Determining the right drug dose can be confusing. Based on several factors—including age, sex, weight and lifestyle—the dose you take for a particular drug will vary. Physicians take these factors into consideration when writing drug prescriptions (and there are instructions in the drug package), but it can be helpful to know some of these factors before beginning a medication regimen. It’s important to let your doctor know about any health changes, adverse drug reactions or other drugs you may be taking before a dose is determined.
What is a Dose?
A therapeutic dose is the specific amount of drug you take, measured in weight (grams), quantity (e.g. capsules or tablets) or volume (e.g. mL or drops). Sometimes a dose may be measured by the number of inhalations or sprays (e.g. for nasal sprays). Determining the amount, and the frequency with which you take a drug, is called a dosage regimen.
Determining a Dosage Regimen
A dosage regimen might be: 3.5 tablets, once per day (mornings), with food, for eight weeks. Other regimens might include injections, suppositories or liquid solutions. The optimal dosage regimen produces the best health outcomes with the least harmful side effects. A doctor will determine the best regimen by taking into account:
- Age – Drug dosing has a lot to do with metabolism, which tends to vary with age. Infants and young children require lower doses than adults, while the elderly may require more or less based on their overall health.
- Weight – Also related to metabolism, a patient’s weight determines the optimal dose. The less you weigh, the less you should probably take.
- Drug Form – Most drugs will go through an absorption process before circulating freely in the bloodstream. Oral drugs and injections to fat and muscle are absorbed to varying degrees, while intravenous injections enter the bloodstream directly.
- Other Drugs – Certain drugs interact or interfere with others. If you’re taking any other drugs, it’s very important to inform your doctor. Other diseases can also impair drug metabolism.
- Sex – Men typically need higher doses than women.
- Ethnicity – Studies have shown that African–Americans tend to require higher doses than Caucasians. Asians tend to require the lowest doses.
- Liver and Kidney Health – Drug metabolism and toxicity is handled by the liver; therefore, patients with impaired livers are particularly sensitive to drugs. Chronic Kidney Disease (CKD) also affects drug metabolism.
- Lifestyle – Smoking, alcoholism, obesity, diet and regularity of exercise affect drug dosage.
- Genetic Factors – Some people are born with sensitivities to certain drugs, such as Warfarin (a blood thinner). Be sure to get tested before taking these drugs.
- Environmental Factors – Studies have shown that drug metabolism can be affected by stress, occupational exposures, sunlight, pressure changes, pregnancy and changes in overall health.
What You Can Do
When taking a medication, it’s a good idea to keep an eye on how you’re feeling. Every drug has side effects, but you probably shouldn’t feel ill or incapacitated. Consult with your doctor on what to expect. She will monitor your health and, when necessary, change the dosage regimen to fit your individual needs.