Gregory A. Lewbart, MS, VMD, DACZM, DECZM (Zoo Health Management)
College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA
Invertebrate pharmacology with regard to veterinary medicine and health management is still in its early stages. Much of how veterinarians practice in this area is based on experience, anecdotal information, and clinical trials. Most of the pharmacokinetic data available pertains to just a few taxa (honeybees, horseshoe crabs, decapod crustaceans, and certain mollusks). These notes contain doses and references for this latter group and some other information based on information in the peer-reviewed literature and, in some cases, review articles and textbooks.
Invertebrate animals comprise over 95% of the animal kingdom’s species, yet nonparasitic invertebrates are vastly underrepresented in the typical veterinary school curriculum, and relatively little is known about therapeutic pharmacology for this immense number of species, who all have just one thing in common: they lack a vertebral column. In fact, many invertebrates are more closely related to some vertebrates than each other.
These notes and the accompanying lecture provide a brief introduction to some of the more prominent invertebrate groups (coelenterates, mollusks, crustaceans, spiders, horseshoe crabs, insects, and echinoderms) and review the state of the science with regard to chemotherapeutics and pharmacokinetics. This manuscript is by no means comprehensive; it is primarily meant to inform the interested clinician on the possibilities related to working with drugs and invertebrates, and the most current publications in this area.
This large phylum includes the comb jellies (ctenophores), hydrozoans (hydras, fire coral, Portuguese man o’ war), scyphozoans (jellyfishes), and anthozoans (stony corals, soft corals, sea anemones). This is an economically important group for research, environmental monitoring, public and private display, and tourism. Coral reefs collectively are one of the most beautiful, diverse, and fragile ecosystems on the planet. Jellyfish exhibits are now some of the most popular displays in public aquariums and upscale restaurants throughout the world.
Ampicillin. Used to control white band disease in Acropora at a dose of 100 mg/L every 12 hours for seven days.40
Chloramphenicol. Used as an immersion at 10–50 mg/L for several days with a 100% water change every 24 hours. This regimen is not based on a pharmacokinetics study; the values are taken from review articles and textbooks.10,38,39
Lugol’s iodine (5%). Used as an immersion for corals and anemones. It is an antiseptic that will cauterize wounds. It is a strong oxidizing agent, and some corals are sensitive, including Xenia sp., Anthelia spp., and Pachyclavularia spp. If corals appear stressed, then remove immediately.39
Paromomycin. Used to control white band disease in Acropora at a dose of 100 mg/L every 12 hours for six days.40
Tetracycline. Used for bacterial infections as a 10 mg/L immersion. No pharmacokinetics data, and positive results are anecdotal.30,39
Diflubenzuron. To control parasitic amphipods of the jellyfish, Chrysaora sp. The dose is 0.03 mg/L for seven days.17
Fresh water. A 1–3-minute dip is commonly used to treat for ectoparasites such as turbellarians (flatworms). Caution must be taken to make sure the fresh water is pH matched to the sea water. Corals (hard and soft) should be monitored closely, and when possible, biotest with one small or less valuable specimen first.39
Levamisole. Used as an immersion for helminths at 8 mg/L for 24 hours. This regimen is well tolerated by many species of stony corals.39
Milbemycin oxime. Used as a treatment for “red bug” on Acropora corals. Red bugs are actually the copepod Tegastes acroporanus. The dose is 0.167 µg/L of the otic solution (MilbeMite®) for six hours.15
The gastropods belong in the phylum Mollusca and include over 80,000 marine, freshwater, and terrestrial species. All gastropods have a ventrally flattened foot that provides locomotion along the various surfaces of their habitats. The group includes snails, slugs, sea hares, nudibranchs, slipper shells, conchs, whelks, and abalone, among many others. The use of gastropods as laboratory animals and in aquaculture is limited but does occur. They are important display and food animals. Investigators working on the sea hare, Aplysia, were awarded a Nobel Prize for medicine or physiology in 2000.
Clove oil (Eugenol). Used for apple snails at 0.35 g/L as an immersion.20
Ethanol (5%). Has been used as an immersion anesthetic for aquatic gastropods including abalone.26
Ethanol/methanol (10%). The trade name for this compound is Listerine®, and it has been used in cultured Lymnaea to effect.47
Magnesium chloride. Can be used as an immersion (normally 7.5%) in many aquatic gastropods. Queen conchs have been anesthetized with 30 g/L.1
Magnesium sulfate. Used in abalone at between 4 and 22 mg/L as an immersion.46
Sodium pentobarbital. Can be used at 1 ml/L for abalone to effect or 400 mg/L to effect. Note this is a controlled drug.5
There are about 650 species of cephalopods, a taxon that includes the octopuses, squids, cuttlefish, and the chambered nautilus. This is an important economic group in that they serve as a food source for humans and other animals, are popular display animals, and have been frequently employed in a variety of research projects. Their acute vision, manual dexterity, and intelligence make them fascinating animals to observe and study. Unfortunately, most species are short-lived in the wild and captivity.
Enrofloxacin. The dose is 5 mg/kg IV, 10 mg/kg PO, and 2.5 mg/L as a 5-hour immersion. Dosing interval has not been worked out, and these values are from the European squid.25
Ethanol. Has been used as an immersion anesthetic in many cephalopods at a variety of concentrations from 1.5–10%.24,27
Magnesium chloride. Used in European cuttlefish at 6.8 g/L25 and 32.5 g/L in octopus.24
This class of mollusks contains many common animals, including the clams, mussels, oysters, and scallops. This is an extremely economically important group, especially as a food source for humans. Many species are both captured and cultured for food worldwide. There are more than 10,000 recognized species, found in fresh water, estuarine and marine surface waters. Bivalves fill a critical niche within aquatic ecosystems, the majority functioning as living filters. They comprise a large portion of the shell fauna collected by amateur or professional conchologists on beaches and freshwater stream banks, and historically have played a significant role in the apparel industry as a source of buttons, or pearls, and as a frequent item on the shelves of novelty shops. Bivalves are popular in display aquariums (private and public aquaria) and as research animals.
Enrofloxacin. Used as a 5 mg/L immersion in Manila clams.14
Propylene phenoxetol. Use 1–3 ml/L of a 1% solution for oysters.32
The crustaceans are a highly successful class of the phylum Arthropoda. This group includes the well-known lobsters, crabs, crayfish, shrimp, barnacles, and hermit crabs. Numerous other taxa belong to this class, including isopods, amphipods, and brine shrimp. Economically, this is one of the most important groups of invertebrates. Its members are important for food, research, and as display animals.
Enrofloxacin. The dose is 10–20 mg/kg IM for Chinese mitten crabs.41
Oxolinic acid. Given intrasinus at a dose of 10 mg/kg for kuruma shrimp.42
Oxytetracycline. Given intrasinus at 25 mg/kg in kuruma shrimp,42 10 mg/kg intrasinus in tiger shrimp,43 and 50 mg/kg PO in both species.43 For gaffkemia (Aerococcus viridans) in American lobsters, use 2.2 mg/g of food.9
Sulfadimethoxine. For American lobsters, the dose is 42 mg/kg intrapericardial.8
Sulfamethoxazole trimethoprim. For bioencapsulation in brine shrimp. Use toe tread white shrimp by combining 20–40% trimethoprim sulfamethoxazole with a lipid emulsion (Selco, INVE Aquaculture) at a concentration of 1:5.13
Clove oil (Eugenol). Approximately 125 mg/L as an immersion.19
Ketamine. Can be used at 1 mg/kg IM for Australian giant crabs.19
Lidocaine. Given to shrimp IM at 0.4–1 mg/kg.11
Xylazine. For giant Australian crabs at a dose of 16–22 mg/kg IV.19
This is a huge group of animals (over 30,000 species) that belong to the class Arachnida. Less conspicuous arachnids include the mites, ticks, and scorpions. Numerous texts describe the biology, natural history, and husbandry of these fascinating creatures. Tarantulas (not true spiders) represent an important group of commonly kept arachnids that occasionally require medical care.
Alfaxalone. Given to tarantulas at a dose of 200 µg/kg intracardiac.23
Carbon dioxide. Normally used in an anesthetic chamber at 3–5%.26
Isoflurane. Normally used in an anesthetic chamber at 5% with 1 L/minute oxygen flow18,49 but can be used with a cotton ball with adequate protection/separation for the spider.6
Ketamine. Given intracardiac at 20 mg/kg along with 200 µg/kg alfaxalone.23
Morphine. Given intracardiac at 5 mg/kg along with 200 µg/kg alfaxalone.23
Sevoflurane. Normally used in an anesthetic chamber at 5% with 1 L/minute oxygen flow.50
Xylazine. Given intracardiac at 20 mg/kg along with 200 µg/kg alfaxalone.23
Limulus polyphemus, the American horseshoe crab, is actually not a crab at all but a member of the class Merostomata in the phylum Chelicerata. Horseshoe crabs are more closely related to arachnids than crustaceans. This is the only species that lives on the Western Atlantic coast, but there are other species of horseshoe crabs that occur in Asia. Limulus is a very important animal for biomedical research and is used as bait and fertilizer (controversial) as well as being an important display and touch tank animal in public aquaria. Investigators examining vision and the Limulus lateral eye were awarded the Nobel Prize for medicine or physiology in 1967.
Itraconazole. Given IV at a dose of 10 mg/kg.3
Oxytetracycline. The dose is 25–50 mg/kg IV.33
This is by far the largest group of invertebrates and possibly the most economically important. Insects are loved and despised worldwide and occupy nearly all niches except the marine environment. They are important as a human food source in parts of the world and both sustain and destroy agricultural crops, depending on the species of insect and plant. Much of the veterinary-pertinent literature focuses on the honeybee (Apis mellifera).
Oxytetracycline. For treatment of American and European foulbrood in honeybees at a dose of 200 mg/colony every 4–5 days for three treatments.46 Note, there is a lot of resistance now.2,21 Those treating honeybees need to recognize they are considered food animals in the United States, and proper Veterinary Feed Directive measures need to be followed.
Tylosin. For treatment of American foulbrood in honeybees at a dose of 200 mg/colony every 4–5 days for three treatments.35,46 Those treating honeybees need to recognize they are considered food animals in the United States, and proper Veterinary Feed Directive measures need to be followed.
Amitraz. For control of mites (acariasis) in honeybees.45,46 Use as directed but realize many factors are involved with a hive mite infestation.36
Formic acid. For control of mites (acariasis) in honeybees.45,46 Commercial packaging should be consulted prior to use.
Fumagillin. For control of nosemosis (a microsporidian parasite) in honeybees.45,46 Use as directed and consult packaging.7,22,29
Menthol. For control of mites (acariasis) in honeybees.45,46 Commercial packaging should be consulted prior to use.
Thymol. For control of mites (acariasis) in honeybees.12,46 Commercial packaging should be consulted prior to use.
This interesting and diverse group of animals includes the sea stars, brittle stars, sea cucumbers, sea urchins, sea biscuits, and crinoids (feather stars). Many are commonly displayed in aquaria and used in research. Humans do not consume most species, but the gonads of sea urchins and the tunic of sea cucumbers are popular fare in some countries and restaurants in the United States that serve sushi.
Enrofloxacin. For green sea urchins, 10 mg/kg ICe or 10 mg/L as a 6-hour immersion.34 For purple sea stars, 5 mg/kg ICe or 5 mg/L as a 6-hour immersion.37
Oxytetracycline. For chocolate chip sea stars, 10–15 mg/L immersion every 48–72 hours for 3–5 treatments.28
Tris EDTA and neomycin (Tricide-Neo®). For cushion sea stars with cutaneous ulcers, use 100 ml/L for 45 minutes every 24 hours for 7 days.28
Magnesium chloride. Use a 1:1 mixture of seawater and 7.5% MgCl2.28,31
Propylene phenoxetol. For sea cucumbers, use 2 ml/L to effect.44
Tricaine methanesulfonate (MS-222). For purple sea urchins, use 0.4–0.8 g/L immersion to effect.4
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