These agents stimulate respiration through direct action on respiratory centers in the medulla or cerebrospinal axis and may cause general arousal. They are classified as acidifiers, analeptics, specific agents targeting opioid receptors, non-specific stimulants like caffeine and amphetamines, carotid chemoreceptor stimulants, and pulmonary surfactants. Nikethamide and doxapram are prototypical drugs that act as respiratory stimulants by exciting carotid and aortic chemoreceptors.

2. These are the agents which stimulate respiration in sub-convulsive doses. They are also called restorative or strengthening drugs. They act
directly on respiratory centers in medulla or on cerebrospinal axis and may cause general arousal.
Classification of Drugs
(I) Acidifiers
• Acetazolamide
(II) Analeptics
• Amiphenazole
• Doxapram
• Prethcamide
• Ethamivan
• Ethyl and propyl butamide
• Leptazole
• Nikethamide
(III) Specific agents
• Nalorphine
• Naloxone
• Naltrexone
(IV) Non-specific agents
• Amphetamine
• Antialdosterone
• Caffeine
• Ephedrine
• Progesterone
• Protriptylline
• Theophylline
(V) Carotid chemoreceptor stimulants
• Almitrine
• Doxapram
(VI) Pulmonary surfactants
• Beractant
• Poractant alfa
(VII) A drop of smelling ammonia or alcohol in nose in hysterical fainting

3. PROTOTYPE DRUGS
NIKETHAMIDE
It is a pyridine derivative, effective in respiratory depression.
Pharmacological actions
 BP-it raises the blood pressure by stimulating medullary centers.
 CNS-tremors, convulsions and excitement.
 Respiration-reverse respiratory depression of morphine and chloral hydrate.
Mechanism of action
It stimulates chemoreceptors of carotid and aortic vessels and may cause central excitation. It increases the sensitivity of
depressed respiratory centers to CO2.
ADME
Usually given intravenously, converted into nicotinamide and excreted as N-methyl nicotinamide.
Dose
2ml of 25% solution every 4-6 hourly
Adverse effects
Convulsions
CNS-depression
Pruritis
Anxiety
GIT-upset
Uses
It is preferred in following cases-
 Coma or fainting
 Hypnotic drug poisoning
 Suffocation on drowning
 Acute respiratory insufficiency
 Apnea in premature infants
 Respiratory failure due to removal of hypoxic derives as a result of too high O2 concentration to patients with
chronic lungs disease.
 Failure to ventilate spontaneously after general anesthesia.

4. DOXAPRAM
It is a short acting CNS stimulating agent, stimulates cerebrospinal axis. It is safe and effective analeptic, used in the treatment of
postoperative respiratory depression and acute respiratory failure.
Pharmacological actions
 Enhances tidal volume and rate of respiration
Mechanism of action
Stimulates respiratory center through carotid and aortic chemoreceptors in postanaesthetic period
ADME
Administered orally or through intravenous infusion, t1/2 is 3-4 hours, mainly metabolized in liver by oxidation.
Contra-indicated in-
Severe hypertension
Status asthaticus
Coronary artery disease
Thyrotoxicosis
Epilepsy
Physical obstruction of respiratory tract
Dose
0.5-1.5mg/kg/i.v. at the rate of 5mg/min. or 40-80mg/i.m./i.v.
Adverse effects
• Agitation, Arrhythmias
• Convulsions
• Dizziness
• Hyperexcitability
• Hypertension
• Muscle twitching
• Perineal warmth
• Perspiration
• Pruritus
• Raised BP & HR
• Reduces gastric emptying
• Restlessness
• Shivering
• Sweating
• Tachycardia
• Tremors
• Vertigo
• Vomiting

5. Uses
It is preferred in the following cases-
 Apnoea in neonats
 Postoperative respiratory depression
 Acute respiratory failure
 Chronic obstructive pulmonary disease