Clovirex 5%w/w Cream (Each tube contains Acicclovir 5%)

Indications

• Herpes simplex virus infections (genital herpes)
• Herpes simplex encephalitis
• Varicella-zoster virus infections (shingles)
• Chickenpox
• Prophylaxis in immunocompromised patients at risk of herpes infections

Dosage

Children: Refer to BNF for Children for specific dosing guidelines based on the condition being treated.

Adults: Refer to BNF for specific dosing guidelines based on the condition being treated.

Mechanism of action

Acyclovir is a guanosine analogue that becomes phosphorylated by viral thymidine kinase to its active form, acyclovir triphosphate. This active metabolite competitively inhibits viral DNA polymerase, leading to premature termination of the viral DNA chain. Acyclovir also incorporates into the growing viral DNA strand, which ultimately prevents further viral replication.

Pharmacodynamics

The drug demonstrates selective toxicity, as it is preferentially activated in infected cells, leading to a higher concentration of the active form in cells where the virus is present. This selectivity helps to minimize damage to healthy cells. Acyclovir is effective against both HSV-1 and HSV-2 as well as VZV, exhibiting reduced effectiveness against other viruses.

Pharmacokinetics

Acyclovir is well absorbed after oral administration, with bioavailability ranging from 15-30%. It is widely distributed in body tissues and fluids, including the central nervous system. The drug is primarily eliminated by renal excretion, with approximately 62-91% of an administered dose recovered in urine as unchanged drug. The elimination half-life is approximately 2.5 to 3 hours in patients with normal renal function. Dosage adjustment is necessary in patients with renal impairment.

Contra-indications

• Hypersensitivity to aciclovir or any of its components
• Severe renal impairment

Adverse effects

• Nausea
• Diarrhea
• Headache
• Dizziness
• Rash
• Nephrotoxicity
• Neurotoxicity (including tremors, confusion, seizures)

Interactions

• Probenecid may reduce the renal clearance of aciclovir, increasing the risk of toxicity
• Other nephrotoxic agents may increase the risk of renal impairment
• Zidovudine may increase the risk of hematological toxicity

Precautions

• Ensure adequate hydration to minimize the risk of renal toxicity
• Use with caution in patients with renal impairment
• Monitor renal function during therapy, especially in high-dose regimens
• Consider alternative therapies in severe cases of dehydration

Pregnancy

Aciclovir is classified as pregnancy category B. Limited data suggest it is not associated with fetal harm, but caution is advised.

Breast-feeding

Aciclovir is excreted in breast milk. Caution should be exercised when administering to nursing mothers.

Storage

Store at room temperature, away from moisture and heat. Protect from light.

Formulations

• Oral tablets
• Oral suspension
• Topical cream
• Intravenous solution