Liquid dosage forms
This group includes aqueous, hydroalcoholic, alcoholic, and oily solutions, as well as mixtures and suspensions. The main advantage of solutions is rapid and complete absorption, since the active substance is already in a dissolved state, bypassing the disintegration stage (characteristic of tablets).
The rate of absorption from suspensions depends on the degree of dispersion. The smaller the particle size of the active substance, the faster the effect develops. Surfactants 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 substance to enter the bloodstream:
- Disintegration — the breakdown of the tablet into small particles due to special disintegrating excipients.
- Dissolution — the transition of the substance into solution within the intestinal contents.
- Diffusion — the 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 medium of the intestine. To accelerate absorption, manufacturers use micronization (reducing particle size to increase the contact area), increase the total number of particles, or use water-soluble salts of the active substance. The absorption kinetics (including the time to reach maximum concentration) also depend on the degree of hydration, tableting technology, and filler composition.
Modified release
To maintain a stable plasma concentration of the drug and avoid sharp fluctuations, extended-release dosage forms (formae prolongatae) are created.
They allow for a significant reduction in dosing frequency. For example, while a conventional nifedipine preparation must be taken 3 times a day, its extended-release form requires administration only 1–2 times daily.
Protection from the aggressive GI environment
In the gastrointestinal tract, drugs are exposed to destructive chemical factors. Hydrochloric acid (Acidum hydrochloricum) in the stomach inactivates acid-labile drugs (e.g., benzylpenicillin), while proteolytic enzymes degrade polypeptide-natured substances (insulin).
To solve this problem, enteric-coated forms are used—tablets or capsules with an acid-resistant coating. They serve two purposes:
- Protect the active drug substance from degradation in the acidic environment of the stomach.
- Protect the gastric mucosa from the direct irritating effect of the drug.
Such forms dissolve 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 irritating effect, it is pre-mixed with mucilages (mucilagines), which coat and protect the mucous membrane.
Briefly: answers to topical questions
What types of liquid dosage forms are used in medical practice?
Liquid dosage forms include solutions, suspensions, emulsions, mixtures, infusions and decoctions, tinctures, extracts, новогаленовы препараты [novogalenicals], mucilages and syrups, eye drops, and aerosols. Solutions can be aqueous, hydroalcoholic, oily, and alcoholic; solutions for injection also exist.
Which groups of medicinal substances are destroyed in the stomach and require enteric coatings?
In the stomach, acid-labile substances and polypeptide-structure preparations are destroyed under the influence of an aggressive chemical environment. Enteric-coated dosage forms are used to protect them.
- Acid-labile substances — destroyed by hydrochloric acid (Acidum hydrochloricum). This group includes natural penicillins for parenteral administration (e.g., benzylpenicillin).
- Polypeptide-structure substances — destroyed by digestive proteolytic enzymes. An example of such a substance is insulin.
Enteric-coated forms pass through the stomach unchanged and disintegrate only in the small intestine (intestinum tenue), which protects the active substance from degradation.
What types of solid dosage forms exist besides tablets and capsules?
In addition to tablets and capsules, solid dosage forms include powders, dragees, granules, pills, medicinal teas, spansules, lozenges, pastilles, suppositories, lyophilizates, and implants.
Class and exam questions
Why do solutions work faster than tablets?
In solutions, the substance is already dissolved. A tablet, however, must undergo disintegration (breakdown into particles) and dissolution in the intestine before absorption begins.
How does particle size affect absorption?
Reducing particle size (micronization) increases their total contact area with the intestinal mucosa, which significantly accelerates diffusion and absorption.
Why are extended-release drugs needed?
They provide a delayed, controlled release of the substance, maintaining its stable concentration in the blood and allowing the patient to take the medication less frequently.
What is the purpose of enteric coatings?
The acid-resistant coating prevents the tablet from dissolving in the stomach. This protects the drug from destruction by hydrochloric acid and the gastric mucosa from the irritating effect of the drug. Release occurs in the small intestine.
What else to study on this topic
- Excipients: fillers, disintegrants, and surfactants
- Calculation of the absorption rate constant
- Physicochemical properties of the substance (hydration, micronization)
- Mucilages (mucilagines) in the formulation of therapeutic enemas
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