Single-dose bioavailability of oral and intramuscular thiocolchicoside in healthy volunteers

A single dose of 8 mg of thiocolchicoside was administered to 12 healthy volunteers according to a Latin square design, either as tablets (reference), oral solution, or intramuscular injection. Serum thiocolchicoside concentrations showed an absorption phase followed by a biexponential decay with a terminal half-life (t1/2 beta) of approximately 5 h, similar for the three formulations. The relative bioavailability of both oral formulations was approximately 25%, compared to the intramuscular formulation. There was a trend for the oral solution to have a slightly larger AUC and Cmax, as well as a slightly shorter Tmax, than the tablet formulation. However, the comparison of the two oral forms did not show statistically significant differences in the pharmacokinetic parameters Cmax, Tmax, and AUC, suggesting that the Coltramyl tablets have an adequate in vivo dissolution profile.

Pharmacokinetics and absolute bioavailability of colchicine after i.v. and oral administration in healthy human volunteers and elderly subjects

The pharmacokinetics of colchicine were studied in six healthy male and four elderly female volunteers after i.v. and oral administration. Plasma samples were collected over 72 h and assayed for colchicine by a specific and sensitive radioimmunoassay. Plasma concentration-time curves were fitted using a three-compartmental model after i.v. administration of 0.5 mg (healthy volunteers) and 1 mg (elderly group) colchicine. The first distribution half-life (t1/2 lambda 1) was short: 9.2 min in healthy volunteers and 3.0 min in the elderly group; the second distribution half-life (t1/2 lambda 2) was of the same order for both groups, 1.2 h. Plasma elimination half-lives were also in the same range: 30 h for healthy volunteers versus 34 h for the elderly subjects. Mean residence time was also in the same range in the two groups: 27 h in healthy volunteers and 21 h for elderly subjects. The volume of distribution (Vz) was 6.7 l.kg-1 for the healthy group and 6.3 l.kg-1 for the elderly group, while Vss was smaller: 4.2 l.kg-1 for healthy volunteers and 2.9 l.kg-1 for elderly subjects. Total body clearance was 10.5 l.h-1 for healthy and 5.5 l.h-1 for elderly subjects. After oral administration of 1 mg, lag-time was 14 min in healthy volunteers and 11 min in elderly subjects. Maximal plasma concentration was 5.5 ng.ml-1 at 62 min in the healthy group, while in the elderly group Cmax was 12 ng.ml-1 at 87 min. Mean absolute bioavailability of the tablet was the same in both groups, 44% for healthy volunteers and 45% for elderly subjects.

[Immunotherapy of drug poisoning]

Immunotherapy of drug intoxications is based on intravenous administration of antibodies or antibody Fab fragments specific to a drug. Mechanism of action involves toxin complexation in the antibody distribution space resulting in a gradient efflux of the toxin from its binding site by dissociation of toxin-receptor to the vascular space. Reversal of toxic effects by specific Fab fragments has been demonstrated experimentally for digitalis, colchicine and tricyclic antidepressants. The intravenous administration of antibodies or Fab fragments alters toxin pharmacokinetics including tissular depletion, plasma redistribution and decrease of systemic clearance. Benefit of this therapy in clinical toxicology has been clearly shown for cardiac glycosides but has to be confirmed for colchicine and tricyclic antidepressants. Safety and efficacy of specific Fab fragments should permit an extension of this antidotal procedure towards other toxins.

Effect of colchicine-specific Fab fragments on the hepatic clearance of colchicine

The influence of colchicine-specific Fab fragments on hepatic metabolism and biliary excretion of colchicine was studied in the isolated perfused rat liver. Isolated rat livers were perfused for 180 min with either [3H]colchicine (initial concentration: 50 ng/ml) or Fab-[3H] colchicine in a stoichiometrical proportion at a constant flow of 100 ml/min in a recirculating system. Based on perfusate concentrations, the hepatic extraction ratio of colchicine was more than 15-fold decreased when colchicine was bound to Fab fragments (E = 0.011 +/- 0.001) than when it was infused alone (E = 0.16 +/- 0.01) (p < 0.01). The extensive binding of colchicine to Fab over the experimental period as demonstrated by equilibrium dialysis (97 +/- 2%) prevented hepatic uptake. At the end of the colchicine perfusion experiment, 74.2 +/- 4.9% of the radioactivity infused was excreted by the biliary route. In contrast, biliary excretion of radioactivity was 10-fold lower when [3H]colchicine was perfused complexed with Fab fragments (p < 0.01). However, the metabolic profile of colchicine was not affected by Fab fragments. The apparent half-life of colchicine metabolites calculated from biliary data was similar to that of colchicine, indicating that the biliary excretion of these metabolites was formation rate-limited. Inhibition of colchicine uptake by specific Fab fragment was confirmed in vitro with isolated hepatocytes.

Colchicine disposition in human leukocytes after single and multiple oral administration

Inasmuch as leukocytes were reported to be an active pharmacologic compartment, colchicine disposition was determined in plasma, granulocytes, and mononuclear cells in healthy volunteers after 1 mg oral single and multiple doses. After the single dose, maximal colchicine concentration was observed at 1 hour in plasma and 47 hours later in leukocytes. This delay was confirmed by the slow accumulation of colchicine by lymphocytes in culture. In the multiple-dose study, mean granulocyte colchicine concentration (20 to 53 ng/10(9) cells) were twofold higher than in mononuclear cells (9 to 24 ng/10(9) cells). Mean predicted colchicine multiple-dose granulocyte and mononuclear cell concentrations were 2.5-fold and ninefold higher, respectively, than those measured. After the last dose, colchicine decreased, with half-life values between 41 and 46 hours for leukocytes and 49 hours for plasma. This study validates leukocytes as a microcompartment whose kinetics correlates with colchicine biologic effects.

Effect of fat substitutes, sucrose polyester and tricarballylate triester, on digitoxin absorption in the rat

The effect of non-absorbable fat substitutes (sucrose polyester (SPE) and tricarballylate triester (TCTE)) on [3H]digitoxin intestinal absorption was studied in the rat using a small intestine in-situ perfusion technique. The effect of SPE and TCTE was compared with that of sunflower oil, oleic acid, and saline. After 120 min perfusion, 5% SPE emulsion significantly reduced (P < 0.001) digitoxin absorption compared with all other treated groups. Five per cent TCTE emulsion had a less marked effect than SPE (P = 0.0002) and did not differ from sunflower oil. No difference was found between saline and 5% oleate emulsion, which did not reduce digitoxin absorption compared with other treated groups (P < 0.02). When taurocholic acid and lipase were added, results for the saline-, TCTE-, and SPE-treated groups were similar to those above, but the sunflower oil-treated group showed significantly enhanced (P < 0.01) digitoxin absorption. Thin-layer chromatography of the lipid phases showed hydrolysis of sunflower oil in the presence of taurocholic acid and lipase, but not of TCTE or SPE. The inhibitory effect of the non-absorbable fat substitutes on digitoxin absorption could be related to drug sequestration by the persistent oil phase constituted by the undigested and then unabsorbed fat substitutes. That part of digitoxin dissolved in the undigested oil phase is consequently unavailable for intestinal absorption.

Development of a sensitive radioimmunoassay for Fab fragments: application to Fab pharmacokinetics in humans

Anti-sheep Fab fragment antisera were produced in rabbits using sheep digoxin-specific Fab fragments (Digidot) as immunogen. These antisera were used for the development of a radioimmunoassay (RIA) of sheep Fab fragments in human plasma and urine using 125I-labeled Fab fragments. Interference in the assays by digoxin, human proteins, and antibodies from different species was insignificant, but cross-reactivity between anti-sheep Fab antisera and goat IgG or Fab fragments was 22 to 67%. The limit of detection was 0.1 microgram/mL and the assay was linear over a 0.6-28 micrograms/mL range of Fab fragments. Intra- and interassay coefficients of variation were less than 6.9 and 10.5%, respectively. Accuracy of plasma and urine assays at various Fab fragment levels ranged from 96 to 106%. RIA was applied to the pharmacokinetic study of sheep digoxin-specific Fab fragments in one patient acutely intoxicated by digitoxin and treated with Digidot. The Fab elimination half-life was 12.1 hr. Steady-state volume of distribution and total-body clearance were 10.8 L and 23.4 mL/min, respectively. Unchanged Fab fragments (50 kD) and degradation products (25 kD) isolated by gel filtration chromatography of a urine sample cross-reacted with the anti-Fab antiserum.

Monoclonal antibodies in hapten immunoassays

This review deals with the potency of monoclonal antibodies (MAbs) to haptens in immunoassays. Specificity and affinity of MAbs to haptens are the major determinants to be considered. Specificity of MAbs depends on the selection of the hapten coupling site to the carrier protein and the antigen used for the screening of MAbs. Nevertheless, cross-reactivity can occur with compounds related to the hapten. This polyspecificity may be circumvented with the use of many MAbs, as has been demonstrated for MAbs to cyclosporine. Affinity of MAbs to haptens is often lower than that of corresponding polyclonal antibodies (PAbs), thereby limiting assay sensitivity. Low affinity is more frequently observed with low molecular weight (100-300) haptens than with larger haptens, such as digoxin or cyclosporine. Affinity enhancement by increasing resemblance to the immunogen can be effective in resolving the lack of sensitivity. With suitable selection strategies. MAbs exhibit real advantages over classical PAbs to haptens because large amounts of worldwide standardized reagents can be prepared.

Analytical control procedures of immunoreactivity for IgG and Fab fragments specific to haptens

This study investigates immunoreactivity control procedures, i.e., specificity, affinity constant (Ka), and specific active binding sites (SABS), for polyclonal anticolchicine, monoclonal antidigitoxin IgG and Fab fragments, and antidigoxin Fab fragments (Digidot). Preliminary control procedures for IgG and Fab fragment purity indicated that all reagents were immunologically pure. All IgG and Fab fragments exhibited similar cross-reactivity and Ka. No decrease in percentage of Fab fragment SABS was observed after papain cleavage of anticolchicine and antidigitoxin IgG. Nevertheless, only 4.3 +/- 1.2% of nonimmunopurified anticolchicine polyclonal Fab fragments and 76.2 +/- 2.3 to 88.7 +/- 2.5% of different batches of immunopurified anti-digoxin Fab (Digidot) were active, the latter percentage being in the range of the 85% specified by the manufacturer. Only 58 +/- 3% of digitoxin-specific monoclonal IgG was active and 67 +/- 7% of its Fab fragments. Results show the importance of determining the ratio of SABS to presumed total specific binding sites for pharmaceutical monoclonal and polyclonal antibody preparations against haptens.

Colchicine-specific Fab fragments alter colchicine disposition in rabbits

High-affinity goat antibodies and Fab fragments (Ka = 1.1 x 10(10) M(-1) specific to colchicine were prepared to study their effect on colchicine pharmacokinetics in rabbits. First, colchicine disposition kinetics were investigated in four control rabbits after administration of 0.1 mg/kg i.v. Total and free plasma and urine colchicine were assayed by specific radioimmunoassay. The mean elimination half-life of total plasma colchicine was 16 +/- 2.9 h. Colchicine has a large volume of distribution (8.8 +/- 1.8 l/kg) and a low systemic clearance (114.6 +/- 3.4 ml.h-1.kg-1). Renal clearance represented 30.7 +/- 1.9% of total body clearance. The free plasma colchicine fraction was 70% after equilibrium dialysis. Second, 1.5 h after injection of 0.1 mg/kg colchicine, four rabbits were infused over 0.25 h with colchicine-specific Fab fragments at a half-stoichiometrically equivalent dose compared to the colchicine dose. Within 15 min after Fab infusion, total colchicine concentrations increased 10- to 16-fold. Mean area under the plasma concentration-time curves increased 20-fold compared to controls. The free plasma fraction decreased to an undetectable level over a period of 2 h. The Fab fragment administration also produced, respectively, a 24- and 17-fold decrease in the volume of distribution and systemic clearance. Colchicine recovered in urine was significantly higher than in the control group: 44.7 +/- 2.3 and 30.9 +/- 2% of the dose, respectively (P less than .05). These data suggest that high-affinity colchicine-specific Fab fragments can sequestrate and extract colchicine from tissues to the vascular compartment with subsequent colchicine excretion by the renal route.

[Combined ursodeoxycholic acid plus colchicine--treatment of primary biliary cirrhosis: results of a placebo-controlled double-blind study]

In the present pilot study we investigated the effects of urso treatment alone in comparison to a combined treatment with urso plus colchicine in PBC. 22 patients with PBC in the histological stages 1-3 entered the study. All patients were pretreated with urso alone (10-12 mg/kg) for 12 months. Thereafter treatment was continued in a double-blind randomized fashion with urso plus placebo or urso plus colchicine (1 mg/day) for another 12 months. During the initial 12 months urso treatment liver function tests improved significantly in all patients, pruritus improved in 60% of patients. After randomization to the different treatment groups the biochemical parameters stabilized at the lower level and no significant differences could be found between urso plus placebo and urso plus colchicine treatment concerning aminotransferases, alkaline phosphatase, bilirubin, cholinesterase, albumin or cholesterol. The results of this pilot study suggest that the addition of colchicine to an initial urso treatment does not lead to further improvement of aminotransferases, alkaline phosphatase, bilirubin or clinical symptoms like pruritus.

Pharmacokinetics of colchicine: a review of experimental and clinical data

Thanks to the development of a sensitive and specific radioimmunoassay for colchicine, the pharmacokinetics of colchicine is now well-established after single oral doses. Absorption is characterized by a zero-order rate constant while disposition appears biexponential with a rapid distribution phase (t1/2 = 1.8 h) and a long elimination phase (t1/2 = 20 h). All studies confirm the large total body clearance (35 l/h) predominantly by the extrarenal route and the large distribution volume (700 l). Further studies need to be performed to investigate colchicine absorption and to describe the metabolic pathway of the drug. To date, relationships between colchicine plasma levels and pharmacological effects have not been defined. Monitoring of plasma levels in patients with familial Mediterranean fever should improve treatment with colchicine. However, the therapeutic range has not been precisely determined. The use of colchicine in the treatment of liver cirrhosis and primary biliary cirrhosis is a recent development; so, assuming that a large part of total body clearance depends on hepatic function, the influence of hepatic diseases on colchicine disposition needs to be investigated in order to define the most appropriate therapeutic dosing.

Temperature-dependent immunoreactive assay to screen for digoxin-like immunoreactive factor(s)

Endogenous circulating digoxin-like immunoreactive factors (DLIF) are known to cross-react with antibodies to digoxin and to inhibit Na+/K(+)-transporting ATPase (Na+K+ATPase; EC 3.6.1.37). Moreover, increasing the immunoassay temperature from 4 to 37 degrees C markedly decreases DLIF from human cord serum. We tested several compounds, including hormonal steroids, bile salts, lipids, and methionine-enkephalin, for their ability to cross-react with two commercially available 125I digoxin RIAs, to inhibit porcine Na+K+ATPase, and to see whether they present the same incubation temperature dependence as human cord serum. Except for methionine-enkephalin, all compounds were inhibitors of Na+K+ATPase in the range of 1-10 mmol/L. Progesterone exhibited the highest cross-reactivity in the two RIAs. The apparent digoxin immunoreactivity for the majority of the cross-reacting steroids, bile salts, and linoleic acid was markedly decreased by increasing the incubation temperature from 4 to 37 degrees C, whereas estriol, pregnanediol, and nonspecific compounds (e.g., ethanol, human serum albumin) did not appear to be temperature-sensitive. Both lysophosphatidyl lipids gave an increased apparent digoxin concentration with increasing incubation temperature. Our data suggest that numerous weakly cross-reactive compounds can parallel the response of human cord serum. However, the temperature-dependent effect could be an additional criterion for identifying DLIF.

Temperature-dependent immunoreactive assay to screen for digoxin-like immunoreactive factor(s)

Endogenous circulating digoxin-like immunoreactive factors (DLIF) are known to cross-react with antibodies to digoxin and to inhibit Na+/K(+)-transporting ATPase (Na+K+ATPase; EC 3.6.1.37). Moreover, increasing the immunoassay temperature from 4 to 37 degrees C markedly decreases DLIF from human cord serum. We tested several compounds, including hormonal steroids, bile salts, lipids, and methionine-enkephalin, for their ability to cross-react with two commercially available 125I digoxin RIAs, to inhibit porcine Na+K+ATPase, and to see whether they present the same incubation temperature dependence as human cord serum. Except for methionine-enkephalin, all compounds were inhibitors of Na+K+ATPase in the range of 1-10 mmol/L. Progesterone exhibited the highest cross-reactivity in the two RIAs. The apparent digoxin immunoreactivity for the majority of the cross-reacting steroids, bile salts, and linoleic acid was markedly decreased by increasing the incubation temperature from 4 to 37 degrees C, whereas estriol, pregnanediol, and nonspecific compounds (e.g., ethanol, human serum albumin) did not appear to be temperature-sensitive. Both lysophosphatidyl lipids gave an increased apparent digoxin concentration with increasing incubation temperature. Our data suggest that numerous weakly cross-reactive compounds can parallel the response of human cord serum. However, the temperature-dependent effect could be an additional criterion for identifying DLIF.

Reversal of murine colchicine toxicity by colchicine-specific Fab fragments

High-affinity Fab fragments (2 x 10(10) M-1) specific to colchicine were produced to evaluate their potency in reversing murine colchicine intoxication. Intraperitoneal injection of a 4.46 mg/kg colchicine dose was lethal for 100% of mice. 1.5 h after colchicine administration, a group of 10 mice was treated with colchicine-specific Fab fragments at a half-stoichiometrical dose compared to the colchicine dose by intravenous and intraperitoneal routes. 70% of the Fab-infused mice survived (P less than 0.01). This high efficiency of colchicine-specific Fab fragments in reversing acute murine colchicine toxicity suggests that Fab fragments would be an efficient antidote for the treatment of human colchicine poisoning.

Relationship between red blood cell potassium and plasma digitoxin concentrations in intoxicated patients

After severe acute self-poisoning by cardiac glycosides, significant and persistent depletion of red blood cell K+ due to inhibition of Na+K+ ATPase is seen. Because of a delay between the time course of plasma digitalis concentrations and that of red blood cell K+ depletion, no direct relation exists between the two, and RBC K+ has hitherto not been considered useful as prognostic indicators of clinical outcome. In an effort to solve this problem, red blood cell K+ was measured by atomic absorption spectrophotometry and plasma digitoxin concentration assayed in six patients admitted to an intensive care unit after digitoxin self-poisoning. Using the effect compartment model of Sheiner, a relationship based on a sigmoid Emax model was able to relate the digitoxin concentration at the action site to red blood cell K+ depletion. Thus the duration of red blood cell K+ depletion could be predicted from two relative simple in vitro assays. Since RBC K+ is a marker of the inhibition of Na+K+ ATPase by digitoxin, this method could be of use for the management of patients self-poisoned with digitalis.

Morphine pharmacokinetics and pain assessment after intracerebroventricular administration in patients with terminal cancer

Morphine pharmacokinetics and pain relief were evaluated after intracerebroventricular administration of morphine (0.4 +/- 0.11 mg) in seven patients with cancer suffering from intractable pain. Ventricular cerebrospinal fluid (CSF), lumbar CSF, and plasma morphine concentrations were analyzed by a specific morphine radioimmunoassay. A two-compartment model was sufficient to describe the kinetics of morphine in ventricular CSF. Morphine diffuses to the lumbar level, and the mean maximum concentration was 192 +/- 105 ng/ml at 4.5 +/- 1.3 hours. Ventricular and lumbar CSF morphine kinetics showed a similar decline during the elimination phase, with terminal half-lives of 3.8 +/- 0.6 hours and 4.2 +/- 1.6 hours, respectively. Pain relief was evaluated by a visual analog scale: the test showed a rapid onset of analgesia (less than 10 minutes). Analgesic effectiveness reached a maximum between 6 and 10 hours. The relationship between pharmacologic effect and morphine concentrations in ventricular CSF resulted in an anticlockwise hysteresis curve. The presence of morphine in lumbar CSF suggested an additive spinal action of morphine, which probably plays a role in the duration of analgesia.

Highly specific radioimmunoassay for digoxin using a monoclonal antibody selected for lack of interference by digoxin-like immunoreactive substances in cord blood sera

Four digoxin radioimmunoassays (RIA) were evaluated using four antidigoxin monoclonal antibodies (MAb) with different binding specificities for digoxin metabolites and other glycosides. These RIA have been used to measure the apparent digoxin concentrations in the sera of patients treated with digoxin, in cord blood sera and in rat intestine aqueous extracts. Two MAb strongly recognized digoxin-like immunoreactive substances (DLIS) in cord blood sera and in rat intestine aqueous extract. In contrast, one MAb (2C2), which recognizes active digoxin metabolites and does not cross-react with inactive metabolites nor with digotoxin, showed no reactivity with DLIS in the cord blood sera tested. This MAb was used in a new digoxin RIA that was rapid, sensitive, reproducible, and specific for digoxin and its active metabolites.

Existence of a digitalis-like compound in the human fetus

Digoxin-like inhibitors of Na+,K(+)-ATPase have been implicated in several pathophysiological problems in the perinatal period. Aqueous endogenous digoxin-like immunoreactive substance (DLIS) was extracted from 9 different organs of a 24-week-old human fetus whose mother died after paraquat poisoning. The results indicate that this endogenous DLIS has a wide distribution in fetal tissues. The highest levels were found in gut and adrenals, and there was a correlation between these high levels and the inhibition of Na+,K(+)-ATPase. The hypothesis that DLIS originated in the fetus is of particular relevance.

Dose-dependent reversal of acute murine colchicine poisoning by goat colchicine-specific Fab fragments

The use of colchicine-specific Fab fragments is of interest in human poisoning. In the present study, we show the efficacy of Fab fragments in reversing colchicine toxicity in mice. High affinity antibodies (Ka = 2 x 10(10) M-1) against colchicine were raised in goats; Fab fragments were purified by DEAE chromatography after papain hydrolysis of IgG. Mice were intoxicated with a 100% lethal colchicine dose (3.8 mg/kg). When a half molar dose (M/2) of Fab fragments in relation to the colchicine dose was intravenously and intraperitoneally administered 90 min after colchicine infusion using a multiple dosage schedule, 80% of the Fab-treated mice survived compared to the control group which did not receive Fab fragments (P less than 0.01). Using a M/4 and M/8 dose of Fab fragments, the mortality was respectively 50% and 80%. The dose-effect relationship was linear (r = 0.99). Delayed administration of a M/2 dose of Fab fragments 6 h after colchicine administration resulted in 50% survival (P less than 0.01). Body temperature and body weight were selective markers of the severity of the intoxication. In the control group, a marked decrease of body temperature was observed following the first few hours after the intoxication (-21% compared to basal value 48 h after colchicine). In the Fab-treated group, the decrease was inversely related to the Fab fragment dose. Body temperature returned to the basal values 7 days after intoxication. A progressive decrease in body weight was concomitantly observed in intoxicated mice until death, while values returned to baseline 9 days after colchicine in surviving Fab-treated mice.

Extrahepatic metabolism of morphine occurs in humans

The pharmacokinetics of morphine was studied in six patients in whom a radiologic localization of an insulinoma was to be performed under general anesthesia. Sampling was done in the peripheral artery, the mesenteric vein in five of the six patients, the hepatic vein, and the peripheral vein, as well as in urine. Hepatic blood flow was estimated by an indocyanine green infusion technique at the end of the radiologic procedure. Morphine terminal half-life was 92 +/- 9 minutes, total body clearance was 1260 ml.min-1, and the hepatic extraction ratio was 0.65 +/- 0.11. No concentration gradient was observed between the artery and the superior mesenteric vein, showing that no gut wall metabolism of morphine occurred. The total body clearance exceeded the hepatic clearance by 38%. It was concluded that the extrahepatic extraintestinal clearance of morphine probably occurred through the kidney.

1-Methyl-4-phenylpyridinium (MPP+) does not exhibit paraquat-like immunoreactivity

The structural analogy of paraquat with 1-methyl-4-phenylpyridinium (MPP+) has been implied in the aetiology of Parkinson's disease. The cross-reactivity of MPP+ to a specific antibody to paraquat was assessed by radioimmunoassay and was found to be very low. The results suggest that this polyclonal paraquat antibody does not mimic the MPP+ receptor.

Reversal of advanced colchicine toxicity in mice with goat colchicine-specific antibodies

Colchicine-specific antibody (IgG(C] was tested in mice for reversal of colchicine toxicity. The mouse model was chosen because it reflects human pathophysiology in colchicine poisoning. IgG(C) was administered when at least 85% of colchicine was distributed in tissues. It resulted in a dramatic decrease in lethality from 85% (control group) to 10% (treated group). The decrease in toxic effects was confirmed by evaluating physiological parameters. The recovery of thermoregulation was very rapid in mice treated with IgG(C), while recovery in body weight was less marked. IgG(C) administration, therefore, decreases the intensity but may extend the duration of colchicine toxicity (reversible binding). The total neutralizing binding capacity of IgG(C) used was such that administered IgG(C) neutralizing binding sites were either 7 or 15% of the injected colchicine dose. In spite of this low neutralizing capacity the treatment was successful because of the ability of IgG(C) to buffer the amount of colchicine molecules on the critical slope of the dose-lethality curve.

The effect of nortriptyline-specific active immunization on amitriptyline toxicity and disposition in the rabbit

Rabbits were actively immunized by a conjugate of nortriptyline (NT) to study the effect of specific anti-NT antibodies on toxicity and disposition of amitriptyline (AT). Control and immunized rabbits received 115 mg/kg AT intraperitoneally (i.p.). The lethality dose (LD) profile exhibited a gentle slope; LD100 and LD0 were separated by 100 mg/kg. Mortality was significantly reduced from LD67 to LD43 (P less than 0.05). Total plasma concentrations of the toxin were increased in the immunized group compared to the control group. AUC0.5-24 h value was 5-fold higher in the immunized group than in the control group. Moreover, a smaller fraction of unbound toxin in plasma was observed in the immunized group than in the control group. These observations indicate that AT was actively sequestered by antibodies. The intensity of this phenomenon was a function of both the antibody affinity constant (10(9) M-1) and the neutralizing capacity (varying from 0.005 to 0.2 mg/kg) of the circulating antibodies in each immunized rabbit. Results clearly show that anti-NT antibodies are able to effectively sequestrate AT.

Specific anti-digoxin Fab fragments: an available antidote for proscillaridin and scilliroside poisoning?

The purpose of this study was to evaluate the capacity of specific anti-digoxin Fab fragments to bind to and neutralize scilliroside and proscillaridin in acute poisoning. Apparent affinity constants were determined with values of 2.6 10(8)M-1 for scilliroside and 3.8 10(7)M-1 for proscillaridin. These results are in accordance with a possible in-vivo neutralization of these toxins.

In vivo spectrophotometric determination of striatal acetylcholinesterase activity: the modulation induced by the antidepressant amitriptyline

A new technology called in vivo spectrophotometry was applied to the quantitative determination of the variations in local acetylcholinesterase (AChE) activities. Repeated measurements of the enzyme activities in the same live animal allowed the study of the in vivo inhibition of AChE by amitriptyline. Interactions between AChE and this tricyclic antidepressant were investigated at the striatal level in anesthetized rats. In this anesthetized model, AChE assays were shown to be stable for approximately 8 h. The dose-effect relationship was explored in the 2.5- to 50-mg/kg amitriptyline range. A reversible inhibition was observed after acute amitriptyline administration. The maximum of inhibition appeared between 90 and 210 min after the intoxication and reached up to 22% for the 50-mg/kg dose. The threshold dose was established as 8 mg/kg. Evidence for an indirect interaction between tricyclic antidepressant and AChE was demonstrated when the total integrity of the biological system was preserved.

Toxicokinetics of paraquat in humans

1. The toxicokinetics of paraquat were studied in 18 cases of acute human poisoning using a specific radioimmunoassay. Plasma paraquat concentration exhibited a mean distribution half-life (t1/2 alpha) of 5 h and a mean elimination half-life (t1/2 beta) of 84 h. Cardiovascular collapse supervened early during the course of the intoxication and was associated with the distribution phase. Death related to pulmonary fibrosis occurred late and was associated with the elimination phase. 2. Pharmacokinetic analysis of urine paraquat excretion confirmed the biphasic decline of paraquat. Moreover, renal paraquat and creatinine clearances were not correlated but renal paraquat clearance was never higher than the renal creatinine clearance. 3. Tissue paraquat distribution was ubiquitous with an apparent volume of distribution ranging from 1.2 to 1.6 l/kg. Muscle could represent an important reservoir explaining the long persistence of paraquat in plasma and urine for several weeks or months after poisoning.

Influence of goat colchicine specific antibodies on murine colchicine disposition

The potential use of colchicine-specific antibodies (IgG(C)) to overcome colchicine intoxication in mice is of interest in human poisoning. Pharmacokinetics in mice are similar to those in humans. A short distribution half-life (t 1/2 a = 34 min) is associated with a long elimination half-life (t1/2 beta = 48 h) together with a large volume of distribution at steady-state (Vss = 2.5 l/kg) and a low total body clearance (ClT = 1 ml/min/kg). This extensive and rapid distribution to tissues impairs the success of conventional therapies. Despite the administration of a relatively low amount of IgG (C) (15% binding sites vs, colchicine molecules), the beneficial effect of IgG(C) is demonstrated by the alteration in colchicine pharmacokinetics which occurs rapidly following IgG(C) administration as demonstrated by rise in blood toxin concentrations (4-fold relative to IgG(N)-treated controls). This sequestration in the blood is associated with a colchicine redistribution from peripheral to the blood compartment. This extraction effect is revealed by lower colchicine tissue levels in IgG(C)-treated mice than in controls. As a consequence, Vss decreased in the IgG(C) group. Moreover, ClT is diminished in the IgG(C)-treated group because the relatively large immunoglobulin can not be excreted renally. In addition to this toxin displacement, study of free and bound colchicine plasma levels shows a lower percentage of free toxin in the IgG(C)-treated group (33 to 0%) compared to 70% in the control group. This pharmacokinetic study provides evidence that the administration of IgG(C) alters the colchicine disposition by sequestrating and extracting colchicine in blood compartment.

Pharmacokinetics/bioavailability of colchicine in healthy male volunteers

In a randomized 2-way cross-over study with twelve healthy male volunteers, two colchicine preparations (tablets, A vs. oral solution, B) were tested. The preparations were administered as single doses of 1 mg; prior to and up to 72 h after medication blood samples were collected and the plasma colchicine concentrations determined. Additionally urine samples were collected at 0-2, 2-4, 4-6, 6-8, 8-10, 10-24, 24-48, 48-72 and 72-96 h intervals. The colchicine plasma and urine concentrations were determined by a newly developed and validated RIA method. The mean area under the plasma concentration-time curve (AUC-1, AUC-3) was calculated as 23.95 +/- 12.10 (AUC-1) and 26.73 +/- 12.75 (AUC-3) h.ng/ml after application of A and 28.01 +/- 14.74 (AUC-1) and 31.57 +/- 16.58 (AUC-3) h.ng/ml after application of B, respectively. Mean peak plasma concentrations of 4.15 +/- 2.35 (A) and 4.88 +/- 3.90 (B) ng/ml were reached at 1.15 +/- 0.38 (A) and 1.13 +/- 0.42 (B) h after application. The mean terminal half-lives accounted for 9.31 +/- 3.98 (A) and 10.57 +/- 5.53 (B) h. The mean total clearance (Cl/F) and volume of distribution (V/F) were found to be 40.12 +/- 20.87 (A) and 46.58 +/- 24.65 (B) l/h and 472.59 +/- 196.46 (A) and 624.89 +/- 304.09 (B) l, respectively. The mean total amount excreted in urine (Ae) was 172.66 +/- 91.51 (A) and 174.85 +/- 63.53 (B) micrograms.(ABSTRACT TRUNCATED AT 250 WORDS)

Model-independent pharmacokinetics of colchicine after oral administration to healthy volunteers

The pharmacokinetics of colchicine were studied after oral administration of three doses (0.5, 1.0 and 1.5 mg) to nine healthy male volunteers according to randomized cross-over design. Plasma and urine samples were collected during 48 h after ingestion, and assayed for colchicine levels by a specific and highly sensitive radio-immunoassay. Pharmacokinetic parameters t1/2 beta, AUC, MRT, CIT/F, CIR, Vd area/F) were calculated by model-independent methods and compared across doses by multiway analysis of variance. Terminal half-life (15.5-19.2 h), mean residence time (15.7-20.3 h), oral systemic (32.2-40.3 l/h) and renal (3.9-4.7 l/h) clearances, and oral volume of distribution (11.4-14.9 l/kg) did not differ significantly between doses, whereas the area under the concentration-time curve was proportional to dose. Our results show that: 1. within the dose range studied (0.5-1.5 mg), the pharmacokinetics of colchicine are linear; 2. monitoring colchicine levels up to 48 hours yields much larger estimates of terminal half-life and volume of distribution than previously reported from considerably shorter studies.

The effect of colchicine-specific active immunization on colchicine toxicity and disposition in the rabbit

Anti-colchicine antibodies raised in rabbits are effective at protecting rabbits from acute colchicine intoxication. The positive effect depends on the ratio between the binding site capacity of the specific antibodies and the colchicine dose. Immunized rabbits receiving 6 mg/kg colchicine intravenously (LD100) died within 8 h as rapidly as those of the non-immunized control group. In contrast, if the colchicine dose was reduced to 3 mg/kg (LD83), rabbits were protected and mortality decreased to 17%. Study of plasma colchicine pharmacokinetics indicated that colchicine was totally sequestrated by antibodies in the 3 mg/kg group and only 55-80% sequestrated in 6 mg/kg group. This sequestration contributed to reducing colchicine diffusion into tissues (the volume of distribution decreased 7-fold) and to increasing the terminal half-life and the total body clearance of the drug. Moreover, as the slope of the dose-lethality curve was steep, a small binding capacity was sufficient to neutralize colchicine toxicity at 3 mg/kg. Results clearly indicate that anti-colchicine antibodies are able to effectively sequestrate colchicine. Moreover, the amount of circulating antibodies is a crucial limiting factor for the effectiveness of immunotoxicotherapy.

Immunotoxicotherapy: present status and future trends

Immunotoxicotherapy (ITT) is currently used in humans for the treatment of snake venom and cardiac glycoside poisoning. Other toxins have been studied in animals or in vitro to assess their suitability as candidates for detoxification by specific antibodies. Testing conditions are often empirical suggesting that numerous improvements need to be introduced in ITT. Basic mechanisms in ITT include three phases: sequestration, extraction and elimination. The pharmacokinetics of these three phases depend on the type of antidotal binding site (ABS). IgG or its Fab2, Fab or Fv fragment are the possible choices. The Fab fragment is the most frequently used ABS because of its diffusion properties in the peripheral compartments and its renal excretion by glomerular filtration. Toxicokinetic and pharmacokinetic considerations indicate that the dosage cannot be satisfactorily calculated from stoichiometric principles. Study of the toxin dose-lethality curves shows that ABS dosage can be lowered. Moreover, clinical data reveal that some FAb fragments are directly eliminated without acting on toxin molecules. In order to counteract these drawbacks, a compromise between dosage and duration of infusion is suggested. Other improvements will stem from advances in immunologic methodology. Monoclonal and chimeric antibodies are new tools that will help resolve the clinical problems of immunogenicity and adverse reactions associated with polyclonal ABS.

Zero-order absorption and linear disposition of oral colchicine in healthy volunteers

The pharmacokinetics of colchicine has been studied in nine healthy male volunteers after oral doses of 0.5, 1, and 1.5 mg as tablets. Plasma and urine samples were collected over 48 h and analysed for colchicine by radioimmunoassay. Individual colchicine concentration profiles in plasma and urine were well described by a two-compartment open model with zero-order input. Considering the absorption variables as specific to each experiment, the lag time (0-0.35 h) and duration (0.39-2.38 h) of absorption were found to be independent of dose, while the zero-order rate constant of absorption (k0) increased linearly with dose. Disposition variables were taken as common to the three experiments, except in six subjects in whom renal excretion varied significantly across experiments in a dose-independent manner. For seven subjects the terminal half-life was 19.4 h, the oral apparent volume of distribution at steady-state (Vss/f) was 691 l, and the oral systemic clearance (CL/f) was 33.1 l.h-1. In the two other subjects, the values were unreliable, but the estimated terminal half-life was greater than 48 h, Vss/f ranged from 1690 to 3480 l, and CL/f was in the range of the other subjects in 1 subject, and it was about 15 l.h-1 in the other. In the latter subject, these estimates, together with the observation that plasma concentration reached a plateau at 2 to 5 h after ingestion, suggest enterohepatic cycling of colchicine. Overall, the disposition of colchicine was linear in the dose range 0.5-1.5 mg, with a long terminal half-life, and absorption obeyed zero-order kinetics, with k0 proportional to dose.

Toxicokinetics of paraquat through the heart-lung block. Six cases of acute human poisoning

A technique is described in which the toxicokinetics of paraquat on passage through the heart and lung were studied by means of blood samples drawn simultaneously from the pulmonary and radial arteries in six cases of acute human life-threatening paraquat intoxications. There was a trend for the radial plasma concentrations of paraquat to be greater than or equal to the pulmonary concentrations. This data suggests that from a clinical point of view the distribution of paraquat into the lungs is not a slow process. There may also exist some efflux of the paraquat into the circulation. This efflux of paraquat may result from direct lung and/or heart injury induced by massive paraquat poisoning.

Disposition of monodesethylamodiaquine after a single oral dose of amodiaquine and three regimens for prophylaxis against Plasmodium falciparum malaria

The disposition of monodesethylamodiaquine was studied in four healthy subjects after a single oral dose of 10 mg/kg amodiaquine base. Amodiaquine was not found in any sample, but the major metabolite monodesethylamodiaquine was detected and was assumed to be the sole derivative that contributed significantly to antimalarial activity in the blood. The best fit for the decay of the metabolite was obtained with a three-compartment model. The half-lives of the first two phases were 3.2 to 11.4 h for t1/2 alpha 1 and 22.7 to 50.3 h for t1/2 alpha 2 in plasma. The half-life of the terminal phase (t1/2 beta) was between 9 and 18.2 days. The concentration in whole blood was 4- to 6-times higher than in plasma. Three schedules (alternate days, weekly, daily) of the conventional prophylactic dose of 10 mg/kg per week were compared in six other healthy subjects. There were significant differences in the plasma monodesethylamodiaquine levels between the three schedules.

Pharmacokinetics of unchanged morphine in normal and cirrhotic subjects

Published reports of morphine pharmacokinetics differ, perhaps because of analytical discrepancies and different study protocols. A highly specific radioimmunoassay (N-carboxymethylnormorphine RIA) was used to measure unchanged morphine in plasma in six normal subjects and in eight cirrhotic patients with hypoalbuminemia, hyperbilirubinemia, and prolonged prothrombin time. All subjects received a single intravenous bolus of morphine hydrochloride (0.1 mg/kg). Peripheral blood samples were collected at frequent intervals from 2 min to 36 hr after injection. In cirrhotic patients as compared with normal subjects, terminal half-life of unchanged morphine was longer (201 +/- 39 vs 111 +/- 32 min (mean +/- SD), P less than 0.01) and total body clearance was slower (21 +/- 7.5 vs 33.5 +/- 8 ml X min-1 X kg-1, P less than 0.05). The apparent volume of distribution and the steady-state volume of distribution did not differ in the two groups. In conclusion, cirrhotic patients have a prolonged terminal half-life of unchanged morphine that is attributable to a decrease in total body clearance.

Morphine pharmacokinetics in renal failure

The effect of chronic renal failure (RF) on the pharmacokinetics of morphine was studied in nine patients with end-stage RF, aged 58 +/- 8 yr (SD), and in seven control patients, aged 58 +/- 15 yr, undergoing peripheral surgery under general anesthesia. All patients received 0.2 mg X kg-1 as an intravenous bolus injection. Blood samples were collected over a 36 h period, and plasma concentrations were measured using a specific radioimmunoassay method. Unchanged morphine could be identified for only 12 h in all patients. The mean plasma concentrations of unchanged morphine were similar in the two groups, except in the first sample (5 min) where it was higher (P less than 0.05) in RF group. Patients with RF had a significantly smaller (P less than 0.05) central compartment (0.3 +/- 0.2 l X kg-1 versus 0.8 +/- 0.4 l X kg-1) than in the controls. Volume of distribution at steady state was also significantly (P less than 0.05) decreased in RF patients (2.8 +/- 1.0 l X kg-1) versus 3.7 +/- 1.2 l X kg-1 in the normal patients. The total apparent volume of distribution, the elimination half-life, and the plasma clearance were similar in the two groups. Identical peak levels of morphine metabolites were observed in the two groups, but plasma concentration of morphine metabolites was undetectable after 12 h in the control group and remained at a high level of 82 +/- 49 ng X ml-1 at 24 h and 83 +/- 57 ng X ml-1 at 36 h in RF patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic value of plasma and urine paraquat concentration

A non-exponential mathematical equation was used to extrapolate the 'predictive line' for plasma paraquat concentrations beyond 24 h. Plasma paraquat concentrations were measured in 30 patients who were admitted more than 24 h after overdose. The extrapolated line accurately predicted the outcome in 27 of these 30 patients. Urine paraquat concentrations were measured in 53 patients. All patients with urine paraquat concentrations of less than 1 mg/l (colourless or light blue test result using the colorimetric test) within 24 h of overdose survived. In contrast, patients with urine paraquat concentrations of more than 1 mg/l had a high probability of death. Even if plasma paraquat concentrations have a higher predictive value, urine data may contribute to a more rapid evaluation of prognosis.

Elimination of paraquat

There is a striking discrepancy between the efficacy of the kidneys, haemodialysis and haemoperfusion in removing paraquat from the body and the poor prognosis of paraquat poisoning even when the blood and urine concentrations (which are good indices of concentrations in lung and other tissues) are very low. Extracorporeal elimination techniques have been used world-wide in paraquat poisoning. Do they remove paraquat effectively? Certainly. Do they increase the survival rate? Probably not. The reason being that when these techniques of elimination are initiated, potentially lethal concentrations of paraquat have already been attained in the highly vascular tissues of vital organs and in pneumocytes. The data presented here suggest that the successful treatment of paraquat poisoning will not be achieved by modification of toxicokinetics.

Endogenous digitalis-like immunoreactive substances in cord serum characterized by anti-digitoxin and anti-digoxin antibodies. Effect of modulated incubation conditions

Digoxin-like immunoreactive substances (DLIS) have been extensively described in biological fluids of pregnant women, neonates and renal impaired patients, by the use of several digoxin immunoassays. In this paper a similar interference with anti-digitoxin antibodies is reported by investigating 20 cord sera. By increasing both the time and the temperature of the incubation, the levels of digitalis-like immunoreactive substances may be modulated and decreased to zero. Digitoxin- and digoxin-like immunoreactive substances have been successfully extracted with methanol and concentrated from cord serum. Our data suggest the competitive nature of DTLIS and DLIS interactions with digitalis antibodies. They also show a means of minimizing these interferences in routine digitalis immunoassays.

[Guidelines for prescription of the assay of digitalis glycosides by immunologic methods]

Digoxin, digitoxin and acetyldigitoxin are the most widely prescribed of cardiotonic glycosides. Analytical exploration can be performed by a single assay when only one compound is prescribed or by multiple assays in cases of imprecise prescription or when several glycosides are given concomitantly. In addition, the metabolic transformation of digitoxin into digoxin and the presence of endogenous "digitalis-like compounds" mean that a number of precautions must be taken during prescription. These examples underline the ambiguity of the so-called "digitalinaemia" prescriptions and the need for biologists to be supplied with maximum information by clinicians.

Specific interaction between antidigoxin antibodies and digoxin-like immunoreactive substances in cord serum

Digoxin-like immunoreactive substances (DLIS) have been quantified by two different digoxin radioimmunoassays (RIA) in 47 cord sera. The mean DLIS value (in digoxin equivalents) ranged from 0.960 (SD 0.184) to 0.181 (SD 0.104) nmol/L between the two different kits and different lot numbers of the reagents. One of the RIA methods showed an obvious lot-to-lot effect. The use of a longer incubation interval and a higher incubation temperature markedly decreased cross reactions with DLIS. The effect of modifying the incubation conditions in RIA is similar to that described for assays of steroids because the dissociation rates of the immunocomplex play a critical role. Data suggest a specific interaction between DLIS and digoxin antibodies. Control of the incubation conditions is recommended, to decrease or increase the amount of the DLIS in cord serum specimens.

Rate-limiting diffusion processes following intrathecal administration of morphine

Morphine concentrations in plasma in five patients following intrathecal (i.t.) administration and in five other patients following intravenous (i.v.) administration were measured by a specific RIA sensitive to 0.1 ng/ml. Pharmacokinetic analysis showed a similar apparent total body clearance of morphine following both i.t. and i.v. administration, and complete bioavailability of i.t. morphine to the systemic circulation. This indicates that morphine is probably not metabolised in the CNS and that all of an i.t. dose diffuses from CSF to the plasma compartment. However a marked decrease in the i.t. terminal rate constants, involving a flip-flop phenomenon, contributed to the prolonged terminal half-life of i.t. morphine. The slow diffusion of morphine from the i.t. space to the plasma compartment can account for the prolonged analgesia following i.t. administration.