AMINOPHYLLINE

• Acute severe asthma
• Reversible airways obstruction

Interactions

• Several medications may increase or decrease theophylline concentration
• Always check current BNF Appendix 1

• Check potassium normal

Weight

• In obese patients (actual body weight (ABW) >120% ideal body weight (IBW), IBW used to calculate the dose(s)
• In not overweight patients (including underweight), ABW used to calculate the dose (s)
• Use these weights to calculate both maintenance and loading dose

Preparations

• Aminophylline injection = 25 mg/mL, 10 mL ampoules

Diluents

• Sodium chloride 0.9%, glucose 5%

Loading dose

• Only if patient has NOT received any theophylline/aminophylline within last 24 hr, give loading dose

Dose amount and rate

Monitor

• Heart rate continuously during infusion

Risk of markedly reduced aminophylline clearance

• Elderly patients
• Liver failure, heart failure
• Viral infection or prolonged fever
• Concurrent treatment with
• ciprofloxacin, clarithromycin
• cimetidine, erythromycin,
• fluconazole, fluvoxamine,
• propranolol, allopurinol,
• oral contraceptives, and calcium channel blockers
• refer to BNF Appendix 1 for full list of interactions

Maintenance dose in markedly reduced clearance

• Give continuous IV infusion at 0.25 mg/kg/hr
• Add 250 mg (10 mL) to 500 mL of diluent after first removing 10 mL from the bag
• Concentration = 250 mg in 500 mL = 0.5 mg/mL

Maintenance dose with normal clearance

• Give continuous IV infusion at 0.5 mg/kg/hr
• Add 250 mg (10 mL) to 500 mL of diluent after first removing 10 mL from the bag
• Concentration = 250 mg in 500 mL = 0.5 mg/mL

Symptoms/signs of toxicity

• Vomiting which may be severe and intractable
• Agitation, restlessness, dilated pupils
• Sinus tachycardia and hyperglycaemia

Loading dose given

• Monitor heart rate continuously throughout infusion
• Check serum potassium 1–2 hr after dose

Potassium

• Monitor serum potassium daily while infusion continues

Theophylline

• Draw samples from opposite arm to that receiving infusion

Initial level

• Monitor serum theophylline 4–6 hr after starting maintenance infusion
• If level is ≤20 mg/L, maintain rate of infusion
• If level is >20 mg/L and patient has symptoms or signs of toxicity, stop infusion
• repeat level every 6 hr until <20 mg/L
• then restart infusion at a reduced rate and repeat level at 4–6 hr
• If level is >20 mg/L and patient has no symptoms or signs of toxicity, reduce rate of infusion
• repeat level at 4­–6 hr

Steady state

• Monitor serum theophylline after 24 hr to check steady-state concentration
• Target range = 10–20 mg/L
• Adjust maintenance dosage of aminophylline according to plasma theophylline concentration
• relationship is linear, so doubling dosage will double steady-state concentration