Pharmacokinetics of the chemoprophylactic and chemotherapeutic trypanocidal drug isometamidium chloride (Samorin) in cattle

Pharmacokinetics of the prophylactic and therapeutic trypanocidal drug isometamidium chloride were examined comprehensively for the first time in cattle using a recently described, highly sensitive ELISA. Cattle were administered single intravenous (N = 4) or intramuscular (N = 5) doses of isometamidium at a rate of 1.0 mg x kg(-1) body weight. Concentration data were analyzed over at least 14 days (intravenous treatment) or 30 days (intramuscular treatment) using compartmental and noncompartmental methods. After intravenous administration, apparent volumes of the central compartment (mean = 0.695 liter x kg(-1); range = 0.59-0.95) were large, and volumes of distribution at steady-state (mean = 24.5 liter x kg(-1): range = 18.5-39.3) were particularly large. After intramuscular administration, there was considerable individual variability in Cmax (mean = 111 ng x ml(-1); range = 37-197) and other pharmacokinetic parameters. Absorption kinetics seemed to be multifunctional, with fast and slow components; the mean t(max) was only 36 min (range = 20-60), although the mean absorption time was 282 hr, and the mean terminal elimination phase half-life after intramuscular administration (286 hr; range = 215-463) was over twice that after intravenous administration (mean = 135 hr; range = 123-165). The overall absolute bioavailability of intramuscular-administered isometamidium was 65.7%. These findings were consistent with extensive tissue binding at the intramuscular injection site to form a primary depot responsible for most of the prolonged chemoprophylactic effect of isometamidium, and an additional role for significant secondary drug depots formed by tissue binding elsewhere, particularly after intravenous administration.

An oral platelet-activating factor antagonist, Ro-24-4736, protects the rat kidney from ischemic injury

The role of platelet-activating factor (PAF) in ischemic acute renal failure was evaluated by administering an oral PAF antagonist (Ro-24-4736) to rats prior to or after interruption of blood flow to both kidneys for 30 min. In animals treated with the PAF antagonist prior to ischemia, renal function was less impaired and histological abnormalities was less pronounced when compared with postischemic kidneys from vehicle-treated animals. Serum creatinine (mg/ dl) 24 h following renal ischemia was 1.58 +/- 0.17 in the PAF antagonist-treated rats compared with 2.19 +/- 0.15 in rats given placebo (P < 0.01). There was less necrosis in the outer medulla of kidneys of PAF antagonist-treated animals (P < 0.01). Tissue myeloperoxidase activity at 48 and 72 h postischemia was lower in kidneys of PAF antagonist-treated rats (P < 0.05). The PAF antagonist was also protective when administered 30 min but not 2 h following the ischemic insult. The coincident use of anti-intercellular adhesion molecule-1 monoclonal antibody did not confer additional protection over that observed with the oral PAF antagonist alone. These data suggest that PAF contributes to the pathophysiology of renal ischemic injury, perhaps by its effects on leukocyte-endothelial interactions. An orally active PAF antagonist can protect against the development of ischemic acute renal failure.

Pharmacokinetics, bioavailability and tissue residues of [14C]isometamidium in non-infected and Trypanosoma congolense-infected Boran cattle

In this paper, pharmacokinetics, bioavailability and tissue residues are reported in non-infected and Trypanosoma congolense-infected Boran steers following either intravenous or intramuscular injection of [14C]isometamidium at a dose rate of 1 mg kg-1 body weight. Two differently labelled compounds of isometamidium were used; 6-14C (ISMM-1) and ring-U-14C (ISMM-2). The cattle were divided into 5 groups: group 1 consisted of 3 non-infected cattle treated with ISMM-1 by intravenous injection; group 2 consisted of 2 non-infected cattle treated with ISMM-1 by intramuscular injection; group 3 consisted of 2 Trypanosoma congolense-infected cattle given similar treatment as group 2 cattle; group 4 consisted of 3 non-infected and group 5 of 2 infected cattle treated with ISMM-2 by intramuscular injection. Radioactivity was measured in plasma, urine, faeces and tissues, and drug concentrations were calculated. Data obtained following i.v. treatment were best described by tri-exponential equations with half-lives of 0.13, 1.22 and 120.7 h. Bioavailability of the intramuscular dose was 58% in group 2 cattle. The major route of excretion was in faeces. Approximately 80% of the intravenous dose given was excreted within 21 days out of which only 18% was through urine. Total residues accounted for approximately 15% the total dose given. Drug residues remained high in organs with excretory functions including the liver and kidneys.

Comparative evaluation of the prophylactic effect of slow release devices containing homidium bromide and isometamidium on Trypanosoma congolense in rabbits

Two consecutive experiments were carried out to evaluate the prophylactic effect of biodegradable slow release devices (SRD), containing either isometamidium or homidium bromide. Rabbits subcutaneously implanted with SRD, were challenged with different Trypanosoma congolense stocks at regular intervals between 1 and 6.5 months after treatment. In a first experiment the efficacy of two types of isometamidium-SRD (poly(D,L-lactide) and poly(D,L-lactide-co-glycolide)) was compared with the classical intramuscular (i.m.) injection of the drug. Since the former polymer gave an average protection period, which was much longer than the other isometamidium formulation, a second experiment was carried out to evaluate the prophylactic effect of poly(D,L-lactide) SRD, containing either isometamidium or homidium bromide, with that of the i.m. injections of the same drugs at a dose of 1 mg kg-1. The average protection period of the homidium bromide SRD was significantly longer than that of the i.m. injected drug (112 vs. 49 days). No significant difference was obtained, however, when isometamidium was administered either as a SRD or as an i.m. injection. The average protection periods were, respectively, 106 +/- 37 days and 84 +/- 18 days. When breakthrough isolates derived from SRD-treated animals were compared with the original stocks of T. congolense, the former showed some loss of sensitivity to homidium bromide. No difference in sensitivity was observed, however, for isometamidium.

No evidence for mediation of ischemic preconditioning by alpha 1-adrenergic signal transduction pathway or protein kinase C in the isolated rat heart

The purpose of this study was to elucidate the role of activation of the alpha 1-adrenergic signal transduction pathway and of protein kinase C (PKC) in the mechanism of protection of functional recovery by ischemic preconditioning in the isolated perfused rat heart. After a stabilization period, nonpreconditioned and preconditioned isolated perfused rat hearts were subjected to sustained ischemia for 25 and 30 minutes of reperfusion. Preconditioning consisted of three episodes of 5 minutes of ischemia, interspersed with 5 minutes of reperfusion. The endpoint was postischemic functional recovery. The effectiveness of preconditioning in the presence of the alpha 1-adrenergic blocker prazosin, the selective PKC blockers chelerythrine and bisindolylmaleimide (BIM), and the ability of repetitive alpha 1-adrenergic activation to mimic preconditioning were compared with the appropriate nonpreconditioned and preconditioned control groups. Alpha 1-adrenergic blockade with prazosin (3 x 10(-7) M) during the preconditioning phase did not abolish the protective effect of preconditioning on functional recovery, and repeated intermittent alpha 1-adrenergic activation with phenylephrine in different concentrations (1 x 10(-8) to 3 x 10(-5) M) did not mimic the protective effect of preconditioning. PKC blockade with the selective PKC inhibitors, chelerythrine (10 microM) and BIM (4 microM), did not abolish the protective effect of preconditioning on functional recovery is isolated perfused rat hearts when given either during the preconditioning phase or shortly before the onset of sustained ischemia. The characteristic metabolic changes of preconditioning during sustained ischemia, namely, energy sparing as manifested in reduced accumulation of lactate, were also not abolished by preconditioning in the presence of selective PKC blockers. We conclude that no evidence could be found for alpha 1-adrenergic or PKC activation in the mechanism of ischemic preconditioning in the isolated rat heart.

Noxious thermal and chemical stimulation induce increases in 3H-phorbol 12,13-dibutyrate binding in spinal cord dorsal horn as well as persistent pain and hyperalgesia, which is reduced by inhibition of protein kinase C

We have previously suggested that protein kinase C (PKC) contributes to persistent pain in the formalin test. This study compared the effects of pharmacological inhibition of PKC with either GF 109203X or chelerythrine on persistent pain following noxious chemical stimulation with its effects on mechanical hyperalgesia, which develops in the hindpaw contralateral to an injury produced by noxious thermal stimulation. Furthermore, we have assessed changes in membrane-associated PKC in spinal cord in response to both noxious chemical and thermal stimulation. Nociceptive responses, to a hindpaw injection of 50 microliters of 2.5% formalin, and flexion reflex thresholds, to mechanical stimulation (Randall-Selitto test) in the hindpaw contralateral to a thermal injury (15 sec immersion in water at 55 degrees C), were assessed following intrathecal injection of PKC inhibitors (GF 109203X or chelerythrine). Changes in the levels of membrane-associated PKC, as assayed by quantitative autoradiography of the specific binding of 3H-phorbol-12,13-dibutyrate (3H-PDBu) in spinal cord sections, were assessed in rats after noxious chemical (50 microliters of 5.0% formalin) and noxious thermal (90 sec immersion in water at 55 degrees C) stimulation. Inhibitors of PKC (GF 109203X, chelerythrine), produced significant reductions of nociceptive responses to 2.5% formalin, as well as a significant reduction in the mechanical hyperalgesia in the hindpaw contralateral to a thermal injury. In addition, both noxious chemical and thermal stimulation produced significant increases in specific 3H-PDBu binding in the dorsal horn of the lumbar spinal cord, likely reflecting alterations in membrane-associated PKC. The results provide both pharmacological and anatomical evidence that persistent pain produced by chemical stimulation with formalin and mechanical hyperalgesia in the hindpaw contralateral to a thermal injury are influenced by the translocation and activation of PKC in spinal cord dorsal horn neurons.

Functional interaction between dopamine D1 and D2 receptors in 'MPTP' monkeys

We have studied the motor response induced by independent administration of 4 different doses of a dopamine D2 [(+)-PHNO] and a dopamine D1 (CY 208-243) receptor agonist in 5 MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) monkeys. Both drugs had similar antiparkinsonian effects and both elicited choreic dyskinesias. Simultaneous administration of (+)-PHNO [(+)-4-propyl-9-hydroxynaphthoxazine] and CY 208-243 [(-)4,6,6a,7,8,12b-hexahydro-7-methylindolo[4,3a-b]phenan thyxidine] did not result in modification of the dose-response curve induced by each dopamine receptor agonist given alone. Pretreatment with the dopamine D1 receptor antagonist SCH 23390 (0.8 mg/kg) and the dopamine D2 receptor antagonist sulpiride (60 mg/kg) reduced the magnitude and the duration of the motor response induced by (+)-PHNO and CY 208-243, respectively, but did not modify the intensity and characteristics of choreic dyskinesias. These results demonstrate that the motor effects and the dyskinesias cannot be dissociated by selective dopamine D1 and D2 receptor stimulation. It appears that stimulation of dopamine D1 and D2 receptors by endogenous dopamine is required to obtain the full motor response induced by selective dopamine receptor agonists as demonstrated by the reduction of the motor improvement found after pretreatment with SCH 23390 and sulpiride.

Isometamidium concentrations in the sera of Boran cattle: correlation with prophylaxis against tsetse-transmitted Trypanosoma congolense

Fifteen Boran cattle from a trypanosomiasis-free area were injected intramuscularly with isometamidium chloride at a dose of 1 mg/kg body weight. Thereafter, the cattle were challenged at monthly intervals with Glossina morsitans centralis infected with one of three populations of Trypanosoma congolense (IL 3893, IL 3889 or IL 1180) until all animals became infected. Isometamidium concentrations in the sera of these cattle were measured using a competitive enzyme-linked immunosorbent assay over the first 105 days following treatment. All cattle challenged with IL 3893 or IL 3889 developed infection following the first challenge, at which time the mean serum drug concentration in all treated cattle was 6 ng/ml. Cattle challenged with IL 1180 became infected following 6 to 8 monthly challenges. The mean serum drug concentration in these cattle at the time of their third monthly challenge with IL 1180 was 0.75 ng/ml. Trypanosome populations IL 3893 and IL 3889 were considered to be highly resistant to isometamidium, while IL 1180, relatively sensitive. It was therefore concluded that T. congolense persisting at serum isometamidium concentrations greater than 0.75 ng/ml can be considered moderately resistant, while those persisting at concentrations greater than 6 ng/ml can be considered markedly resistant. These results will be most valuable in the investigation of isometamidium resistance of T. congolense in the field.

Disposition and metabolism of Ro 24-4736 in the rat

Ro 24-4736, a new platelet activating factor antagonist, is currently under preclinical and clinical development. The tissue distribution of the 14C-label in male rats following a single intravenous dose of 1.0 mg/kg of 14C-Ro 24-4736 indicated appreciable uptake by the liver, kidney, heart and gastrointestinal tract. Peak plasma and tissue concentrations were seen at 5 minutes after dosing except for the small intestine (4 hrs) and abdominal fat, stomach and large intestine (4 hrs). Thereafter, the 14C-label rapidly declined in all tissues. At 48 hours, only 3.5% of the dose was present in the tissues, and 6.1% in the lumen of the gastrointestinal tracts. The excretion of 14C was essentially completed; 94% of the administered 14C was excreted in the feces and 4.0% in the urine. Overall recoveries of the administered 14C label ranged from 96 to 116%. The purified major 14C-labelled component in the fecal extracts yielded essentially the same NMR spectrum as authentic Ro 24-4736 which accounted for 11% of the dose. In vitro incubations of Ro 24-4736 with rat liver 9S supernatant in an NADPH generating system produced two metabolites. NMR spectra indicated that one metabolite was hydroxylated at carbon-1 while the other one contained a hydroxyl at carbon-10 of the parent molecule. Interestingly, the sites of hydroxylation were at carbons C1, and C10 bearing the protons guarding the bay area of the phenanthrenoid ring, rather than carbons of the phenyl-methyl-thienotriazolodiazepine moiety.

Effect of adding the D1 agonist CY 208-243 to chronic bromocriptine treatment. I: Evaluation of motor parameters in relation to striatal catecholamine content and dopamine receptors

A group of four cynomolgus monkeys previously rendered parkinsonian by the toxin 1-methyl-4-phenyl,1,2,3,6-tetrahydropyridine (MPTP) were observed in locomotion cages equipped with photocells during four periods of 7 days during which they received saline or two doses of the D1 agonist CY 208-243. The larger dose of 0.5 mg/kg produced a significant increase in locomotion in three of four animals. A second group of eight monkeys also previously rendered parkinsonian by MPTP and having received no other treatment were given a daily treatment of bromocriptine 1.66 mg/kg orally daily during 4 weeks. In four of the animals, after a week on bromocriptine alone, the D1 agonist CY 208-243 was added in increasing doses of 0.05, 0.1, and 0.5 mg/kg. The motor response as measured by locomotion, hand dexterity, and a disability score improved progressively at least in some of the animals on bromocriptine alone. The addition of CY 208-243 produced a more striking improvement of all three parameters, which appeared to be dose dependent. Biochemical analysis of the brain of these animals plus one control and one MPTP untreated monkey showed a > 90% loss of dopamine in the striatum in six of the eight treated monkeys. Both D2 and D1 dopamine receptors were increased in density by denervation, but both treatments abolished this increase for the D2 receptors while increasing the affinity of the D1 receptors.

A preliminary study on the absorption of isometamidium chloride (Samorin) in the stomach and small intestine of rat

The levels of absorption of isometamidium chloride (Samorin) in the stomach and intestine of the rat were determined because of problems usually associated with parenteral administration of the drug. The in situ loop method and in situ recirculation technique were used to determine the absorption of the drug in the stomach and intestine respectively. 54.8% of isometamidium chloride was absorbed in the stomach in 30 minutes while 2% was absorbed in the intestine in one hour. These results warrant the comparative study of the blood and tissue concentrations of isometamidium chloride following oral and parenteral administration.

The influence of the size of the initial inoculum on the efficacy of isometamidium (samorin) on a stock of Trypanosoma congolense

The effect of the number of trypanosomes in the initial inoculum on the minimum curative dose, was determined for an experimental infection of Trypanosoma congolense in mice treated with isometamidium. Mice were infected by the intravenous route and were then treated three hours later by intraperitoneal injection. The minimum curative dose was shown to be dependent on the size of the initial inoculum, with a difference of a factor of 7.5 as the initial inoculum was increased from 10(3) to 10(6) trypanosomes per mouse. It is concluded that this may be a significant variable for in vivo drug sensitivity test, and may also have implications for treatment of infections in the field.

Therapeutic activity of isometamidium chloride in Boran cattle against a tsetse-transmitted clone of Trypanosoma congolense with a low level of drug resistance

Experiments were conducted with a clone of Trypanosoma congolense, IL 3580, which exhibited a low level of resistance to isometamidium chloride. Five cattle were treated intramuscularly with isometamidium chloride at a dose rate of 0.5 mg kg-1 body weight (BW) and challenged 28 days later with 5 Glossina morsitans centralis infected with T. congolense IL 3580. All 5 cattle and 15 untreated steers challenged on the same day became parasitaemic by day 15 post-infection. Thus, at a dose of 0.5 mg kg-1 BW, the prophylactic action of isometamidium chloride did not extend to 28 days following treatment. Subsequently, the 20 steers were divided into 4 groups of 5 animals each and treated with isometamidium chloride at one of the following dose rates; 0.5 or 1.0 mg kg-1 BW intramuscularly and 0.5 or 1.0 mg kg-1 BW intravenously (Groups A, B, C and D, respectively). Group A consisted of the 5 animals that had previously been treated with isometamidium chloride. Animals relapsed in all groups except those in Group B, treated intramuscularly with isometamidium chloride at a dose of 1.0 mg kg-1 BW. Four of the 5 animals in Group A, treated intramuscularly with isometamidium chloride at a dose of 0.5 mg kg-1 BW relapsed following a mean interval of 16 days post-treatment. Similarly, infections in all animals in Groups C and D, given intravenous injections of isometamidium chloride at a dose of 0.5 and 1.0 mg kg-1 BW, respectively, were not eliminated as a result of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of intrastriatal application of directly and indirectly acting dopamine agonists and antagonists on the in vivo release of acetylcholine measured by brain microdialysis

The effect of intrastriatal application of D-1, D-2 and indirect dopaminergic drugs on the release of striatal acetylcholine as a function of the post-implantation intervals was studied using in vivo microdialysis. The dopamine D-2 agonists LY 171555 and (-)N0437 inhibited the release of striatal acetylcholine to 40% of control values 16-24 h after implantation of the dialysis cannula. When LY 171555 was infused 40-48 h after implantation of the dialysis cannula, the response was attenuated to 20% of control values. Meanwhile, the effectiveness of infusions of the antagonists (-)sulpiride and haloperidol was augmented from a non significant effect at 16-24 h to a 150% increase 40-48 h after implantation of the cannula. Infusions of the dopamine releasing agent amphetamine or the dopamine uptake inhibitor nomifensine resulted in a dose-dependent increase in the overflow of dopamine. Not until a sevenfold increase in the level of dopamine was seen, the release of acetylcholine was significantly affected. This hyporesponsiveness of the striatal cholinergic interneurons to endogenous dopamine could not be attributed to dopamine D-1 receptor activation, since no effects on striatal acetylcholine release were found by intrastriatal infusions of the selective D-1 agonist CY 208-243 or the selective D-1 antagonist SCH 23390. The results indicate that dopamine D-2 receptors are involved in the regulation of striatal acetylcholine release and that these receptors are tonically occupied by endogenous dopamine under the present experimental conditions 40-48 h after probe implantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Trypanosomiasis control in Boran cattle in Kenya: a comparison between chemoprophylaxis and a parasite detection and intravenous treatment method using isometamidium chloride

Two methods of trypanosome control in Boran cattle kept under very high trypanosomiasis risk were compared: the traditional intramuscular isometamidium chloride prophylaxis with a parasite detection and intravenous isometamidium chloride treatment method. The results were related to a control group under diminazene aceturate treatment. Isometamidium chloride at 0.25 mg/kg as routinely used by the ranch was of little benefit by either method, with breakthrough infections occurring as early as one week after treatment. When isometamidium chloride at 1 mg/kg was used, the curative intravenous method appeared to be superior to the intramuscular prophylaxis with regard to cost of drugs and to a 31% higher weight gain over a 30 week period. Weekly infection rates in the intravenous group decreased over time, despite an increasing trypanosomiasis challenge, with a mean interval of 6.4 weeks between treatments as compared with 4.3 weeks in a diminazene aceturate control group. It was concluded that isometamidium chloride given intravenously had not only a very good therapeutic but also a considerable prophylactic effect of not less than four weeks.

Therapeutic and prophylactic activity of isometamidium chloride against a tsetse-transmitted drug-resistant clone of Trypanosoma congolense in Boran cattle

An investigation was conducted on the therapeutic and prophylactic activity of isometamidium chloride (SamorinR) in Boran (Bos indicus) cattle against a Trypanosoma congolense clone, IL 3270. This clone was derived, without drug selection, from a stock originally isolated in Burkina Faso and has previously been shown to be resistant to isometamidium in both cattle and mice using an infection and treatment regimen. A group of 5 cattle were treated intramuscularly with 1.0 mg kg-1 isometamidium chloride and 28 days later challenged with Glossina morsitans centralis infected with T. congolense IL 3270. All 5 cattle and 17 untreated cattle challenged on the same day became parasitaemic by day 16 post challenge, indicating that prophylaxis did not extend to 28 days post treatment. The cattle were then treated with isometamidium chloride at one of the following doses and by different routes of administration; 1.0 or 2.0 mg kg-1 intramuscularly, 0.25, 0.5, 0.75 or 1.0 mg kg-1 intravenously. Infections relapsed in all cattle at an interval of 12-21 days following treatment, with the exception of those treated with 2.0 mg kg-1 intramuscularly in which the development of relapse infections was delayed. Similar studies were also conducted with a highly sensitive clone of T. congolense, IL 1180. Infections in cattle with this clone were eliminated by intravenous treatment with 0.25 mg kg-1 isometamidium chloride or intramuscular treatment with 0.5 mg kg-1 isometamidium chloride. Thus, although intravenous administration of isometamidium eliminated a fully sensitive infection, treatment by this route appeared not to enhance the therapeutic efficacy of the drug in the treatment of a T. congolense clone which expresses a high level of resistance.

Isometamidium in pigs: disposition kinetics, tissue residues and adverse reactions

The disposition and adverse effects of the anti-trypanosomal drug isometamidium in pigs were evaluated. Following intramuscular administration of the drug at doses of 0.5, 15 and 35 mg kg-1, the drug was rapidly absorbed within 15 to 30 minutes to reach maximum plasma concentrations of 12 to 477 (n = 6), 302 to 655 (n = 4) and 1620 (n = 1) ng ml-1, respectively. No drug was detectable in plasma (less than 5 ng ml-1) 24 hours after drug administration at the three doses used. The half-lives of disappearance of the drug from plasma during the terminal phase were 7.12 h for the pigs given a dose of 15 mg kg-1, and 7.20 h for the pig which received a dose of 35 mg kg-1. At all the intramuscular injection sites, high drug concentrations were found six weeks after administration. The most dramatic adverse reactions observed were: one death after intramuscular administration at a dose of 35 mg kg-1 to two animals, and two deaths after intravenous administration at a dose of 2 mg kg-1 to two animals. For all these cases, the immediate cause of death was acute cardiovascular collapse. Biochemical analyses and gross and histological examinations showed that the animals that tolerated the high doses of 15 and 35 mg kg-1 given intramuscularly had extensive and severe tissue damage at the injection sites. Significant increases in plasma gamma-glutamyltransferase and alanine aminotransferase following drug administration suggested a degree of hepatobiliary damage.

Notes on the routine intravenous use of isometamidium in the control of bovine trypanosomiasis on the Kenya coast

Various chemotherapeutic regimes were used to control trypanosomiasis in 3,000 Boran cattle on an estate on the Kenya coast. Recently the therapeutic use of isometamidium by the intravenous route was adopted to treat individual trypanosome-infected cattle. This was in order to overcome tissue reactions encountered after intramuscular injection and also to control a "thin cow" syndrome attributed to chronic trypanosomiasis. Toxic side effects were eliminated by careful attention to the intravenous technique which was safely used in calves, pregnant cattle and bulls. Weekly blood sampling and treatments of infected individuals resulted in a reduction of cases from 2,187 to 208 out of 46,495 and 46,329 samples examined in 1985 and 1986 respectively. The standard of management was very high and although this routine successfully controlled bovine trypanosomiasis on this estate its application elsewhere is likely to be limited.

Pharmacokinetic and histopathological investigations of isometamidium in cattle

The absorption and distribution patterns of the trypanocidal drug isometamidium and its effect on tissues in cattle were characterised. After intramuscular administration of a prophylactic dose of 0.5 mg kg-1 bodyweight, the drug was rapidly detectable in serum at a mean maximum concentration of only 20 ng ml-1 and declined to concentrations of lower than 10 ng ml-1 within two hours. High drug concentrations were maintained at the injection site and in the liver and kidney for at least six weeks. At the injection site, tissue damage was severe and extensive, whereas in the liver and kidney no histopathological lesions were seen.

Phase 1 trial of levonantradol in chemotherapy-induced emesis

Levonantradol is a synthetic cannabinoid with demonstrated preclinical antiemetic activity. The current phase I trial was undertaken to determine: 1) the maximally tolerated dose; 2) the side effects at the different dosage levels; and 3) to evaluate the antiemetic efficacy of levonantradol in patients receiving emesis-producing chemotherapy. Thirty-four patients received 52 courses of levonantradol. Concurrent chemotherapy most frequently consisted of high dose cisplatin (120 mg/m2), either alone or in combination with other agents. Levonantradol dosage was escalated through seven treatment levels (0.5-4.0 mg per dose) and was given intramuscularly every 4 hours. Toxicity was similar to that observed with other cannabinoids and primarily consisted of dizziness (65%), burning and erythema at the injection site (48%), mild sedation (44%), orthostatic hypotension (37%), dysphoria (29%), and urinary retention (10%). Marked urinary retention occurred in three of seven patients at the 4.0 mg per dose level, and two of 24 patients at either the 2.5 mg and 3.0 mg levels. Major or minor antiemetic responses (0-2 or 3-5 emetic episodes, respectively) occurred in 23% of patients receiving cisplatin and in 53% of patients receiving non-cisplatin containing chemotherapy. Intramuscular levonantradol can be given safely at doses up to 3.0 mg/kg, with toxicity and antiemetic efficacy similar to that observed with other cannabinoids.

Effects of single and repeated daily injections of morphine, clonidine and l-nantradol on responding of squirrel monkeys under escape titration

Lever pressing of monkeys was maintained under a titration schedule in which responses decreased shock intensity which otherwise was increased at a fixed rate. The opioid morphine, the antihypertensive clonidine and the cannabinoid l-nantradol each resulted in a dose-related increase in shock intensity, although l-nantradol and clonidine were 10 to 30 times more potent than morphine. Morphine and l-nantradol resulted in markedly higher shock intensities only at doses that severely disrupted responding, whereas clonidine resulted in higher shock intensities over a broader dose range without disrupting responding. Marked tolerance developed for the shock-increasing effects of morphine (3.0 mg/kg) and l-nantradol (0.3 mg/kg) within 10 to 15 sessions, but only partial tolerance developed for shock-increasing effects of clonidine (0.3 mg/kg) after up to 35 sessions. The shock-increasing effects of chronically administered clonidine were antagonized by the alpha-2 adrenoceptor antagonist yohimbine but not by the alpha-1 adrenoceptor antagonist prazosin. When effects of acute injections were redetermined after 1 month without drug, the effects of clonidine, but not morphine or l-nantradol, were the same as before chronically administered drug. The influence of behavioral processes on the long-lasting effects of drugs seemed greater for morphine and l-nantradol than for clonidine.

Preliminary pharmacokinetic study of isometamidium chloride in camels

Isometamidium chloride was given to camels at a single intravenous dose rate of 0.5 or 1 mg kg-1 and the plasma drug concentration measured spectrophotometrically at frequent intervals for up to 48 hours. Isometamidium chloride concentrations were found to be 9.8 +/- 0.2 and 8.7 +/- 0.2 micrograms ml-1 half an hour after treatment with 1 and 0.5 mg kg-1, respectively, and 1.7 +/- 0.3 and 0.7 +/- 0.3 micrograms ml-1 after 24 hours. No measurable drug concentration was found 48 hours after dosing.