Injection techniques

Administration of medicine by injection is often referred to as giving by the parenteral route (this means that the treatment does not enter the body via the digestive system). Effective administration of medicine is a key part of most veterinary treatments and many medications are most effective when given by injection or may only be available by this route. Administration of medicine by injection is essential for some drugs that are destroyed by acids in the stomach.

Injections can be given into:

• Muscle (intramuscular).
• Tissue under the skin (subcutaneous).
• Circulation (intravenous).
• Skin (intradermal).
• Body cavities (abdominal, ie intraperitoneal or thoracic, ie intrapleural).
• Intraosseous (into the bone marrow cavity).

Your veterinarian will have the experience to be able to offer a variety of injection techniques for your guinea pigs, but this factsheet will only consider the subcutaneous (SC) route as this is the technique most likely to be encountered by guinea pig owners. For other techniques your guinea pig would be admitted into the veterinary practice for treatment.

The area used for administering the injection should be as clean as possible. If the coat is very dirty, it should be clipped and cleaned. An injection should never be given through dirty or infected skin as bacteria will be pushed into the deeper layers of the skin/bloodstream by the needle, causing potentially serious infections.

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.

This is the route used for administration of most injections. Guinea pigs have a fat pad around and over the top of their back, behind their head which runs about half way down their back. Injecting into this area can be painful for the guinea pig, so it is important to try to avoid this area and inject further down their back, into the loose skin. There are few important (or easily damaged) structures under the skin, so this is a very safe route of medicine administration. This route is unsuitable for administration of irritant medications as they may cause skin necrosis and sloughing.

• Make sure your pet is gently but securely held, ensuring that it cannot run away from you or turn around whilst you are trying to inject into the scruff. You may need someone to help you, especially when first attempting this technique. It is better to sit on the floor, so the guinea pig cannot accidently fall and injure themselves if they do panic.
• Gently lift the loose skin with your second finger and thumb of one hand and with the first finger gently push the skin downwards to help form a triangle and also the insertion point for the needle. With the other hand securely hold the syringe and needle making sure that if the guinea pig moves then the syringe is not dropped (do not have your finger over the plunger of the syringe in case of accidental injection).
• The needle should be inserted at a 45° angle towards the base of the lifted skin being careful not to inject your finger and thumb holding the scruff. If the needle is inserted in the skin at too steep an angle then there is a likelihood of intramuscular injection, or worse accidently hitting the spinal column.
• Insert the needle with one gentle positive movement – try to avoid hesitating as this can lead to the guinea pig resenting the injections. It is not uncommon for guinea pigs to squeak when injections are given, but it is best to get the injection done as efficiently as possible, as it is important your guinea pig receives their medication. Once inserted, the plunger of the syringe should be gently pulled back to ensure correct placement before giving the medication. If air enters the syringe then the needle is most likely not in the subcutaneous layer but through the skin and out the other side. The needle and syringe should then be retracted a small amount and the plunger retracted again. If blood enters the syringe remove the syringe and needle from the skin and start the process again. If pressure is felt when the plunger is pulled back you should be in the subcutaneous layer and injecting of the medication can begin. When finished remove the needle and syringe and gently rub the area.

Your veterinarian will dispense the most appropriate size needles and syringes. The size (gauge) needle will depend upon the medication being injected. Some medications are thick so need a larger gauge needle to ensure the medication can be injected without forcible pressure having to be applied. The size syringe will depend upon the amount of the medication being given. It is imperative to ensure you draw up the correct dose each time and change the needle before injecting, so it is new and has not been blunted when the medication was draw up through the bung. Always use a new syringe and needle for each injection.

Always take used syringe and needles back to your veterinarian to dispose of. Your veterinarian should supply you with a sharps container so you can place the used needles in there. Do not recap needles – this is a needle stick risk. Your veterinarian should show you how to draw medication up, how to change the needle and how to dispose of needles and syringes after use.

If given correctly, serious SC injection problems are rare, although not unheard of. Some common problems may include:

• The medication coming out of the skin – this happens if the needle has gone in and out of the skin. You should stop the injection, change the needle and reinject the medication.
• Soreness around the injection site – try and vary where you inject slightly each time, to minimize this from happening. If you are concerned, then contact your veterinarian.
• The needle and syringe separating when injecting and medication coming out of the syringe – this is often because the syringe and needle are not attached properly. You should remove the needle from the guinea pig, dispose of it in the sharps bin and use a new needle to inject the mediation, ensuring it is attached properly.

If you have any problems or concerns you should speak to your veterinarian. It may be that they will demonstrate again how to inject or the medication needs changing.