Extensions

What can this model tell us?

It is possible to alter the dose amount and the frequency to dramatically change the concentration of penicillin in the blood stream. In most cases the therapeutic level--the lowest level where the drug actually does some good-- for penicillin is around 0.55mg/ml. For curing some infections where the resistance is higher the therapeutic level will be higher.

Try a dosage of 1000 mg, once a day. What happens?

The spread of the medicine over a prescribed time is very important. If you decided to take all your pills for the entire day at one time every day, it will result in huge peaks and troughs in the concentration of drug. The level at times can be so high it is dangerous (maybe toxic) and at other times there will be so little drug that it is not effective. Neither of these extremes is the best way to treat the infection.

Try a dosage of 100 mg eight times a day. How long is it between doses at this frequency? Is it convenient to take a drug this often?

This dosage puts the concentration exactly at the therapeutic level for almost all the time. Since that is the goal of the physician, this seems to be an ideal dosage. However, it is impractical to take your medicine every three hours. Therefore it is necessary to strike a balance between personal convienece and the positive effects of the medicine.

Try a dosage of 250 mg once a day. What happens? Try a dosage of 2000 mg once a day. What happens?

If you take a smaller dose, even if you take it for several more days, it is not effective. Since the therapeutic level is never reached, the drug is wasted. On the other hand, if you take a much greater dose for just a few days, you might reach a toxic concentration. Also, not all of the pathogen may be eliminated, even though it reached a therapeutic concentration.

Try taking a normal dosage for only a few days. What happens?

While it may seem that the concentration is sufficient to clear up the infection, it is necessary to continue taking the medication for the prescribed duration. Even though symptoms may disappear within a few days of the start of the prescription, if you do not finish the course, the pathogen may not be completely eliminated. If a pathogen is still present, even in small amounts, it can start to multiply again and cause a recurrence, which could be even more virulent or resistant than the original infection. The most sensitive pathogens will be eliminated early in the course of treament, so the pathogen which remains will be the strongest and most resistant to treatment. This cycle encourages the growth and spread of antibiotic resistant strains.