Theophylline

CLINICAL USE

Reversible airways obstruction Acute severe asthma

DOSE IN NORMAL RENAL FUNCTION

Oral: depends on preparation used IV: Deteriorating asthma not previously treated with theophylline: 5 mg/kg (250– 500 mg) (as aminophylline) over at least 20 minutes Acute severe asthma: 500 mcg/kg/hour (as aminophylline) adjusted according to plasma-theophylline levels

PHARMACOKINETICS

Molecular weight : 180.2

%Protein binding : 35–60

%Excreted unchanged in urine : 10

Volume of distribution (L/kg) : 0.3–0.7

half-life – normal/ESRD (hrs) : 3–12/Unchanged

DOSE IN RENAL IMPAIRMENT

GFR (mL/MIN)

20 to 50 : Dose as in normal renal function

10 to 20 : Dose as in normal renal function

<10 : Dose as in normal renal function. See ‘Other Information’

DOSE IN PATIENTS UNDERGOING RENAL REPLACEMENT THERAPIES

CAPD : Not dialysed. Dose as in GFR <10 mL/min

HD : Dialysed. Dose as in GFR

<10 : mL/ min

HDF/high flux : Dialysed. Dose as in GFR

<10 : mL/ min

CAV/VVHD : Not dialysed. Dose as in normal renal function

IMPORTANT DRUG INTERACTIONS

Potentially hazardous interactions with other drugs

Antibacterials: increased concentration with azithromycin, clarithromycin, erythromycin, ciprofloxacin, norfloxacin and isoniazid; decreased plasma levels with erythromycin if erythromycin taken 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

–

Route

Oral, IV

Rate of Administration

At least 20 minutes or 500 mcg/kg/hour depends on indication

Comments

–

OTHER INFORMATION

Therapeutic levels should be in the range

10 to 20 : mg/litre (55–110 micromols/litre) 50% of dose is removed by haemodialysis Studies have used it to protect against contrast nephropathy, with conflicting results .

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