Diazepam

Contraindicated in patients with severe chronic obstructive pulmonary disease, respiratory failure, or any condition causing significantly compromised ventilatory capacity. Risk of respiratory arrest.

Both obstructive and central sleep apnoea are worsened by benzodiazepine-induced muscle relaxation and respiratory depression. Increased frequency and severity of apnoeic episodes, with risk of nocturnal hypoxemia.

Dose reduction required in hepatic impairment. Half-life approximately doubles. Oxazepam or lorazepam (which undergo direct glucuronidation unaffected by liver disease) are preferred alternatives.

CYP2C19 poor metabolizers (frequency: ~2% European, ~13% East Asian, up to 57% Oceanian populations) require dose reduction. Genotyping should be considered in patients with unexpectedly prolonged or intense effects.

Late third-trimester use and exposure during labor associated with floppy infant syndrome — symptoms persisting hours to months. First-trimester data inconclusive: early studies suggested cleft palate and cardiac malformation risk, later studies found no clear increase. Use only when benefit clearly outweighs risk.

Excreted in breast milk at low levels. Risk of infant sedation, poor feeding, and weight gain problems. The long half-life of nordiazepam increases accumulation risk with repeated maternal dosing.

Markedly extended half-life (80–100 hours vs 24–48 hours in younger adults) creates substantial accumulation risk. Associated with increased fall risk, cognitive impairment, and epidemiological associations with dementia. Dose reduction and extended dosing intervals required.

Co-administration with opioids (heroin, fentanyl, morphine, oxycodone, methadone) without intensive clinical monitoring carries unacceptable mortality risk. Benzodiazepines are present in ~30% of opioid overdose deaths.

Benzodiazepine-induced muscle relaxation via spinal and brainstem α2/α3 receptors compounds the existing neuromuscular blockade. Risk of respiratory muscle failure.

Active alcohol use with diazepam produces additive-to-supra-additive CNS depression. Cross-dependence complicates treatment. The combination exceeds the impairment produced by either substance alone.