What is the interaction that contraindicates renin inhibitors with ACE inhibitors?

The interaction that contraindicates renin inhibitors with ACE inhibitors is primarily due to the fact that both classes of drugs work on the renin-angiotensin-aldosterone system, but at different points. Renin inhibitors, such as aliskiren, block the activity of renin itself, preventing the conversion of angiotensinogen to angiotensin I. On the other hand, ACE inhibitors block the conversion of angiotensin I to angiotensin II. By utilizing both these agents together, there's an additive effect on renin-angiotensin blockade, which can lead to significant hypotension and an increased risk of renal impairment and hyperkalemia.

The other options don't directly convey this critical interaction. While both renin inhibitors and ACE inhibitors can increase potassium levels, the primary concern with combining these agents is the enhanced effects on the renin-angiotensin system and the potential for hypotension and renal issues when used together. The option indicating that both inhibit renin production accurately reflects the underlying mechanism of interaction that makes the combination contraindicated.