Ritonavir, and possibly indinavir, are predicted to reduce metabolism of buspirone. A single case report describes Parkinson-like symptoms attributed to concurrent use of buspirone withritonavir and also possibly indinavir.
Clinical evidence,mechanism, importance and management
A 54-year-old man who had been taking high-dose buspirone (40 mg every morning and 30mg every evening) developed Parkinson-like symptoms about 6 weeks after starting to take ritonavir 400mg and indinavir 400 mg,both twice daily. The dose of buspirone was reduced to 15mg three times daily,ritonavir and indinavir were discontinued, and amprenavir 1.2 g twice daily was started. The Parkinson-like symptoms were reduced after about one week and completely resolved after 2 weeks. Buspirone is metabolised by cytochrome P450 isoenzyme CYP3A4, and it is probable that ritonavir, and possibly, but to a lesser extent, indinavir, inhibited metabolism of buspirone resulting in toxic levels (See reference number 1). This appears to be an isolated case report however, manufacturer of buspirone usually recommends that a lower dose of buspirone (2.5 mg twice daily in UK) should be used with potent inhibitors of CYP3A4,(See reference number 2)such as ritonavir.
Clay PG,Adams MM. Pseudo-Parkinson disease secondary to ritonavir-buspirone interaction.Ann Pharmacother (2003) 37, 202–5.
Buspar (Buspirone hydrochloride). Bristol-Myers Pharmaceuticals. UK Summary of productcharacteristics,March 2007.