Ionized species are trapped in urine and cleared quickly.

Weak acids: Phenobarbital, methotrexate, aspirin. Trapped in basic environments. - Treat overdose with sodium bicarbonate to alkalinize urine.

Weak bases: TCAs, amphetamines. Trapped in acidic environments.- Treat overdose with ammonium chloride to acidify urine.

TCA toxicity is generally treated with sodium bicarbonate to overcome the sodium channel-blocking activity of TCAs but not for accelerating drug elimination.