Adding isotretinoin to lithium carbonate probably caused mild lithium toxicity

To the Editor

After careful consideration of the risk of precipitating a depressive episode, I and a dermatologist decided to prescribe isotretinoin for an 18-year-old female with several years of history of unequivocal bipolar I disorder. Inflammatory acne vulgaris would have been likely to cause scarring without this treatment. She was taking controlled-release lithium carbonate 800 mg at night, achieving serum levels 12 hours after the previous dose of 0.8 mmol/L prior to commencing isotretinoin. Serum creatinine was 57 µmol/L (50–90) with an estimated glomerular filtration rate of >60.

She is very insightful and her parents and I believe she never misses doses of medication.

Subsequent to commencing isotretinoin 20 mg three times weekly, the lithium level obtained was 1.1 mmol/L 12 hours after the previous dose. She was taking no other medication. She said she had been feeling unwell, ‘a little strange in my head’, and as if she had a hangover, on the combination. After reducing the dose of lithium to 600 mg at night these symptoms resolved and the lithium level returned to 0.8 mmol/L. She did not become depressed.

Using a search strategy of ‘isotretinoin AND lithium’ via Embase, MEDLINE, and PsychINFO, English language only, no reports of isotretinoin causing elevated lithium levels were found.

Note that the datasheet for isotretinoin states haematuria and proteinuria can occur rarely, and hyperuricaemia has been reported.