Reasons To Take Drugs According To Prescribed Duration And Frequency

Medications are meant to diagnose, prevent, treat, manage, etc of disease. To achieve any of the above, the medication is to be taken as prescribed. The formula, strength, dosage, dosage frequency and duration depends on the severity of the disease, type of drug, age of the patient and so many other factors.

One thing many patients find hard to understand is why take a drug more than once. They believe that many drugs especially antibiotics stay in the body for a very long time or even for life hence achieve therapeutic effects. This wrong notion is preventing some from getting better with drugs. This is because they fail to adhere to their prescribed medication.

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Disease conditions are of two natures. Some are caused by living things while the others are caused by change in the body physiology. The drugs used to treat both work in different ways. Drugs that treat change in body physiology tend to correct it. Rarely will a dose achieve this. On the other hand, anti infective agents tends to render the infective agent powerless or better still kill it. This may require a dose or more.

To understand prescription of drugs, let us look at dosage strength and loading dose, maintenance dose, dosage frequency and dosage duration.

Dosage Strength And Loading Dose

So many factors determine the strength of a drug for a patient. They are age, weight, disease condition and severity of infection. We all know the correlation between age, weight and dosage strength. However, many patients find it hard to understand how and severity of infection and disease condition has to do with their dosage strength.

Dosage duration and frequency

To illustrate how severity of infection affect dosage strength, lets us use an illustration of Mike Tyson. It will be easy for Mike Tyson, the boxer to beat off two adult male. However, his physical strength and skills will not carry him when confronted with a crowd of let's say 20 adult men. It will require up to 5 Mike Tyson to achieve such a feat. We can use this illustration to explain dosage strength. A minor infection may require a lower strength while a stronger infection will require a higher strength.

Still using Mike Tyson illustration to explain loading dose, sending just two Mike Tyson to fight off 20 adult men will result in the men overpowering the Mike Tyson because they have number to their advantage. To prevent this, more Mike Tyson will be needed. So the first dose should be high. But this is not always the case. Using a high loading dose is only of advantage in certain disease condition. Low loading dose is needed in certain disease state especially when the drug has side effects that can be avoided with dose. And low loading dose is used in some cases to investigate the patient response to the drug before dose adjustment. The choice of the strength of loading dose is dependent on factors such as side effects, toxicity, severity of disease, type of disease and if it is an infection minimum inhibitory concentration (MIC).

Some drugs can be used to treat more than one disease condition. With the same mechanism of action but different target, the dosage strength and loading dose can either be increased or reduced to achieve therapeutic effects.

In theory, loading dose is to establish a steady state volume of distribution in plasma cell. The half life of the drug may take a while. The drug can stay in the body for days, weeks, months or even in some very few cases years. However, the level of the drug in the body keeps dropping by half after every half life.

Maintenance Dose

Still using the illustration of Mike Tyson, 5 Mike Tyson could beat up about 15 adult men out of the 20 before getting exhausted. The remaining 5 men should not be left to stand if not they will do some damage to the exhausted 5 Mike Tyson and others around. A second and subsequent dose may be required to combat the last adult men standing. Unleash at least a new Mike Tyson to fight them off. If the second Mike Tyson failed to eliminate all remaining five adult men, another Mike Tyson may be needed to finish off the last adult men off.

What if 20 Mike Tyson is unleashed to fight off all 20 adult men? This is a very good option but toxicity issues prevent such therapy.

But because some of these things happen in the human body, we cannot tell when the final adult men standing have been eliminated. Scientists only make use of laboratory results and signs to consider the effect of maintenance dose.

Some disease conditions can be taken care of in the system with just a loading dose. Example is anthelmintics, emetics and analgesic. For those that require maintenance dose, the subsequent doses will be selected to achieve a constant therapeutic plasma concentration. But how frequent should the Mike Tyson be sent to the battle field?

Dosage Frequency

The dosage frequency is how frequent a drug is to be taken. This is determined by the minimum and maximum amount of the drug in the body to produce a particular biological response. The strength of the drug is is selected to produce a peak plasma concentration or steady state within the limits of therapeutic range. For microbial, the range is the MIC. The calculation is done such that the minimum and maximum IC is within therapeutic range. That is the time it will take for the maximum plasma concentration to decrease to a point below which the desired response no longer occurs. When the minimum concentration of a drug is equal to half of the maximum concentration, the dosing interval is the half life of the drug.

The dosage frequency is based on the time the drug concentration in the body goes below the therapeutic range. That is when another dose is calculated to be taken.

Sustained release and it's equivalent are designed to release a predetermined concentration of the drug over a period of time into the body from a single dose. This keeps a steady state concentration. This can help reduce dosing frequency but that does not alter the pharmacokinetics or dynamic of the drug.

Dosing Duration

For how long a drug is to be given depends on the severity of the disease, efficacy of the drug and the half life of the drug. Some drugs can be used for days or months or years or even for life. This is because the drugs do not stay in the body forever. It may require a maintenance dose for it to effectively manage the disease. However, the infection can be treated with  just a dose as the causative organism can be eliminated with some single dose. In many other cases, the drug will need to be in the body for a long time. In such cases, each dose help reduce the effect of the disease state until a time will come whereby the disease would have been reduced to the nearest minimum or eliminated.

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Let's us use the Mike Tyson illustration one more last time to explain. If Mike Tyson is to fight a crowd of 20 adult men, he will need to do it gradually. If he can beat 5 at the start, that will reduce the number of adult men to 15. Before those beaten 5 will have time to get up again or regain strength, another Mike Tyson will be unleashed into the others. If the other was able to beat another 5, that will reduce the number of adult men to 10. The cycle will continue until the last adult male is defeated.

So when next you visit your pharmacist, please follow the prescription on how to use the drug. If you are not clear,ask for the dosage, frequency and duration.

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