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Table 5 Synthetic oxytocin dose regimens, maternal levels and total dose calculations

From: Maternal and newborn plasma oxytocin levels in response to maternal synthetic oxytocin administration during labour, birth and postpartum – a systematic review with implications for the function of the oxytocinergic system

Synthetic oxytocin (SOT):

Infusion rate (mU/min)

OR Intramuscular injection in International Units (IU)

OR Controls

(Sampling details)

Maternal oxytocin levels (mean, pg/mL)

Calculated total SOT (IU) per hour

Calculated total SOT (IU) if dose given over 8 hours (unless stated)

Comments

Intrapartum

Data from Fuchs (1983) n = 15 labour induction, n = 17 spontaneous labour

  Basal levels pre-labour

17.4

Nil

Nil

Doubling infusion rate approx doubled oxytocin levels

Oxytocin levels below 10 mU/min are within range of levels in women with no SOT (See Table 3 for details)

  Spontaneous 1st stage

45.4

Nil

Nil

 SOT: 1–3 mU/min

21.1

0.06–0.18 

0.5–1.4 

   4–6 mU/min

49.1

0.24–0.36

1.9–2.9

   7–9 mU/min

58.8

0.42–0.54

3.4–4.3

   10–16 mU/min

110

0.6–0.96

4.8–7.7

Data from Furuya (1988) n = 5 labour induction (Data estimated from Fig. 7)

  Basal levels pre-labour

2

  

No control group without SOT

Doubling infusion rate approx tripled oxytocin levels

  SOT: 12 mU/min

8

0.6 IU

4.8 

   16 mU/min

17

0.9

7.2

   20 mU/min

19

1.2

9.6

   24 mU/min

38

1.4

11.2

   32 mU/min (n = 3)

55

1.9

15.2

Postpartum (vaginal birth)

Data from Thornton (1988) n = 25 postpartum SOT, n = 15 no postpartum SOT

Sampled every 30 sec for 15 min, starting just before birth

  No SOT:

 

Nil

Nil

Standard postpartum intramuscular injection (5 IU SOT with 0.5 mg ergometrine)

Peak oxytocin levels 3-fold higher than peak physiological levels, as measured in this postpartum study

Total dose: 5 IU SOT

   before birth

3.2

  

   at 5–15 min

6.4

  

   mean peak

11.6

  

5 IU intramuscular (IM) SOT at birth of anterior shoulder:

 

5

5 (single dose)

   before birth

3.1

  

   at 5–15 min

15.9

  

   mean peak

30.5

  

Data from Gibbens (1972) n = 10 postpartum SOT IM; n = 14 postpartum SOT IV bolus

Sampled frequently for 60 min, starting just before birth (Data estimated from Fig. 1)

  SOT IM:

 

Nil

Nil

Standard postpartum injection (5 IU SOT with 0.5 mg ergometrine) given IM/IV at birth of anterior shoulder

Total dose: 5 IU SOT

Rapid high peak following IV bolus, peaking at 1 min

Gradual lowering but prolonged peak following IM

   before birth

< 1.2

  

   at 1 min

40

  

   at 3 min

50

  

   at 6 min

45

  

   at 30 mins

18

  

  SOT IV:

 

5

5 IU (single dose)

   before birth

< 1.5

  

   at 30 sec

330

  

   at 1 min

550

  

   at 3 min

280

  

   at 6 min

100

  

   at 30 min

20

  

Data from Fuchs (1982) n = 10 postpartum SOT, n = 10 no postpartum SOT

Sampled just before birth and 5 min, 30 min, 2 hours postpartum

  No SOT:

 

Nil

Nil

Postpartum infusion dose relatively high compared to labour

Oxytocin levels 8–10-fold higher than physiological levels, as measured in this postpartum study

Total dose: 12-18 IU SOT

   at 5 min

41.1

  

   at 30 min

29.1

  

   at 120 min

29.4

  

SOT infusion at 100–150 mU/min, reduced over 2 hours

 

6–9

12–18 (over 2 hours)

   at 5 min

93.4

  

   at 30 min

275

  

   at 120 min

127

  
  1. Units: IU: international units; mU: milliUnits; pg: picograms; mL: millilitres
  2. Oxytocin conversions: 1 IU = 1000 mU; 1 mU = 1000 μU; 1 mg = 1000 μg; 1 μg = 1000 ng; 1 ng = 1000 pg; 1 IU = 1.67 μg; 1 mU = 1.67 ng; 1 μg = 0.6 IU; 1 ng = 0.60 mU; 1 pg/mL = 1 pmol/L = 1pM
  3. Abbreviations: approx approximately, IM intramuscular, IV intravenous, min minutes, sec seconds, SOT synthetic oxytocin
  4. See Table 3 for full details of studies