FACTORS INFLUENCING DRUG ACTION
A number of factors other than medication itself can affect its action. The identical drug and dosage may affect different client differently.
l. Developmental factors
· During pregnancy women must be very careful about taking medication. It may affect the development of growing foetus, especially in the first trimester.
· Most of the drugs are contraindicated because of the adverse effect on foetus.
· Infants usually requires a small dosage because of their body size and immaturity of their organs, especially the liver and kidney.
· In adolescence or adulthood, allergic reactions may occur to drugs formerly tolerated,
· Older adults may have different response to medication due to physiological changes that accompany again.
· Liver and kidney function changes, which results in the accumulation of drug with in the body.
· Older adults often experience a decreased gastric motility, decreased gastric acid production and blood flow which can impair drug absorption.
· Older adults may also experience a decreased number of protein binding sites and change in blood brain barrier. The later permits fat soluble drugs move rapidly in to the brain causes dizziness and confusion.
Differences in the way men and women respond to a medication are chiefly related to the distribution of body fat, fluid and hormonal differences.
3. Cultural, Ethnic and Genetic variations
· A client responds to a drug is influence by age, gender, size and body composition. This variation is known as drug polymorphism.
· Drug metabolism is genetically determined and as a result, race may affect a drug response. This is called genetic polymorphism.
· Cultural factors and practices can also affect a drug action, because of the gene that control liver metabolism vary and some clients may have a slow metabolism.
· Certain medications may work well at therapeutic dosages for some ethnic groups but be toxic for others. E.g. antipsychotic and anti-anxiety drugs Asian need only lower dosage due to slower metabolism than that African Americans, Hispanics, & Caucasians.
· Cultural factors and practices (values and beliefs) can also affect a drugs action. For e.g. herbal remedies may speed LIP or slow down the metabolism of prescribed medication
Nutrients can affect the action of a medication. For an instance, vitamin k in green vegetables can counteract the effect of an anti-coagulant such as warfarin.
· The client's environment may affect the action of drugs, particularly those used to alter mood and behaviour.
· Environmental temperature may also affect drug activity. When environmental temperature is high, the peripheral blood vessels dilate, thus intensifying the action of vasodilators.
· In contrast, a cold climate and consequent vasoconstriction inhibit the action of vasodilators, but enhance the action of vasoconstrictors.
· A noisy environment may alter the action of analgesics and sedatives.
6. Psychological factors
A client's expectation about what a. drug can do can affect the response to the medication. A client, for an instance, who believes that the codeine is ineffective as an analgesic may experience no relief from pain after it is given.
7. Illness and Disease
· Illness and disease can also affect the action of a drug.
· Aspirin can reduce the body temperature of a fever client, but has no effect on the body temperature of a client without fever.
· Drug action is altered in clients with circulatory, liver or kidney dysfunction.
8. Time of administration
· The time of administration of oral drugs affects the relative speed with which they act. Orally administered medications are absorbed more quickly, if the stomach is empty.
· Oral medication taken two hours before meals acts faster than the drug taken after meals.
· Some medications for e.g. Iron preparations irritate the gastric tract and need to be given after a meal, when they will be better tolerated.
· A client's sleep wake rhythm may affect the action of a drug.
· Circadian variations in urine output and blood circulation for e.g. may affect the client's response to a drug.