Which drugs are cleared by dialysis? Understanding the factors influencing dialyzability

October 13, 2025 •

4 min read

Over 2 million people worldwide receive dialysis treatment for kidney disease, making it a critical consideration for managing chronic conditions. For these patients, understanding which drugs are cleared by dialysis is essential for ensuring medication efficacy and preventing toxicity. The dialyzability of a medication is influenced by its specific physical and chemical properties.

Quick Summary

This article explores the pharmacokinetic principles that determine a drug's dialyzability, including its molecular weight, protein binding, and volume of distribution. We provide examples of medications that are significantly cleared during dialysis and those that are not, highlighting the critical role of careful medication management for patients with kidney failure.

Key Points

Low Molecular Weight: Drugs with smaller molecules are more easily cleared by dialysis as they can pass through the membrane pores.
High Protein Binding Reduces Dialyzability: Drugs that are extensively bound to plasma proteins are less likely to be removed during dialysis, as only the unbound fraction is filterable.
Large Volume of Distribution Impedes Clearance: Medications that distribute widely into body tissues rather than remaining in the bloodstream are poorly cleared by dialysis.
Dosing Timing is Crucial: Dosing for highly dialyzable drugs is often adjusted to be administered after a dialysis session to maintain therapeutic levels.
Dialysis Membrane Matters: Modern high-flux dialysis membranes can clear some larger molecules more effectively than older membranes.
Common Examples Exist: Specific examples like lithium and certain antibiotics (e.g., amoxicillin) are dialyzable, while others like digoxin and many psychiatric medications are not.

For patients with end-stage renal disease (ESRD), dialysis is a life-sustaining treatment that removes waste products and excess fluid from the blood. However, this process can also inadvertently remove certain medications from the body, affecting their therapeutic levels. Understanding the principles of drug dialyzability is crucial for healthcare providers and patients alike to prevent subtherapeutic dosing or drug accumulation.

Factors Determining Which Drugs are Cleared by Dialysis

The extent to which a drug is removed during dialysis, known as its dialyzability, depends on a combination of the drug's inherent properties and the technical specifications of the dialysis procedure. A detailed understanding of these factors allows clinicians to make necessary dose adjustments.

Molecular Weight

One of the most predictable factors affecting dialyzability is the drug's molecular weight (MW). The dialysis membrane, or dialyzer, acts as a filter with specific pore sizes.

Smaller molecules: Drugs with a low molecular weight (typically less than 500 Da) are able to pass through the pores of the dialysis membrane easily and are therefore more dialyzable.
Larger molecules: Drugs with a higher molecular weight may be too large to pass through the membrane and are poorly dialyzed, if at all.

Protein Binding

In the bloodstream, many drugs bind to plasma proteins, such as albumin. This binding significantly impacts dialyzability.

Unbound drugs: Only the unbound, or "free," fraction of a drug can pass through the dialysis membrane.
Highly protein-bound drugs: Drugs that are highly bound to protein are not efficiently removed by dialysis because the bound molecules are too large to cross the membrane. For example, drugs with more than 94% protein binding are not significantly cleared.

Volume of Distribution

Volume of distribution ($V_d$) is a theoretical measure of how widely a drug distributes throughout the body's tissues. It indicates whether the drug remains primarily in the bloodstream or disperses into other tissues.

Low $V_d$: Drugs with a small volume of distribution remain largely within the plasma, making them more accessible to the dialysis filter and thus more dialyzable.
High $V_d$: Drugs with a large volume of distribution are widely distributed in the tissues and have low concentrations in the blood. This makes them poorly dialyzable, as only a small fraction is available to be filtered.

Dialysis Procedure and Membrane Characteristics

Modern high-flux dialysis membranes are more permeable and have larger pore sizes than older, low-flux membranes, which can increase the dialyzability of larger molecules. Dialysate and blood flow rates, as well as treatment duration, also influence drug clearance.

Examples of Dialyzable and Non-Dialyzable Drugs

Dialyzable Medications

1. Antibiotics: Many beta-lactam antibiotics are low molecular weight and have low protein binding, making them highly dialyzable. Examples include:

Amoxicillin
Cefepime
Vancomycin (clearance can vary based on membrane type)

2. Cardiac Medications: Some cardiac drugs are significantly cleared, requiring careful timing or dose adjustment.

Atenolol and Metoprolol (certain beta-blockers)
Lisinopril (ACE inhibitor)
Sotalol (antiarrhythmic)

3. Overdose/Toxin Clearance: Dialysis is often used as a treatment for overdoses involving substances with properties favorable for clearance.

Lithium
Salicylates (aspirin)
Ethylene glycol and methanol

Non-Dialyzable Medications

1. Antibiotics: Some antibiotics are highly protein-bound or have a large volume of distribution, limiting their removal.

Rifampin and Isoniazid (antituberculosis drugs)
Ceftriaxone
Clindamycin

2. Cardiac Medications: Many cardiovascular drugs are not significantly removed due to high protein binding and large $V_d$.

Carvedilol (beta-blocker)
Digoxin (cardiac glycoside)
Calcium Channel Blockers (e.g., amlodipine)

3. Psychotropic Medications: Many psychiatric medications are poorly cleared due to their lipophilic nature, high protein binding, and large $V_d$.

SSRIs (e.g., most antidepressants)
Amitriptyline (tricyclic antidepressant)
Haloperidol (antipsychotic)

Comparing Dialyzable vs. Non-Dialyzable Drugs


Characteristic	Dialyzable Drugs	Non-Dialyzable Drugs
Molecular Weight	Typically low (< 500 Da)	Often high (> 500 Da)
Protein Binding	Low to moderate (< 80%)	High (> 90%)
Volume of Distribution ($V_d$)	Small	Large
Route of Elimination	Significant renal clearance	Significant non-renal clearance (e.g., hepatic metabolism)
Typical Dosing Adjustment	Often requires post-dialysis dosing or reduced dosage	Little to no dose adjustment needed for dialysis

Conclusion

For patients on dialysis, the dynamic relationship between a drug's pharmacokinetic properties and the dialysis process is a crucial element of care. The dialyzability of a medication, determined by factors like molecular weight, protein binding, and volume of distribution, dictates whether a dose adjustment or specific timing is necessary. High-flux modern dialyzers have changed the landscape, but the core principles remain. Patients and their healthcare teams must maintain open communication and regularly review medication lists to ensure optimal therapeutic outcomes and avoid complications associated with inappropriate drug levels. Accurate and up-to-date prescribing information is essential for tailoring drug regimens to each patient's needs.

Medication Management in Dialysis

Managing medications in patients on dialysis is a complex task that requires constant vigilance and close collaboration with a healthcare team, including a nephrologist and pharmacist. Key considerations include:

Timing of Doses: Dosing for dialyzable drugs is often timed to occur after a dialysis session to prevent the medication from being immediately cleared.
Dose Reduction: For dialyzable drugs, doses may need to be significantly reduced to compensate for the decreased clearance in patients with kidney failure.
Monitoring Drug Levels: For certain medications, therapeutic drug monitoring may be necessary to ensure that concentrations remain within a safe and effective range.
Avoiding Nephrotoxic Drugs: Even though kidneys are failing, certain drugs can still have toxic effects. Nephrotoxic medications should be avoided or used with extreme caution.

The Role of the Pharmacist

Pharmacists with expertise in nephrology are invaluable members of the dialysis care team. They can provide essential services, including:

Conducting monthly medication reviews.
Creating up-to-date medication lists.
Assisting with medication reconciliation during transitions of care.
Providing patient education on how to manage their complex medication regimens.

By staying informed and working together, patients and healthcare providers can navigate the challenges of medication management on dialysis, improving patient safety and quality of life.

Frequently Asked Questions

The primary principle is filtration based on the drug's physical and chemical properties. Small, water-soluble drugs that are not heavily bound to plasma proteins are more easily filtered by the dialysis membrane.

Highly protein-bound drugs are poorly dialyzed because only the free, unbound fraction of the drug can pass through the membrane. The protein-drug complex is too large to be filtered out.

No, not all antibiotics. While many beta-lactam antibiotics are dialyzable and require adjustment, others that are highly protein-bound or undergo non-renal elimination, such as rifampin and doxycycline, do not require significant dose changes.

A drug's volume of distribution ($V_d$) indicates where it resides in the body. Drugs with a large $V_d$ are distributed widely in the tissues, leaving only a small amount in the bloodstream to be cleared during dialysis. Therefore, drugs with a large $V_d$ are poorly dialyzable.

It varies widely. Some beta-blockers, like atenolol, are significantly cleared, while others, like carvedilol, are not. Digoxin, a cardiac glycoside, is also not typically removed by dialysis.

The healthcare team, including the nephrologist and pharmacist, will determine the correct dose and timing for the medication. For dialyzable drugs, doses may be administered after a dialysis session to ensure effectiveness.

Yes, lithium is a low molecular weight, water-soluble substance with a small volume of distribution, making it highly dialyzable. Dialysis is a key treatment for lithium toxicity.