Major
Enalapril × Lithium
Angiotensin-converting enzyme inhibitors (ACEi)×Psycholeptics. Lithium
Mechanism
Enalapril (ACE-I) lowers glomerular filtration rate and activates sodium reabsorption in the proximal tubules. Lithium follows sodium: its reabsorption rises and serum levels increase by 25–50% over 3–4 weeks.
Symptoms
Tremor, muscle twitching, nausea, diarrhoea, confusion, ataxia. Severe cases include seizures, coma, and nephrogenic diabetes insipidus with dehydration. Symptoms emerge when serum lithium exceeds 1.2 mmol/L.
Management
Reduce lithium dose by 25–30% when starting enalapril; check serum lithium at 1 and 4 weeks. Alternative antihypertensives in bipolar patients: a beta-blocker or a calcium channel blocker (amlodipine).