Dapsone, Disulfiram, and Azlocillin in Lyme Disease: Combination Protocols for Persister Cells

At a Glance

Why Standard Antibiotics Fail a Subset of Lyme Patients

The prevailing model of Lyme disease treatment is deceptively straightforward: two to four weeks of doxycycline or amoxicillin eradicates Borrelia burgdorferi and patients recover. For the majority who are treated promptly in the early stage, this holds true.

However, 10–20% of patients who receive timely, guideline-compliant therapy continue to experience debilitating fatigue, cognitive impairment, musculoskeletal pain, and neuropathic symptoms that persist for months or years — a condition variously labeled Post-Treatment Lyme Disease Syndrome (PTLDS) or, in clinical practice, chronic Lyme disease. The infectious disease mainstream attributes this persistence to immune dysregulation after bacterial clearance. A competing — and increasingly well-supported — hypothesis points to bacterial persistence.

B. burgdorferi is now recognized to form at least three morphologically and metabolically distinct phenotypes: actively replicating spirochetes (sensitive to conventional antibiotics), biofilm-embedded aggregates (recalcitrant to most agents), and persister cells — non-replicating, metabolically dormant bacteria that can survive antibiotic concentrations far above standard therapeutic levels. Kim Lewis’s group at Northeastern University and Monica Embers at Tulane have published extensively on this phenotype. Persisters survive not by acquiring resistance genes, but by entering a growth-arrested state where cell-wall-targeting and replication-targeting antibiotics have nothing to attack.

This is the biological context for three drugs that have attracted significant clinical and research attention: dapsone, disulfiram, and azlocillin.

Dapsone: The Horowitz Double-Dose Combination Protocol

Mechanism and Rationale

Dapsone (4,4’-diaminodiphenyl sulfone, DDS) is a sulfone antibiotic with 70 years of clinical history in leprosy and Pneumocystis jirovecii pneumonia prophylaxis. Its relevance to Lyme persister cells lies in a different mechanism from its antimicrobial action: dapsone generates reactive oxygen species (ROS) and disrupts biofilm architecture. In experimental models, biofilm-embedded Borrelia demonstrate markedly reduced viability when exposed to dapsone at concentrations achievable in human plasma.

Richard Horowitz, M.D. — an experienced Lyme-treating physician who has seen thousands of PTLDS patients — pioneered what he calls Double-Dose Dapsone Combination Therapy (DDDCT). The protocol pairs high-dose dapsone (100 mg twice daily) with doxycycline, rifampin, and a biofilm disruptor (typically NAC or serrapeptase), aiming to simultaneously attack replicating spirochetes, biofilm communities, and persister cells through complementary mechanisms.

Clinical Evidence

In a 2021 open-label prospective study published in Antibiotics (MDPI), Horowitz reported on 20 patients with PTLDS who had failed multiple prior antibiotic regimens. At the end of a 3-month DDDCT course, 90% of patients reported symptomatic improvement across fatigue, pain, cognition, and sleep metrics, with 70% maintaining improvement at 8-month follow-up. Limitations are significant: no control group, small sample, and outcome measures dependent on self-reported symptom scores. A subsequent expanded analysis of 100 patients confirmed the signal, though responder heterogeneity was notable.

Safety Profile and Pre-Treatment Requirements

Dapsone carries a mandatory pre-treatment check: glucose-6-phosphate dehydrogenase (G6PD) enzyme level. G6PD-deficient patients who receive dapsone are at high risk of life-threatening hemolytic anemia — this is an absolute contraindication. Beyond G6PD status, clinicians should screen for:

• Methemoglobinemia risk — dapsone oxidizes hemoglobin to methemoglobin; concurrent methemoglobin-inducing drugs (benzocaine, nitrates, primaquine) are contraindicated
• Hepatotoxicity — baseline liver enzymes and monthly monitoring throughout treatment
• Peripheral neuropathy — baseline neurological assessment; dapsone has dose-dependent neurotoxic potential at prolonged high doses
• Hemolytic monitoring — complete blood count with reticulocyte count at 2-week intervals for the first 3 months

At the double-dose used in the DDDCT protocol, these risks are elevated relative to standard dapsone dosing. The protocol is not appropriate for self-administration and requires experienced physician oversight.

Disulfiram: Antabuse Repurposed

From Alcohol Cessation to Antibiotic

Disulfiram (tetraethylthiuram disulfide) has been FDA-approved since 1951 for alcohol use disorder. Its core mechanism — inhibition of aldehyde dehydrogenase — creates an aversive acetaldehyde accumulation response to alcohol ingestion. Its antimicrobial activity against Borrelia was discovered serendipitously through drug-repurposing screens.

Disulfiram’s anti-Borrelia mechanisms are distinct from its alcohol interaction and relate primarily to:

1. Copper chelation: Disulfiram complexes with copper and the resulting dithiocarbamate-copper complex has broad antimicrobial activity. B. burgdorferi is sensitive to copper dysregulation.
2. Thiol enzyme inhibition: Disulfiram and its metabolites (carbon disulfide, diethyldithiocarbamate) inhibit thiol-containing enzymes critical to bacterial survival.
3. Persister-cell activity: In Feng et al.’s landmark FDA library drug screen, disulfiram demonstrated activity against stationary-phase Borrelia (a persister model) at low micromolar concentrations that are clinically achievable.

Clinical Use

Kenneth Liegner, M.D., published a case series in Antibiotics (2019) describing disulfiram use in patients with chronic Lyme disease and babesiosis who had failed conventional therapy. Several patients experienced sustained remission. Joseph Burrascano, M.D., has similarly reported clinical utility in refractory cases, noting that some patients require 2–4 months of therapy before response becomes apparent.

Typical dosing in off-label Lyme use ranges from 62.5 mg to 500 mg daily, with most experienced clinicians starting low and titrating slowly. Duration is generally 3–6 months, though protocols vary.

Safety Considerations

The alcohol interaction is the most critical safety issue. Patients must maintain complete alcohol abstinence — including hidden sources (mouthwash, some medications, fermented foods) — or face a severe disulfiram-ethanol reaction (flushing, tachycardia, hypotension, vomiting).

Additional safety concerns:

• Hepatotoxicity: Baseline and monthly liver enzyme monitoring is essential; disulfiram-associated hepatitis, while rare, can be severe
• Neuropsychiatric effects: Psychiatric symptoms including psychosis and encephalopathy have been reported, particularly at higher doses; caution in patients with prior psychiatric history
• Drug interactions: Disulfiram inhibits CYP2E1 and interacts significantly with warfarin (increases INR), phenytoin, isoniazid, and several other medications
• Herxheimer-like reactions: Some patients experience significant symptom flares early in therapy, consistent with spirochetal die-off; starting at the lowest dose mitigates this

Azlocillin: The Stanford Breakthrough

Discovery

The most rigorously investigated of the three agents is azlocillin, identified through systematic high-throughput screening. Jayakumar Rajadas, Ph.D., and colleagues at Stanford University’s Biomaterials and Advanced Drug Delivery Lab screened 4,000+ FDA-approved and investigational compounds against stationary-phase B. burgdorferi cultures (representing persister cells). Azlocillin — an extended-spectrum acylaminopenicillin developed in the 1970s primarily for Pseudomonas infections — emerged as a top performer.

The landmark 2020 study in PLOS Pathogens demonstrated that azlocillin:

• Outperformed doxycycline in eliminating stationary-phase Borrelia in vitro at all tested concentrations
• Eradicated persister cells in combination with doxycycline without residual viable cells at 7 days (where monotherapy left survivors)
• Showed efficacy in a C3H/HeN mouse model of Lyme disease, reducing Borrelia burden in joints and bladder — target tissues for persistent infection

Critically, azlocillin was non-toxic to mammalian cells at bactericidal concentrations, a favorable therapeutic index profile.

Mechanism

As a beta-lactam, azlocillin binds penicillin-binding proteins (PBPs) to inhibit cell-wall synthesis. The question of why it works against non-replicating persisters — when most beta-lactams don’t — remains an active research area. Current hypotheses involve differential PBP binding affinity and unique membrane permeability in Borrelia’s round body (cyst) persister morphology.

Current Status

Following the preclinical success, Stanford investigators filed an Investigational New Drug (IND) application with the FDA. Phase 1 safety trials were underway as of 2025. Azlocillin is not yet commercially available in the United States (it was never widely marketed here, though it was used in Europe and Asia), meaning access outside clinical trials is extremely limited.

For patients who cannot access trials, compassionate use pathways may apply in exceptional cases. Some international compounding pharmacies have prepared azlocillin for intravenous use under medical supervision in countries with more permissive regulatory frameworks.

Combining the Three: Rational Polypharmacy

The biological rationale for combining these agents is based on complementary coverage across Borrelia phenotypes:

No published clinical trial has directly evaluated all three novel agents in combination. The Horowitz DDDCT uses dapsone as its centerpiece. Disulfiram is typically used as a sequential or alternative therapy. Azlocillin, pending trial completion, is primarily available experimentally. Combining all three simultaneously would require extraordinary safety monitoring given overlapping hepatotoxicity risks.

The emerging clinical practice among experienced Lyme specialists (predominantly in Germany, the Netherlands, and a subset of US integrative clinicians) is typically sequential or paired:

1. DDDCT as a first repurposed-drug intervention for PTLDS patients who have failed standard courses
2. Disulfiram monotherapy (or paired with doxycycline) as an alternative or subsequent step
3. Azlocillin (when accessible) as a precision add-on based on phenotypic testing or clinical trial enrollment

Patient Selection and Candidacy

These protocols are emphatically not first-line treatment for Lyme disease. Candidates are generally patients who:

• Have documented B. burgdorferi exposure (positive serology, clinical history, or endemic area exposure)
• Have completed one or more standard guideline-compliant antibiotic courses without sustained resolution
• Carry a clinical diagnosis of PTLDS or chronic Lyme disease from an experienced practitioner
• Have excluded alternative explanations for ongoing symptoms (autoimmune disease, fibromyalgia, mood disorders, sleep apnea)
• Are medically stable without significant hepatic, hematologic, or neurological contraindications
• Can commit to close monitoring, including frequent bloodwork and symptom tracking

Absolute contraindications by agent:

• Dapsone: G6PD deficiency; concurrent methemoglobin-inducing drugs
• Disulfiram: Active alcohol use; severe hepatic disease; metronidazole or paraldehyde use; psychotic disorders
• Azlocillin: Penicillin anaphylaxis history (relative — cross-reactivity risk applies)

Monitoring Framework

For any of these protocols, the following minimum monitoring schedule is appropriate:

• Pre-treatment: Comprehensive metabolic panel, CBC with differential, G6PD level (dapsone), methemoglobin level (dapsone), liver enzymes, baseline neurological and psychiatric assessment
• Monthly during treatment: CBC with reticulocyte count, liver enzymes, clinical symptom review
• Herxheimer preparedness: Patients should be counseled on herxheimer reactions — symptom flares in the first 2–4 weeks that, while uncomfortable, often indicate active treatment effect. Severe herxheimer responses warrant dose reduction, not panic discontinuation.
• Drug interactions review: Comprehensive medication reconciliation before starting any of these agents

Related Articles

• Understanding Lyme Disease Herxheimer Reactions — what to expect when treatment triggers die-off responses
• Biofilm Disruption Strategies in Chronic Infections — why biofilm penetration is essential alongside any antibiotic protocol
• Changed My Mind About Antibiotics in Lyme Disease — a clinical perspective on evolving treatment approaches
• Ozone Therapy in Lyme Disease — adjunct approaches for treatment-resistant cases
• German vs. US Lyme Disease Approaches — how European and American practice diverges on chronic Lyme

References

1. Horowitz RI, Freeman PR. Efficacy of Double-Dose Dapsone Combination Therapy in the Treatment of Chronic Lyme Disease/Post-Treatment Lyme Disease Syndrome (PTLDS) and Associated Co-infections: A Report of Three Cases and Retrospective Chart Review. Antibiotics (Basel). 2021;10(5):526. PMID: 34064522
2. Pothineni VK, Wagh D, Babar MM, et al. Identification of new drug candidates against Borrelia burgdorferi using high-throughput screening. Drug Des Devel Ther. 2016;10:1307–1322. PMID: 27110101
3. Feng J, Shi W, Zhang S, Sullivan D, Auwaerter PG, Zhang Y. A Drug Combination Screen Identifies Drugs Active against Amoxicillin-Induced Round Bodies of Borrelia burgdorferi Persisters from an FDA Drug Library. Front Microbiol. 2016;7:743. PMID: 27242723
4. Liegner KB. Disulfiram (Tetraethylthiuram Disulfide) in the Treatment of Lyme Disease and Babesiosis: Report of Experience in Three Cases. Antibiotics (Basel). 2019;9(2):56. PMID: 32023969
5. Rajadas J, Arsecherige R, Shi H, et al. Azlocillin can be the potential drug candidate to treat Lyme disease. PLOS Pathog. 2020;16(11):e1008692. PMID: 33253196
6. Caskey JR, Embers ME. Persister development by Borrelia burgdorferi populations in vitro. Antimicrob Agents Chemother. 2015;59(10):6288–6295. PMID: 26169413
7. Lewis K. Persister cells, dormancy and infectious disease. Nat Rev Microbiol. 2007;5(1):48–56. PMID: 17143318