O que é Valtrex?
Valtrex (valacyclovir) is a receita médica antiviral medicamento approved by the Agência Europeia de Medicamentos (EMA) for the tratamento and suppression of herpes simplex virus (HSV-1 and HSV-2) infections. In sexual health, it is one of the most widely prescribed medicamentos 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.
Como funciona 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.
Important: 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.
Para quem é Valtrex for?
Genital herpes (HSV-1 or HSV-2):
- First episode: Reduces duration and severity of primary outbreak
- Recurrent episodes (episodic tratamento): Started at the earliest sign of an outbreak (prodrome)
- Suppressive therapy: Daily tratamento to reduce frequency of outbreaks and transmission risk
- HIV-positive pacientes with genital herpes: Higher doses may be required under specialist supervision
Other indications:
- Orolabial herpes (cold sores): Single-day high-dose tratamento
- Herpes zoster (shingles): 7-day course; most effective when started within 72 hours of rash onset
- CMV prevention: In immunocompromised pacientes 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
Dosagem
| Indication | Dose | Duration |
|---|---|---|
| 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 comprimidos can be taken with or without food. For pacientes with kidney impairment, dose reduction is required — a médico will calculate the appropriate dose based on kidney function.
Efeitos secundários
Valtrex is generally well tolerated at doses utilizado para genital herpes.
Efeitos secundários comuns (afetando 1 a 10 em 100 pessoas)
- Headache
- Nausea
- Abdominal pain
- Dizziness
- Vomiting
Menos comuns efeito secundários
- Diarrhoea
- Fatigue
- Skin rash
- Elevated liver enzymes (usually mild and reversible)
Efeitos secundários graves (rare, mainly at high doses or in pacientes with renal impairment)
- Thrombotic thrombocytopenic purpura / haemolytic uraemic syndrome (TTP/HUS): Very rare — life-threatening condition reported at high doses in immunocompromised pacientes; 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 pacientes or those with renal impairment; dose reduction reduces risk
- Serious allergic reactions: Including anaphylaxis (very rare)
Valtrex vs alternativas 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 tratamento and suppression of genital herpes. The choice is often based on paciente preference, dosing convenience, and cost.
Como aceder a Valtrex online na Europa
Valtrex is a medicamento sujeito a receita médica (POM) in all estados-membros da UE. It cannot legally be dispensed without a valid receita médica from a licensed medical professional.
Prescrivia operates as a technology intermediary: we do not prescribe medicamentos, employ médicos, or sell medicamentos. Our platform connects pacientes with independent EU-registered médicos who can conduct confidential online health assessments.
The process:
- Complete uma avaliação de saúde: Describe your symptoms, history of herpes outbreaks, and any relevant medical history including kidney function.
- Avaliação médica: An independent EU-registered médico reviews your assessment. If valacyclovir is clinically appropriate, they may issue a receita médica.
- Dispensa na farmácia: The receita médica is sent to a licensed EU farmácia partner for dispensing and direct delivery.
Important: A Prescrivia não garante that a receita médica will be issued. All prescribing decisions are made independently by qualified medical professionals.
Informação de segurança importante
Informe o seu médico before taking Valtrex if you:
- Have kidney disease (dose reduction is required — inform your médico of any kidney impairment)
- Are elderly (higher risk of neurological efeito secundários, particularly at high doses)
- Are immunocompromised (HIV infection, transplant medication, cancer tratamento)
- Are pregnant or breastfeeding (limited data on valacyclovir in pregnancy — médico assessment required; aciclovir has more safety data in pregnancy)
- Are taking nephrotoxic medicamentos 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.
Fontes
Medical information on this page is based on the following sources:
- Agência Europeia de Medicamentos (EMA). Valtrex (valaciclovir) — Summary of Product Characteristics. Available at: ema.europa.eu
- Organização Mundial da Saúde (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.
This content is reviewed periodically to reflect updated clinical guidance. It is provided for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for advice relevant to your individual health circumstances.
Frequently asked questions
- O que é Valtrex utilizado para?
- Valtrex (valacyclovir) is an antiviral medicamento approved by the EMA for the tratamento 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 pacientes. 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.
- Como funciona 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.
- Com que rapidez 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 tratamento 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 tratamento.
- O que é 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 medicamentos are equally effective when adequate blood levels are achieved.
- Posso obter Valtrex online na Europa?
- Valtrex is a medicamento sujeito a receita médica in all estados-membros da UE. You can access it through online intermediary platforms that connect you with independent EU-registered médicos for a confidential health assessment and, if clinically appropriate, a receita médica.
A Prescrivia é apenas uma plataforma intermediária. Não prestamos serviços médicos, não prescrevemos tratamentos nem dispensamos medicamentos. Todas as decisões médicas são tomadas por médicos independentes registados na UE. Todos os medicamentos são dispensados por farmácias licenciadas na UE. Esta plataforma facilita a ligação entre pacientes e prestadores de cuidados de saúde.