The intramuscular route requires that the active principle be appropriately formulated, then dissolved in an aqueous liquid or in an oily liquid.
Administration routes
- enteral
- Oral
- Sublingual
- Rectal
- parenteral
- Intravenous
- Intramuscular
- subcutaneous
- INHALATION
- TRANSCUTANEOUS
The dissolved active ingredient is injected into some muscle areas of our body, which are mainly the buttocks, the deltoids of the shoulder and the thigh muscles. Like all routes of administration, even the intramuscular one requires special precautions, such as the use of specialized personnel (even if the injection technique can be easily learned) and the use of specific equipment (aseptic syringes).
The rate of absorption of the active principle administered intramuscularly may depend on the type of spraying of the tissue (absorption in the deltoid is faster than that in the buttock), the type of vascularization, the amount of adipose tissue (the more adipose tissue is present and the more slowly the active principle is distributed), from the characteristics of the drug and the active principle, from the properties of the solution and from the use of the enzyme hyaluronidase. The latter, in fact, depolymerizes collagen, reducing its consistency and increasing the total area of contact.
Intramuscular injection does not involve the administration of large quantities of solution or suspension (max 5 ml.). The solutions that are injected can be at non-physiological pH or at physiological pH. If the pH of the solution is not physiological there will be a possible precipitation of the active ingredient, with consequent delay in reaching the site of action. Conversely, if the pH of the solution is physiological, the absorption of the active ingredient increases accordingly.
Intramuscular injectable solutions, in addition to being of the aqueous type, can also be of the oily type and in this case the absorption of the active principle is slowed down. This method is mainly used in RETARD formulations, precisely because they gradually release the active ingredient, thus also reducing the frequency of administration.
The advantages of the intramuscular route are:
- reliability;
- precision;
- quick action.
Absorption is rapid, more than in the subcutaneous route;
Drugs that are too irritating to the subcutaneous route may be administered intramuscularly;
Absorption can be made faster or slower; for example, it is generally quick for aqueous solutions. The oily solutions are instead absorbed more slowly than the aqueous ones (from a few hours to a few weeks) and the aqueous suspensions more slowly than the aqueous solutions.
The potential disadvantages of the intramuscular pathway are:
- ache;
- local tissue necrosis;
- vascular or nerve injury;
- bacterial contamination.
- it is more painful than the subcutaneous route;
- the rate of absorption of the same drug can vary greatly if the local blood flow is varied by local heating, massage or exercise;
- vasoconstriction with drugs cannot be used to slow absorption, as can be done in the subcutaneous way;
- it is not used during treatment with anticoagulants;
- in practice it can cause local muscle damage with increased levels of ck (creatine kinase) (interference with diagnostic tests).
