Click here to view guidance from UK Medicines Information.
The above means that both mtx & oseltamivir (tamiflu) are excreted by the kidneys. If taking both drugs, the tamiflu will be excreted first possibly leading to increased mtx in the blood leading to toxicity.Summary
The SmPC for oseltamivir (Tamiflu®) states that care should be taken when using oseltamivir in patients who are taking methotrexate, because of a theoretical risk of increased methotrexate plasma levels leading to toxicity.
Oseltamivir, a pro-drug, is metabolised by hepatic esterases to active oseltamivir carboxylate which is then excreted via the kidney by glomerular filtration and active tubular secretion.
Methotrexate, a drug with a narrow therapeutic margin, is excreted via the same active tubular secretion pathway and competition for this pathway is the basis of the proposed interaction.
There are no published reports of an interaction occurring in clinical practice.
The proposed interaction is unlikely to be of clinical significance and the US prescribing information for oseltamivir does not specifically mention the possibility of an interaction with methotrexate.
Patients taking high dose methotrexate as part of a chemotherapy regimen or low dose methotrexate for the treatment of inflammatory conditions, such as arthritis or psoriasis should be given oseltamivir, if required. Patients on high dose methotrexate will be routinely monitored for toxicity.
There is no clinical evidence in the literature of an interaction between oseltamivir (tamiflu) and methotrexate. The only place that mentions a possible interaction is the SmPC (Summary of Product Characteristics) and i dare say thats just to cover themselves.
Royal College of Physicians Guidance
Guidance for hospital medical specialties on adaptations during a pandemic influenza outbreak
Summary
Preparations for pandemic influenza has been developed by the Royal College of Physicians to help hospitals and staff coordinate care during an influenza outbreak.
The document is designed to indicate how specialties could adjust their patterns of work in order to cope during an influenza pandemic when staff and facilities available to care for patients may be reduced. The intended audience for this guidance is those involved in managing and strategic planning of clinical services, and clinical staff working in hospital specialties. Each specialty section has been written by an expert in the field. The document is not designed to provide detailed operational guidance for responding to an influenza pandemic.
The suggested blue and yellow card system (Appendix) of identifying patients who may or may not need to be seen urgently is a way of organising outpatient referrals in a pandemic, which could be used by consultants in consultation with Trust management.
http://www.rcplondon.ac.uk/pubs/contents/ce8398cc-a20b-4f41-bea6-f32f7a320835.pdf
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