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This is super confusing, I'm sorry!

The homework:
You have to administer simultaneously two drugs which are each 90% protein bound when administered separately. Please use the law of mass action to calculate how do you have to change the administered doses to obtain the same free drug concentration as in the case when each drug is administered individually. Consider free protein and total drug-bound protein concentrations unchanged (10% and 90% respectively), when both drugs are administered.

Hint: in the law of mass action, replace receptor concentration with protein concentration and drug-receptor complex concentration with drug-protein complex concentration. Instead of concentrations, use percentages. When the 2 drugs are administered together, divide the total complexed protein in two, one half for each drug. Free drug concentration will increase by the same amount that its drug-protein complex decreases.

1. Write the law of mass action separately for each drug when administered individually, indicating the concentrations for each component in the binding equilibrium 0.33 pts
2. Write the law of mass action for each drug when administered together, again indicating concentrations for each component 0.33 pts
3. Indicate how will you change doses for each drug when administered together and by how much. 0.33 pts

Observation: this is an oversimplified example. Usually protein binding sites don’t saturate so fast.

The Law of Mass Action:
L = ligand
R= receptor
D= drug
K A,L= association constant of L-R complex
K D,L= dissociation constant of L-R complex

[L] + [R] <--> [L-R]
K D,L= [L][R]/ [L-R] = 1/K A,L

(A drug interferes with Ligand binding and L-R complex formation)

[D] + [R] <--> [D-R]
K D,D= [D][R]/ [D-R]

I have no idea what to solve for, but this is what I have.

[L] + [R] <--> [L-R]
[.1] + [.9] <--> [1]

K D,L= [L][R]/ [L-R] = 1/K A,L
K D,L= [.1][.9]/[1] = 1/K A,L
K D,L = .09/1 which = 1/ K A,L
so K D,L= .09K
A, L= 11.11

...and now I'm stuck

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  • Pharmacology -

    1. Discuss the two phases in the pharmaceutic phase?
    2. Identify and describe the four phases of the pharmacokinetic phase.
    3. What is the difference in absorption difference in lipid-soluble and water-soluble? How does this affect drug absorption?
    4. Describe the “first-pass” effect and its’ importance.
    5. Identify and discuss the factors that alter bioavailability.
    6. How does protein binding affect the availability of the drug?
    7. What is meant by half-life (t1/2)?
    8. What are some forms of excretion?
    9. How does Creatinine clearance effect excretion and drug dosing?
    10. Describe the differences between onset of action, peak action and duration of action.
    11. What is the difference between agonist and antagonists, non-selective and selective?
    12. Which is better, a high or low therapeutic range (window)and why?
    13. How do side effects, adverse reactions and toxic effects differ?
    14. Identify and discuss the "Five-Plus-Five Rights" of drug administration.
    15. Describe the common dosing times and when a drug should be administered.
    16. Describe the factors that modify drug response.
    17. What are the different forms for drug administration? Special considerations?
    18. Differentiate between the different injection techniques.
    19. Identify 3 client teaching points regarding medication administration.

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