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2D Structure
Also known as: Proazamine, 60-87-7, Diphergan, Protazine, Prometazin, Promethazin
Molecular Formula
C17H20N2S
Molecular Weight
284.4  g/mol
InChI Key
PWWVAXIEGOYWEE-UHFFFAOYSA-N
FDA UNII
FF28EJQ494

A phenothiazine derivative with histamine H1-blocking, antimuscarinic, and sedative properties. It is used as an antiallergic, in pruritus, for motion sickness and sedation, and also in animals.
Promethazine is a Phenothiazine.
1 2D Structure

2D Structure

2 Identification
2.1 Computed Descriptors
2.1.1 IUPAC Name
N,N-dimethyl-1-phenothiazin-10-ylpropan-2-amine
2.1.2 InChI
InChI=1S/C17H20N2S/c1-13(18(2)3)12-19-14-8-4-6-10-16(14)20-17-11-7-5-9-15(17)19/h4-11,13H,12H2,1-3H3
2.1.3 InChI Key
PWWVAXIEGOYWEE-UHFFFAOYSA-N
2.1.4 Canonical SMILES
CC(CN1C2=CC=CC=C2SC3=CC=CC=C31)N(C)C
2.2 Other Identifiers
2.2.1 UNII
FF28EJQ494
2.3 Synonyms
2.3.1 MeSH Synonyms

1. Atosil

2. Diphergan

3. Diprazin

4. Hydrochloride, Promethazine

5. Isopromethazine

6. Phenargan

7. Phenergan

8. Phensedyl

9. Pipolfen

10. Pipolphen

11. Proazamine

12. Promet

13. Prometazin

14. Promethazine Hydrochloride

15. Prothazin

16. Pyrethia

17. Remsed

18. Rumergan

2.3.2 Depositor-Supplied Synonyms

1. Proazamine

2. 60-87-7

3. Diphergan

4. Protazine

5. Prometazin

6. Promethazin

7. Prothazin

8. Vallergine

9. Dimapp

10. Fargan

11. Procit

12. Phenargan

13. Phensedyl

14. Promazinamide

15. Promezathine

16. Isophenergan

17. Diprazine

18. Diprozin

19. Fenetazina

20. Histargan

21. Provigan

22. Thiergan

23. Fenazil

24. Hiberna

25. Phargan

26. Prorex

27. Tanidil

28. Pyrethiazine

29. Avomine

30. Lilly 1516

31. Prometazina

32. Promethacon

33. Promethegan

34. Promethazinum

35. Promethiazine

36. Iergigan

37. Lercigan

38. Pilpophen

39. Proazaimine

40. Prometasin

41. Pyrethia

42. Lilly 01516

43. N-(2'-dimethylamino-2'-methyl)ethylphenothiazine

44. Skf 1498

45. (2-dimethylamino-2-methyl)ethyl-n-dibenzoparathiazine

46. Wy 509

47. 10-[2-(dimethylamino)propyl]phenothiazine

48. Rp 3277

49. Lergigan

50. Romergan

51. 10-(2-dimethylaminopropyl)phenothiazine

52. Dimethylamino-isopropyl-phenthiazin

53. N,n,alpha-trimethyl-10h-phenothiazine-10-ethanamine

54. N-dimethylamino-2-methylethyl Thiodiphenylamine

55. A-91033

56. Nci-c60673

57. 10-(2-(dimethylamino)-2-methylethyl)phenothiazine

58. 10h-phenothiazine-10-ethanamine, N,n,alpha-trimethyl-

59. 3277 Rp

60. (+/-)-promethazine

61. 10-(2-(dimethylamino)propyl)phenothiazine

62. Phenothiazine, 10-(2-dimethylaminopropyl)-

63. N,n-dimethyl-1-(10h-phenothiazin-10-yl)propan-2-amine

64. Nsc-30321

65. Chembl643

66. 60-87-7 (free Base)

67. 10h-phenothiazine-10-ethanamine, N,n,.alpha.-trimethyl-

68. Chebi:8461

69. Ff28ejq494

70. Antiallersin

71. Fenetazine

72. Phenerzine

73. Pipolphene

74. Camergan

75. Metaryl

76. Pelpica

77. Pilothia

78. Promacot

79. Promergan

80. Promesan

81. Prometh

82. Promethazinehcl

83. Phenothiazine, 10-[2-(dimethylamino)propyl]-

84. Phenoject-50

85. Dimethyl[1-(10h-phenothiazin-10-yl)propan-2-yl]amine

86. Rp-3277

87. Ncgc00015817-05

88. Prometazine

89. Prothazine

90. Valergine

91. Dsstox_cid_3518

92. Dsstox_rid_77061

93. Dsstox_gsid_23518

94. Pro-50

95. Promethazine [inn:ban]

96. Prometazina [inn-spanish]

97. Promethazinum [inn-latin]

98. Cas-60-87-7

99. Ccris 7056

100. Hsdb 3173

101. Dimethylamino-isopropyl-phenthiazin [german]

102. Einecs 200-489-2

103. Promethazine (jan/inn)

104. Nsc 30321

105. Phenothiazine, 10-(2-(dimethylamino)propyl)-

106. N,n-dimethyl-1-phenothiazin-10-ylpropan-2-amine

107. Brn 0088554

108. Unii-ff28ejq494

109. Sominex

110. Phenergan Base

111. Sr-01000002993

112. 38878-40-9

113. Remsed (salt/mix)

114. 3389 R.p.

115. Pyrethia (salt/mix)

116. Pipolphen (salt/mix)

117. Spectrum_000868

118. Prestwick0_000888

119. Prestwick1_000888

120. Prestwick2_000888

121. Prestwick3_000888

122. Spectrum2_000840

123. Spectrum3_001019

124. Spectrum4_001149

125. Spectrum5_000977

126. Promethazine [mi]

127. (.+/-.)-promethazine

128. 10h-phenothiazine-10-ethanamine, N,n,alpha-trimethyl-, Radical Ion(1+)

129. Promethazine [inn]

130. Promethazine [jan]

131. Promethazine [hsdb]

132. Schembl4700

133. Promethazine [vandf]

134. Lopac0_000899

135. Oprea1_758749

136. Bspbio_000676

137. Bspbio_002777

138. Kbiogr_001697

139. Kbioss_001348

140. Promethazine [mart.]

141. 4-27-00-01253 (beilstein Handbook Reference)

142. 73745-50-3

143. Divk1c_000005

144. Promethazine [who-dd]

145. Spbio_000799

146. Spbio_002895

147. (dimethylamino-2-propyl-10-phenothiazine Hydrochloride

148. Bpbio1_000744

149. Gtpl7282

150. Dtxsid7023518

151. Kbio1_000005

152. Kbio2_001348

153. Kbio2_003916

154. Kbio2_006484

155. Kbio3_001997

156. Pwwvaxiegoywee-uhfffaoysa-

157. Ex-a891

158. N,n-dimethyl-1-(10h-phenothiazin-10-yl)-2-propanamine

159. N,n-dimethyl-1-phenothiazin-10-yl-propan-2-amine

160. Ninds_000005

161. Hms2089e08

162. N,n-dimethyl-1-phenothiazin-10-ylpropan-2-amine Hydrochloride

163. Nsc30321

164. Tox21_110227

165. Bdbm50017696

166. Mfcd00066294

167. Akos015962127

168. Tox21_110227_1

169. 4182 R.p.

170. Ccg-109848

171. Db01069

172. Sdccgsbi-0050874.p005

173. Idi1_000005

174. Ncgc00015817-03

175. Ncgc00015817-04

176. Ncgc00015817-06

177. Ncgc00015817-08

178. Ncgc00015817-09

179. Ncgc00015817-10

180. Ncgc00015817-11

181. Ncgc00015817-12

182. Ncgc00015817-14

183. Ncgc00015817-17

184. Ncgc00015817-24

185. Ncgc00089735-02

186. Ncgc00089735-03

187. Ac-15939

188. Nci60_001878

189. Sbi-0050874.p004

190. Ab00053535

191. Ft-0700342

192. S5196

193. Wln: T C666 Bn Isj B1y1&n1&1

194. C07404

195. D00494

196. F17386

197. Ab00053535-12

198. Ab00053535_13

199. 10h-phenothiazine-10-ethanamine,n,n,b-trimethyl-

200. L000495

201. Q422970

202. J-690333

203. 10h-phenothiazine-10-ethanamine,n,.alpha.-trimethyl-

204. Sr-01000002993-10

205. 10-(2-dimethylamino-2-methylethyl)phenothiazine

206. (+/-)-10-(2-(dimethylamino)propyl)phenothiazine

207. N,n-dimethyl-1-(10h-phenothiazin-10-yl)-2-propanamine #

208. N,n,.alpha.-trimethyl-10h-phenothiazine-10-ethanamine

209. 10h-phenothiazine-10-ethanamine, N,n,.alpha.-trimethyl-, (+/-)-

2.4 Create Date
2005-03-25
3 Chemical and Physical Properties
Molecular Weight 284.4 g/mol
Molecular Formula C17H20N2S
XLogP34.8
Hydrogen Bond Donor Count0
Hydrogen Bond Acceptor Count3
Rotatable Bond Count3
Exact Mass284.13471982 g/mol
Monoisotopic Mass284.13471982 g/mol
Topological Polar Surface Area31.8 Ų
Heavy Atom Count20
Formal Charge0
Complexity298
Isotope Atom Count0
Defined Atom Stereocenter Count0
Undefined Atom Stereocenter Count1
Defined Bond Stereocenter Count0
Undefined Bond Stereocenter Count0
Covalently Bonded Unit Count1
4 Drug and Medication Information
4.1 Drug Information
1 of 2  
Drug NamePromethegan
PubMed HealthPromethazine (Rectal)
Drug ClassesAntiemetic, Antivertigo, Gastrointestinal Agent
Drug LabelEach rectal suppository contains 12.5 mg or 25 mg promethazine HCl with ascorbyl palmitate, colloidal silicon dioxide, white wax, hard fat, and glyceryl monostearate. Promethazine HCl Suppositories are for rectal administration only.Promethazine HCl...
Active IngredientPromethazine hydrochloride
Dosage FormSuppository
RouteRectal
Strength50mg
Market StatusPrescription
CompanyG And W Labs

2 of 2  
Drug NamePromethegan
PubMed HealthPromethazine (Rectal)
Drug ClassesAntiemetic, Antivertigo, Gastrointestinal Agent
Drug LabelEach rectal suppository contains 12.5 mg or 25 mg promethazine HCl with ascorbyl palmitate, colloidal silicon dioxide, white wax, hard fat, and glyceryl monostearate. Promethazine HCl Suppositories are for rectal administration only.Promethazine HCl...
Active IngredientPromethazine hydrochloride
Dosage FormSuppository
RouteRectal
Strength50mg
Market StatusPrescription
CompanyG And W Labs

4.2 Therapeutic Uses

Anti-Allergic Agents; Antiemetics; Antipruritics; Histamine H1 Antagonists; Sedatives, Nonbarbiturate

National Library of Medicine's Medical Subject Headings online file (MeSH, 2009)


/Promethazine/ is indicated for the amelioration of allergic reactions to blood or plasma. /Included in US product label/

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


/Promethazine/ is indicated in anaphylaxis as an adjunct to epinephrine and other standard measures after the acute symptoms have been controlled. /Included in US product label/

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


/Promethazine/ is indicated for other uncomplicated allergic conditions of the immediate type when oral therapy is impossible or contraindicated. /Included in US product label/

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


For more Therapeutic Uses (Complete) data for Promethazine (12 total), please visit the HSDB record page.


4.3 Drug Warning

/BOXED WARNING/ WARNING: Respiratory Depression - Pediatrics. /Promethazine/ injection should not be used in pediatric patients less than 2 years of age because of the potential for fatal respiratory depression. Postmarketing cases of respiratory depression, including fatalities, have been reported with use of promethazine in pediatric patients less than 2 years of age. Caution should be exercised when administering promethazine injection to pediatric patients 2 years of age and older.

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


/BOXED WARNING/ WARNING: Severe Tissue Injury, Including Gangrene. /Promethazine/ injection can cause severe chemical irritation and damage to tissues regardless of the route of administration. Irritation and damage can result from perivascular extravasation, unintentional intra-arterial injection, and intraneuronal or perineuronal infiltration. Adverse event reports include burning, pain, erythema, swelling, sensory loss, palsies, paralysis, severe spasm of distal vessels, thrombophlebitis, venous thrombosis, phlebitis, abscesses, tissue necrosis, and gangrene. In some cases, surgical intervention, including fasciotomy, skin graft, and/or amputation have been required. Due to the risks of intravenous injection, the preferred route of administration of promethazine injection is deep intramuscular injection. Subcutaneous injection is contraindicated.

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


... Extrapyramidal reactions ... fairly common, usually 3 types ... Parkinsonian-like syndrome ... dystonia and dyskinesia, including torticollis, tics, and other involuntary muscle movements ... akathisia, shown by restlessness ... hyperreflexia, reported in newborn ... ./Phenothiazines/

Osol, A. and J.E. Hoover, et al. (eds.). Remington's Pharmaceutical Sciences. 15th ed. Easton, Pennsylvania: Mack Publishing Co., 1975., p. 1021


Promethazine injection is contraindicated in comatose states.

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


For more Drug Warnings (Complete) data for Promethazine (55 total), please visit the HSDB record page.


4.4 Minimum/Potential Fatal Human Dose

3(?). 3= MODERATELY TOXIC: PROBABLE ORAL LETHAL DOSE (HUMAN) 0.5-5 G/KG, BETWEEN 1 OZ & 1 PINT (OR 1 LB) FOR 70 KG PERSON (150 LB).

Gosselin, R.E., H.C. Hodge, R.P. Smith, and M.N. Gleason. Clinical Toxicology of Commercial Products. 4th ed. Baltimore: Williams and Wilkins, 1976., p. II-222


4.5 Drug Indication

Promethazine tablets and suppositories are indicated to treat rhinitis, allergic conjunctivitis, allergic reactions to blood or plasma, dermographism, anaphylactic reactions, sedation, nausea, vomiting, pain, motion sickness, and allergic skin reactions. Promethazine cough syrup with phenylephrine and codeine is indicated to relieve cough and upper respiratory symptoms, and nasal congestion associated with allergy or the common cold.


FDA Label


5 Pharmacology and Biochemistry
5.1 Pharmacology

Promethazine is is a histamine H1 antagonist that can be used for it's ability to induce sedation, reduce pain, and treat allergic reactions. Promethazine's effects generally last 4-6h but can last up to 12h. Patients should be counselled regarding CNS and respiratory depression, reduce seizure threshold, and bone marrow depression.


5.2 MeSH Pharmacological Classification

Antipruritics

Agents, usually topical, that relieve itching (pruritus). (See all compounds classified as Antipruritics.)


Anti-Allergic Agents

Agents that are used to treat allergic reactions. Most of these drugs act by preventing the release of inflammatory mediators or inhibiting the actions of released mediators on their target cells. (From AMA Drug Evaluations Annual, 1994, p475) (See all compounds classified as Anti-Allergic Agents.)


Histamine H1 Antagonists

Drugs that selectively bind to but do not activate histamine H1 receptors, thereby blocking the actions of endogenous histamine. Included here are the classical antihistaminics that antagonize or prevent the action of histamine mainly in immediate hypersensitivity. They act in the bronchi, capillaries, and some other smooth muscles, and are used to prevent or allay motion sickness, seasonal rhinitis, and allergic dermatitis and to induce somnolence. The effects of blocking central nervous system H1 receptors are not as well understood. (See all compounds classified as Histamine H1 Antagonists.)


5.3 FDA Pharmacological Classification
5.3.1 Active Moiety
PROMETHAZINE
5.3.2 FDA UNII
FF28EJQ494
5.3.3 Pharmacological Classes
Phenothiazines [CS]; Phenothiazine [EPC]
5.4 ATC Code

D - Dermatologicals

D04 - Antipruritics, incl. antihistamines, anesthetics, etc.

D04A - Antipruritics, incl. antihistamines, anesthetics, etc.

D04AA - Antihistamines for topical use

D04AA10 - Promethazine


R - Respiratory system

R06 - Antihistamines for systemic use

R06A - Antihistamines for systemic use

R06AD - Phenothiazine derivatives

R06AD02 - Promethazine


5.5 Absorption, Distribution and Excretion

Absorption

A 25mg dose of intramuscular promethazine reaches a Cmax of 22ng/mL. Intravenous promethazine reaches a Cmax of 10.0ng/mL, with a Tmax of 4-10h, and an AUC of 14,466ng\*h/mL. Oral promethazine is only 25% bioavailable due to first pass metabolism. Oral promethazine reaches a Cmax of 2.4-18.0ng/mL, with a Tmax of 1.5-3h, and an AUC of 11,511ng\*h/mL.


Route of Elimination

An intravenous dose of promethazine is 0.64% eliminated in the urine as the unchanged parent drug, 0.02-2.02% in the urine as desmethylpromethazine, 10% in the urine as promethazine sulfoxide.


Volume of Distribution

The volume of distribution of promethazine is approximately 970L or 30L/kg.


Clearance

The intravenous clearance of promethazine is approximately 1.14L/min. The renal clearance of promethazine is 5.9mL/min and the renal clearance of promethazine sulfoxide is 90.4mL/min.


Promethazine is well absorbed from the GI tract and from parenteral sites. Plasma concentrations of promethazine required for sedative effects are unknown. The onset of sedative effects occurs within 20 minutes following oral, rectal, or IM administration, and within 3-5 minutes following IV administration. The duration of sedative effects varies but may range from 2-8 hours depending on the dose and route of administration.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2608


Promethazine is widely distributed in body tissues. Compared with other organs, lower concentrations of the drug are found in the brain, but this concentration is higher than the plasma concentration.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2608


Promethazine has been reported to be 93% protein bound when determined by gas chromatography and as 76-80% bound when determined by high-performance liquid chromatography.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2608


Promethazine readily crosses the placenta. It is not known whether the drug is distributed into milk.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2608


For more Absorption, Distribution and Excretion (Complete) data for Promethazine (9 total), please visit the HSDB record page.


5.6 Metabolism/Metabolites

Promethazine is predominantly metabolized to promethazine sulfoxide, and minorly to desmethylpromethazine and a hydroxy metabolite. Hydroxylation of promethazine is predominantly mediated by CYP2D6.


Promethazine hydrochloride is metabolized in the liver, with the sulfoxides of promethazine and N-desmethylpromethazine being the predominant metabolites appearing in the urine.

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


Most metabolites of phenothiazines are pharmacologically inactive; however, certain metabolites (eg, 7-hydroxychlorpromazine, mesoridazine) show moderate pharmacologic activity and may contribute to the action of the drugs. There is limited evidence to indicate that some phenothiazines (eg, chlorpromazine) may induce their own metabolism. /Phenothiazine General Statement/

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2511


First order kinetics observed for oxidation of promethazine HCl in aqueous solution. Reaction rate was pH dependent up to pH 5. Cu ions increased rates as did Fe. Under anaerobic conditions, Cu and Fe were required for the reaction. Isolation of products carried out by tlc.

UNDERBERG WJ; J PHARM SCI 67(AUG) 1128-1138 (1978)


Incubation of promethazine (Ia) and desmethylpromethazine (Ib) with 9000g supernatant fractions of rabbit liver homogenate resulted in formation of N-dealkylated, N-oxygenated and ring-hydroxylated products. The N-oxidation products identified by t.l.c. and mass spectra using synthetic reference products are promethazine-N-oxide (IX) and the nitrone (VIII), which is believed to be formed chemically and metabolically from the metabolite N-hydroxydesmethylpromethazine (VII).

PMID:7314643 Clement B, Beckett AH; Xenobiotica 11 (9): 609-18 (1981)


To determine which cytochrome P450 form is involved in the promethazine [10-(2-dimethylaminopropyl) phenothiazine] metabolism, in vitro analysis using human liver microsomes were performed. Promethazine was mainly biotransformed to ring-hydroxylated, S-oxidized and N-demethylated metabolites. The promethazine hydroxylase in human liver microsomes was inhibited by SKF-525A, propranolol, sparteine, quinidine and anti-CYP2D6 serum suggesting involvement of a P450 related to CYP2D6. Lineweaver-Burk plots for the hydroxylation, S-oxidation and N-demethylation indicated that the hydroxylation occurred with a low K(m) value in human liver microsomes. Microsomes from genetically-engineered human B-lymphoblastoid cells expressing CYP2D6 hydroxylated promethazine most efficiently as compared to other P450 forms, indicating that it was the principal P450 responsible for the metabolism of promethazine in human liver microsomes. The inhibition of CYP2D6-catalysed bufuralol 1'-hydroxylase by various histamine H3 antagonists including promethazine suggested that promethazine and some other histamine H1 antagonists could be inhibitors of this P450 in human liver microsomes.

PMID:8946477 Nakamura K et al; Pharmacogenetics 6 (5): 449-57 (1996)


Promethazine has known human metabolites that include N-Methyl-1-(10H-phenothiazin-10-yl)propan-2-amine, Promethazine N-glucuronide, and Promethazine sulfoxide.

S73 | METXBIODB | Metabolite Reaction Database from BioTransformer | DOI:10.5281/zenodo.4056560


5.7 Biological Half-Life

The elimination half life of promethazine is approximately 12-15h.


Following intravenous administration in healthy volunteers, the plasma half-life for promethazine has been reported to range from 9 to 16 hours. The mean plasma half-life for promethazine after intramuscular administration in healthy volunteers has been reported to be 9.8 +/- 3.4 hours.

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


Half-life: 12 hours

Young, L.Y., M.A. Koda-Kimble (eds.). Applied Therapeutics. The Clinical Use of Drugs. 6th ed. Vancouver, WA., Applied Therapeutics, Inc. 1995., p. 21-6


5.8 Mechanism of Action

Promethazine is a an antagonist of histamine H1, post-synaptic mesolimbic dopamine, alpha adrenergic, muscarinic, and NMDA receptors. The antihistamine action is used to treat allergic reactions. Antagonism of muscarinic and NMDA receptors contribute to its use as a sleep aid, as well as for anxiety and tension. Antagonism of histamine H1, muscarinic, and dopamine receptors in the medullary vomiting center make promethazine useful in the treatment of nausea and vomiting.


Promethazine is a phenothiazine derivative with potent sedative properties. Although the drug can produce either CNS stimulation or CNS depression, CNS depression manifested by sedation is more common with therapeutic doses of promethazine. The precise mechanism of the CNS effects of the drug is not known.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2608


Although it has been reported that the drug has slight antitussive activity, this may result from its anticholinergic and CNS depressant effects. In therapeutic doses, promethazine appears to have no substantial effect on the cardiovascular system. Although rapid IV administration of promethazine may produce a transient fall in blood pressure, blood pressure usually is maintained or slightly elevated when the drug is given slowly.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2608


Promethazine hydrochloride is a phenothiazine derivative which possesses antihistaminic, sedative, antimotion-sickness, antiemetic, and anticholinergic effects. Promethazine is a competitive H1 receptor antagonist, but does not block the release of histamine. Structural differences from the neuroleptic phenothiazines result in its relative lack (1/10 that of chlorpromazine) of dopamine antagonist properties.

US Natl Inst Health; DailyMed. Current Medication Information for PHENERGAN (promethazine hydrochloride) injection, solution (November 2009). Available from, as of June 25, 2010 https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=13417


The development of phenothiazine derivatives as psychopharmacologic agents resulted from the observation that certain phenothiazine antihistaminic compounds produced sedation. In an attempt to enhance the sedative effects of these drugs, promethazine and chlorpromazine were synthesized. Chlorpromazine is the pharmacologic prototype of the phenothiazines. The pharmacology of phenothiazines is complex, and because of their actions on the central and autonomic nervous systems, the drugs affect many different sites in the body. Although the actions of the various phenothiazines are generally similar, these drugs differ both quantitatively and qualitatively in the extent to which they produce specific pharmacologic effects. /Phenothiazine General Statement/

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 2510


For more Mechanism of Action (Complete) data for Promethazine (18 total), please visit the HSDB record page.