Carbamazepine and oxcarbazepine: mania evidence, autoinduction, HLA and hyponatraemia (MEQ)

(i) Antimanic evidence. Modern teaching centres on Weisler multicentre RCTs of extended-release carbamazepine capsules as monotherapy superior to placebo in bipolar I manic or mixed episodes (2004 and 2005), with pooled confirmation (2006). Historical lineage: Ballenger and Post (1980) early CBZ for manic-depressive illness; Okuma (1979) double-blind CBZ versus chlorpromazine in mania. Position CBZ as a rational alternative when lithium/valproate unsuitable, not always first over SGAs/lithium in network algorithms.[1][2][3][4]

(ii) Autoinduction. CBZ induces its own CYP3A4-mediated metabolism over the first weeks. Clearance rises; trough levels often fall at a constant dose. Recheck trough after induction settles (commonly around 3–5 weeks) and after interacting drug changes; may need upward dose titration. Do not treat a week-1 level as a permanent set-point.[1]

(iii) HLA-B*1502. Strong association with CBZ-related SJS/TEN in Han Chinese and other at-risk East/South-East Asian groups (Chung). Prospective screening with CBZ avoidance in carriers can prevent CBZ-SJS/TEN (Chen). For this Han Chinese patient: arrange HLA-B*1502 testing before first dose when available; if positive, do not start CBZ; counsel all patients on rash stop rules regardless.[5][6]

(iv) Oxcarbazepine comparison. Structural relative (MHD active metabolite); typically less CYP induction than CBZ but greater hyponatraemia risk (Dong). Weaker bipolar RCT portfolio than ERC-CBZ mania programme. Wagner 2006: OXC not superior to placebo in youth bipolar RCT — illustrates limited efficacy certainty even if this patient is adult; do not market OXC as automatic “safer CBZ.” Cross-reactivity possible after CBZ SCAR — never use OXC as casual rechallenge after SJS/TEN. Monitor Na closely if OXC chosen.[7][8]

(v) Levels and interactions. Teaching trough window often ~4–12 mg/L (µg/mL); individualise to response and toxicity (diplopia, ataxia, sedation). CBZ is a strong enzyme inducer: hormonal contraceptives fail (dual contraception when relevant), many antipsychotics/antidepressants/warfarin levels may fall — full medication review mandatory. Baseline FBC, LFT, Na, pregnancy test when relevant, interaction list, SCAR counselling.[1][6][8]