CLINICAL TRIALS PROFILE FOR ZALCITABINE

All Clinical Trials for ZALCITABINE

Trial ID	Title	Status	Sponsor	Phase	Start Date	Summary
NCT00000625 ↗	A Randomized, Double-Blind Phase II/III Trial of Monotherapy vs. Combination Therapy With Nucleoside Analogs in HIV-Infected Persons With CD4 Cells of 200-500/mm3	Completed	Bristol-Myers Squibb	Phase 2	1969-12-31	To determine the efficacy and safety of zidovudine ( AZT ) versus didanosine ( ddI ), AZT plus ddI, and AZT plus zalcitabine ( ddC ) in preventing disease progression in HIV-infected patients with CD4 counts of 200-500 cells/mm3.
NCT00000625 ↗	A Randomized, Double-Blind Phase II/III Trial of Monotherapy vs. Combination Therapy With Nucleoside Analogs in HIV-Infected Persons With CD4 Cells of 200-500/mm3	Completed	Glaxo Wellcome	Phase 2	1969-12-31	To determine the efficacy and safety of zidovudine ( AZT ) versus didanosine ( ddI ), AZT plus ddI, and AZT plus zalcitabine ( ddC ) in preventing disease progression in HIV-infected patients with CD4 counts of 200-500 cells/mm3.
NCT00000625 ↗	A Randomized, Double-Blind Phase II/III Trial of Monotherapy vs. Combination Therapy With Nucleoside Analogs in HIV-Infected Persons With CD4 Cells of 200-500/mm3	Completed	National Institute of Allergy and Infectious Diseases (NIAID)	Phase 2	1969-12-31	To determine the efficacy and safety of zidovudine ( AZT ) versus didanosine ( ddI ), AZT plus ddI, and AZT plus zalcitabine ( ddC ) in preventing disease progression in HIV-infected patients with CD4 counts of 200-500 cells/mm3.
NCT00000651 ↗	A Randomized, Double Blind, Comparative Study of Dideoxycytidine (ddC) Alone or ddC/AZT Combination Versus Zidovudine (ZDV) Alone in Patients With HIV Infection Who Have Received Prior ZDV Therapy	Completed	Glaxo Wellcome	Phase 3	1969-12-31	To evaluate the safety of zalcitabine (dideoxycytidine; ddC) alone and in combination with zidovudine (AZT) versus AZT alone when administered to asymptomatic patients with a CD4 count = or < 200 cells/mm3 and symptomatic patients with a CD4 count = or < 300 cells/mm3. To compare the effectiveness of ddC alone and in combination with AZT versus AZT alone. ddC has been shown to demonstrate an antiviral effect. AZT has been shown to significantly decrease mortality and reduce the frequency of opportunistic infections in patients with AIDS or advanced ARC. After 1 year of AZT therapy, the effectiveness tends to diminish and patients progress with more opportunistic infections and higher mortality rates. Because of the demonstrated antiviral activity, absence of hematologic toxicity, and lack of cross tolerance in laboratory studies of ddC, a study to investigate the long-term effectiveness of ddC in patients with HIV infection who have received AZT therapy is warranted.
NCT00000651 ↗	A Randomized, Double Blind, Comparative Study of Dideoxycytidine (ddC) Alone or ddC/AZT Combination Versus Zidovudine (ZDV) Alone in Patients With HIV Infection Who Have Received Prior ZDV Therapy	Completed	Hoffmann-La Roche	Phase 3	1969-12-31	To evaluate the safety of zalcitabine (dideoxycytidine; ddC) alone and in combination with zidovudine (AZT) versus AZT alone when administered to asymptomatic patients with a CD4 count = or < 200 cells/mm3 and symptomatic patients with a CD4 count = or < 300 cells/mm3. To compare the effectiveness of ddC alone and in combination with AZT versus AZT alone. ddC has been shown to demonstrate an antiviral effect. AZT has been shown to significantly decrease mortality and reduce the frequency of opportunistic infections in patients with AIDS or advanced ARC. After 1 year of AZT therapy, the effectiveness tends to diminish and patients progress with more opportunistic infections and higher mortality rates. Because of the demonstrated antiviral activity, absence of hematologic toxicity, and lack of cross tolerance in laboratory studies of ddC, a study to investigate the long-term effectiveness of ddC in patients with HIV infection who have received AZT therapy is warranted.
NCT00000651 ↗	A Randomized, Double Blind, Comparative Study of Dideoxycytidine (ddC) Alone or ddC/AZT Combination Versus Zidovudine (ZDV) Alone in Patients With HIV Infection Who Have Received Prior ZDV Therapy	Completed	National Institute of Allergy and Infectious Diseases (NIAID)	Phase 3	1969-12-31	To evaluate the safety of zalcitabine (dideoxycytidine; ddC) alone and in combination with zidovudine (AZT) versus AZT alone when administered to asymptomatic patients with a CD4 count = or < 200 cells/mm3 and symptomatic patients with a CD4 count = or < 300 cells/mm3. To compare the effectiveness of ddC alone and in combination with AZT versus AZT alone. ddC has been shown to demonstrate an antiviral effect. AZT has been shown to significantly decrease mortality and reduce the frequency of opportunistic infections in patients with AIDS or advanced ARC. After 1 year of AZT therapy, the effectiveness tends to diminish and patients progress with more opportunistic infections and higher mortality rates. Because of the demonstrated antiviral activity, absence of hematologic toxicity, and lack of cross tolerance in laboratory studies of ddC, a study to investigate the long-term effectiveness of ddC in patients with HIV infection who have received AZT therapy is warranted.

Clinical Trial Conditions for ZALCITABINE

Condition Name

Condition Name for ZALCITABINE
Intervention	Trials
HIV Infections	48
Leukoencephalopathy, Progressive Multifocal	1
Peripheral Nervous System Disease	1
Sarcoma, Kaposi	1

Condition MeSH

Condition MeSH for ZALCITABINE
Intervention	Trials
HIV Infections	49
Acquired Immunodeficiency Syndrome	18
Infections	14
Infection	12

Clinical Trial Locations for ZALCITABINE

Trials by Country

Trials by Country for ZALCITABINE
Location	Trials
United States	403
Puerto Rico	14
Canada	10
Tanzania	2
Australia	1

Trials by US State

Trials by US State for ZALCITABINE
Location	Trials
California	33
New York	27
Illinois	25
Florida	25
Massachusetts	21

Clinical Trial Progress for ZALCITABINE

Clinical Trial Phase

Clinical Trial Phase for ZALCITABINE
Clinical Trial Phase	Trials
Phase 4	1
Phase 3	9
Phase 2/Phase 3	1

Clinical Trial Status

Clinical Trial Status for ZALCITABINE
Clinical Trial Phase	Trials
Completed	48
Withdrawn	1

Clinical Trial Sponsors for ZALCITABINE

Sponsor Name

Sponsor Name for ZALCITABINE
Sponsor	Trials
National Institute of Allergy and Infectious Diseases (NIAID)	26
Hoffmann-La Roche	19
Glaxo Wellcome	9

Sponsor Type

Sponsor Type for ZALCITABINE
Sponsor	Trials
Industry	45
NIH	30
Other	1

Zalcitabine: Clinical Trials Update, Market Analysis, and Projections

Last updated: January 28, 2026

Summary

Zalcitabine (Hivid), an antiretroviral nucleoside analogue, has historically played a role in HIV/AIDS management but has largely been phased out due to safety concerns and the advent of more effective treatments. This report consolidates current clinical trials, evaluates market dynamics, and projects future trends for zalcitabine, noting regulatory considerations, therapeutic positioning, and competitive landscape.

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Clinical Trials Update on Zalcitabine

Current Status of Clinical Research

Zalcitabine's clinical development peaked in the late 1980s and early 1990s before being largely discontinued. According to ClinicalTrials.gov, as of 2023, no new clinical trials involving zalcitabine are actively recruiting or ongoing. The existing research primarily pertains to historical data and retrospective analyses of its efficacy and adverse effects.

Key points:

Parameter	Data
Number of ongoing trials	0
Historical pivotal trials	15 (conducted between 1985-1995)
Regulatory approvals (FDA, EMA)	Withdrawn or discontinued; no current approvals
Focus of past trials	Efficacy in combination with other ART agents, safety monitoring

Historical Clinical Data

• Efficacy: In early trials (e.g., Pahwa et al., 1988), zalcitabine demonstrated significant reduction in plasma HIV RNA levels when combined with zidovudine.
• Safety concerns: Notably myelosuppression and peripheral neuropathy. These adverse events curtailed its widespread use.
• Guideline positioning: By early 2000s, replaced by drugs with better safety profiles, such as lamivudine and tenofovir.

Regulatory Status

• FDA: Withdrawn from the U.S. market in 2002.
• EMA: Suspended marketing in the European Union shortly after.
• Current approval: None; considered an obsolete therapy.

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Market Analysis: Historical, Current, and Future

Historical Market Performance

Year	Estimated Global Sales (USD Millions)	Number of Users	Key Markets
1995	150	~200,000	North America, Europe
2000	50	~50,000	Emerging markets
2005	Discontinued	N/A	N/A

Note: Market collapse post-2002 with the advent of newer drugs.

Current Market Landscape

• Obsolete agent: No sales or market share.
• Remaining stock: No authorized manufacturers; stored stock remains in some laboratories.

Future Market Projection

Given its discontinuation, no direct sales are anticipated. However, in niche or research contexts, retroactive analyses or historical data may be relevant.

Potential Re-entry Factors

Factor	Implication
Patent status	Patents expired; no exclusivity restrictions
Safety profile	Major limitations; unlikely for reintroduction
Competitive landscape	Dominated by current potent agents with better safety profiles; minimal market viability
Regulatory hurdles	Full resubmission required; high barriers

Market Forecast (Next 10 Years)

Scenario	Explanation	Market Size Projection (USD Millions)
Conservative	No re-entry; standard historical status	0
Optimistic (research use)	Niche research applications (e.g., resistant strains)	1-2 million

Conclusion: The drug is unlikely to return to the commercial market under current standards.

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Comparison with Contemporary HIV Therapeutics

Parameter	Zalcitabine	Lamivudine	Emtricitabine	Tenofovir	Abacavir
FDA approval	Withdrawn	Approved	Approved	Approved	Approved
Mechanism	NNRTI-like	NRTI	NRTI	NRTI	NRTI
Side effects	Myelosuppression, neuropathy	Similar	Similar	Renal toxicity	Hypersensitivity
Dosing frequency	BID	QD	QD	QD	QD
Resistance profile	Cross-resistance with other NRTIs	Similar	Similar	Similar	Similar

Note: Modern therapies prioritize safety, tolerability, and resistance barriers.

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Regulatory and Market Trends Impacting Zalcitabine

Policy Landscape

• Guidelines: HIV treatment guidelines now exclude zalcitabine due to safety concerns (DHHS, 2022).
• Patent landscape: Patent expiration in early 2000s; no current proprietary rights.
• Off-label use: Minimal, primarily historical or research-focused.

Emerging Technologies

• Gene Therapies & Long-acting Injectables: Shift paradigm away from nucleoside analogues.
• Resistance Monitoring: Enhanced genomic tools reduce reliance on older drugs.

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Deep-Dive: Key Displacement Factors

• Safety Profile: Myelosuppression and peripheral neuropathy significantly limit use.
• Efficacy: Lower potency compared to drugs like tenofovir, abacavir.
• Market Competition: With newer, safer, and more convenient agents, zalcitabine's role diminishes.
• Regulatory Decisions: Discontinuation across jurisdictions limits clinical or commercial prospects.

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FAQs

Q1: Is zalcitabine currently approved for any indication?
A: No. Zalcitabine is withdrawn globally and not approved for any current clinical use.

Q2: Can zalcitabine be used in research or off-label settings?
A: While possible in specialized research contexts, its use is largely obsolete due to safety concerns and availability issues.

Q3: Are there any ongoing clinical trials involving zalcitabine?
A: No active trials are registered as of 2023; the drug is considered obsolete.

Q4: Why was zalcitabine discontinued?
A: Due to safety issues, particularly myelosuppression and neurotoxicity, and the advent of superior agents.

Q5: Could future modifications restore zalcitabine’s market viability?
A: Unlikely. The safety profile and market competition favor newer drugs; modifications would require extensive development and regulatory approval.

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Key Takeaways

• Clinical Development: Zalcitabine's initial promise was overshadowed by toxicity, leading to withdrawal from markets nearly two decades ago.
• Market Status: Entirely obsolete, with no current sales or regulatory approvals.
• Future Potential: Minimal; research applications may persist but are unlikely to reinstate its market role.
• Competitive Environment: Modern ART agents offer better efficacy, safety, and convenience, rendering zalcitabine irrelevant.
• Strategic Implication: Investment or focus on drugs with proven safety and therapeutic advantages remains preferable.

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References

[1] AIDSinfo. (2022). Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents with HIV. National Institutes of Health.
[2] Pahwa, S., et al. (1988). Clinical efficacy of zalcitabine in HIV treatment. Journal of Infectious Diseases, 157(6), 1140-1146.
[3] ClinicalTrials.gov. (2023). Zalcitabine Trials. U.S. National Library of Medicine.
[4] European Medicines Agency. (2002). Instance of drug withdrawal.
[5] U.S. Food and Drug Administration. (2002). Drug discontinuation announcement.

Note: All data are consolidated as of 2023; future developments may alter the landscape.