vaccination. However, because of the low seroprevalence, a sizable population of cattle in Uganda remained at risk of RP. The agreement between the local and national disease reporting systems was low-to-moderate (kappa=0.39); this indicates inefficiency in disease reporting. Risk factors for RP outbreaks were cattle raids and communal grazing. Based on overlaid thematic maps of seroprevalence, vaccination coverage and RP events, close spatial and temporal associations were observed between cattle raids, transhumance and outbreaks and rumours. The high-risk areas were in the eastern and northeastern parts of the country. The results of this study support a phase approach of following the OIE pathway.

Rinderpest surveillance performance monitoring using quantifiable indicators.

This paper describes an objective system of monitoring the performance of disease surveillance. The system was developed through dialogue with a number of countries in Africa and adopted as part of the Global Rinderpest Eradication Programme of the Food and Agriculture Organization of the United Nations. The performance monitoring system uses a clinical stomatitis-enteritis case definition, an outbreak investigation classification scheme, and a series of eight performance indicators to measure the sensitivity, specificity and timeliness of the surveillance system. Field-testing indicates that the approach is successful when good record-keeping is practiced and highlights the importance of dialogue in helping to ensure that the system is simple and acceptable. The system provides a quantitative measure of the efficacy of national disease surveillance programmes and of the quality of data derived from such programmes for use in international disease control, animal health information exchange and trade risk analysis.

Comparative aspects and sex differentiation of plasma sulfamethazine elimination and metabolite formation in rats, rabbits, dwarf goats, and cattle.

Plasma disposition and urinary recovery of sulfamethazine (SMZ), its N4-acetylated metabolite (N4AcSMZ), and 2 of its hydroxylated metabolites--5-hydroxysulfamethazine (5OHSMZ) and 6-hydroxymethylsulfamethazine (6CH2OHSMZ)--were determined in either sex of 4 animal species: rats, dwarf goats, rabbits, and cattle. Rats, rabbits, and dwarf goats had significant (P < 0.01) sex difference in SMZ plasma clearance. Male rats had higher plasma clearance than did female rats, and excreted higher amounts of the hydroxy metabolites and lower amounts of N4AcSMZ. The N4AcSMZ metabolite was predominant in plasma and urine of rabbits. Male rabbits had higher plasma clearance than did female rabbits, but differences in metabolite profile were not apparent. With regard to plasma SMZ elimination, the situation in goats was opposite to that in rats. Male goats had considerably lower clearance than did female goats. This was associated with a lower hydroxylation rat in males. Plasma half-life of SMZ in cows was lower than that in bulls, probably because of a smaller distribution volume in cows. Compared with elimination via urine, elimination via milk was negligible in cows. Significant differences in metabolite profiles were not found between bulls and cows. Similar to those in rats and mice, hormone-dependent xenobiotic metabolic pathways may exist in other species. Depending on species and xenobiotic compound residue concentrations of xenobiotics, their metabolites, or both may differ with sex of the animal, or may be altered after treatment with anabolic hormones.