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Hepirax Dispersible

PRESENTATIONS
Hepirax Dispersible 200 mg
A blue, shield-shape, dispersible tablet embossed with 'CCM' and '200' on the same side and plain on the other side. Each tablet contains 200 mg acyclovir.
Hepirax Dispersible 400 mg
A pink, shield-shape, dispersible tablet embossed with CM and '400' on the same side and plain on the other side. Each tablet contains 400 mg acyclovir.

INDICATIONS
For the treatment of Herpes simplex virus infection of the skin and mucous membranes, including initial and recurrent genital herpes.
For the suppression (prevention of recurrence) of recurrent Herpes simplex infections in immunecompetent patients.
For the prophylaxis of Herpes simplex infections in immunocompromised patients.
For the treatment of Varicella (Chickenpox) and Herpes Zoster (Shingles) infections.

DOSAGE AND ADMINISTRATION

Herpes simplex
Treatment
Adult : 200 mg (400 mg in the immunocompromised or if absorption impaired) five times daily at 4-hourly intervals for 5 to 10 days.
Child : under 2 years, half adult dose; over 2 years, adult dose.

Prophylaxis in the immunocompromised

Adult : 200 - 400 mg four times daily.
Child : under 2 years half adult dose; over 2 years, adult dose.


Prevention of recurrence
Adult : 200 mg four times daily at 6-hourly intervals or 400 mg twice daily at 12-hourly intervals, possibly reduced to 200 mg 2 or 3 times daily and interrupted every 6 - 12 months.

Patients with renal impairment
In patients with impaired renal function, the recommended doses will not lead to accumulation of acyclovir above levels that have been established safe by intravenous infusion. For patients with severe renal impairment (creatinine clearance less than 10 ml/minute), a dosage of 200 mg twice daily at 12-hourly intervals is recommended.


Varicella and herpes zoster
Treatment
Adult : 800 mg taken five times daily at 4-hourly intervals for 7 days.
Child : varicella, 20 mg/kg (max. 800 mg) four times daily for 5 days; under 2 years 200 mg four times daily; 2 - 5 years 400 mg four times daily; over 6 years 800 mg 4 times daily. Treatment should be initiated at the earliest sign or symptom of chickenpox.


Patients with renal impairment
It is recommended to adjust dosage to 800 mg twice daily, at 12-hourly interval for patients with severe renal impairment (creatinine clearance less than 10 ml/min) and to 800 mg three times daily, at intervals of approximately 8 hours, for patients with moderate renal impairment (creatinine clearance in the range 10 - 25 ml/min).


Genital herpes infections
Initial therapy

200 mg every 4 hours while awake, five times a day, for ten days.


Recurrent infections, intermittent therapy
200 mg every 4 hours while awake, five times a day, for five days.


Recurrent infections, chronic suppressive therapy
400 mg twice a day; or 200 mg three to five times a day.


ADMINISTRATION
Hepirax dispersible tablet may be swallowed whole with a little water or dispersed in a minimum of 50 ml of water.


MODE OF ACTION
Acyclovir is a synthetic purine nucleoside analogue with in vitro and in vivo inhibitory activities against human herpes viruses, including herpes simplex virus (HSV) type 1 and 2, and varicella-zoster viruses (VZV). Acyclovir is converted into the monophosphate by the viral thymidine kinases with subsequent conversion to diphosphate and the active triphosphate through intracellular conversion. The active triphosphate form inhibits viral DNA synthesis and replication by interfering with the herpes virus DNA polymerase enzyme as well as being incorporated into viral DNA. This process is highly selective for infected cells.


Acyclovir has no activity against latent viruses, but there is some evidence that it inhibits latent herpes simplex virus at an early stage of reactivation.

 

PHARMACOLOGY/PHARMACOKINETICS

Absorption:
About 15-30% of a dose of acyclovir given by mouth is absorbed from the gastrointestinal tract. A dose of 200 mg acyclovir every 4 hours by mouth is reported to produce maximum and minimum steady state plasma concentration of 0.7 and 0.4 g per ml respectively; equivalent values following 400 mg doses are 1.2 and 0.6 g per ml. The absorption is not significantly affected by food.


A single dose of two tablets of Hepirax dispersible 200 mg is reported to produce maximum plasma concentration (Cmax) of 0.7 g/ml. The time to reach peak plasma concentration (Tmax) is 1.3 hour.


Distribution:
Acyclovir is widely distributed to tissues and body fluids. The highest concentrations are found in kidneys, liver and intestines. Acyclovir also crosses the placenta and is excreted in breast milk in concentration approximately 3 times higher than those in maternal serum.

Metabolism:
The major metabolite by hepatic metabolism is 9-carboxy methoxy methyl guanine, which accounts for 9 to 14% of dose. Plasma protein binding is low (9 to 33%). Therefore, drug interactions involving binding site displacements are not anticipated.

Half-life:
The terminal half-life is about 2 to 3 hours for adults without renal impairment. The half-life may increase up to 19.5 hours in anuric patients. During haemodialysis the half-life is reduced to 5.7 hours, with 60% of a dose of acyclovir being removed in 6 hours.

Elimination:
Approximately 14% of total dose of acyclovir on oral administration is excreted unchanged in urine. It is excreted through the kidneys by both glomerular filtration and tubular secretion. Faecal excretion may account for about 2% of dose.

CONTRAINDICATIONS
Acyclovir is contraindicated in patients known to be hypersensitive to acyclovir.

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