Sammanfattning Hepatit B virus (HBV) tillhör familjen hepadnavirus och kronisk HBV finns hos ungefär 257 miljoner människor. Kronisk HBV kan orsaka levercirros och hepatocellulärt karcinom (HCC) och andra svåra leversjukdomar vilket leder till 887,000 dödsfall per år. Symptomen för HBV är illamående, gulsot och mörkfärgat urin. HBV smittas genom sexuell kontakt och infekterat blod. Det smittas alltså vid barnafödsel, sprutor vid droganvändning och dålig hygien inom sjukvården. Det finns vaccin att ta för att förhindra spridningen av viruset. De behandlingar som finns för de som drabbas är antivirala läkemedel som är nukleos(t)id analoger och peginterferoner.  Syftet med arbetet var att se om det är mer effektivt att använda kombinationsterapi med de antivirala läkemedlen adefovir (ADV) och lamivudin (LAM) jämfört med monoterapi med adefovir. Fem randomiserade kontrollerade studier söktes fram från pubmed. Resultaten från de studierna jämfördes sedan.  Studierna visade att kombinerad läkemedelsterapi med ADV och LAM var mer effektivt än monoterapi med ADV. ADV och LAM i kombination visades mer effektivt eftersom det var fler patienterna i den gruppen som fick en inte detekterbar mängd HBV-DNA, fler patienter som fick en normal nivå av alaninaminotransferas (ALAT) och färre patienter som visade på utveckling av resistens mot ADV.  Slutsatsen är att kombinationsterapi med ADV och LAM var mer effektivare än monoterapi med ADV. Det är för att när läkemedlen används tillsammans är de mer effektivare på att hämma viruset och minskar risken för att viruset ska kunna utveckla resistens. / Abstract Hepatitis B virus (HBV) belongs to the hepadnavirus family and chronic HBV is present in approximately 257 million people. There is acute and chronic HBV types of infection. About two-thirds of those with acute HBV have mild symptoms. The rest get more pronounced symptoms such as nausea, fatigue and even jaundice. It then counts as chronic HBV if the person has high levels of the surface antigen for hepatitis B (HBsAg) for more than six months. Chronic HBV can cause liver cirrhosis and hepatocellular carcinoma (HCC) and other severe liver diseases leading to 887,000 deaths per year. HBV is transmitted through sexual contact, infected blood in contact with a wound and during childbirth. There are vaccines to take to prevent the spread of the virus. The treatments available for those affected by the virus are antiviral drugs that are nucleos(t)ide analogues and peg interferons. The aim of the study was to see if it is more effective to use combination therapy with the antiviral drugs adefovir (ADV) and lamivudine (LAM) compared to monotherapy with adefovir. The method used was to select five studies that were randomized controlled trials. The studies were taken from pubmed. After the studies were selected, they were compared with each other. The parts of the study that were focused on were how many patients received an undetectable level of HBV DNA, how many patients received a normal level of alanine aminotransferase (ALAT) and how many patients developed resistance to ADV. The studies showed predominantly that combined drug therapy with ADV and LAM was more effective than monotherapy with ADV. ADV and LAM in combination proved to be more effective as more patients in the group receiving ADV and LAM received an undetectable amount of HBV DNA, more patients received a normal level of ALAT and fewer patients showed the development of resistance to ADV. The results show that ADV and LAM are better at reducing the viral load. This combination also lowers the level of ALAT, which means that those patients do not have as high a risk of damaging their liver. It is also important that patients do not develop resistance to the treatment, which leads to discomfort and an increased viral load again. Avoiding the development of resistance is important as it allows patients to undergo treatment for a long time. The conclusion is that combination therapy with ADV and LAM was more effective than monotherapy with ADV. This is because when the drugs are used together, they are more effective at inhibiting the virus and reduce the risk of the virus being able to develop resistance.