Tubes containing gel (SST and PST) are NOT acceptable
Units : ug/L
Therapeutic range : 100 - 2000 (diazepam)
Toxic effects from: > 3000 (diazepam)
The quoted therapeutic range is for trough concentrations; specimens should be collected shortly before administering the next dose of the drug.
Uncertainty of Measurement: 12%
Principle : Liquid Chromatography Mass Spectrometry (LCMS)
Diazepam: Diagnostic Use and Interpretation
Diazepam is widely prescribed for the treatment of anxiety disorder, as a sedative-hypnotic and an anticonvulsant. After oral administration, it is rapidly absorbed from the gut and metabolizes to nordiazepam, temazepam and oxazepam. Its primary metabolite is nordiazepam, which is pharmacologically active. Nordiazepam is also a metabolite of clorazepate, chlordiazepoxide, and parazepam. The half-life of diazepam is 21-37 hours.
Diazepam intoxication following over dosage is not an infrequent occurrence. Overdose with diazepam generally results in drowsiness, ataxia and muscular weakness. However, over dosage with benzodiazapines alone rarely leads to fatal outcomes, despite very high doses and high plasma concentrations (ten fold greater than therapeutic range). Severity of intoxication appears to be influenced by co-ingestion of other CNS depressants such as ethanol, barbiturates, analgesics, or tricyclic antidepressants.
Quantitation of diazepam in serum or plasma may help optimize chronic dosing, verify compliance, and identify changes in pharmacokinetics. There is a direct relationship between dose and trough serum concentration in patients who are compliant with treatment and in steady state.
The method used to measure Diazepam (TMS) will also detect its metabolites and other benzodiazepines. The other benzodiazepines cannot be accurately quantified but their presence will be commented upon.
References :
1. Baselt, RC: Disposition of toxic drugs and chemicals in man. 8th edition. Chemical Toxicology Institute, Forster City, CA, 2008; pp 424-426.
2. Ruhterford DM., et al. Plasma concentrations of diazepam and desmethyldiazepam during chronic diazepam therapy. Br. J. clin. Pharmac. 1978, 6:69-73
3. Divoll M , et al. Benzodiazepine overdosage: Plasma concentrations and clinical outcome . Psychopharmacology, 1981, 73: 381-383
4. Greenblatt DJ, et al. A large-sample study of diazepam pharmacokinetics. Ther Drug Monit. 1989, 11(6):652-657.
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Centrifuge and separate blood as soon as possible after collection.
If sending within Auckland then sample can be sent refrigerated (2-8 degrees) or at ambient temperature (8-24 degrees).
If sending from outside Auckland then send sample refrigerated (2-8 degrees).
Note: If temperature during shipping is likely to exceed 24 degrees then results may not always be reliable.