Administration of medicine by injection is often referred to as giving drugs by the parenteral route. The other main means of administering treatment is via the mouth and digestive system – the oral route. Effective administration of medicine is a key part of most veterinary treatments and many medications are most effective when given by injection. Administration of medicine by injection is also essential for some drugs that are destroyed by acids in the stomach, e.g. insulin.
Injections can be given into:
muscle (intramuscular injection)
tissue under the skin (subcutaneous injection)
veins (intravenous injection)
skin (intradermal injection)
body cavities, i.e. the abdominal cavity (known as intraperitoneal injection) or thoracic cavity (known as intrapleural injection)
bone (intraosseous injection).
Abbreviations are often used for injection routes, e.g. IM for intramuscular; SC or SQ for subcutaneous, and so on. This factsheet will only consider the intramuscular and subcutaneous routes as these are the techniques most likely to be encountered by cat owners.
Clean techniques should always be used when administering injections. If the coat is very dirty it should be clipped and cleaned. Skin should be swabbed with alcohol. Never administer an injection through dirty or infected skin.
Different formulations of injection are used for the different routes and it is particularly important not to administer an injection directly into the blood unless it is specifically recommended for this route.
Subcutaneous ('under the skin') injection
This is the route used for administration of most injections and vaccinations/boosters. Domestic animals have plenty of loose skin so it is very simple to lift a flap of skin and insert a needle into the subcutaneous tissue. There are very few important (or easily damaged) structures under the skin so this is a safe route of medicine administration; it is also usually quite painless.
Owners can easily be taught to give injections in this way, e.g. owners of diabetic animals are taught how to administer insulin subcutaneously so that they can give regular injections to their pet at home. This route is not suitable for administration of irritant medications as they may cause severe skin reaction and damage.
Intramuscular ('into muscle') injection
Drugs given into muscles are absorbed very quickly because there is a good blood supply to muscle tissue. Injection into muscle is not without some risk since there are many important structures e.g. arteries, veins and nerves running through the muscle tissue. It is important to check that the needle has not accidentally been placed in a blood vessel (particularly an artery) in the muscle, before giving the injection.
Once the needle has been inserted into the muscle, gentle suction should be applied to the syringe to ensure that blood does not flow back into the needle. If blood does flow back, a different injection site should be chosen. This technique can also be used for subcutaneous injections, though penetration of a blood vessel is far less likely to occur here.
Appropriate sites for intramuscular injection are:
the quadriceps (muscle on the front of the thigh)
lumbodorsal muscles (muscles either side of the lumbar spine)
the triceps muscle (behind the humerus (arm bone) in the front leg).
The hamstrings (muscles at the back of the thigh) should generally be avoided due to the possibility of damage to the important sciatic nerve that runs in this area. Volumes of injection should not be more than 2 ml in cats.
Intramuscular injections are more painful than subcutaneous ones. Good technique minimizes this but even so, many animals will react to the injection. A positive action for insertion of needles into muscles reduces muscle damage and pain and massaging the site after injection disperses the injection and may help to reduce pain. Use of a fine needle minimizes discomfort. Owners are not often called upon to give intramuscular injections but they may be asked to hold their pet while it receives one.
Some drugs are specially formulated so that they are more slowly absorbed and can sit in the muscle, being absorbed gradually over many months and producing a long-acting effect (so called ‘depot injections’).
Other injection routes
The other injection routes mentioned above are mainly used in hospitalized animals and are given by those professionally trained to do so. These routes may be used for specific purposes – often because a very fast reaction to the drug being administered is sought, as in intravenous injections of anaesthetics. Shaved or clipped areas on the cat’s leg usually show where an intravenous injection has been given.
The lining of the respiratory tract is thin and vascular and absorption of some drugs from this site can be very rapid. Intranasal vaccines, e.g. for kennel cough in dogs, are given into the nose and the live virus is able to penetrate the lining of the nose. Nebulised drugs can be used for the treatment of respiratory disease and administration by this route allows rapid penetration to the local site where they are to have their action. However, the use of nebulised drugs means that the patient must breathe air containing the drug. Nebulised drugs can be delivered via a face mask although many conscious patients will not tolerate a face mask, so a special nebulisation chamber is often required.
In cardiac arrest, adrenaline is sometimes administered through the endotracheal tube and absorption via this route is rapid and the technique is much safer than the alternative, intracardiac adrenaline injection.
What happens if I 'miss' with an injection?
This may happen when you are learning to give injections, especially when using the very fine ultra-sharp needles used for insulin administration. It is easy to penetrate two layers of skin so that the drug ends up on the coat instead of under the skin. If you are absolutely sure the cat received no drug, it is safe to repeat the injection. If some may have been received, the safest course of action is to give no more. Contact your vet for advice.
What do I do with used needles?
After use it is very important that needles have their protective caps securely replaced to prevent someone becoming injured. The used needles and syringes should then be carefully stored in a sealed container or ‘sharps’ box and returned to the veterinary practice for safe disposal.
Should I wear gloves when injecting?
Wearing disposable gloves is a useful measure for giving injections. Your veterinary practice may be able to order large boxes of these for you, which is more economical than buying from a pharmacy, etc. Some owners prefer not to wear gloves as they feel it is more awkward.
I accidentally pricked myself while giving my pet an injection. What should I do?
First cap the needle and syringe carefully and put it out of harm’s way. Then thoroughly wash your finger with soap and water for 5 minutes, preferably using a soft nail brush on the affected area. Dry the skin and apply a bandage. You should contact both your veterinarian and your doctor for advice. Note that any lasting harm is very unlikely indeed.