Raltegravir binds to divalent cations such as iron, calcium, magnesium and forms a complex at the level of the gastro-intestinal tract which results in less raltegravir being absorbed. Coadministration of raltegravir (400 mg single dose) with a Forceval multivitamin tablet (containing 108 mg calcium, 12 mg iron and 30 mg magnesium) did not significantly affect the pharmacokinetics of raltegravir (Cmax, Cmin and AUC decreased by 12%, 10% and 17%, respectively). However, since the content of divalent cations is variable among multivitamins preparations, caution is recommended when prescribing multivitamins. Administration of raltegravir 400 mg twice daily and multivitamins should be separated by at least 6 hours. Importantly, drug-drug interaction studies with antacids containing divalent cations have shown a more pronounced reduction in raltegravir Cmin when raltegravir was administered once daily compared to a twice daily regimen. A similar effect for multivitamins containing divalent cations cannot be excluded, therefore, twice daily administration of raltegravir should be preferred.