Have you ever noticed how some medicines get absorbed into your body faster than the others? It happens because of the higher bioavailability of those drugs. Bioavailability acts as a bridge between the chemical substance and our internal system. Pharmaceutical companies take several factors into consideration to create medicine with higher bioavailability.
Some of the factors that play into bioavailability during drug development are:
Route of Intake
The first factor affecting bioavailability is how we are going to apply the drug. For instance, an intravenous injection usually has a 100% bioavailability. With IV, we can place the drug directly into our circulatory system. But the formulation for a drug absorbed through the gastrointestinal tract will be drastically different. The drug development will then have to take into consideration the size and rate of dissolution. The rate of absorption will be different again for topical drugs. None of these drugs will achieve bioequivalence.
Intended effect
The bioavailability of a drug will also depend on its intended effect. We design most drugs to be absorbed into the body as fast as possible. However, there are still plenty of controlled-release forms used for drugs with short elimination half-life and a shorter duration of effect. Lowering the bioavailability of drugs ensures more uniform delivery of the substances. This process also minimizes its adverse effects.
Dosage Form
The form in which we develop the drug plays a role in determining its bioavailability. For instance, the same drug taken orally shows 2 to 5 fold differences in their bioavailability and bioequivalence depending on dosage forms (e.g. – tablets, solutions, capsules, etc.). By a general rule of thumb, solutions have the highest bioavailability. Coated tablets have the lowest bioavailability. The same idea applies to topical drugs. Creams get absorbed much faster than ointments.
Manufacturing Factors
Several manufacturing factors are responsible for varying bioavailability of drugs. For instance, in the case of manufacturing oral tablets, the factors are:
- Method of Granulation- In general, wet-granulation makes the tablets dissolve faster. This helps in the absorption by our body. But the wet granulation method also has some disadvantages, one of them being the chemical degradation of the drug. A more recent procedure that has been gaining traction in the pharmaceutical community is the APOC. This method grinds the drug until spontaneous agglomeration occurs. The granules of such tablets have a larger surface area helping our body absorb them faster.
- Compression Force- A higher compression force decreases the wettability of the tablet. This inhibits its dissolution time. One the other hand, it crushes the particles into smaller forms. Smaller particles effectively increase the surface area of interaction. This enhances water penetration, and thus its rate of absorption. The compression force is a nuanced calculation that we need to take into consideration.
Physicochemical Composition
The physical and chemical nature of the drugs and its excipients also determine its bioavailability. For instance, we cannot use intravenous solutions that have the highest bioavailability, for drugs with low aqueous solubility. Chemically unstable drugs will need extra coatings to prevent them from premature dissolution. This decreases its bioavailability. The pH balance of the drug’s composition and its intended area of application also determines the bioavailability of drugs.
We take all these factors into careful consideration while developing a drug. Pharmaceutical companies achieve optimum bioequivalence only when all these complications are perfectly balanced.