Interactions may occur as a result of increased or decreased lithium levels, or may act through other mechanisms, the most important being neurotoxicity which may occur at therapeutic levels when other drugs which act centrally on the CNS are taken concurrently.
Interactions which increase lithium concentrations
Co-administration of the following drugs with lithium may lead to increased lithium concentrations and a risk of toxicity:
• Any drug which may cause renal impairment has the potential to cause lithium levels to rise, thereby causing toxicity. If the use of the drug is unavoidable, carefully monitor lithium blood level and adapt dosage as necessary.
• Antibiotics (metronidazole, tetracyclines, co-trimoxazole, trimethoprim), N.B. Toxic symptoms may also occur at low or normal levels when used in conjunction with co-trimoxazole or trimethoprim. Lithium toxicity has been reported on isolated occasions in patients receiving spectinomycin.
• Non-steroidal anti-inflammatory drugs (including selective cyclooxygenase (COX) II inhibitors); monitor serum lithium concentrations more frequently if NSAID therapy is initiated or discontinued.
• Drugs affecting the renin angiotensin system (ACE inhibitors, Angiotensin II receptor antagonists).
• Diuretics (including herbal preparations). In addition to the effects noted above, thiazide diuretics show a paradoxical antidiuretic effect resulting in possible water retention and lithium intoxication. Loop diuretics (furosemide and bumetanide, and etacrynic acid) seem less likely to cause lithium retention, although caution is warranted.
• Other drugs affecting electrolyte balance, e.g. steroids, may alter lithium excretion and should therefore be avoided.
Interactions which decrease serum lithium concentrations:
Co-administration of the following drugs with lithium may lead to decreased lithium concentrations and a risk of loss of efficacy:
• xanthine derivatives (e.g. theophylline, caffeine).
• products containing large quantities of sodium e.g. sodium bicarbonate.
• carbonic anhydrase inhibitors.
• Urea.
• empagliflozin.
• dapagliflozin.
Interactions which may not be associated with increased or reduced lithium levels:
Concomitant use of the following drugs may precipitate symptoms of toxicity when the lithium level is within the normal range:
• antipsychotics, including the atypical antipsychotics olanzapine,
• clozapine and haloperidol at high doses
• carbamazepine
• phenytoin
• methyldopa
• clonazepam
• tricyclic and tetracyclic antidepressants
• calcium channel blockers. These drugs may cause neurotoxic reactions at therapeutic levels
• neuromuscular blocking agents. Lithium may cause neurotoxic reactions at therapeutic lithium levels.
Selective serotonin re-uptake inhibitors (SSRIs): Concurrent use with lithium may precipitate a serotonergic syndrome.
Non-steroidal anti-inflammatory drugs including COX II inhibitors: monitor serum lithium concentrations more frequently if NSAID therapy is initiated or discontinued
Triptans: lithium toxicity reported suggestive of serotonin syndrome.
Neuromuscular blockers: Lithium may prolong the effects of neuromuscular blocking agents.
Drugs which lower seizure threshold
Caution is advised if lithium is co-administered with drugs that lower the epileptic threshold (see section 4.4). e.g. antidepressants, antipsychotics, anaesthetics and theophylline.
Drugs which prolong the QT interval
Lithium can cause an increase in the QTc interval, particularly at higher blood levels. Therefore, concurrent use of drugs which have a risk of prolonging the QTc interval should be avoided (see section 4.4), and consideration be made of other potential risk factors such as increasing age, female sex, congenital long QT syndrome, cardiac and thyroid disease and the following metabolic disturbances: hypocalcaemia, hypokalaemia, hypomagnesaemia.
The following products have a high risk of causing QT prolongation and torsade de pointes:
• Class Ia antiarrhythmics, (ajmaline, cibenzoline, disopyramide, hydroquinidine, procainamide, quinidine),
• Class III antiarrhythmics (amiodarone, azimilide, cibenzoline, dofetilidem, ibutilide, sotalol),
• Antipsychotics (amisulpride, haloperidol, droperidol, mesoridazine, pimozide, sertindole, thioridazine and clozaril),
• Antibiotics (intravenous erythromycin, sparfloxacin),
• Serotonin antagonists (ketanserin, dolasetron mesylate),
• Antihistamines (astemizole, terfenadine),
• Antimalarials (artemisinin derivatives, mefloquine, halofantrine),
• Other: arsenic trioxide, cisapride and ranolazine.
ECG should be performed after initiation of treatment and at any point where the patient becomes symptomatic or when there are changes in disease or treatment which may increase the risk of interaction or arrhythmia.
Topiramate: In healthy volunteers, there was an observed reduction (18% for AUC) in systemic exposure for lithium during concomitant administration with topiramate 200 mg/day. In patients with bipolar disorder, the pharmacokinetics of lithium were unaffected during treatment with topiramate at doses of 200 mg/day; however, there was an observed increase in systemic exposure (26% for AUC) following topiramate doses of up to 600 mg/day. There have been reports on lithium toxicity when concurrently administered with topiramate. Lithium levels should be closely monitored when co-administered with topiramate.
Non-Drug Interactions:
• Low sodium diet. Rapid reduction of sodium intake may cause raised lithium levels.
• Intercurrent illness may cause lithium toxicity.