You should be concerned about IV'ing antimuscarinic tropanes from belladonna. You should be concerned about IV'ing toxic ergot alkaloids. You should be concerned about IV'ing barbiturates. I would not recommend injecting inderal either. All of these things seem to have competing psychoactive, toxic and cardiovascular effects. Injecting this mixture of substances really sounds like a bad idea.
According to this site the amobarbital doseage is:
Amobarbital doseage; For injection dosage form:
* For trouble in sleeping:
Adults—65 to 200 mg, injected into a muscle or vein.
Children up to 6 years of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 2 to 3 mg per kg (0.9 to 1.4 mg per pound) of body weight, injected into a muscle.
Children 6 years of age and over—Dose is based on body weight and must be determined by your doctor. The usual dose is 2 to 3 mg per kg (0.9 to 1.4 mg per pound) of body weight, injected into a muscle, or 65 to 500 mg injected into a vein.
* For daytime sedation:
Adults—30 to 50 mg two or three times a day, injected into a muscle or vein.
* For sedation before surgery:
Children—Dose is based on body weight and must be determined by your doctor. The usual dose is 3 to 5 mg per kg (1.4 to 2.3 mg per pound) of body weight or 65 to 500 mg per dose, injected into a vein.
* For control of seizures:
Adults and children 6 years of age and over—65 to 500 mg per dose, injected into a vein.
Children up to 6 years of age—Dose is based on body weight or size and must be determined by your doctor. The usual dose is 3 to 5 mg per kg (1.4 to 2.3 mg per pound) of body weight, injected into a muscle or vein.