fANL MUNUGKRAPHS VULUME 24

Drugs with secondary amino groups usually react more efficiently to form the cor-
responding N-nitrosated drug: piperazine gave a 62% yield (pH 3.0, 25°C, 10 minutes’

N-NITROSATABLE DRUGS - 30

The relative concentrations of the reactants provide an adequate excess of nitrite to

oe . : - romote the reaction, and the absolute concentrations are appropriate to the s
reaction time) (Mirvish, 1975); phenmetrazine, up to 48 or 31% after 180 minutes in rat ore ; nahi

rabbit stomach, respectively, with 0.8 or 4 mmol NaNO, {Greenblatt e¢ a/., 1972): etham.

3.15, 37°C, 60 minutes) (Kinawi & Schuster, 1978).

Some drugs, such as chlordiaze
& Preussmann, 1975), react via
pounds at least as intermediates,

mentation reactions (Mergens et al, 1979).

The inde
{see below} js

a
cases, unrealistically high doses of precurso
cant results. One solution ta this problem
formed at realistic levels of exposure.
ibsorption rate from the gtomach, a
metabolism is usually not known, t
body fluids is also difficult.

Because the rate of.
@surements in biood or net

It may therefore be useful to study the nitrosation of drugs in vitro under standard

onditions.
Nitrosation assay procedure {NAP test) (WHO, 1978)

If valid comparisons are to be made, the reactions must be carried out under standard
sonditions for set times, and the identity and yield of N-nitroso compounds established by
nass spectrometry or other appropriate methods. The WHO Expert Group recommended a
‘Nitrosation Assay Procedure’ (NAP test) that must conform to the following criteria:

Concentration of drug: 10 mmol/}
Concentration of nitrite: 40 mmol/t
Reaction temperature: 37°C

pH: 3-4

Reaction times: 1 hour and 4 hours

available methods for measuring the resulting V-nitroso compounds, At 37°C there is little
or no decompesition of nitrous acid;
sutol, 61% (pH 3.0, 37°C, 15 minutes) (Montesano er a/., 1974}; and ephedrine, 4% (pH, Pp y

the pH range 3-4 is optimal for most nitrosation
ailing in the stomach during digestion. Reaction
y and slowly reacting compounds, respectively, and
to completion. . If, however, some of the products
time may need to be altered following a detailed

en to eliminate preformed nitrosamines
alder et a/., 1978: Eisenbrand et al., 1979), insofar as this is possible.

Table 3. The relative N-nitrosation of selected drugs: percent nitrosamine yleld
in a defined nitrosation assay procedure (NAP test)”

100-,

50  Aminophenazone
101

7 Phenacetin

FF Lucanthone
04

> Tolazamide

‘Pp Chlorpheniramine sad oxytetracyctine
Quinacrine
P Disulfiram and methapyrilene

- Chlorpromazine

~ Methadc...

| Dextropropoxyphene

* From WHO (1978)