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Personalised medicine is a targeted approach to the prevention, diagnosis and treatment of disorders on the basis of the specific genetic profile of the patient. Pharmacogenetics research shows that differences in the genetic profile of patients explain the interindividual differences in efficacy and side effects of medicines. Although there are high expectations of personalised medicine and pharmacogenetics in healthcare, both are only used to a limited extent to date. Pharmacogenetics seems particularly important in diseases with a poor prognosis and treatments with potentially serious side effects. Pharmacogenetics testing is reimbursed in the case of serious side effects or unexpected ineffectiveness. 95% of patients in the Netherlands have at least one abnormality in the panel of genes for which guidance is available. The KNMP (Royal Dutch Pharmacists' Association) provides dosing advice based on genotype for 80 medicines, 27 of which are regularly prescribed in primary health care.

De reactie op een geneesmiddel verschilt sterk tussen patienten. Een deel van deze verschillen kan worden verklaard door variatie in het genetisch profiel (DNA). Farmacogenetica probeert tot een geneesmiddelentherapie op maat te komen voor de individuele patient, door rekening te houden met deze verschillen. In deze bijdrage worden de achtergrond en algemene begrippen van farmacogenetica beschreven en relevante ontwikkelingen en toepassingsmogelijkheden voor de huisarts besproken.

Cyclosporin is an immunosuppressive agent with a wide range of therapeutic uses. In transplant patients, it is used for the prevention of rejection and graft-versus-host reactions. The metabolism and bioavailability of cyclosporin can be significantly and persistently influenced through induction of CYP3A4 caused by the concomitant use of rifampicin. However, awareness of the need for the timely and frequent monitoring of cyclosporin levels during and especially after treatment with rifampicin has not fully been addressed. Here, we describe 3 patient cases concerning significant episodes of sub-therapeutic cyclosporin levels after short-term rifampicin therapy. Rifampicin was administered for three to five days and decreased cyclosporin levels were observed ± 7 days after the initiation of rifampicin, and continued during the following weeks even after the cessation of rifampicin therapy. Cyclosporin dosage-adjustments were made based on the cyclosporin blood levels and all 3 patients showed good therapeutic and clinical responses.