Measurements in Pharmacology

Introduction

Measurements in pharmacology are taken in a variety of ways. Each system used in pharmacology must be understandable and convertible for real world usage. The measurement and ultimate dosage of a prescription needs to correlate with the specific needs, characteristics, and diagnosed illnesses of each patient.

 

Effects of Drug Dosages and Actions

No two people respond exactly alike to medications. Even the same person may not respond to the same drug the same way if a different dose is administered or administered at a different time of day or via a different route. Besides its properties of absorption, distribution, metabolism, excretion, and interaction with other medications, a drug's action and effect on the body are influenced by the patient's age, weight, diet, gender, genetics, and chronic diseases. The bodies of the very young and the very old don't respond in exactly the same ways as "average" adults. Drugs distribute differently in bodies that are very lean or very high in fat content. The physician will take these variables into account when prescribing dosages. 

Let's examine some of the common variables that have an effect on the dosage of a medication.

1. Age. The very young may be more sensitive to medications because of immature body organs. On the other hand, older adults are more sensitive than younger adults because of decreased function of organs, especially the liver and kidneys.

Gender. Women may require a lower dose of some medications because of their smaller size and higher average body fat. Body fat serves as a reservoir for fat-soluble medications and can therefore slow the excretion of those drugs.

Mental attitude. Let's not overlook the power of positive thinking! Having a healthy attitude about a drug's potential action tends to have a synergistic effect. In fact, scientific studies have shown that sometimes a positive physical response can be all in the mind. Patients in experiments have reported feeling better after being given a placebo, a substance that looks like a medication but doesn't contain any active drug. On the other hand, pessimism can diminish the effectiveness of a drug.

2. Weight. For drug therapy to be effective, a certain concentration of the drug in the patient's body is needed for the desired therapeutic effects. Doses may need to be altered for patients who don't fall into the "normal" weight and age range. Patients who are heavier may require higher doses of medication compared to a patient with less body fat or mass.

Sometimes, dosages for medications are calculated on the basis of body surface area (BSA) . This method is often used for calculating chemotherapeutic drugs. The BSA accounts for the relationship of the patient's weight to height.

3. Diet. A healthy diet is always good to help promote health. Even a healthy diet can affect the potency, availability, metabolism, absorption, and therapeutic effect of medications. A poor diet or one that's high in fat may slow the metabolism of some drugs.

Chronic diseases. Chronic diseases affecting the renal system and hepatic system will affect the dosage required for a medication. The hepatic system works to metabolize the medications, and the renal system works to eliminate them from the body. If either of these systems is impaired, it will result in medication building up in the patient's system.

4. Children. A child's ability to absorb, metabolize, and excrete medications is very different from an adult's ability. Drug dosages for children are based on the child's body surface area (BSA) rather than age. Age isn't a reliable guide for dosing medications in infants and children. As a child grows, the dose needed will increase. Medications should be recalculated regularly to make sure the dose is in the therapeutic range.

 

Before we end this section on the variables that may effect medications, let's look at some of the terminology that has developed around medicine dosages.

Minimum dose is the smallest amount of a medication that would have any effect. In other words, any less wouldn't do any good.

Maximum dose is the largest amount of medication that can be given to an individual before it has a toxic effect. In other words, any more would be toxic.

Loading dose is an initial high dose to "load up" the bloodstream with the drug.

Maintenance dose is the amount of medication necessary to keep a steady drug level.

Lethal dose is the amount of medication that would cause death.

Usual dose is the customary dose for body weight.

 

Polypharmacy

Polypharmacy refers to the simultaneous use of a number of drugs to treat a single patient for one or more conditions. Polypharmacy is more likely to occur in older adults, who are more likely to be treated for multiple chronic disease processes.

However, it can occur in any patient who is taking many medications for multiple health conditions. This problem is increased when a patient also takes over-the-counter medications, vitamins, and herbal supplements.

Sometimes, polypharmacy is easy to spot when a patient is receiving more than one medication from a drug class or several different medications from different classes to treat the same condition.

Often, new medications are added to the patient's regimen to treat the side effects of another medication, thereby leading to the patient taking even more medication. This increases the likelihood of a negative outcome or effect, such as an adverse drug reaction or interaction.

 

Key Points

• The metric system is a system of decimal measurement based on meter (length), liter (volume), and gram (weight).
• The apothecary system is occasionally used for weighing and calculating drugs and is based on grain (weight) and minim (volume).
• The household measurement system uses basic tools of measurement that can be found around the house, such as droppers, teaspoons, cups, and so on.
• Healthcare professionals must often convert units of one measurement system into units of another measurement system, most commonly time and temperature.
• There are two commonly used standards for time, the 12-hour clock, which uses a.m. and p.m. designations, and the 24-hour clock, also known as military time.
• There are two temperature scales in use: Celsius (or centigrade) and Fahrenheit. On the Celsius scale, 0°C is the freezing point of water, and 100°C is the boiling point. On the Fahrenheit scale, 32°F is the freezing point of water, and 212°F is the boiling point.
• There are many variables to be taken into account when prescribing doses, including age, weight, and mental attitude, among others.
• Polypharmacy refers to the simultaneous use of a number of drugs to treat a single patient for one or more conditions. It also increases the likelihood of a negative outcome or effect such as an adverse drug reaction or interaction.