Medication Administration Routes and Techniques: Oral, Injectable, Eye, Ear and More

Introduction

A route of administration is the way a drug enters the body: by mouth, by injection, on the skin, into the eye or ear, into the rectum or into the airways. Technicians give most of the treatments in a hospital and teach owners how to give medications at home, so route technique is daily work. The wrong route, the wrong site or the wrong volume can make a drug fail, cause pain or injure a nerve.

The VTNE content outline lists "Administer medications via the appropriate routes (including but not limited to topical, intravenous, subcutaneous)" as Domain 5 Task G, and "Routes of administration of pharmacological, chemical, and biological agents" as Knowledge Statement 9.¹ This guide covers oral, injectable, eye, ear, skin, rectal and inhaled routes, safe sites and volumes, and the five rights check that comes before every dose.

Key facts

How the VTNE tests this

• Choose the route or site that is safe for a given drug, species and volume (Domain 5 Task G; K9).¹
• Identify the nerve or structure put at risk by a poor injection site, such as the sciatic nerve in the caudal thigh.
• Order a set of eye medications correctly and state the waiting time between them.
• Calculate a dose volume, or a maximum SC fluid volume for one site.
• Pick the correct client instruction for home medication, such as following a feline doxycycline tablet with water.

Core concepts

Enteral, parenteral and topical

Enteral routes use the gut, mostly the oral route (PO, per os). Merck defines a parenteral route as any route other than oral, with topical forms treated separately. The four main parenteral routes are intravenous (IV), intramuscular (IM), subcutaneous (SC) and intra-articular (IA).⁴ Onset after an IV dose is seconds; after IM, SC and IA injections it is minutes.⁴

Why the site and volume matter

Muscle is tightly packed and cannot expand to hold a large volume without trauma, so IM doses are small. Many IM products are poorly soluble depot drugs, and some are mildly irritating.² Injecting an irritating drug into muscle, or hitting a nerve, can cause paresis, paralysis and muscle necrosis.⁶ In contrast, dogs and cats have abundant loose tissue under the skin that accepts large volumes.²

Not every injectable is safe under the skin. Always confirm that a product is approved for the SC route; abscesses and tissue necrosis can follow the wrong product.² SC absorption depends on hydration and circulation, so the SC route is not recommended for a patient in hypovolemic shock.²

Topical, transdermal and inhaled routes

Topical drugs act on the skin, eye or ear. Transdermal products cross the skin to act on the whole body. Transdermal gels such as methimazole are applied to the inner surface of the pinna, which makes dosing easy in cats.⁴ Merck lists methimazole for feline hyperthyroidism as PO or transdermal.¹² Inhaled drugs reach the airways at high concentration with smaller doses and fewer systemic effects than oral or injected drugs; delivery is by nebulizer or metered-dose inhaler (MDI).⁴

Procedure or technique

Before every dose: the five rights

1. Right patient: check the cage card, the name and the record.
2. Right medication: read the label and compare it with the order.
3. Right dose: recheck the calculation and the concentration on the vial.
4. Right route: match the order (PO, SC, IM, IV) to the product label.
5. Right time: give the dose on schedule, then record it.¹¹

Oral tablets and capsules

1. Dogs: try hiding the pill in a small portion of food first, after offering one or two unbaited portions.²
2. If food will not work, put the thumb through the gap behind the canine tooth and touch the hard palate to open the mouth. Press down on the lower incisors with the hand holding the pill.²
3. Place the pill on the back of the tongue, close the mouth and watch for a nose lick, which suggests a swallow.²
4. Cats: tilt the head up slightly, open the mouth by pressing down on the mandible, and drop the pill as far back on the tongue as possible. A pilling syringe may help, but it can injure the hard palate if the cat struggles.²
5. For doxycycline in cats, follow the pill with about 5 mL of fluid.⁹

Oral liquids

Pull the lip commissure out to make a cheek pouch. Keep the head level so the liquid does not run into the larynx, and put the dose into the pouch so it flows between the teeth.²

Subcutaneous injection

1. Choose the skin over the dorsum from the shoulders to the lumbar area. The dorsal neck is used less because the skin is more sensitive and patients may jump.²
2. For small volumes under 2 mL, such as vaccines, use a 22 to 25 gauge needle.²
3. Lift a fold of skin, insert the needle into the base of the fold and inject. Then pinch the site for a few seconds so the drug does not leak back onto the skin.²
4. For SC fluids use isotonic fluid only, a 16 to 22 gauge needle, and warm the fluid. Check for back-leakage after removing the needle.²

Intramuscular injection

1. Keep the volume small. Never inject into the neck muscles.²
2. Use the lumbodorsal (epaxial) muscles beside the spinous processes unless the animal is very thin. The quadriceps on the front of the thigh is another site; in cats it has been recommended over the caudal thigh.²⁵
3. Insert at a slight angle in a thin animal and perpendicular in an obese one.²
4. Pull back on the plunger before injecting. This checks that a vein was not entered by mistake. It matters most with oil or microcrystalline suspensions and potent drugs.²

Intradermal injection

Intradermal injections are used mainly for skin testing. Clip with a No. 40 blade and do not scrub, because scrubbing inflames the skin and spoils the test. Insert a 25 to 27 gauge needle bevel up and inject a 0.05 to 0.10 mL bleb, which should look translucent. A common error is going too deep, into the subcutaneous tissue.²

Eye medications

1. Put drops on the inner canthus without touching the eye with the bottle tip. More than 2 drops just washes out of the conjunctival sac.²
2. Apply ointment as a 1/8 inch strip on the upper sclera or lower lid margin so blinking spreads a film over the cornea.²
3. With more than one product, wait 5 minutes between them, and give solutions and suspensions before gels and ointments. Ointment last, because thick products block absorption of anything given after them.³

Ear, rectal and inhaled routes

Otic (ear) products: powders are generally contraindicated in the ear canal. A few drops of solution or a thin film of ointment is enough; then massage the ear gently to spread it down the canal.²

Rectal: some emergency drugs can be given per rectum when no vein is available. Merck lists diazepam at 1 to 2 mg/kg per rectum for emergency seizure control, against 0.5 mg/kg IV, so the rectal dose is higher.¹⁰

Inhaled: in cats, albuterol (salbutamol) from an MDI is given through a spacer device. The spacer attaches to a face mask for a conscious cat, or to the endotracheal tube in an anesthetized cat.⁸

Sources: Ford and Mazzaferro (Kirk and Bistner's Handbook); Merck Veterinary Manual; Dell'Apa et al. 2024.²³⁴⁵⁹

Source: Turner et al. 2011, J Am Assoc Lab Anim Sci, Table 1. These are research guidelines and may be lower than clinical practice volumes; the SC fluid volume for cats in Table 1 comes from a clinical source.⁶

Flowchart

Species differences

• Dogs: pills can often be hidden in food. Large dogs can take more than 200 mL of SC fluid in one location.²
• Cats: pilling needs care, because even cooperative cats bite, and forcing pills is not a technique to expect of inexperienced owners. Liquid or compounded forms may suit home care better.² Follow doxycycline tablets with fluid.⁹ In a 48-patient study of sciatic nerve injury, IM injection caused 2 of the 10 cat cases and none of the dog cases.⁵
• Cat vaccine sites: AAHA/AAFP 2020 does not recommend vaccinating in the interscapular space. Distal limb injection is recommended so that an injection-site sarcoma could be removed by amputation with 5 cm margins; the distal tail is another option.⁷
• Rabbits: a common SC site is the scruff, and IM injections go into the lumbar epaxial muscles or quadriceps, only in large rabbits and only with a small volume.¹³
• Large animals: IM injection is common in large animals but is often avoided in small species because of their small muscle mass.⁶

Calculation

Safety, legal and client education

• Teach the owner with a demonstration, then let them do the technique in the hospital. This improves compliance.²
• Do not expect clients to force tablets into a cat; the risk of a bite is real. Ask the veterinarian about liquid or mixed-in options.²
• Tell cat owners to follow each doxycycline tablet with food or about 5 mL of water.⁹
• Record every dose: drug, dose, route, time and who gave it. The five rights are a core administration safety step.¹¹
• Transdermal gels are absorbed through skin. Apply to the inner pinna as directed.⁴

Common mistakes and exam traps

Quick review

1. Five rights: medication, dose, time, route, patient.
2. IV onset is seconds; IM and SC onset is minutes.
3. SC is the most common parenteral route in dogs and cats.
4. Cats take about 10 to 20 mL/kg SC fluid per site.
5. IM volumes are small; never IM in the neck.
6. Lumbodorsal muscles or quadriceps for IM; caudal thigh risks the sciatic nerve.
7. Aspirate before every non-IV injection.
8. Intradermal bleb: 0.05 to 0.10 mL, 25 to 27 gauge needle, no scrub.
9. Eye: drops before ointment, 5 minutes apart, never touch the eye with the tip.
10. Ear: no powders; massage after instilling.
11. Doxycycline pills in cats: follow with about 5 mL of fluid.
12. Cat MDI: use a spacer and face mask.