General psychiatry Flashcards
Lithium - distribution in body after a dose?
Concentrated in thyroid and kidney
Lithium - excretion?
Almost wholly excreted in urine.
Depends on: GFR, reabsorption at proximal renal tubules, alkaline urine.
Lithium toxicities and association serum level:
Lithium toxicity:
0.6-1mmol/L - tremor
1.5-3mmol/L - diarhorrea, ataxia, thirst
>3mmol/L - confusion, spasticity, seizures, dehydration, coma.
Hypothyroidism and CKD are ASEs that are not serum level dependent.
Agents that reduce lithium clearance:
- THIAZIDE DIURETICS (classic interaction leading to toxicity)
- K+-sparing diuretics
- ACEi
- Most NSAIDs
- Loop diuretics can either increase or decrease serum levels!
Any condition causing volume depletion or renal impairment will increase reabsorption of lithium
(eg. GI losses, acute decompensated HF, cirrhosis, diuretics, NSAIDs, ACEi).
Agents that increase lithium clearance:
- Sodium bicarbonate - this works because increased plasma bicarb leads to greater urinary bicarb excretion. However, because bicarb is an ANION, there is need for a CATION to also be excreted, hence lithium is booted out.
- Loop diuretics
(though can decrease clearance by causing volume depletion - VERY IMPORTANT) - Osmotic diuretics
Renal toxicities of lithium:
- Nephrogenic diabetes insipidus (resistance to ADH)
- Distal RTA (incomplete) - increased backflow of H+ ions. urine pH >5.3, but extracellular pH and [HCO3-] are WNL
- Nephrotic syndrome (not common)
- Oedema during manic phase ?due to increased salt intake - Chronic interstitial nephritis, fibrosis and CKD (related to duration and cumulative dose)
- HyperPTH and HyperCa2+ (with hypocalciuria)
How do you treat nephrogenic DI due to lithium toxicity?
- CEASE LITHIUM if possible
- DI usually reversible
- but may have progressed to irreversible stage - If need to continue lithium then trial AMILORIDE
- decreases accumulation of lithium in collecting tubular cells by inhibiting the epithelial Na+ channels
- will not be effective if reached irreversible stage (ie. no longer lithium-dependent)
If amiloride is not successful, then try usual treatment for nephrogenic DI:
- Low Na+ diet
- Thiazide diuretic: to diminish distal water delivery or upregulate aquaporin receptors
- NSAIDs: to decrease the synthesis of prostaglandins
- DDAVP (desmopressin) - to provide supraphysiologic ADH levels and overcome partial resistance.
NOTE: VERY important to monitor lithium levels during use of amiloride, thiazide diuretics, and NSAIDs, as they all decrease clearance.
What effect will CO2 retention have on lithium levels?
Increased PaCO2
- -> acidification of blood and urine
- -> decrease in lithium excretion
- -> increase in serum lithium level
What distinguishes the atypical from the typical antipsychotics?
Give a few examples of each category.
Atypical antipsychotics are less likely to cause extrapyramidal side effects than the older typical antipsychotics.
This is because they cause less inhibition of D2 receptors (dopamine Rc type 2 - in substantia nigra), and act on other dopamine Rc subtypes (eg. 3, 4 - in mesolimbic system).
Typicals (work predominantly on D2-R): haloperidol, chlorpromazine, thioridazine, flupenthixol, zuclopenthixol.
Atypicals: risperidone, clozapine, olanzapine, quetiapine, amisulpride, apiprazole.
The atypical antipsychotics may be more sparing of dopamine pathways in the substantia nigra (and thus less likely to cause EPSEs), but they can cause other ASEs by affecting other dopaminergic pathways.
Give some examples.
Affect on projections to hypothalamus and pituitary.
–> Increased appetite (olanzapine = #1, clozapine) (hypothal)
–> increased prolactin –> gynaecomastia, sexual dysfunction (risperidone)
EPSEs which can be seen more commonly with older antipsychotics:
- Akithesia: restlessness
- Dystonia: muscle spasm
- Parkinsonism: rigidity, tremor
- Tardive dyskinesia: choreoathetoid movements - often orobuccal region.
Older antipsychotics can also have secondary negative symptoms.
Main ASEs of clozapine:
BM suppression
severe myocarditis
Cholinergic effects - hypersalivation
constipation and ileus
weight gain
Schizophrenia subtypes:
- Paranoid
- Disorganisned
- Catatonic
(organic brain syndrome: waxy flexibility, mutism, posturing) - Delusional disorder
“Older” antidepressants: main ASEs and some drug examples.
Drowsiness Blurred vision Confusion Constipation Urinary retention (anticholinergic effects)
Cardiotoxic in OD
Eg. Amitriptyline, imipramine, dothiepin.
withdrawal effect is usually over stimulation of the cholinergic (nausea, diarrhoea) and things like insomnia
their actual mech of action is likely blockade of the norAd reuptake
SSRIs: main ASEs and some drug examples.
Effects on sleep (insomnia), sex (impotence) and gut (N/V)
Not cardiotoxic in OD.
Fluoxetine (prozac)
Sertraline (zoloft)
Citalopram (cipramil)
Paroxetine