If one of the following drugs is initiated, lithium dosage should either be adjusted or concomitant treatment stopped, as appropriate.
Interactions which increase lithium concentrations
• Metronidazole may reduce lithium renal clearance.
• Non-steroidal anti-inflammatory drugs including selective cyclo-oxygenase (COX) 2 inhibitors (monitor serum lithium concentrations more frequently if NSAID therapy is initiated or discontinued)
• ACE inhibitors
• Angiotensin II receptor antagonists.
• Diuretics (thiazides show a paradoxical antidiuretic effect resulting in possible water retention and lithium intoxication). Should be prescribed with extreme caution and careful monitoring. Similar precautions should be exercised on diuretic withdrawal. Note that thiazides show a paradoxical antidiuretic effect resulting in possible water retention and lithium intoxication. If a thiazide diuretic has to be prescribed for a lithium-treated patient, lithium dosage should first be reduced and the patient re-stabilised with frequent monitoring. Similar precautions should be exercised on diuretic withdrawal. Loop diuretics seem less likely to increase lithium levels.
• Other drugs affecting electrolyte balance, e.g. steroids, may alter lithium excretion and therefore should be avoided.
• Tetracyclines.
Interactions which decrease serum lithium concentrations
Serum lithium levels may be decreased due to an increase in lithium renal clearance in case of concomitant administration of one of the following drugs:
• urea
• xanthines (such as caffeine and theophylline)
• sodium bicarbonate containing products
• Diuretics (osmotic and carbonic anhydrase inhibitors)
• Calcitonin.
Co-administration of the following drug with lithium may lead to decreased lithium concentrations and a risk of loss of efficacy:
• empagliflozin
• dapagliflozin.
Interactions causing neurotoxicity
• Neuroleptics (particularly haloperidol at higher dosages), flupentixol, risperidone, diazepam, thioridazine, fluphenazin, chlorpromazine and clozapine may lead in rare cases to neurotoxicity in the form of confusion, disorientation, lethargy, tremor, extrapyramidal symptoms and myoclonus. Co-administration of lithium with neuroleptics increases the risk of Neuroleptic Malignant Syndrome (NMS), which may be fatal. Discontinuation of both drugs is recommended at the first signs of neurotoxicity.
• Methyldopa
• Triptan derivatives and/or serotonergic antidepressants such as Selective Serotonin Re-uptake Inhibitors (e.g. fluvoxamine and fluoxetine) as this combination may precipitate a serotonergic syndrome, which justifies immediate discontinuation of treatment.
• Calcium channel blockers may lead to a risk of neurotoxicity in the form of ataxia, confusion and somnolence, reversible after discontinuation of the drug. Lithium concentrations may be increased.
• Carbamazepine may lead to dizziness, somnolence, confusion and cerebellar symptoms such as ataxia.
• Tri-cyclic antidepressants.
Other
Topiramate
In healthy volunteers, there was an observed reduction (18% for AUC) in systemic exposure for lithium during concomitant administration with topiramate 200mg/day. In patients with bipolar disorder, the pharmacokinetics of lithium were unaffected during treatment with topiramate at doses of 200mg/day; however, there was an observed increase in systemic exposure (26% for AUC) following topiramate doses of up to 600mg/day. There have been reports of lithium toxicity when concurrently administered with topiramate. Lithium levels should be closely monitored when co-administered with topiramate.
Caution is advised if lithium is co-administered with other drugs that prolong the QT interval (see Sections 4.4 and 4.8), e.g. Class IA (e.g. quinidine, disopyramide), or Class III (e.g. amiodarone) antiarrhythmic agents, cisapride, antibiotics such as erythromycin, antipsychotics such as thioridazine or amisulpride. The list is not comprehensive.
Caution is advised if lithium is co-administered with drugs that lower the epileptic threshold (see Section 4.4), e.g. antidepressants such as SSRIs, tricyclic antidepressants, antipsychotics, anaesthetics, theophylline. The list is not comprehensive.
Lithium may prolong the effects of neuromuscular blocking agents. There have been reports of interaction between lithium and phenytoin, indometacin and other prostaglandin-synthetase inhibitors.
Raised plasma levels of ADH may occur during treatment.
Serotonin syndrome
Serotonin syndrome is a potentially life-threatening adverse reaction, which is caused by an excess of serotonin (e.g. from overdose or concomitant use of serotonergic drugs), necessitating hospitalisation and even causing death.
Symptoms may include:
- Mental status changes (agitation, confusion, hypomania, eventually coma)
- Neuromuscular abnormalities (myoclonus, tremor, hyperreflexia, rigidity, akathisia)
- Autonomic hyperactivity (hypo or hypertonia, tachycardia, shivering, hyperthermia, diaphoresis)
- Gastrointestinal symptoms (diarrhoea)
Strict adherence to the recommended doses is an essential factor for the prevention of the occurrence of this syndrome.