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.

Food additives and contaminants

This much-publicised aspect of food production is well provided for in food legislation. A number of specific regulations exist to control any additives and contaminants that may be present in foods, either by direct addition or through indirect absorption. The adding of

colourants is an example of direct addition. Colouring can only be added to a food if the legislation for that food permits it, and only one or more of the colours listed in the regulations can be added. It may not be added in greater quantity than prescribed and it must comply with the standard of purity laid down in the regulation.

An example of indirect absorption is the maximum amount of lead that may be present in food, irrespective of the source. If you're about to argue that there shouldn't be any lead in your food at all, consider that the word 'source' includes the soil in which the plant is grown, the food consumed by an animal used for meat, or equipment in which a food is processed.

Chemicals- cause for concern?

An increasingly large number of additives and processing methods are used to produce the food we eat every day and understandably, public concern is once again on the increase. The amount of chemical substances used in food processing is possibly the major source of worry. Yet the use of these chemicals has been given the green light by legislators, or they would not be present in just about every food on our supermarket shelves.

Why are chemicals necessary in foods? In the simplest terms, because food itself is nothing but chemicals. In fact, the common foods we eat every day are such complex mixtures of chemicals that it would take a brash scientist indeed to assert that the composition of any single food is completely known. Even mother's milk - the only product designed by nature exclusively as a food for mankind - is known to contain more than 140 chemicals!

Perhaps it is worth pointing out that many of the chemicals which man produces are exact copies of those already found in nature. Just one example of this is vitamin C, a vital nutrient which of course occurs abundantly in foods such as citrus fruit and tomatoes. The vitamin C produced by man is identical to the natural chemical, both in terms of chemistry and efficacy, and its widespread use is the only reason scurvy is no longer the scourge of many populations whose normal diets do not provide sufficient of/this essential vitamin.

Interestingly, only a small proportion of pest resistance in plants is manmade. Plants develop their own defence mechanisms against pests and these include the use of natural toxins. Indeed, breeding crops for pest resistance may actually increase their natural toxin levels. For example, it is known that a pest-resistant potato had to be removed from the marketplace in the USA when its natural solanine and chaconine concentrations were found to have reached highly toxic levels. Similarly, a pest-resistant celery had to be discarded when workers handling it suffered outbreaks of dermatitis. It was belatedly discovered that the concentrations of 8-methoxypsoralen (a carcinogen) had inadvertently been increased ten-fold! Unfortunately, since new `disease-resistant' crops are not subjected to the same regulatory scrutiny imposed on man-made pesticides, we may never know how the risks and benefits of reducing pesticide use versus natural toxin consumption ultimately balance out.

To a large extent, the assumption that nature is benign has become ingrained in consumers' minds and even embodied in our regulatory codes. Biological materials are regarded as innocent until proven guilty, while man-made ones are assumed guilty until proven innocent. Without a proper body of balanced scientific scrutiny to back them up, assumptions such as these are not only simplistic - they could bedangerous.

However, solutions to problems such as the above will no doubt be found as more and more research is done in this area; there is no doubt that biotechnology will have an increasingly dramatic impact on the agriculture of the future. The genetic improvement of agricultural crops so that they become more resistant to disease, viruses and drought is clearly an important goal in a world already struggling to feed its billions of inhabitants. While the development of pest-resistant plants may never totally replace the need for agricultural chemicals, it could certainly help to decrease our dependence on them and so lessen the level of contamination to the environment - one of the majorconcerns of our times.

Labelling - 'preventing deception and fraud' continue...

Labelling and current legislation

At present under South African food law, certain terms are already ⁴prohibited. For example, no foodstuff may be labelled with the words 'recommended by doctors' or 'medically recommended' or imply the same; nor may the words 'health', 'healthy', 'heal', 'cure' or 'restorative' be used, implying that the food has health-giving properties.

The law also requires food producers to list ingredients in order of the _quantities in which they are present in a product. Hence, a product labelled as containing 'meat and soya' in that order would have more meat than soya. Nutritional content is not required by law, but if a producer wishes to state this on a package, it must be headed 'Nutritional Information'. The producer must indicate what percentage of the RDA (Recommended Daily Allowance) of the specific nutrient is present per serving and the order in which the nutrients are listed is stipulated. There must also be an indication of the energy content of the food to the nearest kilojoule per serving. Even the word 'serving' is prescribed by the legislation and 'means the mass, volume or number, as the case may be, which is recommended by the manufacturer as the amount to be taken on its own or as part of a meal ...'.

Perhaps this is where some consumers may have a difference of opinion with the manufacturers: the consumer sees the purchase as a meal, whereas the manufacturer regards it 'as part of a meal'. Either that or there are a lot of not-so-hungry manufacturers out there!

By law, the weight or volume of all packaged foods has to be stated on the package and this must refer to the actual usable quantity of food; for example, a 250 g pack of teabags must literally contain 250 g of tealeaves when weighed without the individual bags or box in which they are packaged. Another example of this type of legislation is applicable to eggs, which are graded and labelled according to strictly controlled weight regulations.

'Negative' claims

It is generally accepted that a manufacturer may extol the virtues of his product or the method of its manufacture, provided that the information given can be justified. However, any claim that denounces food ingredients, whether outright or by innuendo, deserves intense scrutiny. Over the last few years, some irresponsible promotional campaigns have stated or implied that foods containing certain permitted additives are less wholesome, less safe or less healthy than those without these additives. Conversely, it has been stated or implied that foods without certain permitted additives are more wholesome and safer, or healthier, than those with additives.

Admittedly, it is sometimes important to draw the consumers' attention to the fact that a foodstuff does not contain a substance, particularly if this fact could change the consumer's attitude to the product. For example, canned foods generally do not contain preservatives; evaporated milk does not contain added sugar (sucrose), yet in both cases, many people believe that they do. Because of the trend towards 'naturalness', more and more consumers are opting for additive-free foods and so of course manufacturers want to let the buying public know if their products conform to this 'ideal' - that's simply good marketing and the words 'contains no preservatives or additives' on a label don't necessarily imply that a product is any better than one with additives.

Then there are those ambiguous expressions, 'sugar free' and `no sugar added'. What most people don't realise is that the 'sugar' referred to here is sucrose (cane sugar) and that these products may well contain other types of 'natural' sugar - for example the milk sugar, lactose, present in an ingredient such as skim milk powder. These and similar expressions should only be used if the information is followed closely by an equally clear statement indicating which sugars are present or have been added to the food.