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 allows higher active drug levels to be reached, 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. For genital herpes, valaciclovir is often the preferred choice because of its more convenient dosing schedule.

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 of valaciclovir is 54%
• The bioavailability of aciclovir from valaciclovir is about 3.3 to 5.5 times higher than after taking aciclovir tablets
• 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 drug levels
• Fewer tablets per day
• Better compliance

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:

• Simpler 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
• As initial infections can be more severe, it may be necessary to extend treatment to 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)
• With or without meals
• For 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 case of:

• Hypersensitivity to valaciclovir or aciclovir

Dose adjustment in case of:

• Renal insufficiency (important!)
• Elderly patients
• Dehydration

Pregnancy and breastfeeding: Can be used if there is an appropriate indication. Many years of experience, no known risks to the child.

Common (1-10%):

• Headache
• Nausea

Uncommon (0.1-1%):

• Dizziness
• Abdominal pain
• Vomiting
• Skin rash
• Photosensitivity

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

• Neurological symptoms (confusion, hallucinations)
• Kidney problems
• Thrombotic microangiopathy (in immunosuppressed patients)

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

Interactions:

• Nephrotoxic medications – additive burden 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 on:

• Hormonal contraception
• Common everyday medications