Role of P-glycoprotein in colchicine and vinblastine cellular kinetics in an immortalized rat brain microvessel endothelial cell line

Uptake and efflux of colchicine and vinblastine, whose effects are related to their high-affinity binding to tubulin, were studied in the immortalized rat brain microvessel endothelial cell line RBE4. At 10 nM extracellular drug concentration, uptake equilibrium was approached at 45 hr for colchicine, but at only 3.5 hr for vinblastine. After 1 hr preincubation with 200 nM colchicine or vinblastine, drug efflux fitted biexponential kinetics with an initial fast phase (half-life = 2.2 min and 9.6 min, respectively) and a later slow phase (half-life = 3.6 hr and 1.8 hr, respectively). After 6 hr preincubation with 200 nM colchicine, only the slow phase (half-life = 3.6 hr) could be observed. The colchicine and vinblastine uptake rate was increased by cyclosporin A, an inhibitor of the drug efflux pump P-glycoprotein, which is expressed at the blood-brain barrier. Whereas cyclosporin A decreased vinblastine efflux, its effect on colchicine efflux was apparent after only 13 hr washout and was associated with the re-uptake by cells of colchicine molecules. Differences in uptake kinetics of colchicine and vinblastine could be related to differences in their lipid solubility, and mainly in their binding affinities to tubulin. Differences in efflux kinetics could in addition be explained by the involvement of P-glycoprotein in the efflux of vinblastine, whereas efflux of colchicine was not influenced by this pump. Indeed, binding of colchicine to tubulin would imply that most intracellular colchicine may be inaccessible to P-glycoprotein. In the case of a cytotoxic drug such as colchicine, which is tightly bound to intracellular receptors, the role of P-glycoprotein within the blood-brain barrier would be more to protect the brain against entry of this drug than to detoxify the brain by its extraction.

Effect of antivenom on venom pharmacokinetics in experimentally envenomed rabbits: toward an optimization of antivenom therapy

Antivenomous immunotherapy is still used empirically. To improve the efficacy and safety of immunotherapy, we studied the effects of administering antivenom antibodies (F(ab')2) on the pharmacokinetics of the Vipera aspis venom in rabbits. Free venom levels were measured by enzyme-linked immunosorbent assay and total concentrations were quantified by measuring the radioactivity of trichloroacetic acid-precipitable radioiodinated venom. The intravenous infusion of 125 mg of antivenom 7 h after intramuscular injection with 700 microg x kg(-1) of V. aspis venom produced a redistribution of the venom antigens from the extravascular to the vascular space. Moreover, anti-venom antibodies were able to neutralize the totality of venom antigens in the vascular space, because no free plasma venom was detectable by enzyme-linked immunosorbent assay within 15 min after antivenom injection. Similar effects were obtained after injection of 25 mg of antivenom; however, the venom was only partially neutralized with lower doses (5 and 2.5 mg). We further established that intravenous injection is the most efficient route for antivenom administration, and we examined the effects of early and late immunotherapy. Finally, the efficacy of Fab antibodies was compared with that of F(ab')2; the plasma redistribution and the immunoneutralization of the venom were lower than those induced after injection of the same dose of F(ab')2. The difference between the effects of F(ab')2 and Fab could be explained by the differential pharmacokinetics of the two fragments.

Immunoreactivity of a new generation of horse F(ab')2 preparations against European viper venoms and the tetanus toxin

The immunoreactivity of the current and the new more purified, pasteurized preparations of horse F(ab')2 against the tetanus toxin and Vipera aspis venom was investigated with a biosensor based on technology using the optical phenomenon of surface plasmon resonance. Immunoreactivity data were compared with seroneutralization titres to investigate immunoreactivity-immunoprotection efficacy relationships. The association-dissociation rate and affinity constants of the current and the new tetanus toxin-specific F(ab')2 preparations were similar, at about 10(4) M-1 sec-1, 10(-4) sec-1 and 10(8) M-1, respectively. Similar values were found using a solid immunoradiometric assay. To assess the immunoreactivity of V. aspis venom-specific horse F(ab')2, the mol. wt and percentage of the antigenic fractions of V. aspis venom were determined. Western blotting of electrophoresis gels showed four antigenic fractions of V. aspis venom (mol. wts 17,500, 28,500, 32,000 and 60,000), which represented 6, 3.4, 17.7 and 5% of total venom, respectively. Association and dissociation rate constants were in the same range as those of the tetanus toxin-F(ab')2 interactions for each of the four antigenic fractions. Seroneutralization of both tetanus toxin and V. aspis by the corresponding specific F(ab')2 showed that the LD50 mg-1 protein was 1.76-fold and 1.51-fold higher with the new than with the current preparations, respectively. These improvements in efficacy were in close agreement with the higher immunoreactive fraction ratios, which were 2-fold and 1.8-fold higher with the new preparations. These results demonstrate that the removal of non-IgGT immunoglobulins and the pasteurization treatment have no overall influence on F(ab')2 affinity but improve the specific activity of these new antitoxin horse F(ab')2.

Pharmacokinetics of heterologous and homologous immunoglobulin G, F(ab')2 and Fab after intravenous administration in the rat

Because few pharmacokinetic studies of antibodies and their fragments have compared the influence of species origin and antibody size, the plasma pharmacokinetics of a single intravenous dose (0.7 mg kg-1) of 125I-labelled mouse, rat and human immunoglobulin G (IgG), and mouse F(ab')2 and Fab were investigated in the rat. IgG reached equilibrium after six distribution half-lives, i.e. only 36-50 h post-dosing, and the distribution volume was about four times the rat plasma volume. IgG elimination half-lives ranged from 5.33 to 8.10 days. Fragmentation of IgG into smaller fragments, F(ab')2 and Fab, resulted in pharmacokinetics that were molecular-weight-dependent with volume of distribution and systemic clearance values inversely related to antibody size. We conclude that antibody variability in terms of species origin and size influences antibody pharmacokinetics and should be carefully studied before selection of the best antibody for a clinical application.

Effect of the P-glycoprotein inhibitor, SDZ PSC 833, on the blood and brain pharmacokinetics of colchicine

The effect of the multidrug resistance-reversing agent, SDZ PSC 833, on blood and brain pharmacokinetics of a P-glycoprotein substrate, colchicine, was investigated using simultaneous blood and brain microdialysis in freely moving rats. The use of microdialysis for pharmacokinetic studies was validated by comparing the blood concentrations of colchicine obtained by microdialysis with those obtained by direct blood sampling. The rats received either SDZ PSC 833 (2.3 mg/kg i.v. bolus followed by 16.7 microg/min/kg i.v. infusion during all the experiment) and colchicine (1 mg/kg i.v. bolus followed by 12.5 microg/min/kg i.v. infusion during 2 hours) or colchicine alone (the same dosage with SDZ PSC 833 vehicle). The SDZ PSC 833 treatment resulted in important modifications of colchicine blood pharmacokinetics: the unbound colchicine blood concentration at steady-state was enhanced from 149.6 +/- 9.9 to 333.5 +/- 81.7 ng/ml indicating a two-fold decrease in colchicine clearance. Moreover the coadministration of SDZ PSC 833 increased the brain penetration of colchicine by a factor of 10, at least. This enhancement could not be exactly assessed because the brain dialysate concentrations of control group were below the limit of detection. Nevertheless, the large increase of colchicine brain penetration is consistent with the hypothesis that SDZ PSC 833 is able to inhibit the P-glycoprotein pump present at the blood-brain barrier.

Markedly altered colchicine kinetics in a fatal intoxication: examination of contributing factors

1. Colchicine poisoning, which is relatively rare, is associated with significant morbidity and mortality. Whilst a new treatment modality, in the form of colchicine-specific Fab fragments is on the horizon, currently available therapy is largely supportive. 2. The elimination of colchicine occurs primarily by hepatic metabolism, following a first-order process, with significant enterohepatic circulation. Renal extraction is responsible for approximately 20% of colchicine elimination. 3. We report a case of colchicine intoxication, complicated by the presence of co-ingestants, in which serum colchicine concentrations remained quasi-constant over the 3 days of the patient's survival, consistent with marked alterations both in metabolism and excretion. The initial presentation was relatively benign but the subsequent course was one of severe colchicine poisoning, resulting in death. 4. Severe colchicine toxicity appears to have resulted in a vicious cycle of progressive organ dysfunction and impaired elimination. 5. Josamycin, one of the co-ingestants and an inhibitor of P-glycoprotein, the membrane pump responsible for multidrug resistance, may have played a significant role in impeding the cellular and biliary elimination of colchicine. Co-ingested opioid and anticholinergic compounds may have altered colchicine absorption and gastrointestinal transit. 6. This case serves as a reminder of the need for attention to co-ingested drugs, to early aggressive therapy, and if available, to consideration of immunotherapy.

Immunoreactivity and pharmacokinetics of horse anti-scorpion venom F(ab')2-scorpion venom interactions

The immunoreactivity and pharmacokinetics of a new horse F(ab')2 scorpion antivenom and its effect on Buthus occitanus mardochei venom plasma disposition in the rabbit were studied. The scorpion venom-specific F(ab')2 affinity constant determined by immunoradiometric assay was 1.6 +/- 0.6 10(8) M-1. One group received a F(ab')2 bolus dose of 9.57 mg.kg-1 i.v. bolus or i.m.. The plasma F(ab')2 concentration followed a biexponential decline after i.v. administration with distribution and elimination half-lives of 2.54 +/- 0.36 and 49.52 +/- 3.07 hr, respectively. The total volume of distribution (Vdss or Vd beta) was between 230 and 255 ml.kg-1. Total body clearance was 3.56 +/- 0.34 ml.kg-1.hr-1. After intramuscular administration, Tmax was 48 hr and the absolute bioavailability was 36%. Two other groups of rabbits received i.v.60 micrograms.kg-1 B. occitanus mardochei venom either alone (control group) or followed by 3 mg.kg-1 scorpion venom-specific F(ab')2 administered by intravenous infusion 1.75 hr later. In the rabbits treated with horse F(ab')2 antivenom the venom concentration profile was initially identical to that observed in the control group which received venom alone before F(ab')2 administration. Subsequent infusion of antivenom induced a 1.5-fold elevation of the plasma venom concentration with a Tmax 0.5 hr after F(ab')2 administration. The AUC was 10-fold higher in the F(ab')2-treated group than in the control group in the post-F(ab')2 infusion period. Twelve hours after F(ab')2 administration the venom disposition declined with a terminal half-life equal to that of F(ab')2 (49.49 +/- 7.53 hr). These data show the ability of F(ab')2 to alter venom pharmacokinetics and demonstrate that the scorpion toxins adopt the F(ab')2 elimination properties.

Effects of mode of inhalation of carbon monoxide and of normobaric oxygen administration on carbon monoxide elimination from the blood

1. The half-life of carbon monoxide (CO) in blood was studied retrospectively in 26 fire victims and in 19 cases of CO poisoning. Normobaric oxygen therapy was administered via mechanical ventilation in 19 fire victims, and by facial mask to the rest of the casualties. 2. Arterial pH was significantly lower (P < 0.05) and PaO2 significantly greater (P < 0.01) in the mechanically ventilated fire victims compared to the spontaneously breathing fire victims. 3. The blood CO half-lives were 91 +/- 38 min for the 26 fire victims and 87 +/- 40 min for the 19 pure CO intoxications. 4. The blood CO half-lives were 92 +/- 40 min for the 19 mechanically ventilated fire victims and 87 +/- 37 min for the 26 spontaneously breathing subjects. 5. We conclude that the elimination of CO from blood was a slow process with no significant effects on the blood CO half-life of either the cause of the CO poisoning or the mode of normobaric oxygen therapy. These data suggest that enhancement of the elimination of carbon monoxide by normobaric oxygen in both pure CO poisoning and fire victims is more difficult to achieve and more complex than has previously been reported.

Role of P-glycoprotein in the blood-brain transport of colchicine and vinblastine

Classically, drug penetration through the blood-brain barrier depends on the lipid solubility of the substance, except for some highly lipophilic drugs, like colchicine and vinblastine, both substrates of P-glycoprotein, a drug efflux pump present at the luminal surface of the brain capillary endothelial cells. Colchicine and vinblastine uptake into the brain was studied in the rat using the in situ brain perfusion technique and two inhibitors of P-glycoprotein, verapamil and SDZ PSC-833. When rats were pretreated with PSC-833 (10 mg/kg, intravenous bolus), colchicine and vinblastine uptake was enhanced 8.42- and 9.08-fold, respectively, in all the gray areas of the rat brain studied. The mean colchicine distribution volume was increased from 0.67 +/- 0.41 to 5.64 +/- 0.70 microliters/g and vinblastine distribution volume from 2.74 +/- 1.15 to 24.88 +/- 4.03 microliters/g. When rats were pretreated with verapamil (1 mg/kg, intravenous bolus), colchicine distribution volume was increased 3.70-fold. The increase in colchicine and vinblastine did not differ between the eight brain gray areas. PSC-833 and verapamil pretreatment had no influence on the distribution volume of either drug in the choroid plexus. Nevertheless, distribution volumes remained small, considering the highly lipophilic nature of the substances. We suggest that P-glycoprotein is either only partially inhibited (difficulty of fully saturating P-glycoprotein, especially under in vivo conditions) or not the only barrier to these two drugs.

Oral absorption characteristics and pharmacokinetics of colchicine in healthy volunteers after single and multiple doses

Colchicine is an antimitotic drug used to treat gout and familial Mediterranean fever. Absolute bioavailability, pharmacokinetics, and absorption characteristics of colchicine after single 1.0-mg doses in oral solution or tablet form or 0.5-mg intravenous doses were compared in 6 subjects. This study was combined with 14 days of multiple-dose administration of 1.0-mg colchicine tablets in 6 subjects. Serial blood samples were collected for 48 hours after administration of single doses and for 120 hours after the last dose in the multiple-dose regimen. Plasma colchicine profiles as measured by radioimmunoassay were analyzed using deconvolution and compartmental methods. After intravenous bolus injection of colchicine, the area under the concentration-time curve (AUC) was 61.2 +/- 12.7 ng.hr/mL, steady-state volume of distribution (Vss) was 419 +/- 95 L, systemic clearance (Cl) was 8.5 +/- 1.8 L/hr, and the terminal half-life (t1/2) was 57.8 +/- 10.7 hours. After oral administration in solution form, peak plasma concentrations (Cmax) of 6.50 +/- 1.03 ng/mL were reached at time (tmax) 1.07 +/- 0.55 hours, with a rate of 0.109 +/- 0.024 hr-1 (Cmax/AUC); bioavailability was 47 +/- 14%. Oral tablets yielded similar Cmax, tmax, and Cmax/AUC values, but AUC was significantly lower. Most participants exhibited a secondary peak within 6 hours of administration, possibly in relation to a second absorption site or enterohepatic recirculation. This second absorption process was significantly longer than the first one, and accounted for a similar amount of colchicine absorbed. From the multiple-dose study, a model including an alteration of colchicine absorption due to possible drug-induced gastrointestinal modifications allowed better determination of steady-state plasma concentrations of colchicine.

Facilitation of imipramine efflux from the brain by systemic specific antibodies

1. This study investigated the capacity of circulating anti-tricyclic antidepressant (TCA) IgG to increase the efflux of imipramine (Imip) from the rat brain. 2. A tracer amount of [3H]-Imip (40 pmol) was injected into the cerebral lateral ventricle and its efflux was determined in control rats and in rats given anti-TCA antibody. The monoclonal anti-TCA IgG1 was injected i.v. 48 h before Imip at 4 IgG:Imip molar ratios (10, 100, 1000 and 10,000). The [3H]-Imip in arterial and venous plasma was measured for up to 60 min, and in the brain and peripheral organs (heart, liver, lung, kidney) 5 and 60 min after Imip injection. 3. The arterial plasma concentration of Imip in control rats was significantly higher (26.7 +/- 2.1 pM) than the venous one (17.7 +/- 2.0 pM) at 5 min, indicating that Imip released from brain becomes distributed in peripheral tissues. These concentrations were not significantly different at 60 min suggesting that Imip was, at this time, redistributing from extravascular tissues to the blood. In rats given anti-TCA IgG, any Imip leaving the brain was immediately bound by the circulating antibody at 5 min. This greatly reduced the Imip in the heart (63.9%) and lung (61.3%) at the highest IgG:Imip ratio. The brain Imip was markedly lower at 60 min (31.5% with an IgG Imip ratio of 1000 and 57.5% at a ratio of 10,000). The two lowest IgG:Imip ratios had less effect on the plasma Imip because of the relative low affinity of the anti-TCA IgG (3.8 x 10(7) M-1). 4. These data indicate that the anti-TCA IgG facilitated the efflux of Imip from the brain, even though these antibodies cannot cross the blood-brain barrier. This may be an efficient system for increasing drug organ clearance, as more than half the Imip in the brain was actively removed by the antibody in 1 h.

Colchicine in breast milk of patients with familial Mediterranean fever

OBJECTIVE

To clarify whether colchicine is excreted in breast milk, and to compare its concentrations in the serum and breast milk of lactating women who have familial Mediterranean fever (FMF).

METHODS

Using a specific radioimmunoassay, we determined colchicine concentrations in the serum and breast milk of 4 patients at various time points, following oral administration of the drug. The study evaluated 4 patients with FMF who had been taking colchicine on a long-term basis.

RESULTS

Colchicine was found to be excreted in breast milk. Its levels ranged between 1.9 and 8.6 ng/ml, which were similar to those found in the serum (parallel concentration time curves). However, there appeared to be a considerable variation in colchicine milk concentration among the different patients, which might be related to individual breast milk composition and, possibly, to other nutritional or metabolic factors.

CONCLUSION

The extensive peripheral tissue binding and relatively low concentration of colchicine in breast milk suggests that the amount ingested by the infant is small. Furthermore, based on our clinical experience, nursing appears to be safe for lactating women with FMF who continue to take colchicine.

Interspecies scaling of clearance and volume of distribution for digoxin-specific Fab

Digoxin-specific Fab are recognized to be effective in the treatment of acute cardiac glycoside poisoning but no pharmacokinetic studies have been performed in human volunteers. We thus propose an allometric approach among three mammalian species to predict Fab pharmacokinetic parameters in humans. Plasma disposition of digoxin-specific Fab was studied at a 20 mg/kg i.v. dose in mice, rats, and rabbits. Fab plasma concentration was determined by a sensitive and specific radioimmunoassay. Allometric equations showed that the pharmacokinetic parameters (distribution volumes (Vc (ml) = 0.084 W0.96; Vdss (ml) = 0.24 W0.96; Vd beta (ml) = 0.55 W0.96, r2 = 1), total body clearance (Cltot (ml/hr) = 0.61 W0.67, r2 = 0.999), and terminal half-life (t 1/2 beta (hr) = 0.63 W0.29) correlated with body weight. The Fab plasma concentration-time data plotted as a complex Dedrick relationship were superimposable. Using these allometric techniques, Vdss, Vd beta, Cltot and t 1/2 beta were calculated as 10.75 liter, 24.64 liter, 17.9 ml/min, and 16 hr, respectively, for a human subject of 70 kg body weight. These values are in accordance with those previously described in digoxin-Fab-treated patients (body weight = 61 +/- 3 kg, Vd beta = 24.9 +/- 3. 7 liter; Cltot = 20.8 +/- 2.1 ml/min; t 1/2 beta = 14.3 +/- 1.8 hr). Results indicate that the primary Fab pharmacokinetic parameters can be reasonably estimated in man using pharmacokinetic data from three animal species.

Dose-dependent reversal of digoxin-inhibited activity of an in vitro Na+K+ATPase model by digoxin-specific antibody

We investigated the potency of digoxin-specific Fab fragments to reverse digoxin-induced Na+K+ATPase inhibition in rat brain microsomes according to (a) the extent of initial inhibition of Na+K+ATPase and (b) the neutralizing dose of antibody. Mathematical analysis of the digoxin concentration-Na+K+ATPase inhibition curve supports the existence of 2 digoxin sensitive Na+K+ATPase isoforms. The IC50 was 1.3 x 10(-4) M and 2.5 x 10(-8) M for the low (alpha 1) and high (alpha 2) digoxin affinity isoenzyme, respectively. The reversal of digoxin-induced Na+K+ATPase inhibition was dependent on the digoxin-specific Fab concentration. The maximal effect was observed when the Fab:digoxin ratio was stoichiometrical and addition of an excess of antibodies did not result in a complete reversal of inhibition at the 4 digoxin concentrations studied. This simple and rapid in vitro model will be a useful tool to predict the efficacy of a new generation of antibodies.

Omeprazole and lansoprazole are not inducers of cytochrome P4501A2 under conventional therapeutic conditions

OBJECTIVES

Claims that substituted benzimidazole molecules induce cytochromes P4501A2 are still controversial. This study was undertaken to evaluate their inducing potency under conventional therapeutic conditions.

METHODS

Twelve healthy non-smoking young volunteers were given 20 mg omeprazole or 30 mg lansoprazole daily, in random order, for 2 weeks, separated by a 3 week wash-out period. We evaluated the CYP1A2 activity by the ratio of the molar urinary concentrations (CUM ratio) of the three end products of the paraxanthine demethylation of caffeine over the molar concentration of a paraxanthine 8-hydroxylation product.

RESULTS

This urinary metabolite ratio has previously been shown to be correlated with caffeine clearance. There was slight but non-significant enhancement of the CUM ratio after 2 weeks of treatment with omeprazole (3.62 (1.58) on Day 15 vs 3.09 (1.43) on Day 1), and after lansoprazole (4.26 (2.3) vs 3.65 (2.36)). Similarly, one week of treatment did not significantly alter the CUM ratio after omeprazole or lansoprazole (3.11 (1.58) and 3.28 (1.59), respectively on Day 8).

CONCLUSION

The results show that both omeprazole and lansoprazole in the daily recommended therapeutic doses of 20 mg and 30 mg, respectively, have no influence on the metabolism of caffeine, and therefore no influence on cytochrome CYP1A2 activity.

Dose-dependent delivery of colchicine to the rat hippocampus by microdialysis

The time courses of the colchicine delivery and diffusion rate in the brain were studied by microdialysis in the rat. Microdialysis allowed the exposure of the brain tissue to colchicine to be regulated, unlike a bolus injection. Colchicine was infused directly into the dorsal hippocampus at 40 ng/ml and 40 micrograms/ml, for 8 h. The amount of colchicine delivered to the brain and the diffusion rate from the probe were dose-dependent: colchicine diffusion into the brain was linear at 40 ng/ml but tended to plateau after 4 h at 40 micrograms/ml. The drug actually delivered with the higher dosage was only about 50% of that predicted from a constant diffusion. The total amount delivered at 40 ng/ml was 3.73 +/- 0.14 ng and at 40 micrograms/ml, it was 2.06 +/- 0.20 micrograms. Thus tissues surrounding the infusion site were saturated at high concentration and no more colchicine was diffused. Postmortem measurements of colchicine concentration in the forebrain confirmed these findings. Hence, the way in which colchicine is delivered to the brain is a critical factor for induction of its neurotoxic effects. These data open the way to a research on the correlation between local brain concentrations of colchicine and neurodegenerescence.

A dose-searching trial of an anti-LFA1 monoclonal antibody in first kidney transplant recipients

25.3, a mouse IgG1 monoclonal antibody (MoAb), directed at the alpha chain of the LFA1 molecule (CD11a) has been used in prophylaxis of rejection in recipients of cadaveric kidney graft. Promising clinical results have been obtained for both tolerance and efficacy [1]. The aim of this trial was to determine the optimal dosage, base on a pharmacokinetic-pharmacodynamic analysis of the data obtained from the 15 patients included in this dose-searching study. Biological parameters, such as circulating levels and functional inhibition (as detected in an adhesion assay of patient lymphocytes), were measured during and after treatment. A Hill relation was calculated between the effect and the concentration measured and led us to select a 15 mg/day dose for further clinical trials, with a loading dose of 30 mg. An additional group receiving this protocol was submitted to the same calculation, and the results from this last group were in agreement with this previous analysis.

Immunoglobulin G, F(AB')2, and fab fragment uptake kinetics in isolated perfused rat liver and rat hepatic cells

The interaction of 125I-radiolabeled immunoglobulin G (IgG), F(ab')2, and Fab fragments with different modes of production (polyclonal or monoclonal), belonging to different subclasses (IgG1 and IgGT) and derived from different sources (mouse, rat, and horse) with liver, was investigated by using isolated perfused rat liver and isolated rat hepatic parenchymal cells (PCs) and non-parenchymal cells (NPCs) in suspension. Lactosaminated-bovine serum albumin (Lac-BSA) and formaldehyde-bovine serum albumin were used as markers of specific binding to PCs and NPCs, respectively. Using the isolated perfused rat liver model, data clearly indicated a very weak hepatic extraction ratio (< 0.003) for IgGs and fragments in comparison with Lac-BSA (extraction ratio = 0.398) over the 3 hr of the experiments. No breakdown or higher molecular weight compounds were observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Biliary excretion of IgGs and fragments ranged from 0.07 to 0.3%, mainly as free iodine-125. In contrast, 7% of Lac-BSA was excreted unchanged in bile, and 10% of free iodine was excreted at 3 hr. In vitro binding studies showed no specific binding of any antibody and fragment proteins at 4 degrees C or 37 degrees C. In contrast, saturable uptake was observed for Lac-BSA with PCs and formaldehyde-bovine serum albumin with NPCs. Both models demonstrated that nonspecific antibody/fragment interactions occurred with rat liver. Several hypotheses can be formulated to explain why liver-antibody interactions depend on more complex antibody molecular states (aggregated structure and immune complex) rather than the monomeric structure investigated in the present study.

4-methylpyrazole monitoring during haemodialysis of ethylene glycol intoxicated patients

4-methylpyrazole (4-MP) was administered IV during haemodialysis of two ethylene glycol-intoxicated patients with anuric renal failure. The plasma 4-MP concentration decreased after each pass through the dialyser, indicating its dialysability in humans. In these two cases, the extraction coefficient was 0.78 and 0.71, and the mean dialysance was calculated to be 137 and 117 ml.min-1, corresponding to a 4-MP removal rate of 83 and 50 mg.h-1, respectively. The results imply that a higher rate of 4-MP infusion would be needed to replace 4-MP lost due to metabolism and to haemodialysis. The treatment of two ethylene glycol poisoned patients who were haemodialysed raised the problem of the dialysance of 4-MP. A recent study in pigs indicated that the amount of 4-MP removed by haemodialysis was significant [8]. No data were available for man. The aim of the study was to evaluate the dialysability of 4-MP in the two intoxicated patients, and to estimate how to compensate for 4-MP elimination during haemodialysis.

Relationship between morphine analgesia and cortical extracellular fluid levels of morphine and its metabolites in the rat: a microdialysis study

1. The effect of morphine (10 mg kg-1, s.c.) on the analgesic response measured by the tail-flick method was determined in male Sprague-Dawley rats. The analgesic response to morphine was correlated with the levels of morphine and its metabolites collected by microdialysis from the cortical extracellular fluid (ECF). 2. The analgesic response to morphine lasted for 4 h. The concentration of morphine during a 4 h collection period was significantly higher than the metabolites concentration. The relative concentration of morphine and its metabolites during the 4 h period was 70 and 30% respectively. 3. The analgesic response during the first 2.25 h period accounted for more than 82% of the total analgesia as determined by the area under the time-response curve (AUC). The concentration of morphine and its metabolites during the same period were 78 and 22%, respectively, but they did not differ during the 2.25-4.0 h period (52 and 48%). 4. The half-life for morphine and its metabolites were similar, the maximal achievable concentration Cmax and AUC0-4 h were lower for metabolites but the time to reach maximum concentration was higher for morphine metabolites than for morphine. The ratio of the concentration of metabolites to the concentration of morphine in the cortical ECF increased with time whereas the analgesic response to morphine decreased with time. 5. At several time points following morphine injection even though the levels of morphine were the same, the concentration of metabolites (mainly M3G) differed and thus the ratio [metabolite/morphine]. A plot of [metabolite]/[morphine] vs. analgesia gave a high correlation coefficient. Since M3G has been shown to be antianalgesic and is the only metabolite of morphine in the rat, it is concluded that the levels of this metabolite may regulate the analgesic effect of morphine in the rat.

Affinity and dose-dependent digoxin Na+K+ATPase dissociation by monoclonal digoxin-specific antibodies

The effect of three monoclonal digoxin-specific antibodies and of polyclonal Digidot as reference on digoxin dissociation from rat brain Na+K+ATPase microsomes was studied to determine the role of the affinity constant (Ka) and dose of the antibody on the rate of digoxin dissociation from Na+K+ATPase. Stoichiometrical doses of 1C10, 6C9, 9F5 IgG, and Digidot (Ka = 6 10(9), 3.1 10(8), 2.5 10(7), and 8.5 10(9) M-1, respectively) resulted in digoxin dissociation related to Ka. When the IgG:digoxin molar ratio increased from 0.25 to 10, digoxin dissociation from Na+K+ATPase sites also increased according to the Hill equation, allowing comparative parameters among the three antibodies to be determined. 1C10 IgG was 2- and 10-fold more efficacious than 6C9 and 9F5, respectively. This in vitro model appears to be a useful predictive screening assay before in vivo experimentation.

Pharmacokinetics of thiocolchicoside in humans using a specific radioimmunoassay

The myorelaxant thiocolchicoside (TC), an analogue of colchicine (COL), was assayed in plasma and urine by a radioimmunoassay (RIA) using a cross-reacting COL-specific polyclonal antibody. Cross-reactivity was 56% for TC, giving a limit of quantification of 0.5 ng/ml and a linear response from 0.5 to 100 ng/ml. Specificity was checked by cross-reactivity studies with COL analogues and by using liquid chromatography and RIA in tandem on urine samples. Two immunoreactive peaks were detected, but the nonspecific peak represented < 2% of the total urine concentration of TC. Pharmacokinetics of TC following infusion of 4 mg in two subjects revealed a moderate distribution (Vss from 31 to 35 L) and mainly extrarenal elimination (75% of the total body clearance). Terminal half-lives ranged from 2.4 to 2.7 h in plasma and from 3.2 to 3.7 h in urine.

[Colchicine: recent data on pharmacokinetics and clinical pharmacology]

Colchicine is widely used in the treatment of acute goutty arthritis. Recently, colchicine was shown to be effective in inflammatory diseases such as familial Mediterranean fever. Two proteins can modulate its pharmacokinetics: tubulin, the specific intracellular receptor for colchicine which determines the plasma half-life, and P-glycoprotein, an active efflux pump towards some anticancer drugs which regulates colchicine absorption, distribution, and elimination. Therapeutic dosage is monitored empirically, by the control of the balance between the occurrence of side effects and the clinical efficacy. Recently, using a specific and sensitive radioimmunoassay, the investigation of plasma concentrations during single and multiple dose studies has allowed to define the colchicine pharmacokinetic parameters. Following oral route, colchicine bioavailability is extremely variable (from 24 to 88% of the administered dose), the distribution volume is elevated (7 l/kg) but the binding to albumin is moderate. Colchicine elimination occurred mainly via hepatic pathways and the elimination half-life ranged from 20 to 40 hours. In multiple dose study (1 mg/d), the steady-state is reached 8 days after the first oral administration and plasma concentrations ranged from 0.3 to 2.5 ng/ml. Pharmacokinetic/pharmacodynamic studies show that the biological effects of colchicine were not related to plasma concentrations but with intraleukocyte concentrations. Drug interactions may occur when colchicine is associated to drugs which interact with cytochrome P450 and/or P-glycoprotein and modify renal and/or hepatic clearances. The therapeutic drug monitoring of colchicine during these circumstances could allow to prevent the observation of side effects.

Snake F(ab')2 antivenom from hyperimmunized horse: pharmacokinetics following intravenous and intramuscular administrations in rabbits

PURPOSE

The pharmacokinetics of a currently available horse F(ab')2 antivenoms to Vipera aspis, V. ammodytes, and V. berus (Ipser Europe) and a new more purified and pasteurized preparation (SAV) was investigated in the rabbit.

METHODS

An immunoradiometric assay using an affinity-purified goat IgG horse F(ab')2 specific and the same IgG labelled with iodine 125 as a tracer was developed. The limit of quantification in plasma was 0.032 microgram/ml. Specificity study showed that mouse F(ab')2 and Fab did not cross-react.

RESULTS

Pharmacokinetic analysis showed that the plasma F(ab')2 concentration followed a biexponential decline after intravenous bolus administration with distribution and elimination half-lives of 2.66 +/- 0.18 hrs and 49.69 +/- 4.13 hrs, respectively. The total volume of distribution (Vdss or Vd beta) was between 209 and 265 ml.kg-1 and was similar to the volume of the extracellular fluid in the rabbit (300 ml.kg-1). Total body clearance ranged from 3.33 to 3.96 ml.h-1.kg-1. After intramuscular administration which was only investigated with SAV, Tmax was 48 hrs and the absolute bioavailability was 42%.

CONCLUSIONS

No difference in pharmacokinetics was observed between the two antivenom preparations following the intravenous administration. In contrast, a reduced rate and extent of absorption was shown following intramuscular administration.

Efflux of intracellular colchicine in lymphocytes with colchicine-specific Fab fragments

Uptake of [3H]colchicine (2.5 ng/ml) by human lymphocytes in culture was slow in the length of time to reach steady state (> 48 hr) and was limited in the maximal intracellular colchicine amount (1-2% of total extracellular colchicine). Efflux of intracellular colchicine was investigated 40 hr after colchicine cell exposure by using either washing of the extracellular medium or adding different colchicine-specific Fab fragments:colchicine dose molar ratios of 0.5, 1 and 5. Except for the 0.5 dose molar ratio, the kinetics of [3H]colchicine efflux from lymphocytes induced by extracellular specific Fab fragments were similar to those obtained by washing and were characterized by a first-order decline with half-lives ranging from 15.5 to 16.4 hr. These half-lives were in the same range as those characterizing the dissociation of colchicine from the intracellular tubulin receptor. Our data demonstrate that a tightly bound intracellular toxin may be extracted by antibody with high affinity for the toxin present in the extracellular space at a rate depending on the rate of dissociation of the toxin from its receptor.

Analgesic response and plasma and brain extracellular fluid pharmacokinetics of morphine and morphine-6-beta-D-glucuronide in the rat

The analgesic effects of subcutaneously administered morphine and morphine-6-beta-D-glucuronide (M6G) were determined in male Sprague-Dawley rats. Morphine produced a dose-dependent (2.5 to 10.0 mg/kg) analgesic response as measured by the tail-flick test. M6G in the same doses as morphine produced a greater degree of analgesia with longer duration of action. The concentrations of M6G and morphine were determined in plasma as the protein unbound form after the use of an equilibrium dialysis technique and in BECF after administration of the drugs (10.0 mg/kg s.c.). The concentrations of morphine and M6G in BECF were determined by using microdialysis. The concentration of M6G in plasma and BECF at each time interval after its administration was much higher than morphine. The maximal concentrations in plasma and AUC0-infinity values for M6G were, thus, significantly higher for M6G than for morphine in plasma and BECF. In BECF, the Tmax value for M6G was lower than for morphine, but the t1/2 beta values did not differ. In plasma, Tmax and T1/2 values for M6G and morphine did not differ, but volume of distribution and total clearance values for M6G were lower than for morphine. It is concluded that per milligram, M6G has a much higher analgesic potency than morphine in the rat and these differences may be related, in part, to the higher levels of M6G in comparison to morphine in plasma and BECF.

Pharmacokinetics of lithium in plasma and red blood cells in acute and chronic intoxicated patients

Lithium disposition in plasma, red blood cells (RBC) and urine was studied in acute self-poisoned patients upon chronic lithium therapy (n = 4) and in chronic intoxicated patients receiving oral lithium (n = 10). Following acute intoxication upon chronic lithium therapy, lithium pharmacokinetics did not differ from previous reports. Terminal plasma half-life ranged from 19.0-29.0 h and RBC/plasma ratio was 0.32 +/- 0.11. The distribution volume of the terminal phase, Vz, was estimated at 0.84 +/- 0.32 l/kg and renal clearance was 0.38 +/- 0.11 ml/mn/kg. After chronic intoxication lithium pharmacokinetics differed from those of the acute patients. Terminal plasma half-life ranged from 36.5-79.4 h and zero-order decline appeared in 8 of the 10 patients. The RBC/plasma ratio was 0.87 +/- 0.22 on admission. Vz was estimated at 0.71 +/- 0.27 l/kg and renal clearance was 0.16 +/- 0.07 ml/mn/kg. These modifications in lithium elimination kinetics could be related to the decrease in the glomerular filtration rate with age or renal dysfunction in this group of patients.

Monoclonal digoxin-specific antibodies induce dose- and affinity-dependent plasma digoxin redistribution in rats

The effect of three monoclonal digoxin-specific antibodies on total and free digoxin plasma disposition was studied in rats in order to determine the role of affinity constant (Ka) and dose. Thirty minutes after digoxin infusion, administration of a stoichiometrical dose of the ICIO, 6C9 and 9F5 IgG (Ka = 6 10(9), 3.1 10(8) and 2.5 10(7) M-1, respectively) resulted in a plasma digoxin increase linearly related to Ka. The mean free plasma digoxin was 0.6 +/- 0.4, 7.8 +/- 3.3 and 43 +/- 22% respectively after 1C10, 6C9, and 9F5 IgG infusion in comparison to 70 +/- 9% in the control group. When the IgG:digoxin ratio increased from 1 to 5, plasma digoxin Cmax and AUCT also increased as a function of both affinity (Ka) and dose (N), but not linearly. The product of NKa defined an immunoreactivity factor that was well fitted to the digoxin redistribution parameters (Cmax and AUCT) by a Hill equation.

Immunoreactivity of endogenous digitalis-like substances in cord blood sera studied with antidigitoxin monoclonal antibodies

The presence of digitoxin-like immunoreactive substances, whose nature is yet unknown, has been demonstrated in the umbilical cord blood. We selected six antidigitoxin monoclonal antibodies (MAb) having different specificity profiles concerning digitoxin analogs and steroid hormones. These antibodies were tested in a digitoxin radioimmunoassay (RIA). With the help of this technique, we measured the concentrations of apparent digitoxin in the cord blood drawn either at birth or in utero from mothers not undergoing any digitalis treatment. In the cord blood of newborns, the concentrations of apparent digitoxin, measured by the two MAbs that have the highest cross-reactions with dehydroepiandrosterone (DHEA) (123A23 and 145A41), were two or three times higher than with the other antibodies. In the fetal cord blood, where the concentration of DHEA is five to seven times lower than that observed at birth, these antibodies revealed a threefold lower concentration of apparent digitoxin than that observed in blood drawn at birth. Furthermore, MAbs that had similar specificities towards digitoxin analogs and steroids showed different measurements of digitoxin-like concentrations. These observations suggest that digitoxin-like immunoreactive compounds detected by the RIA may constitute a group of different molecules, one of which would be the DHEA.

Brain microdialysis in the mouse

Microdialysis of small brain areas of OF1 mice is shown to be feasible using the smallest commercially available probes (CMA/11). The brain areas studied were the dorsal hippocampus and nucleus accumbens. The basal concentrations of biogenic amine metabolites in dialysate samples were measured by HPLC with electrochemical detection (ED). The basal levels of MHPG, DOPAC, and HVA in the dorsal hippocampus were obtained immediately after probe insertion, whereas the basal 5-HIAA concentration gradually declined. The stable levels of DOPAC, HVA, and 5-HIAA in the nucleus accumbens were reached in 80 min. Histological controls showed the tract of the dialysis membrane within the studied sites. This procedure could allow simultaneous correlation of the neurobiochemical changes and pharmacological responses, and could facilitate further biochemical and pharmacokinetic research in the mouse.

Inhibition of colchicine absorption by the fat substitutes, sucrose polyester and tricarballylate triester, in the rat

The effect of non-absorbable fat substitutes (sucrose polyester (SPE) and tricarballylate triester (TCTE)) on the enterohepatic circulation of colchicine was studied in the rat. In a first experiment, emulsions of either sunflower oil (SFO), SPE, or TCTE, were introduced into the ligated small intestine and compared to a control group receiving physiological saline. All the groups received colchicine as an intravenous bolus. The plasma levels of colchicine in all groups was not affected, and luminal samples indicated that SPE and TCTE have no influence on the biliary excretion of colchicine (a previous experiment in bile duct-cannulated rats showed that SPE and TCTE, introduced by intragastric tube, have no effect on bile flow rate). In a second experiment, colchicine diluted in bile was mixed with saline or emulsions of either SFO, SPE or TCTE, and introduced into the ligated small intestine. The area under the curve and the maximal plasma concentration of colchicine were reduced when the drug was mixed with SPE or TCTE rather than saline (p < 0.0005). After 150 min, luminal samples were taken and showed significantly higher (p < 0.034) concentrations of colchicine in both SPE and TCTE groups compared to the saline group, indicating a significant inhibition of reabsorption of biliary colchicine. In conclusion, the non-absorbable fat substitutes, SPE and TCTE, did not influence biliary excretion of colchicine but reduced its reabsorption, thus altering its enterohepatic circulation.

Cyclosporin absorption is impaired by the fat substitutes, sucrose polyester and tricarballylate triester, in the rat

The effect of non-absorbable fat substitutes (sucrose polyester (SPE) and tricarballylate triester (TCTE)) on cyclosporin A (CsA) intestinal absorption was studied in the rat using in situ perfusion and gastric intubation techniques. A first experiment using the recirculating intestinal perfusion model showed that emulsions of either 5% SPE or TCTE significantly reduced (p < 0.0008) CsA absorption, whereas no difference was found between results for saline and 5% olive oil emulsion. In single-pass intestinal perfusion experiments SPE dose-dependently inhibited CsA absorption at SPE concentrations of 0.31% (p < 0.0004) and higher. Using gastric intubation, whole blood CsA concentrations significantly decreased when administered with SPE and TCTE in comparison with olive oil (p < 0.04). These results confirm that the CsA fraction dissolved in the undigested oil phase, constituted by the undigested and nonabsorbed fat substitute, is unavailable for intestinal absorption.

Binding of colchicine and thiocolchicoside to human serum proteins and blood cells

The binding of 3H-colchicine and its derivative 3H-thiocolchicoside to human serum, purified human proteins and blood cells was studied by equilibrium dialysis and centrifugation. Binding of colchicine and thiocolchicoside to human serum was 38.9 C +/- 4.7 and 12.8 C +/- 5.3%, respectively, essentially to albumin. Protein binding was not dependent on the concentration of either drug between 10(-10) and 10(-5)M. The binding of colchicine and thiocolchicoside to isolated erythrocytes (55 C +/- 5.6 and 16.5 C +/- 2.1%, respectively) decreased markedly in the presence of human serum proteins, i.e. in whole blood (38.7 C +/- 3.1 and 3.4 C +/- 0.8%). Binding of colchicine and thiocolchicoside to other blood cells was very low C < 3%). These binding properties in the blood compartment do not predispose colchicine and thiocolchicoside to be pharmacokinetically sensitive to binding displacement by drug interactions.

Plasma and cerebrospinal fluid concentrations of morphine and morphine glucuronides after oral morphine. The influence of renal failure

BACKGROUND

In patients with renal failure, morphine may cause prolonged narcosis and respiratory depression. Accumulation of the pharmacologically active metabolite morphine-6-glucuronide (M-6G) may explain this effect of morphine in patients with renal failure. After a single oral dose, morphine and its conjugates were measured in the plasma and the cerebrospinal fluid (CSF) in patients with renal failure.

METHODS

Eight patients with normal renal function and six patients with renal failure requiring dialysis were studied after operation under spinal anesthesia. Plasma and CSF concentrations of morphine, morphine-3-glucuronide (M-3G), and M-6G were measured by high-pressure liquid chromatography every 4 h for 24 h after an oral dose of 30 mg morphine.

RESULTS

The area under morphine plasma concentration-time curve from 0 to 24 h increased from 38 +/- 4 ng.ml-1 x h in patients with normal renal function to 110 ng.ml-1 x h in those with renal failure (P < 0.01). In patients with renal failure, plasma concentrations of M-3G and M-6G were higher at 4 h and remained at an increased level until the end of the study. The peak CSF concentration of morphine at 8 h was similar in those with renal failure or normal renal function, 1.8 +/- 0.4 and 2.0 +/- 0.6 ng.ml-1 respectively. M-3G and M-6G in CSF reached a maximum at 12 h in patients with normal renal function, whereas in those with renal failure the concentrations gradually increased so that the highest concentrations were observed at 24 h. At 24 h, CSF M-6G concentration was 15 times greater in patients with renal failure than in those with normal renal function.

CONCLUSIONS

We conclude that M-3G and M-6G readily cross the blood-brain barrier in patients with normal renal function or with renal failure. In patients with renal failure, the retention of plasma M-6G induces a progressive accumulation of this active metabolite in CSF; this accumulation may explain the increased susceptibility to morphine in patients with renal failure.

Colchicine concentration in leukocytes of patients with familial Mediterranean fever

Free and total plasma, granulocyte and mononuclear cell colchicine concentrations were measured by radioimmunoassay in 30 patients with familial Mediterranean fever treated with colchicine 0.5 to 2 mg day-1. Colchicine concentrations showed a large intersubject variability in plasma (0.13-1.75 ng ml-1), granulocytes (4 to 64 ng/10(9) cells), and mononuclear cells (11.4 to 57.6 ng/10(9) cells). Whereas unbound and total plasma colchicine concentrations were well correlated, no correlation was found between total or free plasma and granulocyte or mononuclear cell colchicine concentrations and dose of administered colchicine. In contrast, total or free plasma and granulocyte or mononuclear cell colchicine concentrations were correlated using a hyperbolic function indicating saturable colchicine distribution in both leukocyte populations.

Morphine disposition in opiate-intoxicated patients: relevance of nonspecific opiate immunoassays

The use of routine nonspecific immunoassays to detect or quantitate opiates in biological fluids raises the question of the relevance of such immunoassays in the investigation of opiate overdose disposition. We investigated the plasma disposition of morphine in 13 patients intoxicated by the intravascular (i.v.) (n = 5) or oral routes (n = 8) using both a highly morphine-specific antibody radioimmunoassay (RIA) and a nonspecific morphine RIA. Both RIAs showed a first-order elimination rate after i.v. intoxication (apparent plasma terminal half-life ranged from 2.9 to 4.7 hours for unchanged morphine and from 3.2 to 4.9 hours for total opiates) and a persistent opiate concentration with rebound after oral ingestion, suggesting a slow release of opiates from the gastrointestinal tract, in dealers and bodypackers. Moreover, i.v. and oral kinetic data were similar for the two RIAs, except for the ratio between total and unchanged morphine concentrations. The nonspecific morphine assay gave a threefold to 16-fold higher concentration than the specific morphine assay but with parallel kinetics for all patients. We conclude that the current, routine nonspecific morphine immunoassays could be a valuable analytical tool for investigating opiate toxicokinetics.

[Colchicine poisoning apropos of a pediatric case]

Colchicine has been widely used in the treatment of gout and familial mediterranean fever. Overdose is rare mostly in childhood. Colchicine overdose always causes gastrointestinal side effects, bone marrow depression and sometimes neuropathy. The mechanism of colchicine upon the microtubules, provides a better understanding of the pharmacology and also of the multiorgan involvement. We report the case of a ten year old child who ingested 0.6 mg/kg colchicine with a good outcome.

Association constants of monoclonal antibodies for hapten: heterogeneity of frequency distribution and possible relationship with hapten molecular weight

Using published data, we have investigated the relationship of the association constant (Ka) of 265 MAbs for haptens with molecular weights ranging from 111 to 1202 Da. The study indicates that: (1) differences of a factor 10(3)-10(5) are frequently found between the lowest and the highest value of Ka for the same hapten; (2) the relationship between log Ka and the hapten molecular weight of either the native drug or the molecular entity used for the Ka determination is described by a hyperbolic function; (3) beyond a critical molecular weight of approximately 300-325 Da, the log Ka reaches a plateau at a maximal value near 10(-12) M-1.

Colchicine disposition in patients with familial Mediterranean fever with renal impairment

OBJECTIVE

To assess the pharmacokinetics of serum colchicine in patients with familial Mediterranean fever (FMF) with renal impairment.

METHODS

Using a specific radioimmunoassay we determined serum colchicine concentration at various time points following oral administration of a single dose of the drug.

RESULTS

Patients with renal insufficiency had a mean +/- SD apparent total colchicine clearance of 0.168 +/- 0.063 l/h/kg, apparent volume of distribution of 4.56 +/- 1.64 l/kg and elimination half-life (t1/2) of 18.8 +/- 1.2 h. Patients with FMF with normal kidney function had a mean clearance of 0.726 +/- 0.110 l/h/kg, volume of distribution of 4.87 +/- 2.05 l/kg and terminal t1/2 of 4.4 +/- 1.0 h.

CONCLUSION

The kidneys have an important role in the clearance of colchicine. Caution should be exercised in the use of colchicine in patients with renal insufficiency.

Radioimmunoassay of colchicine with antisera exhibiting variable cross-reactivity

Colchicine-specific antibodies were produced in either goats or rabbits immunized with three different colchicine haptens conjugated to bovine serum albumin (BSA) at different coupling sites on the three rings of colchicine. Antibodies exhibited a variable cross-reactivity for metabolites and structural analogs of colchicine, which were dependent on the site at which colchicine coupled to the protein carrier. Specificity was also checked on urine samples by separating metabolites using high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA) in tandem. The three antisera presented similar high-affinity constants for colchicine of the order of 10(10) M-1. A sensitive RIA for plasma colchicine was developed with each antiserum. The limit of detection of the three RIAs was 0.2 ng/ml. The inter- and intraassay coefficients were < 13%. RIA was linear up to 8 ng/ml. This RIA procedure was used to study the pharmacokinetics of a single dose of 1 mg oral colchicine in healthy volunteers and the colchicine concentrations of 27 plasma samples from patients on long-term colchicine treatment. No significant differences in plasma colchicine concentrations using the three assays were observed. This RIA procedure appears suitable for plasma colchicine pharmacokinetics and monitoring investigations.

Plasma kinetics and biliary excretion of colchicine in patients with chronic liver disease after oral administration of a single dose and after long-term treatment

Plasma kinetics and biliary excretion of colchicine in patients with chronic liver disease were evaluated after oral administration of a single dose and after long-term treatment. A single oral dose of 1 mg colchicine led to a mean peak concentration of 3.60 +/- 1.04 ng/ml at a peak time of 2.16 +/- 0.34 h and a mean area under the plasma concentration time curve, extrapolated from time 0 to infinity, of 24.90 +/- 8.47 ng.h/ml. Comparable values were obtained after repeated administration. Distribution half-life was 2.83 +/- 0.74 h, and terminal plasma half-life was 9.81 +/- 2.08 h; the mean apparent volume of distribution and the mean apparent plasma clearance were 1448 +/- 4061 and 175.3 +/- 47.6 1/h, respectively. Colchicine concentrations in bile (2025 +/- 1368 ng/ml) were clearly higher than in plasma. Long-term treatment with colchicine (1 mg/day) in patients with various stages of primary biliary cirrhosis (PBC) was associated with colchicine concentrations varying from < 0.15 to 2.0 ng/ml, with a slight tendency to higher concentrations in PBC stages III-IV than I-II. Although about 20% of colchicine is excreted in bile within 24 h, accumulation of colchicine may appear only in patients with advanced liver disease and cholestasis.

Pharmacokinetics of Vipera aspis venom after experimental envenomation in rabbits

Toxicokinetic studies of Vipera aspis venom were performed in rabbits after experimental envenomation. Venom proteins with a molecular weight greater than 6 kDa (high-molecular weight proteins) and which reacted in enzyme-linked immunosorbent assay with specific antiviper venom Fab'2, were also responsible for the lethal potency and the capillary permeability increasing activity of the venom. Conversely, low-molecular weight proteins were not detected by enzyme-linked immunosorbent assay and were pharmacologically inactive. The toxicokinetics of both classes of venom components were studied, using high-molecular weight and low-molecular weight radiolabeled proteins as well as enzyme-linked immunosorbent assay. After intravenous injection, Vipera aspis venom in plasma followed a biexponential decline with a distribution half-life of 0.7 hr and an elimination half-life of 12 hr. The distribution volume was 1.2 l.kg-1 and the systemic clearance was 84 ml.hr-1.kg-1. Venom levels in plasma after intramuscular injection of three doses (300, 500 and 700 micrograms/kg) of venom increased within the few hours after the venom administration to reach maximal values proportional to the injected doses. They subsequently followed a monoexponential decline, with an apparent terminal half-life of 32.5 hr. Absorption was a kinetically complex process, rapid during the first 24 hr and continued at a slower rate over the subsequent 72 hr. Bioavailability of venom was about 65%, regardless of the administered dose, and less than 5% of venom injected was excreted by the renal route.

Antibody treatment of toxin poisoning--recent advances

The major responses to the administration of specific antibody or toxin-specific fragment are described. Toxin sequestration depends on the extent and rate of antibody distribution, the antibody affinity and its ability to form a non-active immune complex. Toxin redistribution is mainly influenced by the reversible binding and efflux kinetics of the toxin from the receptor. Finally, toxin elimination adopts the antibody elimination properties for low molecular weight compounds. These three basic mechanisms of the immuno-detoxification process could be optimized by designing the ideal antibody, in terms of size and origin, to inactivate the toxic properties. Calculation of the amount of infused antibody should be derived from the slope of the dose-effect curve rather than stoichiometrically.

Morphine and morphine metabolite kinetics in the rat brain as assessed by transcortical microdialysis

Morphine (M), morphine 3-glucuronide (M3G) and morphine 6-glucuronide (M6G) were subcutaneously administered at 10 mg/kg in three groups of six awake rats. A transverse microdialysis probe was implanted in the brain cortex and dialysates were collected every 30 minutes for a period of 4 hours. Dialysates were measured by two different opiate radioimmunoassays. Maximum brain opiate concentrations, 41 +/- 10 ng/ml (M), 147 +/- 27 ng/ml (M3G), 177 +/- 43 ng/ml (M6G), were reached at the same Tmax, 0.75 h, and elimination half-lives ranged from 0.99 to 0.81 h for the 3 compounds. Kinetic parameters confirmed that penetration and elimination rates in the extracellular space of the rat brain cortex for the 2 hydrophilic M metabolites were similar to those of M. These results indicate for the first time that, in spite of their structural differences, glucuronide metabolites of M are capable of crossing the blood-brain-barrier (BBB) at the same rate as morphine does, but in higher amount.