Drug interactions are preventable in virtually every case. However, physicians and pharmacist must know what medications a patient is taking in order to head off trouble. Patients should inform physicians and pharmacist about other prescriptions as well as any vitamin or mineral supplements or over the counter medications they take routinely.
If a person is receiving (or is about to receive) interacting drug, there are several ways to head off potential problems. Sometimes the best way to avoid an adverse drug interaction is simple for the doctor not to prescribe the interacting drugs. Several different medicines are available for the treatment of most disorders, and it may be possible to select an alternative to one of the interacting drugs.
If a patient truly needs both interacting drug, other preventive measures may be called for. Sometimes the dose of one of the drugs can be adjusted to correct for the alteration caused by the drug interaction. Sometimes the physician will need to monitor the patient` s response more carefully. Sometimes the interaction can be prevented by spacing the doses of the interacting drugs appropriately or by giving one of the drugs by a different route of administration.
Using these and other methods a doctor can typically prevent the adverse effects of drug interactions. But prevention must be a cooperative effort between the patient, the doctor and the pharmacist.
Exercise 2. Study the tables and give your comments.
Selected drug- drug interactions are listed in Table 1 and 2. The interactions included were chosen because of the widespread use of some of these medications, and because their effects are seemed “clinically significant”- that is, their effects have been detected in the human body as opposed to being observed only in animal studies.
It is very important to note here that anyone taking any of the medications listed in the tables should not alter the dose of his or her medication without the prescribing doctor` s consent and supervision. Patients should discuss all medication-related questions with their physicians and pharmacists.
TABLE 1: INTERACTIONS WITH DRUGS TAKEN FOR HYPERTENSION
(Brand names of drugs are shown in boldface in the table, generic names are in plain type.)
DRUGS
INTERACTS WITH
RESULTS AND PRACTICAL TIPS
diltiazem (Cardizem)
lithium ( Cibalith–S, Eskalith, Lithane, Lithobid and other)
This interaction could lead to neurotoxicity. Possible symptoms include nausea, vomiting, muscular incoordination and ringing in the ears.
May increase the amount of nifedipine in the blood, thereby increasing the antihypertensive effect. Possible nifedipine toxicity– evidenced by symptoms such as dizziness, flushing and headache – may occur.
nifedipine (Adalat, Procardia XL)
barbiturates
Significantly decreases the amount of nifedipine available in the body, possibly leading to a decreased effect of the nifedipine. This effect is particularly likely when nifedipine is taken orally.
( Much of the evidence for this interaction comes from studies of phenobarbital, but other barbiturates are expected to interact similarly.)
TABLE 2: INTERACTIONS WITH DRUGS TAKEN
TO FIGHT INFECTION
(Brand names of drugs are shown in boldface in the table, generic names are in plain type.)
DRUGS
INTERACTS WITH
RESULTS AND PRACTICAL TIPS
amoxicillin (Amoxil, Larotid, and other); penicillin V (Ledercillin VK, Pen-Vee K, V-Cillin K, Veetids)
estrogen containing oral contraceptives such as Brevicon, Demulen, Enovid, Lo/Ovral, Norinyl, Ortho Novum, Ovcon, Ovral, Tri-Norinyl,Tri-Phasil and many others.
Although aminopenicillins (such as amoxicillin) may reduce the efficacy of oral contraceptives, this result is probably rare. Menstrual irregularities, such as spotting or breakthrough bleeding, may be a sign that this interaction is occurring. Other types of penicillins and other oral antibiotics in general may produce similar effects.
Recommendation: Women wishing to avoid pregnancy would be prudent to institute another from of contraception – in addition to use of their oral contraceptive – while taking amoxicillin or other penicillins in this class ( i.e., aminopenicillins).
ciprofloxacin (Cipro)
- dairy products
- multivitamin supplements
- antacids that contain aluminum or magnesium
Greatly diminishes absorption of ciprofloxacin.
Cations (e.g., calcium, magnesium, iron, aluminum, etc.) bind with ciprofloxacin and markedly reduce its absorption, possibly leading to decreased antibiotic effect.
Do not take ciprofloxacin and cations ( such as iron- containing vitamin supplements, dairy products, antacids, etc.) simultaneously. Ciprofloxacin should be taken at least two hours before or six hours after taking diary products vitamins or antacids to minimize the occurrence of this interaction.
erythromycin
terfenadine (Seldane), astemizole (Hismanal)
Erythromycin may cause increased plasma levels of Seldane or Hismanal, which could lead to cardiac arrhythmias. Changes in the EKG namely prolonged QT interval – have been observed in patients combining erythromycin with these allergy medications. This interaction is serious. How often this interaction occurs is unknown, yet caution is certainly warranted.
DRUGS
INTERACTS WITH
RESULTS AND PRACTICAL TIPS
erythromycin
theophylline ( Primatene Tablets, Slo-Bit, Theo-Dur, Theo-24, Uniphyl and other)
Erythromycin may increase the amount of theophylline in the blood. Although most people do not seem to have much trouble with this interaction, some develop theophylline toxicity. Symptoms of theophylline toxicity include nausea, vomiting, diarrhea, headache, irritability, nervousness, rapid heartbeat, insomnia and tremor. In serious cases, seizure can occur.
The effect is usually delayed, so that theophylline concentrations start to rise after 5-7 days of treatment with erythromycin.
erythromycin
triazolam (Halcion)
This combination can lead to a substantial increase in the concentration of triazolam in the blood, possibly increasing its sedative effect, which could lead to drowsiness, impaired ability to concentrate and forgetfulness.
Recommendation: if signs of triazolam toxicity are present, a patient may wish to discuss this with his or her physician; dosage reduction may be necessary.
Calcium supplements, calcium- fortified vitamins and foods containing calcium may substantially reduce the absorption of tetracycline, thereby diminishing its effects. The absorption of related compounds (i.e., doxycycline, minocycline) when taken with calcium is also reduced, but to a lesser extent.
Foods with moderate to high amounts of calcium include milk, yogurt, cheese, sardines, salmon, soybeans, tofu, broccoli and turnip greens.
Recommendation: Do not take tetracycline and calcium products simultaneously. In fact avoid taking any cations ( e.g., iron, magnesium, zinc, aluminum)with tetracycline at least two hours before or at least four hours after eating dairy products or calcium containing vitamins.
Table 3 identifies some well-documented effects cigarette smoking has on certain medication. (it` s important to note here that – regardless of the effect a patient` s smoking may have on a prescribed medication – patient should never change the dose of a medication he or she is receiving without checking with the prescribing physician.
Table 3: EFFECT OF CIGARETTE SMOKING
ON MEDICATIONS
DRUG
EFFECT ON CIGARETTE SMOKERS
theophylline (used to treat asthma)
Smoking may lead to a decrease in the effect of theophylline. Cigarette smoke increases the production of the enzymes in the liver responsible for metabolizing this medication as a result. Less of the medication enters the blood, and a decreased response may ensue.
tacrine (used to help manage Alzheimers disease)
Smoking may lea to a decrease in the effect of tacrine.
insulin (used to manage diabetes mellitus, a condition that results in excessively high amounts of sugar in the blood and urine)
An insulin-dependent who smokes heavily may require a 15% to 30% higher dose of insulin that a nonsmoker.
flecainide (used to treat life threatening arrhythmias – irregularities of the heartbeat and heart rhythm of the heart)
Smoking may decrease the amount of flecainide in the body. A doctor may decrease the amount of flecainide in body. A doctor may need to prescribe a higher dose of this medication to a smoker than to otherwise similar nonsmokers.
Exercise 3. Give the written summary of the article. Concentrate on the following:
1. Drug interaction and its consequences
a) desirable; b) adverse; c) inconsequential.
2. Increased effect of a medication and the type and severity of symptoms that develop.
3. Decreased effect of a medication.
4. Cigarette smoking, efficacy of drugs and adverse health effects.
Read the following texts and do the tasks that follow them.
