Chapter 8 Qs: Drug Monitoring Flashcards
Most suitable approach to monitoring statins
think most suitable option e.g. statins
→ myopathy if RFs (personal/FH of muscular disorders/toxicity, +++alcohol, renal impairment, hypothyroidism, elderly) = check baseline creatine kinase.
→ if no RFs, measure serum ALT
Q8.1: IV Vancomycin Monitoring
Q8.1: IV vancomycin.
- Check serum creatinine at baseline, as clearance of vancomycin reduced in renal dysfunction + important for choosing dosing regimen.
- 2 classic S/Es = nephrotoxicity + ototoxicity.
Q8.3: Phenytoin monitoring
- Phenytoin given at initial loading dose of IV 1200mg + maintenance dose 300mg orally daily.
- Day 14 trough = 54micromoles/L (in N range).
- So, 300mg is a reasonable dose.
- Post-dose phenytoin levels not routinely required as half-life of phenytoin ~24h so significant diurnal variation unlikely after 14days.
- N range should be considered in context of patient – if no seizures, don’t increase dose.
- If S/Es despite N trough level, then decrease dose (if seizures controlled) or seek alternative.
Q8.4: Lithium Drug monitoring
- Recommended sampling time for lithium = 12h after last dose. N RR = 0.4-0.8mmol/L.
- FBCs not routinely required.
- Routine serum lithium monitoring = weekly after initiation + after each dose change until stable concentrations, then every 3 months thereafter.
- Sodium depletion >risk of lithium toxicity so avoid diet changes.
Routine serum-lithium monitoring should be performed weekly after initiation and after each dose change until concentrations are stable, then every 3 months for the first year, and every 6 months thereafter. Patients who are 65 years and older, taking drugs that interact with lithium, at risk of impaired renal or thyroid function, raised calcium levels or other complications, have poor symptom control or poor adherence, or whose last serum-lithium concentration was 0.8 mmol/litre or higher, should be monitored every 3 months. Additional serum-lithium measurements should be made if a patient develops significant intercurrent disease or if there is a significant change in a patient’s sodium or fluid intake
Q8.5: Methotrexate Drug Monitoring
- Methotrexate can cause fatal blood dyscrasias.
- FBC is monitored regularly, but once stabilised, reduce to 2-3months.
- CXR not needed at baseline.
- Due to risk of liver cirrhosis, don’t start if LFTs abnormal.
- If significant WBC/platelets drop, must STOP it.
- Predominantly renally excreted so toxicity more likely if renal dysfunction.
Q8.6: Olanzapine Drug Monitoring
- For olanzapine, fasting blood glucose should be measured at baseline as hyperglycaemia + diabetes can occur.
- Baseline ECG only indicated if CV disease or RFs.
Q8.7: COCP drug monitoring
- For COCP (ethinylestradiol), measure BP as HTN >risk of arterial disease associated with contraceptive medication.
- Don’t need monitoring of serum creatinine, resting HR, serum AST or haemoglobin.
Q8.8:Amiodarone Drug monitoring
- For amiodarone, do baseline CXR.
- T3, TSH + T4 all needed as T4 may be raised without hyperthyroidism.
- Monitor LFTs regularly throughout not just if suspected hepatotoxicity.
- Dose of amiodarone independent of renal function (renal failure not a S/E).
- Commence with caution if hypokalaemia as increased risk of arrhythmias.
Q8.9:Carbimazole drug monitoring
- Carbimazole + sore throat = infection from possible BM suppression – so need FBC with neutrophil count.
- Throat swab won’t reveal BM suppression.
- Blood cultures indicated later.
- Carbimazole can cause hepatic disorders (option is to measure ALT), but not key here.
- TFTs not relevant first-line.
Q8.10:Gentamicin Drug Monitoring
- For multiple daily dose regimen, 1 hour peak serum concentration should be 3-5mg/L for treatment of endocarditis (just check BNF for this).
- Gentamicin principally renally excreted from body, so renal dysfunction >toxicity risk, so monitor renal function at regular intervals.
Q8.11: ACEi Drug Monitoring
ACE-i known to cause hyperkalaemia + hyponatraemia – in some cases, AKI. Check U&Es at baseline + after every dose change.
ACE-i do not affect HR, urinary sodium not a suitable method, urine output measurement not practical in primary care setting, can measure serum levels of ACE but not relevant for monitoring – and also elevated in sarcoidosis.
Q8.12:Digoxin Drug Monitoring
- Plasma digoxin concentration not measured unless toxicity/non-compliance/inadequate effect (even though listed first on BNF, it doesn’t say to monitor it per se).
- Digoxin predominantly renally excreted so measure serum creatinine.
- BP + CXR + serum sodium not required – not specific as doesn’t cause hypotension, no pulmonary S/Es + not specific enough and checked as part of U&Es.
- Serum potassium more relevant as hypokalaemia increases risk of digoxin toxicity.
Q8.13: Sodium Valproate Drug Monitoring
- Sodium valproate therapy → hepatotoxicity + liver function – measure at baseline + regular intervals throughout duration.
- Pancreatitis = S/E but amylase only measured if symptoms.
- Vitamin D supplements considered as S/E is osteoporosis but not checked at baseline.
- Serum potassium not required.
- Renal function not routinely required as neither significantly renally excreted nor nephrotoxic.
Q8.14: Clozapine Drug Monitoring
- Clozapine = risk of neutropenia + fatal agranulocytosis, so monitor FBCs weekly for 18months – all must register with clozapine monitoring service.*
- Serum creatinine not routinely required.*
- If leucocytes or neutrophils drop, then STOP clozapine immediately – don’t just reduce the dose!*
