The required dose of apomorphine is ascertained by an apomorphine response (challenge) test. The challenge is necessary to determine that the patient has a positive response to apomorphine, to establish the dose required to produce this response, and to identify their susceptibility to potential side effects such as postural hypotension, hallucinations, nausea or excessive somnolence.
Patients treated with apomorphine will usually need to start domperidone at least two days prior to initiation of therapy.
When apomorphine is used in combination with domperidone, risk factors in the individual patient should be carefully assessed. This should be done before treatment initiation, and during treatment. Important risk factors include serious underlying heart conditions such as congestive cardiac failure, severe hepatic impairment or significant electrolyte disturbance. Also medication possibly affecting electrolyte balance, CYP3A4 metabolism or QT interval should be assessed. Monitoring for an effect on the QTc interval is advisable.
An ECG should be performed:
- prior to treatment with domperidone
- during the treatment initiation phase
- as clinically indicated thereafter
The test procedure may be performed as outlined below.1
The appropriate dose for each patient is established by incremental dosing schedules.
The following schedule is suggested when the response test is performed using Dacepton® 10mg/ml solution for injection:
- 1 mg of apomorphine hydrochloride hemihydrate (0.1 ml), that is approximately 15-20 micrograms/kg, may be injected subcutaneously during a hypokinetic, or ”off” period and the patient is observed over 30 minutes for a motor response.
- If no response, or an inadequate response, is obtained a second dose of 2 mg of apomorphine hydrochloride hemihydrate (0.2 ml) is injected subcutaneously and the patient observed for an adequate response for a further 30 minutes.
- The dosage may be increased by incremental injections with at least a forty minute interval between succeeding injections until a satisfactory motor response is obtained.