ramipril and diclofenac

Pharmacodynamic interaction. Diclofenac inhibits cyclooxygenase, reducing renal prostaglandin synthesis. Prostaglandins maintain afferent arteriolar dilation and renal blood flow, especially in volume-depleted states. Ramipril inhibits angiotensin-converting enzyme, reducing angiotensin II formation and causing efferent arteriolar dilation. The combined effect reduces glomerular filtration pressure, increasing the risk of acute kidney injury. Diclofenac also promotes sodium and water retention, which can blunt the antihypertensive effect of ramipril.

Patients may experience a rise in serum creatinine, reduced blood pressure control, and worsening of heart failure or oedema. This is particularly likely in the elderly, those with pre-existing renal impairment, on diuretics, or dehydrated. In most cases, the effect is reversible after stopping the NSAID, but acute renal failure can occur in high-risk patients.

Avoid co-prescription where possible, especially in patients at high risk (elderly, dehydration, diuretic use, pre-existing renal disease, heart failure). If combined use is unavoidable, use the lowest effective dose of diclofenac for the shortest duration, ensure adequate hydration, and monitor blood pressure and renal function (serum creatinine, potassium) at baseline and within 1 to 2 weeks after starting or changing therapy. Consider alternative analgesia such as paracetamol.

Well established through clinical studies and meta-analyses. Documented in major drug interaction databases and national formularies. The interaction is clinically significant and carries a recognised risk of renal impairment and reduced antihypertensive effect.