Many patients have asked the same question: Why can someone else take a medication exactly as instructed on the label, while I am told to reduce the dose, extend the dosing interval, or even switch to a different drug?

The answer is that medication dosing is not a one-size-fits-all approach. Standard dosages are typically established based on adults with normal liver and kidney function. For patients with hepatic or renal impairment, however, even commonly used medications such as cold remedies, antibiotics, or antihypertensive drugs may require dose adjustments and individualized treatment plans.

The reason lies in the fact that the liver and kidneys are the body’s most important organs for drug metabolism and elimination. When either organ’s function declines, the way medications are processed, cleared, and retained in the body changes significantly. Continuing to use standard doses under these circumstances may increase the risk of drug accumulation and adverse reactions.

Therefore, dose adjustment in patients with liver or kidney dysfunction has become a key component of safe medication use, clinical pharmacy, and precision medicine.

---

I. What Roles Do the Liver and Kidneys Play in Drug Metabolism?

After a medication enters the body, it generally undergoes four major pharmacokinetic processes:

• Absorption
• Distribution
• Metabolism
• Excretion

Collectively, these processes are known as pharmacokinetics (ADME).

Among these organs:

• The liver is the body’s primary drug-metabolizing organ.
• The kidneys are responsible for eliminating most drugs and their metabolites.

Under normal physiological conditions, medications follow a balanced cycle of absorption, action, metabolism, and elimination, allowing blood drug concentrations to remain within a safe and therapeutic range.

However, once liver or kidney function declines, this balance is disrupted. Drug clearance slows, blood concentrations rise, and medications remain in the body much longer than expected.

As a result, the same standard dosage may no longer be safe.

---

II. Why Does Liver Impairment Require Dose Adjustments?

The liver is often described as the body’s largest “chemical factory.” Many medications must first be metabolized by the liver before they can be inactivated or eliminated.

When patients develop conditions such as:

• Chronic hepatitis
• Liver cirrhosis
• Fatty liver disease
• Liver failure

their ability to metabolize medications may decrease significantly.

This can lead to several important consequences.

1. Slower Drug Clearance

Reduced hepatic metabolism means medications remain in circulation for a longer period, causing higher plasma drug concentrations.

Even standard doses may gradually accumulate after repeated administration.

2. Increased Risk of Drug Accumulation

Many drugs depend heavily on hepatic metabolism.

When metabolism slows, medications cannot be eliminated efficiently, increasing the likelihood of:

• Excessive drug exposure
• Drug toxicity
• Serious adverse reactions

3. Altered Drug Efficacy

Some medications are actually prodrugs, meaning they require liver metabolism before becoming therapeutically active.

If liver function is severely impaired, these drugs may not be adequately activated, reducing their clinical effectiveness despite normal dosing.

4. Additional Burden on the Liver

Certain medications possess inherent hepatotoxicity.

Examples include some:

• Antibiotics
• Antituberculosis drugs
• Antifungal medications
• Anticancer agents
• Herbal medicines

Long-term or high-dose administration may further aggravate existing liver injury.

Therefore, physicians usually individualize treatment according to:

• Severity of liver disease
• Liver function laboratory tests
• Drug metabolism characteristics
• Expected treatment duration
• Overall patient condition

Rather than relying solely on the dosage recommended in the package insert, clinicians evaluate whether dose reduction, interval extension, or medication replacement is necessary to maximize efficacy while minimizing toxicity.

---

III. Why Are Patients with Kidney Impairment More Prone to Drug Accumulation?

If the liver is responsible for processing medications, the kidneys are responsible for clearing them.

A large proportion of drugs and their metabolites are eliminated through renal excretion. When kidney function declines, this elimination process slows significantly.

Common causes of impaired renal function include:

• Chronic kidney disease (CKD)
• Diabetic nephropathy
• Hypertensive nephropathy
• Acute kidney injury (AKI)

As kidney function deteriorates, the glomerular filtration rate (GFR) decreases, reducing the body’s ability to eliminate medications.

Several important consequences may follow.

1. Retention of Drugs and Metabolites

Medications that are normally eliminated through urine remain in the body much longer.

Repeated dosing may gradually increase blood drug concentrations beyond the intended therapeutic range.

2. Increased Risk of Drug Toxicity

Patients with renal impairment are more susceptible to adverse effects from medications such as:

• Certain antibiotics
• Antidiabetic medications
• Anticoagulants
• Antiviral agents
• Some chemotherapy drugs

Without appropriate dose adjustment, toxicity may develop even when standard doses are prescribed.

3. Higher Risk of Electrolyte Imbalances

Some medications influence the body’s regulation of:

• Potassium
• Sodium
• Magnesium
• Body fluids

When kidney function is impaired, these electrolyte disturbances may become more severe, increasing the risk of cardiac arrhythmias and other complications.

4. Prolonged Drug Half-Life

Drug half-life refers to the time required for the blood concentration of a medication to decrease by half.

When renal clearance declines, a medication that normally remains in the body for only several hours may persist for much longer.

A prolonged half-life often requires:

• Lower individual doses
• Longer dosing intervals
• More frequent monitoring

For this reason, evaluation of kidney function has become an essential step before prescribing many commonly used medications.

---

IV. Why Do Older Adults Require Special Attention?

Older adults represent one of the largest populations affected by declining liver and kidney function.

As people age, several physiological changes naturally occur:

• Hepatic blood flow gradually decreases.
• Drug-metabolizing enzyme activity declines.
• Glomerular filtration rate decreases.
• Overall drug clearance becomes less efficient.

These age-related changes mean that medications remain in the body longer than they would in younger adults.

At the same time, many elderly patients live with multiple chronic diseases, including:

• Hypertension
• Diabetes mellitus
• Coronary artery disease
• Chronic kidney disease
• Osteoarthritis and other musculoskeletal disorders

As a result, long-term use of multiple medications has become increasingly common.

Polypharmacy Increases Medication Risks

The use of multiple medications—commonly referred to as polypharmacy—substantially increases the likelihood of:

• Drug-drug interactions
• Drug accumulation
• Adverse drug reactions
• Medication errors
• Hospitalization related to medication problems

Studies have consistently shown that the risk of adverse drug events rises as the number of medications increases.

For older adults, medication management therefore extends beyond selecting the correct drug. Physicians and pharmacists must also evaluate:

• Organ function
• Existing medical conditions
• Potential drug interactions
• Overall medication burden
• Functional status

Individualized dosing has become one of the cornerstones of geriatric medicine.

Because every older patient presents a unique combination of physiological changes and chronic diseases, treatment plans should be regularly reviewed and adjusted to maintain both safety and therapeutic effectiveness.

---

V. How Are Dose Adjustments Made in Clinical Practice?

Dose adjustment does not simply mean prescribing less medication. Instead, clinicians evaluate multiple patient-specific factors before determining the most appropriate treatment regimen.

Important considerations include:

• Liver function parameters (ALT, AST, bilirubin, albumin, etc.)
• Kidney function parameters (eGFR, serum creatinine, creatinine clearance)
• Drug metabolism and elimination characteristics
• Patient age and body weight
• Comorbidities
• Treatment goals
• Potential drug-drug interactions

Based on these assessments, physicians may adopt one or more of the following strategies.

1. Reducing the Dose

For medications that are eliminated more slowly, decreasing the amount administered each time can help maintain safe drug concentrations.

For example:

• 100 mg → 50 mg
• 20 mg → 10 mg

Lower doses may reduce the risk of toxicity while maintaining therapeutic effectiveness.

2. Extending the Dosing Interval

In some situations, the dose remains unchanged, but the interval between doses is increased.

Examples include:

• Twice daily → Once daily
• Every 24 hours → Every 48 hours

This strategy allows additional time for the body to eliminate the medication before the next dose.

3. Selecting Alternative Medications

Some drugs rely heavily on hepatic metabolism or renal excretion, whereas others do not.

When appropriate, clinicians may choose medications that:

• Have less hepatic metabolism
• Are minimally eliminated through the kidneys
• Present a lower risk of organ toxicity

Changing to a safer alternative can often reduce medication-related complications.

4. Ongoing Monitoring

Dose adjustment is not a one-time decision.

Patients with liver or kidney impairment often require regular follow-up assessments, including:

• Liver function tests
• Kidney function tests
• Blood electrolyte monitoring
• Therapeutic drug monitoring (when applicable)

Treatment plans should be adjusted whenever laboratory results or clinical conditions change.

Individualized medication management is therefore a dynamic process rather than a fixed prescription.

---

Conclusion

The standard dosage printed on a medication label is generally established for adults with normal liver and kidney function. It should not be assumed to be appropriate for every patient.

In individuals with hepatic or renal impairment, drug metabolism and elimination may change substantially. Continuing to use standard doses without considering organ function can increase the risk of drug accumulation, adverse reactions, and treatment-related toxicity while potentially reducing therapeutic effectiveness.

For this reason, assessment of liver and kidney function, individualized dose adjustment, and continuous medication monitoring have become fundamental principles of modern precision medicine.

As clinical pharmacy, pharmacogenomics, and intelligent prescribing technologies continue to evolve, individualized dosing strategies are becoming increasingly important in improving medication safety and optimizing therapeutic outcomes.

As a professional platform focused on global pharmaceutical information and medication management, DengYueMed continues to monitor advances in rational drug use, precision medicine, and patient safety. By sharing the latest developments in clinical pharmacy and evidence-based medication management, DengYueMed aims to help healthcare professionals and patients better understand individualized therapy while promoting safer and more effective medication use worldwide.