With a drug allergy, the body’s immune (defence) system reacts to a medication. In this type of ADR, the immune system sees the drug as a challenge that needs to be removed. Skin rash is a mild sign of this reaction, and can range from a rash like the measles to hives. Moderate signs include fever, swollen and aching joints, and swollen lymph nodes. Severe reactions include the swelling of vital organs, such as kidneys. There can even be anaphylaxis, a reaction that closes off breathing.
Certain drugs often cause allergic reactions, including:
If you have an allergic reaction to a drug, even a mild one, get advice from your health care provider. If your skin reacts mildly, the doctor may switch you to another medication. An antihistamine might also provide relief. If the reaction is moderate or severe, stop taking the medication immediately! Get medical advice as soon as possible.
An anaphylactic drug reaction is life threatening and requires immediate attention. Signs include:
If you think you are experiencing anaphylaxis, have someone drive you to the hospital immediately or call 911 for an ambulance.
A side effect is any undesirable effect caused by a medication’s normal action. When you buy a medication, you usually receive an information leaflet. This lists all possible side effects that can occur when taking that drug. The information comes from drug studies done both before and after a drug is available. When a side effect occurs in more than one per cent of those using a particular medication, it is linked to the medication.
The information in the leaflet may be a bit overwhelming. Some side effects listed may be severe or even life threatening. Keep in mind that this is just a complete list, and that certain effects are very rare.
On the other hand, you may experience a side effect that is not listed. Health Canada’s website has a place to report any effects not listed in the drug information leaflet. These reports may then be added to the safety information about a medication.
Some side effects are related to the dose (amount) of medication taken. They may be reduced or even eliminated by taking a lower dose. To have your dose changed, always consult your health care provider.
Other side effects are temporary as you start a new medication. They may improve or even disappear as your body adjusts. Beginning with a lower dose can sometimes prevent such side effects. Gradually increase the amount taken until you are at the recommended dose.
If you’re thinking of using another medication to manage a common side effect, talk with your health care provider first. You must be sure that the drug will not interact with any medications you use or make your medical conditions or allergies worse.
Table 1: Suggested ways to manage side effects
|Area affected||Side effect||Suggested non-drug remedies|
|Central nervous system||Sedation or dizziness||
|Gastrointestinal||Nausea and vomiting||
|Skin||Photosensitivity (light sensitive)||
|* Unless this might cause a drug-food interaction|
Contact your health care provider immediately if any drug side effect worries you. If a side effect is bothering you and does not go away, switching to a different medication may be best. Side effects that require immediate medical attention include:
With drug-food interactions, the food you eat affects the way your body takes in or gets rid of a drug. This in turn affects how much drug is available to your body.
Some medications are broken down by various liver enzymes. Other medications are eliminated from the body through the kidneys as urine. Foods can affect liver enzymes, in turn affecting how quickly or slowly a drug leaves the body. The longer a medication stays in your body, the greater the effect. As well, the longer it remains, the greater the risk you will react badly to it. Certain foods compete with medications to be eliminated through the kidneys. This increases the time that a drug is in the body.
Some foods affect how the stomach or intestines absorb medication. The process of eating prompts the release of acids to digest food. Some drugs absorb better when the stomach is less acidic. High fibre meals speed up the time stomach contents take to pass through the body. Less time in transit means less time for a drug to be absorbed. Certain vitamins in a food may also bind to a drug, stopping it from working.
Separating the time when you eat, or have an offending food, by at least two hours may prevent drug-food interaction. For instance, the antibiotic Cipro™ reacts to calcium. If you take Cipro™ at the same time, very little of the medication will be absorbed. It is better to take the two at different times.
In some cases, you may need to cut an offending food entirely while on a medication. A classic example involves grapefruit juice and grapefruit products. Grapefruit stops the liver enzyme that breaks down certain drugs, such as Lipitor™, Valium™, Adalat™, and Renedil™.
Drug-drug interactions occur when two or more drugs react with each other when taken together.
Table 2. Examples of drug-drug interactions
|Absorption change||A drug causes more or less of another drug to be absorbed by the body.||Antacids can interact with many drugs and so should be taken at least two hours apart from other medications.
Iron and calcium stop each other from being absorbed and should be taken at different times.
|Elimination change||A drug causes another drug to be removed from the body more quickly or slowly than normal.||Biaxin™ causes Lipitor™ to be removed more slowly from the body. Lipitor™ is usually stopped while Biaxin™ is used. Dilantin™ causes estrogen to be removed more quickly from the body. Women taking estrogen-containing oral contraceptives should be on higher doses of the contraceptive while using Dilantin™.|
|Additive side effects||Two drugs share the same side effect.||Both alcohol and codeine (such as in Tylenol™ No. 3) can sedate and affect motor control|
|Contradictory effects||A drug has the opposing effect to another drug.||Ventolin™ causes the bronchial airways in the lungs to open, while Lopresor™ does the exact opposite. Someone with asthma should not take Lopresor™ to treat high blood pressure.|
Some medications can make an existing medical condition worse. For instance, the common medications below could be dangerous for someone with high blood pressure.
Table 3. Drugs that increase blood pressure
|Condition||Drugs to avoid|
|High blood pressure||Decongestants, such as pseudoephedrine, phenylephrine, oxymetazoline|
|NSAIDs (non-steroidal anti-inflammatory drugs), such as ibuprofen, naproxen, Celebrex™|
|Corticosteroids, such as prednisone|
|Diet drugs, such as Meridia™|
|Various herbs, such as caffeine, guarana or ginseng|
With some medical conditions, certain drugs absolutely must not be taken. In other situations, where benefits outweigh the risks, you will be advised to use the drug cautiously. You would then watch for any signs that your condition is getting worse.
The way that medications affect your body is very complex. While many people use medications without problems, knowing about ADRs can help prevent or manage them.
If you take medication, be aware of possible side effects, interactions and effects on medical conditions. Make sure your doctor, pharmacist or nurse practitioner know all your drug allergies, medical conditions, and current medications (including herbal supplements and vitamins). Wear a medical bracelet that lists all allergies and medical conditions.
Your pharmacist will always listen to your concerns or questions. Be sure to talk to your health care provider before you stop taking a medication, adjust the dose or change to another because of an ADR. Suddenly stopping or adjusting the dose of a medication may complicate the problem.