Blood testing in a laboratory

Case 5 - Before prescribing oral chloramphenicol

The patient described in step 3.4 was also taking warfarin for atrial fibrillation.

Chloramphenicol interacts with many medications so it is important to check the patient’s current drug list before prescribing. Severe drug-drug interactions (as defined by the British National Formulary) include: fosphenytoin, glibenclamide, gliclazide, glimepiride, glipizide, phenytoin, tacrolimus and tolbutamide (increases exposure to all of these drugs). It potentially increases the anticoagulant effect of warfarin, although that subsequently proved not to be a problem in this patient, perhaps because of the relatively low dose prescribed. Nevertheless, closer monitoring (weekly) of the patient’s INR (international normalised ratio) was undertaken initially.

The manufacturer advises to avoid use in pregnancy and breast feeding due to the risk of ‘grey-baby syndrome’.

Dose reduction and close monitoring is advised in hepatic impairment and use is not recommended in severe renal impairment (there was no liver or renal impairment in patient described in step 3.4).

Therapeutic drug monitoring is recommended with a target peak plasma concentration (2 hours after administration by mouth, intravenous injection or infusion) of 10–25 mg/litre with the pre-dose (‘trough’) concentration not exceeding 15 mg/litre (Source: British National Formulary).

Chloramphenicol can also cause the following adverse effects:

  • blood disorders

  • depression

  • diarrhoea

  • dry mouth

  • erythema multiforme

  • glossitis

  • headache

  • nausea

  • nocturnal haemoglobinuria

  • optic neuritis

  • peripheral neuritis

  • reversible and irreversible aplastic anaemia (with reports of resulting leukaemia)

  • stomatitis

  • urticarial rash and vomiting

In particular, regular full blood count monitoring is advisable given concerns about haematological adverse effects.

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