Abstract
Melarsomine is used intramuscularly to destroy adult heartworms when treating canine heartworm disease (HWD). This drug is highly irritative and can elicit local complications. Therefore, melarsomine should be injected into the paralumbar muscles by strictly adhering to the manufacturers' prescriptions. However, it is not known how to determine the optimal location of the needle during the injection process. Ultrasonography (US) of the epaxial (paralumbar) musculature was used as a new method to measure the cross-sectional diameter of the paralumbar musculature, to determine the required location of the injection needle, and to study the local side effects in two dogs with HWD. The macroscopic appearance of the melarsomine solution during injection was demonstrated by video imaging. Melarsomine was not fully gravitating, but its majority was spreading along the thickest fascia of the musculature. Three minutes thereafter, no ultrasound signs of the melarsomine solution were seen, suggesting a full absorption at least ultrasonographically. This procedure was simulated in vitro with methylene blue solution having the same appearance. Removing the injection needle only after 5 min post-injection could prevent undesirable leakage of the drug through the injection channel into the subcutaneous tissue. Ultrasonography can be a useful aid during the treatment of HWD with melarsomine according to this preliminary study.
Introduction
Heartworm disease (HWD) caused by the filaroid helminth Dirofilaria immitis is a parasitosis widely spread in several continents including Europe (Morchón et al., 2012). The emerging nature of HWD is mainly due to global changing (warming-up) of the climate, by providing even more places for the living conditions of mosquitoes acting as vectors of D. immitis (Fuehrer et al., 2021). Nowadays, HWD has an endemic occurrence also in several Southern and Middle-European countries including Hungary (Genchi et al., 2011; Farkas et al., 2014, 2020). The diagnosis of HWD is based on parasitological laboratory methods, and even subclinically infected dogs need to be treated (Nelson et al., 2020; AHS Guidelines, 2020; Becker et al., 2022). The internationally accepted therapeutic scheme is the three-dose alternate melarsomine treatment regimen recommended by the American Heartworm Society (AHS). This therapeutic protocol consists of the application of macrocyclic lactones against microfilariae as well as against L3 and L4 (larvae), doxycycline for the elimination of the symbiotic Wolbachia bacteria, and melarsomine dihydrochloride (henceforward melarsomine) to kill adult heartworms (HWs). Melarsomine, distributed under the commercial name Immiticide by Boehringer Ingelheim (https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=7b8c0f90-412b-4bd1-9b2b-afd8078e8ecf&type=display) or Diroban by Zoetis Inc. (https://www2.zoetisus.com/content/assets/docs/Petcare/diroban-prescribing-information.pdf), is accepted worldwide and this is the only drug authorised by the FDA in the USA against adult HWs (ESCCAP Guidelines 05, 2012; AHS Guidelines, 2020). Melarsomine has a narrow therapeutic range which should be taken into consideration to avoid potential systemic side effects such as coughing, anorexia, vomiting, diarrhoea or, rarely, neurological alterations. This drug is highly irritative when applied intramuscularly and can often cause – usually temporary – local irritation and pain reaction (https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=7b8c0f90-412b-4bd1-9b2b-afd8078e8ecf&type=display; https://www2.zoetisus.com/content/assets/docs/Petcare/diroban-prescribing-information.pdf). Sometimes, more severe sterile inflammation might occur. In addition to the relatively mild, usually reversible local alterations, more severe complications, including sterile abscess formation, have also been described (Maxwell et al., 2014; Bagi et al., 2017). Two reports have also been published on severe neurological complications affecting the relevant segment of the spinal cord (Hettlich et al., 2003; Moore et al., 2013).
As to the directions of the manufacturers, provided in its label, melarsomine should be injected into the epaxial (more precisely into the paralumbar) musculature, being one of the thickest muscles in dogs with a comprehensive blood supply. The latter is important to provide rapid absorption of the drug (Page, 2008). The highly irritative nature of melarsomine is illustrated in the directions of the manufacturers. As such, different injection needles should be used for suction of the drug from the vial for the injection itself to avoid contamination of the tissues along the outer part of the needle. Alternate lumbar sites should be used during the three-dose melarsomine treatment, and superficial injection or leakage should be avoided (https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=7b8c0f90-412b-4bd1-9b2b-afd8078e8ecf&type=display; https://www2.zoetisus.com/content/assets/docs/Petcare/diroban-prescribing-information.pdf). Proper application with strict adherence to the manufacturers' description can decrease the chance for local complications (Hettlich et al., 2003; Moore et al., 2013). Although these directions are quite detailed, it is not known how to determine the optimal positioning and depth of the injection needle within the paralumbar muscles to minimise local reactions and to avoid more severe complications.
There are few publications on ultrasonography being used for imaging the epaxial (paralumbar) muscles both in human and veterinary medicine (Hides et al., 2008; Stubbs et al., 2010; Haro et al., 2013; Freeman et al., 2017, 2019). Recently, Alaman et al. (2022) have reported on the ultrasound-guided approach to the dorsal aspect of the quadratus lumborum muscle (D-QL) and on evaluation of the spread of methylene blue dye in canine cadavers. However, we did not find reports dealing with the application of ultrasonography in vivo to aid any intramuscular injections in dogs.
Our hypothesis was that ultrasonography can help with the injection technique by providing exact measurement of the cross-sectional diameter of the paralumbar muscles, and it can also be used for the follow-up of the local reactions caused by melarsomine. Our research group has recently reported on the application of moxidectin and ultrasound-aided injection of melarsomine during the American Heartworm Society recommended treatment protocol in 44 Dirofilaria immitis infected dogs (Vörös et al., 2022). Although ultrasonography has been applied in that study for optimising the location of melarsomine injection and following the local effects of this drug, no detailed methodology could be provided because of the limited extent of that article. In this paper, we describe the method of ultrasonographically-aided intramuscular melarsomine injection and present some illustrating cases of this technique.
Materials and methods/Results
In the dogs presented in the study, HWD was confirmed by laboratory methods (Becker et al., 2022) and was treated with the AHS therapeutic protocol (Nelson et al., 2018; AHS Guidelines, 2018). Written owner consent was obtained from each owner for the examinations and treatment as well as for the scientific use of the data gained.
Before the administration of the melarsomine injections, each dog was sedated with butorphanol (Alvegesic® 10 mg/mL inj. ALVERRA and WERFFT GmbH, Vienna, Austria) given deeply intramuscularly into the scapular musculature in a dosage of 0.4 mg/kg.
Dogs were separated in a quiet, darkened room together with their owner to avoid any stressors acting against the sedative effects. The aims of sedation were (1) to immobilise the patients during melarsomine injection and to avoid activity of the lumbar musculature and (2) to utilise the analgesic effect of butorphanol during the post-injection phase. A steady state of sedation was achieved in each dog after 25–30 min. In this phase, the patients remained conscious but became calm and less reactive to their surroundings, but were still able to walk with some trembling.
The dogs were positioned in sternal recumbency on the examination table and pre-injection ultrasonography was performed with a MyLab Gold 40 ultrasound machine (ESAOTE, Italy) equipped with a 6–8 MHz convex abdominal and a 12–18 MHz linear transducer. Ultrasonography of the paralumbar muscles was done as described for the multifidus muscle in humans (Hides et al., 2008). The location of the approximate injection site was chosen between the 3rd and 5th lumbar vertebrae according to the manufacturers' guidance. This was determined by palpating and counting the spinal processes of the lumbar vertebrae, starting just behind the ribcage (i.e., after the last thoracic vertebra). Meanwhile, the paralumbar musculature was also palpated to estimate its most prominent/thickest part. The hair was clipped at this area, copious ultrasound gel was applied, and oblique horizontal planes were produced with the ultrasound probe. These planes were aimed to be perpendicular to the paralumbar muscles, whilst achieving and measuring the largest diameter (thickness) of the musculature. Then, the ultrasound gel was removed carefully and the optimal site for the injection was marked with a felt marker and the area was disinfected with alcohol. The patient was immobilised by the owner and by one assistant. Melarsomine injection was applied as demonstrated in Fig. 1 in dog 1, a Hungarian Vizsla of 27 kg body weight. The needle was inserted approximately into the middle of the muscles based on the pre-injection measurements described above.
In Dog 2, a mixed breed of 29.4 kg body weight, the injection needle was removed right after the injection and the injection site was compressed with a gauze pad for 10 min. Meanwhile, the dog was still restrained on the examination table. These measures were intended to avoid the movement of the dog during the absorption of melarsomine from the muscles. Despite these actions, the melarsomine solution was leaking and flowing out from the injection channel to the surface of the skin at the injection puncture site when the needle was pulled out. Then, severe post-injection swelling with moderate pain was observed a few days later. The course of the ultrasonographic alterations of dog 2 is demonstrated in Figs 2–4. This dog had a body condition score (BCS) of 4/5 with a relatively thick subcutaneous tissue layer which might have contributed to the leakage.
Therefore, the injection technique was modified in the way that the needle was left in place for 5 min after injection of the melarsomine solution when still providing immobilisation of the patient. In dog 3, a Miniature Dachshund dog of 5 kg body weight, we recorded the injection process right through the event (Suppl. Video 1). During this process, we experienced that the drug was not fully gravitating, i.e., flowing to the deepest point of the musculature, towards the vertebrae, but its majority was spreading (more or less) horizontally along the deep thoracolumbar fascia of the musculature (see as an echogenic line on this video recording). Then, 3–5 min after the injection, only minimal ultrasonographic signs of the melarsomine solution were observed, indicating a nearly full absorption at least ultrasonographically (Suppl. Video 2).
These illustrations show that rather severe alterations were found in dog 2, when the needle was removed right after the injection, compared with dog 3 where the needle was left in place for 5 min after the injection. The macroscopic alterations observed and palpated in the paralumbar region, and the macroscopic healing process (decrease in swelling and local sensitivity) occurred in accordance with diminishing of the ultrasound findings.
To simulate the injection process in vitro, 5–10 mL methylene blue solution was injected into the epaxial lumbar musculature of three carcasses under ultrasound guidance as described above. Shortly after the injection, the spot of injection was dissected. A longitudinal distribution of methylene blue was found along with the muscle fibres in the m. longissimus (Fig. 5). The length of distribution varied between 6 and 10 cm in the bodies.
Discussion
We found ultrasonography of the paralumbar musculature to be a useful tool for determining the optimal injection site of the highly irritative melarsomine solution. In this way, the required location of the needle pinpoint could be allocated for the injecting process. Based on our preliminary results, by keeping the injection needle in place for about five minutes seems to provide enough time for the absorption of the drug. This can prevent melarsomine leaking into the subcutaneous tissue when the needle is being removed. According to the results of the current work, it can be hypothesised that this technique can minimise or even prevent local complications. By checking the injection site, it is possible to estimate the potential local consequences and the grade of the healing process as well (Vörös et al., 2022).
Regarding analgesia and sedation before and during the injection period, there is no agreement in the literature, and it is not mentioned in the prescriptions of the manufacturers either. In our recent work on the treatment of 44 dogs with heartworm disease (Vörös et al., 2022), we used the synthetic opioid butorphanol, due to its sedative and analgesic effects with minimal cardiovascular sequelae (Hammond et al., 2008; Vin Veterinary Drug Handbook, 2021). Not sedating the patients can lead to reluctance and movement (or even struggling). This can lead to spreading (leaking) of melarsomine close to the nerves or even to the spinal cord of the relevant lumbar region. This was suspected to happen in the case report of Hettlich et al. (2003), resulting in severe neurological complications. Moore et al. (2013) suggested that an inadvertent application of melarsomine into the epidural space or even into the spinal cord could have been responsible for the neurological complications of their case. Other proposed options might include migration of the solution either along fascial planes or along nerve roots into the epidural space (Hettlich et al., 2003). A gradually expanding epidural abscess was suggested as a cause of chronic progressive myelopathy in a dog and this might have been due to the close location of the injection site to the vertebral column (Moore et al., 2013).
Webster et al. (2014) described the functional anatomy of the epaxial musculature in cadavers of sprinting and fighting dogs. However, the comparative anatomy related to the ultrasound appearance of the paralumbar/epaxial musculature is not known. We have demonstrated the distribution of melarsomine in vivo and simulated it in vitro with methylene blue solution with similar results.
There are obvious limitations of the present work. This is only a description and illustration of the technique without prospective follow-up of clinical cases. The rapid absorption of melarsomine demonstrated in the present study is mentioned but not detailed in the labels of the manufacturers (https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=7b8c0f90-412b-4bd1-9b2b-afd8078e8ecf&type=display; https://www2.zoetisus.com/content/assets/docs/Petcare/diroban-prescribing-information.pdf). Melarsomine is absorbed quickly, and it reaches its maximum concentration in the blood in about 11 min (Page, 2008). However, we did not find literary information on the full post-injection absorption (i.e., disappearance) of this drug from the musculature. The precise determination of melarsomine absorption could be made only by high-performance liquid chromatography (HPLC) of muscular biopsy samples taken from the places of the injection. This is not an option in clinical cases and would need experimental studies. In a recent research, we have successfully applied our currently reported technique in 44 dogs with HWD (Vörös et al., 2022). Those patients were treated according to the AHS recommendation which was expanded with some new therapeutic measures. Melarsomine was injected intramuscularly as described in the present article and post-therapeutic local complications were detected and followed by physical examination as well as by ultrasonography of the paralumbar muscles (Vörös et al., 2022). That publication is partially based on the present preliminary study which has been cited in that paper as ‘under review’. Therefore, the current manuscript can be considered as a preceding preliminary work.
Ethical statement
The first author, Károly VÖRÖS is a member of the Editorial Board.
Acknowledgements
The authors express their thanks to Prof. Róbert Farkas, DVM, PhD, DSc, as well as to Mrs Mónika Gyurkovszky (Department of Parasitology and Zoology of the University of Veterinary Medicine Budapest, UVMB) for performing the parasitological laboratory examinations. This research was funded by the KK 69P02RM06 research project (2017) and by the NKB project (2018), both provided by the UVMB. The study was also supported by the Doctoral School of the UVMB as part of the doctoral thesis of ZB.
Supplementary material
Supplementary video 1. YouTube link: https://www.youtube.com/watch?v=4QlM34AFM7o. Video image of dog 3 during insertion of the needle and distribution of melarsomine within the lumbar musculature (see text for explanation). A 6 MHz convex abdominal transducer was used for this image to allow simultaneous needle insertion and video recording. The resolution of this transducer is lower, compared to the 18 MHz linear transducer applied for Figs 2–4.
Supplementary video 2. YouTube link https://www.youtube.com/watch?v=JSXVDwGX9Ns. Video image of dog 3 after five minutes of melarsomine injection into the lumbar musculature (see text for explanation). A 6 MHz convex abdominal transducer was used for this image to allow simultaneous needle insertion and video recording. The resolution of this transducer is lower, compared to the 18 MHz linear transducer applied for Figs 2–4.
Supplementary data to this article can be found online at https://doi.org/10.1556/004.2022.00034.
References
AHS Guidelines (2018): American Heartworm Society (AHS) 2018 guideline committee. In: Nelson, T. C., McCall, J. W., Jones, S. and Moorhead, A. (eds) Prevention, Diagnosis, and Management of Heartworm Infection in Dogs, 2018. www.heartwormsociety.orgveterinaryresourcesamerican-heartworm-society-guidelines. Accessed on 18/09/2018 at http://www.heartwormsociety.org.
AHS Guidelines (2020): American Heartworm Society (AHS) 2020 guideline committee. In: Nelson, T. C., McCall, J. W., Jones, S. and Moorhead, A. (eds) Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria Immitis) Infection in Dogs (Reviewed and Updated 11-13-20), 2020. Accessed on 08/05/2021 at http://www.heartwormsociety.org.
Alaman, M., Bonastre, C., de Blas, I., Gomez-Alvarez, C. M. and Laborda, A. (2022): Description of a novel ultrasound-guided approach for a dorsal quadratus lumborum block: a canine cadaver study. Vet. Anaesth. Analg. 49 ,118–125.
Bagi, F., Vörös, K. and Túri, Á. (2017): Preliminary experiences of the diagnosis and complex treatment of canine heartworm disease: 38 cases [in Hungarian, with English abstract]. Magy. Allatorvosok 139 ,203–213.
Becker, Zs., Holló, N., Farkas, R., Gyurkovszky, M., Reiczigel, J., Olaszy, K., Vári, Z. and Vörös, K. (2022): Serodiagnostic difficulties and possibilities of heartworm disease in regions where both Dirofilaria immitis and Dirofilaria repens infections occur. Acta Vet. Hung. 70 ,92–99.
ESCCAP Guidelines 05 (2012): Control of Vector-borne Diseases in Dogs and Cats. 2nd edition. https://www.esccap.org/uploads/docs/znkh6j1d_0775_ESCCAP_Guideline_GL5_v8_1p.pdfLast access: 09.15.2019.
Farkas, R., Gyurkovszky, M., Lukács, Z., Aladics, B. and Solymosi, N. (2014): Seroprevalence of some vector-borne infections of dogs in Hungary. Vector Borne Zoonotic Dis. 14 ,256–260.
Farkas, R., Mag, V., Gyurkovszky, M., Takács, N., Vörös, K. and Solymosi, N. (2020): The current situation of canine dirofilariosis in Hungary. Parasitol. Res. 119 ,129–135.
Freeman, L. M., Sutherland-Smith, J., Prantil, L. R., Sato, A. F., Rush, J. E. and Barton, B. A. (2017): Quantitative assessment of muscle in dogs using a vertebral epaxial muscle score. Can. J. Vet. Res. 81 ,255–260.
Freeman, L. M., Michel, K. E., Zanghi, B. M., Vester Boler, B. M. and Fages, J. (2019): Evaluation of the use of muscle condition score and ultrasonographic measurements for assessment of muscle mass in dogs. Am. J. Vet. Res. 80 ,595–600.
Fuehrer, H-P., Morelli, S., Unterköfler, M. S., Bajer, A., Bakran-Lebl, K., Dwużnik-Szarek, D., Farkas, R., Grandi, G., Heddergott, M., Jokelainen, P., Knific, T., Leschnik, M., Miterpáková, M., Modrý, D., Petersen, H. H., Srírnisson, K., Rataj, A. V., Schnyder, M. and Strube, C. (2021): Dirofilaria spp. and Angiostrongylus vasorum: current risk of spreading in Central and Northern Europe. Pathogens 10 ,1268.
Genchi, C., Mortarino, M., Rinaldi, L. Cringoli, G., Traldi, G. and Genchi, M. (2011): Changing climate and changing vector-borne disease distribution: the example of Dirofilaria in Europe. Vet. Parasitol. 176 ,295–299.
Hammond, R., Christie, M. and Nicholson, A. (2008): Opioid analgesics. In: Madison, J. E., Page, S. W. and Church, D. B. (eds) Small Animal Clinical Pharmacology. 2nd edition. Elsevier Ltd., Suite 1800, Philadelphia, USA. pp. 309–329.
Haro, P., Laredo, F., Gil, F., Belda, E., Ayala, M. D., Soler, M. and Agut, A. (2013): Ultrasound-guided dorsal approach for femoral nerve blockade in cats: an imaging study. J. Feline Med. Surg. 15 ,91–98.
Hettlich, B. F., Ryan, K., Bergman, R. L., Marks, S. L., Lewis, B. C., Bahr, A., Coates, J. R., Mansell, J. and Barton, C. L. (2003): Neurologic complications after melarsomine dihydrochloride treatment for Dirofilaria immitis in three dogs. J. Am. Vet. Assoc. 223 ,1456–1461.
Hides, J., Stanton, W., McMahon, S., Sims, K. and Richardson, C. (2008): Effect of stabilization training on multifidus muscle cross-sectional area among young elite cricketers with low back pain. J. Orthop. Sports Phys. Ther. 38 ,101–108.
Maxwell, E., Ryan, K., Reynolds, C. and Pariaut, R. (2014): Outcome of a heartworm treatment protocol in dogs presenting to Louisiana State University from 2008 to 2011: 50 cases. Vet. Parasitol. 206 ,71–77.
Moore, S. A., Mariani, C. L., Van Wettere, A. and Borst, L. B. (2013): Chronic compressive myelopathy and progressive neurologic signs associated with melarsomine dihydrochloride administration in a dog. J. Am. Anim. Hosp. Assoc. 49 ,389–393.
Morchón, R., Carretón, E., González-Miguel, J. and Mellado-Hernández, I. (2012): Heartworm disease (Dirofilaria immitis) and their vectors in Europe – new distribution trends. Review article. Front. Physiol. 3 ,196.
Page, S. W. (2008): Antiparasitic drugs. In: Madison, J. E., Page, S. W. and Church, D. B. (eds) Small Animal Clinical Pharmacology. 2nd edition. Elsevier Ltd., Suite 1800, Philadelphia, USA. pp. 198–260.
Stubbs, N. C., Riggs, C. M., Hodges, P. W., Jeffcott, L. B., Hodgson, D. R., Clayton, H. M. and McGowan, C. M. (2010): Osseous spinal pathology and epaxial muscle ultrasonography in Thoroughbred racehorses. Equine Vet. J. 42 ,654–661.
Vin Veterinary Drug Handbook (2021): https://www.vin.com/members/cms/project/defaultadv1.aspx?pid=13468accessed on 10/19/2021.
Vörös, K., Becker, Zs., Kónya, R., Arany-Tóth, A. and Farkas, R. (2022): Application of moxidectin and ultrasound-aided injection of melarsomine during the American Heartworm Society recommended treatment protocol in Dirofilaria immitis infected dogs. Vector Borne Zoonotic Dis. 22 ,382–390.
Webster, E. L., Hudson, P. E., and Channon, S. B. (2014): Comparative functional anatomy of the epaxial musculature of dogs (Canis familiaris) bred for sprinting vs. fighting. J. Anat. 225 ,317–327.