Need help from a REALLY REALLY GOOD chemist

[pengko]

Time released medicine (or called slow releasing (SR) medicine) is a
beneficial product for patients. The basic design of this type of medicine is
active ingridients coated with special soluble polymer. Let assume a polymer M
has zero order decomposed rate at 0.05 mg/s in blood. Please design a new time
released drug A for twice-a-day dosage.

Thanks b4.

 

[chemisttree]

You need to know the therapeutic dose, the absorption and the elimination rate to begin to answer this one. Also, time-released drugs are not usually taken intraveinously (decomposition rate in blood?).

 

[pengko]

You need to know the therapeutic dose, the absorption and the elimination rate to begin to answer this one. Also, time-released drugs are not usually taken intraveinously (decomposition rate in blood?).

im not quite sure myself. this question is given by my lecturer. you sure we need to know the therapeutic dose, the absorption and the elimination rate to begin answering this question?

 

[chemisttree]

Well you certainly need to get past the idea of a time release material that is in contact with blood! Encapsulating anything larger than a red blood cell will clog all of your capillary beds (lungs, kidneys, retina, etc...).
I know this because I've investigated this in animals.

"you sure we need to know the therapeutic dose, the absorption and the elimination rate to begin answering this question?"

Yes. The pharmokinetics of drug release must relate in a logical way to the pharmokinetics of the drug in the body.

Think of it this way... Assume that you are neglecting the diffusion effect of the drug through the solubilizing polymer (a MASSIVE assumption). At the instant the polymer encapsulant completely reveals the drug (to blood?) the body takes up the drug as a bolus (another MASSIVE assumption). This is, in effect, a time delay for administering the bolus. If many tiny time capsules with different thicknesses of polymer are employed, the drug is administered nearly continuously as each fraction of the total dose encapsulated in this time delay solubilizing polymer reveals its tiny load of drug. During all this time the drug is being metabolized and eliminated. If the rate at which the drug is being presented is less than the rate at which the drug is being degraded/eliminated, the drug will never achieve therapeutic levels.

Your lecturer is probably asking you to think about encapsulating several fractions of the drug in varying thicknesses designed to deliver a therapeutic dose, say, every 4 or 6 hours. The thickness of the polymer surrounding each fraction of the dose should be designed to deliver some dose at 4 and 6 hours. Most drugs are dosed at levels much higher than therapeutic levels so that the compound remains in the therapeutic range for a reasonable amount of time before it is eliminated or degraded in the body.

So, to accurately answer this question you need to know the therapeutic blood level and the rate at which the drug is eliminated. Tailor the release rate of the encapsulated micropills to deliver a therapeutic level of the drug over 12 hours.

 

[pengko]

oh my god chemistree. you ARE GOOD! really! thanks heaps for the explanation. will ask for further information from my lecturer about this. once again, thanks heaps!

 

[chemisttree]

Don't forget to ask about this information:

"Let assume a polymer M zero order decomposed rate at 0.05 mg/s in blood"

This sounds more like the rate of elimination of the drug itself than the rate at which the polymer solubilizes. Were it the polymer solubilization rate, it would have units of mg/s(area) where (area) would be in m^2, ft^2, in^2, cm^2, etc... It also fits with the information that this is the rate in blood.

 

[pengko]

It's an open question related to this question

Dear genius chemistree, my lecturer said that the question i asked you before is an open question related to this question:

Drug A is consumed corresponding to a first order rate law with a half life 3.5 hour in the human body. The effective concentration for drug A is between 0.3 ~ 1.2 mg/L and deadly concentration (maximum tolerance) is over 1.8 mg/L. If we simplify the problem by assuming drug A can be immediately and homogeneously distributed in the body
Question:
a. How are you going to give drug A prescription to an adult with 70 kg? (please assume that 50L is the fluid volume in a 70kg adult.)

b. When will the drug concentration reach a stead-state under your prescription?

From my observation, I can't really see the connection between this question with the question I asked you before.

Thanks heaps.

 

[pengko]

genius chemistree. where are you?

 

[chemisttree]

If the lecturer is now asking you to answer the new questions (a and b in post #7), you can go here for some help:

http://www.boomer.org/c/p1/index.html

 

[pengko]

no no chemistree. you got me wrong. the real question is still

Time released medicine (or called slow releasing (SR) medicine) is a
beneficial product for patients. The basic design of this type of medicine is
active ingridients coated with special soluble polymer. Let assume a polymer M
has zero order decomposed rate at 0.05 mg/s in blood. Please design a new time
released drug A for twice-a-day dosage.

The lecturer is only saying it is an open related question with the questions i said b4 (which has a and b questions)

 

[chemisttree]

OK. The rate of dissolution of the polymer shell is given by the zero order relation:

d[M]/dt = -kT + [Mo], where k = 0.05 mg/s and [Mo] is the initial weight of the special polymer coating.

For a twice daily dosing, there must be a therapeutic amount of the medication released immediately and an equal amount released 6 hours later (if it remains in the therapeutic range for 6 hours) or multiple fractions released throughout 12 hours to counteract the elimination rate of the drug. Since you were not given this information initially, assume that the drug can remain therapeutic for 6 hours and formulate a dosage containing a therapeutic amount of unprotected drug and a therapeutic amount that is encapsulated. It should release drug at T=0 and T=6 hours (express this in seconds). Find [Mo] that will completely dissolve in 6 hours using d[M]/dt = -kT + [Mo] and use this amount of special polymer to coat the fraction of the new formulation that will represent the time delayed dose.

 

[pengko]

Thanks heaps chemistree