Psychotropic medications are widely used and need to be considered in an impatient setting primary in the case of potential interaction or withdrawal.
On lithium
A fantastic drug with numerous problems. The popularity of lithium seems to have waned, perhaps people have become scared of old-fashioned medicines… Many of the hesitations around lithium are founded: it will destroy the kidneys over the course of life-long treatment.
The dose of lithium is completely irrelevant, its therapeutic effect is determined by serum concentration (as one would expect).
The therapeutic range is 0.6-1.2mmol/L.
Toxicity
Lithium toxicity can manifest at levels over 1.0mmol/L. It may have a varied presentation but in mild cases usually manifests as vomiting and diarrhoea. The potential volume depletion can worsen the situation.
Lithium is distributed into the central nervous system later and the resultant toxidrome is typically one of altered mental status, tremor, hyperreflexia, ataxia, and nystagmus.
Interaction
Lithium is not metabolised and is excreted unchanged in the urine. There are no significant pharmacokinetic interactions, and the only likely pharmacodynamic interaction is the precipitation of serotonin syndrome.
Any other medication that may impact on renal clearance such as NSAIDs, diuretics and RAAS modulators may increase the serum concentrations and cause toxicity. Lithium wasting by any cause may cause a sharp decline in serum concentration and lead to psychiatric decompensation.
On clozapine
Another fantastic drug, this time new-age, but with the same shroud of nervousness. It carries a risk of myeloid failure (neutropenia or agranulocytosis) which, while uncommon (about 1%), is significantly dangerous to warrant concern.
While the risk of granulocytopenias falls significantly after the first year, the rick of constipation does not.
Other side effects:
- Constipation
- Sedation
- Tremor
- Orthostatic hypotension
- Decreased seizure threshold
- Other anticholinergic effects
Monitoring
Life-long haematological monitoring is required, and intense monitoring is conducted at commencement of treatment.
Constipation
This accounts for over a third of medical admissions for patients on clozapine and can very quickly become life-threatening. There are lots of protocols but the long and short is that it should be treated aggressively.