Session #2004

There are a lot of similarities between small animals and reptiles. That said, there are also differences, but these differences can make a difference between treatment success and failure when not heeded.

The fundamental principle to be followed when treating reptiles is to make sure that they are at their preferred optimal temperature when administering treatments. The preferred optimal temperature zone (POTZ) for numerous reptile species can easily be found in the literature or online at a number of sites.

When a reptile is at its POTZ, the response to medications can be predicted—as they tend to respond like a mammal when properly warmed. When their core body temperatures are too low, there is no way to anticipate how their ill bodies will handle the medication.

It is the rare reptile patient (exceptions are severe traumas) that cannot wait 12–24 hours to be properly warmed up and prepared for diagnostics and therapeutics.

Administering Medications

Before administering any treatment to an ill reptile, you should always take the patient’s core body temperature. This is done in a fashion similar to the procedure in mammals. Caution should be taken when inserting the thermometer in the vent, as there is a blind pocket in the cranial portion of the cloaca (the corprodeum). This is easily, accidentally, penetrated when using a pointed or sharp plastic thermometer. Soft, flexible, electronic thermometers are the best to use.

Oral Route (PO)

There is an old adage in small animal medicine that “if the mouth works, use it.” I believe that this is true in reptiles as well. Of course, you have to remember the caveat—they have to be properly warmed.

There has always been a belief that you should not use oral medications in herps. It has been shown that oral medications work fine in the properly prepared patient. Even if the patient is aggressive, has facial injuries, or just can’t be manipulated, it is still possible to place an esophagostomy tube which is commonly done in chelonians, and occasionally lizards and crocodilians. Snakes are generally easy to tube and E-tubes are rarely warranted.

This author prefers to send home reptile patients on oral medications rather than injectable drugs. When the owner is properly prepared, and the patient is properly maintained, oral medications are an effective and safe way to prescribe home therapy.

Subcutaneous (SC)

Reptiles don’t have the voluminous SC space that is seen in mammals. More importantly, the SC space is not well vascularized in herps, making administration of medications in this location less efficiently absorbed.

Snakes have a SC lateral sinus that runs along the entire side of the animal. It is readily found between the epaxial muscles and the top of the ribs. When entered with a needle, the fluid medication (chemotherapeutics or fluids) readily runs along this space down the side of the patient. By utilizing this space, you minimize the obvious stretching of the skin seen with SC injections and, theoretically, decrease any potential pain associated with the administration of larger volumes of fluids.

In squamates, there is generally an obvious lateral skin fold extending from just cranial to the thigh to the axilla. In most lizards, there is minimal SC space between the scapula, a site commonly used in mammals, and it is not recommended.

In chelonians, if it is possible to access the axillary or prefemoral regions, there is ample SC space for administering fluids or injections. Some chelonians will withdraw into their shell making access difficult. It may be possible to administer SC by using long needles inserted between the limb and the shell, but this is not recommended as there is no way to adequately prep the skin before the injection.

Crocodilians can be administered SQ fluids along their lateral body wall similar to lizards.

Hyaluronidase (an enzyme derived from bovine testicular tissue) administration has been advocated for enhancing SC fluid absorption in various species, including reptiles. Hyaluronidase lyses hyaluronic acid, which is part of the ground substance that binds the interstitium. In humans, it has been used for facilitating fluid and drug absorption from the subcutaneous space and reducing pain during chronic fluid administration. However, studies performed in cancer patients found no comparable difference between the duration of fluid at the administration site or the presence of pain in patients who received hyaluronidase during chronic subcutaneous fluid administration to those who did not. No studies have been performed to advocate its use for fluid replacement in the reptile.

Finally, regarding SC administration of medications in herps, some drugs are irritating or have extreme pH values and have been shown to cause scarring and depigmentation to the skin post treatment. Clients should be warned of this possibility.

Intracoelomic (ICe)

ICe fluid administration is commonly performed in reptile patients. Again, if the patient is properly warmed, this route can be effective, especially for larger amounts of fluid.

Caution should be taken to avoid damaging internal structures when inserting the needle. Gently placing the patient in dorsal recumbency, with the head angled slightly down, allows the viscera to slide forward with gravity, providing a small target just ventrocranial to the thighs. If the needle is directed parallel to the body wall and aimed slightly ventrally, it is less likely that organs, or lungs and air sacs, may be entered.

Always aspirate before administering—if blood, air, or any fluid is withdrawn, remove the needle, and start fresh with a new syringe of medication.

Intramuscular (IM)

Before a discussion of IM injection locations is covered, it is necessary to have a brief discussion on the reptilian renal portal system (RPS) and hepatic portal system (HPS).

Many of the drugs, especially the antibiotics, that are used in reptile patients are eliminated via the kidneys. Historically, authors have stated that drugs should not be administered in the caudal half of a reptile’s body in order to avoid the RPS. Thoughts have concentrated on the fact that either the drugs would suffer a first pass effect (and subsequently be rendered ineffective) or enter the kidneys in such high concentrations that renal toxicity might be a concern (especially with drugs such as the aminoglycosides).

Studies on the RPS in Chelonia (Holz, Lewbart) have demonstrated a difference in the plasma concentrations of certain drugs when administered either in the forelimb or the hindlimb musculature. In one study, there was a significant difference between the two injection sites for the drug cephazolin, a drug known to be cleared by tubular secretion, but not gentamicin, a drug that is cleared by glomerular filtration.

In regards to the significant decrease in blood levels for the former drug, the author speculated that there was, in fact, no clinical significance since, although the levels had dropped, they were still above the MIC necessary for successful therapy.

The conclusion here was that drugs eliminated via tubular secretion may be affected by the RPS, owing to the fact that the blood returning from the caudal limbs and the tail appears to course through the kidneys prior to returning to the systemic circulation. Drugs cleared from the body by glomerular filtration were not affected, apparently, because the blood bypasses that anatomical location.

In reality, that is a gross oversimplification. Blood may change flow in and around the RPS dependent on many different factors. Body temperature and hydration status are the main two determinants. In addition, there are 10,000+ species of reptiles, and hundreds of medications that have yet to be studied. The work done so far is an important first step in understanding the black box of therapeutics in reptilian patients, but caution must be taken when making generalizations. If necessary, it would be best to err on the conservative side, and if any doubt exists regarding the best administration site for a given medication, the cranial half of the patient’s body should be chosen.

Medications that are conjugated and eliminated via the liver should also be administered via the front legs to avoid a first pass effect (the HPS). Studies looking at sedatives administered via the rear legs have shown diminished effect when compared to giving the same dose of the drug in the front legs.

Remember, when giving medications by the IM route, the patient must be properly warmed prior to administration. IM sites are limited in snakes to the epaxial muscles along either side of the spine. In some emaciated, or very small animals, this can be challenging, and the injections are often SC rather than IM.

In lizards, IM sites include the epaxial muscles, as in snakes, the quadriceps, and triceps. I try to avoid the caudal thigh so as not to accidentally traumatize the sciatic nerve. I have seen animals develop paresthesias in the rear feet secondary to ketamine and enrofloxacin administration in the biceps femoris group.

Although theoretically, IM injections can be administered into the large tail muscles in the larger lizards, I generally don’t use this site. I had one case in a water dragon where calcium gluconate was given into the tail, and within a week, the tail sloughed off distally to the injection site.

Several medications can be irritating or even caustic. For example, enrofloxacin (United States product) has a pH of 11. It is only labelled for a single IM injection. When given IM, it can cause severe muscle necrosis and sloughing of the skin.

IM injections in crocodilians are similar to those given in lizards.

In chelonians, again, the limiting factor is access to the limbs. If possible, for the appropriate medications, this author prefers the quadriceps or pectoral muscles. The large pectoral muscles, just under the front legs and dorsal to the plastron, are an excellent place for IM injections. There is generally a large muscle mass present and minimal critical structures present that may cause potential injection site complications.

Intravenous (IV)

The IV route is preferred in life-threatening conditions. Hypothermia and dehydration will not interfere with systemic absorption when drugs are given IV. That said, remember that whenever possible, the patient should be properly warmed, or at least in the process of being warmed, when IV therapy is started.

IV administration is possible in snakes but is limited. Intracardiac administration is possible in emergency situations—caution should be taken not to administer medications that could be caustic to the myocardium. In addition, IV administration can be performed into the ventral coccygeal tail vein or the jugular vein. If a continuous IV is needed or if repeat IV administration is warranted, placing a jugular catheter is advised and not difficult.

The dorsal palatal vein is readily visible in snakes, and theoretically, can be used for IV access. But, extreme caution should be taken as this vein tends to bleed excessively and, especially in a conscious patient, can be difficult to establish adequate hemostasis. I do not recommend using this vein unless the animal is under general anesthesia.

In lizards, IV medications can be given in the ventral coccygeal vein or the jugular veins. It is possible to utilize the brachial veins or the femoral veins in larger animals, but they are surrounded by nerves and lymphatic channels, making placement difficult if not risky.

Again, if repeat IV access is needed, placing an IV catheter is recommended. The jugular veins or the cephalic vein in larger lizards are the preferred sites.

This author adamantly recommends against using the ventral abdominal vein due to the risk of accidentally penetrating abdominal viscera, thus resulting in iatrogenic coelomitis.

Intraosseous (IO)

Administering medications via the IO route is generally limited to fluid therapy via an IO catheter. Caution should be taken not to administer any medication IO that may be caustic to the bone marrow.

IO catheters are generally placed into either the proximal tibia, through the crest, or directed distally into the tibia. Alternately, some clinicians prefer to enter the femur since it is a larger bone, entering the femur just proximal to the stifle and directing the needle proximally toward the hip. I caution against this technique, especially in species with a patella.

Finally, IO placement generally requires general anesthesia as it is painful, and if not properly prepped and maintained, can result in permanent damage to the bone (osteomyelitis) and joint if it is accidentally penetrated during placement. I recommend attempting IV placement prior to IO access.