Lecture 6: solutions 1 Flashcards
What is the advantage of solutions?
- They are easily swallowed
- They are readily absorbed as its already dissolved in the molecular form
- Promotes rapid drug action so its useful in emergencies
- Solutions provide dose uniformity where the liquid solution can be measured accurately
- Easier to manufature compared to tablets
What are the disadvantages of solutions?
- Inherently unstable and the drug is prone to hydrolysis
- Many drugs are poorly soluble in water
- More prominent taste compared to a tablet
- Bulky for the patient to carry and more expensive to transport compared to solid dosage forms
- More prone to spillage or leakage
What is the minimum quality of water used for the preparation of official substances and other bulk pharmaceutical ingredients?
Drinking water
and that is only used in the early stages for cleaning pharmaceutical manufacturing equipment and product contact components
What are the two types of water used in preparation?
Bulk water and packaged water
When are non aqueous solvents used?
- When the drug is insufficiently soluble or stable in aqueous systems
- When the product is intended for specific properties such as sustained drug absorption.
Why are non aqueous solutions limited to intramuscular and topical routes?
Due to their unpalatability, toxicity, irritancy or immiscibility with physiological fluids.
How do you choose the appropriate pharmaceutical buffer?
- Ensure the pH range of the buffer is close to the required pH
- Ensure the buffer is stable in storage (its pH doesn’t change)
- Formulation compatibility because some ions are not suitable for biological pH control.
Why might pH of buffers change during storage?
- Glass containers (soda lime glass) are alkaline and can cause the pH to increase
- Acidity from CO2 from dissolved air
Which buffers are unsuitable for biological pH control and why?
- Phosphate and carbonate buffers
- They precipitate calcium ions by forming insoluble calcium phosphate or calcium carbonate
What is specific acid catalysis?
When an acid accelerates the hydrolysis of drugs in solution.
What is specific base catalysis?
When a base accelerates the hydrolysis of drugs in solution.
How do you obtain the pH-rate profile of a drug?
- Subject the drug in solution to various pH and obtain the rate constant (k obs) at each pH
- Construct the pH-rate profile by plotting log k obs against pH
What is the purpose of the pH rate profile?
To study the hydrolysis kinetics of a drug at various pH
How do you determine the pH of maximum stability from a pH-rate profile?
The pH of maximum stability is the lowest point(s) on the graph
Can there be a range of pH of maximum stability from a pH-rate profile?
Yes
either one point or multiple
What is rheology?
A term to describe the flow of liquids and the deformation of solids.
What is viscosity?
The expression of the resistance of a fluid to flow
What happens to the viscosity of a liquid when temperature is increased?
It decreases
In which cases is parenteral administration beneficial over oral?
- Unconscious patient
- Get around drug degradation in the GI tract
- Emergency use for life threatening conditions
- For drug accumulation at the site of action.
What are the key requirements of parenteral formulations?
- Free of microorganisms, pyrogens and particulate matter
- Must be aqueous for IV administration
- pH should be close to physiological pH
- Isotonic
- Multi dose products must contain preservatives
Which products (aqueous or non aqueous) are sterilized using steam sterilization?
Aqueous
What are the ways by which parenteral formulations are sterilized?
- Steam sterilization: using steam sterilizers or autoclaves to kill microorganisms by causing protein coagulation or degradation
- Dry heat sterilization: use hot air oven or tunnel to sterilize by causing oxidation of cell components
Which products (aqueous or non aqueous) are sterilized using dry heat sterilization?
Non - aqueous
What are colligative properties?
They are physical properties that depend primarily on the concentration of solute particles (molecules or ions) in the system
(when the solutions are dilute)
What are iso-osmotic fluids?
Solutions which display colligative properties similar to those of biological fluids
What are isotonic solutions?
Solutions which have similar colligative properties as biological fluids and have tissue compatibility (non-toxic to tissues)
What is Osmole?
The amount of substance that needs to be dissolved to give 1 mole of particles
What is the osmolarity of physiological fluids?
270-300 mOsmole/L
What is the NaCl equivalent (E) of a solute?
The amount of NaCl that will produce the same osmolarity as 1g of the solute.
