Parenteral drug products are the dosage forms intended for administration by a route that does not involve the gastrointestinal (GI) tract

Subcutaneous route of drug administration

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Subcutaneous route of drug administration

The SC route is used for small volume injections, typically 2 mL or less. Subcutaneous means under the skin. SC injections are administered beneath the surface of the skin, between the dermis and muscle. Medications administered by this route are slowly absorbed and consequently have a slower onset of action than medications given by IV or IM routes. Drugs often given by this route include epinephrine, insulin, heparin, scopolamine, and vaccines. Small injection volume often puts limitations on the drugs that can be administered by this route. For example, high dose drugs that tend to become highly viscous at high concentrations, such as most globular proteins, are usually difficult to formulate as subcutaneous injectable dosage forms.

Special forms of subcutaneous route

Novel modalities of subcutaneous drug delivery include dermojets, pellet implantation, device implantation

1. Dermojet: Dermojets are high-velocity jets of drug solution projected into the subcutaneous tissue, enabling virtually painless administration. This projection of the drug is done at a very high velocity and so the drug passes through the various layers and finally, gets deposited in the subcutaneous tissue. Since there are no needles involved, this technique is suitable for mass injections.

2. Implantation of pellets:The drug is incorporated in form of solid pellets and is placed under the skin for sustained release over a long period of time.

3. Nonbiodegradable and biodegradable implants: Here, the crystalline drug is incorporated in tubes or capsules and planted under the skin like the pellets. The nonbiodegradable ones have to be removed after some time but biodegradable implants don’t pose this problem. The examples of drugs administered via this route are- the oral contraceptive levonorgestrel incorporated in silastic capsules for longer duration of action, insulin incorporated in mechanical pumps, local anesthetics, and vaccines which are preferred by this route as the active protein moiety directly reaches the lymphoid tissues through the lymphatics without any interference from any other enzyme.


The location of injection is important for subcutaneous injections. The drug needs to be injected into the fatty tissue just below the skin. Some areas of the body have a more easily accessible layer of tissue, where a needle injected under the skin will not hit muscle, bone, or blood vessels.

The most common injection sites are:

  • Abdomen: at or under the level of the belly button, about two inches away from the navel
  • Arm: back or side of the upper arm
  • Thigh: front of the thigh

Equipment used for subcutaneous injections includes:

  1. Medication: Vials of liquid medication can be single-use or multiuse. Vials can also be filled with a powder to which liquid needs to be added.
  2. Syringes: The needles are short, at 5/8 inches long. The thickness of the needle is usually 25 or 27 gauge. There may be other options for doses more than 1 mL or for children or people with visual impairments.
  3. Auto-injector pen: Some medications are available in a “pen” with a short single-use needle screwed onto the end of a pen-shaped, multiuse vial. The amount of medication needed is then dialed in at the end. As mentioned earlier, emergency medications like epinephrine can also come in this form.

Advantages of subcutaneous route of drug administration

  1. It is a good route of administration especially in skin infections.
  2. It is relatively safer than intravenous and intramuscular routes.
  3. Absorption is slower thus, it is a good route if a prolonged effect is to be achieved.
  4. Self-administration is possible as the injection need not be penetrated deeply.
  5. Depot preparations for sustained action can be made.

Disadvantages of subcutaneous route of drug administration

  1. If the drug is irritating it might cause the sloughing off of the skin epitheral tissue.
  2. It is suitable only for nonirritant drugs.
  3. Drug absorption is slow; hence it is not suitable for emergency.
  4. Similar to the i.m. route, only small volumes can be administered.

Complications of subcutaneous injection

If you’ll be doing this type of injection for more than one dose or for multiple days, you’ll need to rotate the injection sites. This means that you shouldn’t inject medicine into the same spot twice in a row.

For example, if you injected medicine into your left thigh this morning, use your right thigh this afternoon. Using the same injection site over and over again can cause discomfort and even tissue damage.

As with any injection procedure, infection at the site of injection is a possibility. Signs of infection at the injection site include:

  • severe pain
  • redness
  • swelling
  • warmth or drainage

These symptoms should be reported to your physician immediately.

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