Species differences in the pharmacokinetics and metabolism of reparixin in rat and dog.

The pharmacokinetics and metabolism of reparixin (formerly repertaxin), a potent and specific inhibitor of the chemokine CXCL8, were investigated in rats and dogs after intravenous administration of [14C]-reparixin L-lysine salt. Protein binding of reparixin was investigated in vitro in rat, dog, rabbit, cynomolgus monkey and human plasma. Plasma protein binding of reparixin was >99% in the laboratory animals and humans up to 50 microg ml-1, but lower at higher concentrations. Although radioactivity was rapidly distributed into rat tissues, Vss was low (about 0.15 l kg-1) in both rat and dog. Nevertheless, reparixin was more rapidly eliminated in rats (t1/2 approximately 0.5 h) than in dogs (t1/2 approximately 10 h). Systemic exposure in dog was due primarily to parent drug, but metabolites played a more prominent role in rat. Oxidation of the isobutyl side-chain was the major metabolic pathway in rat, whereas hydrolysis of the amide bond predominated in dog. Urinary excretion, which accounted for 80-82% of the radioactive dose, was the major route of elimination in both species, and biotransformation of reparixin was complete before excretion.

Absorption, distribution, metabolism and excretion of the cholecystokinin-1 antagonist dexloxiglumide in the dog.

Single oral doses of 14C-dexloxiglumide were rapidly and extensively absorbed in dogs and also eliminated rapidly with a short half-life. Following single intravenous doses, dexloxiglumide was characterised as a drug having a high clearance (30.7 and 27.0 ml/min/kg in males and females respectively), a low volume of distribution (Vss, 0.34 and 0.27 L/kg in males and females respectively) and a moderate systemic availability (about 33%). It was extensively bound to plasma proteins (89%). Dexloxiglumide is mainly cleared by the liver. Its renal clearance was minor. In only the kidney, liver and gastrointestinal tract, were concentrations of 14C generally greater than those in plasma. 14C concentrations generally peaked at 0.25h and declined rapidly during 24h being present only in a few tissues (such as the kidney, liver and gastrointestinal tract) at 24h. Single intravenous or oral doses were mainly excreted in the faeces (77-89%), mostly during 24h. Urine contained up to 7.5% dose. Mean recoveries during 7 days ranged between 93-97%. Biliary excretion of 14C was prominent (64% dose during 24h) in the disposition of 14C which was probably also subjected to some limited enterohepatic circulation. Unchanged dexloxiglumide was the major component in plasma. Urine and faeces contained several 14C-components amongst which unchanged dexloxiglumide was the most important (eg. about 55% dose in faeces). LC-MS/MS of urine and bile extracts showed that dexloxiglumide was metabolised mainly by O-demethylation and by conjugation with glucuronic acid.

Absorption, distribution, metabolism and excretion of the cholecystokinin-1 antagonist dexloxiglumide in the rat.

Single oral doses of 14C-dexloxiglumide were rapidly and extensively absorbed in rats, and eliminated more slowly by females than by males. The respective half-lives were about 4.9 and 2.1 h. Following single intravenous doses, dexloxiglumide was characterised as a drug having a low clearance (6.01 and about 1.96 ml/min/kg in males and females respectively), a moderate volume of distribution (Vss, 0.98 and about 1.1 L/kg in males and females respectively) and a high systemic availability. It was extensively bound to plasma proteins (97%). Dexloxiglumide is mainly cleared by the liver. Its renal clearance was minor. In only the liver and gastrointestinal tract, were concentrations of 14C generally greater than those in plasma. Peak 14C concentrations generally occurred at 1-2 h in males and at 2-4 h in females. Tissue 14C concentrations then declined by severalfold during 24 h although still present in most tissues at 24 h but only in a few tissues (such as the liver and gastrointestinal tract) at 168 h. Decline of 14C was less rapid in the tissues of females than in those of males. Single intravenous or oral doses were mainly excreted in the faeces (87-92%), mostly during 24 h and more slowly from females than from males. Urines contained less than 11% dose. Mean recoveries during 7 days when 14C was not detectable in the carcass except in one female rat ranged between 93-101%. Biliary excretion of 14C was prominent (84-91% dose during 24 h) in the disposition of 14C which was also subjected to facile enterohepatic circulation (74% dose). Metabolite profiles in plasma and selected tissues differed. In the former, unchanged dexloxiglumide was the major component whereas in the latter, a polar component was dominant. Urine, bile and faeces contained several 14C-components amongst which unchanged dexloxiglumide was the most important (eg. up to 63% dose in bile). LC-MS/MS showed that dexloxiglumide was metabolised mainly by hydroxylation in the N-(3-methoxypropyl)pentyl sidechain and by O-demethylation followed by subsequent oxidation of the resulting alcohol to a carboxylic acid.

Pharmacokinetics and metabolism of the anti-oestrogen droloxifene in female human subjects.

1. Single oral doses of a solution formulation of (14)C-droloxifene citrate (141 mg) appeared to be rapidly and well absorbed in four post-menopausal female subjects. Peak plasma concentrations (C(max)) of total (14)C (1260 ng eq. ml(-1)), droloxifene (196 ng ml(-1)) and the major metabolite droloxifene glucuronide (851 ng eq. ml(-1)) occurred at 0.9-1.1 h (T(max)) and declined bi-exponentially with terminal half-lives of 45.0, 31.6 and 32.0 h respectively. The mean AUCs of droloxifene and the major metabolite were 21 and 37% respectively that of total (14)C. 2. Total (14)C was excreted slowly, mainly in the faeces. Mean totals of 6.6 and 90.3% of the dose were excreted in the urine and faeces respectively during 11 days. The data were consistent with biliary excretion and enterohepatic circulation of the major metabolite, droloxifene glucuronide. 3. GC-MS showed that the major (14)C-components in 0-24-h urine were droloxifene (mean 0.4% dose) and its glucuronide (2.3% dose), and in faeces were droloxifene (60.2% dose) and N- desmethyldroloxifene (4.2% dose). Other components in faeces corresponded chromatographically to reference standards, droloxifene N-oxide (1.9% dose), side-chain hydroxylated droloxifene (dimethylamine moiety of droloxifene side-chain replaced by hydroxyl, 1.3% dose) and droloxifene glucuronide (10.7% dose). The latter was resistant to enzymic hydrolysis by the beta-glucuronidase used. 4. Intersubject variability in the pharmacokinetics of droloxifene in this study was relatively low (CV < 20% for AUC and half-life).

Oxidative damage to DNA in patients with cystic fibrosis.

Patients with cystic fibrosis (CF) may be more susceptible to oxidative-cell injury due to impaired absorption of dietary-antioxidants. In addition, recurring pulmonary infections regularly subject them to oxidative stress. Our objective was to determine whether the concentration of urinary 8-hydroxydeoxyguanosine (oh8dG), a marker of free radical-induced DNA damage, is elevated in CF patients and to correlate its excretion with clinical status. The first morning void of urine was collected from 13 CF patients and 10 control children of similar age. To determine clinical status, forced expiratory volume (FEV1) and forced ventilatory capacity (FVC) and a Taussing-Schwachman score were obtained for each patient. Urinary oh8dG was measured by high performance liquid chromatography (HPLC) with electrochemical detection and the concentration normalized against creatinine concentration. The mean concentration (+/- SD) of urinary oh8dG was significantly higher in the CF group (2.78 +/- 1.21 vs. 1.51 +/- 0.38 nmol/mmol creatinine). A significant positive correlation was found between urinary oh8dG concentration and plasma alpha-tocopherol concentration in the CF patients (r = 0.947, p = 0.0001), suggesting that vitamin E might be involved in the excretion of oh8dG. However, no correlation was found between urinary oh8dG in CF and markers of lung function or the qualitative index of clinical status. These results confirm that patients with CF are susceptible to oxidative-induced DNA damage, although this appears to be independent of clinical status. Increased DNA damage may explain, in part, why CF patients have a higher incidence of malignancy compared to normal healthy age-matched controls.

Evidence for the involvement of oxygen-derived free radicals in ischaemia-reperfusion injury.

Six patients undergoing vascular reconstructive surgery were examined for evidence of oxygen-derived free radical (ORF) damage to the protein, immunoglobulin G (IgG). OFR damage was determined as an increase in the fluorescence (ex 360 nm em 454 nm) to ultraviolet absorption (280 nm) ratio of IgG, representing N-Formyl kynurenine and other as yet unidentified fluorophores. The IgG ratio was found to increase slightly during ischaemia and to undergo marked elevation upon reperfusion (275 +/- 405% baseline value at 40 min post-clamp; mean +/- sd). A high ratio was maintained post-reperfusion, even after 60 min reperfusion. Determination of thromboxane B2, (TXB2), leukotriene B4, (LTB4) and 6-keto prostaglandin F1 alpha, (PGF1a), revealed a decrease in their concentrations during ischaemia and a transient, marked increase on reperfusion. Only TXB2 concentrations were found to correlate with the IgG ratio (negative correlation, p < 0.05). No correlation was observed between von Willebrand antigen factor, a marker of endothelial cell damage and fluorescent IgG ratio. However, levels of the factor increased slightly during ischaemia and more sharply upon reperfusion. These preliminary results therefore suggest that a more likely source of the OFRs responsible for IgG damage is endothelial cell xanthine oxidase, rather than cyclo-oxygenase or lipoxygenase.

Hemodialysis and iopamidol clearance after subclavian venography.

RATIONALE AND OBJECTIVES: The dialyzability of iopamidol is unknown and was investigated in patients undergoing long-term hemodialysis for chronic renal failure. METHODS: Ten patients received 30 ml Niopam 300 (Bracco SpA, Milan, Italy) (identical to 18372 mg iopamidol) intravenously into a forearm vein to investigate for occult subclavian stenosis. RESULTS: The elimination half-life of iopamidol before hemodialysis was 69.6 hours and during 4 hours of hemodialysis was 3.5 hours. A single 4-hour hemodialysis cleared 55.7% (95% Ci 51-5-59.8) of the administered dose, while second and third dialyses cleared 25.3% (95% Ci 21.4-29.1) and 10.1% (95% Ci 7.7-12.6) of the administered dose, respectively. Two patients with significant residual urine excretion excreted more than 10% of the administered dose in the urine. For anuric patients, extrarenal clearance provided total body clearance of up to 0.266 L/hr. CONCLUSIONS: Hemodialysis is a rapid and efficient means of clearing iopamidol provided it is performed soon after the contrast study.

Clearance of iopamidol, a non-ionic contrast medium, by CAPD in patients with end-stage renal failure.

In normal healthy subjects radiographic contrast media are cleared by the kidneys with a half-life of approximately 2 h and a total body clearance of 8 l/h. The mechanism of contrast clearance has not been previously investigated in chronic renal failure patients undergoing continuous ambulatory peritoneal dialysis (CAPD). A study was undertaken to investigate the pharmacokinetics of a non-ionic water soluble radiographic contrast medium (iopamidol) in 10 patients stabilized on CAPD. All patients (eight male, two female) aged 22-68 years (median 53 years) had injection of 30 ml of iopamidol 300 via a forearm vein to investigate subclavian vein patency following previous cannulation for haemodialysis. Venous blood samples, CAPD dialysate and urine were collected for seven days post injection. The mean plasma half-life was 37.9 h (SD 10.6) (range 24.1-57.2 h) for the CAPD patients and was greatly prolonged in comparison to healthy subjects. The total body clearance of iopamidol was also greatly reduced (0.377 l/h). CAPD removed an average of 53.6% of the administered dose (range 36.3-80.8%) whilst an average of 26.9% was excreted in the urine (range 1.3-56.3%). The combined renal and dialysate clearance was up to 93% of the administered dose over the period of the study. There is therefore some evidence for a small extra renal clearance of iopamidol in end-stage renal failure patients. This study has shown for the first time that patients with end-stage renal failure undergoing CAPD have significantly delayed elimination of contrast medium. This should be taken into consideration when extensive or prolonged investigations using contrast medium are proposed.

Effect of sulphasalazine on antibody response to oral antigen.

Cholera toxin was orally administered to mice concurrently receiving sulphasalazine (SASP) dissolved in L-lysine, or a control substance (L-lysine alone). Circulating antibodies to cholera toxin of IgM, IgG and IgA class were determined by direct ELISA at day 7, 14, 21 and 28. Although both groups made a significant antibody response to the antigen, mice receiving SASP tended to produce lower levels. These were significant for IgA on day 21 (P = 0.013), and for days 7-28 (P = 0.009), and 14-28 (P = 0.007). Overall, considering all antibody classes together from day 7 to 28, there was a significant effect in the SASP treated group (P = < 0.04). It appears that SASP exerts a mild immunomodulatory effect on the mucosal immune system. Further work is obviously required to substantiate these findings. The effect on the gut mucosal immune system of a drug known to ameliorate rheumatoid arthritis may offer an insight into the aetiopathogenesis of this disease.

Possible protein binding displacement interaction between glibenclamide and metolazone.

The effects of metolazone on the protein binding of glibenclamide were studied. It was found that increasing metolazone concentrations up to 100 ng/ml had no significant effect on the protein binding of glibenclamide studied at 10 micrograms/ml. Metolazone is unlikely to cause a clinically significant increase in the free fraction of glibenclamide in patients receiving both drugs.

Variable metabolism of pinacidil: lack of correlation with the debrisoquine and trimethylamine C- and N-oxidative polymorphisms.

1. The urinary excretion of pinacidil and its N-oxide in man was found to vary over a five-fold range. 2. Studies in individuals with inherited deficiencies for C-hydroxylation (debrisoquine type) and trimethylamine N-oxidation showed that the N-oxidation of pinacidil did not co-segregate with these oxidative polymorphisms. 3. It is concluded that the variable N-oxidation of pinacidil is most likely to be due to variations in the activity of the P-450 isozymes rather than in the microsomal flavoprotein containing mixed-function amine oxidase of Ziegler which is considered to be responsible for the N-oxidation of trimethylamine.

The effect of ageing on the pharmacokinetics of dihydrocodeine.

Although poor renal function reduces clearance of dihydrocodeine in man, and renal impairment occurs with ageing, no significant differences occurred in the handling of single doses of dihydrocodeine between elderly patients and young, normal subjects. After multiple dosing, the maximum concentration was significantly different between the groups, being higher in the elderly. The increase in the area under the curve in the elderly was 25% greater than in the young on chronic therapy. This difference was not statistically significant, but was likely to be of clinical significance. The elderly patients' mean creatinine clearance (61.8 ml per min) was significantly lower than that in the young (137 ml per min), and there was a significant correlation between the half-life at single dosing and the blood urea concentration. Variability in all measurements was marked in both groups, and hence no clear guidelines can be given on therapeutic dosing. The small initial dose with alterations thereafter depending on clinical effect is the best advice.

Accumulation of pinacidil N-oxide during chronic treatment with pinacidil.

The effects of acute and chronic administration of a slow-release preparation of pinacidil have been studied in eight normotensive volunteers aged 40-57 years. Continuous administration of 20 mg b.i.d. pinacidil had no effect on serum pinacidil concentrations measured as AUC (0-9 h), but accumulation of the principal metabolite, pinacidil pyridine-N-oxide was found to occur. There were no significant changes in erect and supine blood pressure and heart rate from the pretreatment levels on days 1,15 or 29. Chronic administration of pinacidil caused a significant increase in weight over the total period of study. There were also significant changes in mean sodium (+2.38 mmol/l) and alkaline phosphatase (+15.75 iU/l) from the start to the end of pinacidil therapy but values were within the normal ranges, except for one alkaline phosphatase. There were significant changes in the following haematological parameters over the period of pinacidil therapy; leukocytes (-1.49 x 10(9)/l), haemoglobin (-0.56 g/dl), MCH (-1.1 pg), MCHC (-1.22 g/dl), platelet MCV (-0.90 fl).

Effects of food on the bioavailability of sustained-release pinacidil in humans.

The effects of a standard breakfast meal on the bioavailability of a sustained-release tablet formulation of pinacidil [(+/-)-2-cyano-1- (4-pyridyl)-3-(1,2,2-trimethylpropyl)guanidine monohydrate) were investigated in eight healthy volunteers. Concomitant food intake resulted in significantly increased maximum measured serum pinacidil concentrations, Cmax, (172 +/- 21 versus 102 +/- 49 ng/mL, p less than 0.05), and relative bioavailability, measured as AUCo-infinity (904 +/- 189 versus 697 +/- 279 ng.h/mL, p less than 0.05). The time to maximum serum concentration (tmax) was not affected by food (2.3 +/- 1.3 versus 3.3 +/- 1.2 h, p greater than 0.05), and the terminal elimination half-life, (t1/2z) was significantly decreased (4.7 +/- 2.2 versus 2.3 +/- 0.4 h, p less than 0.05).

Effects of formulation on the pharmacokinetics of orally administered pinacidil in humans.

Serum concentrations, relative bioavailability, and urinary excretion of pinacidil [(+/-)-2-cyano-1-(4-pyridyl)-3-(1,2,2-trimethylpropyl) guanidine monohydrate] from two sustained-release oral formulations (tablet and capsule) were compared in 12 healthy volunteers. Maximum measured serum concentrations (Cmax) from the sustained-release tablet and capsule did not differ significantly (75 +/- 17 versus 70 +/- 14 ng/mL, p greater than 0.05), but the time to achieve maximum concentration (tmax), was longer for the capsule (2.4 +/- 1.8 versus 0.98 +/- 0.5 h, p less than 0.05). There was no significant difference in bioavailability between the formulations, as measured by the area under the concentration-time curve (AUC0-8 h; 279 +/- 99 versus 311 +/- 85 ng.h/mL, p greater than 0.05). Twenty-four hour urinary excretion of both pinacidil and its major metabolite, pinacidil pyridine-N-oxide, was similar for both tablet and capsule preparations (3.9 +/- 1.2 and 55 +/- 19% versus 4.4 +/- 1.0 and 55 +/- 14%, respectively, of the administered dose, p greater than 0.05).

The pharmacokinetics of timegadine and two of its metabolites after multiple oral dosing, and the effects of concomitant administration of ibuprofen.

A 250 mg tablet of timegadine was given twice daily for 15 days to 13 healthy volunteers. On Day 16 a single morning dose of timegadine was supplemented by two 200 mg tablets of a proprietary brand of ibuprofen. Serum concentrations of timegadine were measured by high pressure liquid chromatography, and steady state was achieved between Days 5 and 8. Serum concentrations of two metabolites of timegadine, MI and MII were measured by thin layer chromatography by Leo Pharmaceutical Products, Denmark. Ibuprofen did not significantly affect the serum half-time of timegadine, but did reduce the maximum measured serum timegadine concentration, the area under the serum concentration versus time curve and the time to achieve maximum measured serum concentration. Serum liver enzymes remained within the normal ranges and there were no changes in hepatic microsomal enzyme activity as assessed by urinary excretion of D-glucaric acid.

Pharmacokinetics and beta-blocking effects of timolol in poor and extensive metabolizers of debrisoquin.

We studied the pharmacokinetics and beta-blocking effects of a single, oral 20 mg dose of timolol in six poor metabolizers (PMs) and six extensive metabolizers (EMs) of debrisoquin. The plasma timolol concentration was significantly higher in PMs than in EMs. There was a fourfold difference in mean AUC (1590 +/- 1133 vs. 394 +/- 239 ng X hr/ml; P less than 0.01) and a twofold difference in mean t1/2 (7.5 +/- 3 vs. 3.7 +/- 1.7 hours; P less than 0.01), reflecting differences in oral clearance (13.1 +/- 7.8 vs. 48.5 +/- 23.2 L/hr; P less than 0.01). The degree of beta-blockade was greater in PMs than in EMs at 12 hours (30.9% vs. 18.2%; P less than 0.05) and at 24 hours (28.3% vs. 13.1%; P less than 0.05). In the group as a whole the metabolic ratio correlated positively with both kinetic data and beta-blockade, but some overlap was observed. Hence timolol metabolism appears to be subject to debrisoquin-type polymorphism, which results in interphenotypic variation in plasma concentration and beta-blocking effect.

Serum concentrations and urinary excretion of pinacidil and its major metabolite, pinacidil pyridine-N-oxide following i.v. and oral administration in healthy volunteers.

Serum concentrations of pinacidil and its major metabolite pinacidil pyridine-N-oxide were determined following administration of both an intravenous solution and a sustained release oral preparation to healthy volunteers. Mean bioavailability of pinacidil was 57.1 +/- 13.7%. Following intravenous administration, the mean AUC0-8 h metabolite/AUC 0-8 h pinacidil ratio was 0.559 +/- 0.272 and after oral administration, 0.825 +/- 0.656. Only one subject had serum metabolite concentrations in excess of pinacidil during the intravenous study whereas three subjects achieved metabolite concentrations in excess of pinacidil during the oral study. The mean serum elimination half-life of metabolite was significantly longer than parent drug following intravenous administration (P less than 0.01) but not after oral administration. No significant difference was found in the maximum measured metabolite concentration (Cmax.m) between the studies. The time to Cmax.m was significantly delayed (P less than 0.001) following oral dosage. Twenty four hour urinary excretion of metabolite was significantly increased (P less than 0.001) following oral administration whilst that of pinacidil was decreased (P less than 0.02). These results suggest that pinacidil pyridine-N-oxide may be a 'first-pass' metabolite of pinacidil. In most patients pinacidil pyridine-N-oxide is unlikely to contribute significantly to the hypotensive effect of pinacidil.

The protein binding of timegadine determined by equilibrium dialysis.

The protein binding of timegadine to albumin, serum, plasma and plasma enriched with the acute phase reactants alpha 1-acid glycoprotein, alpha 1-anti-trypsin and C-reactive protein was determined by equilibrium dialysis. The effects of other analgesic and anti-inflammatories (indomethacin, ketoprofen, paracetamol and sodium salicylate) and other basic drugs (disopyramide, lignocaine, propranolol and quinidine) on the binding of timegadine were also determined. Timegadine binding was concentration-dependent up to 0.5 micrograms/ml, but independent above this level up to 10.0 micrograms/ml, the mean and standard error being 93.8 +/- 0.5%. Albumin accounted for only 32.4% of timegadine bound to plasma. Plasma enrichment with the acute phase reactants led to significant increases in timegadine binding. Simultaneous dialysis with other drugs caused significant decreases in timegadine binding.