Antibiotic formulations Flashcards
3 reasons for many formulations
Clinical need
Patient type
Drug molecule characteristics
Clinical need
Location of drug action
Rapid onset of action
Patient type
e.g. children cannot swallow solid dosage forms (tablets)
+ unconcious patients can’t take some dosage forms (intravenously is the best option)
Drug molecule characteristics
Poorly soluble / sparingly soluble drugs
Chemical instability
Poor bioavailability after oral delivery
Manufacturing issues
% of the human body made up of water
60% - blood is water based
What characteristics should drugs be to be transported within aqueous fluids?
Hydrophobic because they can partition across lipid membrane + bind with receptors in pockets
What is the Noyes-Whitney equation?
dm/dt = DA(Cs - C)/H
It explains the rate of dissolution of a solid drug is controlled
What does D mean in the NW equation?
Diffusion coefficient
What does A mean in the NW equation?
Surface area of drug particle
What does Cs mean in the NW equation?
Saturated drug concentration
What does C mean in the NW equation?
Bulk drug concentration
What does H mean in the NW equation?
Boundary thickness
What are the formulation factors on rate of dissolution?
Effect of
- Drug particle size
- Stirring
- Drug solubility
- Fluid volume surrounding drug particle
Most drugs are either…
Weak acid or base
If weak acid is protonated…
Uncharged
Which state of weak acid has lower solubility?
Unionised HA has lower solubility than ionised A-
Solubility of unionised HA form in water
Insoluble
Henderson - Hasselbach equation for weak acid
pka = pH + log HA / A-
always unionised form over ionised
If weak base is protonated BH+…
Charged
Henderson - Hasselbach equation for weak base
pka = pH + log BH+/ B
What do disperse systems have?
2 phases
not a single liquid, solid or gas
how are disperse systems beneficial?
Offer pharmacist lots of formulations
- Suspensions
- Emulsions
- Aerosols
- Foams
- Creams
- Ointments
- Liposomes
Disadvantage of disperse systems
Complex + unstable
