Medical Pharmacology Chapter 36: Antiviral Drugs
Antiviral Drugs
Anti-viral drugs with activity against HIV (Human Immunodeficiency Virus)
Viral Transmission2
The risk of acquiring HIV following transfusion of 1 unit of infected blood has been estimated at 90%.9
Concentrated blood products derived from multiple units of pooled blood also have been responsible for HIV transmission.9
These blood products accounted for an early high prevalence of HIV infection among those individuals with hemophilia who received coagulation factor replacement concentrated from many units of blood.
In March 1985 screening of all donated blood was initiated and subsequent to routine heat/solvent detergent treatment of clotting factor concentrates resulted in a dramatic decline in new transfusion-associated HIV infections.9
Appropriate HIV inactivation in clotting factor concentrates have been detailed.
The risk of HIV infection occurring as a result of receiving one unit of blood which tested negative for HIV-1 antibodies is about one in 500,000 or less.9
In the U.S. the estimated HIV infection risk for transfused screen blood is about 1 in 1.5 million units.2
An infected mother may transmit HIV virus to the fetus during pregnancy, delivery, or through breast-feeding.2
In some developing countries this transmission mode is especially important as the ratio of infected women to infected men is about 1:1.2
Fetal transmission may occur early (first or second pregnancy trimester), although is most likely during the perinatal period.
Prophylactic antiviral drug therapy to the mother during pregnancy, labor, delivery and to the fetus following birth is an effective approach to this transmission mode.
Absent antiviral treatment, however, mother to infant/fetus HIV transmission likelihood is about 20% in industrialized countries and about 30% in developing nations.
The most likely single factor accounting for relatively higher HIV-1 transmission rates is higher maternal levels of plasma viremia.
A number of other factors have been implicated.2
In the contemporary circumstance in which HIV-positive pregnant women receive combination antiviral drugs, along with cesarean section delivery, the likelihood of mother-to-child transmission is likely less than 1% and is an unusual clinical occurrence in the US and other developed countries.2
Short duration treatment with zidovudine (AZT) by itself or in combination with lamivudine (3TC) even late in the pregnancy and then to the infant for a week or less dramatically reduces infant transmission, compared to placebo.
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Similarly, short-duration antiretroviral agent such as single-dose nevirapine (Viramune) may also be effective and especially important in low-to mid-income nations due to low drug cost and given that perinatal care may not be available, with pregnant women perhaps seen by the health care provider for the first time around delivery.
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The availability of "effective combination antiretroviral therapy" or cART in developing nations has had a important, beneficial effect, not only for the woman but also blocking HIV maternal-fetal transmission and protecting against later transmission by breast-feeding.2
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