Clinically important drug interactions with disease-modifying antirheumatic drugs.

Rheumatic diseases are mostly chronic in nature and often require long term drug treatment. An increasing number of disease-modifying antirheumatic drugs (DMARDs) are used earlier in the course of disease and increasingly in combination with each other. Often there is comorbidity with ensuing pharmacotherapy, especially in the elderly, and therefore the risk of unwanted drug interactions increases. Awareness of these interactions is important in order to either avoid or manage them. Antimalarials, gold, penicillamine (D-penicillamine), sulfasalazine and azathioprine have few clinically important drug interactions. The renal excretion of the antifolate methotrexate is affected by drugs that influence kidney function. This is of particular importance in patients with compromised renal function, e.g. the elderly. Other drugs with influence on folate metabolism, such as trimethoprim, should not be given concomitantly. Cyclosporin is an agent recently introduced in rheumatological practice, and shows a myriad of clinically significant drug interactions mainly based on interference with its metabolic degradation by cytochrome P450 3A, leading to increased or decreased blood concentrations and toxicity or lack of effect. Although most of these interactions with cyclosporin are described in organ transplant patients, they may apply to rheumatological practice as well.