Understanding Pharmaceutical Dosage Forms
Oral Forms
Completely different drugs can have the same dosage form and be used in different parts of the body. For example, tablets can be for vaginal or sublingual use, or granules may be for topical or oral intake. It is very important to know the dosage form because it is the basis on which the drug is presented, and different designs of a particular pharmaceutical dictate: the route of administration, the correct administration, and when drug action occurs.
Oral Forms: Modified Release
This is one of the most important sections. Oral preparations are usually those that, in daily practice, are more subject to processes such as grinding, dissolution, administration via nasogastric tube (NGT), etc. Any of these procedures can alter the function of the drug or lead to side effects if the drug’s design is intended for release in a specific manner or place.
Systems for Rapid Dissolution or Dispersion
These dissolve immediately in the oral cavity, and the drug is immediately available for absorption. Some may have pre-gastric absorption. It is not necessary to take them with water. They are very useful when there are problems with swallowing, vomiting, etc. (e.g., Feldene®).
Slow-Release Systems
Drug release begins in the intestines; the medication passes through the stomach intact. These oral forms have an enteric coating. They resist the acid secretions of the stomach, finally disintegrating in the small intestine. They are used to protect drugs that are altered by gastric juices or to protect the gastric mucosa from irritants. These drugs usually start acting 2-4 hours after administration.
Continuous Release Systems
These have a much more complex design, and through different mechanisms (osmotic pumps, microporous membranes, pH-dependent systems, gels, etc.), they provide a uniform and constant release of the active ingredient over 8, 12, 24, or even 48 hours, achieving sustained therapeutic levels. This results in:
- A very simple regimen, such as taking a single tablet per day instead of one every 8 hours.
- Fewer side effects.
- Lower toxicity.
Forms for the Sublingual Route
These tend to be compressed tablets without a coating, or they may be in spray or liquid form. The active ingredient is usually not very soluble and is ionized, which are characteristics of drugs that easily cross biological barriers. An example is nitroglycerin (Cafinitrina®).
Forms for Rectal Administration
These are usually creams, gels, or suspensions that are not sterile. They can be systemically acting drugs that, due to their characteristics, either irritate the gastric mucosa or are destroyed by digestive enzymes. Drugs are often topical with local action, such as antihemorrhoidal ointments or suppositories like laxatives and local micro-enemas containing glycerine.
Forms for Injection: IM, IV, SC, Spinal (Epidural and Intrathecal), Intra-arterial
These are always prepared sterile.
- IV: Dosage forms are never emulsions or suspensions.
- IM: There are “depot” forms. These are sustained-release forms with prolonged action. They are very useful in psychiatric treatment because the patient receives one injection every 2-4 weeks.
- Intra-arterial: This route admits very few types of dosage forms and very few drugs, almost exclusively saline (NaCl 0.9%), heparin sodium, some cytostatic radiological contrasts, or some with local action.