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Sildenafil

Clinical Effects:

SILDENAFIL
  • USES: Smooth muscle relaxant used for erectile dysfunction and pulmonary hypertension. Sildenafil is also abused, often in conjunction with other drugs to enhance sexual performance. PHARMACOLOGY: Inhibition of cGMP specific phosphodiesterase type-5 (PDE5) in smooth muscle in the pulmonary vascular bed in the lungs and the corpus cavernosum of the penis. TOXICOLOGY: Overdose causes excessive vasodilatation resulting in hypotension, tachycardia, headache, priapism, facial flushing, dizziness, and general weakness. EPIDEMIOLOGY: Poisoning is uncommon and rarely severe. MILD TO MODERATE TOXICITY: Headache, facial flushing, dizziness, general weakness, priapism and vertigo. SEVERE TOXICITY: Severe effects may include significant hypotension, tachycardia, and generalized weakness. Theoretically, CNS depression, cerebral ischemia, and other end-organ ischemia are possible after severe overdose, but have not been reported. A young adult developed recurrent tonic-clonic seizures after misusing sildenafil (100 mg). ADVERSE EFFECTS: Facial flushing, rash, diarrhea, dyspepsia, dizziness/vertigo, headache, abnormal vision, nasal congestion, hypotension, tachycardia, myocardial infarction, non-arteritic ischemic optic neuropathy, priapism (rare), and musculoskeletal pain have been reported.

Range of Toxicity:

SILDENAFIL
  • TOXICITY: ADULT: Adults who ingest less than 800 mg typically have symptoms consistent with therapeutic dosing. However, one adult developed rhabdomyolysis after ingesting 250 mg of sildenafil and improved with supportive care. In another case, a young adult developed recurrent tonic-clonic seizures after misusing sildenafil 100 mg; no intervention was needed. Doses in excess of 2000 mg have caused hypotension and tachycardia. Fatalities are exceedingly rare. PEDIATRIC: A 2-year-old developed persistent facial flushing, painful transient penile engorgement, bilateral rhonchi, and diarrhea after ingesting approximately 1.5 pills (75 mg) of sildenafil. THERAPEUTIC: ADULT: ERECTILE DYSFUNCTION: Usual dose is 50 mg taken approximately 1 hour prior to sexual activity (range, 0.5 to 4 hours before sexual activity); dose range: 25 to 100 taken once per day. PULMONARY HYPERTENSION: ADULT: 20 mg 3 times daily (given every 4 to 6 hours). PEDIATRIC: Safety and efficacy of sildenafil for pediatric pulmonary hypertension has not been established.

Treatment:

SILDENAFIL
  • Support: MANAGEMENT OF MILD TO MODERATE TOXICITY: The vast majority of sildenafil overdoses requires only supportive care; activated charcoal is indicated if patients present shortly after ingestion. Treat headache, facial flushing, dizziness and general weakness with IV fluids. Hypotension and tachycardia are generally mild and well tolerated and usually respond to IV fluids. MANAGEMENT OF SEVERE TOXICITY: Patients who experience respiratory compromise or significant CNS depression require early endotracheal intubation for airway protection. While activated charcoal is indicated in these cases, is should be performed only in patients who can protect their airway or who are intubated. Patients with persistent hypotension despite intravenous fluids require vasopressors, theoretically alpha agonists norepinephrine and phenylephrine may be more effective.
  • Decontamination: PREHOSPITAL: Activated charcoal should be given to those who are able to reliably protect their airway and IV fluids should be given for hypotension or tachycardia. HOSPITAL: Activated charcoal should be given to those who are able to reliably protect their airway. Fatalities are extremely rare and gastric lavage is generally not indicated.
  • Airway management: It is unlikely that a patient with an isolated sildenafil overdose will require airway management. Perform early in patients with severe intoxication (ie, seizures, dysrhythmias, severe delirium, CNS or respiratory depression).
  • Antidote: No specific antidote for sildenafil exists. IV fluids and peripheral vasopressors are the primary treatment of choice.
  • Tachycardia: Reflex tachycardia is usually seen from hypotension.
  • Seizure: Unlikely, but can be due to cerebral ischemia. Correct hypotension and treat with benzodiazepines.
  • Priapism: An immediate urological consult is necessary. Clinical history should include the use of other agents (ie, antihypertensives, antidepressants, illegal agents) that may also be contributing to priapism. In a patient with ischemic priapism the corpora cavernosa are often completely rigid and the patient complains of pain, while nonischemic priapism the corpora are typically tumescent, but not completely rigid and pain is not typical. Aspirate blood from the corpus cavernosum with a fine needle. Blood gas testing of the aspirated blood may be used to distinguish ischemic (typically PO2 less than 30 mmHg, PCO2 greater than 60 mmHg, and pH less than 7.25) and nonischemic priapism. Color duplex ultrasonography may also be useful. If priapism persists after aspiration, inject a sympathomimetic. PHENYLEPHRINE: Dose: Adult: For intracavernous injection, dilute phenylephrine with normal saline for a concentration of 100 to 500 mcg/mL and give 1 mL injections every 3 to 5 minutes for approximately 1 hour (before deciding that treatment is not successful). For children and patients with cardiovascular disease: Use lower concentrations in smaller volumes. NOTE: Treatment is less likely to be effective if done more than 48 hours after the development of priapism. Distal shunting (NOT first-line therapy) should only be considered after a trial of intracavernous injection of sympathomimetics.
  • Monitoring of patient: Monitor vital signs and mental status. Sildenafil plasma levels are not clinically useful or readily available. In addition, sildenafil is not detected on a urine drug screen. No specific lab work is needed in most patients. Obtain an ECG and institute continuous cardiac monitoring in patients with moderate to severe toxicity (ie, tachycardia, hypotension, ataxia, coma, and diarrhea). Monitor renal function, troponin and liver enzymes in patients with prolonged hypotension, seizures or coma to screen for end organ damage. Ensure good neurological exam as patients are at elevated risk for stroke.
  • Enhanced elimination procedure: Because sildenafil is highly protein bound and is not eliminated in the urine, hemodialysis and hemoperfusion are not expected to be of benefit in overdose.
  • Patient disposition: HOME CRITERIA: Asymptomatic children (other than mild drowsiness) with small ingestions and asymptomatic adults who have inadvertently ingested an extra dose may be managed at home. OBSERVATION CRITERIA: Symptomatic patients, those with deliberate ingestions or children with significant ingestions should be referred to a health care facility for observation for 6 to 8 hours. All symptomatic patients should be sent to a health care facility for observation for 6 to 8 hours. ADMISSION CRITERIA: Patients with significant persistent CNS depression (ie, weakness, ataxia, vertigo, coma) or those with persistent abnormal vital signs such as tachycardia and hypotension should be admitted. Patients with coma, seizures, dysrhythmias, or end organ damage should be admitted to an intensive care setting. CONSULT CRITERIA: Consult a poison center or medical toxicologist for assistance in managing patients with severe toxicity (ie, dysrhythmias, severe hypotension, coma) or in whom the diagnosis is not clear.
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