Theophylline and CYP1A2
Theophylline has a narrow therapeutic window and is cleared by CYP1A2. Slow metabolism, enzyme inhibitors or stopping smoking can push levels into the toxic range.
Why does CYP1A2 matter for Theophylline?
Theophylline has a narrow therapeutic window and is cleared by CYP1A2. Slow metabolism, enzyme inhibitors or stopping smoking can push levels into the toxic range. CYP1A2 is the enzyme that clears caffeine, and it also metabolises clozapine, olanzapine, theophylline and melatonin. Unlike most pharmacogenes, its activity is driven at least as much by environment as by genotype: smoking and cruciferous vegetables induce it, oral contraceptives and fluvoxamine inhibit it. The *1F variant makes the enzyme more inducible, which is why the same coffee affects a smoking *1F/*1F carrier and a non-smoking *1A/*1A carrier so differently.
What does CPIC recommend for each CYP1A2 phenotype on Theophylline?
The guidance below is the CPIC recommendation for prescribers, reproduced for reference. It is written for a clinician who knows the whole picture — never start, stop or change a medicine on the basis of this page.
| Phenotype | CPIC-based guidance |
|---|---|
| Ultrarapid Metabolizer | May need higher theophylline dose. Monitor serum levels. |
| Normal Metabolizer | Standard theophylline dosing with serum level monitoring. |
| Intermediate Metabolizer | Consider reduced dose. Monitor serum levels more frequently. |
| Poor Metabolizer | Dose reduction required. Risk of theophylline toxicity (nausea, tachycardia, seizures). |
Which CYP1A2 alleles decide the phenotype?
The phenotype is read from the two CYP1A2 star alleles a person carries. The full allele table, with the defining variants and their population frequencies, is on the CYP1A2 gene page.
The inducibility variant *1F (rs762551) is on every major consumer chip. Because CYP1A2 activity depends heavily on smoking and diet, genotype alone predicts caffeine clearance less well than for other pharmacogenes.
Other drugs affected by CYP1A2
Upload your raw DNA file and see your metaboliser status → · Ask G2: “Does my CYP1A2 genotype affect Theophylline?”
Genetic associations describe risk across populations, not a diagnosis for any one person. Most variants shift risk modestly and act alongside lifestyle, environment and other genes. Consumer DNA chips do not read every position and can be wrong at any single one. For general education only; talk to a clinician or genetic counsellor before acting on anything here, and never change a prescribed medicine without your prescriber.