Lec 21- calculations Flashcards
A reservoir system
- A reservoir progesterone implant of simple circular slab geometry is to be designed using silicone rubber. The required drug release rate is 0.5ug h-1 and the drug reservoir will consist of 0.5cm3 aqueous suspension
- Circular slab, diameter= 1cm (edge effects may be ignored)
- Drug loading in the reservoir= 2mg cm-3
- Maximum aqueous solubility of progesterone= 11ug cm-3
- D.K = 8x10-7 cm2S-1
- Use the following date to calc
- i) Whethre the device contains sufficient drug to maintain the required constant release rate for 28 days
- ii) the thickness of the silicone rubber required
Answer for part i)
Answer for part ii)
An osmotic device
A push-pull osmotic device of active area 5 cm2 uses sodium chloride as the osmotic agent. The osmotic pressure exerted by this solute is 356 atmospheres while the semipermeable membrane, of thickness 150 μm, has a water permeability coefficient of 1 x 10-6 cm2/h atm.
If the drug to be delivered has an aqueous solubility of 0.8 g cm-3 estimate the amount of drug delivered during a four-hour period.
Another osmotic device
An elementary osmotic device is being designed to deliver potassium chloride for electrolyte replacement therapy. The salt is held within a semi-permeable polymeric membrane, volume 0.5 cm3, which is 150 μm thick and which has a total surface area of 5 cm2. The water permeability coefficient for the polymer is 1 x 10-6 cm2 h-1 atm-1. A saturated solution of potassium chloride contains 31.2 g of salt in 100 cm3 of solution and this exerts an osmotic pressure of 245 atmospheres.
Calculate the rate of delivery of KCl from this device and estimate the amount of KCl needed to provide continuous delivery of the salt for a period of 12 hours
- Drug required = sum of drug released + saturated solution in the reservoir
- Amount to be delivered= 12 x 0.02548 = 0.306g
- Amount to saturate device= 0.312 x 0.5 = 0.156g
- Total required= 0.306 + 0.156 = 0.462g
