The smoking ban implemented in the UK this July (Reference Campion, Checinski and NurseCampion et al, 2008) will greatly affect psychiatric in-patients, of whom as many as 74% are smokers (Reference Meltzer, Gill and PetticrewMeltzer et al, 1996). Plasma concentrations of certain psychotropics are known to be affected by smoking status. Smokers are usually prescribed higher doses than non-smokers and abrupt smoking cessation will lead to high plasma concentrations and potentially more side-effects.

Clozapine plasma concentrations can rise 1.5 times in the 2–4 weeks following smoking cessation (Reference de Leonde Leon, 2004) and in some instances by 50–70% within 2–4 days. If baseline plasma concentrations are higher – particularly over 1 mg/litre – the plasma concentration may rise dramatically owing to non-linear kinetics. If patients smoking more than 7–12 cigarettes per day while taking clozapine decide to quit, the dose may need to be reduced by 50% (Reference Haslemo, Eikeseth and TanumHaslemo et al, 2006).

Although patients may not quit during an admission their access to cigarettes may be limited, depending on leave status or other practicalities (e.g. availability of staff to escort them off the ward). The as-required prescription of nicotine replacement therapy, although strictly speaking off-license, may help cravings but it has no effect on clozapine plasma concentration.

All patients should be forewarned that in-patient settings are now smoke-free, and clinicians need to clarify and record smoking status on admission. They will also need to monitor clozapine plasma concentrations in smokers closely during admissions and shortly after discharge. All UK assays are performed at the Toxicology Unit, Kings' College Hospital, London, and electronic access to results is possible after registration (pathologyi.t@kch.nhs.uk). Savings made by clozapine dose reductions will mitigate the additional costs incurred!