Prescription Writing and Pharmacokinetics Overview Flashcards Preview

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Flashcards in Prescription Writing and Pharmacokinetics Overview Deck (18):

Under what classification is Vicodin scheduled?

Vicodin is a schedule 2 drug, as such it must be prescribed by an in-person visit with the physician, not over the phone.


What is special about schedule 5 drugs?

Schedule 5 drugs are frequently OTC, however different states may regulate them differently. Sudafed is available "behind the counter" in Colorado, without a prescription but with ID and in controlled amounts. In OR, it requires a prescription.


What are some current requirements for prescribing controlled drugs?

Any prescription for controlled substance requires a DEA number (physician registers with DEA). Schedule 1 drugs may not be prescribed. All schedule 2-4 drugs require a prescription (CO includes schedule 5). Schedule 2 must be in ink in physicians hand writing, cannot be phoned in, cannot be refilled. Schedule 3-5 can be phoned in, may be refilled up to 5 times in 6 months.


Two top characteristics of prescription fraud.

1) Handwriting is too legible 2) Directions are written in full, no abbreviations.


How many milligrams are in a grain?

64.8 mg per grain


How many grams are in an ounce?

28.35 grams per ounce


How many milliliters are in a teaspoon? In a tablespoon?

5 ml per tsp, 15 ml per tbsp


How many milliliters are in a fluid ounce?

29.56 ml in a fluid ounce


What is a simplified definition of pharmacokinetics?

The change in plasma concentration (Cp) over time.


What does needing to know the actual plasma concentration of a drug in a patient imply about the drug?

It implies that the drug has a narrow therapeutic window.


What is the relationship between the dose of a drug and the resultant Cp?

Cp = (Dose [mg])/(Vd [L]) where Vd (Volume of distribution) is the dilution factor (Assuming that the bioavailability F is 100%)


What is the relationship between the steady state Cp and the maintenance dose?

MD/tau = Cpss x CL where MD is the maintenance dose in mg and tau is the time in hours, thus (mg/hr); Cpss is the steady state concentration in mg/L and CL is the clearance rate in L/hr. Thus Cpss [mg/L] = (MD/tau)/CL {mg/hr/L/hr} (Assuming that the bioavailability F is 100%, and that the system is at steady state, rate in = rate out)


How is bioavailability calculated?

Bioavailability F = (AUC oral)/(AUC iv) It is the ratio of the amount of drug that gets into the blood stream to the total amount of drug (AUC iv is essentially 100% in the blood stream).


Why is rate of absorption of a drug less important than other factors?

If it is an emergency, the drug may be given via IV, and thus its rate of absorption is irrelevant. If it is a long term drug that will be taken for many years, then there is no real rush to get Cp into the therapeutic window and the rate is again irrelevant.


What is the Volume of Distribution, Vd?

Vd is an abstract concept best thought of as a dilution factor. Just as each drug will have its own F, it will also have its own Vd as a characteristic of the drug.


What is the difference between metabolism and excretion of a drug?

Metabolism eliminates drug activity, excretion eliminates the drug itself. Both equally diminish its effectiveness.


What is the implication of drugs that go through cells and in what locations in the body do they need this ability?

There are a few locations in the body where drugs must go through cells and cannot go around them.   The gut, the brain, and the placenta all require transport through cells.   Thus, if a drug can move through the gut into the body, it can also cross into the brain or ino the placenta and exert effects in those locations.   This property may also allow drugs to pass back out of the urine filtrate back into the blood stream.


What is a major tactic in drug metabolism that concerns a drug's ability to cross through cells?

If a drug can be metabolised in such a way that it cannot pass through cells, then it can be eliminated through the urine because it cannot cross back into the blood stream at that point.