Why prescription drug can work differently for different people

Imagine two people taking the same medication at the same dose—yet one feels immediate relief while the other suffers from side effects or sees no improvement at all. Why does this happen? The answer lies in the intricate and deeply personal science of how our bodies interact with drugs. From genetics and metabolism to age, lifestyle, and underlying health conditions, every individual is a unique biological puzzle.

 

Genetic Differences:

One of the primary reasons why prescription drugs can affect people differently is due to genetic variations. Every individual carries a unique set of genes that influence how their body processes medications. This field of study is known as pharmacogenomics, which looks at the relationship between our genes and how we respond to drugs.

Different people may have variations in the genes that control drug metabolism. For example:

       Cytochrome P450 Enzymes: These enzymes are responsible for breaking down many drugs in the liver. Variations in the genes that produce these enzymes can make a person a fast metabolizer, slow metabolizer, or even an ultra-rapid metabolizer. A fast metabolizer may break down a drug too quickly, making it less effective, while a slow metabolizer may process the drug too slowly, leading to higher concentrations in the blood and potential side effects.

       Drug Receptors and Transporters: Some people have genetic variations that affect the receptors on their cells, which are responsible for binding drugs and triggering their effects. Similarly, drug transporters determine how efficiently a drug is absorbed into the bloodstream, distributed to tissues, and eliminated from the body.

Pharmacogenomics has opened the door to personalized medicine, which tailors drug prescriptions based on an individual's genetic profile. This approach has been shown to improve the efficacy and safety of treatment, reducing the likelihood of adverse drug reactions.

 

How Age Alters Drug Response

Age plays a crucial role in how the body processes medications. Newborns, children, and elderly individuals all have different physiological characteristics that can impact drug absorption, distribution, metabolism, and elimination.

      Children: Their liver enzymes and kidneys may not be fully developed, meaning they may metabolize drugs differently than adults. In fact, some drugs may require lower doses for children to avoid toxicity.

       Elderly Adults: As we age, kidney function tends to decline, and liver enzymes may become less efficient. This means that elderly people are at higher risk for drug accumulation and adverse effects, especially with medications that are excreted through the kidneys or liver.

Moreover, hormonal changes, such as those occurring during pregnancy or menopause, can alter the way drugs work in the body. For example, pregnancy increases blood volume, which can dilute drugs and decrease their effectiveness. On the other hand, hormone replacement therapies can affect how certain medications interact with the body.

 

 Body Weight and Composition:

Another factor that influences how a drug works in the body is body weight and composition. People with a higher proportion of body fat versus lean muscle mass may experience different drug effects compared to those with a higher muscle-to-fat ratio. This is because fat and muscle tissues handle drugs differently.

      Fat-Soluble Drugs: Some medications are lipophilic (fat-soluble), meaning they are more likely to be stored in fat cells. For people with higher body fat, these drugs may stay in the body longer and be released more slowly, potentially leading to a prolonged effect.

      Water Soluble Drugs: Medications that are more hydrophilic (water-soluble) are usually distributed in the bloodstream and lean muscle. People with a higher percentage of muscle mass may experience faster drug elimination due to a larger volume of distribution.

The size of a person also plays a role in drug dosing. 

      Overweight individuals may need higher drug doses to achieve the same therapeutic effect as someone with a lower body weight.

 

Environmental and Lifestyle Factors:

Lifestyle habits such as smoking, alcohol consumption, and diet can significantly influence how prescription drugs work. These factors can alter the body’s absorption, metabolism, and excretion processes.

       Diet: The food you eat can affect drug absorption. For instance, some foods may increase the absorption of certain drugs, while others (like grapefruit) can interfere with drug metabolism by inhibiting liver enzymes.

       Smoking: Smokers may metabolize drugs more quickly than non-smokers due to the induction of liver enzymes by chemicals in cigarette smoke. This means a smoker might need a higher dose of a medication to achieve the desired effect.

      Alcohol: Chronic alcohol use can alter liver function and increase the risk of liver toxicity with certain medications. Alcohol may also enhance or block the effects of drugs, leading to unpredictable outcomes.

 

Impact on Drug Metabolism:

Existing health conditions can also impact how medications work. People with chronic conditions like liver disease, kidney disease, heart conditions, or diabetes may have altered drug responses due to impaired organ function.

      Liver Disease: Since the liver is responsible for metabolizing many drugs, liver disease can cause a person to metabolize drugs more slowly, leading to increased drug levels in the bloodstream and a higher risk of toxicity.

      Kidney Disease: The kidneys are responsible for excreting many drugs from the body. Impaired kidney function may lead to drug accumulation and the potential for side effects.

     Heart Disease and Hypertension: These conditions can alter blood circulation, affecting how drugs are distributed throughout the body and influencing their effectiveness.

 

The Mechanism of Action:

Before we dive deeper into personalized medicine, it's crucial to understand how medications act in the body. Drugs generally work by interacting with specific molecules, enzymes, or receptors in the body. However, the way they are processed and the intensity of their effects can differ significantly between individuals.

 

Phases of Drug Action:

1.      Absorption

Mechanism: After administration, especially orally, a drug must cross cellular membranes to enter the bloodstream. This process depends on the drug's physicochemical properties, such as solubility and ionization. Lipophilic (fat-soluble) drugs easily pass through lipid-rich cell membranes, while hydrophilic (water-soluble) drugs may require transport proteins or channels.

2. Distribution

Mechanism: Once in the bloodstream, the drug distributes throughout the body. Factors influencing distribution include blood flow to tissues, the drug's affinity for tissue and plasma proteins, and the permeability of cell membranes. For instance, the blood-brain barrier restricts many drugs from entering the central nervous system unless they are sufficiently lipophilic.

3. Metabolism

Mechanism: The liver is the primary site for drug metabolism, where enzymes transform drugs into more water-soluble metabolites for excretion. This occurs in two phases:

Phase I (Functionalization Reactions): This step includes processes like oxidation, reduction, or hydrolysis, which help to either add or reveal certain chemical groups on the drug molecule. These changes make the drug easier for the body to handle. The cytochrome P450 enzyme family—especially CYP3A4—does most of this work.

Phase II (Conjugation Reactions): In this phase, the drug (or what’s left after Phase I) gets joined with natural substances in the body, like glucuronic acid or sulfate. This makes the drug more water-soluble, so it can be more easily removed from the body. 

4. Excretion

Mechanism: The kidneys primarily excrete drugs and their metabolites via urine. Other routes include bile (feces), sweat, saliva, and exhalation. The efficiency of excretion depends on factors like renal function and the drug's properties.

 

How Drugs Work at the Cellular Level:

Drugs act in the body by binding to specific receptors, interacting with enzymes, or altering the function of ion channels. These interactions can stimulate or block certain processes in the body, leading to therapeutic effects. However, genetic variations in receptors, enzymes, and other molecular targets can make a drug’s effect stronger or weaker, or even cause adverse reactions.

      Receptors: Drugs can bind to cell receptors, triggering a chain reaction that results in therapeutic effects (e.g., pain relief or lowering blood pressure).

     Enzymes: Some drugs work by inhibiting or activating enzymes that control biochemical pathways. For instance, statins lower cholesterol by blocking enzymes involved in cholesterol production.

     Ion Channels: Certain drugs influence ion channels that control the electrical activity of cells, impacting functions such as heart rhythm or nerve signaling.

 

Genetic Variability in Mechanisms of Action:

      Receptor Sensitivity: People with genetic variations in drug receptors may have more or fewer receptors available for drug binding, affecting the drug's potency and side effects.

     Enzyme Efficiency: Variations in metabolic enzymes like CYP450 affect how drugs are broken down, influencing how quickly they work and whether side effects occur.

     Ion Channel Function: Mutations in ion channel genes can make individuals more or less sensitive to drugs that affect those channels, such as antiarrhythmic drugs or antiepileptic drugs.

The Impact of Genomic Variations on Drug Responses:

This review article focuses on how genetic polymorphisms in drug-metabolizing enzymes, transporters, and receptors affect pharmacokinetics and pharmacodynamics. It highlights several well-known gene-drug interactions, such as CYP2C19 and clopidogrel, where genetic differences can significantly alter drug effectiveness.

  Key points

• Genetic variations in enzymes like CYP450 can lead to differences in drug metabolism.
•  Personalized dosing can reduce the risk of adverse drug reactions by accounting for genetic variations in drug metabolism.
•  CYP2C19 and its interaction with clopidogrel (a blood thinner) are a key example of genetic influence on drug efficacy.

  From:  https://pubmed.ncbi.nlm.nih.gov/

 

 

Real-Life Example: A Baby's Life Saved with Personalized Medicine

In a groundbreaking case, a baby named KJ Muldoon was diagnosed with a rare genetic disorder that caused dangerous ammonia buildup in his blood. Traditional treatments were not effective. Scientists developed a personalized gene-editing therapy using CRISPR technology to correct the specific genetic mutation causing the problem. After receiving this tailored treatment, KJ showed significant improvement, meeting developmental milestones and reducing his need for medication.

 

The Future of Personalized Medicine in Oncology

This review focuses on the role of genomic medicine in cancer care, including the use of biomarkers to predict which treatments will be most effective. It emphasizes the growing importance of targeted therapies, such as EGFR inhibitors for non-small cell lung cancer.

Key points

•  Genomic testing in cancer helps identify specific mutations, enabling targeted therapies that are more effective than traditional chemotherapy
• Biomarkers are increasingly being used to tailor cancer treatments, improving prognosis and reducing side effects.
• Next-generation sequencing is a critical tool for identifying mutations in cancer cells and guiding treatment decisions.

 From: https://www.researchgate.net/

 

 The Future of Personalized Medicine:

Healthcare is shifting toward precision medicine, with exciting innovations:

• Genomic Cancer Testing: Matches therapies to individual tumor profiles.
• AI and Machine Learning: Predicts drug responses from complex genetic data.
• Affordable Sequencing: Enables broader access to genomic insights.

"As this field evolves, we may soon see a future where prescriptions are as unique as our DNA."

Conclusions:

Personalized medicine, or the practice of characterizing an individual patient on several levels (genomic, biochemical, behavioral, etc.) that might shed light on their response to an intervention, and then treating them accordingly, is a necessity given the fact that clinically meaningful inter-individual variation has, and will continue to be, identified. The availability of modern biomedical technologies such as DNA sequencing, proteomics, and wireless monitoring devices has enabled the identification of this variation, essentially exposing the need for the personalization of medicine at some level.

 The future challenges associated with this reality will be to not only improve the efficiency in the way in which individuals are characterized, but also in the way in which personalized medicines are crafted and vetted to show their utility. This is not to say that interventions that work ubiquitously, i.e., the traditional single-agent blockbusters, should be ignored if identified, but rather that they might be very hard to identify going forward. There are a few other issues associated with personalized medicine that may be hard to overcome in the near term. 

For example, the need for large data collections to identify factors that discriminate groups of individuals that might benefit more from one or another intervention could create concerns about privacy and the data from those individuals possibly being used for nefarious purposes 81, 82, 83. Fortunately, this issue is not necessarily unique to health care settings, whether current or future, as it has plagued many other industries, including the banking, marketing, and social media industries. Strategies exploited in these other industries could be used in health care settings as well. In addition, developing more efficient ways of manufacturing and generating personalized medicines (for example, concerning cell replacement therapies or mutation-specific drugs that work for a small fraction of patients) is crucial to meet the demands of all patients. =

Conclusion From: https://www.sciencedirect.com/science/article/pii/S0015028218304072#sec6

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