Monepantel-based anthelmintic combinations to optimize parasite control in cattle

Improvement in the use of existing anthelmintics is a high priority need for the pharmaco-parasitology research field, considering the magnitude and severity of anthelmintic resistance as an important issue in livestock production. In the work described here, monepantel (MNP) was given alone or co-administered with either macrocyclic lactone (ML) or benzimidazole (BZ) anthelmintics to calves naturally infected with ML- and BZ-resistant gastrointestinal (GI) nematodes on two different commercial cattle farms. Both pharmacokinetic (PK) and efficacy assessments were performed. On Farm A, male calves (n = 15 per group) were treated with either MNP orally (2.5 mg/kg), IVM s.c. (0.2 mg/kg), ricobendazole (RBZ) s.c. (3.75 mg/kg) or remained untreated. On Farm B, eight groups (n = 15) of male calves received treatment with either: MNP, abamectin (ABM, oral, 0.2 mg/kg), RBZ (s.c., 3.75 mg/kg), albendazole (ABZ, oral, 5 mg/kg), MNP+ABM, MNP+RBZ, MNP+ABZ (all at the above-mentioned routes and doses) or remained untreated. Seven animals from each treated group (Farm B) were randomly selected to perform the PK study. MNP and its metabolite monepantel sulphone (MNPSO2) were the main analytes recovered in plasma after HPLC analysis. The combined treatments resulted in decreased systemic exposures to MNP parent drug compared with that observed after treatment with MNP alone (P < 0.05). However, the systemic availability of the main MNP metabolite (MNPSO2) was unaffected by co-administration with either ABM, RBZ or ABZ. Efficacies of 98% (Farm A) and 99% (Farm B) demonstrated the high efficacy of MNP given alone (P < 0.05) against GI nematodes resistant to ML and BZ in cattle. While the ML (IVM, ABM) failed to control Haemonchus spp., Cooperia spp. and Ostertagia spp., MNP achieved 99% to 100% efficacy against those nematode species on both commercial farms. However, MNP alone failed to control Oesophagostomum spp. (60% efficacy) on Farm A. The co-administered treatments MNP+ABZ and MNP+RBZ reached a 100% reduction against all GI nematode genera. In conclusion, the oral treatment with MNP should be considered to deal with resistant nematode parasites in cattle. The use of MNP in combination with BZ compounds could be a valid strategy to extend its lifespan for use in cattle as well as to reverse its poor activity against Oesophagostomum spp.

Pharmacokinetics and milk excretion pattern of eprinomectin at different dose rates in dairy cattle

This study aimed at determining the plasma disposition kinetics of eprinomectin (EPM) and EPM excretion pattern through milk after topical administration to dairy cattle at the recommended dose of 0.5 mg/kg and at 1 and 1.5 mg/kg. A high variability in the plasma concentration profiles was observed among animals, particularly in the Cmax values, with a coefficient of variation between 39 and 53%. The Cmax and AUC values were significantly affected by the dose administered at 1.5 mg/kg. However, such differences did not seem to follow a linear pattern among treatments. These parameters did not differ among dose rates after dose normalization; nevertheless, the simulation of a linear kinetic disposition showed a mean plasma AUC value of 254 ng.d/ml instead of the observed value of 165 ng.d/ml. EPM concentration profiles in milk were significantly lower than those measured in plasma. The Cmax and AUC milk-to-plasma ratios ranged from 0.14 to 0.26 and 0.16 to 0.21, respectively (p>0.05). The low milk-to-plasma ratio of EPM accounted for a low percentage of the fraction of the administered dose excreted through milk, being significantly higher at a dose rate of 0.5 mg/kg (0.07%) of EPM than at 1.5 mg/kg (0.04%) (p<0.05). The topical administration of EPM to lactating dairy cows at higher doses than that recommended for gastrointestinal nematodes showed a milk excretion pattern with a zero milk withdrawal period. In conclusion, the administration of topical EPM formulation at 1 or 1.5 mg/kg may be a valuable tool to be used in regional strategic deworming programs aimed to control ectoparasite infections in dairy production systems.

Comparative tissue pharmacokinetics and efficacy of moxidectin, abamectin and ivermectin in lambs infected with resistant nematodes: Impact of drug treatments on parasite P-glycoprotein expression

The high level of resistance to the macrocyclic lactones has encouraged the search for strategies to optimize their potential as antiparasitic agents. There is a need for pharmaco-parasitological studies addressing the kinetic-dynamic differences between various macrocyclic lactones under standardized in vivo conditions. The current work evaluated the relationship among systemic drug exposure, target tissue availabilities and the pattern of drug accumulation within resistant Haemonchus contortus for moxidectin, abamectin and ivermectin. Drug concentrations in plasma, target tissues and parasites were measured by high performance liquid chromatography. Additionally, the efficacy of the three molecules was evaluated in lambs infected with resistant nematodes by classical parasitological methods. Furthermore, the comparative determination of the level of expression of P-glycoprotein (P-gp2) in H. contortus recovered from lambs treated with each drug was performed by real time PCR. A longer persistence of moxidectin (P < 0.05) concentrations in plasma was observed. The concentrations of the three compounds in the mucosal tissue and digestive contents were significant higher than those measured in plasma. Drug concentrations were in a range between 452 ng/g (0.5 day post-treatment) and 32 ng/g (2 days post-treatment) in the gastrointestinal (GI) contents (abomasal and intestinal). Concentrations of the three compounds in H. contortus were in a similar range to those observed in the abomasal contents (positive correlation P = 0.0002). Lower moxidectin concentrations were recovered within adult H. contortus compared to abamectin and ivermectin at day 2 post-treatment. However, the efficacy against H. contortus was 20.1% (ivermectin), 39.7% (abamectin) and 89.6% (moxidectin). Only the ivermectin treatment induced an enhancement on the expression of P-gp2 in the recovered adult H. contortus, reaching higher values at 12 and 24 h post-administration compared to control (untreated) worms. This comparative pharmacological evaluation of three of the most used macrocyclic lactones compounds provides new insights into the action of these drugs.

Pretreatment with the inducers rifampicin and phenobarbital alters ivermectin gastrointestinal disposition

The goal of the study was to evaluate the effects of rifampicin (RFP) and phenobarbital (PBT) on the plasma and gastrointestinal disposition kinetics of ivermectin (IVM) subcutaneously administered to Wistar rats. Fifty seven rats were used. Animals in Group I were the noninduced (control) group. Those in Groups II and III received a treatment with RFP (160 mg/day) and PBT (35 mg/day), respectively, both given orally during eight consecutive days as induction regimen. The IVM pharmacokinetic study was started 24 h after the RFP and PBT last administration. Animals received IVM (200 microg/kg) by subcutaneous injection. Rats were sacrificed between 6 h and 3 days after IVM administration. Blood and samples of liver tissue, intestinal wall and luminal content of jejunum were collected from each animal. IVM concentrations were measured by high performance liquid chromatography. IVM disposition kinetics in plasma and tissues was significantly modified by the PBT treatment, but not by RFP. Despite the enhanced CYP3A activity observed after the pretreatment with RPF and PBT, there were no marked changes on the percentages of IVM metabolites recovered from the bloodstream in induced and noninduced animals. An enhanced P-glycoprotein-mediated intestinal transport activity in pretreated animals (particularly in PBT pretreated rats) may explain the drastic changes observed on IVM disposition.

Classification of pediatric migraine: proposed revisions to the IHS criteria

The International Headache Society classification lends itself to modification to significantly improve the diagnostic sensitivity of migraine in the pediatric population. Children and adolescents require special modifications relating to duration, location, quality of intensity, and symptoms related to photophobia and phonophobia. We propose specific criteria for pediatric migraine with and without aura which are more sensitive. Forty-five children and adolescents seen at a headache center were evaluated, retrospectively, comparing diagnostic criteria of the International Headache Society, Vahlquist, and the proposed revised IHS classification for clinical diagnosis by a single examiner (pediatric neurologist)--comparing diagnostic rates for migraine of the total sample: IHS (53%), Vahlquist (69%), and IHS-R (80%) and evaluating a subset of those patients less than 12 years (n = 22): IHS (50%), Vahlquist (68%), and IHS-R (73%). The proposed revisions to IHS for pediatric migraine were more sensitive than existing criteria. These revisions may help to form the basis for future research guidelines and for further modifications to improve the diagnostic sensitivity of pediatric migraine using the IHS model.

The mechanism of the inhibitory action of neurotensin on pentagastrin-stimulated gastric secretion in dogs

Neurotensin is a potent inhibitor of pentagastrin-stimulated gastric acid secretion. This study was done to investigate the possible role of vagal innervation and of prostaglandins on this inhibitory effect. Five dogs with gastric cannulas were infused with pentagastrin (1 microgram per kilogram of body weight each hour) for 210 minutes. In the 60 to 150 minute period, neurotensin (5.5 micrograms per kilogram of body weight each hour) was infused. Neurotensin significantly decreased pentagastrin-stimulated gastric acid output, while the simultaneous administration of indomethacin (bolus of 1 milligram per kilogram of body weight plus infusion of 0.5 milligrams per kilogram each hour) abolished the effect of neurotensin. After truncal vagotomy, the inhibitory effect of neurotensin was again studied. Since the sensitivity of the stomach to pentagastrin decreased after vagotomy, the dose of pentagastrin was doubled (2 micrograms per kilogram of body weight each hour) in order to achieve acid stimulation comparable with the levels before vagotomy. After vagotomy, neurotensin inhibited the effect of pentagastrin in a manner similar to that shown before vagotomy. The inhibitory potency of neurotensin on gastrin-stimulated gastric secretion is independent of the vagus, but requires intact synthesis for prostaglandins.

Distribution of neurotensin in the canine gastrointestinal tract

The distribution of immunoreactive neurotensin in the canine gastrointestinal tract from the esophagus to the rectum, as well as in the pancreas, was determined by a specific neurotensin radioimmunoassay. Immunoreactive neurotensin was found throughout the gastrointestinal tract and in the pancreas. The highest concentrations of immunoreactive neurotensin were found in the mucosal extracts of the jejunum (422 +/- 68 ng/gm) and ileum (3025 +/- 289 ng/gm). Small but substantial amounts of immunoreactive neurotensin were found in the esophagus, fundus (includes fundus and corpus), antrum, duodenum, colon, and pancreas. The concentrations of neurotensin in the mucosal extracts of the jejunum and ileum increased in a graded fashion from the proximal jejunum to the distal ileum. The neurotensin concentration in extracts of the seromuscular layers of jejunum (73 +/- 14 ng/gm) and ileum (187 +/- 38 ng/gm) were statistically higher in comparison with other gut loci.

Regulation of gastric acid secretion by secretin and serotonin

We have tested the interaction between serotonin and secretin in pentagastrin-induced gastric acid secretion in six dogs prepared with Thomas gastric and duodenal cannulas. We further examined the effect of methysergide, a serotonin antagonist, on gastric acid secretion. The intravenous administration of serotonin or secretin alone significantly inhibited pentagastrin-induced gastric acid secretion. The combined administration of serotonin and secretin inhibited gastric acid secretion to a greater magnitude than either secretagogue alone. The administration of methysergide diminished basal concentrations of secretin on gastric acid secretion. Methysergide also enhanced the stimulatory activity of pentagastrin-induced gastric acid secretion. The inhibitory action of intraduodenal acidification of pentagastrin-induced gastric acid secretion was reversed by methysergide.