Liquid Dosage Forms
This group includes aqueous, hydroalcoholic, alcoholic, and oily solutions, as well as mixtures and suspensions. The main advantage of solutions is extremely rapid and complete absorption, since the active substance is already in dissolved form, bypassing the disintegration step required for tablets.
Absorption rate from suspensions depends on the degree of dispersion. The smaller the active substance particle size, the faster the effect develops. Surfactants (surface-active agents) may be added to further increase dispersion and improve absorption.
For example, the concentration of acetylsalicylic acid (Acidum acetylsalicylicum) in the blood half an hour after taking a solution is twice as high as after taking a conventional tablet.
Solid Dosage Forms
Oral administration (per os) of tablets (tabulettae) or capsules (capsulae) involves a multi-step process for the drug to enter the bloodstream:
- Disintegration — breakdown of the tablet into smaller particles due to special disintegrating excipients.
- Dissolution — transition of the substance into solution within the intestinal contents.
- Diffusion — movement of the dissolved drug toward the mucous membrane for subsequent absorption.
The rate-limiting factor here is the rate of molecular diffusion in the aqueous environment of the intestine. To accelerate absorption, manufacturers use micronization (reducing particle size to increase contact area), increase the total number of particles, or use water-soluble salts of the active substance. Absorption kinetics (including the time to reach maximum concentration) also depend on the degree of hydration, tableting technology, and excipient composition.
Modified Release
To maintain a stable plasma concentration of the drug and avoid sharp fluctuations, extended-release dosage forms (formae prolongatae) are utilized.
They significantly reduce administration frequency. For example, while a standard nifedipine preparation must be taken 3 times a day, its extended-release form requires administration only 1–2 times daily.
Protection from the Harsh GI Environment
In the gastrointestinal tract, medications are exposed to destructive chemical factors. Hydrochloric acid (Acidum hydrochloricum) in the stomach inactivates acid-labile drugs (e.g., benzylpenicillin), while proteolytic enzymes break down polypeptide substances (such as insulin).
To solve this problem, enteric-coated forms are used—tablets or capsules with an acid-resistant coating. They serve two functions:
- Protect the drug substance itself from degradation in the acidic environment of the stomach.
- Protect the gastric mucosa from the direct irritating effect of the drug.
Such forms disintegrate and release the active substance only after passing into the small intestine (intestinum tenue).
Rectal Administration
Forms for rectal administration include suppositories (suppositoria) and therapeutic enemas (clysmata). The average volume of a therapeutic enema is about 50 mL. If the administered substance has an irritant effect, it is pre-mixed with mucilages (mucilagines), which envelop and protect the mucous membrane.