Valaciclovir

Valaciclovir is a prodrug that is converted into aciclovir in the body. It provides the same antiviral effect against herpes viruses but is better absorbed by the body. This makes higher active drug levels achievable, and taking it is simpler (fewer tablets per day).

The medication is used for the treatment and prophylaxis of genital herpes, cold sores, and shingles.

Valaciclovir is known under the brand name Valtrex®.

Valaciclovir is rapidly converted into aciclovir in the body:

Pharmacokinetics:

• After oral intake, valaciclovir is rapidly and almost completely converted into aciclovir
• The bioavailability of aciclovir after taking 1000 mg valaciclovir is 54%
• By comparison: aciclovir tablets have a bioavailability of only 15-30%
• Higher aciclovir levels in the blood are possible

Mechanism of action (identical to aciclovir): 1. Activation by viral thymidine kinase 2. Inhibition of viral DNA polymerase 3. DNA chain termination 4. Halting of viral replication

Advantages over aciclovir:

• Better absorption from the intestine
• Higher active ingredient levels
• Fewer tablets per day

Valaciclovir is suitable for:

• Genital herpes (initial infection and recurrences)
• Suppressive therapy for frequent genital herpes
• Cold sores
• Shingles
• Reducing the risk of transmission to partners

Advantages:

• Easier to take than aciclovir
• Well suited for long-term prophylaxis
• Proven reduction of transmission to partners

Same limitations as aciclovir:

• Does not cure herpes
• Should be started early
• Dose adjustment in renal insufficiency

Genital herpes – initial infection:

• 500 mg 2x daily for 10 days

Genital herpes – recurrence:

• 500 mg 2x daily for 3-5 days

Suppressive therapy:

• 500 mg 1x daily (with <10 recurrences/year)
• 1000 mg 1x daily (with ≥10 recurrences/year)
• 500 mg 1x daily to reduce transmission

Cold sores:

• 2000 mg 2x daily for 1 day (12 hours apart)

Shingles:

• 1000 mg 3x daily for 7 days

Available strengths:

• 500 mg tablets
• 1000 mg tablets

How to take:

• With plenty of water (at least 200 ml)
• Regardless of meals
• With multiple doses: evenly spaced intervals

During an acute outbreak:

• Start as early as possible
• Ideally at the first tingling
• The earlier, the better the effect

Suppressive therapy:

• Every day at about the same time
• Do not forget – regular intake is important
• A trial discontinuation is possible after 6-12 months

Important: Drink enough fluids during treatment to protect the kidneys.

Do not use in cases of:

• Hypersensitivity to valaciclovir or aciclovir

Dose adjustment in cases of:

• Renal insufficiency (important!)
• Elderly patients

If there is a risk of fluid deficiency (dehydration): Ensure adequate fluid intake. Such a risk can occur particularly in elderly patients.

Pregnancy and breastfeeding: Only use during pregnancy if the potential benefit outweighs the potential risks. Only limited data are available on valaciclovir. Experience so far with valaciclovir and aciclovir does not indicate birth defects or harm to the unborn or newborn child. During breastfeeding, only use with caution and only if medically necessary. Aciclovir, into which valaciclovir is converted in the body, passes into breast milk.

Very common (10% or more):

• Headache

Common (1-10%):

• Nausea
• Dizziness
• Vomiting
• Skin rash
• Photosensitivity

Uncommon (0.1-1%):

• Abdominal pain
• Confusion, hallucinations (mostly with impaired kidney function)

Rare (especially at high doses/with renal insufficiency):

• Neurological disorders (e.g. seizures, psychoses, coma)
• Kidney problems
• Thrombotic microangiopathy (in immunosuppressed patients)

Compared with aciclovir: Similar side effect profile, since valaciclovir is converted into aciclovir.

Interactions:

• Nephrotoxic medications – additive strain on the kidneys
• Mycophenolate – increased levels
• Cimetidine, probenecid – delayed excretion

In renal insufficiency: Dose reduction required, since aciclovir is excreted via the kidneys.

No relevant effect:

• Hormonal contraception
• Common everyday medications