Groprinosin

Inosine pranobex (trade names Imunovir, Groprinosin, Isoprinosine) is a synthetic compound consisting of inosine, acedoben (p-acetamidobenzoic acid), and dimethylaminoisopropanol in a 1:3 molar ratio. It exerts dual pharmacological effects: immunomodulation and direct inhibition of viral replication.

On the immunological side, the drug polarizes the adaptive immune response toward the Th1 pathway, elevating interleukin-2 (IL-2) and interferon-gamma (IFN-γ) production by T lymphocytes and enhancing T-helper cell proliferation and blastogenesis that has been suppressed by viral infection. It also acts as a thymus hormone analog, restoring cellular immune competence. Notably, it rapidly expands circulating natural killer (NK) cell populations; within approximately 1.5 hours of administration a durable rise of approximately twofold or greater in NK cells has been documented, sustained throughout treatment with intact granzyme A and perforin expression. Via purine metabolic pathways and increased intracellular tricarboxylic acid cycle intermediates, the drug upregulates NKG2D ligand expression on virus-infected host cells, making them more recognizable to cytotoxic lymphocytes.

The antiviral mechanism is attributed to inhibition of viral RNA synthesis and a shift in host cell translational resources toward cellular rather than viral mRNA, limiting the virus's ability to commandeer host protein synthesis. Together, these actions counter viral-induced lymphopenia, augment both innate and adaptive responses, and support immune surveillance against infected cells.

Multiple randomized controlled trials have evaluated inosine pranobex across several indications, yielding varying results by population and clinical context.

For acute respiratory viral infections, a Phase 4 double-blind, placebo-controlled multicentre trial (n=463, conducted at 25 sites in the Czech Republic and Slovakia) administered 3 g/day for seven days. The primary endpoint of time to complete symptom resolution was not statistically significant in the overall population (HR 1.175; p=0.324). A significant benefit was observed only in a pre-specified subgroup of non-obese patients under 50 years without comorbidities (HR 1.307; p=0.018).

A Phase 3 double-blind, placebo-controlled trial in mild to moderate COVID-19 (n=416) demonstrated significantly higher clinical response and cure rates on Day 6, with faster recovery (median 6 days vs. 8 days in the placebo group) using 50 mg/kg/day for 10 days alongside standard care; no treatment-related mortality was observed.

In HIV-infected patients without manifest AIDS, the Scandinavian Isoprinosine Study Group trial (n=866 across 21 centers in Denmark and Sweden) found that 1 g three times daily for 24 weeks significantly delayed progression to AIDS: 2 treated patients progressed versus 17 on placebo (p less than 0.001; odds ratio 8.6 favoring treatment).

For subclinical HPV infection of the vulva, a double-blind RCT (n=46 evaluable) showed significant morphological epithelial improvement in 63.5% treated versus 16.7% placebo at 2 months (p=0.005) using 1 g three times daily for six weeks. A 2021 narrative review of inosine pranobex for cervical HPV-positive patients concluded there is strong evidence from prospective and observational studies supporting both standalone and combination therapy in reversing HPV-induced cervical changes.

A small pilot study in ME/CFS (n=16) reported NK cell enhancement and clinical improvement in 60% of treated patients; its limited size precludes definitive conclusions.

Typical dosage: 500-1000 mg (three times daily).

Dosing varies by indication. The drug has held marketing authorization in approximately 43 countries since 1971; it is not FDA-approved in the United States.

• Acute viral infections (general): 50 mg/kg/day in 3 to 4 divided oral doses, typically 3 g/day up to a maximum of 4 g/day. The most common clinical regimen is two 500 mg tablets three times daily (3 g/day) for 7 to 14 days.

• Herpes simplex (licensed regimen per Imunovir SPC): 1 g orally four times daily for 7 to 14 days.

• Genital warts, adjunctive (licensed): 1 g three times daily for 14 to 28 days alongside local destructive therapy.

• COVID-19 (Phase 3 trial regimen): 50 mg/kg/day (maximum 4 g/day) in 3 to 4 divided doses for 10 days in addition to standard care.

• HIV immune support (Scandinavian trial): 1 g three times daily for 24 continuous weeks.

• SSPE (licensed indication): 50 to 100 mg/kg/day in divided doses every 4 hours (maximum 3 to 4 g/day), under specialist supervision.

The standard available tablet strength is 500 mg. Long-term use requires periodic monitoring of serum uric acid, liver function, full blood count, and renal function per the licensed prescribing information; adequate hydration is recommended to reduce uric acid-related risk.

The dosages above describe regimens reported in clinical trials and approved prescribing practice in jurisdictions where the drug holds a marketing authorization. This information is provided for educational purposes only and does not constitute medical advice; dosing decisions should be made by a qualified healthcare professional in accordance with applicable regulations.

No compound-specific stability data has been identified for this peptide. The general lyophilized-peptide handling framework applies — see Storage & handling for temperature, reconstitution diluent, and beyond-use dating principles.

The best-documented combination use is adjunct inosine pranobex with local ablative therapies for HPV-associated lesions. One study reported that relapse at 8 months fell from 32% with ablation alone to 7% when inosine pranobex was added, suggesting meaningful reduction in viral recurrence when local treatment is combined with immunostimulation. A 2021 cervical HPV review cited viral elimination rates of up to 98% in combined regimens, though heterogeneity in study designs limits generalizability. The UK-licensed prescribing information (Imunovir SPC) specifically authorizes adjunctive use alongside ablative or cytotoxic local treatment for genital warts.

In the Phase 3 COVID-19 trial, the drug was administered as an adjunct to standard of care rather than as monotherapy.

The Imunovir SPC notes a pharmacokinetically relevant interaction with zidovudine (AZT): inosine pranobex increases AZT bioavailability and intracellular phosphorylation, which was historically relevant in HIV combination regimens.

Use alongside valacyclovir or low-dose naltrexone in ME/CFS and herpesvirus-associated conditions is reported in clinical practice and patient communities; no controlled combination data exist for these applications and such use remains anecdotal.

Groprinosin is not currently FDA-approved for any indication. It is generally classified as a research compound. Regulatory status varies by country.

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Reported side effects: Possible GI upset, elevated uric acid

Inosine pranobex has been in continuous clinical use since 1971. Its safety record across both controlled trials and post-marketing surveillance spanning more than five decades is broadly favorable.

The most pharmacologically predictable and best-characterized adverse effect is a transient, dose-dependent rise in serum and urinary uric acid resulting from inosine catabolism through the purine degradation pathway. This is classified as "very common" in the licensed UK prescribing information, is more pronounced in males and elderly patients, and normalizes after discontinuation. It carries a clinically relevant risk of gout exacerbation and uric acid nephrolithiasis in predisposed individuals; periodic uric acid monitoring is required during prolonged treatment.

Other reported adverse effects include headache, dizziness, nausea, vomiting, epigastric discomfort, rash, pruritus, arthralgia, and fatigue. Transient elevations in liver transaminases, alkaline phosphatase, and blood urea nitrogen have been documented but are generally mild. Post-marketing reports include urticaria, angioedema, and rarely anaphylaxis.

Absolute contraindications include hypersensitivity to the formulation, active gout, and established hyperuricemia. The drug should not be used in severe renal or hepatic impairment and is used only with caution in patients with a history of urolithiasis. Concurrent use with immunosuppressants (cyclosporine, tacrolimus) may reduce pharmacodynamic efficacy; the SPC advises administering the drug after, not simultaneously with, such agents. Safety in pregnancy has not been established and use is not recommended.

Long-term tolerance studies extending to approximately seven years recorded only occasional transient nausea; no consistent cardiovascular, hematological, or major organ toxicity has been identified in controlled trial data.