Aminophylline

CLINICAL USE

Reversible airways obstruction

Acute severe asthma

DOSE IN NORMAL RENAL FUNCTION

Modified release: 225–450 mg twice daily IV loading dose: 5 mg/kg (250–500 mg) Maintenance dose: 0.5 mg/kg/hour adjusted according to levels

PHARMACOKINETICS

Molecular weight : 420.4

%Protein binding : 40–60 (theophylline)

%Excreted unchanged in urine :

<10 :

Volume of distribution (L/kg) : 0.4–0.7 (theophylline)

half-life – normal/ESRD (hrs) : 4–12/Unchanged (theophylline)

DOSE IN RENAL IMPAIRMENT

GFR (mL/MIN)

20 to 50 : Oral: Dose as in normal renal function and adjust in accordance with blood levels IV: Dose as in normal renal function and adjust in accordance with blood levels

10 to 20 : Oral: Dose as in normal renal function and adjust in accordance with blood levels IV: Dose as in normal renal function and adjust in accordance with blood levels

<10 : Oral: Dose as in normal renal function and adjust in accordance with blood levels IV: Dose as in normal renal function and adjust in accordance with blood levels

DOSE IN PATIENTS UNDERGOING RENAL REPLACEMENT THERAPIES

CAPD : Not dialysed. Dose as in GFR <10 mL/min Monitor blood levels. See ‘Other Information’

HD : Not dialysed. Dose as in GFR <10 mL/min. Monitor blood levels. See ‘Other Information’

HDF/high flux : Unknown dialysability. Dose as in GFR <10 mL/min Monitor blood levels. See ‘Other Information’

CAV/VVHD : Not dialysed. Dose as in GFR=10– 20 mL/min Monitor blood levels. See ‘Other Information’

IMPORTANT DRUG INTERACTIONS

Potentially hazardous interactions with other drugs

Antibacterials: increased concentration with azithromycin, clarithromycin, erythromycin, ciprofloxacin, norfloxacin and isoniazid; decreased erythromycin levels if erythromycin is given orally; increased risk of convulsions if given with quinolones; rifampicin accelerates metabolism of theophylline

Antidepressants: concentration increased by fluvoxamine – avoid concomitant use or halve theophylline dose and monitor levels; concentration reduced by St John’s wort – avoid concomitant use

Anti-epileptics: metabolism increased by carbamazepine and primidone; concentration of both drugs increased with phenytoin

Antifungals: concentration increased by fluconazole and ketoconazole

Antivirals: metabolism of theophylline increased by ritonavir

Calcium-channel blockers: concentration increased by diltiazem and verapamil and possibly other calcium-channel blockers

Tacrolimus: may increase tacrolimus levels

Ulcer-healing drugs: metabolism inhibited by cimetidine; absorption possibly reduced by sucralfate

ADMINISTRATION

Reconstition

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Route

IV, oral

Rate of Administration

Loading dose over 20 minutes by slow IV injection

Comments

Can be added to glucose 5%, sodium chloride 0.9% and compound sodium lactate

Minimum volumes range from 2–25 mg/ mL, give concentrated solution via central line.

OTHER INFORMATION

Aminophylline: 80% theophylline + 20% ethylenediamine

In bodily fluids, aminophylline rapidly dissociates from ethylenediamine and releases free theophylline in the body. It is therefore not present in the body long enough to be dialysed, whereas theophylline is dialysed, see theophylline monograph

Optimum response obtained at plasma theophylline levels of 10 to 20 mg/L (55–110 micromol/L)

Increased incidence of GI and neurological side effects in renal impairment at plasma levels above optimum range

See how to identify renal failure stages according to GFR calculation

See how to diagnose irreversible renal disease

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