I understand there are two main types of resistance testing, phenotyping and genotyping. Phenotyping actually runs multiple drug response curves against the main viral strains amplified in a laboratory. Genotyping sequences or probes for either known mutations associated with resistance or uses a database to compare mutations against known phenotypic resistance. What are the preferred indications for genotyping versus phenotyping? What is the best way to be sure that the genotype interpretation is highly correlated with anticipated phenotypic expression in the patient? —Mark Majkowski, DDS
Dr. Brian Conway responds: The relationship between genotype and phenotype is the subject of ongoing debate. There are no clear data on the specific indication for the use or one test over another in any specific circumstance. Genotyping is a bit less expensive and the results may be available more rapidly. However, phenotyping is a more direct (and, possibly, more easily understandable) measure of the efficacy of a given drug against the isolate under evaluation. Rules for the correlation of genotype with phenotype are being developed on an ongoing basis. For now, the best interpretation of the genotype (based on current knowledge) is provided with most clinical reports you will see. (8/1/2000)
