Many individual factors will determine an individual’s clinical response to a drug. Some of these have already been identified but additional factors will also be considered here. The nurse prescriber should be fully aware of these factors and they should be incorporated into the client assessment before decisions are made about which drug to prescribe. In addition, they should be considered when monitoring drugs which are already being used by the client, whether the drugs are prescribed or obtained ‘over-the-counter’.

• Age. The very young and the elderly particularly have problems related to their ability to metabolise and excrete drugs. Neonatal hepatic enzyme systems are not fully effective, so drug metabolism will be reduced and there is an increased risk of toxicity. In the elderly, delayed metabolism by the liver and a decline in renal function means delayed excretion by the kidneys and drug action may be prolonged. Complicated drug regimes may be difficult for the elderly to follow which may mean inadequate or excessive doses of drugs are consumed.

• Body weight. The size of an individual will affect the amount of a drug that is distributed and available to act. The larger the individual, the larger the area for drug distribution. Lipid-soluble drugs may be sequestered in fat stores and not available for use. This is the reason that some drugs are given according to the client’s body weight ie. x milligrams per kilogram of body weight. All clients should have their weight recorded and this should be reassessed regularly if the client is receiving long term drug treatment.

• Pregnancy and lactation. Lipid-soluble, unionised drugs in the free state will cross the placenta eg. opiates, warfarin. Some may be teratogenic and cause foetal malformation. Drugs can also be transferred to the suckling infant via breast milk and have adverse effects on the child eg. sedatives, anticonvulsants and caffeine. A full drug history should be obtained pre-conception where possible or as soon as pregnancy has been diagnosed. Women must be educated not to take medication without consulting a physician, pharmacist, midwife or nurse.

• Nutritional status. Clients who are malnourished may have altered drug distribution and metabolism. Inadequate dietary protein may affect enzyme activity and slow the metabolism of drugs. A reduction in plasma protein levels may mean that more free drug is available for activity. A loss of body fat stores will mean less sequestering of the drug in fat and more drug available for activity. Normal doses in the severely malnourished may lead to toxicity. Nutritional assessment of clients is, therefore, essential and malnutrition should be managed accordingly.

• Food-drug interactions. The presence of food may enhance or inhibit the absorption of a drug. For example, orange juice (vitamin C) will enhance the absorption of iron sulphate, but dairy produce reduce the absorption of tetracycline. Monoamine oxidase inhibitors must not be taken with foods rich in tyramine, such as cheese, meat yeast extracts, some types of alcoholic drinks and other products, due to toxic effects occuring, such as a sudden hypertensive crisis. Nurses should have some knowledge of common food-drug interactions and drug administration may need timing in relation to mealtimes.

• Mental and emotional factors. Many factors may affect a client’s ability to comply with their drug regime. These include confusion, amnesia, identified mental illness, stress, bereavement and many others. These types of problems may lead to inadequate or excessive use of medication resulting in unsuccessful treatment or serious adverse effects. The nurse must consider these issues in the client assessment.