[Heroin. II. Preparation, hydrolysis, stability, pharmacokinetics].

Heroin is prepared by treating morphine with acetyl chloride or acetic anhydride. It is a simple reaction and the yields are generally quantitative. Nowadays the whole process is illegal. Morphine is the major alkaloid present in the opium poppy. Opium is manufactured illicitly then morphine is extracted from it in clandestine laboratories. Numerous studies were carried out on heroin to investigate its rate of hydrolysis. It has been shown that heroin is rapidly deacylated in aqueous solution at alkaline or acidic pH to form 6-acethylmorphine and finally, to morphine. Heroin also rapidly decomposes in biological medium yielding first 6-acetylmorphine and then morphine. Hydrolysis can be performed in blood and in tissue homogenates. Heroin can be administered by several routes. Smoking and intravenous administration are preferred, but intranasal, intramuscular and subcutaneous administration are also common. Recently, there has been a shift in heroin use patterns from injection to sniffing and smoking. Sharing of the injection equipment can result in several severe infectious diseases, such as AIDS, hepatitis B and C. Soon after administration, heroin metabolizes to 6-acetylmorphine and morphine. Most of the pharmacological activities of heroin are due to these active metabolites. Therefore, knowledge of distribution of 6-acetylmorphine and morphine is essential to understand pharmacological properties of heroin. Heroin, which is relatively nonpolar compound compared with morphine, has high lipid solubility facilitating rapid absorption from the bloodstream and passage through the blood-brain barrier. When heroin is administered by intravenously the drug takes 10 s to reach the brain i.e. pharmacological effects appear quickly.