Andi Cahyadi
Ganciclovir is a guanosine nucleoside analogue, homologue Acyclovir and
the first antiviral drug effective in treating cytomegalovirus in humans.
Ganciclovir inhibits not only herpes virus but also the transformation of
lymphocytes by the Ebstein Barr Virus. (Crumpacker, 1996; Marshall and Koch,
2009)
Mechanisms and How to Work Ganciclovir
Ganciclovir in vivo transformed into Ganciclovir triphosphate which
inhibits viral DNA polymerase, including Herpes Simplex Virus and CMV, by way
of competitive inhibitors on deoksiguanosine triphosphate formation in viral
DNA elongation. (Marshall and Koch, 2009) After removing pyrophosphate,
Ganciclovir monophosphate binds to the end of the formation thereby inhibiting
replication of DNA chains. (Crumpacker, 1996) Unlike acyclovir, Ganciclovir is
not an absolute chain terminator so that the sub-genomic fragment of CMV
remains synthesized in short segment. All antiviral drugs work because of its ability
to inhibit CMV DNA synthesis and inhibits elongation in DNA replication. In the
cells infected with herpes simplex virus, thymidine kinase phosphorylate the
virus into a form Ganciclovir monophosphate and cellular enzymes further modify
Ganciclovir Ganciclovir monophosphate to triphosphate which can inhibit viral
DNA synthesis. (Crumpacker, 1996)
CMV does not have the enzyme thymidine kinase homologous and as an
alternative is to phosphorylate UL97 gene product Ganciclovir. CMV UL97 kinase
gene insertion into the vaccinia virus Ganciclovir incentives make recombinan
virus susceptible to Ganciclovir. (Crumpacker, 1996)
Left half Ganciclovir triphosphate in CMV-infected cells was 16.5 hours
compared to acyclovir triphosphate which is only 2.5 hours. In the circumstances
molar base, Ganciclovir not as effective as acyclovir triphosphate as a DNA
polymerase inhibitor, but the concentration of CMV in CMV-infected cells ten
times greater than with acyclovir. Ganciclovir triposfat high levels and a long
intracellular half-life makes Ganciclovir is considered to be superior compared
with acyclovir in inhibiting replication of CMV. (Crumpacker, 1996; Marshall
and Koch, 2009)
Pharmacokinetic and Toxicity of Ganciclovir
Giving intravenous Ganciclovir 5 mg/kg in one hour produces the peak
concentration in serum 8.3 g/ml at the end of infusion. Ganciclovir in the
plasma half-life was 2.9 hours and the average clearance of 3.9 ml per kilogram
per minute. Twelve hours after the infusion, serum concentrations of less than
0.5 ug/ml. Regimen from 7.5 to 10.0 mg Ganciclovir per kilogram of body weight
divided in 2 doses per day will produce peak serum concentrations from 4.5 to
10 ug/ml. Ganciclovir had the blood brain barrier penetration to produce a
concentration in cerebrospinal fluid 0.7 ug/ml when measured simultaneously in
plasma levels of 2.2 ug/ml within 3.5 hours after administration of intravenous
2.5 mg/kg. After treatment with Ganciclovir 1000 mg orally 3 times per day, maximum
and minimum concentration in plasma was 1.2 and 0.2 ug/ml. Ganciclovir oral
bioavailability is between 6-9%. Serum concentration has been entered in the
ED50 in most isolates of CMV (0.2 to 1.6 g/ml). (Crumpacker, 1996)
Ganciclovir causes granulositopenia, thrombocytopenia, azoospermia and
increased serum creatinine. Patients with CMV retinitis treated with
intravenous Ganciclovir 3 months, 40% will have granulositopenia (neutrophil
count <1000 per cm3) and 15% had thrombocytopenia <50,000 cm3. Granulositopenia
and thrombocytopenia did not look after Ganciclovir was stopped except for one
patient who suffered irreversible neutropenia and Pseudomonas sepsis. Anemia
may also appear on the long-term treatment. The incidence of thrombocytopenia
and granulositopenia on oral administration is rare than intravenously.
Granulositopenia can be prevented by giving recombinant granulocyte colony
stimulating factor or granulocyte macrophage colony stimulating factor.
Patients will have a lower granulositopenia episode. (Crumpacker, 1996)
Twenty percent of the 20 people who received bone marrow transplant will
experience an increase in serum creatinine over 2.5 mg/dl (221 μmol per liter)
after 120 days of intravenous Ganciclovir. Serum creatinine returned to normal
after Ganciclovir was stopped. Ganciclovir is more dangerous when used in
conjunction with a toxic drug in the bone marrow such as zidovudine. Eighty
percent of the 40 people require a dose reduction because of hematological
toxicity of Ganciclovir and zidovudine. (Crumpacker, 1996) azoospermia
associated with the provision of Ganciclovir on animal studies due to a direct
effect on sperm production constraints. Testicular endocrine function is not
affected but the data on experimental animals showed suppression of fertility
may occur. (Crumpacker, 1996)
Clinical Use Ganciclovir
Ganciclovir inhibits the growth of CMV from laboratory isolates and
clinical isolates with plasma concentrations of 0.1 to 1.6 ug / ml.
(Crumpacker, 1996) Ganciclovir is more active than acyclovir in inhibiting
replication of CMV. In tissue culture, Ganciclovir has antiviral activity
against viruses amazing Herpes Simplex type 1 and 2, Varicela Zoster virus,
Ebstein-Barr Virus and Human Herpes Virus 6. (Crumpacker, 1996) Ganciclovir is
less effective against human adeno virus, human papilloma virus, Influenza
virus and other RNA viruses. (Crumpacker, 1996; Marshall and Koch, 2009)
Ganciclovir is a synthetic nucleotide analog guanosine acyclik,
phosphorylated to triphosphate in the cell and acts as an inhibitor of viral
DNA synthesis. In preliminary data, it is effective for treating symptomatic
CMV. (Whitley et al, 1997) Phase II study, Ganciclovir showed improvement or
stabilization of hearing 4 of 30 infants with congenital CMV infection are
symptomatic after 6 months or more. (Whitley et al, 1997) During the treatment
period, expenditure decreased quantitatively virus in urine, but after
treatment, again as in earlier viremia before treatment. (Leung et al, 2003)
phase III randomized study, Ganciclovir beneficial in children with severe
congenital CMV infection. (Pass, 2002) central nervous system damage that has
occurred can not be repaired but the damage can be prevented before they
happen. Ganciclovir for the treatment of lost hearing in children with CMV
asipmtomatik is rare. (Leung et al, 2003) Ganciclovir Side effects include bone
marrow suppression and toxic to the gonads should be a lot of rethinking.
(Numazaki and Chiba, 1997), but not enough data to decide termination of the
use of Ganciclovir in the treatment of neonatal CMV hepatitis
REFERENCES
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Marshall BC, Koch WC. Antivirals for cytomegalovirus infection in
neonates and infants: focus on pharmacokinetics, formulations, dosing, and
adverse events. Paediatr Drugs. 2009;11(5):309-21.
Crumpacker, CS. Ganciclovir. New Engl J Med 1996;335:721–729.
Numazaki K, Chiba S. Current aspects of diagnosis
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Leung AKC, Sauve RS, Davies D. Congenital
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Pass RF. Cytomegalovirus infection. Pediatr Rev
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