What is Valtrex?
Valtrex (valacyclovir) is a prescription antiviral medicine approved by the European Medicines Agency (EMA) for the treatment and suppression of herpes simplex virus (HSV-1 and HSV-2) infections. In sexual health, it is one of the most widely prescribed medicines for genital herpes — both for treating active outbreaks and for long-term daily suppressive therapy to reduce the risk of recurrent episodes and transmission to sexual partners.
Valacyclovir is the L-valyl ester prodrug of aciclovir. When taken orally, valacyclovir is rapidly and almost completely converted to aciclovir by first-pass metabolism in the intestinal wall and liver, achieving blood levels of aciclovir that are 3–5 times higher than those achievable with equivalent oral aciclovir (Zovirax) doses.
How does Valtrex work?
Valtrex works through its active metabolite aciclovir, using a highly selective antiviral mechanism:
- Conversion to aciclovir: After oral absorption, valacyclovir is converted to aciclovir by the enzyme valaciclovir hydrolase.
- Selective activation by viral thymidine kinase: Aciclovir enters both infected and uninfected cells, but it is selectively phosphorylated to aciclovir monophosphate by viral thymidine kinase — an enzyme present only in cells infected with HSV or VZV. Uninfected cells convert aciclovir inefficiently, giving the drug its selective antiviral activity.
- Further phosphorylation: Cellular enzymes convert aciclovir monophosphate to aciclovir triphosphate, the active inhibitor.
- Viral DNA polymerase inhibition: Aciclovir triphosphate competes with the natural substrate (deoxyguanosine triphosphate) for incorporation into the viral DNA chain. Once incorporated, it acts as a chain terminator — the DNA strand cannot extend beyond the point of aciclovir incorporation.
- Viral replication halted: With DNA synthesis blocked, herpes virus cannot replicate, allowing the immune system to contain the infection.
Importante: Valtrex suppresses active viral replication but does not eliminate the herpes virus, which remains latent in sensory nerve ganglia (nerve cells near the spinal cord) for life.
Who is Valtrex for?
Genital herpes (HSV-1 or HSV-2):
- First episode: Reduces duration and severity of primary outbreak
- Recurrent episodes (episodic treatment): Started at the earliest sign of an outbreak (prodrome)
- Suppressive therapy: Daily treatment to reduce frequency of outbreaks and transmission risk
- HIV-positive patients with genital herpes: Higher doses may be required under specialist supervision
Other indications:
- Orolabial herpes (cold sores): Single-day high-dose treatment
- Herpes zoster (shingles): 7-day course; most effective when started within 72 hours of rash onset
- CMV prevention: In immunocompromised patients post-transplant (specialist management)
Valtrex is not effective against:
- HIV or other retroviruses
- HPV (genital warts)
- Bacterial or fungal infections
- Cytomegalovirus (CMV) at standard doses — CMV requires higher doses and specialist supervision
Posología
| Indicación | Dosis | Duración |
|---|---|---|
| First episode genital herpes | 1 g twice daily | 10 days |
| Recurrent genital herpes (episodic) | 500 mg twice daily | 3–5 days |
| Recurrent genital herpes (single day) | 2 g twice daily | 1 day |
| Suppressive therapy | 500 mg once daily | Ongoing (review annually) |
| Suppressive (>9 episodes/year) | 1 g once daily | Ongoing |
| Cold sores | 2 g twice daily | 1 day |
| Shingles | 1 g three times daily | 7 days |
Valtrex tablets can be taken with or without food. For patients with kidney impairment, dose reduction is required — a doctor will calculate the appropriate dose based on kidney function.
Efectos secundarios
Valtrex is generally well tolerated at doses used for genital herpes.
Efectos secundarios frecuentes (afectan a entre 1 y 10 de cada 100 personas)
- Headache
- Nausea
- Abdominal pain
- Dizziness
- Vomiting
Efectos secundarios poco frecuentes
- Diarrhoea
- Fatigue
- Skin rash
- Elevated liver enzymes (usually mild and reversible)
Serious side effects (rare, mainly at high doses or in patients with renal impairment)
- Thrombotic thrombocytopenic purpura / haemolytic uraemic syndrome (TTP/HUS): Very rare — life-threatening condition reported at high doses in immunocompromised patients; not associated with standard doses in immunocompetent individuals
- Acute kidney injury: Risk increased with dehydration or pre-existing kidney disease; adequate hydration is important
- Neurological effects: Confusion, hallucinations, agitation — more common in elderly patients or those with renal impairment; dose reduction reduces risk
- Serious allergic reactions: Including anaphylaxis (very rare)
Valtrex vs alternative herpes antivirals
| Medicine | Active Metabolite | Oral Bioavailability | Dosing (episodic, genital herpes) | Dosing (suppressive) |
|---|---|---|---|---|
| Valtrex (Valacyclovir) | Aciclovir | ~55% (as aciclovir) | 500 mg twice daily (3–5 days) | 500 mg once daily |
| Famvir (Famciclovir) | Penciclovir | ~77% (as penciclovir) | 125 mg twice daily (5 days) | 250 mg twice daily |
| Zovirax (Aciclovir) | Aciclovir | ~15–30% | 200 mg 5× daily (5 days) | 400 mg twice daily |
Why Valtrex is often preferred over Zovirax: Valacyclovir’s higher bioavailability means it can achieve therapeutic aciclovir levels with fewer daily doses — typically twice daily versus the five-times-daily schedule required with oral aciclovir. This makes it more convenient and improves adherence, particularly for suppressive therapy.
Valtrex vs Famvir: Both are clinically comparable for the treatment and suppression of genital herpes. The choice is often based on patient preference, dosing convenience, and cost.
How to access Valtrex online in Europe
Valtrex es un medicamento sujeto a prescripción médica en todos los estados miembros de la UE. No puede dispensarse legalmente sin una receta válida de un profesional médico autorizado.
Prescrivia opera como intermediario tecnológico: no prescribimos medicamentos, no empleamos médicos ni vendemos medicamentos. Nuestra plataforma conecta a los pacientes con médicos independientes registrados en la UE que pueden realizar evaluaciones de salud en línea confidenciales.
El proceso:
- Complete una evaluación de salud: Describe your symptoms, history of herpes outbreaks, and any relevant medical history including kidney function.
- Revisión médica: Un médico independiente registrado en la UE revisa su evaluación. If valacyclovir is clinically appropriate, they may issue a prescription.
- Dispensación en farmacia: La receta se envía a una farmacia asociada autorizada de la UE para su dispensación y entrega directa.
Importante: Prescrivia no garantiza que se emita una receta. Todas las decisiones de prescripción son tomadas de forma independiente por profesionales médicos cualificados.
Información importante de seguridad
Informe a su médico antes de taking Valtrex si usted:
- Have kidney disease (dose reduction is required — inform your doctor of any kidney impairment)
- Are elderly (higher risk of neurological side effects, particularly at high doses)
- Are immunocompromised (HIV infection, transplant medication, cancer treatment)
- Are pregnant or breastfeeding (limited data on valacyclovir in pregnancy — doctor assessment required; aciclovir has more safety data in pregnancy)
- Are taking nephrotoxic medicines or those that affect kidney function
Suppressive therapy and transmission: Daily suppressive therapy reduces but does not eliminate the risk of HSV transmission. Consistent use of condoms provides additional risk reduction. Disclosing herpes status to sexual partners allows them to make informed decisions about their sexual health.
No cure: Valtrex and other herpes antivirals reduce viral replication and alleviate symptoms but do not eliminate the herpes virus. The virus remains latent and may reactivate throughout a person’s lifetime. Treatment can effectively manage the condition for many people.
Fuentes
La información médica de esta página se basa en las siguientes fuentes:
- European Medicines Agency (EMA). Valtrex (valaciclovir) — Summary of Product Characteristics. Disponible en: ema.europa.eu
- World Health Organization (WHO). Herpes simplex virus — Fact sheet. who.int
- Corey L, et al. Once-daily valacyclovir to reduce the risk of transmission of genital herpes. N Engl J Med. 2004;350:11–20.
- Gupta R, et al. Genital herpes. Lancet. 2007;370(9605):2127–2137.
Este contenido se revisa periódicamente para reflejar las directrices clínicas actualizadas. Se proporciona únicamente con fines informativos y no constituye asesoramiento médico. Consulte siempre a un profesional sanitario cualificado para obtener asesoramiento relevante para sus circunstancias de salud individuales.
Frequently asked questions
- What is Valtrex used for?
- Valtrex (valacyclovir) is an antiviral medicine approved by the EMA for the treatment of genital herpes (herpes simplex virus types 1 and 2), cold sores (orolabial herpes), shingles (herpes zoster), and the prevention of cytomegalovirus (CMV) disease in transplant patients. In sexual health, it is most commonly used to treat genital herpes outbreaks and as daily suppressive therapy to reduce the frequency of recurrences and the risk of transmission to sexual partners.
- How does Valtrex reduce herpes transmission?
- Valtrex taken daily as suppressive therapy reduces asymptomatic viral shedding — the release of herpes virus from the skin even in the absence of visible sores — which is a major mechanism of HSV transmission. A landmark clinical trial (Corey et al., 2004) showed that daily valacyclovir 500 mg reduced transmission of genital herpes from infected to uninfected partners by approximately 48% compared to placebo, when combined with condom use.
- How quickly does Valtrex work for a herpes outbreak?
- Valtrex is most effective when started as early as possible — ideally within 24 hours of symptoms appearing (tingling, itching, or the first signs of sores). Starting treatment promptly can reduce the severity, duration, and pain of an outbreak. Symptoms typically improve within 2–3 days and outbreaks resolve within 4–7 days with early treatment.
- What is the difference between Valtrex and Zovirax?
- Valtrex (valacyclovir) is a prodrug that is converted to aciclovir in the body after absorption. The key advantage of Valtrex over Zovirax (aciclovir) is significantly higher oral bioavailability: valacyclovir achieves approximately 3–5 times higher blood levels than equivalent oral aciclovir doses. This allows less frequent dosing — typically twice daily compared to five times daily for aciclovir. Both medicines are equally effective when adequate blood levels are achieved.
- Can I get Valtrex online in Europe?
- Valtrex es un medicamento sujeto a prescripción médica en todos los estados miembros de la UE. Puede acceder a it through online intermediary platforms that connect you with independent EU-registered doctors for a confidential health assessment and, if clinically appropriate, a prescription.
Prescrivia es únicamente una plataforma intermediaria. No prestamos servicios médicos, no prescribimos tratamientos ni dispensamos medicamentos. Todas las decisiones médicas son tomadas por médicos independientes registrados en la UE. Todos los medicamentos son dispensados por farmacias autorizadas de la UE. Esta plataforma facilita la conexión entre pacientes y profesionales sanitarios.