Drugs that cause increased excretion of nutrients

Diuretics are frequently taken to correct oedema (water retention) which results from a medical disorder. While they are successful in reducing the excess water level in the body, they also result in the excretion of larger amounts of potassium and magnesium. Patients being treated on a regular basis with thiazide diuretics should therefore increase their intake of foods which are high in potassium such as bananas, orange juice and potatoes.

Alcohol as a drug

Alcohol is regarded as both a drug and a food, since it supplies 29 kilojoules per gram. Because it has mood-altering effects and interferes with the absorption, metabolism and excretion of certain drugs and nutrients, it should possibly be treated with more respect than is usually the case. The reason why the effects of alcohol are felt so swiftly is that it takes a direct route into the system, traveling via the stomach to the small intestine, from where it is quickly absorbed into the blood. A small amount evaporates through the breath and perspiration, but most of it has to be processed by the liver before it isexcreted from the body via the urine.

A regular, excessive alcohol intake decreases the absorption of folic acid, thiamin, vitamin B6, vitamin B12, magnesium, zinc and other trace minerals. High alcohol consumption also tends to go hand in hand with a general decrease in food intake. Alcohol is used as a base in many over-the-counter medications and, ironically, some addicts find all-night chemists a useful secondbest after closing time at the pub!

When combined with the use of other drugs, alcohol can cause serious complications. This is because alcohol itself is a powerful drug and generally speaking, when two or more drugs are taken at the same time they often have a different (and more pronounced) effect than either produces on its own. In addition, if they both act on the same system in the body, their combined effect is often more powerful than might be expected. For example:

• In combination with barbiturates: Both alcohol and phenobarbital (a barbiturate) are depressants. When taken together, even at very low doses, these drugs may increase central nervous system depression and can be fatal.
• In combination with aspirin: Alcohol tends to irritate the stomach lining; when taken in combination with aspirin, which is also an irritant, it can cause internal bleeding.

Other medication: When alcohol is consumed with some antidepressants (ie monoamine-oxidase inhibitors) it may increase blood pressure to a dangerous level. Alcohol combined with antialcohol (Antabuse), antidiabetic and many other medications can lead to abdominal cramps, flushing and vomiting.

Drugs in disguise

Many of us know people who imbibe tea made with loquat leaves for their diabetes, or swear by certain home-brewed herbal mixtures for a multitude of ills. It would certainly be unrealistic to assume that drugs come only in the form of pills or potions created in a laboratory - the early use of the poppy for its narcotic effects is well known - but there are considerable advantages to obtaining one's medication from a pharmacist and not from the garden. These include the fact that the quantity of a compound can be controlled in a pill but not in a leaf, the question of year-round availability and, not least, the convenience.

Some foods are well-known for their adverse drug effects. Liquorice, for example, contains a compound which can cause raised blood pressure if eaten in quantity by people sensitive to this particular substance. Another interesting example (although not of local relevance) is a type of broad bean known as a lava bean' which has a drug-like effect in certain people. Some members of the population in Mediterranean countries have a metabolic defect which causes jaundice, blood in the urine and other symptoms if they eat this variety of bean.

Diet and Drug Interaction

The use of drugs or medication to maintain or restore health has increased tremendously during the past 20 years.

A 'drug' may be defined broadly as any chemical substance that is not one of the basic nutrients (proteins, carbohydrates, fats, minerals and vitamins) and which, when taken in, changes the body's structure or function. Incidentally, according to this definition, even ordinary table salt could be labelled a drug! For the purpose of this article, however, the term 'drug' will mean a non-food substance that is deliberately introduced into the body in order to produce some physiological or psychological effect. Of course drugs act in a variety of different ways, depending on their particular applications, which may be any of the following:

• relief of symptoms (such as headaches)
• prevention of illness (as in the case of vaccines used against diseases such as polio)
• control of chronic conditions such as high blood pressure
• treatment of certain diseases (for example, antibiotics which are used to treat tuberculosis).

How do drugs work?

What determines how a certain drug acts on a specific problem? Why does one have an effect on the blood vessels and another on the lungs? The answer to these questions has to do with the concept of 'receptor sites' - the idea that a drug has its effect only at specific spots within cells where the drug molecule 'fits'. (A molecule is the smallest unit of a chemical substance such as a drug.) These drug molecules do not act on the whole cell, but only at the receptor sites - and only on those cells with receptor sites that are compatible with the drug molecule. The diagram on the following is a representation of the way in which this compatibility works.

Prescription drugs - handle with care!

Whenever your doctor prescribes a medication, make sure that either he/she or your pharmacist gives you the following information:

• The name of the drug (many drugs go by different names)
• The reason you are taking it
• How the drug should be taken (before or after meals, with water, fruit juice or milk, etc)
• The dosage safety level of the drug (to prevent overdosing if you have to use the drug in an emergency)
• How often you should take the drug
• The length of time you should continue to take it
• Whether taking the drug requires any change in your diet or activities (For example, certain drugs may not be taken with alcohol and others may cause drowsiness or interfere with your coordination.)
• What side effects can you expect? (All drugs cause side effects,ranging from the trivial to the serious.)

The drug/diet link

After many years of research, health professionals have established that foods and nutrients do interact with drugs to a significant extent. In other words, medication can have an effect on a person's health and conversely, food can influence a drug's effectiveness. The risk that a drug might have an adverse nutritional effect or that drugs and food might be incompatible becomes particularly relevant when:

• the drug is an 'anti-nutrient' (in other words, it acts like a nutrient even though it is not one)
• a drug which has adverse nutritional effects is taken for a long time
• the patient is taking more than one drug at a time
• a patient's diet is either nutritionally inadequate or the patient is already malnourished
• drugs are used excessively (or there is abuse of prescription or over- the-counter drugs)
• food and/or drugs are not being properly absorbed due to disease
• the patient is not given special diet instructions when necessary
• physicians, pharmacists and dietitians are unaware of the risks involved.

The use of medication may influence nutrient intake, absorption, metabolism or excretion; in the same way, foods or their components may affect the absorption, metabolism and excretion of drugs. To paraphrase this, drugs and foods can interact by one of the following mechanisms:

• Drugs plus foods (nutrients) = changed drug effect
• Drugs plus foods (nutrients) = changed nutritional balance

Vitamin supplements - the facts

Most doctors and dietitians agree that an adequate diet selected from a range of foods in the Five Food Groups and taken in the recommended portion sizes, will ensure a satisfactory intake of all nutrients, including vitamins. However, it is also recognised that vitamins which are constantly needed in the metabolism can be compared to an integral part of a work force on a factory assembly line. Each worker has a specific and vitally important role to play and his absence can jeopardise the smooth running of the whole system.

In the case of an unsatisfactory vitamin intake, one should first and foremost try to rectify the situation by improving one's diet, as food sources of vitamin also include other essential nutrients - some of which may still be unknown. Incidentally, the reason for choosing a food source rather than a vitamin in pill form is not that one's system absorbs it better - the body is in fact unable to distinguish between natural and synthetic compounds in this way. Each vitamin - whether manmade or naturally available - is a very specific compound with a unique molecular structure which is handled by the body in a particular way.

Supplements should however be considered only if, for some reason, your vitamin needs exceed your dietary intake. For example, people on strict long-term weight-reducing diets, heavy smokers and drinkers, pregnant women taking a less-than-optimal diet to cover the needs of two, or people living in isolated areas (or away on expeditions) who are unable to obtain the necessary variety of foods, may all benefit from vitamin supplements. (Incidentally, a pregnant woman should always take a supplement under a doctor's supervision only.)

A recent study (by Macfarlane et al) on 774 Indian women in Durban showed that 25% had iron deficiency anaemia and an additional 17% showed sub-clinical signs of this deficiency disease. The authors concluded that South African Indian women should receive iron supplementaton during pregnancy, as their cultural dietary habits promote an inadequate intake of this important trace element.

It has also been found that heavy smokers need more vitamin C than do non-smokers, as smoking seems to reduce the availability of vitamin C in food to the body.

The dangers of the overdose

Megadoses of vitamins are a different story. Some people assume that if a small amount of a vitamin supplement is useful under certain circumstances, more would be even better, but this is not so - in fact, abnormally large quantities of the fat-soluble vitamins (A,D,E and K) can be toxic as they accumulate in the body and excesses are not immediately lost in the urine, as is usually the case with water-soluble vitamins. However, care should be taken even with the latter: cases of `rebound scurvy' have occurred in babies whose mothers have taken excessive amounts of vitamin C during pregnancy - with the result that the baby's body reacts as if deprived when it has to depend on its own food intake after birth.

A recent study (by Read et al) in which people in seven states in the USA were questioned about their health beliefs showed that regular supplement users (who were predominantly married Caucasian women between the ages of 20 and 79) believed that supplements decreased their susceptibility to health problems ranging from colds to heart attacks and cancer, and/or reduced the severity of those problems. They also found that the higher the user's level of education, the larger the number of supplements taken, but the bottom line of the study was that more non-users rated their health as 'excellent' than regular users. The authors concluded that it remains a paradox that the well-educated, settled members of the community who are in a position to obtain all their nutrient requirements from a balanced diet, continue to be the most regular users of vitamin and mineral supplements.

How food affects drugs

In order to work properly, drugs must be present in the correct amounts at the receptor sites of the cell membranes. A number of factors can affect the way in which a drug works and, therefore, its effect on the body. Food is one of the most important of these factors. It can affect the absorption of a drug, its movement through the blood, its metabolism and its excretion.

Food and drug absorption

When drugs are taken orally, their absorption is influenced in different ways by the presence of food in the digestive tract. For example, food causes increased secretion of hydrochloric acid (HCl) in the stomach which can result in the destruction of some penicillin antibiotics that are taken by mouth. For this reason, penicillin should always be taken 1 hour before or 3 hours after meals.

Calcium in milk and dairy products tends to bind with tetracycline antibiotics to form non-absorbable compounds, with the result that the drug is lost in the stool. This means that these foods should not be eaten at the same time or within a few hours of taking the medication. However, the instruction 'Not to be taken with milk products' which sometimes appears on medicine labels can be misleading as it does not mean that you cannot consume any milk products while you are on the medication.

Iron salts (such as ferrous sulphate) can also bind with tetracycline antibiotics and result in the loss of the antibiotic. Therefore, anyone using an iron supplement as well as a tetracycline should take them at least two hours apart.

On the other hand, the absorption of some drugs can be increased when they are taken with foods. For example, foods with a high fat content increase the absorption of Griseofulvin, an antibiotic and antifungal drug. Iron supplements are also absorbed better when they are taken with vitamin C or foods rich in vitamin C, such as orange and guava juice. Interestingly, although some drugs (such as aspirin) are absorbed better on an empty stomach, they should nevertheless be taken with food - or at least milk - because of their irritating effect on the stomach lining.

Food and drug metabolism

Certain reactions inside the body can chemically change a drug (`metabolize' it) so that it is quite a different compound by the time it leaves the bloodstream. For example, some drugs combine with body proteins as they move through the bloodstream, which has the effect of preventing these drugs from entering the cells where they were intended to act. Others are broken down into smaller chemical components by the liver, the kidneys and the digestive tract. The metabolism of specific drugs can be influenced by the following in food: protein content, alcohol content, charcoal broiling, certain types of vegetables, caffeine intake, dietary fibre and the times food is eaten in relation to drug intake.

Food and the excretion of drugs

When metabolized by the body, some food alters the pH of the urine making it either more or less acidic - which in turn affects the excretion of drugs and therefore, the duration of their effects. For example, if excretion is decreased, more of the drug will be reabsorbed into the blood and its effects will be prolonged.

As an illustration, vitamin C makes the urine more acidic, thereby reducing the excretion of acidic drugs like phenobarbital and aspirin. When taking an antibiotic for a urinary tract infection, it is beneficial to acidify the urine, because this will result in decreased excretion of the antibiotic.

What drugs should you take when?

In order to minimize the adverse effects of foods on drug absorption, metabolism and excretion, the timing of drug administration in relation to food intake is very important. This is why it is essential to adhere to any such instructions which may accompany a prescribed drug. For example:

• If rapid absorption of the drug is desired, the doctor/pharmacist may specify on the prescription that the drug should be taken before meals.
• Drugs that irritate the stomach (such as indomethacin, phenobarbitone) should be taken when the stomach is 'cushioned' with food. In this case, the prescription should specify that the drug is to be taken after (or in the middle of) a meal.
• Fat-soluble drugs should not be taken with a fatty meal, since the medication will be absorbed with the fat content in the food; because fat is digested slowly, the drug may not be absorbed into the bloodstream as rapidly as it should be.
• Acetylsalicylic acid, Bisacodyl, Erythromycin and tetracyclines should not be taken with milk (see above).
• Ampicillin, Cloxacillin and Erythromycin-based drugs, as well as stearate and Penicillin G should not be taken with fruit juices or carbonated beverages.