Absorption: Well absorbed from PO dosage forms; absorption from extended-release dosage forms is slow but complete.

Distribution: Widely distributed; crosses the placenta and into breast milk; does not distribute into adipose tissue.

Metabolism and Excretion: 90% metabolized by the liver to several metabolites (including the active metabolites, caffeine, and 3–methylxanthine); metabolites are renally excreted; 10% excreted unchanged by the kidneys.

Half-life: Theophylline—Premature infants: 20–30 hr; Term infants: 11–25 hr; Children 1–4 yr: 3.4 hr; Children 6–17 yr: 3.7 hr; Adults: 9–10 hr (↑ in patients >60 yr, patients with HF or liver disease; ↓ in cigarette smokers ).

TIME/ACTION PROFILE (bronchodilation)

ROUTE	ONSET†	PEAK	DURATION
PO	rapid	1–2 hr	6 hr
PO-ER	delayed	4–8 hr	8–24 hr
IV	rapid	end of infusion	6–8 hr

†Provided that a loading dose has been given and steady-state blood levels exist