(1994; 115 pages) [French] [Spanish]
Step 3A: Are the active substance and dosage form suitable for this patient?
We assume that all your P-drugs have already been selected on the basis of efficacy. However, you should now verify that the drug will also be effective in this individual patient. For this purpose you have to review whether the active substance is likely to achieve the therapeutic objective, and whether the dosage form is convenient for the patient. Convenience contributes to patient adherence to the treatment, and therefore to effectiveness. Complicated dosage forms or packages and special storage requirements can be major obstacles for some patients.
The safety of a drug for the individual patient depends on contraindications and interactions; these may occur more frequently in certain high risk groups. Contraindications are determined by the mechanism of action of the drug and the characteristics of the individual patient. Drugs in the same group usually have the same contraindications. Some patients will fall into certain high risk groups (see Table 5) and any other illnesses should also be considered. Some side effects are serious for categories of patients only, such as drowsiness for drivers. Interactions can occur between the drug and nearly every other substance taken by the patient. Best known are interactions with other prescribed drugs, but you must also think of over-the-counter drugs the patient might be taking. Interactions may also occur with food or drinks (especially alcohol). Some drugs interact chemically with other substances and become ineffective (e.g. tetracycline and milk). Fortunately, in practice only a few interactions are clinically relevant.
Table 5: High risk factors/groups
History of drug allergy
Exercise: patients 13-16
Verify in each of these cases whether the active substance and dosage form of your P-drug is suitable (effective, safe) for this patient. Examples are discussed below.
Man, 45 years. Suffers from asthma. Uses salbutamol inhaler. A few weeks ago you diagnosed essential hypertension (145/100 on various occasions). You advised a low-salt diet, but blood pressure remains high. You decide to add a drug to your treatment. Your P-drug for hypertension in patients under 50 is atenolol tablets, 50 mg a day.Patient 14:
Girl, 3 years. Brought in with a severe acute asthmatic attack, probably precipitated by a viral infection. She has great difficulty in breathing (expiratory wheeze, no viscid sputum), little coughing and a slight temperature (38.2°C). Further history and physical examination reveal nothing. Apart from minor childhood infections she has never been ill before and she takes no drugs. Your P-drug for such a case is a salbutamol inhaler.Patient 15:
Woman, 22 years, 2 months pregnant. Large abscess on her right forearm. You conclude that she will need surgery fast, but in the meantime you want to relieve the pain. Your P-drug for common pain is acetylsalicylic acid (aspirin) tablets.Patient 16:
Boy, 4 years. Cough and fever of 39.5°C. Diagnosis: pneumonia. One of your P-drugs for pneumonia is tetracycline tablets.
Patient 13 (hypertension)
Atenolol is a good P-drug for the treatment of essential hypertension in patients below 50 years of age, and it is very convenient. However, like all beta-blockers, it is relatively contraindicated in asthma. Despite the fact that it is a selective beta-blocker, it can induce asthmatic problems, especially in higher doses because selectivity then diminishes. If the asthma is not very severe, atenolol can be prescribed in a low dose. In severe asthma you should probably switch to diuretics; almost any thiazide is a good choice.
Patient 14 (child with acute asthma)
In this child a fast effect is needed, and tablets work too slowly for that. Inhalers only work when the patient knows how to use them and can still breathe enough to inhale. In the case of a severe asthma attack this is usually not possible; moreover, some children below the age of five may experience difficulties with an inhaler. Intravenous injection in young children can be very difficult. If an inhaler cannot be used, the best alternative is to give salbutamol by subcutaneous or intramuscular injection, which is easy and only briefly painful.
Patient 15 (abscess)
This patient is pregnant and will soon be operated on. In this case acetylsalicylic acid is contraindicated as it affects the blood clotting mechanism and also passes the placenta. You should switch to another drug that does not interfere with clotting. Paracetamol is a good choice and there is no evidence that it has any effect on the fetus when it is given for a short time.
Patient 16 (pneumonia)
Tetracycline is not a good drug for children below 12 years of age, because it can cause discolouration of the teeth. The drug may interact with milk and the child may have problems swallowing the large tablets. The drug and, if possible, the dosage form, will therefore have to be changed. Good alternatives are cotrimoxazole and amoxicillin. Tablets or parts of tablets could be crushed and dissolved in water, which is cost-effective if you can clearly explain the procedure to the parents.3 You could also prescribe a more convenient dosage form, such as a syrup, although this is more expensive.
3 This is a cheap and convenient way of giving a drug to a small child. However, it should not be done with capsules nor with special tablets such as sugarcoated or slow-release preparations.
In all these patients your P-drug was not suitable, and in each case you had to change either the active substance or the dosage form, or both. Atenolol was contraindicated because of another disease (asthma); an inhaler was not suitable because the child was too young to handle it; acetylsalicylic acid was contraindicated because it affects the blood clotting mechanism and because the patient is pregnant; and tetracycline tablets were contraindicated because of serious side effects in young children, possible interactions with milk, and inconvenience as a dosage form.