The usage of antivirals
According to The Norwegian Drug Wholesales statistics database, the sales of antiviral drugs measured in defined daily doses (DDDs) continued to increase in 2018. However, price reduction for some of the drugs used in treatment of HIV and hepatitis C virus (HCV) has resulted in a reduction in cost, despite the continuous increase in sales measured in DDDs and number of users. Both for HIV- and HCV-drugs, there has been a significant change in the pattern of use with a transition from single ingredient drugs to fixed combinations. In 2018, 95% of the patients treated for HCV used fixed combination drugs, a significant increase from 27% in 2016, and none in 2014.
No mutations conferring resistance against oseltamivir or zanamivir were detected in the 2018/19 season. All circulating influenza strains are currently resistant to adamantanes. The reference laboratory does therefore not routinely analyze for adamantine resistance. In Norway, only oseltamivir is currently available for antiviral treatment of influenza.
Human immunodeficiency virus-1
Surveillance drug-resistance mutations (SDRMs) were detected in 9.2% of samples from patients with newly diagnosed HIV-1 infection in Norway in 2018. This is a small increase compared to previous years, but the number of samples analyzed for primary drug resistance was lower in 2018 compared to 2017. The prevalence of transmitted drug resistance has been stable for the past few years with only minor variation. In 2018 only mutations associated with resistance against non-nucleoside- (5.9%) and nucleoside-
(5.0%) reverse transcriptase inhibitors were detected, and no mutations affecting protease inhibitors were found.
Hepatitis B virus
In 2018, 20 patient samples were submitted for hepatitis B virus (HBV) antiviral resistance testing. Among these, only four cases of resistance were detected, all against entecavir. Among samples submitted primarily for HBV-genotyping (n=245), no drug resistance mutations were detected.
Given the large number of patients on treatment, the burden of resistance against HBV antivirals seems to be low in Norway. However, the data is limited due to the low frequency of testing and should therefore be interpreted with caution.
Human herpes viruses
In 2018, the reference laboratory received 27 samples from 22 patients for cytomegalovirus resistance testing. Resistance mutations were detected in samples from two patients. In most cases, therapy failure is not due to resistance against antiviral drugs.
Five herpes simplex samples were analyzed for antiviral drug resistance. A mutation associated with aciclovir resistance was detected in one of the samples. Despite an increasing consumption of aciclovir for both therapeutic and prophylactic treatment, treatment failure is rare, indicating a low frequency of drug resistance.
Hepatitis C virus
Resistance testing for HCV is currently not available in Norway, and there is no surveillance of drug resistant HCV in Norway. If HCV resistance testing is needed, samples are sent to laboratories in Sweden. A sequencing method for resistance testing of HCV is under development at the NIPH, and the status of this ongoing work is described in the report.