Can someone die after taking an overdose of Dopaquel?

First of all, let me tell you how sorry I am for the loss of your brother! I am sure this is very hard for you. It is never easy to lose someone and to lose them unexpectedly, I think, is worse than losing someone after a long illness. It is possible to OD on any drug, even over the counters and vitamins can cause OD if too many are taken for the body to cope with. It certainly sounds like he had some schizophrenic qualities and quetiapine is used for this. Some of the main side effects:
Nervous System: Infrequent: abnormal dreams, dyskinesia, thinking abnormal, tardive dyskinesia, vertigo, involuntary movements, confusion, amnesia, psychosis, hallucinations, hyperkinesia, libido increased2, urinary retention, incoordination, paranoid reaction, abnormal gait, myoclonus, delusions, manic reaction, apathy, ataxia, depersonalization, stupor, bruxism, catatonic reaction, hemiplegia; Rare: aphasia, buccoglossal syndrome, choreoathetosis, delirium, emotional lability, euphoria, libido decreased2, neuralgia, stuttering, subdural hematoma.

Body as a Whole: Frequent: flu syndrome; Infrequent: neck pain, pelvic pain2 suicide attempt, malaise, photosensitivity reaction, chills, face edema, moniliasis; Rare: abdomen enlarged.

Digestive System: Frequent: anorexia; Infrequent: increased salivation, increased appetite, gamma glutamyl transpeptidase increased, gingivitis, dysphagia, flatulence, gastroenteritis, gastritis, hemorrhoids, stomatitis, thirst, tooth caries, fecal incontinence, gastroesophageal reflux, gum hemorrhage, mouth ulceration, rectal hemorrhage, tongue edema; Rare: glossitis, hematemesis, intestinal obstruction, melena, pancreatitis.

Cardiovascular System: Infrequent: vasodilatation, QT interval prolonged, migraine, bradycardia, cerebral ischemia, irregular pulse, T wave abnormality, bundle branch block, cerebrovascular accident, deep thrombophlebitis, T wave inversion; Rare: angina pectoris, atrial fibrillation, AV block first degree, congestive heart failure, ST elevated, thrombophlebitis, T wave flattening, ST abnormality, increased QRS duration.

Respiratory System: Frequent: cough increased, dyspnea; Infrequent: pneumonia, epistaxis, asthma; Rare: hiccup, hyperventilation.

Metabolic and Nutritional System: Infrequent: weight loss, alkaline phosphatase increased, hyperlipemia, alcohol intolerance, dehydration, hyperglycemia, creatinine increased, hypoglycemia; Rare: glycosuria, gout, hand edema, hypokalemia, water intoxication.

Skin and Appendages System: Infrequent: pruritus, acne, eczema, contact dermatitis, maculopapular rash, seborrhea, skin ulcer; Rare: exfoliative dermatitis, psoriasis, skin discoloration.

Urogenital System: Infrequent: dysmenorrheal2, vaginitis2, urinary incontinence, metrorrhagia2, impotence2, dysuria, vaginal moniliasis2, abnormal ejaculation2, cystitis, urinary frequency, amenorrhea2, female lactation2, leucorrhea2, vaginal hemorrhage2, vulvovaginitis2, orchitis2; Rare: gynecomastia2, nocturia, polyuria, acute kidney failure.

Special Senses: Infrequent: conjunctivitis, abnormal vision, dry eyes, tinnitus, taste perversion, blepharitis, eye pain; Rare: abnormality of accommodation, deafness, glaucoma.

Musculoskeletal System: Infrequent: pathological fracture, myasthenia, twitching, arthralgia, arthritis, leg cramps, bone pain.

Hemic and Lymphatic System: Infrequent: leukocytosis, anemia, ecchymosis, eosinophilia, hypochromic anemia; lymphadenopathy, cyanosis; Rare: hemolysis, thrombocytopenia.

Endocrine System: Infrequent: hypothyroidism, diabetes mellitus; Rare: hyperthyroidism.
So some of his symptoms may have been side effects. Side effects are increased with higher doses and this drug can certainly be fatal at high doses. It could also be that he had an underlying heart problem that was aggravated by this medication. See below on overdose:
Overdosage

Human Experience

In clinical trials, survival has been reported in acute overdoses of up to 30 grams of quetiapine. Most patients who overdosed experienced no adverse reactions or recovered fully from the reported reactions. Death has been reported in a clinical trial following an overdose of 13.6 grams of quetiapine alone. In general, reported signs and symptoms were those resulting from an exaggeration of the drug’s known pharmacological effects, i.e., drowsiness and sedation, tachycardia and hypotension. Patients with pre-existing severe cardiovascular disease may be at an increased risk of the effects of overdose [see Warnings and Precautions (5.11)]. One case, involving an estimated overdose of 9600 mg, was associated with hypokalemia and first degree heart block. In post-marketing experience, there were cases reported of QT prolongation with overdose. There were also very rare reports of overdose of Seroquel alone resulting in death or coma.

Suicidal Thoughts and Behaviors

Patients, their families, and their caregivers should be encouraged to be alert to the emergence of anxiety, agitation, panic attacks, insomnia, irritability, hostility, aggressiveness, impulsivity, akathisia (psychomotor restlessness), hypomania, mania, other unusual changes in behavior, worsening of depression, and suicidal ideation, especially early during antidepressant treatment and when the dose is adjusted up or down. Families and caregivers of patients should be advised to look for the emergence of such symptoms on a day-to-day basis, since changes may be abrupt. Such symptoms should be reported to the patient's prescriber or health professional, especially if they are severe, abrupt in onset, or were not part of the patient's presenting symptoms. Symptoms such as these may be associated with an increased risk for suicidal thinking and behavior and indicate a need for very close monitoring and possibly changes in the medication [see Warnings and Precautions (5.2)].

I dont know if any of this helps you at all. It is very difficult when you dont have answers to have a sense of closure. Again, I am so sorry for you and your family's loss. I hope at some point you will have peace and a sense of closure.

I sure hope they did a tox screen when they did the autopsy. You can overdose on any medication. I don't understand why it would take so long for an autopsy. Are the authorities aware of what he was saying? He could have been schizophrenic, allot of what he was saying could be paranoid delusions. Did you see him often? Was he suddenly like that, or do you think he could have been getting sick before he had all the symptoms? Did he ever say anything that could mean he was getting suicidal?