Moxidectin: heartworm disease prevention in dogs in the face of emerging macrocyclic lactone resistance

Heartworm (Dirofilaria immitis) disease continues to increase and spread, remaining one of the most important and pathogenic parasitic diseases of dogs, despite the regular use of macrocyclic lactones (MLs) in preventive products. Dogs harboring strains of D. immitis resistant to MLs, the only drug class available for heartworm prevention in the United States, have been documented and proven. As no new products are available utilizing a novel drug class for the prevention of this disease, the only options for combating ML resistance include increasing the dose and/or changing the dosage regime of current MLs, or by optimizing the formulations of MLs currently available. Moxidectin provides a unique opportunity for optimization of the dose and formulation, which may provide improved efficacy against ML-resistant strains. Currently there are oral, topical, and injectable moxidectin products approved for heartworm prevention in the USA. Two new products (ProHeart^® 12 and Simparica Trio^®), available in many countries around the world including the USA, take advantage of the unique attributes of moxidectin for providing robust heartworm prevention against the strains of heartworm to which most dogs in the USA will likely be exposed. Both products have demonstrated 100% preventive efficacy in laboratory studies against recently collected field strains of heartworm, and also in large field studies, where the majority of dogs were living in the southern USA in areas where ML resistance has been confirmed to occur, therefore under elevated heartworm challenge. Based on the data summarized here, these products offer important advances in heartworm prevention and provide additional options for veterinarians and pet owners to protect their dogs from developing heartworm disease.

Cryogenic preservation of Dirofilaria immitis microfilariae, reactivation and completion of the life-cycle in the mosquito and vertebrate hosts

BACKGROUND

The cryopreservation of filarial nematodes has been studied for nearly 70 years. Largely, these studies examined the effectiveness of cryopreservation methods by using the post-thaw survival of microfilariae (mf) and the development to third-stage larvae (L3s) following inoculation into a competent insect vector. Only one study reported complete reestablishment of a filarial nematode (Brugia malayi) life-cycle in a competent vertebrate host from cryopreserved stock. Expanding on this previous research, a cryopreservation method was developed to cryopreserve the mf of the dog heartworm, Dirofilaria immitis.

METHODS

A combination of cryoprotectants, dimethyl sulfoxide (DMSO) and polyvinyl pyrolidone (PVP) at 6% and 4 mM, respectively, provided acceptable post-thaw survival of mf that developed into L3s in Aedes aegypti. L3s developed from cryopreserved and freshly collected mf in mosquitoes were inoculated into ferrets and dogs and were assessed after a sufficient duration post-inoculation for development into adult heartworms.

RESULTS

Fewer adult heartworms derived from cryopreserved stocks of mf were recovered from ferrets compared to adult heartworms derived from freshly collected mf, and the former were smaller by weight and length. The onset of patency (circulating mf) occurred at similar post-inoculation time points and at similar mf densities in dogs infected with L3s sourced from cryopreserved stocks or freshly collected mf. Adults derived from cryopreserved mf have survived and produced viable mf for more than 3 years in dogs. Approximately 60% of inoculated L3s were recovered as adults from dogs at 2 and 3.5 years post-inoculation.

CONCLUSIONS

The results from these direct comparisons demonstrate that cryopreserved mf can develop into L3s in vector mosquitoes and that these L3s are infective to both dogs and ferrets, where they undergo normal development into adult worms. These worms are able to mate and produce viable mf and complete the heartworm lifecycle in dog.

Where are all the anthelmintics? Challenges and opportunities on the path to new anthelmintics

Control of helminth parasites is a key challenge for human and veterinary medicine. In the absence of effective vaccines and adequate sanitation, prophylaxis and treatment commonly rely upon anthelmintics. There are concerns about the development of drug resistance, side-effects, lack of efficacy and cost-effectiveness that drive the need for new classes of anthelmintics. Despite this need, only three new drug classes have reached the animal market since 2000 and no new classes of anthelmintic have been approved for human use. So where are all the anthelmintics? What are the barriers to anthelmintic discovery, and what emerging opportunities can be used to address this? This was a discussion group focus at the 2019 8th Consortium for Anthelmintic Resistance and Susceptibility (CARS) in Wisconsin, USA. Here we report the findings of the group in the broader context of the human and veterinary anthelmintic discovery pipeline, highlighting challenges unique to antiparasitic drug discovery. We comment on why the development of novel anthelmintics has been so rare. Further, we discuss potential opportunities for drug development moving into the 21st Century.

Preventive efficacy of oral moxidectin at various doses and dosage regimens against macrocyclic lactone-resistant heartworm (Dirofilaria immitis) strains in dogs

Background

Moxidectin has previously shown limited efficacy (≤ 44.4%) against confirmed macrocyclic lactone (ML)-resistant Dirofilaria immitis strains at 3 µg/kg after single and multiple oral dosages. Three studies were conducted to evaluate higher oral moxidectin doses for efficacy against confirmed ML-resistant D. immitis strains.

Methods

Dogs were inoculated with 50 D. immitis L3 and randomly allocated to treatments. Study 1: 6 groups of dogs (n = 8) were inoculated with JYD-34 (Day − 30) and treated as follows: T01, negative control; T02–T05, moxidectin at 3, 6, 12 or 24 µg/kg, respectively, on Day 0 only; T06, moxidectin at 3 µg/kg on Days 0, 30 and 60. Study 2: 10 groups of dogs (n = 5) were inoculated (Day − 30) with either JYD-34 (T01, T03–05) or ZoeLA (T02, T06–T10) and treated as follows: T01 and T02, negative controls; T03–T05, moxidectin at 24, 40 or 60 µg/kg, respectively, on Days 0, 28 and 56; T06 and T09, moxidectin at 3 or 60 µg/kg on Day 0 only; T07, T08 and T10, moxidectin at 24, 40 or 60 µg/kg, respectively, on Days 0, 28 and 56. Study 3: 5 groups of dogs (n = 5) were inoculated with ZoeMO (Day − 28) and treated as follows: T01, negative control; T02, moxidectin at 3 µg/kg moxidectin on Day 0 only; T03–T05, moxidectin at 24, 40 or 60 µg/kg, respectively, on Days 0, 28 and 56. All dogs were necropsied for adult heartworm recovery ~ 4–5 months post-inoculation.

Results

All moxidectin-treated dogs showed significantly lower worm counts than controls. The efficacy of moxidectin administered once at 3 µg/kg was 19% (JYD-34), 44.4% (ZoeLA) and 82.1% (ZoeMO). Increasing both the dose and the number of dosages of moxidectin improved efficacy, with 100% protection obtained using three dosages of moxidectin at either 40 µg/kg (JYD-34, ZoeMO) or 60 µg/kg (ZoeLA). Three dosages of 24 µg/kg were also highly effective, providing ≥ 98.8% efficacy for all three strains.

Conclusions

Increasing both the dose and number of consecutive monthly dosages of moxidectin improved the efficacy against ML-resistant heartworms. Based on these data and other technical considerations, the 24 µg/kg dose was considered the optimal dose for further commercial development.

RNA interference in the cat flea, Ctenocephalides felis: Approaches for sustained gene knockdown and evidence of involvement of Dicer-2 and Argonaute2

Effective RNA interference (RNAi) methods have been developed in many pest species, enabling exploration of gene function. Until now RNAi had not been attempted in the cat flea, Ctenocephalides felis, although the development of RNAi approaches would open up potential avenues for control of this important pest. This study aimed to establish if an RNAi response occurs in adult C. felis upon exposure to double-stranded RNA (dsRNA), which administration methods for dsRNA delivery could bring about effective gene knockdown and to investigate dynamics of any RNAi response. Knockdown of 80% of GSTσ was achieved by intrahaemoceolic microinjection of dsGSTσ but this invasive technique was associated with relatively high mortality rates. Immersing C. felis in dsGSTσ or dsDicer-2 overnight resulted in 65% knockdown of GSTσ or 60% of Dicer-2, respectively, and the degree of knockdown was not improved by increasing the dsRNA concentration in the bathing solution. Unexpectedly, the greatest degree of knockdown was achieved with the continuous administration of dsRNA in whole blood via a membrane feeding system, resulting in 96% knockdown of GSTσ within 2 days and sustained up to, at least, 7 days. Thus, unlike in many other species, the gut nucleases do not impair the RNAi response to ingested dsRNA in C. felis. A modest, but significant, upregulation of Dicer-2 and Argonaute2 was detectable 3 h after exposure to exogenous dsRNA, implicating the short-interfering RNA pathway. To our knowledge this study represents the first demonstration of experimentally induced RNAi in the cat flea as well as giving insight into how the gene knockdown response progresses.

Efficacy of oral moxidectin against susceptible and resistant isolates of Dirofilaria immitis in dogs

Background

Monthly topical and sustained-release injectable formulations of moxidectin are currently marketed; however, an oral formulation, while approved at a dose of 3 μg/kg, is not currently marketed in the United States. Although resistance of heartworms to all macrocyclic lactone (ML) heartworm preventives (ivermectin, milbemycin, selamectin and moxidectin) has been demonstrated, to date no data have been reported on the effectiveness of oral moxidectin against recent isolates of Dirofilaria immitis.

Methods

A total of nine studies were conducted to determine the efficacy of moxidectin against a range of older and recently sourced heartworm isolates. Dogs (groups of three to eight) were inoculated with 50 D. immitis infective larvae (L3) from nine different isolates (MP3, Michigan, JYD-34, ZoeMO-2012, ZoeKy-2013, ZoeLA-2013, GCFL-2014, AMAL-2014 and ZoeAL-2015) and treated 28–30 days later with single oral doses of 3 μg/kg of moxidectin. Additionally, one group of dogs that was inoculated with JYD-34 was treated monthly for 3 consecutive months beginning 30 days post inoculation. Dogs were held for approximately 4 months after the initial (or only) treatment and then necropsied for recovery of adult heartworms.

Results

A single dose of 3 μg/kg of moxidectin was 100% effective in preventing the development of five of nine heartworm isolates (MP3, Michigan, ZoeKy, GCFL and ZoeAL isolates), confirming their susceptibility to oral moxidectin at this dose. MP3 and Michigan are isolates sourced from the field more than 9 years ago, while ZoeKy, ZoeAL and GCFL were isolated from the field within the past 2 to 3 years. Against JYD-34, ZoeMO, ZoeLA and AMAL isolates, a single dose of 3 μg/kg of moxidectin was not completely effective, with efficacies of 19%, 82%, 54% and 62%, respectively, demonstrating resistance of these heartworm isolates to oral moxidectin at this dosage. Three consecutive monthly doses of 3 μg/kg of moxidectin were also incompletely effective against the JYD-34 isolate, with an efficacy of 44%. JYD-34 was originally isolated in 2010, while ZoeMO, ZoeLA and AMAL were isolated within the past 2 to 3 years.

Conclusions

A single oral dose (3 μg/mg) of moxidectin was 100% effective in preventing the development of ML-susceptible heartworm isolates while being incompletely effective against ML-resistant isolates.

Evaluation of the efficacy of ProHeart® 6 (moxidectin) against a resistant isolate of Dirofilaria immitis (JYD-34) in dogs

BACKGROUND

In a previous study, it was demonstrated that ProHeart^® 6 (PH6) (moxidectin, Zoetis) provided only about 20% efficacy in a small six-dog study against a macrocyclic lactone -resistant Dirofilaria immitis isolate (Jd2009-2) when dogs were inoculated with infective third-stage larvae (L3) at the end of the dosing period (ie, 180 days post treatment). The objective of the current study was to determine the prophylactic efficacy of a moxidectin sustained-release formulation (PH6) against a confirmed macrocyclic lactone-resistant isolate of D. immitis (JYD-34) in dogs when administered by subcutaneous injection at the labeled dose of 0.17 mg/kg 2 days before L3 inoculation. This was intended to model the scenario where dogs become infected with resistant heartworms at the end of the PH6 treatment period (ie, 6 months post treatment) when dogs would routinely be given another injection under normal field use.

METHODS

Twelve purpose-bred Beagle dogs (six males and six females) were selected and randomly allocated to two groups, untreated controls and PH6-treated dogs in groups of six each. The dogs were ≥8 months old at the start of the study, and using blood samples collected on Day -7 were shown to be negative for adult heartworm antigen and microfilariae. On Day 0, the dogs in the untreated control group were administered saline subcutaneously by injection, and the dogs in the treated group were administered PH6 according to label instructions. On Day 2, each dog was inoculated in the inguinal area with 50 L3 of D. immitis. The dogs were necropsied on Day 150 (148 days post infection), and the worms were collected and counted.

RESULTS

All of the six control dogs were infected and harbored a range of 21 to 37 worms (geometric mean, 25.4; 10.9 males and 13.9 females). Only one of the six PH6 dogs was found to be infected, harboring a single male worm. Efficacy was 99.5% (geometric mean).

CONCLUSION

ProHeart^® 6 was highly effective in preventing the development of heartworms in dogs challenged with a confirmed macrocyclic lactone-resistant heartworm isolate (JYD-34) 2 days prior to treatment.

Genetic profiles of ten Dirofilaria immitis isolates susceptible or resistant to macrocyclic lactone heartworm preventives

BACKGROUND

For dogs and cats, chemoprophylaxis with macrocyclic lactone (ML) preventives for heartworm disease is widely used in the United States and other countries. Since 2005, cases of loss of efficacy (LOE) of heartworm preventives have been reported in the U.S. More recently, ML-resistant D. immitis isolates were confirmed. Previous work identified 42 genetic markers that could predict ML response in individual samples. For field surveillance, it would be more appropriate to work on microfilarial pools from individual dogs with a smaller subset of genetic markers.

METHODS

MiSeq technology was used to identify allele frequencies with the 42 genetic markers previously reported. Microfilaria from ten well-characterized new isolates called ZoeKY, ZoeMI, ZoeGCFL, ZoeAL, ZoeMP3, ZoeMO, ZoeAMAL, ZoeLA, ZoeJYD-34, and Metairie were extracted from fresh blood from dogs. DNA were extracted and sequenced with MiSeq technology. Allele frequencies were calculated and compared with the previously reported susceptible, LOE, and resistant D. immitis populations.

RESULTS

The allele frequencies identified in the current resistant and susceptible isolates were in accordance with the allele frequencies previously reported in related phenotypes. The ZoeMO population, a subset of the ZoeJYD-34 population, showed a genetic profile that was consistent with some reversion towards susceptibility compared with the parental ZoeJYD-34 population. The Random Forest algorithm was used to create a predictive model using different SNPs. The model with a combination of three SNPs (NODE_42411_RC, NODE_21554_RC, and NODE_45689) appears to be suitable for future monitoring.

CONCLUSIONS

MiSeq technology provided a suitable methodology to work with the microfilarial samples. The list of SNPs that showed good predictability for ML resistance was narrowed. Additional phenotypically well characterized D. immitis isolates are required to finalize the best set of SNPs to be used for large scale ML resistance screening.

Thermodynamic temperature assignment to the point of inflection of the melting curve of high-temperature fixed points

The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature.

Metabolomic profiling of permethrin-treated Drosophila melanogaster identifies a role for tryptophan catabolism in insecticide survival

Insecticides and associated synergists are rapidly losing efficacy in target insect pest populations making the discovery of alternatives a priority. To discover novel targets for permethrin synergists, metabolomics was performed on permethrin-treated Drosophila melanogaster. Changes were observed in several metabolic pathways including those for amino acids, glycogen, glycolysis, energy, nitrogen, NAD(+), purine, pyrimidine, lipids and carnitine. Markers for acidosis, ammonia stress, oxidative stress and detoxification responses were also observed. Many of these changes had not been previously characterized after permethrin exposure. From the altered pathways, tryptophan catabolism was selected for further investigation. The knockdown of some tryptophan catabolism genes (vermilion, cinnabar and CG6950) in the whole fly and in specific tissues including fat body, midgut and Malpighian tubules using targeted RNAi resulted in altered survival phenotypes against acute topical permethrin exposure. The knockdown of vermilion, cinnabar and CG6950 in the whole fly also altered survival phenotypes against chronic oral permethrin, fenvalerate, DDT, chlorpyriphos and hydramethylnon exposure. Thus tryptophan catabolism has a previously uncharacterized role in defence against insecticides, and shows that metabolomics is a powerful tool for target identification in pesticide research.

Functional Characterization of a Novel Class of Morantel-Sensitive Acetylcholine Receptors in Nematodes

Acetylcholine receptors are pentameric ligand-gated channels involved in excitatory neuro-transmission in both vertebrates and invertebrates. In nematodes, they represent major targets for cholinergic agonist or antagonist anthelmintic drugs. Despite the large diversity of acetylcholine-receptor subunit genes present in nematodes, only a few receptor subtypes have been characterized so far. Interestingly, parasitic nematodes affecting human or animal health possess two closely related members of this gene family, acr-26 and acr-27 that are essentially absent in free-living or plant parasitic species. Using the pathogenic parasitic nematode of ruminants, Haemonchus contortus, as a model, we found that Hco-ACR-26 and Hco-ACR-27 are co-expressed in body muscle cells. We demonstrated that co-expression of Hco-ACR-26 and Hco-ACR-27 in Xenopus laevis oocytes led to the functional expression of an acetylcholine-receptor highly sensitive to the anthelmintics morantel and pyrantel. Importantly we also reported that ACR-26 and ACR-27, from the distantly related parasitic nematode of horses, Parascaris equorum, also formed a functional acetylcholine-receptor highly sensitive to these two drugs. In Caenorhabditis elegans, a free-living model nematode, we demonstrated that heterologous expression of the H. contortus and P. equorum receptors drastically increased its sensitivity to morantel and pyrantel, mirroring the pharmacological properties observed in Xenopus oocytes. Our results are the first to describe significant molecular determinants of a novel class of nematode body wall muscle AChR.

A comprehensive transcriptomic view of renal function in the malaria vector, Anopheles gambiae

Renal function is essential to maintain homeostasis. This is particularly significant for insects that undergo complete metamorphosis; larval mosquitoes must survive a freshwater habitat whereas adults are terrestrial, and mature females must maintain ion and fluid homeostasis after blood feeding. To investigate the physiological adaptations required for successful development to adulthood, we studied the Malpighian tubule transcriptome of Anopheles gambiae using Affymetrix arrays. We assessed transcription under several conditions; as third instar larvae, as adult males fed on sugar, as adult females fed on sugar, and adult females after a blood meal. In addition to providing the most detailed transcriptomic data to date on the Anopheles Malpighian tubules, the data provide unique information on the renal adaptations required for the switch from freshwater to terrestrial habitats, on gender differences, and on the contrast between nectar-feeding and haematophagy. We found clear differences associated with ontogenetic change in lifestyle, gender and diet, particularly in the neuropeptide receptors that control fluid secretion, and the water and ion transporters that impact volume and composition. These data were also combined with transcriptomics from the Drosophila melanogaster tubule, allowing meta-analysis of the genes which underpin tubule function across Diptera. To further investigate renal conservation across species we selected four D. melanogaster genes with orthologues highly enriched in the Anopheles tubules, and generated RNAi knockdown flies. Three of these genes proved essential, showing conservation of critical functions across 150 million years of phylogenetic separation. This extensive data-set is available as an online resource, MozTubules.org, and could potentially be mined for novel insecticide targets that can impact this critical organ in this pest species.

Development of an in vitro screen for compound bioaccumulation in Haemonchus contortus

The objective of the current study was to establish an in vitro screen and a highly sensitive analytical assay to delineate key physicochemical properties that favor compound bioaccumulation in the L3 life stage of a Haemonchus contortus isolate. Time-dependent studies revealed that absorption and elimination kinetics during the first 6 hr of exposure were sufficient to achieve maximum bioaccumulation for the majority of compounds tested. In subsequent studies, the larvae were incubated for 6 hr in a medium containing 146 compounds (5 μM initial concentration), including both human and veterinary medicines, characterized by a broad range of physicochemical properties. Bioaccumulation of the compounds by the nematodes was determined, and multiple physicochemical descriptors were selected for correlation. Data analysis using Bayes classification model and partial least-square regression revealed that clogD7.4, rotatable bond, E-state, and hydrogen bond donor each correlated with compound bioaccumulation in H. contortus L3. The finding that lipophilicity was critical for transcuticle compound permeation was consistent with previous studies in other parasitic species and in adult H. contortus . The finding of additional physicochemical properties that contribute to compound conformational flexibility, polarity, and electrotopological state shed light on the mechanisms governing transcuticle permeation. The relatively poor correlation between transcuticle and transmembrane permeation indicated the distinct mechanisms of compound permeation, likely due to the different constituents, and their contributions to overall transport function, of the lipid membranes and the porous collagen barrier of the nematode cuticle. Our study, for the first time, establishes a high-throughput screen for compound bioaccumulation in a parasitic nematode and further elucidates physicochemical factors governing transcuticular permeation of compounds. Application of this methodology will help explain the basis for discrepancies observed in receptor binding and whole organism potency assays and facilitate incorporation of drug delivery principles in the design of candidate anthelmintics.

Functional characterisation of a nicotinic acetylcholine receptor α subunit from the brown dog tick, Rhipicephalus sanguineus

Ticks and tick-borne diseases have a major impact on human and animal health worldwide. Current control strategies rely heavily on the use of chemical acaricides, most of which target the CNS and with increasing resistance, new drugs are urgently needed. Nicotinic acetylcholine receptors (nAChRs) are targets of highly successful insecticides. We isolated a full-length nAChR α subunit from a normalised cDNA library from the synganglion (brain) of the brown dog tick, Rhipicephalus sanguineus. Phylogenetic analysis has shown this R. sanguineus nAChR to be most similar to the insect α1 nAChR group and has been named Rsanα1. Rsanα1 is distributed in multiple tick tissues and is present across all life-stages. When expressed in Xenopus laevis oocytes Rsanα1 failed to function as a homomer, with and without the addition of either Caenorhabditis elegans resistance-to-cholinesterase (RIC)-3 or X. laevis RIC-3. When co-expressed with chicken β2 nAChR, Rsanα1 evoked concentration-dependent, inward currents in response to acetylcholine (ACh) and showed sensitivity to nicotine (100 μM) and choline (100 μM). Rsanα1/β2 was insensitive to both imidacloprid (100 μM) and spinosad (100 μM). The unreliable expression of Rsanα1 in vitro suggests that additional subunits or chaperone proteins may be required for more robust expression. This study enhances our understanding of nAChRs in arachnids and may provide a basis for further studies on the interaction of compounds with the tick nAChR as part of a discovery process for novel acaricides.

Derquantel and abamectin: effects and interactions on isolated tissues of Ascaris suum

Startect(®) is a novel anthelmintic combination of derquantel and abamectin. It is hypothesized that derquantel and abamectin interact pharmacologically. We investigated the effects of derquantel, abamectin and their combination on somatic muscle nicotinic acetylcholine receptors and pharyngeal muscle glutamate gated chloride receptor channels of Ascaris suum. We used muscle-strips to test the effects of abamectin, derquantel, and abamectin+derquantel together on the contraction responses to different concentrations of acetylcholine. We found that abamectin reduced the response to acetylcholine, as did derquantel. In combination (abamectin+derquantel), inhibition of the higher acetylcholine concentration response was greater than the predicted additive effect. A two-micropipette current-clamp technique was used to study electrophysiological effects of the anthelmintics on: (1) acetylcholine responses in somatic muscle and; (2) on l-glutamate responses in pharyngeal preparations. On somatic muscle, derquantel (0.1-30μM) produced a potent (IC50 0.22, CI 0.18-0.28μM) reversible antagonism of acetylcholine depolarizations. Abamectin (0.3μM) produced a slow onset inhibition of acetylcholine depolarizations. We compared effects of abamectin and derquantel on muscle preparations pretreated for 30min with these drugs. The effect of the combination was significantly greater than the predicted additive effect of both drugs at higher acetylcholine concentrations. On the pharynx, application of derquantel produced no significant effect by itself or on responses to abamectin and l-glutamate. Abamectin increased the input conductance of the pharynx (EC50 0.42, CI 0.13-1.36μM). Our study demonstrates that abamectin and derquantel interact at nicotinic acetylcholine receptors on the somatic muscle and suggested synergism can occur.

Anthelmintic discovery and development in the animal health industry

Most modern anthelmintics used against human pathogens have come from the animal health (AH) industry. Historically, new molecules were discovered empirically, but recent developments in genomic and screening technologies have significantly enhanced the opportunities for target-based identification of novel therapies. However, drug discovery and development is still a complicated and costly process with high attrition. Absence of a return in investment for tropical parasitic diseases makes it difficult for large pharmaceutical companies to justify seeking antiparasitics for less developed countries in isolation. A partnership in which there is a sharing of costs and leveraging of resources is one way forward and is reflected in the new paradigm of 'integrated drug discovery', where collaborations and networks of academic institutions and industry are working together towards the discovery of new treatments for tropical parasitic diseases.

Untargeted metabolomics reveals a lack of synergy between nifurtimox and eflornithine against Trypanosoma brucei

A non-targeted metabolomics-based approach is presented that enables the study of pathways in response to drug action with the aim of defining the mode of action of trypanocides. Eflornithine, a polyamine pathway inhibitor, and nifurtimox, whose mode of action involves its metabolic activation, are currently used in combination as first line treatment against stage 2, CNS-involved, human African trypanosomiasis (HAT). Drug action was assessed using an LC-MS based non-targeted metabolomics approach. Eflornithine revealed the expected changes to the polyamine pathway as well as several unexpected changes that point to pathways and metabolites not previously described in bloodstream form trypanosomes, including a lack of arginase activity and N-acetylated ornithine and putrescine. Nifurtimox was shown to be converted to a trinitrile metabolite indicative of metabolic activation, as well as inducing changes in levels of metabolites involved in carbohydrate and nucleotide metabolism. However, eflornithine and nifurtimox failed to synergise anti-trypanosomal activity in vitro, and the metabolomic changes associated with the combination are the sum of those found in each monotherapy with no indication of additional effects. The study reveals how untargeted metabolomics can yield rapid information on drug targets that could be adapted to any pharmacological situation.

The transcriptional response of Caenorhabditis elegans to Ivermectin exposure identifies novel genes involved in the response to reduced food intake

We have examined the transcriptional response of Caenorhabditis elegans following exposure to the anthelmintic drug ivermectin (IVM) using whole genome microarrays and real-time QPCR. Our original aim was to identify candidate molecules involved in IVM metabolism and/or excretion. For this reason the IVM tolerant strain, DA1316, was used to minimise transcriptomic changes related to the phenotype of drug exposure. However, unlike equivalent work with benzimidazole drugs, very few of the induced genes were members of xenobiotic metabolising enzyme families. Instead, the transcriptional response was dominated by genes associated with fat mobilization and fatty acid metabolism including catalase, esterase, and fatty acid CoA synthetase genes. This is consistent with the reduction in pharyngeal pumping, and consequential reduction in food intake, upon exposure of DA1316 worms to IVM. Genes with the highest fold change in response to IVM exposure, cyp-37B1, mtl-1 and scl-2, were comparably up-regulated in response to short–term food withdrawal (4 hr) independent of IVM exposure, and GFP reporter constructs confirm their expression in tissues associated with fat storage (intestine and hypodermis). These experiments have serendipitously identified novel genes involved in an early response of C. elegans to reduced food intake and may provide insight into similar processes in higher organisms.

Towards delineating functions within the fasciola secreted cathepsin l protease family by integrating in vivo based sub-proteomics and phylogenetics

BACKGROUND

fasciola hepatica, along with Fasciola gigantica, is the causative agent of fasciolosis, a foodborne zoonotic disease affecting grazing animals and humans worldwide. Pathology is directly related to the release of parasite proteins that facilitate establishment within the host. The dominant components of these excretory-secretory (ES) products are also the most promising vaccine candidates, the cathepsin L (Cat L) protease family.

METHODOLOGY/PRINCIPAL FINDINGS

the sub-proteome of Cat L proteases from adult F. hepatica ES products derived from in vitro culture and in vivo from ovine host bile were compared by 2-DE. The individual Cat L proteases were identified by tandem mass spectrometry with the support of an in-house translated liver fluke EST database. The study reveals plasticity within the CL1 clade of Cat L proteases; highlighted by the identification of a novel isoform and CL1 sub-clade, resulting in a new Cat L phylogenetic analysis including representatives from other adult Cat L phylogenetic clades. Additionally, for the first time, mass spectrometry was shown to be sufficiently sensitive to reveal single amino acid polymorphisms in a resolved 2-DE protein spot derived from pooled population samples.

CONCLUSIONS/SIGNIFICANCE

we have investigated the sub-proteome at the population level of a vaccine target family using the Cat L proteases from F. hepatica as a case study. We have confirmed that F. hepatica exhibits more plasticity in the expression of the secreted CL1 clade of Cat L proteases at the protein level than previously realised. We recommend that superfamily based vaccine discovery programmes should screen parasite populations from different host populations and, if required, different host species via sub-proteomic assay in order to confirm the relative expression at the protein level prior to the vaccine development phase.

Transcriptome analysis of the synganglion from the brown dog tick, Rhipicephalus sanguineus

Tick control strategies rely heavily on chemicals (acaricides), most of which target the central nervous system. With increasing resistance, new acaricides are urgently needed but knowledge of tick neurobiology is surprisingly limited, notably the number of neural-specific gene sequences. One thousand and eight expressed sequence tags (ESTs) were obtained from a normalized cDNA library from Rhipicephalus sanguineus synganglia. Putative functional identities were assigned to 44% whereas 34% were unknown/novel sequences. Of particular interest were ESTs encoding a chitinase-like enzyme, an acetylcholinesterase and four transmembrane receptors including two glutamate-gated chloride channel receptors, a leucokinin-like receptor and a nicotinic acetylcholine receptor alpha-subunit. This study highlights the benefits of using both neural tissues and normalized libraries in an EST-approach for identifying potential acaricide targets expressed as rare transcripts.

Cell-specific inositol 1,4,5 trisphosphate 3-kinase mediates epithelial cell apoptosis in response to oxidative stress in Drosophila

Organismal stress responses to oxidative stress are relevant to ageing and disease and involve key cell-/tissue-specific signal transduction mechanisms. Using Drosophila, an established in vivo model for stress studies, we show that cell-specific inositol phosphate signalling specifically via inositol 1,4,5 trisphosphate 3-kinase (InsP(3) 3-K, IP(3)K), negatively regulates organismal responses to oxidative stress. We demonstrate that the Drosophila Malpighian tubule (equivalent to vertebrate kidney and liver) is a key epithelial sensor for organismal oxidative stress responses: precise targeting of either gain-of-function constructs of Drosophila IP(3)Ks (IP(3)K-1 and IP(3)K-2), or loss-of-function (RNAi) constructs to only one cell type in tubule reversibly modulates survival of stress-challenged adult flies. In vivo, targeted IP(3)K-1 directly increases H(2)O(2) production, pro-apoptotic caspase-9 activity and mitochondrial membrane potential. The mitochondrial calcium load in tubule principal cells-assessed by luminescent and fluorescent genetically-encoded mitochondrial calcium reporters-is significantly increased by IP(3)K-1 under oxidative stress conditions, leading to apoptosis. The Drosophila orthologues of human apoptotic bcl-2 genes include debcl and buffy. Oxidative stress challenge does not modulate gene expression of either debcl or buffy in tubules; and altered debcl expression does not influence survival rates under oxidative stress challenge. Finally, targeted over-expression of either debcl or buffy to tubule principal cells does not impact on tubule caspase-9 activity. Thus, IP(3)K-1 modulates epithelial cell apoptosis without involvement of bcl-2-type proteins.

The nicotinic acetylcholine receptors of the parasitic nematode Ascaris suum: formation of two distinct drug targets by varying the relative expression levels of two subunits

Parasitic nematodes are of medical and veterinary importance, adversely affecting human health and animal welfare. Ascaris suum is a gastrointestinal parasite of pigs; in addition to its veterinary significance it is a good model of the human parasite Ascaris lumbricoides, estimated to infect ∼1.4 billion people globally. Anthelmintic drugs are essential to control nematode parasites, and nicotinic acetylcholine receptors (nAChRs) on nerve and muscle are the targets of cholinergic anthelmintics such as levamisole and pyrantel. Previous genetic analyses of nematode nAChRs have been confined to Caenorhabditis elegans, which is phylogenetically distinct from Ascaris spp. and many other important parasites. Here we report the cloning and expression of two nAChR subunit cDNAs from A. suum. The subunits are very similar in sequence to C. elegans UNC-29 and UNC-38, are expressed on muscle cells and can be expressed robustly in Xenopus oocytes to form acetylcholine-, nicotine-, levamisole- and pyrantel-sensitive channels. We also demonstrate that changing the stoichiometry of the receptor by injecting different ratios of the subunit cRNAs can reproduce two of the three pharmacological subtypes of nAChR present in A. suum muscle cells. When the ratio was 5∶1 (Asu-unc-38∶Asu-unc-29), nicotine was a full agonist and levamisole was a partial agonist, and oocytes responded to oxantel, but not pyrantel. At the reverse ratio (1∶5 Asu-unc-38∶Asu-unc-29), levamisole was a full agonist and nicotine was a partial agonist, and the oocytes responded to pyrantel, but not oxantel. These results represent the first in vitro expression of any parasitic nicotinic receptor and show that their properties are substantially different from those of C. elegans. The results also show that changing the expression level of a single receptor subunit dramatically altered the efficacy of some anthelmintic drugs. In vitro expression of these subunits may permit the development of parasite-specific screens for future anthelmintics.

Ascarid nematodes are major pathogens of humans and livestock. The major method of control is by the use of anthelmintic drugs, many of which target the nervous system. Drugs such as levamisole, pyrantel and oxantel target the nicotinic acetylcholine receptors present on muscle. Nematodes have several such receptors, and until now these have been best understood in the model species Caenorhabditis elegans. We have started to characterise the nicotinic receptors of Ascaris suum, and find that the genetics and pharmacology of the A. suum receptors differ from C. elegans. In both species, nicotine and levamisole preferentially activate different forms of the nicotinic receptor, the N- and L-type, respectively. In C. elegans, the L-type receptor is made up of five subunits, whereas the N-type is a homomer of a sixth subunit. We can recapitulate many of the properties of the A. suum N- and L-type receptors, including their sensitivity to two other important anthelmintics, pyrantel and oxantel, by expressing just two subunits at varying ratios. This has implications for the use of drug combinations and for cross-resistance between nicotinic anthelmintics. It may start to give an explanation for the varying effectiveness of nicotinic drugs against different parasites.

An ivermectin-sensitive glutamate-gated chloride channel from the parasitic nematode Haemonchus contortus

Nematode glutamate-gated chloride channels are targets of the macrocyclic lactones, the most important group of anthelmintics available. In Xenopus laevis oocytes, channels formed by the GluClalpha3B subunit from the parasite Haemonchus contortus were more sensitive to l-glutamate (EC(50) = 27.6 +/- 2.7 microM) than those formed by the homologous subunit from Caenorhabditis elegans (EC(50) = 2.2 +/- 0.12 mM). Ibotenate was a partial agonist (EC(50) = 87.7 +/- 3.5 microM). The H. contortus channels responded to low concentrations of ivermectin (estimated EC(50) = approximately 0.1 +/- 1.0 nM), opening slowly and irreversibly in a highly cooperative manner: the rate of channel opening was concentration-dependent. Responses to glutamate and ivermectin were inhibited by picrotoxinin and fipronil. Mutating an N-terminal domain amino acid, leucine 256, to phenylalanine increased the EC(50) for l-glutamate to 92.2 +/- 3.5 microM, and reduced the Hill number from 1.89 +/- 0.35 to 1.09 +/- 0.16. It increased the K(d) for radiolabeled ivermectin binding from 0.35 +/- 0.1 to 2.26 +/- 0.78 nM. Two other mutations (E114G and V235A) had no effect on l-glutamate activation or ivermectin binding: one (T300S) produced no detectable channel activity, but ivermectin binding was similar to wild-type. The substitution of any aromatic amino acid for Leu256 had similar effects in the radioligand binding assay. Molecular modeling studies suggested that the GluCl subunits have a fold similar to that of other Cys-loop ligand-gated ion channels and that amino acid 256 was unlikely to play a direct role in ligand binding but may be involved in mediating the allosteric properties of the receptor.

Comparative Proteomics of Excretory-Secretory Proteins Released by the Liver Fluke Fasciola hepatica in Sheep Host Bile and during in Vitro Culture ex Host

Livestock infection by the parasitic fluke Fasciola hepatica causes major economic losses worldwide. The excretory-secretory (ES) products produced by F. hepatica are key players in understanding the host-parasite interaction and offer targets for chemo- and immunotherapy. For the first time, subproteomics has been used to compare ES products produced by adult F. hepatica in vivo, within ovine host bile, with classical ex host in vitro ES methods. Only cathepsin L proteases from F. hepatica were identified in our ovine host bile preparations. Several host proteins were also identified including albumin and enolase with host trypsin inhibitor complex identified as a potential biomarker for F. hepatica infection. Time course in vitro analysis confirmed cathepsin L proteases as the major constituents of the in vitro ES proteome. In addition, detoxification proteins (glutathione transferase and fatty acid-binding protein), actin, and the glycolytic enzymes enolase and glyceraldehyde-3-phosphate dehydrogenase were all identified in vitro. Western blotting of in vitro and in vivo ES proteins showed only cathepsin L proteases were recognized by serum pooled from F. hepatica-infected animals. Other liver fluke proteins released during in vitro culture may be released into the host bile environment via natural shedding of the adult fluke tegument. These proteins may not have been detected during our in vivo analysis because of an increased bile turnover rate and may not be recognized by pooled liver fluke infection sera as they are only produced in adults. This study highlights the difficulties identifying authentic ES proteins ex host, and further confirms the potential of the cathepsin L proteases as therapy candidates.

A Drosophila systems approach to xenobiotic metabolism

Insecticide resistance is a major problem for both medicine and agriculture and is frequently associated with overexpression of metabolic enzymes that catalyze the breakdown of pesticides, leading to broad-spectrum resistance. However, the insect tissues within which these metabolic enzymes normally reside remain unclear. Microarray analysis of nine adult tissues from Drosophila melanogaster reveals that cytochrome P-450s and glutathione-S-transferases show highly tissue-specific expression patterns; most were confined to one or more epithelial tissues, and half showed dominant expression in a single tissue. The particular detoxifying enzymes encountered by a xenobiotic thus depend critically on the route of administration. In particular, known insecticide metabolism genes are highly enriched in insect Malpighian (renal) tubules, implicating them in xenobiotic metabolism. The tubules thus display, with the fat body, roles analogous to the vertebrate liver and immune system, as well as its acknowledged renal function. To illustrate this, when levels of a single gene, Cyp6g1, were manipulated in just the Malpighian tubules of adult Drosophila, the survival of the whole insect after 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) challenge was altered, whereas corresponding manipulations in the nervous system or the fat body were without effect. This shows that, although detoxification enzymes are widely distributed, baseline protection against DDT resides primarily in the insect excretory system, corresponding to less than 0.1% of the mass of the organism.

Model-organism genomics in veterinary parasite drug-discovery

A recent article about genomic filtering highlights exciting new opportunities for antiparasitic drug discovery resulting from major advances in genomic technologies. In this article, we discuss several approaches in which model-organism genomics and proteomics could be applied to the identification and validation of novel targets for antiparasitic drug discovery in veterinary medicine.

Proinflammatory chemokine induction in keratocytes and inflammatory cell infiltration into the cornea

PURPOSE

To determine the effect of interleukin (IL)-1alpha and tumor necrosis factor (TNF)-alpha on cytokine, chemokine, and receptor expression in corneal stromal cells; the effect of corneal scrape injury on monocyte chemotactic and activating factor (MCAF) expression and monocyte-macrophage influx into the stroma; and the effect of MCAF and granulocyte colony-stimulating factor (G-CSF) microinjection on inflammatory cell infiltration into the stroma.

METHODS

Gene array technology was used to evaluate changes in cytokine, chemokine, and receptor gene expression in stromal fibroblasts in response to IL-1alpha and TNFalpha. Expression of MCAF mRNA and protein was monitored with an RNase protection assay and Western blot analysis, respectively. Keratocyte MCAF protein expression in the rabbit cornea was detected with immunocytochemistry. After epithelial scrape injury, monocytes-macrophages were detected in rabbit corneas, by immunocytochemistry for monocyte-macrophage antigen. Inflammatory cell infiltration after MCAF and G-CSF microinjection into the stroma of mouse corneas was monitored with hematoxylin and eosin staining.

RESULTS

IL-1alpha or TNFalpha upregulated the expression of several proinflammatory chemokines in stromal fibroblasts in culture. These included G-CSF, MCAF, neutrophil-activating peptide (ENA-78), and monocyte-derived neutrophil chemotactic factor (MDNCF). MCAF mRNA upregulation was confirmed by RNase protection assay, and MCAF protein was detected by Western blot analysis. MCAF protein was detected in keratocytes at 4 hours and 24 hours after epithelial injury, but not in keratocytes in the unwounded cornea. Corneal epithelial injury triggered the influx of monocytes-macrophages into the corneal stroma in the rabbit. Microinjection of MCAF and G-CSF into mouse cornea resulted in the influx of monocytes-macrophages and granulocytes, respectively, into the stroma.

CONCLUSIONS

Proinflammatory chemokine induction in keratocytes is mediated by IL-1alpha and TNFalpha. The proinflammatory chemokines produced by the keratocytes probably trigger the influx of inflammatory cells into the stroma after epithelial injury associated with corneal surgery, contact lenses, or trauma.

High-affinity ivermectin binding to recombinant subunits of the Haemonchus contortus glutamate-gated chloride channel

Glutamate-gated chloride channels (GluCls) are targets for the avermectin anthelmintics. A family of five GluCl subunit genes encoding seven subunits has been identified in Caenorhabditis elegans. We have previously shown that two orthologous genes in the parasite, Haemonchus contortus, encode three GluCl subunits (HcGluClbeta, Hcgbr-2A and Hcgbr-2B) with high amino-acid identity (>80%) to their C. elegans counterparts. We amplified and cloned a further subunit cDNA, HcGluClalpha, from H. contortus eggs. Sequence comparisons suggested that this subunit was closely related to, but not orthologous with, the C. elegans GluClalpha1, alpha2 or alpha3/GBR-2 subunits ( approximately 55% amino-acid identity). The HcGluClalpha cDNA from an ivermectin-resistant isolate contained no coding changes from the wild-type. All of the known H. contortus GluCl cDNA clones were subcloned into the expression vector pcDNA3.1 and transiently expressed in COS-7 cells. As predicted by functional data from the C. elegans orthologues, the Hcgbr-2A and HcGluClbeta subunits failed to bind [3H]ivermectin. The Hcgbr-2B and HcGluClalpha subunits bound [3H]ivermectin with high affinity; the K(d) values were 70+/-16 and 26+/-12 pM, respectively. This binding was inhibited by a variety of avermectins, though cold ivermectin was the most potent inhibitor of [3H] ivermectin binding. Picrotoxin, fipronil, glutamate and GABA all failed to compete for ivermectin binding to either subunit. The affinity of [3H]ivermectin binding to H. contortus L3 P2 larval membrane preparations was re-examined and found to be 70+/-7 pM. The properties of orthologous GluCl subunits are likely to be conserved across species, but the repertoire and relative importance of those subunits may vary.

Formulation and stability of naltrexone oral liquid for rapid withdrawal from methadone

OBJECTIVE

To assess the stability of naltrexone oral liquid prepared from tablets and powder, and to evaluate its use in precipitating rapid withdrawal from methadone.

DESIGN

Naltrexone 1 mg/mL oral liquids were prepared from tablets and powder and stored in the dark at 4, 25, and 70 degrees C. Similar formulations containing 5 mg/mL were stored at 70 degrees C. The 1-mg/mL formulation prepared from tablets was clinically evaluated in inducing rapid withdrawal in two drug-dependent individuals receiving methadone maintenance treatment using a naltrexone dose titration protocol.

SETTING

A university pharmacy school and affiliated urban teaching hospital.

MAIN OUTCOME MEASURES

Samples removed at six time points were analyzed for naltrexone concentration to assess decomposition over 90 days. An opioid withdrawal symptom checklist was used to assess the severity of the withdrawal symptoms prior to, and 30 minutes after, each dose of naltrexone.

RESULTS

Decomposition of naltrexone in all formulations stored at 4 and 25 degrees C was not significant over 90 days. Both patients tolerated naltrexone 1 mg/mL oral liquid, but found it bitter and gritty. Withdrawal symptoms were experienced immediately after the first dose, but were resolving by the end of day 3 of naltrexone treatment, at which stage both patients were able to tolerate a 50-mg tablet of naltrexone as maintenance.

CONCLUSIONS

Naltrexone 1 mg/mL oral liquids prepared from tablets or powder are stable when stored in the dark for 60 days at 4 degrees C and for 30 days at 25 degrees C. The formulation prepared from tablets provides flexible dosing in patients undergoing rapid withdrawal from methadone.

Stability of an extemporaneously compounded levothyroxine sodium oral liquid

The stability of levothyroxine sodium in oral liquid dosage forms compounded from commercially available tablets was studied. Levothyroxine sodium oral liquids (25 micrograms/mL) were prepared from tablets and from powder with and without methylparaben preservative and transferred to amber, high-density polyethylene bottles. Five bottles of each tablet-based formulation were stored at 2-8 degrees C, 23-27 degrees C, and 38-42 degrees C, and five bottles of each powder-based formulation were stored at 38-42 degrees C. On days 3, 8, 14, 22, 31, 61, and 90, samples were taken from each bottle and analyzed for drug concentration by stability-indicating high-performance liquid chromatography. There was significant degradation of levothyroxine sodium in all the formulations. However, the tablet-based formulation without preservative stored at 4 degrees C retained at least 90% of its initial concentration for eight days after compounding. Degradation occurred faster in the tablet-based formulation with preservative. None of the formulations retained > or = 90% initial potency by day 14. An extemporaneous oral liquid formulation of levothyroxine sodium 25 micrograms/mL compounded from crushed tablets was stable for eight days when stored in amber bottles at 4 degrees C.

Fluconazole infused via a nephrostomy tube: a novel and effective route of delivery

Fluconazole is an effective oral or intravenous anti-fungal agent. It undergoes little or no metabolism with 70-80% of the drug excreted unchanged in the urine. There is no readily available information on its effectiveness in treating fungal urinary tract infections in the presence of chronic renal failure. We report a case of chronic renal failure with ureteric obstruction complicated by infection with Candida albicans that was successfully treated by the infusion of fluconazole via a nephrostomy tube. There were no complications related to the use of fluconazole.

Stability of hydrocortisone oral suspensions prepared from tablets and powder

OBJECTIVE

To assess the stability, dosage uniformity, and clinical acceptability of hydrocortisone oral suspensions prepared from tablets and powder.

DESIGN

Hydrocortisone 2.5 mg/mL oral suspensions were stored in the dark for 91 days at 5, 25, and 40 degrees C. Dosage uniformity was assessed by repeated sampling of the formulation prepared from tablets at 5 and 25 degrees C. The formulation was clinically evaluated in 2 pediatric patients.

SETTING

A university pharmacy school and affiliated urban teaching hospital.

PARTICIPANTS

A brother (4 y old) and sister (1 y old) with congenital adrenal hyperplasia maintained on a commercially available hydrocortisone cypionate suspension.

MAIN OUTCOME MEASURES

Samples removed at 5 time points were analyzed for hydrocortisone to assess decomposition over 90 days. Dosage uniformity was evaluated by intra- and interday variability. Palatability was examined in the 2 children and urinary cortisol concentrations were measured in the boy before and 5 days after commencing the formulation prepared from tablets.

RESULTS

Decomposition of hydrocortisone was not significant except in the formulation that was prepared from tablets and stored at 40 degrees C. Dosage uniformity gave coefficients of variation less than 4.5%. The formulation was well-tolerated and resulted in satisfactory urinary cortisol concentrations in the boy.

CONCLUSIONS

The hydrocortisone oral suspensions supply a uniform dose and are chemically stable when stored in the dark at 5 and 25 degrees C for at least 30 days. They provide flexible and convenient dosage forms for pediatric patients.

Adverse reactions associated with nefopam

AIM

To review postmarketing experience of adverse reactions associated with nefopam.

METHODS

Spontaneous reports of adverse reactions associated with nefopam over a 12 year period received by the New Zealand Centre for Adverse Reactions Monitoring were reviewed.

RESULTS

There were 70 reports of adverse reactions thought to be causally related to nefopam, most of which appear to be predictable extensions of the pharmacological effect of nefopam, and included confusion, hallucinations, convulsions, dizziness, headache, sweating, urinary retention, nausea, vomiting, tachycardia and palpitations. The first report of angina is described. Convulsions occurred in a stable epileptic in whom nefopam was contraindicated, and in another where the seizure threshold may have been lowered by a concomitant tricyclic antidepressant.

CONCLUSIONS

Nefopam can cause unpleasant adverse effects and there are important cautions and contraindications with this analgesic. A clearer presentation of its basic pharmacology in the datasheet should help to ensure appropriate use.

A survey of allopurinol dosage prescribing

AIM

To evaluate the appropriateness of allopurinol dosage according to renal function in patients at Dunedin and Wakari hospitals.

METHOD

A prospective survey of all patients receiving allopurinol therapy at Dunedin and Wakari hospitals during a four week period in January/February 1994 was performed. Data were collected from medication charts, patient notes and laboratory records. Dosage prescribed was compared with established guidelines.

RESULTS

Of 46 patients on allopurinol treatment 18 were prescribed at least 100 mg more than the recommended daily dose. Twenty-nine out of the 46 surveyed patients (median age 77 years) had mild to moderate renal impairment.

CONCLUSIONS

A significant proportion of patients were receiving excessive doses. Although information regarding the allopurinol hypersensitivity syndrome and individualised allopurinol dosage is available, it is evident that many practitioners remain unaware of the recommendations.

Evidence for the polymorphic oxidation of debrisoquine and proguanil in a Khmer (Cambodian) population

The frequency distributions of the urinary metabolic ratios of debrisoquine and proguanil were measured in a population of unrelated Khmers. Out of 98 Khmer subjects studied, two were identified as poor metabolisers of debrisoquine when a metabolic ratio of 12.6 was used as the cut off point. This represents a prevalence of debrisoquine poor metabolisers of 2.1% (95% confidence interval 0.25-7.3%) which is similar to other Asian populations. Based on the distribution of the ratio of proguanil to cycloguanil excreted in urine, and using an antimode value of 10, the prevalence of poor metabolisers of proguanil in a Khmer population was estimated to be 18.4% (95% confidence interval 10.9-28.1%). The frequency of poor metabolisers of proguanil in Khmers was higher than that described for Caucasian populations, but similar to most reported results in Asian populations.

Social interaction effects on restrained eating

The eating behavior of college women scoring within either the above-average or middle ranges on the Restraint Scale was compared following brief social encounters with male students or other female students, or a no-encounter control situation. The eating of average restraint women was significantly depressed following interaction with a partner whom the subjects considered attractive. For high restraint women a nonsignificant tendency towards disinhibition of eating following interaction with an attractive other occurred. Personality ratings by partners indicated that high restraint women presented a distinct social persona to male, but not female, strangers in the brief experimental interaction.

Stability of dantrolene oral suspension prepared from capsules

The chemical stability of an extemporaneously compounded dantrolene oral suspension (5 mg/ml dantrolene sodium) in Syrup BP containing citric acid with and without methyl hydroxybenzoate preservative was studied on storage at 5, 25 and 40 degrees C for 150 days in high density polyethylene dispensing bottles. The amount of dantrolene free acid in suspension was monitored by a stability indicating HPLC assay. There was no significant decomposition of dantrolene under all storage conditions irrespective of the presence of preservative. The results show that the formulation of dantrolene oral suspension provides a convenient and stable dosage form for use in pediatric patients and in those unable to swallow capsules. It is recommended that the formulation be stored at room temperature and in the absence of microbiological testing a shelf-life of 30 days is proposed for the product prepared with preserved syrup.

Mexican- and Anglo-American Differences on the Psychological Screening Inventory

This study investigated differences between Mexican- and Anglo-American college students on the Psychological Screening Inventory (PSI; Lanyon, 1970, 1973)-a brief personality instrument designed to detect persons who might benefit from more extensive evaluations in mental health settings. Further, this study controlled for the Mexican Americans' acculturation level, age, and socioeconomic status (SES), as these variables have routinely been shown to covary with other psychosocial variables. From data on 107 Mexican-American and 105 Anglo-American college students, we found that Mexican-American subjects had higher PSI scores on the Alienation and Defensiveness subscales and lower scores on the Social Nonconformity and Expression subscales than did Anglo-American subjects. With acculturation covaried, however, these differences were no longer statistically significant. With age and SES covaried, the two ethnic groups differed on Alienation, Expression, and Defensiveness, suggesting that Mexican Americans' performance on the PSI varies as a function of acculturation, age, and SES. Implications of these findings are discussed.