Gemtesa
adenosine
Generic Name
adenosine
Mechanism
- Rapid, selective adenosine receptor agonist (primarily A1 and A2A).
- Binds to cardiac A1 receptors → inhibits adenylate cyclase → ↓cAMP → hyperpolarization of AV nodal cells.
- Produces a brief episode of AV nodal conduction delay and termination of recurrent PSVT.
- Effects last <2 seconds because plasma adenosine is rapidly metabolized (see PK).
Pharmacokinetics
- Route: IV push (single 10‑30 s infusion).
- Absorption: Immediate; no bioavailability issues.
- Distribution: Widely distributed; small protein binding (~20 %).
- Metabolism: Rapid deamination to inosine by adenosine deaminase (EC 3.5.4.4).
- Elimination: Inosine and unchanged adenosine kidneys; <1 % unchanged.
- Half‑life: ~0.6‑1.2 seconds IV.
- Time to peak effect: <30 seconds; return to baseline within 1–2 minutes.
Indications
- Acute termination of PSVT in adults ≥12 months (including adolescents).
- Detection of intermittent tachyarrhythmias in patients on antiarrhythmic drugs or monitoring for atrial fibrillation.
Contraindications
| Category | Details |
| Absolute |
• Known hypersensitivity to adenosine or any component. • Infants <12 months. |
| Relative |
• Unstable angina or recent myocardial infarction. • Severe aortic stenosis. • Chronic >2:1 AV block, second/third‑degree block. • Use with chronic beta‑blockade, calcium‑channel blockers, or other AV nodal suppressants. |
| Warnings |
• Bronchospasm: contraindicated in reactive airway disease (asthma, COPD). • Bradyarrhythmias: risk of sinus arrest or AV block. • Hypotension: may precipitate in patients with severe volume depletion. • QT prolongation not primary concern but monitor in prolonged use. |
> *Black‑box warning*: Life‑threatening bradyarrhythmias and hypotension have been reported; ensure immediate availability of atropine and a rapid‑acting β‑agonist.
Dosing
- Standard adult dose: 6 mg IV push over 10–30 seconds.
- If no response after 5 s, can repeat up to 12 mg (single additional bolus).
- Pediatric dosing: 0.1‑0.2 mg/kg IV bolus (max 6 mg); same repeat protocol.
- Infusion: Administer via dedicated IV line; immediately flush with 10 mL normal saline.
- Premedication: Not required; avoid pre‑medication that prolongs action (e.g., caffeine).
Adverse Effects
- Common (≤5 %)
- Flushing, chest pain, shortness of breath, dizziness, syncope
- Nausea, vomiting, abdominal discomfort
- Transient palpitations
- Serious (≤1 %)
- Bradycardia, sinus arrest, AV block → require atropine
- Severe hypotension → need fluid resuscitation or vasopressors
- Bronchospasm → treat with bronchodilator (salbutamol)
- Angina, myocardial ischemia (rare)
> *Adverse effect profile is transient due to rapid metabolism; no cumulative toxicity.*
Monitoring
| Parameter | Goal | Comments |
| ECG | Continuous monitoring during and after drug administration | Watch for AV block, junctional rhythm |
| Blood pressure | Continuous or beat‑by‑beat | Avoid severe hypotension; maintain volume status |
| O₂ saturation | Continuous | Detect bronchospasm or hypoxia |
| Symptom diary (chest pain, dyspnea) | Immediate reporting | Helps differentiate from ischemic events |
| Respiratory status | Evaluate in asthmatic or COPD patients | Avoid use or pre‑treat with β‑agonist if necessary |
> *If repeated dosing is needed, allow 30–60 seconds between boluses to ensure clearance.*
Clinical Pearls
- Rapid IV push: The drug must be administered over 10‑30 seconds—any slower will reduce efficacy.
- Pre‑screen for contraindications: Even a single episode of severe bronchospasm can be life‑threatening.
- Keep atropine on hand: For life‑threatening bradycardia or AV block; administer 0.5 mg IV, repeat every 3 min up to 3 mg.
- Avoid use in severe aortic stenosis: High‐dose adenosine can precipitate hypotension and syncope.
- Pediatric dosing: 0.1–0.2 mg/kg ensures therapeutic effect with minimal systemic exposure.
- Use in cardiac monitoring: A single bolus can reveal latent atrial arrhythmia during electrophysiologic study.
- Patient education: Inform about short‑term chest discomfort or flushing; reassure that these are normal.
> Mnemonic: A for Adenosine, P for PSVT, V for AV block (watch for), S for Side‑effects (bronchospasm, hypotension).
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• Key Takeaway: Gemtesa is a short‑acting IV adenosine excelling in the rapid termination of PSVT in adults and children aged ≥12 months. Its brief action demands careful IV delivery, vigilant cardiac monitoring, and immediate availability of rescue agents. Use it judiciously in patients with reactive airway disease or pre‑existing conduction abnormalities.