**10. Pharmacological options**

The main classes of drugs used for sedation analgesia for diagnostic and therapeutic procedures are narcotics, benzodiazepines, systemic anesthetics and reversal agents. They are described briefly in the following paragraphs.

### **10.1 Narcotics**

#### **10.1.1 Fentanyl**

Fentanyl is a fat-soluble drug that rapidly enters the blood–brain barrier. It is more potent and fast acting than both morphine and meperidine. Fentanyl should be administered to children as a slow IV push since rapid administration has been associated with chest wall and glottic rigidity. Fentanyl's onset of action is approximately 30 seconds, and its opioid effects last approximately 30 to 45 minutes. Fentanyl should be administered in small doses to slowly titrate to effect, with several minutes allowed between each dose. Because its termination of action occurs with redistribution rather than from metabolism, the respiratory depressive effects of fentanyl outlast its analgesic effects.

#### **10.1.2 Meperidine and the lytic cocktail**

Until recently, meperidine was a favorite in longer procedures since its clinical duration of action is 2–4 hours. It may be given intravenously in dosage of 0.5–1.0 mg/kg, with maximum being 4 mg/kg. The time of peak effect for meperidine is 1–3 minutes after intravenous administration. In addition to respiratory depression, the active metabolite meperidine (nor-meperidine) may cause seizures. Meperidine should not be used long-term or in patients with poor renal clearance. Special consideration includes avoidance in patients taking monoamine oxidase inhibitors and in patients with cardiovascular instability. The other adverse reactions following meperidine include delirium, nausea, vomiting, urinary retention, pruritis, smooth muscle spasm, and hypotension. Central nervous system toxicity may occur in patients taking tricyclic antidepressants and phenothiazines. Meperidine in the past was commonly used as a cocktail mixed with promethazine and chlorpromazine. The cocktail is still, on occasion, used by some but it has very long sedation duration, anywhere from 7 to 19 hours. It can also be associated with hypotension seizures, extra pyramidal reactions, and severe prolonged life-threatening respiratory depression.
