The mean serum NET concentrations observed 24 h after ingestion of the oral

contraceptive ranged from 0.3-o.7Ilg litre-' (1.I-204nmollitre-l

) for doses 1 and 2, and

0.3-I.51Jg litre"! (1.3-5 .0nmollitre-l

) for doses 4 and 5.

Details ofa further radioimmunoassay for NET have been published by Back eral.

(1978) who raised an antibody of NET-3-carboxymethyloxime linked to bovine

serum albumin in rabbits. Results are presented on plasma concentrations ofNET in

40 women taking cornbinations of NEA + EE sampled 12 h after ingestion of the

tablet during multiple dosing. For women taking Img NEA + 501Jg EE, the mean

plasma NET concentrations was 5.91lg litre:' (l9 .8nmol litre:"), with a range of

1.6-15 .21Jg litrc! (504-5I.1nmol litre"). For women taking 3mg NEA + 50llg EE the

mean value was 8.31Jg litre-' (27 .9nmol litre-') with a range of 3.3-ll.2llg litre"

(l1.I-37 .6nmol litre:'). Finally, the women taking Img NET +201lg EE , the mean

plasma NET was 4.81lg litrc" (l6 .lnmol litre:") with a range of 3.6-6.01Jg litre"!

(l2.1-20.2nmollitre-I

) .

For women taking lrng NEA + 501Jg EE, the 12 h plasma NET concentration

showed a higher mean value (1.711Jg litre'"; 5.7nmollitre-l

) during the second cycle of

treatment than during cycle I (O .58Ilg litre:': 1.9nmollitre-I

) .

An investigation of the 12 h plasma NET concentration in three post-parturn

women studied on day I of the first cycle showed significantly higher values than in

nulliparous women also beginning treatment with the same oral contraceptive. The

plasma half-life ofNET in this study ranged from 6.1-12.3 hin six patients.

Measurements are also presented on sex hormone-binding globulin wh ich

increased in most women during the use of combined oral contraceptives. A good

correlation was found between plasma NET concentration and the sex hormonebinding globulin capacity. As the mean plasma NET concentration in women

receiving a combined O.c. containing 3mg NEA was only 104 times as high as that in

women taking a combined oral contraceptive containing Img NEA, it is possible that

the high dose of progestogen suppresses the oestrogen stimulated increase in sex

hormone-binding globulin, which is known to be a carrier protein for NET in human

blood plasma.

A second paper from this group concerns the kinetics ofNET in women following

single doses. Back eral. (1978) have investigated plasma concentrations ofNET in six

healthy young women aged 21-33 years who received four different preparations

containing NET in a random order. The different preparations used were Img

NEA + 501Jg EE , 1.05mg NET, 3mg NEA + 501Jg EE and Img NET + 501Jg EE given

intravenously. Blood specimens were collected at intervals up to 24 h after dosing,

and NET measured by the same radioimmunoassay as described above. It reports

that NET kinetics were unaffected by concomitant administration ofEE, and that the

bioavailability of NET after an oral Img dose ranged from 47% to 73%, as compared

to an equivalent i.v. dose.

506 M.H. BRIGGS

The plasma concentration decay slope fitted a two component open model with an

initial rapid decay, with a half-life of0.41-2.6 h, followed by a slower ß phase with

a half-life between 4.8 and 12.8 h. Bioavailability of NET following oral adrninistration of 3mg NEA + 501Jg EE appeared to be significantly less than for the lower

dose formulation (between 32% and 70%).

A study of NET pharmacokinetics in Indian women of different socio-economic

groups has been published by Prasad, Narasinga Rao , Sivakumar & Prema (1979).

An evaluation was conducted in 11 women belonging to a low socio-econornic group

and in 5 belonging to a high socio-economic group. A single oral dose ofO.35mg NET

was administered to each woman on an ernpty stornach. Blood specimens were

collected at intervals over the next 24 hand plasma NET was estimated by a radioimmunoassay using an antibody raised in rabbits against NET-3-bovine serum

albumin conjugate. In all subjects, the peak serum concentration of NET occurred

within 1-2 h of ingestion, and NET levels then declined in an exponential manner.

The half-li fe of plasma NET in women of the low socio-economic group was

1.0 ± 0.42 hand 1.5 ± 0.28 h in the higher socio-econornic group. This difference is

statistically significant ofP < 0.05 .

In cornparison, in the study by Stanczyk 1'1 al. (1978) cited above, in American

women the half-life of the first disposition phase ranged from mean values of

2.2-4.4 h for the different commercial oral contraceptive formulations used in that

study. The peak NET values obtained in the Indian two groups were 7.7-12 .31Jg litre-'

(25 .9-41.3nmol litre') and 4.7-14.8~g litre! (l5 .8-49.7nmol litre-'). These values

appear to be significantly higher than the peaks observed in Arnerican women using

the same dose ofNET.

Prasad and colleagues (1979) observed a significant correlation between the

weight/theight)- x 100 index and the half-life of NET in all the women studied,

suggesting a role for nutritional status in the metabolic handling ofNET.

The metabolism ofNET has been compared at 14 different international centres by

Fotherby, Abdel-Rahman, deSouza , Coutinho, Koetsawang, Nukulkarn, Sheth,

Mapa, Gopalan, Plunkett, Brenner, Hickey, Grech, Lichtenberg, Gual, Malina,

Gornez-Rogers, Kwon , Kim, Chan, Rathnam, Landren & Shearman (1979) . Plasma

concentrations were measured at various times following a standard dose (I mg).

lnter-centre differences were of the same order as intra-centre differences and body

size did not appear to influence the rate of NET disappearance from blood. A

summary ofthe mean ranges found in this study is presented in Table 2.

Table 2 Plasma profile ofNET (Img p.o.)*

Mean ofextremes

tnmol litrc:')

Range

4.5-13.1

8.9-18 .8

8.7-20 .0

7.5-16 .1

3.8-9 .2

2.7-6.3

1.1-3.1

Mean

8.8

13.8

14.3

12.8

6.5

4.5

2.2

Time(h)

0.5

1.0

2.0

4.0

8.0

12.0

24.0

* Fotherby 1'1 al. (1979)

EDDA is rapidly deacetylated and oxidised to NET following administration to

humans. Walls, Vose, Horth & Palmer (1977) have discussed the radioimmunoassay

of plasma NET following oral tablets of Img EDDA + 501Jg EE taken by four normal

women. Peak concentrations of 7.2 to 15.31Jg litre-I (24 to 52 nmol litre'") were

CONTRACEPTIVE STEROIDS 507

achieved at 1.3 to 3.0 h after administration. Comparison of mean areas under the

plasma concentration-time curve indicated that the absorption of EDDA could be

monitored by measurements ofplasma NET.

A further study on bioavailability and pharmacokinetics of NET in women

receiving oral EDDA, has been published by Vose , Butler, Williams, Stafford,

Shelton, Rose, Palmer, Breckenridge, Orme & Serlin (1979). Using the same radioimmunoassay for plasma NET as described above, results are presented on plasma

NET responses in 12 healthy women aged 21-37 years who received either oral

contraceptives containing Img EDDA + 501Jg EE, or a solution containing EDA + EE

in ethanol. Using a balanced, eross-over study design, four treatment schedules were

given using oral contraceptive tablets from different batches, or the oral solution. The

total dose in each ofthese single treatments was Img EDDA + 501Jg EE . For the four

treatments, the mean plasma peak concentration of NET ranged from 6.5-8 .71Jg

litre-' (21.8-29 .2nmol litre"). There were no significant differences in the bioavailabilit y of the tablet formuJations, which were essentially bioequivalent to the

alcohol solution. Peak blood NET concentrations were achieved within 4 h of

dosing with EDDA. The plasma NET concentrations decl ined in two ph ases, with

mean terminal elimination hal f-liv es of4.0-6.9 h.

An interesting comparison ofNET pharmacokinetics in women and adult female

rabbits and rhesus monkeys has been published by Prasad , Sivakumar & Narasinga

Rao (1979). Plasma level s ofNET were determined after administering either labelIed

NET or a NET mini-pill. Pharmacokinetic parameters were evaluated by using a

two -compartrnent open model and by graphical and regression ana lysis of plasma

NET data. In rabbits, the drug absorption was found to be rapid and NET peak levels

were attained within 0.5 to 1.0 h. The clearance half-l ives were 1.3 h for ' o : and

10.0 h for 'ß'. In monkeys, plasma NET values showed an inconsistent pattern and

the approximate Tv, was found to lie between 4 and 6 h. The ob served pharrnacokinetics ofNET in rabbits, rather than in monkeys, were closer to those in humans.

On this basis, it would appear that th e rabbit is a suitabJe animal model for studying

effects ofnutritional factors on the pharmacokinetics ofNET.

A study of the pharmacokinetics of NEA in women has been reported by Singh ,

Uni yal, Jha, Murugesan , Takkar, Hingorani & Laumas (1979). Six previously

untreated healthy female volunteers aged 25-35 years rece ived a single intravenous

inje ct ion of tr iti ated NEA dissol ved in 10% alcoholic saline. Blood specimens were

collected at intervals up to 72 h, measurements made of total radioactive steroids,

conjugated steroids, and free steroid. The disappearance curve of NEA showed an

initial rapid disappearance with an average half-life of 7.5 min and a subsequent

slower disappearance with a half-life of 51.5 h. The average metabolic clearance rate

from the plasma ofNEA was 495 lit re da y" . Following intravenous injection , NEA is

rapidly metabolised to NET, wh ich then disappears from the plasma with an average

half-life of 34 .8 h. Unidentified tritiated metabolites persisted in the free steroid

fraction ofplasma in signi ficant amount s for as long as 72 h after the injection.

A radioimmunoassay is described by Saxena, Shrimanker & Fotherby (1977) for

measuring NEE directly in sampies of plasma after methanol prec ipitation. The

method ut ilises an antiserum produced against NEE-3-carboxymethylox ime coupled

to bovine serum albumin. The method is highly specific. Pla sma levels of the NEE

were from 1000-2500pg mi-I I week after inje ction dec reasing to 100-200pg mI-lover

the next 6 week s. The pattern ofNEE concentration s in pla sma was similar to that of

NET itself.

(b) Gonanes

A number of totally synthetic progestogens in th e gonane ser ies have been used

commercially or experimentally as contraceptives. These include NG , used in sorne

countries as the equimolar mixture ofLNG and the dextro-rota ry enantiomer, but in

508 M.H.BRIGGS

most piaces as LNG alone (the hormonall y active stereoisomer). Other gonanes

include the long-acting injectable, NG-pelargonate, and the orally active compounds

norgestimate (the 3-oxime of LNG-17-acetate), and ORG 3969 (lI-methylene-3-

deoxy-LNG).

It is ofconsiderable interest to know ifthe metabolism ofactive LNG is the same or

different to that of dextrorotary-NG. This problem has been investigated by

Sisenwine, Kimmel, Liu & Ruelius (1975) who have administered I.5mg of

14C-labelled compound (either (+)-, (-)-, or (± )-NG) to volunteer women . Mean

percentage recovery of radioactivities was as follows (in 7 da ys): LNG-urine 45 ,

faeces 32 ; (+)-NG-urine 64 , faeces 25 ; NG-urine 58 , faeces 23 . No significant

oestrogen formation was observed with metabolism of LNG, though minor

amounts of phenols were seen with (+)-NG. Other metabolic pathways ma y be

summarised as folIow s: LNG 2 a-hydroxylation, 3 a , 5 ß-reduction,

16P-hydroxylation; (+)-NG-l ß-hydroxylation, 16ß-hydroxylat ion , 16ahydroxylation, o-hornannulation. This paper a lso reviews earlier human studies.

Using specific radioimmunoassays, Mishell, Kletzky, Brenner, Roy & Nicoloff

(1977) have measured seru m levels of NG at intervals after the ingestion of

various NG + EE tablets (0.5mg NG + 501Jg EE , 0.3mg NG + 501Jg EE, 0 .075mg

NG + 301Jg EE . Inhibition of ovulation appears to require a peak concentration in

serum of31Jg litre-' LNG (lO.Inmollitre-l

) and /or a minimum level of hg litre-! LNG

(3.4nmollitre-l

) when the oral contraceptive is taken orally once daily.

An interesting study by Nilsson, Victor & Nygren (1977) shows that the sex

hormone-binding globulin binds LNG in vivo. A minipill containing 301Jg LNG

was given to three women immediately following anormal del ivery, and to three

others who had had a legal abortion. All women had high concentrations of plasma

sex hormone-bind ing globulin and developed plasma concentration s of LNG 6 to 8

times higher than seen in women with normal sex hormone-binding globulin levels

receiving the same minipill. Continued adm inistration was accompanied by a fall in

plasma LNG until the sex hormone-binding globulin concentration dropped to the

usual range. Victor & Johansson (1977) noted reduced plasma SHBG concentration

in women treated with LNG (released from a vaginal ring), but normal values were

restored within three weeks when treatment was withdrawn. Oral administration of

LNG at dail y doses ofO .25mg, 0.5mg or 1.0mg resulted in a doubling ofplasma LNG

concentration on doubling ofthe oral do se. No such correlations between SHBG and

MPA were found in women receiving thi s progestogen .

Studies with tritiated LNG in lactating women are presented by Mützel & EI

Mahgoub (1977). Each of two mothers was given 301Jg of tritiated LNG on the third

da y post-partum and each of two mothers was given the same do se on the seventh,

ele venth and fifteenth da y po st-partum, while on the intervening da ys they recei ved

301Jg of unlabelled LNG. It is concluded that the extent of excretion of LNG and its

metabolites in breast 'm ilk is dependent from the time post-partum when this steroid

is taken. Plasma protein transport capacity and fat content and remaining

composition of the breast milk appear to play a part. Unchanged LNG dominates

quantatively in plasma and milk compared with its metabolites. Following the

administration of 301Jg LNG orally approximately 10-20ng LNG and metabolites

might be ab sorbed daily by the infant from breast milk. Amongst the metabolites

identified in milk are 16-hydroxy-3 a , 5ß-tetrahydro LNG, 6 ß-hydroxy LNG,

16ß-hydroxy LNG, together with a number of non polar compounds. The authors

po int out that quantities of steroids are a pproximately 100,000 sma ller than those

wh ich could be transferred to the in fant in the form of natural stero ids, such as

pregnanediol.

An interesting comparative pharmacokinetic study of three progestogens (LYN,

CPA, LNG) has been published by Humpel, Wendt, Schulze, Dogs, Weiss & Speck

(1977). The micronised compounds, labelIed with either 14C or JH, were administered

CONTRACEPTIVE STEROlDS 509

orally combined with 50~ EE to six women. A 14-day interval was allowed

between doses. Plasma progestogen concentration and total radioactivity were

recorded up to 5 and 8 da ys after ingestion. All progestogens were completely

absorbed at comparable rates. Postmaximum courses of disposition were

characterised by two phases, the first ofwhich had a half-life ofabo ut three hours and

was not substance specific. The half-life ofthe second phase was about the same for

LNG and CPA (1.5 and 1.7 h respectivel y), but was significantly higher for LYN

(2.5 h). Percentages of doses recovered in urine and faeces respectivel y were: LNG

48 ,46, LYN 50 , 39 , CPA 30 , 58 . There was a marked discrepancy between plasma

radioactivity and NET concentration following LYN. This was not due to

unconverted LYN and presumably related to some other metabolite.