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What is Which of the following drugs is most likely to cause myelosuppression and explain in detail?
Ganciclovir It is an analogue of acyclovir which is active against all herpes viruses including H. simplex, H. zoster, EBV and CMV against which it is most active. mech of action:- Ganciclovir is activated intracellularly by virus specific thymidine kinase and its triphosphate nucleotide preferentially inhibits viral DNA polymerase. This active metabolite attains much higher concentration inside CMV infected cells. The precursor cells in bone marrow are also quite sensitive to ganciclovir, and this may account for its bone marrow toxicity. Pharmacokinetics:- It has poor oral absorption, bioavailability of ganciclovir is low (<10%).Valganciclovir, the valyl prodrug, has ~ 8 times higher bioavailability, and is preferred, where available. Ganciclovir and its active metabolite are mostly excreted unchanged in urine.The plasma t 1/2 of ganciclovir is 2-4 hrs, but that of its triphosphate inside CMV infected cells is > 24 hrs. These factors account for its high activity against CMV infections. Systemic toxicity:- Toxicity of ganciclovir is high: bone marrowdepression, rash, fever, vomiting, neuropsychiatric disturbances. uses:- Use is restricted to prophylaxis and treatment of severe CMV infections (pneumonia/colitis/retinitis) in immunocompromised (AIDS, transplant recipient)patients. Treatment may be initiated with i.v. infusion of ganciclovir 10 mg/kg/day which can prevent blindness in AIDS patients with CMV retinitis. Ref:- kd tripathi; pg num:-801