The enzyme CYP3A5 (full name: Cytochrome P450 3A5) is involved in the metabolisation of xenobiotics, such as drugs. The enzyme CYP3A5 demonstrates an overlap in substrate specificity with the enzyme CYP3A4, although the affinity for certain drugs can differ. For most drugs the role played by CYP3A5 is clearly secondary to that of CYP3A4.
Drugs that can be metabolised by the enzyme CYP3A5 are similar in principle to those mentioned under the enzyme CYP3A4. However, the extent to which the CYP3A5 enzyme contributes to total CYP3A activity appears to be limited.
An exception applies in the case of the immunosuppressant tacrolimus; this drug is known to be broken down primarily by the enzyme CYP3A5. At present, however, there are no specific dosage recommendations; in hospitals the correct dose is determined by monitoring patients closely.
Genetic predisposition
The activity of the enzyme CYP3A5 varies from one individual to another.
As a result, the efficacy of a drug can differ from person to person, as can the risk of potential side effects. This variation can be partly explained by genetic variations in the CYP3A5 gene.
When a genotype is determined these variations in the CYP3A5 gene are indicated by two so-called alleles. Each allele has a name consisting of an asterisk (*) and a number. An example of a possible CYP3A5 genotype is CYP3A5*1/*3.
At iGene we determine the following variants (alleles) of the CYP3A5 gene:
CYP3A5*3, CYP3A5*6, CYP3A5*7 and other (classified as CYP3A5*1). The active variant of CYP3A5 (*1) is present in less than 15% of the European population; the majority of Europeans have the inactive variant.