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What is Ledipasvir/sofosbuvir and explain in detail?
Ledipasvir/sofosbuvir, sold under the trade name Harvoni among others, is a medication used to treat hepatitis C. It is a fixed-dose combination of ledipasvir and sofosbuvir. Cure rates are 94% to 99% in people infected with hepatitis C virus (HCV) genotype 1. Some evidence also supports use in HCV genotype 3 and 4. It is taken daily by mouth for 8–24 weeks.It is generally well tolerated. Common side effects include muscle pains, headache, nausea, rash, and cough. It is unclear if use in pregnancy is safe for the baby. Ledipasvir works by decreasing the activity of NS5A and sofosbuvir works by decreasing the activity of NS5B polymerase.Ledipasvir/sofosbuvir was approved for medical use in the United States, in the European Union, and in Canada in 2014. It is on the World Health Organizations List of Essential Medicines.

Medical uses
Cure rates are 94% to 99% in people infected with genotype 1 (46% of HCV cases). It has also been evaluated for the treatment of infection with other hepatitis C genotypes, and has shown promising results in genotypes 3 and 4 (making up 30% and less than 22% of HCV cases respectively).

Resistance
NS5A mutations
Multiple mutations of HCV replicons are necessary to cause a significant effect in resistance due to multiple mechanisms of action. In general, HCV genotype 1a is less resistant to mutation than genotype 1b.For genotype 1b a single amino acid substitution (e.g. L31V) in the replicon had less than a 100 fold increase in resistance to the ledipasvir in Harvoni, while a two amino acid substitution had over a 1000 fold increase in resistance. Genotype 1a had a similar but more substantial increase in resistance with each respective increase in amino acid substitution with resistance associated substitutions at K24R, M28T/V, Q30R/H/K/L, L31M, and or Y93H/N.NS5A polymorphisms also have an effect on viral resistance with the most common resistance-associated amino acid substitutions detected at Q30R, Y93H or N, and L31M in patients with a rapid virological response (RVR). The specific baseline NS5A resistance-associated polymorphisms observed in clinical trials were M28T/V, Q30H, Q30R, L31M, H58P, Y93H, and Y93N in genotype 1a and L28M, A92T, and Y93H in genotype 1b. Patients with multiple baseline NS5A polymorphisms tend to have higher relapse rates when using ledipasvir/sofosbuvir. The difference in relapse rates between treatment naive and treatment experience groups with baseline NS5A polymorphisms ranges from 1% after a 12-week regimen and 0% after a 24-week regimen respectively.

NS5B mutations
A single amino acid substitution S282T contributes to viral resistance and decreases the activity of sofosbuvir in ledipasvir/sofosbuvir by approximately 2 to 18 fold.

Cross resistance
No cross resistance was seen in the combination of ledipasvir and sofosbuvir in ION phase 1,2 and, 3 clinical trials as ledipasvir was fully active against sofosbuvir-resistance-associated substitutions and vice versa.

Side effects
More than 10% of people taking ledipasvir/sofosbuvir have headaches or fatigue; rashes, nausea, diarrhea, and insomnia occur in between 1% and 10% of people taking it.More severe reactions are connected with allergic reactions to the medications and cardiovascular problems. Harvoni side effects are considered relatively mild compared to older interferon-based treatment.
Ledipasvir/sofosbuvir could cause hepatitis B re-activation in people co-infected with hepatitis B and C viruses. The European Medicines Agency recommended screening all people for hepatitis B before starting ledipasvir/sofosbuvir for hepatitis C in order to minimize the risk of hepatitis B reactivation.

Drug interactions
Ledipasvir/sofosbuvir is a substrate for the drug transporters P-Glycoprotein (P-gp) and breast cancer resistance protein (BCRP). Intestinal absorption of these drug transporter substrates may be decreased by inducers such as rifampin and St