Can lithium and buspirone be co‑prescribed in an adult patient with normal renal function and no other serotonergic medications?

Can Lithium and Buspirone Be Co-Prescribed?

Yes, lithium and buspirone can be safely co-prescribed together in adults with normal renal function, as there are no documented pharmacokinetic or pharmacodynamic interactions between these medications. However, specific monitoring considerations apply to each drug individually.

Evidence for Safety of Co-Administration

• No direct drug-drug interaction has been documented between lithium and buspirone in the medical literature 1, 2.
• Buspirone is not listed among medications that alter lithium clearance or increase neurotoxicity risk 1.
• The major drug interactions with lithium involve medications that affect renal function (diuretics, NSAIDs, ACE inhibitors) or cause neurotoxicity (antipsychotics, anticonvulsants, calcium antagonists), none of which apply to buspirone 1, 2.

Individual Monitoring Requirements

For Lithium

• Baseline laboratory assessment should include complete blood counts, thyroid function tests, urinalysis, blood urea nitrogen, creatinine, serum calcium levels, and pregnancy testing in females 3.
• Once stable lithium dosing is achieved, monitor lithium levels, renal and thyroid function, and urinalysis every 3-6 months 3.
• Long-term lithium treatment can cause modest decline in renal function, with approximately 34% of patients developing eGFR <60 mL/min/1.73 m² after chronic use 4.

For Buspirone

• In patients with normal renal function, buspirone requires no special monitoring or dose adjustment 5.
• Buspirone pharmacokinetics are similar in patients with mild to moderate renal impairment compared to those with normal renal function 5, 6.
• Plasma concentrations of buspirone and its active metabolite 1-PP are highly variable regardless of renal function 6.

Important Clinical Considerations

Buspirone may lower seizure threshold, which is relevant when used as an anti-shivering agent in specific clinical contexts 3. This property does not contraindicate its use with lithium but warrants awareness in patients with seizure history.

Buspirone has synergistic effects with other sedating agents 3, though this does not apply to lithium, which is not sedating.

Renal Function Context

Since you specified normal renal function, no dose adjustments are needed for either medication. However, be aware that:

• If renal function declines during lithium therapy, lithium dosing will require adjustment, but buspirone dosing remains unchanged unless severe renal failure develops 5, 4.
• Only in anuric patients would buspirone require a 25-50% dose reduction due to accumulation of its active metabolite 5.