LACTOLOGY FOUNDATION

Antiviral Drugs and Pharmacological Immunomodulators

💊 Mechanisms, Classification and Clinical Use

Antiviral drugs act directly on viruses, while pharmacological immunomodulators regulate the host immune response. In clinical practice, their rational combination is crucial in severe or chronic viral infections, and during breastfeeding additional attention is required to maternal–infant safety.

I. Key Challenges in Treating Viral Infections

1. Viruses are intracellular parasites, which makes selective toxicity difficult because the drug must reach the infected cell without excessive damage to the host tissues.
2. Viruses have high mutation potential, leading to rapid development of resistance, particularly under monotherapy or suboptimal adherence.
3. Many viruses show latency (e.g. herpesviruses, HIV), which necessitates long‑term or even lifelong therapy.

Lactation perspective

• For chronic infections (HIV, hepatitis B/C), therapy is often continuous during pregnancy and breastfeeding; this requires careful drug selection, monitoring of the infant and coordination between infectious disease specialists and lactation consultants.
• The risk–benefit analysis must integrate maternal disease control, drug safety in breast milk, and availability of alternative regimens better studied in lactation.

II. Antiviral Drugs (by Target Virus)

1. Anti‑Herpesvirus Agents

Acyclovir, valacyclovir, famciclovir.
→ Mechanism: Inhibit viral DNA polymerase after activation by viral thymidine kinase, thereby blocking viral DNA replication.
→ Use: Herpes simplex virus (HSV), varicella‑zoster virus (VZV).
→ Resistance: Occurs mainly with deficient or altered viral thymidine kinase.

Lactation note:

• Acyclovir and valacyclovir are generally considered compatible with breastfeeding; drug levels in breast milk are low and oral bioavailability in the infant is limited.
• Short courses for HSV or VZV in the mother are usually acceptable, but premature or medically fragile infants warrant closer monitoring (renal function, hydration, weight gain).

2. Anti‑Influenza Drugs

Oseltamivir (Tamiflu).
→ Mechanism: Neuraminidase inhibitor; prevents release of new viral particles from infected cells.
→ Use: Treatment and prophylaxis of influenza A and B.

Zanamivir (inhaled formulation).

Lactation note:

• Oseltamivir is considered relatively safe during breastfeeding; transfer into breast milk is low and clinical experience is reassuring.
• Inhaled zanamivir has minimal systemic exposure, but asthma or COPD in the mother may limit its use; breastfeeding is usually not a contraindication.

3. Anti‑HIV Drugs – Highly Active Antiretroviral Therapy (HAART)

| Class | Examples | Mechanism |

|-------------------------------------|-------------------------|---------------------------------------------|

| Nucleoside RT inhibitors (NRTI) | Zidovudine, Lamivudine | Inhibit DNA synthesis (nucleoside analogues)

| Non‑nucleoside RT inhibitors (NNRTI)| Efavirenz, Nevirapine | Non‑competitive inhibition of RT |

| Protease inhibitors (PI) | Atazanavir, Ritonavir | Block proteolytic cleavage of viral proteins|

| Integrase inhibitors | Dolutegravir | Block integration of viral DNA into host |

| Fusion inhibitors | Enfuvirtide | Prevent fusion of virus with host cell |

→ Regimen: Always a combination of at least three drugs to prevent resistance.

Lactation note:

• Decisions on breastfeeding in HIV‑positive mothers are complex and highly protocol‑dependent; in some settings breastfeeding is discouraged, in others it is allowed under full suppressive ART and infant prophylaxis.
• Zidovudine and lamivudine have substantial safety data in pregnancy and lactation; protease inhibitors and integrase inhibitors differ in milk transfer and infant exposure, so regimen choice should follow up‑to‑date national and international guidelines.

4. Anti‑Hepatitis B and C Drugs

Hepatitis B: Entecavir, tenofovir → inhibit reverse transcriptase and viral DNA synthesis.

Hepatitis C:

• Sofosbuvir (RNA polymerase inhibitor) + ledipasvir (NS5A protein inhibitor) → very high cure rates (>95%).

Lactation note:

• Tenofovir is generally considered low‑risk in breastfeeding; milk levels are low, and it is widely used in HIV/HBV co‑infection during lactation.
• Data for newer direct‑acting antivirals such as sofosbuvir/ledipasvir are more limited; therapy during breastfeeding should be individualized, often preferring to complete treatment before or after the lactation period when feasible.

5. Anti‑COVID‑19 Drugs

Remdesivir: Inhibits viral RNA‑dependent RNA polymerase.
Nirmatrelvir/ritonavir (Paxlovid): Inhibit the 3CL viral protease.
Molnupiravir: Induces mutations in viral RNA (error catastrophe).!

Lactation note:

• For remdesivir and nirmatrelvir/ritonavir, available data in breastfeeding women are still limited but suggest low milk transfer due to pharmacokinetic properties; decisions should be based on maternal disease severity and alternative options.
• Molnupiravir raises theoretical concerns about mutagenicity; many guidelines recommend avoiding its use during pregnancy and lactation unless no alternative exists.

III. Pharmacological Immunomodulators

Immunostimulation vs Immunomodulation

| Parameter | Immunostimulation | Immunomodulation |

|----------------|----------------------------------------------|---------------------------------------------|

| Action | Stimulates overall immune response (non‑specific)| Regulates (enhances or suppresses) immune activity |

| Focus | Increases general resistance | Balances excessive or insufficient responses |

| Examples | Bacterial lysates (Imudon), β‑glucans | IFN‑α, IL‑2, anti‑TNF preparations (Infliximab)|

| Risks | Autoimmune reactions, cytokine storm | Infections (with suppression), toxicity |

Types of Immunomodulators

1. Immunostimulants (subgroup of immunomodulators)

Interferons (IFN):

• IFN‑α: For hepatitis B/C, certain herpes infections.
• IFN‑β: For multiple sclerosis.

Interleukins (IL):

• IL‑2: For renal cell carcinoma.

Colony‑stimulating factors (G‑CSF):

• Filgrastim → increases neutrophil count in chemotherapy‑induced neutropenia.

Lactation note:

• Cytokine‑based therapies (interferons, IL‑2) are rarely used in breastfeeding women because of their indication profile; if needed, individual risk assessment is mandatory, considering maternal benefit, infant age, and possibility of temporary milk expression and discard.
• G‑CSF (filgrastim) has limited lactation data; potential exposure via milk is low, but neutrophil changes in the infant are theoretically possible, so close clinical observation is advised.

2. Immunosuppressants (also immunomodulators with suppressive effect)

Cyclosporine, tacrolimus → prevention of transplant rejection.
Corticosteroids (e.g. prednisone) → treatment of autoimmune diseases.

Lactation note:

• Low‑dose systemic corticosteroids are usually compatible with breastfeeding; short‑term high‑dose pulses may require timing feeds (e.g. breastfeeding before dose, waiting a few hours) to reduce infant exposure.
• Calcineurin inhibitors (cyclosporine, tacrolimus) can cross into breast milk; breastfeeding is sometimes allowed under strict monitoring of infant renal function and drug levels, but many protocols remain cautious.

3. Monoclonal Antibodies (mAb)

Anti‑TNF‑α (Infliximab, Adalimumab) → rheumatoid arthritis, Crohn’s disease.
Anti‑IL‑6 (Tocilizumab) → arthritis, severe COVID‑19.
Anti‑PD‑1/PD‑L1 (Pembrolizumab) → immuno‑oncology, enabling T‑cell attack against tumors.

Lactation note:

• Many therapeutic antibodies are large molecules with poor oral bioavailability, so infant systemic exposure via breast milk is expected to be low, but long‑term immunological effects are not fully clarified.
• Anti‑TNF agents have accumulating experience suggesting relative compatibility with breastfeeding, whereas immune‑checkpoint inhibitors (anti‑PD‑1/PD‑L1) are generally avoided in lactating women due to theoretical risk of immune dysregulation in the infant.

IV. Side Effects ⚠️

Drug | Common Adverse Effects
Acyclovir | Renal toxicity, neurological disturbances.
Oseltamivir | Nausea, vomiting, psychiatric symptoms.
Interferons | Flu‑like syndrome, depression, hematologic toxicity.
Anti‑TNF therapy | Increased risk of infections (notably tuberculosis), malignancies.
Anti‑PD‑1/PD‑L1 | Immune‑mediated adverse events: colitis, pneumonitis, endocrinopathies.

Lactation‑safety emphasis

• For breastfeeding mothers, adverse effects must be considered both for the woman (tolerability and organ toxicity) and for the infant (potential exposure via breast milk).
• Screening for infections (e.g. tuberculosis before anti‑TNF therapy) and regular clinical evaluation of the infant are integral parts of safe immunomodulatory treatment during lactation.

V. Golden Rules for Therapy Selection

• Antivirals stop viral replication but do not reverse already established tissue damage.
• Immunomodulators regulate the degree of tissue injury and inflammatory response but do not directly eliminate the virus.
• Combined regimens are often necessary in severe or chronic viral infections.

Monitoring parameters:

• Viral load (efficacy of antivirals).
• Immune status (CRP, interleukins, clinical picture).

Types of Immunomodulators – Additional Detail

1. Cytokines:
• Interferons (IFN):
  → IFN‑α: Hepatitis B/C, hepatocellular carcinoma.
  → IFN‑β: Multiple sclerosis.
• Interleukin‑2 (IL‑2): Metastatic renal carcinoma.
2. Monoclonal antibodies (mAb):
• Anti‑TNF‑α (Infliximab, Adalimumab): Rheumatoid arthritis, Crohn’s disease.
• Anti‑IL‑6 (Tocilizumab): Arthritis, severe COVID‑19.
• Anti‑PD‑1/PD‑L1 (Pembrolizumab): Immuno‑oncology.
3. Immunosuppressants:
• Cyclosporine, tacrolimus: Transplant rejection prophylaxis.
• Corticosteroids: Autoimmune diseases.

Lactation note:

• Before starting immunomodulators in a breastfeeding woman, baseline evaluation (e.g. TB test, hepatitis B/C serology) is crucial due to the increased infection risk.
• Live vaccines are contraindicated in markedly immunosuppressed mothers and often in their infants; vaccination schedules may need individual adaptation.

VI. Future Directions: Gene Therapy and mRNA Technologies

mRNA vaccines (e.g. COVID‑19 vaccines) represent a revolution in viral prophylaxis by enabling rapid design and robust immune responses.
CAR‑T cell therapy is emerging for leukemias and lymphomas, reprogramming patient T cells to target malignant cells.

Lactation note:

• mRNA vaccines against COVID‑19 are generally considered compatible with breastfeeding and may provide indirect protection for the infant through maternal antibodies.
• Advanced cell and gene therapies are rarely applied in breastfeeding women; when such treatment is necessary, lactation is often discontinued due to profound and partly unknown immunological effects.

“Antivirals fight the virus today. Immunomodulators balance tomorrow’s response. True healing comes from the alliance between both.”