As part of the PTCB exam, students are expected to have a thorough knowledge of dosage forms. We have already talked about solid dosage forms – such as tablets and capsules. Today, we review the most common liquid dosage forms.
We have all, at some point, used a liquid dosage form. Whether it is a cough medicine or gargling a solution to relieve symptoms affecting the back of the throat – liquid dosage forms are widespread and ubiquitous. As a pharmacy technician, you will be handling these medicines on a daily basis.
Among the many different liquid dosage forms, here are some of the most common:
If you have taken some PTCB practice tests in the past, you may have come across questions on liquid dosage forms. Furthermore, you can expect some questions on dosage forms to appear on the PTCB test.
With dosage forms, there is a lot to learn.
But here, we have covered the broad, essential knowledge that students are expected to know and the most common facts that get tested.
Advantages of liquid dosage forms include:
However, like any dosage form, liquid formulations are not without their disadvantages.
Liquid formulations are structured in the same way as most other medicines – namely, that there is a small amount of active ingredient (drug) dispersed throughout a larger medium. In the case of liquid formulations, active ingredient is dispersed throughout a vehicle.
Note – one of the most common kinds of PTCB exam question is to ask about excipients. This includes vehicles. It is important that students understand the definitions and differences between each kind of excipient!
This “vehicle” could be sugar-based – for example: this is the case with many liquid cough medicines. Children find it easier to ingest cough medicines because of flavoring agents that have been added. The sweetness of the vehicle also helps too. As we have learned, this is not the case with other dosage forms, such as solid or semisolid dosage forms.
There are two ways the drug interacts with the vehicle:
The risk with fine particles is that when the medicine is left stationary in a cupboard or fridge, the fine particles settle to the bottom – forming a kind of cake. That is why it is important to counsel patients to shake the bottle before use.
It re-disperses fine particles throughout the vehicle, allowing for more equal dosing.
Solutions contain solutes (dissolved medicines) within a solvent (liquid vehicle).
The dispersion of the solution is equal. This contrasts with a suspension where it is an unequal distribution of fine particles that are not dissolved.
With solutions, active ingredient is quickly absorbed – whether it be on the skin, through the gastrointestinal tract, or at another site of administration – including the rectal route.
Aqueous solutions have water as the solvent.
Thicker aqueous solutions include syrups – which are a mixture of sugar solution and drug.
There are two primary kinds of non-aqueous solution:
Elixirs are sweetened hydro-alcoholic solutions that taste good, are relatively stable, and which are easy to prepare. The concentration of alcohol is typically between 3 percent and 25 percent.
Tinctures have a much higher alcohol content than elixirs. For example: tincture of iodine. Alcohol levels are typically between 25 percent and 60 percent, though in some cases this is higher.
In the case of tincture of iodine, it has 50 percent alcohol content.
Some liquid solutions have insoluble matter dispersed throughout the vehicle.
As the word suggests, suspensions have particles of drug suspended within the vehicle. If the bottle is not shaken before use, the patient receives only a dose of the vehicle – and almost none of the active ingredient.
Drugs that readily dissolve in a vehicle are said to have a high solubility. Suspensions have a low solubility because the drug fails to completely dissolve in the vehicle. Instead, particles remain dispersed. Suspensions are available for oral, topical, and injectable use.
An example of an oral suspension is amoxicillin 125-500mg of drug per 5mL of dose (teaspoon) of medicine.
In the case of injectable suspensions (such as Kenalog-40), they allow for insoluble drugs to be administered to the body in subcutaneous or intramuscular (IM) form. Injectable suspensions are also used for the purposes of depot injections – where the drug is released over a prolonged period (example: Procaine Penicillin G).
Characteristics of the ideal suspension include:
Emulsions are mixtures that contain two kinds of liquid that do not usually mix. For example – oil and water do not mix. But, in an emulsion, it can be created in such a way as to keep the mixture together as much as possible. This is due to the presence of an excipient called an emulsifying agent.
Examples of emulsifying agents include:
The new 2020 syllabus released by PTCB mention dosage forms as a core subject to prepare for the exam.
Here, we have broadly covered the liquid dosage forms part of the syllabus. Of course, there are many other dosage forms to learn about – including solid dosage forms and semisolid dosage forms, amongst others.
Learning about these dosage forms is important.
Not only do these questions get asked on PTCB practice exams, but they also appear on the real thing. The more questions you practice, the better you can plug knowledge gaps and dominate topics on the day of your exam.
Furthermore, it adds to your future professional knowledge.
Pharmacy technicians handle many different dosage forms daily. It is important for technicians to understand the many key differences between these dosage forms and why one dosage form may be used rather than another form.
Check back to our PTCB Test Prep blog soon for more content to help you master the 2020 PTCB exam.