Drug Factors Affecting Patient Response

Drug Factors

Many drug factors affecting patient response including:

• Drug structure
• Molecular weight
• Time of drug administration
• Drug accumulation
• Drug combination

Drug Structure

• Most drugs have multiple stereoisomers
• Stereoisomers are compounds of the drug that contain the same number of atoms but they differ in spatial arrangement of atoms.
• The receptor site is usually sensitive for one stereoisomer and not sensitive for another , this means that one isomer maybe hundred times more potent than the other
• Sometimes one isomer is beneficial and other is toxic of the same drug
• The sensitivity to certain stereoisomers is different between people

Molecular weight

• Most drugs have molecular weight between 100-1000.
• Drugs larger than 1000 can’t be absorbed.
• The lower the molecular weight is, the better absorption.

Time of drug administration

• Many body function have daily circadian rhythm (e.g. liver metabolism, blood pressure, heart rate, gastric emptying time). And some enzymes responsible for metabolism of drugs are active in the morning or evening.
• Also many diseases are circadian phase dependent. (e.g. asthma attacks at night, myocardial infarction at morning, etc…) Chronopharmacology is the study of how the effects of drugs vary with biological timing (circadian rhythm) and giving the drugs in the best time to get better response and/or to avoid possible side effects

Time of drug administration

• Examples: acute asthma attack is common at the night because of circadian variation of cortisol leading to decrease sympathetic tone and increase parasympathetic tone that lead to bronchoconstriction so it is better to give asthma meds at night
• Blood pressure is at its peak in the afternoon , so it is better to give antihypertensive meds at morning

Drug accumulation

• Drug accumulation occurs when the rate of drug administration exceeds the rate of its elimination and as result of that we get drug accumulation and toxicity
• Drug accumulation occur in increased administration, renal failure, liver failure
• Example is digoxin we give it 5 days a week and we give two days so body eliminate the drug

Drug combination

Drug combination is very common in clinical practice. When two or more drugs are combined together, one of the following may occur: