Aciclovir

Aciclovir is an antiviral medication that is specifically effective against herpes viruses. It is used to treat and prevent herpes simplex infections (genital herpes, cold sores) and herpes zoster (shingles).

The medication can shorten and ease herpes outbreaks, but it cannot eliminate the virus from the body – herpes remains in the body for life and can recur.

Aciclovir is available in various forms: tablets, cream, and as a solution for infusion for severe cases.

Aciclovir acts highly selectively against herpes viruses:

Mechanism of action: 1. Aciclovir is activated by viral thymidine kinase (present only in infected cells) 2. The activated aciclovir triphosphate inhibits viral DNA polymerase 3. It is incorporated into the viral DNA and causes chain termination 4. Viral replication is stopped

Selective action: Since only virus-infected cells have the enzyme needed for activation, healthy cells are barely affected – hence the good tolerability.

Spectrum of activity:

• Herpes simplex type 1 (HSV-1, cold sores)
• Herpes simplex type 2 (HSV-2, genital herpes)
• Varicella-zoster virus (chickenpox, shingles)
• To a lesser extent: Epstein-Barr virus, cytomegalovirus

Aciclovir is suitable for:

• Initial infection with genital herpes
• Recurrent genital herpes
• Long-term prophylaxis in case of frequent recurrences
• Cold sores (herpes labialis)
• Shingles (herpes zoster)

Treatment goals:

• Acute therapy: Shortens the duration and severity of the outbreak
• Prophylaxis: Prevents or reduces recurrences
• Suppressive therapy: Continuous intake in case of very frequent outbreaks

Limitations:

• Only works against herpes viruses
• Cannot remove the virus from the body
• Should be started early in the outbreak

Genital herpes – initial infection:

• 200 mg 5x daily for 5-10 days OR
• 400 mg 3x daily for 5-10 days

Genital herpes – recurrence:

• 200 mg 5x daily for 5 days OR
• 400 mg 3x daily for 3-5 days OR
• 800 mg 3x daily for 2 days

Prophylaxis (suppressive therapy):

• 400 mg 2x daily or
• 200 mg 4x daily

Cold sores:

• Cream (5%) 5x daily for 4-5 days

Shingles:

• 800 mg 5x daily for 7 days

Available forms:

• Tablets 200 mg, 400 mg, 800 mg
• Cream 5%
• Suspension

Tablets:

• Take with plenty of water (at least 200 ml per tablet)
• Regardless of meals
• Evenly spaced intervals between doses
• Drink plenty of fluids throughout the day

Important for effectiveness:

• Start as early as possible (at the first signs, such as tingling)
• Complete the full course of treatment
• If taken 5x daily: about every 4 hours, with a break at night

Cream (cold sores):

• Start at the first tingling
• Apply 5x daily every 4 hours
• With a clean finger or cotton swab
• Use for 4-5 days

Aciclovir must not be used in case of:

• Hypersensitivity to aciclovir or valaciclovir

Caution and dose adjustment in case of:

• Renal insufficiency (dose reduction required)
• Dehydration (drink enough!)
• Elderly patients
• Neurological disorders

Pregnancy and breastfeeding: Aciclovir can be used during pregnancy and breastfeeding if needed. Many years of experience show no increased risks. Nevertheless, only after a doctor's assessment.

Common (1-10%):

• Headache
• Nausea
• Diarrhea
• Abdominal pain
• Fatigue
• Dizziness
• Skin rash (including photosensitivity reactions)
• Itching

Rare:

• Confusion, hallucinations (at high doses, especially with renal insufficiency)
• Kidney problems (with insufficient fluid intake)
• Changes in blood count

With the cream:

• Burning, stinging at the application site
• Skin redness
• Contact dermatitis

Interactions with:

• Probenecid – increases aciclovir levels
• Mycophenolate – increased levels of both substances
• Nephrotoxic medications – additive strain on the kidneys
• Cimetidine – increased aciclovir exposure

Important note: If kidney function is impaired, excretion may be delayed – dose adjustment required.

No relevant influence:

• Hormonal contraception
• Most common medications