Theophylline

Mechanism

Theophylline at toxic doses causes seizures by itself. Bupropion lowers the seizure threshold. High risk even at therapeutic theophylline concentrations.

Symptoms

Seizures (generalised tonic-clonic or focal), agitation, tremor, insomnia. Patients with prior epilepsy or eating disorders are at particular risk.

Management

Avoid the combination, especially in COPD or asthma patients. Alternative antidepressants: sertraline or escitalopram. Alternative bronchodilators: inhaled β2-agonists with anticholinergics.

Mechanism

Carbamazepine induces CYP1A2, which partly metabolises theophylline. Theophylline plasma levels fall by 25–50%; bronchodilator effect weakens.

Symptoms

Recurrence of asthma or COPD symptoms: dyspnoea, wheezing.

Management

During carbamazepine therapy, increase theophylline by 50% with level monitoring at 1–2 weeks. Alternative anticonvulsants without induction: levetiracetam, lamotrigine.

Mechanism

Carvedilol blocks β2-adrenergic receptors (non-selective beta-blocker) and causes bronchoconstriction in asthma or COPD. Theophylline becomes less effective in these conditions.

Symptoms

Recurrence of asthma or COPD symptoms: dyspnoea, wheezing, need for additional short-acting β2-agonist doses. In severe asthma: risk of severe bronchospasm.

Management

Avoid the combination in asthma and severe COPD. In heart failure with mild COPD, a selective beta-blocker (bisoprolol, metoprolol) is preferred. Alternative to theophylline: long-acting inhaled β2-agonists with anticholinergics.

Mechanism

Ciprofloxacin inhibits hepatic CYP1A2, the enzyme that clears theophylline, so theophylline levels rise. The FDA theophylline label puts the increase at about 40%. Theophylline has a narrow margin: per the same label, above 20 mcg/mL both the frequency and severity of adverse reactions increase. The FDA ciprofloxacin label reports serious and fatal reactions with this combination, including cardiac arrest, seizures, status epilepticus and respiratory failure.

Symptoms

Tachycardia, tremor, nausea, vomiting, seizures, arrhythmias when theophylline above 20 mcg/mL.

Management

The combination is avoided, as the FDA ciprofloxacin label states, though no label lists it as a contraindication. A patient on theophylline gets an antibiotic without this interaction, for example amoxicillin-clavulanate for pneumonia. Levofloxacin does not change theophylline levels according to its SmPC, but together with theophylline it markedly lowers the seizure threshold. If ciprofloxacin is still needed, the theophylline SmPC caps the theophylline dose at no more than 60% of the recommended dose. Serum theophylline is measured during the course and after ciprofloxacin stops, and the dose follows the result. Nausea, vomiting, tremor or palpitations call for a same-day level.

Mechanism

An erythromycin metabolite inhibits the liver enzyme CYP3A (CYP3A3 in the label), so theophylline is cleared more slowly: according to the US Food and Drug Administration (FDA) theophylline label, theophylline levels rise by about 35%. At high theophylline doses this rise can reach toxic concentrations (erythromycin SmPC). The effect also runs the other way: with oral erythromycin, erythromycin levels fall by a similar amount and may become subtherapeutic (erythromycin SmPC and theophylline FDA label).

Symptoms

Early signs of excess theophylline: nausea, vomiting, especially repeated, headache, insomnia. At high levels: persistent vomiting, cardiac arrhythmias and intractable seizures that can be fatal. With oral erythromycin, erythromycin levels may fall below the therapeutic range and the infection may respond less well.

Management

The pair is not banned, but the theophylline dose is guided by blood levels. When erythromycin is added, theophylline levels are followed and the dose is reduced to avoid toxic concentrations (erythromycin SmPC). The US Food and Drug Administration (FDA) theophylline label warns that if the total daily dose is not reduced in time, severe and potentially fatal toxicity can occur; levels are measured both when an interacting drug is added and when it is stopped. In most patients steady state is reached after about 3 days of regular dosing (theophylline FDA label). If nausea or vomiting appear, the next theophylline dose is withheld and a level is measured at once (theophylline FDA label). After erythromycin is stopped, theophylline levels fall and the dose is increased back (theophylline FDA label).

Mechanism

Fluvoxamine inhibits CYP1A2, the main clearance route of theophylline. In the study cited in the FDA label, fluvoxamine 50 mg twice daily cut theophylline clearance about 3-fold. Theophylline has a narrow therapeutic range, so a rise of this size can lead to toxicity.

Symptoms

Signs of theophylline toxicity: vomiting, agitation, pressured speech, confusion, fever, tachycardia and low blood pressure. In adults severe toxicity can cause seizures and cardiac arrest, as the theophylline SmPC describes overdose.

Management

If the combination is needed, reduce the theophylline dose to one third of the usual maintenance dose and monitor theophylline blood levels, as the FDA label states. The Spanish fluvoxamine SmPC also asks for careful monitoring and theophylline dose adjustment if needed. An antidepressant without a relevant CYP1A2 effect is sertraline: its SmPC states that it does not inhibit this enzyme to a clinically significant degree.

Mechanism

Phenytoin induces CYP1A2. Theophylline falls 30-50%.

Symptoms

Return of obstructive symptoms.

Management

Theophylline level monitoring with dose adjustment.

Mechanism

Rifampicin induces CYP1A2 and CYP3A4. Theophylline falls 50% – bronchoconstriction breakthrough risk.

Symptoms

Return of dyspnoea, bronchospasm.

Management

Double theophylline dose with blood level monitoring.

Mechanism

Amiodarone inhibits CYP1A2 and CYP3A4 — the key enzymes of theophylline metabolism. Theophylline levels may rise by 30–50%, raising toxicity risk.

Symptoms

Nausea, tachycardia, tremor, insomnia, severe cases: seizures. Symptoms appear at theophylline above 20 mcg/mL.

Management

On starting amiodarone in a theophylline patient, cut theophylline by 30% and check levels at 1–2 weeks (target 10–15 mcg/mL). Bronchodilator alternative: tiotropium or another long-acting muscarinic antagonist.

Mechanism

Azithromycin is a weak CYP1A2 inhibitor (theophylline is a substrate). Theophylline plasma levels may rise slightly. The effect is much smaller than with erythromycin or clarithromycin.

Symptoms

Mostly no changes. In patients with borderline theophylline levels: rare nausea, tachycardia, insomnia.

Management

For short azithromycin courses (3–5 days), no special adjustment. In patients on high theophylline doses (or with renal/hepatic impairment): check theophylline level at 3–5 days.

Mechanism

Bisoprolol is cardioselective, but at high doses (above 10 mg/day) partially blocks β2-receptors and may weaken theophylline's bronchodilator effect in asthma or COPD.

Symptoms

Return of dyspnoea, wheezing, night cough. In severe asthma, bronchospasm is possible.

Management

In mild asthma or COPD, bisoprolol up to 10 mg is acceptable with pulmonary function monitoring. In severe airway obstruction, replace bisoprolol with a non-β2 cardiovascular alternative (amlodipine, ivabradine in heart failure with tachycardia).

Mechanism

Clarithromycin slows the clearance of theophylline by liver enzymes, so theophylline blood levels rise (theophylline SmPC). The US Food and Drug Administration (FDA) gives an average increase of 25% (theophylline FDA label), and the clarithromycin SmPC calls the increase modest but statistically significant (clarithromycin SmPC). Theophylline has a narrow therapeutic range: above 20 mcg/mL, adverse reactions become more frequent and more severe (theophylline FDA label).

Symptoms

Nausea, tachycardia, tremor, insomnia, agitation. At levels above 30 mg/L: seizures and ventricular arrhythmias.

Management

The combination can be used with monitoring. The theophylline SmPC lists clarithromycin among drugs that raise the risk of theophylline overdose and requires these patients to be monitored (theophylline SmPC). The US Food and Drug Administration (FDA) advises measuring the serum theophylline concentration when clarithromycin is added or stopped (theophylline FDA label), especially with high theophylline doses or a baseline level near the upper end of the therapeutic range (clarithromycin FDA label). The therapeutic range is 10–20 mcg/mL (theophylline SmPC). Lower the theophylline dose if needed (clarithromycin SmPC). Ask the patient to report nausea, vomiting, persistent headache, insomnia or a fast heartbeat (theophylline FDA label). If the theophylline dose was lowered, restore it after clarithromycin is stopped, otherwise theophylline levels will fall (theophylline FDA label).

Mechanism

Metoprolol is cardioselective but at high doses antagonises theophylline's bronchodilator effect. In bronchial asthma, control may worsen.

Symptoms

Exertional dyspnoea, wheezing, more frequent asthma attacks. In COPD: symptom exacerbation.

Management

In asthma and COPD with atrial fibrillation or hypertension, metoprolol is preferred at cardioselective doses (up to 100 mg/day) under pulmonary function monitoring. In severe asthma, consider alternatives — diltiazem or verapamil for rate control in atrial fibrillation. Theophylline is second-line in COPD; consider switching to long-acting beta-2 agonists (formoterol).

Mechanism

Propranolol is non-selective, blocks bronchial β2 receptors, and antagonises theophylline's bronchodilator effect. It triggers bronchospasm in COPD or asthma.

Symptoms

Wheezing, dyspnoea, cough, asthma exacerbation. Symptoms appear within hours or days of starting propranolol.

Management

Do not prescribe propranolol in asthma or COPD. For atrial fibrillation, hypertension, or essential tremor in obstructive lung disease, alternatives: cardioselective beta-blockers (bisoprolol, metoprolol, nebivolol) at low doses under pulmonary function monitoring. For migraine prophylaxis, propranolol alternatives: topiramate or candesartan.

Mechanism

Both lower the seizure threshold. Additive risk, especially in theophylline overdose or in patients with epilepsy and prior head trauma.

Symptoms

Tremor, jitters, anxiety; severe cases: seizures. Symptoms appear with theophylline or tramadol dose escalation.

Management

Avoid the combination in epilepsy or prior head trauma. At usual therapeutic theophylline doses and short tramadol courses (3–5 days), the combination is acceptable in young patients. Keep theophylline levels in the lower half of normal range (10–15 mcg/mL). Analgesic alternatives: paracetamol with codeine, or gabapentin for neuropathic pain.